The mechanism of suppressing capacity degradation of high-Al AB5-type hydrogen storage alloys at 60 °C

Excellent high-temperature cycling stability and storage property are obtained by partially substituting Al for Ni in La0.78Ce0.22Ni3.95-xCo0.65Mn0.3Si0.1Alx (x = 0-0.4) alloys, especially at 60 °C. Potentiodynamic polarization, electrochemical impedance spectrum (EIS), inductively coupled plasma-atomic emission spectroscopy and scanning electron microscope analyses are employed to reveal the mechanism of suppressing capacity loss of the alloy. The results demonstrate that partially Al substituting suppresses the pulverization and corrosion tendency of the alloys. Al-containing alloys show improved anti-corrosion capability, and the dissolution of La, Ce, Ni, Co, Mn and Si can be restrained remarkably by sacrificing Al content, thus excellent cycling stability and storage property are obtained. In addition, at higher temperature, the dissolution of Al is the dominant factor that influences the electrochemical properties at the early stage of cycles, promoting the surface catalytic ability. Subsequently, the gradual accumulation of metal hydroxide on the electrode alloy surface protects active metal from further oxidation and corrosion. Novel EIS mode in metal hydride electrode is proposed to study surface corrosion and dissolution behavior at higher temperature.