Degradation and recovery properties in thermochemical hydrogen compression by using TiFe alloy

Abstract

The thermochemical hydrogen compression properties and cyclic durability of titanium-iron (TiFe) alloy were investigated at various temperatures of 200, 300, 450, and 500 °C by examing the achieved maximum pressure variations and hydrogen storage capacity before and after compression cycles. The cyclic durability of the TiFe alloy-based thermochemical hydrogen compressors was different depending on the operating temperature. Below 350 °C, the TiFe alloy-based hydrogen compressors showed stable thermochemical hydrogen compression properties with constantly achieved hydrogen compression pressure, hydrogen storage capacity, and unchanged phases. On the contrary, the reached maximum pressure with heating was gradually decreased during the compression cycles at 450 and 500 °C, suggesting poor durability and degradation at the higher temperature region. During the cycles, lattice strain and dislocation density of the alloy may be induced and lead to increase plateau pressure (hysteresis) without a change in hydrogen storage capacity. However, temperature increase can cause the disproportionation of TiFe around the formed lattice strain and dislocation. Therefore, after cycles at 500 °C, the hydrogen storage capacity is reduced by 30.4%. Furthermore, phase identification by X-ray diffraction measurements and thermal analysis suggested that TiH2, Fe2Ti, and Ti2Fe phases were disproportionately generated from the initial TiFe phase as irreversible hydrogen absorption states and became the dead volume for the cyclic compression cycles. Interestingly, the recovery of the TiFe alloy phase from the disproportionated phase of TiH2, Fe2Ti, and Ti2Fe can be achieved based on the TG-DTA-MS results. Therefore, based on the above results, the degradation and recovery properties in thermochemical hydrogen compression by using TiFe alloy are well understood in this work.