Electrochemical investigation of the anodic corrosion of Pb–Ca–Sn–Li grid alloy in H2SO4 solution

The steady-state and anodic corrosion of Pb–0.17 wt.% Ca–0.88 wt.% Sn, and Pb–0.17 wt.% Ca–0.88 wt.% Sn–0.06 wt.% Li alloys in 4.5 M H₂SO₄ at 25 °C were studied using cyclic voltammetry, linear sweep voltammetry, and electrochemical impedance spectroscopy. The experimental results show that the lithium added to Pb–Ca–Sn alloy increases corrosion resistance in equilibrium potential and inhibits the growth of the anodic corrosion layer.     

Influence of temperature on corrosion behavior of PbCaSnCe alloy in 4.5 M H2SO4 solution

The temperature effect on corrosion behaviors of PbCaSnCe alloy in 4.5 M H₂SO₄ solution was investigated by using potentiodynamic curve, electrochemical impedance spectra (EIS), Mott-Schottky plot and photocurrent response methods. It was found that PbCaSnCe alloy was in passive state in sulfuric acid solution, a passive film can be formed on alloy surface. The compositions of passive films formed at 0.9 V for 2 h under different temperatures were detected by X-ray photoelectron spectroscopy (XPS). The results showed that the film resistance and the transfer resistance decreased with the increment of the solution temperature. Mott-Schottky analysis and the photocurrent response revealed that the passive film exhibited n-type semi-conductive character, the donor density of the passive film decreased with increasing the solution temperature. Photocurrent response revealed that the photocurrent increased with increasing temperature. XPS results indicated that the PbO₂ content in passive films may increase with increasing the solution temperature.     

Corrosion characteristics of SS316L as bipolar plate material in PEMFC cathode environments with different acidities

The corrosion characteristics of SS316L in simulated proton exchange membrane fuel cell (PEMFC) environments with a wide range of H₂SO₄ concentrations have been systematically studied. Electrochemical methods, both potentiodynamic and potentiostatic, are employed to determine the corrosion parameters and the results show that corrosion resistance decreases with increasing H₂SO₄ concentrations. Scanning electron microscope (SEM) is used to examine the surface morphology of the specimens after potentiostatic polarized in simulated PEMFC cathode environments and the results indicate that local corrosion occurs under all the conditions studied and local corrosion is more severe with higher H₂SO₄ concentrations. Auger electron spectroscopy (AES) analysis is used to identify the composition and the depth profile of the passive film formed on the SS316L surface and the results show that the thickness of passive film decreases with increasing H₂SO₄ concentrations. Interfacial contact resistances (ICR) between SS316L polarized and carbon paper are measured and the results show that ICR decreases with increasing H₂SO₄ concentrations. The corrosion mechanisms of SS316L in PEMFC cathode environments are analysed and discussions on choosing simulated PEMFC cathode corrosion environments for accelerated tests are also provided.     

Investigation on the corrosion and hydrogen evolution for AZ91D magnesium alloy in single and anion-containing oxalate solutions

Corrosion characterization of AZ91D alloy was studied in aqueous sodium oxalate solutions with various concentrations using different electrochemical techniques (open circuit potential, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV)). The corrosion rate and consequently the rate and extent of hydrogen evolution were found to increase significantly with increasing oxalate anion concentration and temperature or with decreasing the pH of solution. Increasing additions of various anions over the lower concentration range (0.001-1.0 mM) in the blank oxalate solution increases to a varying extent the corrosion rate of the alloy and hence increases the hydrogen evolution rate and decreases surface film stability in the following order Cl⁻ > SO₄²⁻ > F⁻. On the other hand, addition of phosphate anion exhibits a reverse trend, where the active corrosion rate decreases with increasing PO₄³⁻ anion concentration, implying that this anion acts as a passivator for AZ91D alloy. The obtained electrochemical results are further confirmed by scanning electron microscopy (SEM) analysis.     

Effect of Sn concentration on the corrosion resistance of Pb-Sn alloys in H2SO4 solution

The effect of Sn concentration on the corrosion resistance of Pb-Sn alloy in H₂SO₄ electrolyte was investigated by potentiodynamic polarization. A new approach to calculate the exchange current density, i_corr, was proposed and proved to be in accordance with the experimental results. This study shows that with the increase of alloying Sn, the corrosion rate of the alloy increased and then decreased, with its minimum appearing at 2.60 wt.% Sn. It was also found that the cathodic reaction does not have to be a single-step process, i.e., there are multiple sub-steps involved and complex cations, including H₄³⁺ and H₂⁺, existing in the systems.     

High activity PtPd-WC/C electrocatalyst for hydrogen evolution reaction

Pd modified Pt over a novel support of tungsten carbide nanocrystals (the catalyst denotes as PtPd-WC/C) have been prepared by using an intermittent microwave heating (IMH) method. The as-prepared electrocatalysts are characterized by using the techniques of XRD, SEM, TEM, linear sweeping voltammetry and tested for the hydrogen evolution reaction (HER) in the acidic media. It shows a better performance for the HER on PtPd-WC/C electrocatalyst than that on Pt-WC/C electrocatalyst. In addition, these effects on the catalytic activity by changing environmental temperature and electrolyte concentration were taken into account. Kinetic study shows that the HER on the PtPd-WC/C electrocatalyst gives higher exchange current density in H₂SO₄ solution with high concentration, leading to a lower overpotential and facile kinetics. XRD, SEM and TEM images of PtPd-WC/C show the crystalline features of Pt, Pd and tungsten carbides and indicated the coexistence of these components.     

The effect of Pt loading amount on SO2 oxidation reaction in an SO2-depolarized electrolyzer used in the hybrid sulfur (HyS) process

The effect of Pt loading amount on SO₂ oxidation reaction in an SO₂-depolarized electrolyzer used in the hybrid sulfur (HyS) process for hydrogen generation was investigated by using transmission electron microscopy (TEM), cyclic voltammetry (CV), and linear sweep voltammetry (LSV). From the analysis of the CVs, it was found that the electrochemical active surface area increased as the Pt loading amount increased, while Pt utilization decreased. The CVs obtained in the SO₂-free and SO₂-saturated 50 wt.% H₂SO₄ solutions indicated that the chemical transformation of the adsorbed species to PtO at a higher potential creates passivation layers which partially cover the electrode surface and inhibit SO₂ oxidation reaction. The LSVs revealed that the increase in Pt loading amount resulted in a considerable improvement of SO₂ oxidation kinetics in a low potential region as compared with that in a high potential region. However, the area-specific activity for SO₂ oxidation reaction decreased due to the reduction of Pt utilization.     

Tris(pentafluorophenyl) borane as an electrolyte additive for LiFePO4 battery

The effects of tris(pentafluorophenyl) borane (TPFPB) additive in electrolyte at the LiFePO₄ cathode on the high temperature capacity fading were investigated by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), cyclability, SEM and Fourier transform infrared (FTIR). According to the study results, tris(pentafluorophenyl) borane has the ability to improve the cycle performance of LiFePO₄ at high temperature. LiFePO₄ electrodes cycled in the electrolyte without the TPFPB additive show a significant increase in charge transfer resistance by EIS analysis. SEM and FTIR disclose evidence of surface morphology change and solid electrolyte interface (SEI) formation. FTIR investigation shows various functional groups are found on the cathode material surface after high temperature cycling tests. The results showed an obvious improvement of high temperature cycle performance for LiFePO₄ cathode material due to the TPFPB additive. The observed improved cycling performance and improved lithium ion transport are attributed to decreased LiF content in the SEI film.     

Electrochemical characterization of electrodes in the electrochemical Bunsen reaction of the sulfur–iodine cycle

In the electrochemical Bunsen reaction, SO₂ is oxidized to H₂SO₄ at the anode while I₂ is reduced to HI at the cathode. Both electrodes were electrochemically characterized using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The effects of H₂SO₄ concentration in the anolyte, as well as HI concentration and I₂/HI molar ratio in the catholyte, were explored. The cyclic voltammograms of platinum electrode shift with rising scan rate, indicating the irreversibility of two electrode reactions. The equivalent circuit for the cathode reaction impedance consists of an ohmic resistance of the solution, in series with a parallel combination of a charge transfer resistor and a constant phase element, yet the impedance spectra for the anode reaction can be modeled using a parallel combination of a charge transfer resistor and a constant phase element. The electrode reaction kinetics was also analyzed using the exchange current density (j₀) and the standard reaction rate constant (k⁰). The results indicate that a high electrode reaction rate in the cell can be obtained for a HI concentration of 8 mol/kg_H2O and an I₂/HI molar ratio of 0.5 in the catholyte and a H₂SO₄ concentration of 13 mol/kg_H2O in the anolyte.     

H2SO4 stability of PBI-blend membranes for SO2 electrolysis

For hydrogen to become a serious contender for replacing fossil fuels, the manufacturing thereof has to be further investigated. One such process, the membrane based Hybrid Sulfur (HyS) process, where hydrogen is produced from the electrolysis of SO₂, has received considerable interest recently. Since H₂SO₄ is formed during SO₂ electrolysis, H₂SO₄ stability is a prerequisite for any membrane to be used in this process. In this study, pure as well as blended polybenzimidazole (PBI), partially fluorinated poly(arylene ether) (sFS) and nonfluorinated poly(arylene ethersulfone) (sPSU) membranes were investigated in terms of their acid stability as a function of acid concentration. Membranes were characterized using weight change, TGA, GPC, SEM/EDX and IEC. While a general stability was observed at 30 and 60 wt% H₂SO₄, the blended sFS-PBI and sPSU-PBI showed the highest stability throughout. According to the VI curve obtained for the SO₂ electrolysis, the sPSU-PBI blend membrane performed slightly better than Nafion^®117.     

Direct electrolysis of Bunsen reaction product HI/H2SO4/H2O/toluene mixture for hydrogen production: Pt electrode characterization

In chemical cycles to produce hydrogen, the H₂S splitting cycle and the sulfur-iodine (SI) water splitting cycle both share the Bunsen reaction and HI decomposition. Therefore, they have to overcome the same challenges in the technology development, one of them being the complex and difficult separations of the mixed hydroiodic acid and sulfuric acid solution after the Bunsen reaction. To avoid the separations, this paper studies the electrolysis of the HI/H₂SO₄/H₂O/toluene mixture, focusing on the electrochemical characterization of the Pt electrode by using linear sweep voltammetry (LSV) and cyclic voltammetry (CV). The results show that hydrogen is identified from the gas generated from the cathode in electrolysis. Iodide oxidation is the main reaction in the anode chamber and no significant side reactions are observed. Iodine deposition on the anode surface increases the resistance to iodide diffusion to the anode. However, it can be mitigated by adding toluene in or applying stirring to the anolyte HI/H₂SO₄ solution. The Pt cathode and sulfuric acid catholyte also work stably.     

Influence of cerium (III) ions on corrosion and hydrogen evolution of carbon steel in acid solutions

This paper intended to investigate the influence of rare earth Ce(III) ions on the corrosion behavior of carbon steel in two acid solutions (0.5 M HCl and 0.25 M H₂SO₄) in order to control the rate of hydrogen evolution in those systems. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests were used for corrosion rate and electrochemical impedance evaluation. SEM was used to examine the sample surfaces immersed in acid solutions containing the optimal threshold Ce(III) concentration (0.1 mM). All results reveal that the corrosion resistance of carbon steel in HCl is superior to that in H₂SO₄ due to the higher rate of hydrogen production in the latter. A model for the corrosion process mechanism and inhibition by Ce(III) salt for carbon steel in the two tested media is proposed.     

Pulse electrodeposited PtSn electrocatalyst on a PEDOT/graphene-based electrode for ethanol oxidation in an acidic medium

Pulse electrodeposition of Pt and Sn using 10 mM H₂PtCl₆?6H₂O in 0.10 M H₂SO₄ and 10 mM SnCl₂?2H₂O in 0.10 M HCl was conducted on a support matrix consisting of electropolymerized poly (3,4-ethylenedioxythiophene) (PEDOT) and electrochemically exfoliated graphene oxide (EGO). The Field Emission – Scanning Electron Microscopy (FE-SEM) studies of PtSn/PEDOT/EGO (i.e., PEDOT on EGO) showed a homogeneous globular composite, while PtSn/EGO/PEDOT (i.e., EGO on PEDOT) revealed a heterogeneous composite with wrinkled and globular surface morphologies. An Energy Dispersive X-ray (EDX) analysis (as a percentage of Pt and Sn) of PtSn/PEDOT/EGO is in agreement with the X-ray Photoelectron Spectroscopy (XPS) analysis, indicative of a homogeneous surface for the dispersion of metallic particles. However, the EDX and XPS analyses of PtSn/EGO/PEDOT showed variations in the amount of Pt and Sn, indicative of possible mixing of the EGO and PEDOT support matrices. Cyclic voltammetry (CV) and chronoamperometry using 1.0 M ethanol in 0.1 M H₂SO₄ demonstrated higher electrocatalytic activity (83.7 mA/cm²) and electrochemical stability (29.0% current retention) in PtSn/PEDOT/EGO than PtSn/EGO/PEDOT.     

Electrodeposition of Ni–Co–Sn alloy from choline chloride-based deep eutectic solvent and characterization as cathode for hydrogen evolution in alkaline solution

The electrodeposition of Ni–Co–Sn alloy were carried out at room temperature from the chlorine chloride (ChCl)–ethylene glycol (EG) deep eutectic solvent (DES). For comparison of properties, Ni–Sn and Co–Sn alloys were also deposited using the same solvent. Deposition mechanism, microstructure, and electrochemical properties of the deposits in 1 M KOH solution were investigated. The deposition of Ni, Co, Sn, Ni–Sn, Co–Sn and Ni–Co–Sn on platinum electrode were also studied using cyclic voltammetry. Interestingly, the electrochemical stability of DES is observed to be increased in the presence of Sn²⁺ ions. The X-ray diffraction (XRD) patterns showed only Ni phases indicating that the other elements get incorporated inside the nickel matrix and the lattice constant have linear relation with Sn content in alloy. The morphologies of Ni–Sn and Ni–Co–Sn alloys were observed to be almost same with fine grains, the XRD studies confirm this. The potentiodynamic polarization measurements showed that the Ni–Co–Sn alloy exhibits the lowest corrosion current density (j_corr), noblest corrosion potential (E_corr) and highest exchange current density (j_c) value than the other two binary alloys, indicating that the ternary alloy is a good candidate for Hydrogen Evolution Reaction (HER).     

Synthesis and characterization of Nd doped LiMn2O4 cathode for Li-ion rechargeable batteries

Spinel powders of LiMn_1.99Nd_0.01O₄ have been synthesized by chemical synthesis route to prepare cathodes for Li-ion coin cells. The structural and electrochemical properties of these cathodes were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, cyclic voltammetry, and charge-discharge studies. The cyclic voltammetry of the cathodes revealed the reversible nature of Li-ion intercalation and deintercalation in the electrochemical cell. The charge-discharge characteristics for LiMn_1.99Nd_0.01O₄ cathode materials were obtained in 3.4–4.3 V voltage range and the initial discharge capacity of this material were found to be about 149 mAh g⁻¹. The coin cells were tested for up to 25 charge-discharge cycles. The results show that by doping with small concentration of rare-earth element Nd, the capacity fading is considerably reduced as compared to the pure LiMn₂O₄ cathodes, making it suitable for Li-ion battery applications.     

Electrochemical investigation on the corrosion and hydrogen evolution rate of mild steel in sulphuric acid solution

Corrosion and hydrogen evolution rate of mild steel alloy have been investigated using various electrochemical techniques. Mild steel was polarized vs. saturated calomel electrode (SCE) in naturally aerated 0.1 M H₂SO₄ solution containing three newly synthesized heterocyclic compounds in different concentrations. The data obtained from polarization technique showed that the corrosion current density, i_corr, and the hydrogen evolution rate decrease with increasing concentration of heterocyclic inhibitors in 0.1 M H₂SO₄ medium, indicating a decrease in the corrosion rate of mild steel as well as an increase in the inhibition efficiency (IE) of the newly synthesized inhibitors. The impedance measurements confirmed well the polarization behaviour. Increasing the temperature leads to an increase in corrosion or hydrogen evolution rate of the mild steel and a decrease of the total resistance value (R_T) or the relative thickness (1/C_T) of the film. The obtained results were confirmed by surface examination using scanning electron microscope.     

Corrosion of Pb–Ca–Sn alloy during potential step cycles

Potential step was applied to Pb–Ca–Sn alloy electrode at various potential and time regimes. No severe corrosion was observed during potential step cycle with cathodic potential under −140 mV or over −40 mV versus Pb/PbSO₄ (3.39 M H₂SO₄), or at constant potential without stepping. On the other hand, the Pb–Ca–Sn alloy was severely corroded during potential step with cathodic potential from −120 mV to −60 mV and with anodic potential of +40 mV or more positive. The corrosion could not be decreased with periodical rest at 0 mV, while it could be decreased with periodical reduction at high polarization of, e.g. −160 mV. It was found out that the severe corrosion occurs when the oxidation of Pb to PbSO₄ and partial reduction of passive film of PbSO₄ take turns many times.     

Synthesis, characterization and application of Li3Fe2(PO4)3 nanoparticles as cathode of lithium-ion rechargeable batteries

This work introduces a new method to synthesize Li₃Fe₂(PO₄)₃ nanoparticles in the nanopowder form and study its electrochemical performance by cyclic voltammetry and battery tests. Li₃Fe₂(PO₄)₃ is synthesized by the gel combustion method based on polyvinyl alcohol (PVA) as gel making agent. The optimum conditions of the synthesis include 8 wt% PVA, 0.34 wt% lithium slat, 1 wt% iron salt, 0.57 wt% ammonium dihydrogen phosphate, ethanol-water 50:50 as solvent, 675 °C combustion temperature and 4 h combustion time. Characterization of the samples is performed by the scanning electron microscopy (SEM), transmission electron microscopy (TEM), EDX analysis, XRD patterns, BET specific surface area and DSL size distribution. In the optimum conditions, a nanopowder is obtained that consisting of uniform nanoparticles with an average diameter of 70 nm. The optimized sample shows 12.5 m² g⁻¹ specific surface areas. Cyclic voltammetry (CV) studies show that the synthesized compound has good reversibility and high cyclic stability. The CV results are confirmed by the battery tests. The obtained results show that the synthesized cathodic material has high practical discharge capacity (average 125.5 mAh g⁻¹ approximately same with its theoretical capacity 128.2 mA h⁻¹) and long cycle life.     

Combined cyclic voltammetry and in situ electrochemical atomic force microscopy on lead electrode in sulfuric acid solution with or without lignosulfonate

The effect of lignosulfonate (LS) on electrochemical reaction of lead electrode (as a model of negative electrode) has been investigated in 1 M, 3 M, or 7.1 M H₂SO₄ aqueous solution with 0, 10, 100 or 1000 mg l⁻¹ of LS using cyclic voltammetry (CV) combined with in situ electrochemical atomic force microscopy (EC-AFM), as well as rotating ring disk electrode (RRDE). The anodic peaks of the CVs, which correspond to overall reaction of , shifted positive when LS was added or the concentration of H₂SO₄ was lower. The anodic capacities of the CVs increased with addition of LS when the concentration of H₂SO₄ was lower. When LS was added, the anodic capacities of the CVs usually increased especially in less concentrated H₂SO₄ solution at higher sweep rate, while the anodic capacity slightly decreased in 7.1 M H₂SO₄ solution with addition of LS at sweep rate of 10 mV min⁻¹; that is, in most concentrated H₂SO₄ solution at lower sweep rate in this paper. Two cathodic peaks of the CVs were observed when LS was added, and the peak at lower potential shifted more negative with increase of LS. Lead sulfate crystals dissolved at more negative potential with increase of LS. LS up-took Pb²⁺ ions in H₂SO₄ aqueous solution during discharging.     

Electrolytic Sn/Li2O coatings for thin-film lithium ion battery anodes

Sn/Li₂O composite coatings on stainless steel substrate, as anodes of thin-film lithium battery are carried out in SnCl₂ and LiNO₃ mixed solutions by using cathodic electrochemical synthesis and subsequently annealed at 200 °C. Through cathodic polarization tests, three major regions are verified: (I) O₂ + 4H⁺ + 4e⁻ → 2H₂O (∼0.25 to −0.5 V), (II) 2H⁺ + 2e⁻ → H₂, Sn²⁺ + 2e⁻ → Sn, and NO₃⁻ + H₂O + 2e⁻ → NO₂⁻ + 2OH⁻ (−0.5 to −1.34 V), and (III) 2H₂O + 2e⁻ → H₂ + 2OH⁻ (−1.34 to −2 V vs. Ag/AgCl). The coated specimens are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), and charge/discharge tests. The nano-sized Sn particles embedded in Li₂O matrix are obtained at the lower part of region II such as −1.2 V, while the micro-sized Sn with little Li₂O at the upper part, such as −0.7 V. Charge/discharge cycle tests elucidated that Sn/Li₂O composite film showed better cycle performance than Sn or SnO₂ film, due to the retarding effects of amorphous Li₂O on the further aggregation of Sn particles. On the other hand, the one tested for cut-off voltage at 0.9 V (vs. Li/Li⁺) is better than those at 1.2 and 1.5 V since the incomplete de-alloy at lower cut-off voltage may inhibit the coarsening of Sn particles, revealing capacity 587 mAh g⁻¹ after 50 cycle, and capacity retention ratio C50/C2 81.6%, higher than 63.5% and 49.1% at 1.2 and 1.5 V (vs. Li/Li⁺), respectively.