Amorphous MnO2 has been prepared from the reduction of KMnO4 in ethanol media by a facile one-step wet chemical route at room temperature. The electrochemical properties of amorphous MnO2 as cathode material in sodium-ion batteries (SIBs) are studied by galvanostatic charge/discharge testing. And the structure and morphologies of amorphous MnO2 are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectra. The results reveal that as-synthesized amorphous MnO2 electrode material exhibits a spherical morphology with a diameter between 20 and 60 nm. The first specific discharge capacity of the amorphous MnO2 electrode is 123.2 mAh•g−1 and remains 136.8 mAh•g−1 after 100 cycles at the current rate of 0.1 C. The specific discharge capacity of amorphous MnO2 is maintained at 139.2, 120.4, 89, 68 and 47 mAh•g−1 at the current rate of 0.1 C, 0.2 C, 0.5 C, 1 C and 2 C, respectively. The results indicate that amorphous MnO2 has great potential as a promising cathode material for SIBs.

•The polarity reversal of the Cu–304SS couple in Cl− solution with different pH was investigated.•A typical polarity reversal occurred in the Cu–304SS couple when the solution pH reduced from 2 to 0.•SVET map was used to verify the occurrence of polarity reversal.•The polarity reversal of the Cu–304SS couple is related to formation and dissolution of passive film on 304SS surface.The typical polarity reversal of the Cu–304 stainless steel galvanic couple (Cu–304SS GC) in Cl−-containing solution with different pH was investigated by open circuit potential (OCP), potentiodynamic polarization, and galvanic current techniques in conjunction with scanning vibrating electrode technique (SVET) and scanning electron microscopy (SEM). The results showed that the change in pH of the solution has a significant effect on the corrosion behavior of 304SS. The typical polarity reversal occurs in Cu–304SS GC in Cl− solution with pH 0, in which the red copper is cathodic to 304SS, while in the solution with pH 6, 4, and 2 the red copper is anodic to 304SS. With the decrease in pH, the 304SS changes from the passive state to the activation state due to the dissolution of the passive film on the surface thereby facilitating the polarity reversal of the Cu–304SS GC.

Sodium iron phosphate (Na3Fe2(PO4)3) as cathode material for sodium-ion batteries has been synthesized through a simple method of a solid state reaction. It crystallizes in a monoclinic structure in the space group C2/c. The morphology of the as-prepared sample has been investigated by scanning electron microscopy and transmission electron microscopy. The charge/discharge curves show a very flat plateau at about 2.5 V (vs Na/Na+). The initial specific discharge capacity is 61 mAh g–1 and remains at 57 mAh g–1 after 500 cycles at a current rate of 1 C. X-ray photoelectron spectroscopy measurements indicate that not all of the Fe3+ of Na3Fe2(PO4)3 is reduced during the electrochemical process. The ex-situ X-ray diffraction measurements were applied to research the mechanism of sodium-ion storage; the results indicated that the Na3Fe2(PO4)3 compound partly transformed into Na4Fe2(PO4)3 and Na3+xFe2(PO4)3 compound. These results testify to the potential of monoclinic Na3Fe2(PO4)3 as a cathode material in sodium-ion batteries.Keywords: Ex-situ X-ray diffraction; NASICON; Sodium iron phosphate; Sodium-ion diffusion coefficient; Solid state synthesis; X-ray photoelectron spectroscopy;

•The sodiation process transforms the FePO4 into amorphous and crystallite NaFePO4.•Crystallite NaFePO4 includes triphylite NaFePO4 and maricite NaFePO4.•Sodiated amorphous FePO4 shows higher specific capacities and cyclic stability.•Amorphous FePO4 may have great potential as an electrode material.The structure and electrochemical performance of sodiated iron phosphate were investigated by means of X-ray diffraction, high-resolution transmission electron microscopy and electrochemical measurements. The results indicate that after the sodiation process, all FePO4 samples transform into the amorphous sodium iron phosphate and crystallite NaFePO4, namely triphylite NaFePO4 for amorphous FePO4 and maricite NaFePO4 for trigonal FePO4, respectively. The amorphous FePO4 samples show excellent electrochemical performance in terms of cyclic stability and discharge capacity, while trigonal FePO4 displays poor electrochemical performance. The outstanding electrochemical performance of amorphous FePO4 was attributed to the amorphous and triphylite NaFePO4 with high electrochemical activity. Those findings indicate that amorphous FePO4 can be transformed into active NaFePO4, which may have great potential as an electrode material for sodium-ion batteries.The structural transformation of FePO4 nanoparticles during the sodiation process has been investigated by XRD and HRTEM. The results show that the sodiation process transforms the FePO4 into NaFePO4. Amorphous FePO4 partly transforms into highly active triphylite NaFePO4. Trigonal FePO4 partly transforms into maricite NaFePO4.

•Corrosion of Ti-6Al-4 V manufactured by selective laser melting was investigated.•SLM-produced alloy exhibits a worse corrosion resistance than Grade 5 alloy.•The unfavorable corrosion resistance is related to the dominant α’ and less β–Ti.Electrochemical measurements were performed to investigate the corrosion behavior of Ti-6Al-4 V alloy prepared by selective laser melting (SLM) and commercial Grade 5 sample for comparison. Electrochemical results showed that the SLM-produced sample possesses poorer corrosion resistance than the Grade 5 sample. Microstructure studies suggested that the SLM-produced sample is composed of dominant acicular α’ martensite and some prior β grains, unlike the typical α + β microstructure in Grade 5 sample. The unfavorable corrosion resistance of the SLM-produced sample is related to the considerably large amount of acicular α’ and less β–Ti phase in the microstructure compared to the Grade 5 sample.

•Corrosion resistance of selective laser melted Ti-6Al-4V was investigated.•XY-plane of Selective laser melted alloy shows a better corrosion resistance.•More α’ and less β-Ti weaken the corrosion resistance of XZ-plane.Electrochemical measurements and microstructural analysis were performed to study the corrosion resistance of different planes of Ti-6Al-4V alloy manufactured by selective laser melting (SLM). The electrochemical results suggest that its XY-plane possesses a better corrosion resistance compared to XZ-plane in 1 M HCl solution, in spite of slight difference in 3.5 wt.% NaCl solution, suggesting that the different planes exhibit more pronounced distinction in corrosion resistance in harsher solution system. The inferior corrosion resistance of XZ-plane is attributed to the presence of more α′ martensite and less β-Ti phase in microstructure for XZ-plane than for XY-plane of the SLM-produced Ti-6Al-4V alloy.The SLM-produced Ti-6Al-4V alloy exhibits a higher corrosion rate in 1 M HCl solution than that in 3.5 wt.% NaCl solution and XZ-plane of the SLM-produced Ti-6Al-4V alloy gives rise to the inferior corrosion resistance compared with its XY-plane.

X-ray diffraction, Raman spectroscopy and scanning electron microscopy were employed to investigate the effects of the DC electric field on the composition, formation and structure of corrosion products formed on the surface of the steel immersed in NaCl solution. The results show that goethite (α-FeOOH), akaganeite (β-FeOOH), lepidocrocite (γ-FeOOH) and magnetite (Fe3O4) are the major constituents among the corrosion products. The arrangement of different levels of the DC electric field intensity gives rise to the following results. The little higher DC electric field intensity (around 100–200 kV/m) promotes the crystallinity and growth of γ-FeOOH; obviously, much higher DC electric field intensity (greater than 400 kV/m) prevents the growth of α-FeOOH and facilitates the generation of Fe3O4. Both the promotional growth of γ-FeOOH and suppression of α-FeOOH growth indicated the weakness of the protectiveness of the rust layer. Consequently, the suppression of the transformation of α-FeOOH from γ-FeOOH favors the yield of the Fe3O4, which works as a large cathode area and would be about to quicken the subsequent steel corrosion.

As-prepared polyaniline (PANI) nanorods have been used to synthesize an iron phosphate/polyaniline (FePO4/PANI) composition through the microemulsion technique. After sintering at 460 °C under a nitrogen protective atmosphere, the PANI carbonized, yielding the amorphous iron phosphate/carbonized polyaniline nanorods (FePO4/CPNRs) composite, which acts as the cathode material in sodium-ion batteries (SIBs). The electrochemical performance of FePO4/CPNRs composite shows an initial discharge specific capacity of 140.2 mAh g−1, with the discharge specific capacity being maintained at 134.4 mAh g−1 after the 120th cycle, up to 87.9 % of the theoretical capacity (154.1 mAh g−1 for NaFePO4), as well as an excellent rate capability in sodium-ion batteries. Compared with pure FePO4, the electrochemical performance has been greatly improved. On the one hand, using the CPNRs as conductive medium significantly improves electronic transport. On the other hand, the FePO4 sphere of nanoscale particles, which has a large specific surface area, can promote an active material/electrolyte interface reaction and improve the speed of sodiation and desodiation during the charge and discharge process. The amorphous FePO4/CPNRs composite shows outstanding electrochemical performance as competitive cathode material in SIBs.

In this article, an FePO4/reduced graphene oxide (rGO) nanosheet has been synthesized through a micro-emulsion technique. It exhibits excellent electrochemical performance in discharge-specific capacity and rate capability. The FePO4 nanospheres grow on both sides of the rGO in a single layer by means of a non-covalent bond. The first discharge-specific capacity of this cathode material is up to 130.5 mA h g−1 and remains at 153.4 mA h g−1 after the 70th cycle at 0.1 C. The discharge-specific capacity of FePO4/rGO is maintained at 154.5 mA h g−1, 151.6 mA h g−1, 122.3 mA h g−1 and 100.6 mA h g−1, at 0.1 C, 0.2 C, 0.5 C and 1 C, respectively. The result indicates that the FePO4/rGO nanosheet composite has great potential as a cathode material for the sodium-ion battery.

•Effect of DC electric field on corrosion products formed on steel was investigated.•Corrosion rate increased with the increase of DC electric field intensity.•DC electric field suppressed the growth of α-FeOOH and favoured the yield of γ-FeOOH.•DC electric field affected the composition and structure of corrosion products.The effects of the direct current (DC) electric field on the initial corrosion of steel in simulated solution were investigated using measurements of weight loss and polarization curves, XRD and SEM techniques. The major constituents of the corrosion products are α- and γ-FeOOH in SO42− solution. It was found that the corrosion rate of steel increased with the increase of DC electric field intensity. And the DC electric field suppresses the growth of α-FeOOH and the transformation of γ-FeOOH to α-FeOOH. All these lead to the reduction of the protective ability of rust layer and accelerate further corrosion of steel.

In this article, the structure and electrochemical performance of sodiated iron phosphate (FePO4) synthesized by the micro-emulsion technique have been investigated by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and electrochemical measurement. The results reveal that amorphous FePO4 could be transformed into crystallite sodium iron phosphate (NaFePO4) during electrochemical sodiation. Furthermore, the results of electrochemical testing show that the initial specific-discharge capacity of FePO4 is 142 mA h g−1, and it still delivers a reversible capacity of 130.8 mA h g−1 after 120 cycles. The discharge capacities could attain values of 142 mA h g−1, 119.1 mA h g−1, 91.5 mA h g−1 and 63.5 mA h g−1 at 0.1 C, 0.2 C, 0.5 C and 1 C, respectively. These findings have indicated that NaFePO4 has been formed during the electrochemical process and that amorphous structured FePO4 is one of the most promising “host” materials.

Correction for ‘The transformation from amorphous iron phosphate to sodium iron phosphate in sodium-ion batteries’ by Yao Liu et al., Phys. Chem. Chem. Phys., 2015, 17, 22144–22151.

In this study, a microemulsion technique was applied to prepare an in situ self-assembled core–shell FePO4@MCNT nanowire composite as a cathode material for sodium-ion batteries. Multi-walled carbon nanotubes (MCNTs) were uniformly dispersed using Triton X-100 as a surfactant in the microemulsion system. Subsequently, amorphous FePO4 nanoparticles with a diameter of 10–20 nm were loaded onto the surface of MCNTs during the synthetic process, forming an FePO4@MCNT nanowire composite with three-dimensional mixed conducting networks, with a structure resembling maize. The resulting products were collected by centrifugation and washed three times, and sintered under an N2 atmosphere at 460 °C for 3 h. The discharge specific capacity of FePO4@MCNT was 155.2 mA h g−1 in the initial cycle, which was maintained at 157.2 mA h g−1 after 70 cycles at 0.1 C. The discharge specific capacity at 0.3 C, 0.5 C, and 1.0 C was 133.2 mA h g−1, 122.2 mA h g−1, and 75.3 mA h g−1, respectively, in the range of 1.5–4.2 V. The results show that FePO4@MCNT nanowires are promising candidates as cathode materials in sodium-ion batteries.

Fe1.5(PO4)(OH) loaded with Au (mass ratio = 0, 0.5, 2, 4, 6 %) was synthesized via two steps, combining microemulsion and hydrothermal techniques, and the effects of the Au loading on the electrochemical properties of Fe1.5(PO4)(OH) cathode material were investigated. The structure and morphology were studied by means of X-ray diffraction (XRD) and field emission-scanning electron microscopy (FE-SEM), and the electrochemical performances were characterized by galvanostatic charge and discharge tests. The XRD patterns showed that the Au loading modification did not affect the structure of Fe1.5(PO4)(OH). From the charge and discharge test, it was found that when the mass ratio of Au loading was 2 % the sample exhibited excellent electrochemical properties with an initial specific capacity of 182 mAhg−1 at 0.1 C and less fading of the specific capacity, retaining about 165 mAhg−1 after 25 cycles, which demonstrated that the Au loading is an effective way to improve the electron conductivity of Fe1.5(PO4)(OH). What is more, the electrochemical properties of Fe1.5(PO4)(OH)/Au synthesized at 150 °C for 24 h with a discharge specific capacity of 182 mAhg−1 are better than those of the sample synthesized at 180 °C for 24 h with a discharge specific capacity of 121 mAhg−1, which is attributed to the crystal growth of particles at high hydrothermal temperatures, showing that the particle size also has a significant influence on the electrochemical performance of electrode materials.

Iron-based cathode material, iron phosphate, was prepared by homogeneous co-precipitation followed by spray drying method, where Ce3+doping modifications were carried out to improve the electrical conductivity. Considering that the relationship between structures and performances, calcining temperature and doping concentration were investigated. The physicochemical property of the precursor was analyzed using TG–DSC, the structures and morphologies of samples were characterized by X-ray diffraction and scanning electron microscopy, electrochemical behaviors of samples were analyzed using charge–discharge tests and electrochemical impedance spectrum tests. Results show that the electrochemical performance of iron phosphate was improved by the synthesis condition optimization and doping modification. Fe0.98Ce0.02PO4 calcined at 460°C showed the highest discharge capacity of 100.3 mAh/g for the initial cycle at 0.05C. In addition, the doping mechanism for FePO4 was discussed in this paper.

•A new iron hydroxyl phosphate cathode material was synthesized by a sample hydrothermal method.•We obtained the spherical, cubic, multi-armed and cross-like morphology by adjusting the hydrothermal temperatures.•Iron hydroxyl phosphate exhibited a reversible initial discharge specific capacities of 176 mAh g−1.•The specific capacity retained about 95% of the initial discharge specific capacity after 60 cycles at 0.1C.•The spherical morphology and smaller particle size can improve the electrochemical performances.Iron hydroxyl phosphate, with the formula Fe1.5(PO4)(OH), used as a cathode material in lithium ion batteries, is synthesised by a sample hydrothermal method. Scanning electron microscopy (SEM), X-ray diffraction and galvanostatical charge/discharge tests are employed to characterise the morphology, structure and electrochemical performance of the iron hydroxyl phosphate, respectively. FE-SEM shows that the morphologies are closely related to the hydrothermal temperatures at which they are synthesised. The morphologies, such as spherical, cubic, multi-armed and cross-like structures, could be easily regulated by adjusting the hydrothermal temperature. It is found that different morphologies of iron hydroxyl phosphate gave rise to different electrochemical performances. Compared to the others, iron hydroxyl phosphate spherical composites exhibit not only a high reversible capacity but also good cycling stability, with a reversible initial discharge specific capacity of around 176 mAh g−1 and a remaining 95% of the initial discharge specific capacity after 60 cycles at 0.1C. The improved electrochemical performance is attributed to the spherical morphology and smaller particle size, which increase the reaction interfaces and shorten the diffusion distance of the lithium ions.

FePO4 nanoparticles, acted directly as cathode materials in lithium ion rechargeable batteries, were synthesized by a microemulsion technique. The various grain-sized and crystal-structured FePO4 samples were obtained by sintering at different temperatures (380 °C, 460 °C, 550 °C, 650 °C) for 3 h in air. The structure and morphology were investigated by means of X-ray diffraction (XRD) and field emission-scanning electron microscopy (FE-SEM); the electrochemical properties were characterized by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and galvanostatic charge and discharge tests. Results show that FePO4 sintered at 380 °C and 460 °C for 3 h are amorphous, and with fine sizes in the range of 10–20 nm. Increasing the sintering temperature leads to an increase in grain size and makes the structure change from amorphous to trigonal. The EIS results show that the Rct value of FePO4 sintered at 460 °C is smaller than that sintered at 650 °C. The diffusion coefficients of lithium ion (DLi) of FePO4 sintered at 380 °C, 460 °C, 550 °C and 650 °C measured by EIS are 8.09 × 10−14, 1.06 × 10−13, 4.88 × 10−14 and 2.59 × 10−14 cm2 s−1, respectively. The difference in diffusivity is also confirmed by CV and the DLi values are 6.71 × 10−14, 8.28 × 10−14, 4.89 × 10−14 and 1.60 × 10−14 cm2 s−1, respectively. The correlations between the electrochemical performances of FePO4 and lithium ion diffusion are acquired. The charge and discharge tests show that the initial discharge specific capacity of FePO4 sintered at 460 °C for 3 h reaches 142.3 mAh g−1 at 0.1 °C. These results suggest that nanoparticles and amorphous FePO4 facilitates lithium ion diffusion during the charge/discharge cycles.

The corrosion behaviour of CP-Ti and Ti-TiB composite produced by selective laser melting (SLM) in the artificial simulated body fluid (Hank's solution) at body temperature was investigated systematically by using electrochemical measurements (potentiodynamic polarisation curves and electrochemical impedance spectroscopy), together with some detailed structural characterisations. The results demonstrate that SLM-produced Ti-TiB composite samples possess better corrosion resistance than SLM-produced CP-Ti samples in Hank's solution. Due to these tiny TiB and TiB2 particles acting as the micro-cathode uniformly distributing in titanium matrix, anodic dissolution of titanium matrix in the corrosion process is prominently facilitated in early stages, followed by rapid passivation on the surface. The corrosion mechanism of Ti-TiB composite samples has also been discussed in detail in this paper.

In this study, a microemulsion technique was applied to prepare an in situ self-assembled core–shell FePO4@MCNT nanowire composite as a cathode material for sodium-ion batteries. Multi-walled carbon nanotubes (MCNTs) were uniformly dispersed using Triton X-100 as a surfactant in the microemulsion system. Subsequently, amorphous FePO4 nanoparticles with a diameter of 10–20 nm were loaded onto the surface of MCNTs during the synthetic process, forming an FePO4@MCNT nanowire composite with three-dimensional mixed conducting networks, with a structure resembling maize. The resulting products were collected by centrifugation and washed three times, and sintered under an N2 atmosphere at 460 °C for 3 h. The discharge specific capacity of FePO4@MCNT was 155.2 mA h g−1 in the initial cycle, which was maintained at 157.2 mA h g−1 after 70 cycles at 0.1 C. The discharge specific capacity at 0.3 C, 0.5 C, and 1.0 C was 133.2 mA h g−1, 122.2 mA h g−1, and 75.3 mA h g−1, respectively, in the range of 1.5–4.2 V. The results show that FePO4@MCNT nanowires are promising candidates as cathode materials in sodium-ion batteries.

In this article, an FePO4/reduced graphene oxide (rGO) nanosheet has been synthesized through a micro-emulsion technique. It exhibits excellent electrochemical performance in discharge-specific capacity and rate capability. The FePO4 nanospheres grow on both sides of the rGO in a single layer by means of a non-covalent bond. The first discharge-specific capacity of this cathode material is up to 130.5 mA h g−1 and remains at 153.4 mA h g−1 after the 70th cycle at 0.1 C. The discharge-specific capacity of FePO4/rGO is maintained at 154.5 mA h g−1, 151.6 mA h g−1, 122.3 mA h g−1 and 100.6 mA h g−1, at 0.1 C, 0.2 C, 0.5 C and 1 C, respectively. The result indicates that the FePO4/rGO nanosheet composite has great potential as a cathode material for the sodium-ion battery.

Correction for ‘The transformation from amorphous iron phosphate to sodium iron phosphate in sodium-ion batteries’ by Yao Liu et al., Phys. Chem. Chem. Phys., 2015, 17, 22144–22151.

In this article, the structure and electrochemical performance of sodiated iron phosphate (FePO4) synthesized by the micro-emulsion technique have been investigated by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and electrochemical measurement. The results reveal that amorphous FePO4 could be transformed into crystallite sodium iron phosphate (NaFePO4) during electrochemical sodiation. Furthermore, the results of electrochemical testing show that the initial specific-discharge capacity of FePO4 is 142 mA h g−1, and it still delivers a reversible capacity of 130.8 mA h g−1 after 120 cycles. The discharge capacities could attain values of 142 mA h g−1, 119.1 mA h g−1, 91.5 mA h g−1 and 63.5 mA h g−1 at 0.1 C, 0.2 C, 0.5 C and 1 C, respectively. These findings have indicated that NaFePO4 has been formed during the electrochemical process and that amorphous structured FePO4 is one of the most promising “host” materials.