Characterization and analyses of degradation and recovery of LaNi _4.78Sn_0.22 hydrides following thermal aging

LaNi_4.78Sn_0.22H_x hydride samples were held at a hydrogen content of x > 5.0 (x is H/La atomic ratio) and temperatures above 465 K to accelerate the intrinsic degradation processes. Although Sn-substituted alloys are much more resistant to disproportionation than nearly all other LaNi₅ alloys, the present test conditions did produce substantial degradation. Effects observed included reduction in hydrogen storage capacity, decreases in the plateau pressures, increased slopes of the plateaus, and smaller hysteresis ratios. A regeneration process nearly completely restored the behavior of the degraded LaNi_4.78Sn_0.22 hydride to its initial value. First-principles chemical reaction kinetics and statistical thermodynamics simulations have replicated experimental pressure-composition hydrogen gas absorption isotherms for both initial and degraded LaNi_4.78Sn_0.22 hydride. Neutron diffraction characterization of phase compositions, crystal structures, and hydrogen content have been performed on undamaged, degraded, and regenerated LaNi _4.78Sn_0.22 deuterides.