Electrochemical kinetic properties of AB5-type hydrogen storage alloys with chemically deposited polypyrrole

Abstract

La0.65Ce0.25Pr0.02Nd0.08Ni3.85Mn0.39Co0.73Al0.31 AB5-type alloy was modified via the method of a simple chemical oxidative polymerization of pyrrole (Py) directly occurring on the surface of alloy particles. Field emission scanning electron microscopy and Fourier transform infrared spectroscopy revealed spongy polypyrrole (PPy) films uniformly and continuously deposited on the surface of the alloy particles. The PPy films possessed superior electrochemical redox reversibility, thus facilitating hydrogen protons transferring from electrolyte to electrode interface. Moreover, the PPy films exhibited prominent anti-corrosion properties and reduced the pulverization of the alloy particles. The PPy-coated alloy received remarkable enhancement in rate capability and cyclability compared to those of the bare alloy. Due to the PPy films, the high-rate dischargeability at a discharge current density of 1500 mA g−1 (HRD1500) significantly increased from 18 to 31.6 %, and the capacity retention rate after 200 cycles (S 200) increased from 84.2 to 89.8 %. Meanwhile, the PPy coatings decreased the charge transfer resistance and increased the hydrogen diffusion rate of the alloys, which well conformed with the HRD results.