Intrinsic degradation of FeTi by thermally induced hydrogen absorption-desorption cycling

Abstract The deterioration of the hydrogenation properties of FeTi during thermally induced hydrogen absorption-desorption cycling was investigated using the following: 1. (i) the change in the P-C-T curves as a function of the number of cycles, 2. (ii) X-ray diffraction, and 3. (iii) the thermal desorption of hydrogen after cycling. The results of the thermal desorption of hydrogen provide information about the hydrogen occupation at various interstitial sites, which are distinguished by different binding energies. It was found that the formation of stable hydrides is the source of degradation caused by thermally induced hydrogen absorption-desorption cycling. Thermal cycling of FeTi produces an intrinsic degradation that reduces the hydrogen storage capacity and suppresses the formation of the γ phase in its hydride. Surprisingly, as a result of degradation, the overall rate of the hydrogenation reaction is also decreased. The mechanism of the degradation is probably related to the formation of stable hydrides, which causes a change in the environments of the sites occupied by hydrogen in the neighbour matrix. Most of the properties can be recovered by a simple annealing treatment in vacuum.