The aqueous magnesium ion battery (AMIB) system is an attractive candidate in the aqueous batteries due to its high safety properties, similar electrochemical characteristics to lithium and low cost in energy storage applications. The magnesium octahedral molecular sieves of Mg-OMS-2 and the Mg-OMS-2/Graphene composite, depending on their unique 2 × 2 tunnel structure that can provide enough large pore size for magnesium ions insertion/deinsertion into/from the lattice of host materials, are utilized as the cathode materials in the AMIB system and exhibit good battery performances in the three different magnesium salt electrolytes. The Mg-OMS-2/Graphene, not only maintaining the tunnel structure but also possessing the excellent electrochemical property, obtains better rate ability and cycle performance than that of Mg-OMS-2. Furthermore, the Mg-OMS-2/Graphene//AC system is first assembled as aqueous rechargeable magnesium ion battery capacitor. The discharge capacity of this system remains to be 44.1 mAh g–1 at the current density of 100 mA g–1 after 500 cycles and the capacity retention rate is 95.8%.Keywords: Aqueous battery capacitor; Green energy storage system; Magnesium ion; Nanowire Mg-OMS-2/Graphene;

•Porous Co3O4 nanoflakes are prepared for battery-type supercapacitor application.•The three-step synthesis route includes electrodeposition, in-situ reaction and calcination.•Co3O4 nanoflake exhibits a specific capacity as high as 576.8 C g− 1 at 1 A g− 1.•A remarkable cycling stability with 82% capacity retained is obtained.Ni foam supported Co3O4 nanoflakes is prepared for battery-type supercapacitor application through a simple three-step route. In briefly, Co metals are first deposited on Ni foam with a nanosheet morphology. The CoC2O4 protrudes out from the surface of Co through an in-situ reaction with H2C2O4 to form dendritic-like nanowires morphology. Finally, Co3O4 are obtained through thermal decomposition of the CoC2O4 precursor and the dendritic-like nanowires morphology is melting and transforming into a nanoflakes morphology. The unique architectures morphology with porosity and interconnected channels has great advantages since it can effectively increases the contact surface area with electrolyte, which could significantly not only enhances surface area but also the ion/electron diffusion. Electrochemical tests show that Co3O4 nanoflakes exhibit a high specific capacity up to 576.8 C g− 1 at a current density of 1 A g− 1 and remain 283.7 C g− 1 capacity at a high current density of 50 A g− 1, as well as 82% capacitance retained after 5000 cycles. These above results demonstrate the great potential of Co3O4 nanoflakes in the development of battery-type supercapacitors.

•The Au@Ni NAs electrode displays a 3D nanowire arrays structure with rough surfaces.•It reveals excellent catalytic activity and stability towards NaBH4 oxidation.•It shows an anodic current density of 2.35 A mg−1 at −0.5 V (vs. Ag/AgCl) for NaBH4 oxidation.Novel Au@Ni nanoarrays electrode is facilely obtained by firstly template-assisted electro-deposition of Ni nanowire arrays (NAs), followed by galvanostatic deposition of Au catalysts onto the Ni NAs without any conductive agents and binders. The Au@Ni NAs electrode shows a rough surface and fringe with the diameter of ∼90 nm, which assures a high utilization of Au catalysts and provides a large specific surface area. The elemental distribution of Ni mainly exists in the inner layer of a single Au@Ni nanowire with the diameter ∼56 nm, while the elemental distribution of Au catalysts merely appears in the outer layer to form the unique core-shell nanowire structure. The Au@Ni NAs electrode reveals excellent electrochemical property and desirable stability for catalyzing NaBH4 electro-oxidation in basic solutions. The Au@Ni NAs electrode in the 2.00 M NaOH and 0.24 M NaBH4 solution demonstrates an oxidation current density of 2.35 A mg−1 at −0.5 V (vs. Ag/AgCl), which is much higher than that of the noble metal catalysts previously reported, indicating that this material may be hopefully used as anodic catalysts for applying in fuel cells.Download high-res image (142KB)Download full-size image

•The Ni@TiC NAs electrode displays a special 3D thorn-like microstructure.•The Ni@TiC NAs electrode reveals an excellent catalytic activity and stability for H2O2 electrooxidation.•The DPFC with Ni@TiC NAs anode shows a peak power density of 30.2 mW cm−2 at 20 °C.Thorn-like Ni@TiC NAs and flake-like Co@TiC NAs electrodes without any conductive agent and binder are simply fabricated by the potentiostatic electrodeposition of Ni and Co catalysts on the TiC nanowire arrays (NAs). The electrocatalytic activity of H2O2 oxidation on the Ni@TiC NAs electrodes is better than that on the Co@TiC NAs electrodes. The Ni@TiC NAs electrodes demonstrate a rough surface and have many nano-needles on the rod edges, which assures the high utilized efficiency of Ni catalysts. These particular three-dimensional structures may be very suitable for H2O2 electrooxidation. The anodic current of Ni@TiC NAs anode reaches 0.32 A cm−2 at 0.3 V in 1.0 M H2O2 + 4 M KOH solution. The DPFCs employing Ni@TiC NAs anodes display the peak power density of 30.2 mW cm−2 and open circuit voltage of 0.90 V at 85.1 mA cm−2 with desirable cell stability at 10 mL min−1 flow rate and 20 °C, which is much higher than those previously reported.Download high-res image (215KB)Download full-size image

Pd-Au/TiC electrodes with various three-dimensional structures are obtained by the pulsed potential electro-deposition in PdCl2/HAuCl4 electrolytes. The morphologies of Pd-Au/TiC composite catalysts are significantly dependent on the component of deposited solutions. The surface appearance of Pd-Au catalysts changes from rime-shaped structure, to feather-like construction, then to pineapple root-like structure and finally to flower-like configuration with the increase of PdCl2 content in electrolytes. These particular three-dimensional structures may be very suitable for H2O2 electro-reduction, which assures a high utilization of Pd-Au catalysts and provides a large specific surface area. The electro-catalytic activities of H2O2 reduction on the Pd-Au/TiC electrodes improve as increasing the Pd content in Pd-Au alloy catalysts. The pineapple root-like Pd5Au1/TiC electrode reveals remarkably excellent electrochemical property and desirable stability for catalyzing H2O2 reduction in acid media. The direct peroxide-peroxide fuel cells with a 10 cm3 min−1 flow rate display the open circuit voltage (OCV) of 0.85 V and the peak power density of 56.5 mW cm−2 at 155 mA cm−2 with desirable cell stability, which is much higher than those previously reported.The direct peroxide-peroxide fuel cells using special 3D pineapple root-like Pd-Au/TiC cathode shows a peak power density of 56.5 mW cm−2 at 20 °C.Download high-res image (62KB)Download full-size image

Binder-free Pd decorated Ni nanowire (Pd/Ni NW) electrodes are simply fabricated by template-assisted electrodeposition of nickel nanowires and subsequently by spontaneous growth of palladium electrocatalysts on the nickel nanowire surface. The Pd/Ni NW electrode presents superior electrochemical activity and desirable stability towards NaBH4 electrooxidation in an alkaline environment.

•The Mg-OMS-7 materials are synthesized by a simple hydrothermal method.•The Mg-OMS-7 changes the morphology from micro-rugby to nano-club.•The 1.6-Mg-OMS-7 exhibits a better electrochemical performance.The 1 × 1 magnesium octahedral molecular sieve (Mg-OMS-7), utilizing as cathode material in aqueous rechargeable magnesium ions batteries, is synthesized by a simple one-step hydrothermal method. Meanwhile, by changing the concentrations of H2SO4, the Mg-OMS-7 materials with controllable size and shape are obtained. To check the structure and morphology, the host materials are measured by X-ray power diffraction, scanning, transmission and high-resolution transmission electron microscopy. The electrochemical reaction mechanism is examined by cyclic voltammetry and X-ray photoelectron spectroscopy. The Mg-OMS-7 changes the morphology from micro-rugby to nano-club by controlling the concentrations of H2SO4. The nano-club Mg-OMS-7 which obtained by the 1.6 mol dm− 3 H2SO4 owns a more uniformly distribution and smaller size, which provides the shorter route for magnesium ions insert/deinsert into/from the lattice of host material and exhibits the better rate ability and cycle performance. The initial discharge capacity of this electrode can obtain 283.1 mAh g− 1 at the current density of 10 mA g− 1 in the 0.2 mol dm− 3 Mg(NO3)2 aqueous electrolyte and the specific capacity retention rate is 94.1% after cycling 200 cycles at 100 mA g− 1 in the 0.5 mol dm− 3 Mg(NO3)2 electrolyte.Download high-res image (504KB)Download full-size image

One-dimensional (1D) nanostructures have been identified as the most viable structures for high-performance supercapacitors from the view of high ion-accessible surface area and rapid electron transport path as well as excellent mechanical properties. Herein, we report a “stripping and cutting” strategy to produce 1D carbon nanobelts (CNB) from tofu with irregular structures through a molten salts assisted technique. It is a completely novel and green avenue for constructing 1D carbon materials from biomass, showing large commercial potential. The resultant CNB electrode delivers a high specific capacitance (262 F g−1 at 0.5 A g−1) and outstanding cycling stability with capacitance retention up to 102% after 10 000 continuous charging/discharging cycles. Additionally, a CNB//CNB symmetric supercapacitor and CNB//MnO2–CNB asymmetric supercapacitor are assembled and reach energy densities of 18.19 and 29.24 W h kg−1, respectively. Therefore, such a simple, one-pot and low-cost process may have great potential for preparing eco-friendly biomass-derived carbon materials for high-performance supercapacitor electrodes.

A unique nanostructure electrode consisting of RuO2 nanoparticles with ultra-fine diameter (1.9 nm) anchored on the surface of graphene nanosheets (GNS) and carbon nanotube (CNT) is prepared as a binder-free supercapacitor electrode through two-step electrochemical routes. At first, free-standing GNS and CNT (GC) are directly deposited on the surface of carbon fiber cloth (CFC) to form a cross-linked composite via a cathodic electrophoretic deposition method. Safranin, a kind of cationic organic dye, is introduced in this stage as a new-type dispersant to disperse GNS and CNT in water to form a suspension solution. After the following electro-deposition process, the as-prepared GC composite is uniform covered with RuO2 nanoparticles. Benefiting from the combined advantages of GNS, CNT and ultra-fine RuO2 nanoparticles in such a binder-free structure, the hybrid electrode exhibits a high specific capacitance up to 480.3 F g−1 (based on the total mass of GNS, CNT and RuO2) and remarkable cycling stability (89.4% capacitance retention after 10000 cycles). Furthermore, the assembled symmetric supercapacitor exhibits a high energy density of 30.9 Wh kg−1 and power density of 14000 W kg−1 with excellent stability performance (92.7% capacitance retention after 10000 cycles). Thus, the remarkable performance of the resultant RuO2 electrode has provided a rational design strategy for developing supercapacitors with high energy density.Download high-res image (177KB)Download full-size image

•The nanobelt Mg-OMS-1 is synthesized by sol-gel method.•The Mg-OMS-1 as cathode material is used in aqueous magnesium ion battery.•The specific capacity retention rate is 90.4% after 200 cycles at 100 mA g−1.Aqueous rechargeable magnesium-ion batteries with low cost of magnesium resources have a potential to meet growing requirements for electric energy storage resulted from the similar electrochemical properties to lithium. The Mg1.1Mn6O12·4.5H2O named as magnesium octahedral molecular sieves (Mg-OMS-1) owns nanobelt structures as a cathode material for aqueous magnesium-ion battery. The morphology and structure of Mg-OMS-1 are measured by X-ray diffraction, scanning and transmission electron microscopy. The mechanism of magnesium-ion insertion/deinsertion from this host material and the theory specific capacity of Mg-OMS-1 are determined by cyclic voltammetry, electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy. Mg-OMS-1 displays an excellent battery behavior for Mg2+ insertion and deinsertion in the magnesium-salt aqueous electrolyte. The initial discharge capacity of Mg-OMS-1 electrode can reach 248.8 ± 0.5 mAh g−1 at 10 mA g−1 in the 0.2 mol dm−3 Mg(NO3)2 aqueous electrolyte. Even back to 10 mA g−1 after the rate performance, the discharge capacity can achieve 214.1 ± 0.5 mAh g−1. The specific capacity retention rate is 90.4% after cycling 200 times at 100 mA g−1 in the 0.5 mol dm−3 Mg(NO3)2 electrolyte with a columbic efficiency of 99.7 ± 0.1% in the 5 times experiments.Download high-res image (369KB)Download full-size image

Carbon materials, especially graphene nanosheets (GNS) and/or multi-walled carbon nanotube (MWNT), have been widely used as electrode materials for supercapacitor due to their advantages of higher specific surface area and electronic conductivity, but the relatively low specific capacitance thus results in low energy density hindering their large applications. On the contrary, MnO2 exhibits higher energy density but poor electrical conductivity. In order to obtain high performance supercapacitor electrode, here, combining the advantages of these materials, we have designed a facile two-step strategy to prepare 3D MnO2-GNS-MWNT-Ni foam (MnO2-GM-Ni) electrode. First, GNS and MWNT is wrapped on the surface of Ni foam (GM-Ni) via a “dip & dry” method by using an organic dye as a co-dispersant. Then, by using this 3D GM-Ni as substrate, MnO2 nanoflakes are in-situ supporting on the surface of GNS and MWNT through a hydrothermal reaction. The specific capacitances of MnO2-GM-Ni electrode reach as high as 470.5 F g−1 at 1 A g−1. Furthermore, we have successfully fabricated an asymmetric supercapacitor with MnO2-GM-Ni and GM-Ni as the positive and negative electrodes, respectively. The MnO2-GM-Ni//GM-Ni asymmetric supercapacitor exhibits a maximum energy density of 35.3 Wh kg−1 at a power density of 426 W kg−1 and also a favorable cycling performance that 83.8% capacitance retention after 5000 cycles. These results show manageable and high-performance which offer promising future for practical applications.Download high-res image (237KB)Download full-size image

•FeVO4·0.9H2O and FeVO4·0.9H2O/Graphene as anodes are prepared.•The aqueous magnesium ion full battery is assembled successfully.•It is constructed by FeVO4·0.9H2O/Graphene as anode and Mg-OMS-1 as cathode.•The capacity retention rate of this full battery is 97.2% after 100 cycles.•This device can achieve a high energy density of 58.5 Wh kg−1.Aqueous magnesium ion battery as a new energy storage system is always explored due to excellent properties with high theoretical specific capacity, low-cost and safe aqueous electrolytes. However, the study on available material as anode in aqueous magnesium ion battery is very limited, which is the main reason that the kinetics of multivalent magnesium ions deinserted from the host material is very difficult. In this work, the nanoneedle FeVO4·0.9H2O as available anode material is prepared and further modified by compositing with graphene. The FeVO4·0.9H2O/Graphene composite exhibits the more excellent electrochemical performance, for example, the initial discharge capacity of FeVO4·0.9H2O/Graphene electrode at the current density of 50 mAh g−1 in 1.0 mol L−1 MgSO4 electrolyte is 183.8 mAh g−1, but that of the FeVO4·0.9H2O is 150.3 mAh g−1. Therefore, the aqueous magnesium ion full battery is successfully assembled by FeVO4·0.9H2O/Graphene as anode, 1.0 mol L−1 MgSO4 as electrolyte and Mg-OMS-1 as cathode, which can obtain the discharge capacity of 53.1 mAh g−1 at a current density by calculate the total mass of two electrodes and the a high energy density of 58.5 Wh kg−1.Download high-res image (160KB)Download full-size image

•The mico-sheet Mg-OMS-1 is synthesized by a simple hydrothermal method.•The mechanism of Mg2+ insertion/deinsertion from Mg-OMS-1 is explored.•The electrode exhibits a good electrochemical performance in MgCl2 electrolyte.Aqueous magnesium-ion batteries have shown the desired properties of high safety characteristics, similar electrochemical properties to lithium and low cost for energy storage applications. The micro-sheet morphology of todorokite-type magnesium manganese oxide molecular sieve (Mg-OMS-1) material, which applies as a novel cathode material for magnesium-ion battery, is obtained by the simple hydrothermal method. The structure and morphology of the particles are confirmed by X-ray power diffraction, X-ray photoelectron spectroscopy, inductively coupled plasma, scanning and transmission electron microscopy. The electrochemical performance of Mg-OMS-1 is researched by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and constant current charge-discharge measurement. Mg-OMS-1 shows a good battery behavior for Mg2+ insertion and deinsertion in the aqueous electrolyte. When discharging at 10 mA g−1 in 0.2 mol dm−3 MgCl2 aqueous electrolyte, the initial discharge capacity reaches 300 mAh g−1. The specific capacity retention rate is 83.7% after cycling 300 times at 100 mA g−1 in 0.5 mol dm−3 MgCl2 electrolyte with a columbic efficiency of nearly 100%.Download high-res image (219KB)Download full-size image

•NiFeHCF with ultra-fine particle size are synthesized via a co-precipitation method.•NiFeHCF nanoparticles exhibit high activity and good stability for H2O2 reduction.•A peak power density of 36 mW cm−2 is obtained, higher than that of Pd/CFC.Direct peroxide-peroxide fuel cell (DPPFC) employing with H2O2 both as the fuel and oxidant is an attractive fuel cell due to its no intermediates, easy handling, low toxicity and expense. However, the major gap of DPPFC is the cathode performance as a result of the slow reaction kinetics of H2O2 electro-reduction and thus the target issue is to design cathode catalysts with high performance and low cost. Herein, different with using noble metal of state-of-the-art, we have successfully synthesized ultra-fine NiFe ferrocyanide (NiFeHCF) nanoparticles (the mean particles size is 2.5 nm) through a co-precipitation method, which is used as the cathode catalyst towards H2O2 reduction in acidic medium. The current density of H2O2 reduction on the resultant NiFeHCF electrode after the 1800 s test period at −0.1, 0 and 0.1 V are 121, 93 and 76 mA cm2, respectively. Meanwhile, a single two-compartment DPPFC cell with NiFeHCF nanoparticles as the cathode and Ni/Ni foam as the anode is assembled and displayed a stable OCP of 1.09 V and a peak power density of 36 mW cm−2 at 20 °C, which is much higher than that of a DPPFC employed with Pd nano-catalyst as cathode.

To meet the ever-increasing need for high-efficiency energy storage in modern society, porous carbon materials with large surface areas are typically employed for electrical double-layer capacitors to achieve high gravimetric performances. However, their poor volumetric performances come from low packing density and/or high pore volume resulting in poor volumetric capacitance, which would limit their further applications. Here, a novel and one-step molten salt synthesis of a three-dimensional, densely nitrogen-doped porous carbon (NPC) material by using low-cost and eco-friendly tofu as the nitrogen-containing carbon source is proposed. Hierarchically porous carbon with a specific surface area of 1202 m2 g−1 and a high nitrogen content of 4.72 wt% and a bulk density of ∼0.84 g cm−3 is obtained at a carbonation temperature of 750 °C. As the electrode material for a supercapacitor, the NPC electrode shows both ultra-high specific volumetric and gravimetric capacitances of 360 F cm−3 and 418 F g−1 at 1 A g−1 (based on a three-electrode system), respectively, and excellent cycling stability without capacitance loss after 10000 cycles at a high charge current of 10 A g−1 in KOH electrolyte. Moreover, the as-assembled symmetric supercapacitor exhibits not only an excellent cycling stability with 97% capacitance retention after 10000 cycles, but also a high volumetric energy density up to 27.68 W h L−1 at a current density of 0.2 A g−1, making this new method highly promising for compact energy storage devices with simultaneous high volumetric/gravimetric energy and power densities.

•The electrode shows unique 3D porous nanoarrays structure with a large surface area.•The electrode exhibits superior catalytic activity and stability for H2O2 reduction.•The reduction current density reaches 3.47 A mg−1 at the potential of 0.2 V.Nanoporous palladium supported on the carbon coated titanium carbide (C@TiC) nanowire arrays (Pd NP/C@TiC) are successfully prepared by a facile chemical vapor deposition of three-dimensional (3D) C@TiC substrate, followed by electrochemical codeposition of Pd–Ni and removal of Ni via dealloying. The structure and morphology of the obtained Pd NP/C@TiC electrodes are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) are used to examine the catalytic performances of the electrodes for H2O2 electroreduction in H2SO4 solution. The Pd NP/C@TiC electrode exhibits a largely effective specific surface area owing to its open nanoporous structure allowing the full utilization of Pd surface active sites. At the potential of 0.2 V in 2.0 mol L−1 H2O2 and 2 mol L−1 H2SO4 solutions, the reduction current density reaches 3.47 A mg−1, which is significantly higher than the catalytic activity of H2O2 electroreduction achieved previously with precious metals as catalysts.Download high-res image (195KB)Download full-size image

•A 3D electrode with graphene nanosheet decorated on C/TiC nanowire array is built.•MnO2 nanoflakes uniformly grow on the 3D electrode via a simple hydrothermal method.•The 3D MnO2 nanoflakes electrode exhibits high electrochemical performance.Development of MnO2 based electrode materials for supercapacitor application with high comprehensive electrochemical performance, such as high capacitance, superior reversibility, excellent stability, and good rate capability, is still a tremendous challenge. In this work, a distinctive interwoven three-dimensional (3D) structure electrode with ultra-thin 2D graphene nanosheet decorated on the surface of 1D C/TiC nanowire array is built as the support to immobilize MnO2 nanoflakes (MnO2-Graphene nanosheet-C/TiC nanowire array, denoted as MGCT). Compared with the normal 1D core/shell structure, this novel 3D architecture can dramatically not only increase the surface area for MnO2 loading but also facilitate the ion and electron transfer. The electrochemical performance of the as-prepared 3D MnO2 electrode is evaluated by cyclic voltammetrys, galvanostatic charging-discharging tests and electrochemical impedance spectroscopy, high specific capacitance (856 F g−1 at 2 A g−1), good rate capability (69.1% capacitance retention at 40 A g−1vs 2 A g−1), superior reversibility, and cycling stability (85.7% capacitance retention after 10,000 cycles at 10 A g−1) are obtained, suggesting that this novel structure can offer a new and appropriate idea for obtaining high-performance supercapacitor electrode materials.

•Ni-Co NWAs electrode was fabricated by polycarbonate template.•Ni-Co NWAs electrode with 10% of Co molar ratio shows best catalytic activity.•Direct urea/H2O2 fuel cell shows high output performance with Ni-Co NWAs anode.Nickel-cobalt nanowire arrays (Ni-Co NWAs) electrode is prepared by one-step galvanostatic electrodeposition with a polycarbonate membrane as the template. By adjusting the Co proportion in the Ni and Co bath solution into 10%, the optimal Ni-Co NWAs electrode in terms of relatively lower onset potential and highest current density towards urea electro-oxidation is obtained. Its catalytic performance is investigated by constructing single direct urea/hydrogen peroxide (H2O2) fuel cell. Results show that a peak power density of 7.4 mW cm−2 and an open circuit voltage of 0.92 V are achieved at room temperature when 9.0 mol L−1 KOH and 0.33 mol L−1 urea are used as the anolyte, H2SO4 and H2O2 as the catholyte. Additionally, the urea/H2O2 fuel cell also demonstrates excellent stability during short term duration test.

•A binder-free Cu/Cu foam electrode is prepared by an electrochemical method.•The electrode owns a novel three-dimensional porous structure.•The electrode exhibits superior catalytic activity for hydrazine electrooxidation.A three-dimensional porous copper film is directly deposited on Cu foam by an electrodeposition method using hydrogen bubbles as dynamic template (denoted as Cu/Cu foam). Its electrocatalytic activity toward hydrazine electrooxidation is tested by linear sweep voltammetry, chronoamperometry and electrochemical impedance spectroscopy. Compared with Cu foam, hydrazine electrooxidation on the Cu/Cu foam electrode shows that the onset oxidation potential displays a ~100 mV negative shift, the current density at −0.6 V raises about 14 times, the apparent activation energy and the charge transfer resistance reduce significantly. The increasing electrocatalytic performance for hydrazine electrooxidation is mainly caused by the highly porous structure of the Cu/Cu foam electrode which can provide a large surface area and make electrolyte access the electrocatalyst surfaces more easily. Hydrazine electrooxidation on the Cu/Cu foam electrode proceeds through a near 4-electron process.

•Porous Ni@carbon sponge shows 3D open network structures with a large surface area.•The electrode achieves an onset oxidation potential of 0.24 V (vs. Ag/AgCl).•The electrode exhibits superior catalytic activity (290 mA cm−2) and stability for urea electro-oxidation.Highly porous nickel@carbon sponge electrode with low cost is synthesized via a facile sponge carbonization method coupled with a direct electrodeposition of Ni. The obtained electrodes are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The catalytic performances of urea electro-oxidation in alkaline medium are investigated by cyclic voltammetry (CV) and chronoamperometry (CA). The Ni@carbon sponge electrode exhibits three-dimensional open network structures with a large surface area. Remarkably, the Ni@carbon sponge electrode shows much higher electrocatalytic activity and lower onset oxidation potential towards urea electro-oxidation compared to a Ni/Ti flat electrode synthesized by the same procedure. The Ni@carbon sponge electrode achieves an onset oxidation potential of 0.24 V (vs. Ag/AgCl) and a peak current density of 290 mA cm−2 in 5 mol L−1 NaOH and 0.10 mol L−1 urea solutions accompanied with a desirable stability. The impressive electrocatalytic activity is largely attributed to the high intrinsic electronic conductivity, superior porous network structures and rich surface Ni active species, which can largely boost the interfacial electroactive sites and charge transfer rates for urea electro-oxidation in alkaline medium, indicating promising applications in fuel cells.

•The unique Au nanosheets are electrodeposited uniformly on Ni foam substrate.•Au NSs/Ni foam electrode shows high catalytic activity for NaBH4 electrooxidation.•The surface of a single Au sheet is consisted of many nano-scale corrugations.The unique Au nanosheets (Au NSs) are electrodeposited uniformly on Ni foam substrate via a one-step potentiostatic electrodeposition technique. The electrode is characterized by scanning electron microscopy equipped with energy dispersive X-ray spectrometer and X-ray diffractometer. It shows a unique open structure allowing the full utilization of Au surface active sites. NaBH4 electrooxidation in KOH solution on the Au NSs/Ni foam electrode are studied by linear sweep voltammetry and chronoamperometry. The electrode exhibits a high catalytic performance outperforming the Au particles made by the same method. At the oxidation potential of 0 V, the current density of 827 mA cm−2 can be achieved on Au NSs/Ni foam electrode, and only 219 mA cm−2 was obtained on Au NPs/Ni foam electrode, indicating that the catalytic activity is increased by 278%, which is attributed to the porous 3D structure, ensuring the full utilization of Au surfaces. Besides, H2 generated by NaBH4 hydrolysis can quickly diffuse away from the electrode, preventing surface active sites of Au from blocking by adsorbed gas bubbles.

•CFC supported microspherical Ag is obtained by square-wave potential method.•Ag/CFC electrode has high catalytic activity toward hydrazine oxidation.•Hydrazine oxidation on the electrode proceeds by a near 4-electron pathway.Silver particles with microspheric structure are directly electrodeposited on carbon fiber cloth (CFC) substrate by square-wave potential electrodeposition method. The electrocatalytic behaviors of the Ag/CFC electrode toward hydrazine oxidation in alkaline solution are examined by cyclic voltammetry and chronoamperometry. An onset oxidation potential of -0.5 V and a peak current density of 30 mA cm−2 are achieved in the solution containing 1.0 mol L−1 KOH and 20.0 mmol L−1 hydrazine. The microspheric structure of the Ag/CFC electrode provides large electroactive surface area, hence, abundant active sites are vacant for hydrazine oxidation. The calculated apparent activation energies at different potentials show that hydrazine electro-oxidation at higher potential has faster kinetics than that at lower potential. In addition, the transfer electron number of hydrazine oxidation reaction on the Ag/CFC electrode is close to four, suggesting hydrazine is almost completely electrooxidized on the electrode and the full use of hydrazine fuel is basically achieved.

Nanowire-like Cu(OH)2 arrays, microflower-like CuO standing on Cu(OH)2 nanowires and hierarchical CuO microflowers are directly synthesized via a simple and cost-effective liquid–solid reaction. The specific capacitance of Cu(OH)2, CuO/Cu(OH)2 and CuO are 511.5, 78.44 and 30.36 F g−1, respectively, at a current density of 5 mA cm−2. Therefore, the Cu(OH)2/Cu-foil electrode displays the best supercapacitive performance. The capacitance retention reaches up to 83% after 5000 charge/discharge cycles with the columbic efficiency of ∼98%. More importantly, the nanowire Cu(OH)2 transformed into stable nanosheet CuO after about 600 constant current charge–discharge cycles. Additionally, we fabricate an asymmetric supercapacitor with nanowire Cu(OH)2/Cu-foil as a positive electrode, activated carbon (AC) as a negative electrode and 6 mol dm−3 KOH as electrolyte, which exhibits an energy density of 18.3 W h kg−1 at a power density of 326 W kg−1.

In this article, direct growth of Co3O4 with different morphologies on nickel foam is successfully achieved via a simple hydrothermal method by changing the volume ratio between ethanol and water. The morphology and structure of the as-prepared samples are examined by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy. The electrochemical performance of the Co3O4 electrodes is investigated as pseudocapacitor material by cyclic voltammetry and galvanostatic charge/discharge test in 3 mol L−1 KOH solution. Results show that the solvent composition plays an important role not only in the morphology but also in the capacitance. Co3O4 with a honeycomb structure obtained from the volume ratio of C2H5OH/H2O = 1 exhibits the highest capacitive performance, 2509.4 F g−1 at 1 A g−1 and 1754 F g−1 at 10 A g−1, which is much larger than that prepared in the pure water and pure ethanol solvent. The electrode also has a satisfactory cycling performance with capacity retention of 74% after 1000 cycles at 10 A g−1. The enhanced electrochemical performance is ascribed to the honeycomb nanostructure allowing facile electrolyte flow which speeds up electrochemical reaction kinetics. These findings may open up the opportunity for optimizing the hydrothermal synthesis conditions to control the morphology and performance of the products.

Novel Au nanoparticles (NP), Au pinecones (PC) and Au nanodendrites (ND) supported on carbon coated titanium dioxide (C@TiO2) nanoarrays were successfully obtained through a facile chemical vapor deposition of three-dimensional (3D) C@TiO2 substrate, followed by potential pulse electrodeposition of Au electrocatalysts. The morphology and structure of the open 3D Au–C@TiO2 electrodes was characterized by scanning electron microscopy and X-ray diffractometry. The different morphology of electrodeposited Au can be easily controlled by the applied potential (Eo). Electrochemical methods, including cyclic voltammetry, linear sweep voltammetry and chronoamperometry, were used to examine the catalytic activity of the electrode for H2O2 electroreduction in H2SO4 solution. The Au ND–C@TiO2 electrode exhibited the largest effective specific surface area among the Au–C@TiO2 electrodes, owing to its open nanodendritic structure allowing the full utilization of Au surface active sites. A nearly constant reduction current density of 0.655 A cm−2 was successfully achieved on the Au ND–C@TiO2 electrode at the potential of 0 V in 2.0 mol L−1 H2O2 + 2.0 mol L−1 H2SO4 solution, which was significantly higher than the catalytic activity of H2O2 electroreduction achieved previously with precious metals as catalysts.

A novel Pd/polyaniline/CFC electrode is prepared by electroless deposition of palladium (Pd) onto three-dimensional polyaniline networks. The polyaniline matrix on the carbon fiber cloth (CFC) in the reduction state is electro-synthesized by cyclic voltammetry and has a lower vertex potential of −0.4 V vs. Ag/AgCl. The particle size of the Pd coated on the polyaniline chains is gradiently distributed. The as-prepared Pd/polyaniline/CFC electrode is characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FITR) and X-ray diffraction (XRD). The hydrogen peroxide (H2O2) electro-reduction reaction in H2SO4 solutions on the Pd/polyaniline/CFC electrode is investigated using cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS). The results reveal that the electrode exhibited high catalytic activity and excellent stability in the strong oxidizing solution of H2O2 and H2SO4. Polyaniline itself shows electro-catalytic activity towards H2O2 to some extent involving the chemical–electrochemical (C–E) coupling mechanism.

•Flower-like Co nano-particles are deposited on Ni foam via electrodeposition.•Co NFs/Ni foam electrode shows high catalytic activity for hydrazine electrooxidation.•The single Co nano-flower actually consisted of many ultrathin nano-sheets.Ni foam supporting flower-like Co nano-particles (Co NFs/Ni foam) are successfully synthesized by a simple electrochemical method. The electrodes are characterized by scanning electron microscopy equipped with an energy dispersive X-ray spectrometer, and X-ray diffractometer. Without any conducting carbons and polymer binders, the 3D electrode with a unique structure is directly used as the noble metal-free catalyst for hydrazine oxidation and the catalytic performance is evaluated by voltammetry and chronoamperometry. The Co NFs/Ni foam electrode exhibits excellent catalytic performance and superior stability for hydrazine electrooxidation in alkaline media. In the solution of 1.0 mol L− 1 NaOH + 30 mmol L− 1 N2H4, the oxidation current density at − 0.8 V is 140 mA cm− 2 for the Co NFs/Ni foam electrode, and it is only 42 mA cm− 2 for the Pt/Ni foam electrode. Also, the onset potential for Co NFs/Ni foam electrode can reach to − 1.06 V (only − 0.72 V for Ni foam), suggesting that the high cell voltage of DHFC with Co NFs/Ni foam anode. These merits are benefitting from the unique 3D structure which can ensure high utilization of catalysts.

•Electrodeposition of Co film for spontaneous deposition of Au or Pd is reported.•The 3D porous electrode exhibits good catalytic performance for H2O2 reduction.•The 3D porous electrode is consisted of numerous interconnected nanoparticles.Non-noble metal film electrode (Co/Ni foam) modified with noble metals (Au and Pd) has been reported. Highly porous Co film is firstly prepared electrochemically on the commercial Ni foam substrate and in turn serves as a hard template and a redox inducer for modification by spontaneous deposition of Au or Pd. The electrodes (Au-modified Co/Ni foam and Pd-modified Co/Ni foam) are characterized by scanning electron microscopy equipped with energy dispersive X-ray spectrometer, and X-ray diffractometer. The catalytic performance of the 3D porous electrodes is evaluated by voltammetry and chronoamperometry. Results reveal that Au- and Pd-modified Co/Ni foam exhibit excellent catalytic performance and good stability for H2O2 electroreduction compared with Au and Pd particles supported on Ni foam, benefitting from the unique 3D structure which can ensure high utilization of catalyst and quick releases of gas bubbles produced by H2O2 decomposition from the electrode.

•Ni and Co supported on carbon fiber cloth is prepared by electrodeposition.•High performance direct peroxide–peroxide fuel cells (DPPFC) are demonstrated.•The DPPFC displays a peak power density of 21.6 mW cm−2 at 20 °C.Carbon fiber cloth (CFC) supported Ni and Co electrodes are prepared by electrodeposition (Ni/CFC and Co/CFC). Their catalytic performance for H2O2 electrooxidation in KOH solution is investigated and compared with Au/CFC electrode. Ni/CFC electrode exhibits higher catalytic activity than Au/CFC and Co/CFC electrodes. The performance of a direct peroxide–peroxide fuel cell (DPPFC) with Ni/CFC anode and Pd/CFC cathode is examined. The cell shows a peak power density of 21.6 mW cm−2 at 20 °C and 53.8 mW cm−2 at 50 °C. The cell performance is improved with the increase of anolyte and catholyte flow rate and operation temperature. Results indicates that the performance of DPPFC with low-cost Ni/CFC anodes is comparable with those using precious metal anodes, e.g., Au/CFC and Pd/CFC.

•High electrocatalytic performance, 500 mA cm−2 at −0.3 V in 0.5 mol dm−3 NaBH4.•Hydrogen adsorption capacity of AB5 was improved by the addition of MWNTs.•Investigation for the role of MWNTs in NaBH4 electrooxidation.Catalytic electrodes consisting of MmNi0.58Co0.07Mn0.04Al0.02 (AB5-type alloy) and multi-walled carbon nanotubes (MWNTs) are studied for NaBH4 electrooxidation and are characterized by scanning electron microscope and X-ray diffractometer. The NaBH4 electrooxidation performance on the AB5/MWNTs electrode is tested by cyclic voltammetry and chronoamperometry methods. The electrode performance is significantly affected by the content of MWNTs and the optimized content of MWNTs is found to be 2 wt.%. The steady state current density for NaBH4 electrooxidation at the AB5/MWNTs (2 wt.%) electrode is about twice of that at the AB5 electrode without MWNTs. The utilization efficiency of NaBH4 at the AB5/MWNTs electrode is 61.5% higher than that at the pristine AB5 electrode. The enhanced electrocatalytic activity and NaBH4 utilization at the AB5/MWNTs (2 wt.%) electrode can be attributed to MWNTs, which acts as a hydrogen adsorbent to diminish hydrogen release.

•Fe3O4–Fe nanowires with a large amount of nanoholes directly grown on highly conductive nanofiber arrays are prepared.•The electrode displayed remarkably high capacity, excellent high rate performance and cycling stability.•The electrode has a satisfactory cycling performance with capacity retention of 93.9% after 100 cycles at 1C.A facile and green method is developed to fabricate Fe3O4–Fe nanowires with a large amount of nanoholes directly grown on highly conductive nanofiber arrays. By electrodeposition of Fe clusters on C/TiC nanofiber array, followed by in-situ chemical conversion of Fe to FeC2O4–Fe nanowires and the thermal decomposition of FeC2O4–Fe to Fe3O4–Fe, a Fe3O4–Fe nanocomposite electrode with unique architecture is successfully prepared. The electrode is characterized by means of X-ray diffractometer, scanning electron microscope and transmission electron microscope. Electrochemical properties of the nanowire arrays electrode as the anode of lithium-ion batteries are examined by cyclic voltammetry and galvanostatic charge/discharge test. The electrode displayed remarkably high capacity, excellent high rate performance and superior cycling stability. The reversible capacity of the electrode reached 1012 mAh g−1 at 1C and retained to be 500 and 255 mAh g−1 at 10 and 20C, respectively. It can still deliver a specific capacity of 100 mAh g−1 even at 50C (72 s charge–discharge). The electrode also has a satisfactory cycling performance with capacity retention of 93.9% after 100 cycles at 1C. The magnificent performance can be attributed to the distinct configuration resulting from the novel fabrication process.

•A homogeneous molten salt consisting of (Li,Na,K)2CO3 and CsVO3–MoO3 was prepared.•The operation temperature of DCFC can be reduced by using the novel electrolyte.•The novel electrolyte shows the catalytic activity for the graphite electrooxidation.•The ionic conductivity was increased with the content of CsVO3–MoO3 in electrolyte.The catalytic activity of a homogeneous molten salt consisting of (Li,Na,K)2CO3 with dissolved additions of CsVO3–MoO3 for graphite electrooxidation is investigated. This electrolyte forms a eutectic mixture with low melting point, high stability in the presence of CO2, and catalytic activity for graphite electrooxidation. The current density of graphite electrooxidation in this novel electrolyte reaches 125 mA cm− 2 at − 0.4 V and 750 °C, which is much higher than that obtained in the conventional molten carbonate electrolyte (47 mA cm− 2). More importantly, the addition of CsVO3–MoO3 significantly improves the electrooxidation activity of graphite at low temperature. The onset potential for graphite electrooxidation at 550 °C is negatively shifted by − 0.3 V and the current density at − 0.4 V is increased by 6.7 times by introducing CsVO3–MoO3 into the molten (Li,Na,K)2CO3. The catalytic mechanism of CsVO3–MoO3 is briefly discussed.

•λ-MnO2 is prepared by treating LiMn2O4 with H2SO4.•λ-MnO2 has ideal battery behavior for polyvalent cations (Mg2+, Zn2+) to intercalate/deintercalate in aqueous electrolyte.•λ-MnO2 electrode exhibits a high specific capacity of 545.6 mAh g−1 at 13.6 mA g−1 in 0.5 mol dm−3 MgCl2 electrolyte.A simple acid leaching technique is demonstrated to produce λ-MnO2 by treating LiMn2O4 with H2SO4. λ-MnO2 shows high intercalation capacities as the positive electrode material for rechargeable aqueous batteries. The structure and morphology of the nano-particles are characterized by X-ray power diffraction, inductively coupled plasma, X-ray photoelectron spectroscopy, scanning and transmission electron microscopy. The electrochemical performance of λ-MnO2 is investigated by cyclic voltammetry, constant current charge-discharge tests and electrochemical impedance spectroscopy. λ-MnO2 has ideal battery behaviors for polyvalent cations (Mg2+, Zn2+) to intercalate/deintercalate in the aqueous electrolyte. The λ-MnO2 electrode shows a high initial discharge capacity of 545.6 mAh g−1 at 13.6 mA g−1 in 0.5 mol dm−3 MgCl2 with a columbic efficiency of nearly 100%. In addition, it shows good cycling stability and maintains a capacity of 155.6 mAh g−1 after 300 cycles in 1 mol dm−3 MgCl2 electrolyte.

•3D lamination-like P2-Na2/3Ni1/3Mn2/3O2 assembled with 2D ultrathin nanosheets is synthesized via a facile co-precipitation reaction.•The electrochemical performance of P2-Na2/3Ni1/3Mn2/3O2 electrode in 1 mol L−1 Na2SO4 aqueous electrolyte is first investigated.•P2-Na2/3Ni1/3Mn2/3O2 is capable for Na ions insertion/extraction in Na2SO4 aqueous electrolyte at different rates.•The insertion/extraction behavior of Na ions in 1 mol L−1 aqueous electrolyte is described.Three-dimensional (3D) lamination-like transition metal oxide Na2/3Ni1/3Mn2/3O2, assembled with two-dimensional (2D) ultrathin nanosheets, is successfully synthesized using a combined co-precipitation and thermal treatment method. The material was investigated, for the first time, as the positive electrode material of an aqueous Na-ion capacitor battery. The structure and morphology of the as-prepared material are systematically characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectrometry and X-ray photoelectron spectroscopy. Its performance for Na-ion intercalation/deintercalation in a 1 mol L−1 Na2SO4 aquesous electrolyte is evaluated by cyclic voltammetry, galvanostatic cycling test and electrochemical impedance spectroscopy. The Na2/3Ni1/3Mn2/3O2 electrode is charged between -0.8∼1.0 V (vs. SCE) with no water decomposed. The reversible capacity of the electrode reached 157 mAh g−1 at 0.05 C and retained to be 84 mAh g−1 and 51 mAh g−1 at 0.20 C and 0.50 C, respectively. After 80 cycles at 0.20 C, the specific capacity of Na2/3Ni1/3Mn2/3O2 remains to be 42 mAh g−1. The wide charge/discharge potential range and the high capacity reveal that the 3D lamination-like P2-Na2/3Ni1/3Mn2/3O2 assembled with 2D ultrathin nanosheets can be a promising cathode material for low-cost aqueous Na-ion capacitor battery.

•λ-MnO2 is synthesized via treating LiMn2O4 with H2SO4.•λ-MnO2 electrode exhibits a high specific capacity of 390.7 mAh g−1 at 13.6 mA g−1.•The capacitor battery AC/λ-MnO2 shows a specific energy of 19.7 Wh Kg−1 at a power density of 3500 W Kg−1.A high-performance capacitor battery AC/λ-MnO2 based on Na-ion insertion-deinsertion into λ-MnO2 in 1 mol dm−3 Na2SO4 solution is successfully demonstrated. A simple acid leaching technique is used to produce λ-MnO2 by treating LiMn2O4 with H2SO4. X-ray power diffraction and inductively coupled plasma analysis provide supporting evidences for the extraction of Li+ from the LiMn2O4, and the particle morphology of λ-MnO2 is studied by scanning and transmission electron microscopy. A high specific capacity of 390.7 mAh g−1 is obtained for the λ-MnO2 electrode at a current density of 13.6 mA g−1 with a nearly 100% efficiency. The capacitor battery AC/λ-MnO2 can operate at a cell voltage as high as 2.2 V, and it exhibits a specific energy of 19.7 Wh Kg−1 at a high power density of 3500 W Kg−1 and a high energy density of 71.7 Wh Kg−1 at a low power density of 403 W Kg−1. It has potentials to be used as an energy storage device for the integration of solar and wind power into the electrical power grid.

•Electrodeposition of Au nanothorns supported on Ni foam for NaBH4 oxidation is reported•The unique 3D electrode exhibits good catalytic performance for NaBH4 electrooxidation•The unique 3D electrode is consisted of thorn-like Au with the corrugated appearance.Au NTs/Ni foam electrode with the unique three dimensional network structure is prepared by one-step electrodeposition of thorn-like Au particles onto Ni foam surface without any additives. The morphology of the electrode and distribution of Au on Ni foam surfaces are characterized by scanning electron microscope and energy dispersive X-ray spectrometer. The structure is analyzed using an X-ray diffractometer. The catalytic performance of electrode is evaluated by voltammetry and chronoamperometry. Au thorns display the corrugated appearance with the length of around 1 μm, and the diameter of hundreds of nanometers, even down to several nanometers. Electrochemical measurements reveal that the as-prepared electrode exhibits excellent catalytic performance and good stability for NaBH4 electrooxidation. A limiting current density of 1155 mA cm−2 at −0.16 V in the solution of 2.0 mol L−1 NaOH +0.1 mol L−1 NaBH4 was also successfully achieved, which is much higher than that on the other representative Au electrodes and even higher than Pt nanoparticles reported previously.

•Ni supporting NiCo2O4 nanostructures with various morphologies is prepared.•NiCo2O4 nanostructures show high performance for H2O2 oxidation and reduction.•NiCo2O4 nanostructures possess unique open structure inside their architectures.Ni foam supported-NiCo2O4 nanostructures with various morphologies are successfully prepared by a facile template-free method. The synthesis involves the electrodeposition of the bimetallic (Ni, Co) film on Ni foam support. The NiCo2O4 nanostructures are formed by immersing the bimetallic film in an oxalic acid solution, followed by a calcination progress. The control over NiCo2O4 nanostructures with different morphologies is achieved by adjusting the electrodeposition time and immersing time. The electrode is characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. H2O2 electrooxidation and electroreduction in KOH solution on the NiCo2O4 nanostructures are studied by cyclic voltammetry and chronoamperometry. Results show that NiCo2O4 nanostructures exhibit high performance and superior stability for both H2O2 electrooxidation and electroreduction, resulting from hierarchical porous structure inside their architectures.

In this work, a facile method for the preparation of a series of transition metal oxide–metal nanocomposites (MO–M) (such as NiO–Ni, Co3O4–Co, Fe3O4–Fe and MnO2–Mn) anchored on conductive nanowire arrays (such as TiC–C core–shell nanowires grown on a Ti alloy sheet) is reported for the first time. The obtained composites possess a unique three-dimensional nanostructure and high electronic conductivity. They have diverse applications as electrodes of energy storage devices. High capacitance and high rate capability have been demonstrated using the NiO–Ni@C@TiC nanocomposite as a model electrode, which shows a specific capacitance as high as 1845 F g−1 at a charge–discharge current density of 5 A g−1 and 811.1 F g−1 after cycling 500 times at an extremely high charge–discharge rate of 100 A g−1.

Porous (Co, Mn)3O4 nanowires freely standing on a Ni foam are synthesized via a template-free growth method, followed by a thermal treatment in air. The nanowires are characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy, thermogravimetric analysis and Fourier transform infrared spectroscopy. Their catalytic performance in H2O2 electroreduction is evaluated by linear scan voltammetry and chronoamperometry. Results show that a thermal treatment leads to the conversion of solid nanowires of MnCO3 + CoCO3 to porous nanowires of (Co, Mn)3O4via decomposition and reconfiguration, which is identified to be the catalytic active component for H2O2 electroreduction. Nanowires calcined at 300 °C exhibit the highest activity for H2O2 reduction and a current density of 329 mA cm−2 is obtained in 3.0 mol dm−3 KOH + 0.6 mol dm−3 H2O2 at −0.4 V (vs. Ag/AgCl, KCl). The catalytic activity of (Co, Mn)3O4 nanowires is almost twice than that of Co3O4 nanowires. The role of Mn in improving the catalytic activity is proposed and discussed.

A novel synthesis of Au–Pd alloy nanoparticles supported on carbon fiber cloth (Au–Pd NPs/CFC) via a potential pulse technique is presented. Different composition stoichiometry of Au–Pd nanoparticles are deposited from the aqueous solutions of HAuCl4/PdCl2 mixtures in molar ratios of 5:1, 2:1, 1:1, 1:2 and 1:5. The electrode is characterized by scanning electron microscopy coupled to energy dispersive X-ray analysis (SEM–EDX), transmission electron microscopy (TEM) and X-ray diffractometer (XRD). H2O2 electroreduction in H2SO4 solution on Au–Pd nanoparticles is studied by linear sweep voltammetry and chronoamperometry. The catalytic performance on different composition stoichiometry of Au–Pd nanoparticles increases with the increase of Pd content. Additionally, the flower-like Au–Pd NPs/CFC electrode exhibits the excellent catalytic properties and good stability to H2O2 electroreduction in acid solution, and it outperforms pure Au or Pd catalyst supported on carbon fiber cloth.Highlights► Flower-like Au–Pd NPs are electrodeposited on CFC via potential pulse technique. ► Au–Pd NPs show higher catalytic activity for H2O2 reduction than pure Au or Pd. ► Au–Pd NPs/CFC electrodes with different composition stoichiometry are obtained.

Solid carbon electrooxidation is the anode reaction of a direct carbon fuel cell. In this study, electrooxidation of graphite in molten carbonates containing transition metal oxides (Fe2O3, Co3O4, NiO, and MnO2) is investigated. It is demonstrated that, by dissolving transition metal oxides into the molten Li2CO3–K2CO3, the onset potential for graphite oxidation is significantly shifted to negative value and the oxidation current density is remarkably increased. At 750 °C, NiO causes a negative shift of onset oxidation potential by around 0.3 V and a current density (at −0.4 V) increase by 4.5 times. The coulombic efficiency of graphite oxidation remains above 94% with and without metal oxides. The apparent activation energy is reduced by more than 40 kJ mol−1 by the addition of metal oxides. The working mechanism of the transition metal oxides is interpreted by electronegativity of metal cations, the concentration of oxygen anions and the indirect oxidation pathway via preceding chemical reaction-following electrochemical reaction.Highlights► Graphite electrooxidation activity was remarkably enhanced by transition metal oxides. ► The columbic efficiency of graphite electrooxidation was more than 94%. ► Transition metal oxides reduced the apparent activation energy by 40 kJ mol−1.

Carbon fiber cloth supported micro- and nano-structured Co electrode is prepared by a facile and fast square-wave electrodeposition method. The electrode is characterized by scanning electron microscope and X-ray diffractometer. Its electrocatalytic performance for hydrazine oxidation in alkaline media is investigated by means of cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. Co is uniformly deposited on the carbon fiber surface and presents as nano-sheets and micro-particles intersected mutually. The nano-sheets have a thickness of around 250 nm and the size of the micro-particles is up to around 10 μm. Hydrazine electrooxidation on the electrode occurs via both direct and indirect pathways. The activation energy of the direct electrooxidation of hydrazine is 16.6 kJ mol−1 which is higher than that of the electrooxidation of hydrogen in the indirect pathway (9.9 kJ mol−1).Highlights► Micro/nanostructured Co is deposited on CFC by square-wave potential method. ► Co/CFC electrode shows high electrocatalytic activity for hydrazine oxidation. ► Hydrazine oxidation on Co/CFC electrode occurs via direct and indirect pathways.

•Electrodeposition of Au nanoflowers supported on CFC for ethanol oxidation is reported.•Many thorn-like Au nanostructures have a common basis to form a single flower.•The as-prepared electrode exhibits good catalytic performance for ethanol electrooxidation.Well-defined Au nanoflowers (NFs) have been prepared on carbon fiber cloth (CFC) through a rapid, templateless, surfactantless, electrochemical route. The electrode (Au NFs/CFC) is characterized by scanning electron microscopy equipped with an energy dispersive X-ray spectrometer and X-ray diffractometry. Ethanol elelctrooxidation on the flower-like Au electrode is studied by cyclic voltammetry and chronoamperometry. The effects of applied potential, deposition time, and solution concentration on the morphology of the Au deposits are also discussed in our work. The Au NFs/CFC electrode exhibits much higher catalytic activity and remarkably improved utilization of Au than Au nanoparticles prepared by electrodeposition for ethanol electrooxidation owing to its unique open hierarchical structure. The size- and morphology-controlled Au nanostructures can be a promising candidate as the high performance anode for the application in fuel cells.

•Dendritic Pd supported on CFC is decorated with Au via potential pulse technique.•Au@Pd/CFC electrode shows high catalytic activity for H2O2 reduction and oxidation.•DPPFC obtains a much higher performance based on the Au@Pd/CFC electrodes.Dendritic Au@Pd nanocomposite is uniformly electrodeposited on carbon fiber cloth via a two-step potential pulse technique. The electrode (Au@Pd/CFC) is characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffractometer. It shows a unique open three dimensional structure allowing the full utilization of electrocatalyst. Au is uniformly distributed on the surface of Pd nano-dendrites. H2O2 electrooxidation in KOH solution and electroreduction in H2SO4 solution on the dendritic Au@Pd/CFC electrode are studied by linear sweep voltammetry, chronoamperometry and electrochemical impedance. The electrode exhibits a remarkably higher catalytic activity for both H2O2 electrooxidation and electroreduction than the Pd/CFC electrode. The effects of H2O2, KOH and H2SO4 concentration on the catalytic performance were investigated and the suitable ratios of [H2SO4]/[H2O2] and [KOH]/[H2O2] are determined to be 1 and 4. The cell using it both as the anode and cathode exhibits a much higher performance than those reported in the literatures, that an open circuit voltage is as high as 0.9 V and the peak power density can reach 20.7 mW cm−2 at 20 °C.

•Clusters of Ni nanoparticles were electrodeposited on conductive MWNTs/Sponge layer.•The Ni layer has a unique porous structure and large surface area.•The Ni@MWNTs/Sponge exhibits excellent performance for NaBH4 electrooxidation.A novel Ni electrode with a unique three-dimensional hierarchical macro-porous structure is prepared by electrodeposition of spherical Ni particles onto multi-walled carbon nanotubes (MWNTs) which are assembled on the skeleton of a sponge. The morphology and phase structure of the Ni@MWNTs/Sponge electrode are characterized by a scanning electron microscope, transmission electron microscope and X-ray diffraction spectrometer. The catalytic performance of the Ni@MWNTs/Sponge electrode for NaBH4 electrooxidation is investigated by means of cyclic voltammetry and chronoamperometry. Results show that the Ni@MWNTs/Sponge electrode exhibits a remarkably high catalytic activity and good stability for NaBH4 electrooxidation. The oxidation current density reaches as high as 300 mA cm− 2 at − 0.7 V in 2.0 mol dm− 3 NaOH and 0.1 mol dm− 3 NaBH4, which is significantly higher than that reported for other types of Ni electrodes.

Well-defined Au dendrites supported on carbon fiber cloth are successfully prepared by potential pulse electrodeposition without additives or surfactants. The electrode (D-Au/CFC) is characterized by transmission electron microscopy, scanning electron microscopy and X-ray diffractometry. H2O2 electroreduction in H2SO4 and electrooxidation in KOH solution on the dendritic Au electrode are studied by linear sweep voltammetry and chronoamperometry. The D-Au/CFC electrode exhibits much higher catalytic activity and remarkably improved utilization of Au than Au nanoparticles prepared by the same method for both H2O2 electroreduction and electrooxidation owing to its unique open dendritic structure. The H2O2 electroreduction in H2SO4 solution exhibits much larger overpotentials than the H2O2 electrooxidation in KOH solution on the D-Au/CFC electrode. A high DPPFC performance using it both as the anode and cathode exhibits an open circuit voltage as high as ∼0.8 V and the peak power density can reach 14 mW cm−2 at 20 °C.

Composites of Li4Ti5O12–Ketjen Black (Li4Ti5O12–KB) and Li4Ti5O12–Ketjen Black–multi-walled carbon nanotubes (Li4Ti5O12–KB–MWCNTs) are prepared by a simple solution method. Their morphologies and structures are characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and thermogravimetric analysis. Their electrochemical properties are investigated by galvanostatic charge–discharge test. Li4Ti5O12 particles in Li4Ti5O12–KB and Li4Ti5O12–KB–MWCNT composite have a diameter of ca. 40–60 nm. The discharge specific capacity is 157 (0.1 C), 110 (20 C) and 93 (30 C) mAh g− 1 for Li4Ti5O12–KB composite, and 157 (0.1 C), 133 (20 C) and 105 (30 C) mAh g− 1 for Li4Ti5O12–KB–MWCNT composite. After 100 cycles at 5 C, the discharge capacity retention of Li4Ti5O12–KB and Li4Ti5O12–KB–MWCNTs is 94% and 96%, respectively. Li4Ti5O12 shows asymmetric behavior between charge and discharge. The excellent high rate performance of Li4Ti5O12–KB and Li4Ti5O12–KB–MWCNT composites can be attributed to the reduction of Li4Ti5O12 particle size and the improvement of electronic conductivity due to the uniform distribution of Li4Ti5O12 particles within the carbon matrix conductive network.Highlights► High rate performance of Li4Ti5O12–KB and Li4Ti5O12–KB–MWCNTs are prepared. ► KB prohibits the growth of Li4Ti5O12 particles. ► MWCNTs combine with KB to form a three-dimensional conductive network. ► The asymmetric behavior between charge and discharge of Li4Ti5O12 exists.

Sr-doped Li4Ti5O12 composites are prepared by a solid-state reaction method and characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, and transmission electron microscopy. Their electrochemical properties as the anode material of lithium ion batteries are investigated by galvanostatic charge and discharge tests, cyclic voltammetry and electrochemical impedance spectroscopy. The results show that Sr2 + doping increases the lattice parameter, reduces the particle size, decreases the charge transfer resistance, and significantly enhances the rate capability of Li4Ti5O12. The Sr-doped Li4Ti5O12 exhibits a specific discharge capacity of about 1.62 times that of pristine Li4Ti5O12 at 5 C charge/discharge rate. Sr doping introduces a small amount of SrLi2Ti6O14 to the composites, which also makes a contribution to the specific capacity of Li4Ti5O12 at low charge/discharge potentials.Highlights► Sr2 + doping increases the lattices' parameter and reduces the particle size. ► Sr2 + doping decreases the charge transfer resistance. ► Sr2 + doping significantly enhances the rate capability of Li4Ti5O12.

A high performance direct peroxide–peroxide fuel cell using dendritic Pd supported on carbon fiber cloth as both the anode and the cathode is reported. Effects of the concentration of H2O2, KOH, H2SO4, the operating temperature and the flow rate on the fuel cell performance are investigated. The cell exhibits a much higher performance than those reported in the literature. The open circuit voltage reaches 0.9 V and the peak power density is as high as 14.3 and 58.4 mW cm−2 at 20 °C and 60 °C, respectively, when running on 4.0 mol L−1 KOH + 1.0 mol L−1 H2O2 as the fuel and 2.0 mol L−1 H2SO4 + 2.0 mol L−1 H2O2 as the oxidant, both at a flow rate of 10 mL min−1.Highlights► A high performance direct peroxide–peroxide fuel cell (DPPFC) is demonstrated. ► The Pd/CFC electrode is a good catalyst for the anode and cathode reactions. ► The DPPFC displays a peak power density of 14.3 mW cm−2 at 20 °C.

Dendritic Pd is electrodeposited uniformly on carbon fiber cloth via a potential pulse technique. The electrode is characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffractometer, and it shows a unique open structure allowing the full utilization of Pd surface active sites. H2O2 electrooxidation in KOH solution and electroreduction in H2SO4 solution on the dendritic Pd electrode are studied by linear sweep voltammetry and chronoamperometry. The electrode exhibits a high catalytic performance for both H2O2 electrooxidation and electroreduction, and it outperforms the conventional electrode made with commercial Pd/C powder. KOH and H2SO4 in excess show no improvement to the activity of H2O2 oxidation and reduction, respectively. The overpotential at the same current density for H2O2 electrooxidation in alkaline solution is significantly lower than that for electroreduction in acid medium on the dendritic Pd electrode.Highlights► Dendritic Pd is electrodeposited on CFC via potential pulse technique. ► Pd/CFC electrode shows high catalytic activity for H2O2 oxidation and reduction. ► Pd/CFC electrode shows a unique open structure to make the full utilization of Pd.

Nanostructured CuO with diverse morphology was directly grown on copper foam. Their supercapacitance performance was investigated and correlated with the morphology. CuO nanowires, nanosheets, and flower-like nanostructures were formed on copper foam which acts as both the substrate of CuO formation and the current collector of the electrode. Their morphology was examined by scanning and transmission electron microscopy and their phase structure was analyzed by X-ray diffraction spectroscopy. The supercapacitance of the nanostructured CuO on copper foam was investigated by cyclic voltammetry, galvanostatic charge/discharge measurements and electrochemical impedance spectroscopy. Results showed that the specific capacitance of the nanostructured CuO strongly depends on its morphology and dimension. CuO nanosheets exhibited higher specific capacitance than nanowires and flower-like nanostructure. The specific capacitance of the CuO nanosheets reached 212 F g−1 at a current density of 0.41 mA mg−1 in 6.0 mol dm−3 KOH electrolyte. The capacitance loss is around 15% after 850 charge/discharge cycles at 0.41 mA mg−1 and the majority of capacitance loss occurred in the initial 50 cycles (8.1%).Highlights► Nanostructured CuO with diverse morphologies was directly grown on copper foam. ► The CuO morphology significantly affected its capacitance performance. ► CuO nanosheets exhibited a higher specific capacitance than nanoflowers and nanowires.

The growth of CuO nanosheet arrays on Cu foil was demonstrated. The morphology and structure of the CuO were examined by scanning electron microscopy and X-ray diffraction spectroscopy. The catalytic performance of the obtained CuO/Cu electrode for hydrogen peroxide electroreduction in 3.0 mol dm−3 KOH was evaluated by means of cyclic voltammetry and chronoamperometry. The CuO/Cu electrode shows an onset potential for H2O2 electroreduction comparable to Co3O4 nanowire arrays grown on Ni foam and around 100 mV more negative than precious metal catalysts, such as Pt and Pd, demonstrating its good catalytic activity for H2O2 electroreduction. The stabilized mass current density for H2O2 electroreduction on the CuO/Cu electrode at −0.3 V reached about 57% of that on Co3O4 nanowire arrays grown on nickel foam. Compared to conventional fuel cell electrodes fabricated by mixing active materials with conducting agents and polymer binders, this electrode of CuO nanosheet arrays directly grown on Cu has superior mass transport property, which combining with its low-cost and facile preparation, make it a promising electrode for fuel cell using H2O2 as the oxidant.Highlights► The growth of CuO nanosheet arrays on Cu foil was demonstrated. ► The CuO/Cu electrode shows good catalytic activity for H2O2 electroreduction. ► The CuO/Cu has superior mass transport property and is cheap.

CuO nanosheet arrays freely standing on nickel foam are prepared via a template-free growth method. The morphology of CuO nanosheet arrays is examined by scanning and transmission electron microscopy and the phase structure of nanosheets is analyzed by X-ray diffraction spectroscopy. The supercapacitance of CuO nanosheet arrays is investigated by cyclic voltammetry, galvanostatic charge/discharge test and electrochemical impedance spectroscopy. The results show that the array of CuO nanosheets forms a uniform film of around 5 μm in thickness on nickel foam skeleton. The film is composed of clusters of arrays of nanosheets with a thickness up to around 150 nm. The CuO nanosheet arrays exhibit a specific capacitance of 569 F g−1 at a current density of 5 mA cm−2 in 6.0 mol dm−3 KOH electrolyte. The capacitance loss is less than 17.5% after 500 charge/discharge cycles at 10 mA cm−2 and with columbic efficiency higher than 93%.Highlights► CuO nanosheet arrays on nickel foam are prepared via a facile one-step method. ► Nanosheet array CuO exhibits a high specific capacitance of 569 F g−1 in KOH solution. ► CuO nanosheet arrays electrode has porous structure and high utilization of CuO.

Acetone is the main product of 2-propanol electrooxidation in both acid and alkaline electrolytes; it always co-exists with 2-propanol in the reaction solution due to its liquid nature. Whether acetone will affect the electrooxidation of 2-propanol has not been well documented, which is a key issue that needs to be addressed for the direct 2-propanol fuel cell. In this study, the influence of acetone on the electrooxidation of 2-propanol in alkaline medium is investigated, using state-of-the-art Pd electrode, by cyclic voltammetry and chronoamperometry. The electrode is prepared using a chemical replacement method, by dipping nickel foam into acidified PdCl2 solution, and characterized by scanning electron microscopy. We found that the presence of acetone adversely affects electrooxidation performance of 2-propanol and substantially reduces the oxidation current of 2-propanol on Pd in alkaline medium. The acetone poisoning effect is interpreted by a competitive adsorption mechanism, in which acetone adsorbs onto Pd surface and occupies the active sites for 2-propanol electrooxidation, leading to a significant decrease in the number of these sites for 2-propanol electrooxidation. The results of this study point out that efficient electrocatalysts for 2-propanol electrooxidation in alkaline electrolytes must be non-adsorptive to acetone besides being highly active to 2-propanol oxidation.Research highlights▶ Acetone poisons Pd for 2-propanol electrooxidation in alkaline medium. ▶ Acetone poisoning effect is due to its competitive adsorption on Pd with 2-propanol. ▶ Pd on nickel foam electrodes are prepared by a facile chemical replacement method.

The open circuit potentials (OCPs) of H2O2 at Pt, Pd, Au, and glassy carbon electrodes are measured in H2SO4 and NaOH electrolyte solutions. Effects of concentration of H+, OH− and H2O2 as well as temperature on the OCP of H2O2 are investigated. The OCP of H2O2 is much lower than its theoretical reduction potential in both acidic and basic medium. The OCP is actually a mixed potential of H2O2 electroreduction and electrooxidation simultaneously occurring at electrode surfaces and it is more close to the equilibrium potential of H2O2 electrooxidation rather than electroreduction. The OCP of H2O2 is around 0.77–0.80 V at [H+] = [H2O2] = 1.0 mol dm−3 in H2SO4 solution and is about 0–0.06 V at [OH−] = [H2O2] = 1.0 mol dm−3 in NaOH at 298 K on Pt, Pd, Au and GC electrodes. The OCP of H2O2 is independent of H2O2 concentration within the range of 0.01 to 1.0 mol dm−3. It increases approximately linearly with the logarithm of H+ concentration from 0.02 to 2.0 mol dm−3, decreases with the logarithm of OH− concentration from 0.01 to 1.0 mol dm−3 and decreases with increase of temperature from 278 K to 333 K. The linear equations were presented and discussed.Highlights► OCP of H2O2 is a mixed potential of H2O2 electrooxidation and electroreduction. ► OCP of H2O2 is closer to the equilibrium potential of H2O2 electrooxidation. ► OCP of H2O2 is around 0.8 V in acidic solution and around 0 V in basic solution.

Nanowire arrays of mixed oxides of Co and Ni freely standing on Ni foam are prepared by a template-free growth method. The effects of Ni content on the morphology, structure and catalyst performance for oxygen evolution reaction are investigated by scanning electron microscopy, X-ray diffraction spectroscopy and electrochemical techniques including cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy. A transformation from nanowire arrays to nanoplate arrays is found with the increase of the atomic ratio of Ni to Co in the preparation solution. The NixCo3−xO4 electrode obtained at 1:1 of Ni:Co in the preparation solution exhibits nanowire array structure and has better catalytic performance for oxygen evolution reaction than other NixCo3−xO4 and Co3O4 electrodes. The catalytic activities of the NixCo3−xO4 and Co3O4 electrodes are correlated with their surface roughness. Superior stability of the NixCo3−xO4 nanowire array electrode is demonstrated by a chronopotentiometric test. The reaction orders with respect to OH− on the NixCo3−xO4 electrode are close to 2 and 1 at low and high overpotentials, respectively.

Perovskite-type series of compounds La1−xSrxMnO3 are synthesized by a sol–gel method using Chitosan as the gelling agent. Their catalytic activity for hydrogen peroxide electroreduction in 3.0 mol dm−3 KOH at room temperature is evaluated by means of cyclic voltammetry and chronoamperometry. Effects of annealing temperature and the ratio of La to Sr of La1−xSrxMnO3 on their catalytic performance are investigated. Among this series of compounds, La0.4Sr0.6MnO3 calcined at 650 °C exhibits the highest activity, which is comparable with Co3O4. An aluminum–hydrogen peroxide semi-fuel cell using La0.4Sr0.6MnO3 as cathode catalyst achieves a peak power density of 170 mW cm−2 at 170 mA cm−2 and 1.0 V running on 0.6 mol dm−3 H2O2.

Activation of the MmNi4.03Co0.42Mn0.31Al0.24 hydrogen storage alloy electrode is performed by immersing the electrode in a solution containing 6.0 mol dm−3 NaOH and 0.1 mol dm−3 NaBH4. The effects of activation on the electrocatalytic activity of the electrode for NaBH4 oxidation are investigated by cyclic voltammetry and chronoamperometry. Immersion activation greatly improves the electrocatalytic activity of the alloy electrode. Hydrogen was absorbed in the alloy during the immersion activation treatment and its electrooxidation is responsible for the high initial oxidation current. The stabilized current mainly results from the direct oxidation starting from the borohydride species. The effects of activation on structure and surface chemistry of the alloy are also discussed.

Direct carbon fuel cells are promising power sources using solid carbon directly as fuel. Their performances significantly depend on the electrooxidation activity of carbon fuel. Electrooxidation of activated carbon particulates in molten Li2CO3–K2CO3 was investigated by potentiodynamic and potentiostatic method. Results indicated that the electrooxidation performance of activated carbon was significantly enhanced by pre-soaking with Li2CO3–K2CO3 and by treatment with HF, HNO3 and NaOH, respectively. The onset potential negatively shifted by around 100 mV and the current density increased by around 50 mA cm−2 after pre-soaking. The non-oxidant acids (HF) treatments are more effective than oxidant acid (HNO3) and base (NaOH) treatments. HF treated activated carbon exhibited the highest activity among all the samples. The enhancement in electrooxidation performance can be closely correlated with the increase in surface area and porosity caused by acid and base treatments.

Au/Ni-foam electrodes with three dimensional network structures are prepared by simple spontaneous deposition of nano-sized Au particles onto nickel foam surface in an aqueous solution of AuCl3. Their morphology and catalytic performance for NaBH4 electrooxidation and H2O2 electroreduction in NaOH solution are investigated. Au particles with diameters smaller than 100 nm are uniformly deposited on the whole surface of all skeletons of the nickel foam substrate. The onset potential for NaBH4 electrooxidation and H2O2 electroreduction is about −1.2 V and −0.1 V, respectively. A direct liquid feed alkaline NaBH4–H2O2 fuel cell is constructed using Au/Ni-foam electrode as both the anode and the cathode. The effects of the concentration of NaBH4 and H2O2 and operation temperature on the fuel cell performance are investigated. The fuel cell exhibits an open circuit voltage of about 1.07 V and a peak power density of 75 mW cm−2 at a current density of 150 mA cm−2 and a cell voltage of 0.5 V operating on 0.2 mol dm−3 NaBH4 and 0.5 mol dm−3 H2O2 at 40 °C.

Mg–Li–Al–Sn and Mg–Li–Al–Sn–Ce alloys were prepared using a vacuum induction melting method. Their electrochemical oxidation behavior in NaCl solution was investigated by means of potentiodynamic and chronoamperometric measurements. The surface morphology after discharge was examined using scanning electron microscopy. Utilization efficiency was estimated with a mass-loss method. The results indicated that Mg–Li–Al–Sn has a higher discharge current density but lower utilization efficiency than Mg–Li–Al–Sn–Ce. The typical utilization efficiency after continuous discharging at constant potential of −1.0 for 2 h is 65% and 70% for Mg–Li–Al–Sn and Mg–Li–Al–Sn–Ce, respectively. The utilization efficiency decreased with the increase of anodic potential. Both alloys have similar self-discharge rate in NaCl solution at open-circuit potential.

Ni foam supported-Co3O4 nanowire arrays are prepared by a template-free growth method, followed by a thermal treatment in air, and are characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, infrared spectroscopy, and thermogravimetric and differential thermal analysis. The Co3O4 nanowires have a diameter of about 250 nm, a length up to 15 μm, and a Brunauer-Emmett-Teller surface area of 78.4 m2 g−1. They grow almost vertically from the surface of Ni foam skeleton, pack densely, and uniformly cover the entire surface of Ni foam skeleton. Electroreduction of H2O2 on Co3O4 nanowire arrays in alkaline medium is investigated by cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. The Co3O4 nanowire electrode exhibits superior activity, stability, and mass transport property for H2O2 electroreduction. A current density of 90 mA cm−2 is achieved at −0.4 V in 0.4 mol dm−3 H2O2 and 3.0 mol dm−3 NaOH at room temperature. The per gram current density measured at −0.4 V on Co3O4 nanowires is about 1.5 times of that on Co3O4 nanoparticles.

Mg–Li, Mg–Li–Al and Mg–Li–Al–Ce alloys were prepared and their electrochemical behavior in 0.7 M NaCl solutions was investigated by means of potentiodynamic polarization, potentiostatic current–time and electrochemical impedance spectroscopy measurements as well as by scanning electron microscopy examination. The effect of gallium oxide as an electrolyte additive on the potentiostatic discharge performance of these magnesium alloys was studied. The discharge activities and utilization efficiencies of these alloys increase in the order: Mg–Li < Mg–Li–Al < Mg–Li–Al–Ce, both in the absence and presence of Ga2O3. These alloys are more active than commercial magnesium alloy AZ31. The addition of Ga2O3 into NaCl electrolyte solution improved the discharging currents of the alloys by more than 4%, and enhanced the utilization efficiencies of the alloys by more than 6%. It also shortened the transition time for the discharge current to reach to a steady value. Electrochemical impedance spectroscopy measurements showed that the polarization resistance of the alloys decreases in the following order: Mg–Li > Mg–Li–Al > Mg–Li–Al–Ce. Mg–Li–Al–Ce exhibited the best performance in term of activity, utilization efficiency and activation time.

Mg–Li–Al–Ce–Zn and Mg–Li–Al–Ce–Zn–Mn alloys were prepared using a vacuum induction melting method. Their electrochemical oxidation behavior in 0.7 M NaCl solution was investigated by means of potentiodynamic polarization, potentiostatic oxidation, electrochemical impedance technique and scanning electron microscopy examination. Their utilization efficiencies and performances as anode of metal–hydrogen peroxide semi-fuel cell were determined. The Mg–Li–Al–Ce–Zn–Mn exhibited higher discharge activity and utilization efficiency than Mg–Li–Al–Ce–Zn, and gave improved fuel cell performance. The utilization efficiency of Mg–Li–Al–Ce–Zn–Mn is comparable with that of the state-of-the-art magnesium alloy anode AP65. The magnesium–hydrogen peroxide semi-fuel cell with Mg–Li–Al–Ce–Zn–Mn anode presented a maximum power density of 91 mW cm−2 at room temperature. Scanning electron microscopy and electrochemical impedance studies indicated that the alloying element Mn prevented the formation of dense oxide film on the alloy surface and facilitated peeling off of the oxidation products.

Spinel structure Co3O4 nanoparticles with an average diameter of around 17 nm were prepared and evaluated as electrocatalysts for H2O2 reduction. Results revealed that Co3O4 exhibits considerable activity and good stability for electrocatalytic reduction of H2O2 in 3 M NaOH solution. The reduction occurs mainly via the direct pathway when H2O2 concentration is lower than 0.5 M. An Al-H2O2 semi fuel cell using Co3O4 as cathode catalyst was constructed and tested at room temperature. The fuel cell displayed an open circuit voltage of 1.45 V and a peak power density of 190 mW cm−2 at a current density of 255 mA cm−2 operating with a catholyte containing 1.5 M H2O2. This study demonstrated that Co3O4 nanoparticles are promising cathode catalysts, in place of precious metals, for fuel cells using H2O2 as oxidant.

Pd nanoparticles were immobilized on Au disk electrode and kinetics of hydrogen peroxide electroreduction on the Pd electrode in 0.1 M H2SO4 solution was investigated using a rotating disk electrode method. The phase and particle size of palladium were characterized by XRD measurements. The morphology of Pd on Au was examined using SEM. We found that the hydrogen peroxide reduction on Pd nanoparticles proceeds via a two-electron process. The reaction order is one with respect to hydrogen peroxide. An apparent activation energy of 55 kJ mol−1 was calculated from exchange currents at different temperature. The lower activation energy and higher exchange current density demonstrated that hydrogen peroxide reduction has a faster kinetics than oxygen reduction. Electrolyte anions significantly affect hydrogen peroxide reduction activity, and the activity decreases in the order ClO4- > HSO4- > Cl−, which is consistent with the increasing adsorption bond strength of the anions.

Pd–Ru, Pd and Ru nanoparticles supported on Vulcan XC-72 carbon were prepared by chemical reduction of PdCl2 and/or RuCl3 in aqueous solution using NaBH4 as the reducing agent. Transmission electron microscopy measurements showed that Pd–Ru particles were uniformly dispersed on carbon. The particle size of Pd–Ru is around 5–9 nm. X-ray diffraction analysis indicated that Ru formed alloy with Pd in Pd–Ru/C catalyst. The electroreduction of hydrogen peroxide on Pd–Ru/C, Pd/C and Ru/C in H2SO4 solution was examined by linear sweep voltammetry and chronoamperometry measurements. Results revealed that Pd–Ru/C catalyst exhibited higher electrocatalytic activity for hydrogen peroxide reduction than Pd/C and Ru/C. All the catalysts showed good stability for hydrogen peroxide electroreduction in H2SO4 electrolyte.

The direct carbon fuel cell is a special type of high temperature fuel cell that directly uses solid carbon as anode and fuel. As an electrical power generator for power plants, it has a higher achievable efficiency (80%) than the molten carbonate and solid oxide fuel cells, and has less emissions than conventional coal-burning power plants. More importantly, its solid carbon-rich fuels (e.g. coal, biomass, organic garbage) are readily available and abundant. In this review, some fundamental study results of electrochemical oxidation of carbon in molten salts are summarized. Recent developments in direct carbon fuel cell configurations and performance are also discussed.

•A novel 3D Pd-rGO-C@TiC electrode is successfully fabricated.•Pd is uniformly distributed on the surface of graphene nanosheet and C@TiC nanowire.•The electrode exhibits high performance and good stability for NaBH4 oxidation.Recently, direct borohydride fuel cell (DBFC) has been considering as a promising energy conversion devices. During the development of DBFC, reducing the use of noble metals and increasing the anode performance are the hot topic in recent researches. In this article, reduced graphene oxide nanosheets deposit on C@TiC coaxial nanowire array (rGO-C@TiC) by means of a combine method of chemical vapor deposition and electrodeposition is chosen as 3D current collector for Pd nanoparticles deposition. The morphology and crystal structure of the as-obtained 3D electrode is checked with FESEM, TEM, EDS, and XRD. Results claim that the as-prepared 3D electrode exhibits a mushroom-like structure with the mean diameter size of Pd is 5.32 nm. Their catalytic ability for NaBH4 electro-oxidation is evaluated in a three electrode system by using the method of cycle voltammetry and chronoamperometry, proving that the 3D Pd-rGO-C@TiC electrode has a higher catalytic performance. The oxidation current density of 1.35 A cm−2 mg−1Pd is achieved at −0.6 V. Furthermore, a direct borohydride-hydrogen peroxide fuel cell (DBHPFC) is assembled by using the as-prepared Pd-rGO-C@TiC electrode and a Pd/CFC electrode as anode and cathode catalyst, respectively, and a maximum power density of 68.5 mW cm−2 is obtained. In addition, the assembled DBHPFC shows excellent higher performance based on the mass activity basis (1427.1 W g−1) among those reported literatures, indicating that our Pd-rGO-C@TiC could be acted as a promising cost-effective and ponderable alternative catalyst for NaBH4 electrooxidation.In this paper, a novel 3D electrode for NaBH4 electro-oxidation with rGO nanosheet deposited on C@TiC core–shell nanoarray as a bind-free current collector substrate to support Pd nanoparticles is prepared.

•A 3D electrode with CNT decorated on Ni foam is built for MnO2 growth.•MnO2 nanoflakes uniformly grow on the 3D electrode via a simple hydrothermal method.•MnO2 nanoflakes exhibit a specific capacitance as high as 402.5 F g− 1 at 1 A g− 1.•The asymmetric supercapacitor exhibits an energy density of 25 Wh kg− 1 with 85.3% capacitance retention after 5000 cycles.Designing and fabricating self-supported and binder-free MnO2 nanostructure electrode to overcome their low conductivity for supercapacitor application with high comprehensive electrochemical performance, such as high capacitance, excellent stability, and good rate capability, is still a tremendous challenge. In this paper, carbon nanotubes are uniform covered on nickel foam (denote as CNT/Ni) by a simple dip & dry method to form a 3D skeleton for MnO2 nanosheets deposition (denoted as MnO2-CNT/Ni). Results show the MnO2-CNT/Ni electrode exhibits a unique 3D porous interconnected network with a high specific capacitance of 402.5 F g− 1 at 1 A g− 1 and a favorable cycling performance that 83% capacitance retained after 5000 cycles at a current density of 2 A g− 1. Meanwhile, the MnO2-CNT/Ni//CNT/Ni asymmetric supercapacitor exhibits an excellent energy density of 25 Wh kg− 1 at a power density of 0.9 kW kg− 1 with 85.3% capacitance retention after 5000 cycles. Therefore, such a facile and manageable method to prepare MnO2 electrode with high supercapacitor performance is offering a promising future for practical applications.

To meet the ever-increasing need for high-efficiency energy storage in modern society, porous carbon materials with large surface areas are typically employed for electrical double-layer capacitors to achieve high gravimetric performances. However, their poor volumetric performances come from low packing density and/or high pore volume resulting in poor volumetric capacitance, which would limit their further applications. Here, a novel and one-step molten salt synthesis of a three-dimensional, densely nitrogen-doped porous carbon (NPC) material by using low-cost and eco-friendly tofu as the nitrogen-containing carbon source is proposed. Hierarchically porous carbon with a specific surface area of 1202 m2 g−1 and a high nitrogen content of 4.72 wt% and a bulk density of ∼0.84 g cm−3 is obtained at a carbonation temperature of 750 °C. As the electrode material for a supercapacitor, the NPC electrode shows both ultra-high specific volumetric and gravimetric capacitances of 360 F cm−3 and 418 F g−1 at 1 A g−1 (based on a three-electrode system), respectively, and excellent cycling stability without capacitance loss after 10000 cycles at a high charge current of 10 A g−1 in KOH electrolyte. Moreover, the as-assembled symmetric supercapacitor exhibits not only an excellent cycling stability with 97% capacitance retention after 10000 cycles, but also a high volumetric energy density up to 27.68 W h L−1 at a current density of 0.2 A g−1, making this new method highly promising for compact energy storage devices with simultaneous high volumetric/gravimetric energy and power densities.

Porous (Co, Mn)3O4 nanowires freely standing on a Ni foam are synthesized via a template-free growth method, followed by a thermal treatment in air. The nanowires are characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy, thermogravimetric analysis and Fourier transform infrared spectroscopy. Their catalytic performance in H2O2 electroreduction is evaluated by linear scan voltammetry and chronoamperometry. Results show that a thermal treatment leads to the conversion of solid nanowires of MnCO3 + CoCO3 to porous nanowires of (Co, Mn)3O4via decomposition and reconfiguration, which is identified to be the catalytic active component for H2O2 electroreduction. Nanowires calcined at 300 °C exhibit the highest activity for H2O2 reduction and a current density of 329 mA cm−2 is obtained in 3.0 mol dm−3 KOH + 0.6 mol dm−3 H2O2 at −0.4 V (vs. Ag/AgCl, KCl). The catalytic activity of (Co, Mn)3O4 nanowires is almost twice than that of Co3O4 nanowires. The role of Mn in improving the catalytic activity is proposed and discussed.

One-dimensional (1D) nanostructures have been identified as the most viable structures for high-performance supercapacitors from the view of high ion-accessible surface area and rapid electron transport path as well as excellent mechanical properties. Herein, we report a “stripping and cutting” strategy to produce 1D carbon nanobelts (CNB) from tofu with irregular structures through a molten salts assisted technique. It is a completely novel and green avenue for constructing 1D carbon materials from biomass, showing large commercial potential. The resultant CNB electrode delivers a high specific capacitance (262 F g−1 at 0.5 A g−1) and outstanding cycling stability with capacitance retention up to 102% after 10000 continuous charging/discharging cycles. Additionally, a CNB//CNB symmetric supercapacitor and CNB//MnO2–CNB asymmetric supercapacitor are assembled and reach energy densities of 18.19 and 29.24 W h kg−1, respectively. Therefore, such a simple, one-pot and low-cost process may have great potential for preparing eco-friendly biomass-derived carbon materials for high-performance supercapacitor electrodes.

Binder-free Pd decorated Ni nanowire (Pd/Ni NW) electrodes are simply fabricated by template-assisted electrodeposition of nickel nanowires and subsequently by spontaneous growth of palladium electrocatalysts on the nickel nanowire surface. The Pd/Ni NW electrode presents superior electrochemical activity and desirable stability towards NaBH4 electrooxidation in an alkaline environment.

In this work, a facile method for the preparation of a series of transition metal oxide–metal nanocomposites (MO–M) (such as NiO–Ni, Co3O4–Co, Fe3O4–Fe and MnO2–Mn) anchored on conductive nanowire arrays (such as TiC–C core–shell nanowires grown on a Ti alloy sheet) is reported for the first time. The obtained composites possess a unique three-dimensional nanostructure and high electronic conductivity. They have diverse applications as electrodes of energy storage devices. High capacitance and high rate capability have been demonstrated using the NiO–Ni@C@TiC nanocomposite as a model electrode, which shows a specific capacitance as high as 1845 F g−1 at a charge–discharge current density of 5 A g−1 and 811.1 F g−1 after cycling 500 times at an extremely high charge–discharge rate of 100 A g−1.