Hydrogen desorption kinetics in MmNi4.2Al0.8-H SYSTEM

Hydrogen desorption kinetics were investigated in the MmNi(4.2)Al(0.8)-H system. The pressure-composition; (PC) isotherms for hydrogen absorption and desorption at 288, 298 and 308 K were initially obtained for the activated samples. The desorption reaction rate was found to be of first order with a high hydrogen evolution rate. The reaction rate constants, obtained using the linear rate law, were 11.11 x 10(-3), 20.28 x 10(-3) and 40.00 x 10(-3) s(-1) at 288, 298 and 308 K, respectively. The activation energy for hydrogen desorption reaction, obtained by the Arrhenius equation, was 48.09 kJ/mol H-2, which is comparable to literature data. The first order of reaction and the estimated activation energy indicate that diffusion of hydrogen through the MmNi(4.2)Al(0.8) lattice is the rate controlling step in the hydrogen desorption reaction. (C) 1998 International Association for Hydrogen Energy.