Effective thermal conductivity of dimagnesium iron hexahydride (Mg2FeH6) for heat storage applications

The transient plane source method was applied to measure the effective thermal conductivity in dimagnesium iron hexahydride (Mg2FeH6) prepared in a high-pressure synthesis of 50 temperature-driven de-/hydrogenation cycles. Temperature- and pressure-dependent measurements of the effective thermal conductivity of the as-synthesized Mg2FeH6 powder have been performed. Measurements for as synthesized Mg2FeH6 were carried out between 2 and 100 bar in a temperature range from 50 degrees C to 300 ?degrees C and at 70 bar in a temperature range from 480 degrees C to 520 degrees C during the cycle test. The effective thermal conductivity of the as-synthesized Mg2FeH6 varied between 0.39 W m(-1) K-,(-1) recorded at 50 degrees C and 2 bar of hydrogen gas pressure, and 0.54 W m(-1) K-1, measured at 300 degrees C and 100 bar hydrogen pressure. The effective thermal conductivity increased with elevated hydrogen gas pressure and temperature. An evidence was found that the presence of iron prevents the sintering of the powder, resulting in a constant effective thermal conductivity during all accomplished cycles. The advantage of a non-sintered material resulting in higher hydrogen diffusion, which leads to a faster reaction time. For 50 measured de-/hydrogenation cycles between 480 degrees C and 520 degrees C, the thermal conductivity was found to be constant at around similar to 1.0 W m(-1) K-1 in the dehydrogenated state (70 bar/520 degrees C) and between 0.7 W m(-1) K-1 and 0.8 W m(-1) K-1 in the hydrogenated state (70 bar/480 degrees C).