Hydrogen absorption/desorption thermodynamics and kinetics. Hydrogen capacity measurements were conducted using a Setaram PCTPro system. Samples were loaded into air-tight stainless-steel vessels under an argon atmosphere, connected to the system, and the volume was calibrated using He gas. Samples were desorbed into static vacuum, and hydrogenation was performed under 105 bar hydrogen. Hydrogen was assumed to be the only gaseous product of the reaction, which is likely valid because these materials show high levels of cyclability. The van't Hoff equation was used to determine the enthalpy and entropy of hydrogen absorption: