The lightweight compound material NaNH2–NaBH4 is regarded as a promising hydrogen storage composite due to the high hydrogen density. Mechanical ball milling was employed to synthesize the composite NaNH2–NaBH4 (2/1 molar ratio), and the samples were investigated utilizing thermogravimetric-differential thermal analysis-mass spectroscopy (TG-DTA-MS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) analyses. The full-spectrum test (range of the ratio of mass to charge: 0–200) shows that the released gaseous species contain H2, NH3, B2H6, and N2 in the heating process from room temperature to 400 °C, and possibly the impurity gas B6H12 also exists. The TG/DTA analyses show that the composite NaNH2–NaBH4 (2/1 molar ratio) is conductive to generate hydrogen so that the dehydrogenation process can be finished before 400 °C. Moreover, the thermal decomposition process from 200 to 400 °C involves two-step dehydrogenation reactions: (1) Na3(NH2)2BH4 hydride decomposes into Na3BN2 and H2 (200–350 °C); (2) remaining Na3(NH2)2BH4 reacts with NaBH4 and Na3BN2, generating Na, BN, NH3, N2, and H2 (350–400 °C). The better mechanism understanding of the thermal decomposition pathway lays a foundation for tailoring the hydrogen storage performance of the composite complex hydrides system.Keywords: ball milling; dehydrogenation; hydrogen storage; NaNH2−NaBH4; thermal decomposition;

As a typical multielectron cathode material for lithium-ion batteries, iron fluoride (FeF3) and its analogues suffer from poor electronic conductivity and low actual specific capacity. Herein, we introduce Ag nanoparticles by silver mirror reaction into the FeF3·0.33H2O cathode to build the electronic bridge between the solid (active materials) and liquid (electrolyte) interface. The crystal structures of as-prepared samples are characterized by X-ray diffraction and Rietveld refinement. Moreover, the density of states of FeF3·0.33H2O and FeF3·0.33H2O/Ag (Ag-decorated FeF3·0.33H2O) samples are calculated using the first principle density functional theory. The FeF3·0.33H2O/Ag cathodes exhibit significant enhancements on the electrochemical performance in terms of the cycle performance and rate capability, especially for the Ag-decorated amount of 5%. It achieves an initial capacity of 168.2 mA h g–1 and retains a discharge capacity of 128.4 mA h g–1 after 50 cycles in the voltage range of 2.0–4.5 V. It demonstrates that Ag decoration can reduce the band gap, improve electronic conductivity, and elevate intercalation/deintercalation kinetics.Keywords: Ag-decoration; electronic bridge; FeF3·0.33H2O cathode; kinetics; lithium-ion battery;

Doping modification of electrode materials is a sought-after strategy to improve their electrochemical performance in the secondary batteries field. Herein, polyanion (BO3)3−-doped Li3V2(PO4)3 cathode materials were successfully synthesized via a wet coordination method. The effects of (BO3)3− doping content on crystal structure, morphology and electrochemical performance were explored by X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). All the as-prepared samples have the same monoclinic structure; among them, Li3V2(PO4)2.75(BO3)0.15 sample has relatively uniform and optimized particle size. In addition, this sample has the highest discharge capacity and the best cycling stability, with an initial discharge capacity of 120.4 mAh·g−1, and after 30 cycles at a rate of 0.1C, the discharge capacity still remains 119.3 mAh·g−1. It is confirmed that moderate polyanion (BO3)3− doping can rearrange the electronic structure of the bulk Li3V2(PO4)3, lower the charge transfer resistance and further improve the electrochemical behaviors.

•A wet-chemical coordination approach for Li3V2(PO4)3/C has been developed.•The phase purity and ionic conductivity of Li3V2(PO4)3/C has been improved.•The optimized Li3V2(PO4)3/C shows good capability and cyclic reversibility.•The specific Li+ insertion/extraction mechanism is further confirmed.Lithium vanadium phosphate (Li3V2(PO4)3) is one of the most promising cathode materials for developing practical Li-ion batteries due to its advantages of structural stability, low cost, relatively high energy density. For this purpose, a wet-chemical coordination approach has been applied to synthesis of the Li3V2(PO4)3/C (LVP/C) cathode materials for Li-ion batteries. The structure, morphology, and electrochemical and kinetic behaviors of LVP/C samples calcined at different temperatures are studied. The optimized Li3V2(PO4)3 sample calculated at 850 °C (denoted as LVP-850) exhibits excellent rate performance: at high rate of 0.5, 1, 5, 10 and 20 C, impressive specific capacity of 110.9, 106, 91.2, 83 and 43.6 mAh g−1 can still be attainted, respectively. Even through it recovers back to 0.1 C, the cell can still deliver a capacity of 114.4 mAh g−1 (about 97.9% of the initial capacity). Combined with cyclic voltammetry technique and ex-situ X-ray photoemission spectroscopy (XPS), the Li+ insertion/extraction reaction mechanisms are also confirmed. Such an efficient method plays a critical role in improving rate performance and cyclic reversibility of Li3V2(PO4)3 particles, and should also be appropriate for other functional electrode materials.Download high-res image (208KB)Download full-size image

Pursuing for novel electrode materials is significant for the progress of sodium ion batteries (SIBs). Here, a multilayered electride prepared by simple thermal decomposition of solid Ca3N2, namely Ca2N, is introduced as a new anode material of SIBs for the first time, and a compression molding electrode fabricated by pressing Ca2N powder into nickel foam is applied to protect Ca2N from trace moisture and oxygen. The as-prepared electrode delivers an initial discharge capacity of 1110.5 mAh g–1 and a reversible discharge capacity of ∼320 mAh g–1. These results suggest that Ca2N has a great potential for sodium ion batteries.Keywords: anode; Ca2N; electride; multilayered; sodium ion batteries;

In order to get an element substituted into Na3V2(PO4)3/C in an appointed V site, the simple sol–gel method is used to design and prepare a series of Na-rich Na3+xV2–xNix(PO4)3/C (x = 0–0.07) compounds. To get a charge balance, the ratio of Na, V, and Ni would be changed if Ni goes into a different site. Hence, ICP is applied to probe the real stoichiometry of the as-prepared Na3+xV2–xNix(PO4)3/C (x = 0–0.07). According to the Na/V ratio from the ICP result, it indicates that Ni2+ goes to a V site, and more Na+ will be introduced into the crystal to keep the charge balance. In addition, the crystal structure changes are explored by XRD and Rietveld refinement, it is indicated from the results that Ni2+ doping does not destroy the lattice structure of Na3V2(PO4)3. When applied as Na-storage material, the electrochemical property of all Ni2+ doped Na3+xV2–xNix(PO4)3/C composites have been significantly improved, especially for the Na3.03V1.97Ni0.03(PO4)3/C sample. For example, 107.1 mAh g–1 can be obtained at the first cycle; after 100 cycles, the capacity retention is as high as 95.5%. Moreover, when charging/discharging at a higher rate of 5 C, the capacity still remains 88.9 mAh g–1, displaying good rate performance. The good electrochemical performance is ascribed to the optimized morphology, stable crystal structure, and improved ionic conductivity.Keywords: cathode; Na-rich; Na3V2(PO4)3/C; nickel substitution; sodium ion batteries

As a promising post-lithium battery, rechargeable aluminum battery has the potential to achieve a three-electron reaction with fully use of metal aluminum. Alternative electrolytes are strongly needed for further development of rechargeable aluminum batteries, because typical AlCl3-contained imidazole-based ionic liquids are moisture sensitive, corrosive, and with low oxidation voltage. In this letter, a kind of noncorrosive and water-stable ionic liquid obtained by mixing 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIM]OTF) with the corresponding aluminum salt (Al(OTF)3) is studied. This ionic liquid electrolyte has a high oxidation voltage (3.25 V vs Al3+/Al) and high ionic conductivity, and a good electrochemical performance is also achieved. A new strategy, which first used corrosive AlCl3-based electrolyte to construct a suitable passageway on the Al anode for Al3+, and then use noncorrosive Al(OTF)3-based electrolyte to get stable Al/electrolyte interface, is put forward.Keywords: electrochemical performance; electrolyte; high voltage; rechargeable aluminum battery; [BMIM]OTF ionic liquids

A rechargeable aluminum battery is considered as a promising battery system used in energy storage devices, due to its natural abundance and high capacity. However, fabrication of this battery working at room temperature did not succeed until haloaluminate containing ionic liquids were used as electrolytes. Therefore, anions are expected to have a great effect on performance of rechargeable aluminum batteries. For a complete understanding of the anion-effect, haloaluminate containing ionic liquids prepared with different halogenated imidazole salt and AlCl3/imidazolium chloride mole ratios are studied. The electrochemical window is found to narrow with reducibility of halide ions, which is confirmed by calculation results using the density functional theory (DFT) method. For ionic liquids at different mole ratios, the coexistence of different chloroaluminate anions (Cl−, AlCl4−, Al2Cl7−) is found. When used as an electrolyte in a rechargeable aluminum battery with a V2O5 nanowire cathode, the AlCl3/[BMIM]Cl ionic liquid with the mole ratio of 1.1:1 shows the best performance. The as-assembled cell exhibits a high discharge voltage platform (1 V) and capacity (288 mA h g−1) at the first cycle. Concentration of Al2Cl7− is considered as a key factor in chloroaluminate ionic liquids when used as electrolytes. Furthermore, a slight corrosion is found on the surface of Al metal foil immersed in an AlCl3/[BMIM]Cl = 1.1:1 ionic liquid for 24 h, which may help remove the oxide film on the Al metal foil, so as to improve the charge/discharge performance.

In seeking new sulfone-based electrolytes to meet the demand of 5 V lithium-ion batteries, we have combined the theoretical quantum chemistry calculation and electrochemical characterization to explore several sulfone/cosolvent systems. Tetramethylene sulfone (TMS), dimethyl sulfite (DMS), and diethyl sulfite (DES) were used as solvents, and three kinds of lithium salts including LiBOB, LiTFSI, and LiPF6 were added into TMS/DMS [1:1, (v)] and TMS/DES [1:1, (v)] to form high-voltage electrolyte composites, respectively. All of these electrolytes display wide electrochemical windows of more than 5.4 V, with the high electrolyte conductivities being more than 3 mS/cm at room temperature. It is indicated that to achieve the best ionic conductivity in TMS/DMS cosolvent, the optimized concentrations of lithium salts LiBOB, LiTFSI, and LiPF6 were 0.8, 1, and 1 M, respectively. Furthermore, the vibrational changes of the molecular functional groups in the cosolvents were evaluated by Fourier transform infrared spectroscopy. It is found that lithium salts show strong interaction with the main functional sulfone groups and sulfonic acid ester group, thus playing a vital role in the enhancement of the ionic conductivity and electrochemical stability of the solvent system. These sulfone-based solvents with high electrochemical stability are expected to become a new generation of a high-voltage organic electrolytic liquid system for lithium-ion batteries.Keywords: electrolyte; high voltage; lithium salts; lithium-ion battery; quantum chemical calculation; sulfone-based solvent;

•Na3V2(PO4)3/C nanorods are synthesized by electrospinning combined with sintering.•A high reversible capacity of 116.9 mAh g− 1 is achieved.•The Na+ diffusion coefficient is 5.39 × 10− 13 cm2/s after the first cycle.•The effects of 1D nanorod morphology on the Na+ diffusion are discussed.Morphological control is an effective way to improve the electrochemical properties of electrode materials for rechargeable batteries. In this paper, 1D Na3V2(PO4)3/C nanorods were successfully synthesized by a facile electrospinning method. Using as the cathode of sodium ion batteries, the Na3V2(PO4)3/C nanorods display good electrochemical performance. For example, it shows quite a flat potential plateau around 3.4 V (vs Na+/Na) and delivers an initial capacity as high as 116.9 mAh g− 1 at current density of 0.05 C, which is close to the theoretical capacity of 117.6 mAh g− 1. When cycled at 0.5 C, the initial discharge capacity is 105.3 mA h g− 1, and 92.6% of this value is still retained after 50 cycles. The good electrochemical performance can be ascribed to the short ion diffusion distances induced by the 1D nanorod morphology. The sodium ion diffusion coefficient of Na3V2(PO4)3/C nanorods after the first cycle is 5.39 × 10− 13 cm2/s, which is one order higher than the irregular micron scale Na3V2(PO4)3/C reported before.

•A series of Si/CeO2/Polyaniline composites are synthesized as anode materials.•An initial coulombic efficiency of 87.6% is achieved.•Si/CeO2/Polyaniline remains a specific capacity of 775 mAh/g after 100 cycles.•The Li+ diffusion coefficient is 7.5 × 10− 16 cm2/s.•The synergistic effect of CeO2 and Polyaniline improves the electrochemical performances.Si has very high theoretical specific capacity as an anode material in a lithium ion battery. However, its application is seriously restricted because of relatively undesirable conductivity and poor cycling stability. Here we report Si/CeO2/Polyaniline (SCP) composite as an anode material, which was synthesized by hydrothermal reaction and chemical polymerization. The structures and morphologies of the SCP composites are characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM) and transmission electron microscopy (TEM). It is shown that Si/CeO2 (SC) particles are well coated by PANI elastomer which has good electrical conductivity. The SCP shows larger reversible capacity and better cycling performance compared with pure Si. The first reason is that CeO2 can protect Si from reacting with electrolyte. More importantly, the PANI elastomer can accommodate the volume change of the composite during Li-alloying/dealloying processes, so the pulverization of silicon would be significantly reduced. The SCP material can retain a capacity nearly 775 mAh/g after 100 cycles, while pure Si only shows a capacity of 370 mAh/g after 100 cycles.

•NaNH2–NaBH4 composite is prepared via a liquid-phase ball milling method.•The thermal decomposition activation energy of the sample is only 76.4 kJ mol−1.•The thermal decomposition kinetics is greatly improved without any catalyst.•The multi-effect function of liquid-phase ball milling method is discussed.As a light-weight and low-cost hydrogen storage composite, NaNH2–NaBH4 (molar ratio of 2:1) was prepared by a liquid phase ball milling (LPBM) method under the co-protection of argon and cyclohexane. The structure evolution and the thermal decomposition performance of the as-prepared sample were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermo gravimetric-differential thermal analysis (TG-DTA), respectively. It is found that the interaction of NaNH2 with NaBH4 is enhanced by LPBM, thus causes a preferred orientation for the crystal structure of NaNH2, and the red-shifts of the N–H stretching vibration and the B–H stretching vibration. In addition, the as-prepared NaNH2–NaBH4 (2/1) can achieve a low activation energy of 76.4 kJ mol−1 during the main decomposition stage, which is only 47.9% of that of the one synthesized via a solid state ball milling (SSBM) method, and is very close to that of the Co–B catalyst promoted one. This indicates the LPBM method is an efficient way to get high-performance NaNH2–NaBH4, whose thermal decomposition kinetics can be greatly improved without any catalyst.

Facing the significant applications in energy field, this paper introduces how to construct new high specific energy secondary batteries based on the concept multi-electron reaction and by designing multi-electron electrode materials. Recent progress on those new secondary batteries and their key materials based on the theory of multi-electron reaction are overviewed. Representative multi-electronic electrode materials, such as metal borides, metal fluorides, sulfur composite electrode materials and ferrates are briefly introduced, as well as the new secondary battery systems constructed with these materials. Thus gives the significance of the development based on multi-electron reaction mechanism of secondary batteries and their key materials for new chemical battery systems and related energy materials.

Composite NaNH2–NaBH4 (molar ratio of 2/1) hydrogen storage materials are prepared by a ball milling method with various ball milling times. The compositions and hydrogen generation characteristics are investigated by means of X-ray diffraction (XRD) and thermo gravimetric-differential thermal analysis (TG-DTA). The structural characteristics imply that ball milling produces a new phase of Na3(NH2)2BH4, and mechanical energy accumulated in the ball milling process may be responsible for the phase change of Na3(NH2)2BH4. TG-DTA demonstrates that the phase change temperature of the composite NaNH2–NaBH4 (2/1) ball milled for 16 h is 141.8 °C, and the melting point is 197.3 °C; below 400 °C, composite hydrogen storage material is mainly decomposed to give hydrogen and Na3BN2; while above 400 °C, the previous by-product Na3BN2 continues to decompose so as to give metal Na gradually.Highlights► A new phase of Na3(NH2)2BH4 is detected, and the accumulated mechanical energy may cause the phase change of Na3(NH2)2BH4. ► The decomposition mechanisms of NaNH2–NaBH4 (2/1) are analyzed and illustrated. ► Based on the mass conservation, the theoretic H2 yield of NaNH2-NaBH4 (2/1) exceeds 98%. ► It is an efficient way to improve the H2 yield by suppressing the N2 generation in NaNH2-NaBH4 (2/1).

Pt-WO3 nanoparticles uniformly dispersed on Vulcan XC-72R carbon black were prepared by an ethylene glycol method. The morphology, composition, nanostructure, electrochemical characteristics and electrocatalytic activity were characterized, and the formation mechanism was investigated. The average particle size was 2.3 nm, the same as that of Pt/C catalyst. The W/Pt atomic ratio was 1/20, much lower than the design of 1/3. The deposition of WO3·xH2O nanoparticles on Vulcan XC-72R carbon black was found to be very difficult by TEM. From XPS and XRD, the Pt nanoparticles were formed in the colloidal solution of Na2WO4, the EG insoluble Na2WO4 resulted in the decreased relative crystallinity and increased crystalline lattice constant compared with those of Pt/C catalyst and, subsequently, the higher specific electrocatalytic activity as determined by CV. The Pt-mass and Pt-electrochemically-active-specific-surface-area based anodic peak current densities for ethanol oxidation were 422.2 mA·mg−1Pt and 0.43 mA·cm−2Pt, 1.2 and 1.1 times higher than those of Pt/C catalyst, respectively.

Two kinds of CoX2 (X = Cl−, NO3−) are adopted as the accelerators for the hydrolysis reaction of NaBH4, which is a promising H2-supply method for proton exchange membrane fuel cell (PEMFC). In the reactor, the initial H2 generation is caused by the reaction between pre-infused CoX2 solution and subsequently imported NaBH4 solution, and some precipitates are in situ formed on the catalyst bed by this way; and the following H2 generation is promoted by these precipitates. It is found that there are competitive reactions during H2 generation from an NaBH4 to NaOH solution, the anions of CoX2 are crucial to the reaction pathways, which led to the formation of highly active Co–B or inactive Co(OH)2. The effects of the CoX2 concentration, the NaOH concentration, the NaBH4 feeding rate and the NaBH4 concentration on H2 generation performances are discussed and compared.

Three co-impregnation/chemical reduction methods in acidic solutions of pH < 1, including ethylene glycol (EG), NaBH4, and HCOOH, were compared for Pt-WO3/C catalysts. Pt-WO3/C catalysts containing 10 wt.% and 20 wt.% platinum per carbon were prepared by the three methods; their morphology and electrocatalytic activities were characterized. The 20 wt.% Pt-WO3/C catalyst prepared by the co-impregnation/EG method presented the optimal dispersion with an average particle size of 4.6 nm and subsequently the best electrocatalytic activity, and so, it was further characterized. Its anodic peak current density for ethanol oxidation from linear sweep voltammetry (LSV) is 7.9 mA·cm−2, which is 1.4 and 5.2 times as high as those of the catalysts prepared by co-impregnation/NaBH4 and co-impregnation/ HCOOH reduction methods, 2.1 times as high as that of the 10 wt.% Pt-WO3/C catalyst prepared by co-impregnation/EG method, respectively.

Fourier-transform infrared (FTIR) spectroscopy has been used to identify the solid electrolyte interphase (SEI) formed on Li-doped spinel Li1.05Mn1.96O4 cathode. The major components in the SEI have been assigned, and the formation and evolution of the SEI over the initial charge–discharge cycle are discussed. By Fourier-transform infrared spectroscopy, it has been found that during the charge–discharge process, the SEI can be directly formed on the Li1.05Mn1.96O4 cathode, and is mainly composed of R-CO3Li and Li2CO3. In terms of composition, it is very similar to those formed on a carbon anode. In the initial cycle, the formation of R-CO3Li begins at 4.10 V during the charging process, and becomes more distinct with increasing charge voltage. The formation of Li2CO3 begins at 4.10 V during the discharge process, and becomes more distinct with decreasing discharge voltage. The SEI becomes more evident over subsequent cycles.

High active FeB alloy was prepared by an electric arc method, and used as the anode material for alkaline secondary batteries. The structural characteristics of the as-prepared FeB alloy were studied using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), and the electrochemical performances were investigated using cyclic voltammetry (CV) and charge–discharge test. The FeB alloy achieves an excellent reversible capacity of 312 mA h/g as well as a good cycleability, and is proved to be a promising low-cost and high performance anode material for alkaline secondary batteries.

The Li1+xV3O8 material was successfully synthesized at 450 °C in short sintering duration by microwave sol–gel route. X-ray diffraction suggests oxygen defects in the lattice. Based on Randles–Sevcik formula, cyclic voltammograms measurements were conducted to measure Li+ ion diffusion coefficient. The material exhibits high discharge capacity of 250 mA g−1 at 0.2 mA/cm2 after 30 cycles in the range of 2.0–4.0 V. Alternating current impedance tests show that the growth of the charge transfer resistance at 0.4 mA/cm2 is more rapid than that of at 0.2 mA/cm2 as the galvanostatical charge–discharge continues.

Ternary Mg–Co–B alloys have been successfully synthesized by a chemical reduction method with subsequent heat-treatment at various temperatures. The products thus obtained have been investigated as anode materials in alkaline aqueous KOH + LiOH co-solution. The as-prepared Mg–Co–B alloys have been found to show excellent electrochemical reversibility, as well as considerably high specific capacities of up to 336 mAh/g. The outstanding electrochemical performances of the Mg–Co–B alloys are shown to stem from their specific microstructures, which have been characterized by X-ray diffraction, scanning electron microscopy, BET surface area measurement, and cyclic voltammetry.

Li1+xV3O8 material was synthesized by sintering the gel starting from LiOH·H2O, NH4VO3 and C6H8O7·H2O in a scientific microwave oven with temperature and power control, which is called microwave sol–gel route. The samples sintered by microwave in various durations were investigated via X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammograms (CVs) and charge/discharge test to evaluate the effect of sintering duration. It shows that sintering duration in microwave at 400 °C between 100 and 150 min is a more suitable option for MW-sol–gel route to prepare cathode material Li1+xV3O8. Our paper suggests that the microwave sol–gel route is a rapid and efficient synthetic method for preparing Li1+xV3O8 cathode material.

Polymer electrolyte membranes consisting of a novel hyperbranched polyether PHEMO (poly(3-{2-[2-(2-hydroxyethoxy) ethoxy] ethoxy}methyl-3′-methyloxetane)), PVDF-HFP (poly(vinylidene fluoride-hexafluoropropylene)) and LiTFSI have been prepared by solution casting technique. X-ray diffraction of the PHEMO/PVDF-HFP polymer matrix and pure PVDF-HFP revealed the difference in crystallinity between them. The effect of different amounts of PVDF-HFP and lithium salts on the conductivity of the polymer electrolytes was studied. The ionic conductivity of the prepared polymer electrolytes can reach 1.64 × 10− 4 S·cm− 1 at 30 °C and 1.75 × 10− 3 S·cm− 1 at 80 °C. Thermogravimetric analysis informed that the PHEMO/PVDF-HFP matrix exhibited good thermal stability with a decomposition temperature higher than 400 °C. The electrochemical experiments showed that the electrochemical window of the polymer electrolyte was around 4.2 V vs. Li+/Li. The PHEMO/PVDF-HFP polymer electrolyte, which has good electrochemical stability and thermal stability, could be a promising solid polymer electrolyte for polymer lithium ion batteries.

Co–B alloys were synthesized via a chemical reduction method, and adopted as anode materials for alkaline secondary batteries. The structural evolutions and the electrochemical behaviors of the as-prepared Co–B alloys with increasing heat-treating temperatures were analyzed with X-ray diffraction (XRD), scanning electronic microscopy (SEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV) and charge–discharge test. It is found that the Co–B alloys treated at various temperatures show high reversibility. And the electrochemical activities were found to be dependent on the structural evolutions of the Co–B alloys. The amorphous Co–B alloy treated at 50 °C achieves an excellent discharge capacity of 304 mAh/g in the first cycle, while the Co–B alloy treated at 500 °C shows superior cyclicity.

Ferric catalysts have been synthesized from the reactions between pre-infused ferric salts and simultaneous feeding of NaBH4 solution into a H2 generating reactor, and were proved to accelerate the subsequent H2 generation reaction. It is found that there are competitive reactions during H2 generation which lead to the formation of active FeB or inactive Fe(OH)3. Also, the anion (Cl− or NO3−) in the pre-infused ferric salt is crucial to the reaction pathway. The H2 generation route using FeCl3 as the pre-infused ferric salt shows excellent activity, resulting in a high H2 generation efficiency (over 94%) and an average H2 generation rate of 1.08 L/min.

Cobalt borides were synthesized via chemical reduction method, ball milling method and electric arc method, and adopted as anode materials for secondary alkaline batteries. The crystal structures and BET surfaces of Co–B alloys were characterized and analyzed via X-ray diffraction (XRD) and nitrogen adsorption–desorption test, respectively. The electrochemical activities of Co–B samples were examined by cyclic voltammetry (CV) and charge–discharge test. It shows that the electrochemical performances of Co–B alloy synthesized via chemical reduction method are superior to those of Co–B alloys synthesized via the other methods, which result from its amorphous structure, large surface area, and intact activity centers. The initial discharge capacities of Co–B alloys synthesized via chemical reduction method, ball milling method and electric arc method are 301 mAh/g, 238 mAh/g and 214 mAh/g, respectively.

A flexible hydrogen generation (HG) method based on catalytic hydrolysis of NaBH4 solution is developed. Carbon-supported platinum (Pt/C) samples served as the catalysts, and the catalytic strategies for hydrolysis of NaBH4 solution are analyzed via the studies on apparent morphology, catalytic activity, BET surface, and sustaining H2 supply test. Pt/C catalysts are proved to be excellent accelerators, and Pt-loading plays an important role in the hydrogen generation reactions. For a reactor loaded with 100 mg 13.1% Pt/C catalyst, when 10% NaBH4–5% NaOH solution is pumped into the reactor with a speed of 10 ml/min, it can achieve a maximum HG rate of 29.6 (l/min/g catalyst), and give sustaining H2 supply for a proton exchange membrane fuel cell (PEMFC) with an average HG rate of 23.0 (l/min/g catalyst).

Cobalt boride precursors were synthesized via chemical reaction of aqueous sodium borohydride with cobalt chloride, and followed by heat-treating at various temperatures. The as-prepared Co–B catalysts were characterized and analyzed by X-ray diffraction (XRD), nitrogen adsorption–desorption and catalytic activity test; and were adopted to help accelerating hydrolysis reaction of NaBH4 alkaline solution. The Co–B catalyst treated at 500 °C exhibits the best catalytic activity, and achieves an average H2 generation rate of 2970 ml/min/g, which may give a successive H2 supply for a 481 W proton exchange membrane fuel cell (PEMFC) at 100% H2 utilization.

As a new type of multi-electron transfer device, rechargeable aluminum batteries are promising post-lithium ion batteries owing to their high theoretical energy density. However, it is unknown whether Al3+ can be reversibly stored in the lattice of the host electrode material because of its small cation diameter and high valence state, thus trapping it tightly in lattice or defect sites. Here, we report the reversible storage of Al3+ in V2O5 nanowires. It is found that Al3+ intercalates into crystalized V2O5 nanowires in the first discharge. Meanwhile, this electrochemical intercalation leads to the reduction of V5+ and the formation of an amorphous layer on the edge of nanowires. In the subsequent cycling, a new phase forms along the nanowires’ edges and a two-phase transition reaction occurs. Our findings demonstrate clearly for the first time that it is possible that Al3+ can be inserted into the metal oxide and stored reversibly through intercalation and a phase-transition reaction, which is expected to inspire more comprehensive investigations for rechargeable aluminum batteries.Our findings demonstrate clearly for the first time that Al3+ can insert into the metal oxide reversibly through intercalation and phase transition reaction. The electrochemical insertion and extraction of Al3+ lead to redox of V2O5. Insertion and extraction of Al3+ in V2O5 nanowire result in structure change on the crystalized V2O5 nanowires. Amorphous layers and new phase form along the V2O5 nanowires’ edge during electrochemical reaction.Download high-res image (510KB)Download full-size image

A series of Ni–Co–B catalysts were synthesized by a two-step technique, namely, chemical reduction was used to prepare the precursors, and heat-treatment was used to adjust the crystal structures. The structures of the as-prepared Ni–Co–B catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption–desorption test. The catalytic activities of the Ni–Co–B catalysts for NaBH4 hydrolysis were evaluated in a successive hydrogen generation mode, where a 5%NaBH4 + 1%NaOH solution was pumped into the hydrogen generation reactor with a feeding rate of 5 ml per minute. It is found that the heat-treatment affects the crystal structure, the apparent morphology, the oxidation state, the surface structure, as well as the hydrogen generation performances of the Ni–Co–B catalysts. The sample treated at 673 K achieves an average hydrogen generation rate of 708 ml min−1 g−1catalyst, which can give successive hydrogen supply for an 115 W portable proton-exchange membrane fuel cell (PEMFC).

A rechargeable aluminum battery is considered as a promising battery system used in energy storage devices, due to its natural abundance and high capacity. However, fabrication of this battery working at room temperature did not succeed until haloaluminate containing ionic liquids were used as electrolytes. Therefore, anions are expected to have a great effect on performance of rechargeable aluminum batteries. For a complete understanding of the anion-effect, haloaluminate containing ionic liquids prepared with different halogenated imidazole salt and AlCl3/imidazolium chloride mole ratios are studied. The electrochemical window is found to narrow with reducibility of halide ions, which is confirmed by calculation results using the density functional theory (DFT) method. For ionic liquids at different mole ratios, the coexistence of different chloroaluminate anions (Cl−, AlCl4−, Al2Cl7−) is found. When used as an electrolyte in a rechargeable aluminum battery with a V2O5 nanowire cathode, the AlCl3/[BMIM]Cl ionic liquid with the mole ratio of 1.1:1 shows the best performance. The as-assembled cell exhibits a high discharge voltage platform (1 V) and capacity (288 mA h g−1) at the first cycle. Concentration of Al2Cl7− is considered as a key factor in chloroaluminate ionic liquids when used as electrolytes. Furthermore, a slight corrosion is found on the surface of Al metal foil immersed in an AlCl3/[BMIM]Cl = 1.1:1 ionic liquid for 24 h, which may help remove the oxide film on the Al metal foil, so as to improve the charge/discharge performance.