The effect of al, cr, co and mo additions on the properties of nanocrystalline TiFe0.25Ni0.75-type hydrogen storage electrodes prepared by mechanical alloying

In this paper, we present the effect of Al, Cr, Co and Mo additions on the structure and the electrochemical properties of the nanocrystalline TiFe0.25Ni0.75-type electrode materials. The mechanical alloying (MA) process was used to synthesize these materials. The XRD analysis showed that, firstly, after 25 h of milling, the starting mixture of the elements had transformed into an amorphous phase and, secondly, the annealing in high purity argon at 700°C for 0.5 h led to the formation of the CsCl - type structures with crystallite sizes of about 25 nm. The discharge capacity of the electrode prepared by the application of MA TiFe0.25Ni0.75 alloy powders was degraded strongly with cycling. This may be due to the easy formation of the oxide layer (TiO2) during the cycling. For example, it was found that the respective substitution of Fe by Cr improved the cycle life of the studied electrodes. In the nanocrystalline TiFe0.125Cr0.125Ni0.75 powder the discharge capacity 134 mAhg^-1 was measured on the 10th cycle (at 40 mA g^-1 discharge current). The studies show that the electrochemical properties of nanocrystalline MHx electrodes are a function of the chemical composition of the electrode materials used.