Capacity degradation mechanism of ternary La–Y–Ni-based hydrogen storage alloys

Abstract

La–Y–Ni-based alloys are suitable candidates for hydrogen storage materials. However, their applications are limited by their rapid capacity degradation. In this study, the capacity degradation mechanism of ternary La–Y–Ni-based alloys and the effect of the La/Y ratio on their cyclic stability are investigated from the perspective of electrochemistry and solid/H2 reactions. During hydrogen absorption/desorption on LaY2Ni9, La2Y4Ni21 and La5Y10Ni57 alloys, the discrete expansion/contraction properties of the [AB5] and [A2B4] subunits in the hydrogen solid solution and hydrides leads to the lattice strain, which results in pulverization. Severe pulverization aggravates the oxidation/corrosion of the alloys caused by active La and Y. The amorphization/pulverization and oxidation/corrosion of the alloys can be reduced by adjusting their [AB5]/[A2B4] subunit ratio to decrease the lattice strain; this can enhance their cyclic stability. The cyclic stability of the La–Y–Ni-based alloys in the electrolyte decreases with the lower La/Y ratio. This trend is opposite to that observed in the solid/H2 system. Y-poor and Y-rich alloys are suitable for electrochemical and solid-state hydrogen storage applications, respectively. This work provides insights on improving the cycle life of La–Y–Ni-based hydrogen alloys.