Semi-empirical degradation rate estimation of TiFe1-xMnx alloy for thermochemical hydrogen compression durability tests

Abstract

The substitution effects of Fe by Mn in TiFe1-xMnx (x = 0.1–0.5) alloys on the cyclic durability for thermochemical hydrogen compressors were investigated. In the substitution ratio range of 0.1–0.5, TiFe1-xMnx alloy shows a single CsCl phase structure, and thus is further used for a thermochemical hydrogen compressor at 500 °C. The compression tests are performed for 26 cycles in temperature range from 25 °C to 500 °C. The variation of hydrogen storage capacity during pressure composition isotherm test and structural identification by x-ray diffraction measurements are conducted to investigate the cyclic durability of TiFe1-xMnx alloy at the above compression conditions. The Mn substitution increased the cyclic durability of TiFe for the thermochemical hydrogen compressor, and 30% of Mn (TiFe0.7Mn0.3) is the optimum ratio for the reduction rate of hydrogen storage capacity and achieved maximum pressure. In addition, TiFe0.5Mn0.5, as the respective sample with the maximum capacity loss, was evaluated by the acceleration test to estimate the lifetime of the alloys. The reaction kinetics v0 [(H/M)/s] of the capacity loss of TiFe0.5Mn0.5 is defined as ln v0 = 1.68 ln (PH2/P0) − (2.39 × 1000)/T − 18.967. Therefore, it is possible to predict the durability of TiFe1-xMnx alloy at different pressure and temperature conditions by the presented acceleration test.