Thermodynamics and kinetics of MgH2-nfTa(2)O(5) composite for reversible hydrogen storage application

摘要

The thermodynamics and kinetics of hydrogen absorption-desorption of nfTa(2)O(5)-Mg-MgH2-composite (nf stands for nano-flakes) have been studied. The nfTa(2)O(5)-Mg composite could absorb hydrogen at room temperature (17 A degrees C). The hydrogen desorption of nfTa(2)O(5)-MgH2 composite starts at 200 A degrees C. The remarkably improved hydrogen absorption-desorption of catalyzed Mg-MgH2 could be attributed to the nano-engineered surface by nfTa(2)O(5). 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 nfTa(2)O(5)-MgH2 was found to be 74 +/- 7 kJ/mol. The nfTa(2)O(5)-MgH2 composite has shown cyclic stability up to fifty hydrogen absorption-desorption without significant changes in the kinetics and hydrogen storage capacity.