Catalyzed KSiH3 as a reversible hydrogen storage material

Abstract

Solid-state hydrogen storage through the reversible formation of metallic hydrides is a key issue for the development of hydrogen as an energy vector. Herein we report the hydrogen storage performances of the KSiH₃ phase ball-milled with NbF₅ as a catalyst. The kinetics of hydrogen absorption/desorption are strongly enhanced by the addition of a catalyst as revealed by the large decrease of activation energies for both the absorption and desorption reactions. No disproportionation phenomenon is observed, indicating that the reaction between KSiH₃ and KSi is perfectly reversible with a hydrogen storage capacity of 4.1 wt% H₂. The thermodynamic properties of this KSi/KSiH₃ equilibrium were investigated by plotting PCI curves from 90 °C to 130 °C: an enthalpy of 24.3 kJ mol⁻¹ H₂ and a low entropy change of 59.5 J K⁻¹ mol⁻¹ H₂ are found. This low entropy variation is related to the high mobility of the H atoms in the α-KSiH₃ phase as recently demonstrated by Quasi-Elastic Neutron Scattering (QENS) experiments.