XAS investigation of corrosion characteristics in AB(sub 5) type metal hydride electrodes

摘要

Apart from the stress cracking due to lattice expansion and contraction during cycling, several substituents such as Ce and Co, and additions to the electrolyte such as ZnO have the ability to significantly improve the cycle life and corrosion characteristics in AB5 type metal hydride alloys. In situ XANES and SVET studies reveal that Ce substitution causes a protective passivation layer comprising of Ce oxides. This significantly reduces the extent of corrosion of substituents such as Ni despite greater percent volume expansion and contraction cycle compared with non Ce substituted samples. The Co substitution reduces the extent of percent volume expansion in the lattice cycle and hence the extent of stress cracking. It also segregates to the surface as Co(OH)2 which due to its higher conductivity counters the resistive effects due to build up of surface Ni(OH)2. Addition of ZnO to the electrolyte suppresses corrosion of substituents such as Ni in non Ce substituted alloys resulting in improved cycle life. The effects on Ce substituted alloys is negligible.