Thermodynamics and kinetics of MgH2–nfTa2O5 composite for reversible hydrogen storage application

Abstract

The thermodynamics and kinetics of hydrogen absorption–desorption of nfTa2O5–Mg–MgH2—composite (nf stands for nano-flakes) have been studied. The nfTa2O5–Mg composite could absorb hydrogen at room temperature (17 °C). The hydrogen desorption of nfTa2O5–MgH2 composite starts at 200 °C. The remarkably improved hydrogen absorption–desorption of catalyzed Mg–MgH2 could be attributed to the nano-engineered surface by nfTa2O5. The enthalpies of hydrogen absorption–desorption were found to be 80 ± 2, and 76 ± 3 kJ/mol respectively. The activation energy of hydrogen absorption was evaluated as 49 ± 5 kJ/mol which is same as the energy barrier for diffusion of hydrogen in Mg matrix. The apparent activation of hydrogen desorption of nfTa2O5–MgH2 was found to be 74 ± 7 kJ/mol. The nfTa2O5–MgH2 composite has shown cyclic stability up to fifty hydrogen absorption–desorption without significant changes in the kinetics and hydrogen storage capacity.