Effects Of Polypyrrole Modification On Electrochemical Properties Of La-Mg-Ni-based Hydrogen Storage Alloys

In recent years, the La–Mg–Ni-based alloys used as negative material in metal hydride/nickel(MH/Ni) batteries draw much attention for the outstanding hydrogen storage capacity compared with that of the rare–earth-based AB5-type alloys. However, aiming at widely industrial application, the high rate dischargeability(HRD), cycling stability and other electrochemical properties of La–Mg–Ni-based alloy electrodes still have to be improved. Generally, the characters mentioned above are greatly influenced by the surface performance of the hydrogen storage alloys.In order to improve the electrochemical kinetics of La–Mg–Ni-based alloy, the chemical modification of polypyrrole(PPy) doped with sodium sulfate(Na2SO4) or Nickel(Ni)/PPy composite has been applied on the surface of the La0.80Mg0.20Ni2.70Mn0.10Co0.55- Al0.10 alloy particles.The relatively better condition of chemical modification of PPy doped with Na2SO4 on alloy particles is 318 K and 0.75 g dopant stirring 8 min. SEM, TEM and FT-IR results indicate that the spongy nano-PPy successfully forms on the surface of the alloy particles, and that the PPy nanoparticles distribute uniformly. Owing to the nano-PPy, which possesses excellent electrochemical redox reversibility, electrocatalytic activity and high conductivity, electrochemical kinetics of the alloy electrode is remarkably ameliorated. The high rate dischargeability(HRD) of the treated alloy electrode at 1800 m A g-1 reaches two times of that for the bare alloy meanwhile the discharge voltages increase obviously. The charge-transfer resistance(Rct) of treated alloy electrode markedly decreases; the limiting current density(IL) and the hydrogen diffusion coefficient(D) increase.The relatively better bath concentration of chemical modification of Ni/PPy composite on alloy particles is 1.8 g/L stirring 8 min under 318 K. SEM and TEM results indicate that the spongy nano-PPy and lamellae Ni successfully forms on the surface of the alloy particles. The high rate dischargeability(HRD) of the treated alloy electrode at 1800 m A/g increases 10.2% compared to the bare alloy meanwhile the charge-transfer resistance of treated alloy electrode markedly decreases; the limiting current density and the exchange current density(I0) increase.