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

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/H-2 reactions. During hydrogen absorption/desorption on LaY2Ni9, La2Y4Ni21 and La5Y10Ni57 alloys, the discrete expansion/contraction properties of the [AB(5)] and [A(2)B(4)] 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 [AB(5)]/[A(2)B(4)] 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/ H-2 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.

Automated summary

La-Y-Ni-based alloys have potential as hydrogen storage materials, but their rapid capacity degradation limits their applications. This study investigates the capacity degradation mechanism of these alloys and the effect of the La/Y ratio on their cyclic stability. The expansion/contraction properties of the subunits in the hydrogen solid solution and hydrides lead to lattice strain and pulverization. Adjusting the subunit ratio can decrease lattice strain and improve cyclic stability. The cyclic stability in the electrolyte decreases with a lower La/Y ratio, opposite to the trend observed in the solid/H-2 system. Y-poor and Y-rich alloys are suitable for electrochemical and solid-state hydrogen storage applications, respectively.