A study on the cycling stability of the Ti-V-based hydrogen storage electrode alloys

In this paper, the degradation mechanism of the Ti-V-based multiphase hydrogen storage electrode alloys (Ti_0.8Zr_0.2)(V _0.533Mn_0.107Cr_0.16Ni_0.2) _x (x = 2, 4, 6) during electrochemical cycling has been studied systematically by using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and electrochemical impedance spectroscopy (EIS). The reasons for the improvement in cycling stability of the electrodes with increasing x have also been discussed. The results show that the capacity degradation of the electrode is mainly caused by the following two reasons. The first one is the pulverization of the alloy particles during cycling, which leads to an increase in contact resistance and decrease in electric conductivity between alloy particles. The second one is the oxidation and corrosion/dissolution of the active alloy constituents in alkaline electrolyte during cycling, which leads to an increase in surface reaction resistance and decrease in discharge capacity of the alloy electrodes. With increasing x, the portion of stable and inactive hydride formed in the alloy during cycling decreases, and the pulverization resistance and corrosion resistance are increased. Therefore, the cycling stability is greatly improved for the alloy with higher stoichiometry x.