Hydrogen diffusion behavior in α-solid solution phase of LmNi 3.55Co 0.75Mn 0.4Al 0.3 metal hydride electrode—Effect of temperature

Abstract

The hydrogen diffusion coefficient in an LmNi 3.55Co 0.75Mn 0.4Al 0.3 alloy electrode was evaluated by potential-step method as a function of initial hydrogen concentrations in the bulk of alloy electrode ( C H < 0.1 H/M) and temperature (293–333 K). The hydrogen diffusion coefficient was found to decrease linearly with the increase of C H at all temperatures. However, the slope of this linear dependence was found to reduce with the increasing temperature. The partial interaction Gibbs energy of dissolved hydrogen ( Δ G ¯ int ) revealed a strong influence of temperature on the stability of α-solid solution phase in the alloy electrode. Namely, the Δ G ¯ int gradually increased −25.6 to −2.5 kJ mol −1 with increasing temperature, showing a linear dependence. It is found that the Einstein diffusion coefficient of hydrogen increased also with increasing temperature, and that the apparent energy of activation of hydrogen diffusion is 27.9 kJ mol −1. A novel viewpoint in understanding of the hydrogen diffusion kinetic in hydrogen storage alloys is discussed in view of the thermodynamic stability of the resulting hydrides.