Influence of the stoichiometry on the H-desorption rates measured in solid-gas phase and electrochemical cell for air-exposed LaNi5+x-type alloys

The dehydrogenation of multi-substituted air-exposed LaNi5+x-type materials were investigated both in solid-gas phase and electrochemical cell as a function of their stoichiometry (x=−0.1,0.1,0.3) while keeping a constant plateau pressure by adjusting their composition. The increase of the stoichiometry is accompanied by an increase of the La/Ce ratio and Ni content. In solid-gas phase, the desorption rates were measured in air-exposed samples upon cycling and were found to be sensitive to the stoichiometry. The oxide formation at the surface produces a significant decrease of the solid-gas phase kinetics. An increase of the overstoichiometry leads to lower rates and capacities as well as restrained decrepitation upon H-cycling. Electrochemical measurements of the high rate dischargeability show constant values within the same range.