Insights into the effects of Co and Al on the structural evolution and hydrogen storage properties of La0.25Y0.75MgNi3.5(Co,Al)0.5 alloys

This study examined the effects of the crystal structure, hydrogen storage, and electrochemical performances of La0.25Y0.75MgNi3.5CoxAl0.5−x alloys (x = 0.1, 0.2, 0.3, and 0.4). Analysis of the refined X-ray diffraction patterns revealed that these alloys predominantly exhibit an A2B4-type structure complemented by LaNi5 and (La,Y)2O3 oxide phases. The phase composition of these alloys appears to homogenize as Al is progressively replaced by Co. Notably, Co enhances the maximum hydrogen absorption capacity of the alloy by increasing the lattice interstitial spaces, whereas Al reduces the hysteresis in the pressure–composition isotherms and diminishes the plateau pressure for hydrogen absorption and desorption. The La0.25Y0.75MgNi3.5CoxAl0.5−x alloy electrodes demonstrated consistent improvements in the maximum discharge capacity, cycling, and kinetic performances with increasing Co content. This enhancement is attributed to the impact of Co on grain refinement and the Raney Ni-Co layer with high catalytic activity, which in turn enhance the kinetic and corrosion resistance of the electrodes.