Electrolytic hydriding of TiFe 50/50 alloy

The electrolytic insertion of hydrogen into different samples of the intermetallic compound (IMC) TiFe 50/50 was investigated by voltammetry and galvanostatic charging–discharging cycles in order to devise conditions which would lead to extensive hydriding. The voltammetric pattern achieved in aqueous KOH shows both reduction and oxidation peaks well positive to the hydrogen evolution reaction. Such a pattern can hardly be ascribed to facile insertion–extraction of hydrogen since the charge recovered at the anodic peaks after prolonged cathodic reduction of the IMC represents only a few percent of the theoretical charge capacity of the TiFe hydride. Therefore, the detected peaks are attributed primarily to the redox states of surface Fe. In contrast, TiFe hydriding was seen to occur and its extent to increase progressively after repeated charging–discharging cycles carried out in aqueous K2CO3. Although this latter system appears unsuitable for battery applications owing to the large anodic polarization of hydrogen extraction, it nevertheless represents a possible activation route for hydriding TiFe. Faster and more extensive (>100 mA h g−1) hydriding of the IMC was achieved eventually after poisoning the electrolyte with thiourea.