Effect of morphology on the performance of metal-hydride electrodes

Electrochemical studies on AB2 type Zr0.5Ti0.5V0.6Cr0.2Ni1.2 metal hydride electrodes with varying particle size suggests that the electrodes with alloy particles of about 60 μm yield the optimum performance. The values for diffusion coefficient of hydrogen in the alloy particles > 25 μm are found to be nearly invariant. Both a.c. impedance and linear polarization data on electrodes with varying particle size suggest that the charge-transfer resistance depends on state-of-charge of the electrodes. A comparison of scanning electron micrographs of fresh electrodes and subsequent to their prolonged charge-discharge cycling suggests that the metal hydride particles develop stress-induced cracks owing to their inherent expansion and contraction during the hydriding/dehydriding processes.