SURFACE MODIFICATION TO IMPROVE HYDROGEN ENTRY EFFICIENCY AND STORAGE CAPABILITIES OF METAL HYDRIDE ALLOYS

摘要

Performance improvements in metal hydride alloys can be achieved through different surface modification techniques. A review of the existing literature reveals that surface treatments or microencapsulation with Cu and Pd lead to improving the discharge kinetics and lowering the activation times of hydride electrodes. However, the problem of alloy corrosion is not reduced due to these treatments. Ni coatings reduce the alloy corrosion but increase the weight of the electrode thereby reducing the specific energy and power of the Ni-MH battery. Coating with Co forms a protective Co(OH)_2 layer on the surface of the alloy. This increases the capacity of the electrode. Optimization of Co coating on the surface of the hydride alloy was done and it is found that a 0.8 μm thick coating on the surface of the LaNi_(4.27)Sn_(0.24) alloy gives a good protection for the alloy. The electrode cycled with a constant capacity for more than 200 cycles while the bare alloy failed within 30 cycles.