Influence of B substitution for Ti and Ni on the electrochemical hydriding of TiNi

Nanostructured TiNi0.8B0.2 and Ti0.8B0.2Ni were synthesized by mechanical alloying and by milling with subsequent annealing. X-ray analysis of the as-milled alloys shows a broad diffraction peak, which position corresponds to the cubic TiNi. Annealing for 1 h at 720 deg. C leads to microstructure coarsening and formation of TiNi and Ni3Ti. Boron doped titanium oxide (TiB0.024O2) was also detected in Ti0.8B0.2Ni. Electrochemical hydrogen charge/discharge measurements of the as-milled as well as of the annealed alloys were carried out at galvanostatic conditions. It was found that both alloys studied possessed low discharge capacities, as TiNi0.8B0.2 revealed a higher discharge capacity of 42 mAh/g in the as-milled state. Temperature increase from 23 to 45 deg. C did not result in capacity and cycle life changes. A capacity decrease for the two alloys was observed after annealing at 720 deg. C. Based on potentiostatic experiments the diffusion coefficients of hydrogen in the as-milled alloys were determined: 9.66 x 10-12 cm2/s for TiNi0.8B0.2 and 4.67 x 10-12 cm2/s for Ti0.8B0.2Ni