Effects Of Composite Chemical Plating On The Structure And Electrochemical Properties Of Hydrogen Storage Alloys

This paper briefly introduced and analyzed the research status and development aspect of the surface treatments of hydrogen storage alloys in recent years, and illustrated the composite electroless plating technology in detail.In the experiment, copper and nickel were separately plated on the surfaces of AB₅ type hydrogen storage alloys (LaNi₅) and AB3 type hydrogen storage alloys (LaMg2 Ni_6.0Mn_3.0) first, then copper-nickel composite plating was carried on. Effefcts of the different plating on the structure and the electrochemical properties of the hydrogen storage alloys were systemically studied by changing plating condition, which included the the ion concentration of Cu²⁺ and Ni²⁺ in the plating solution, the pH value and the temperature of the fluid, as well as the plating time.The result showed that the influence of the electroless plate on AB5 type and AB3 type hydrogen storage alloys was consistent, plating copper could improve the activate performance and discharge capacity, but couldn't remarkably ameliorate the cyclic stability; Plating the nickel could strengthen the cyclic stability of the alloys, but the improvement of the activate performance and discharge capacity wasn't obvious compared with the copper plating; The composite plating of copper-nickel then could notability improve the discharge capacity , cyclic stability and other electrochemical properties. Simultaneity the anticorrosive function of the alloys was obviously improved.The effects of plating condition on the electrochemical properties of hydrogen storage alloys were discovered. The concentrition of Cu²⁺ and Ni²⁺ controlled the deposition speed, influenced the rough degree of the plated layer. Plating liquid temperature notabily influenced the plating rate, the reaction was very acute and the process was out of control when the temperature was too high, but the live ion seldom deposited when the temperature was low. Plating time would influence the thickness of the plated layer. The pH was the most important factor, which influenced the anticorrocive ability and anti-powder ability of the alloys surface, and controlled the cyclic stability and the discharge capacity of the alloys. Compared with the non-plated AB3 alloy, the initial discharge capacity of LaMg₂Ni_6.0Mn_3.0 increased 100mAh/g, which was the preferably composite plated alloy, the most discharge capacity raised 60mAh/g without distinct decay through 100 circulations, and the cyclic stability rose notabily. The activity number shortened from 10 times of non-plated alloy to 3 times, notability improved the activity properties. The composite electroless plated showed the overall improvement compared with the non-plated alloys.The XRD showed LaNi₃ and LaNi₅ were the main phases in copper-plated alloys, and besides, CuNi₄O phase was detected. The new phase maybe caused the increment of the capacity of discharge and the activation performance of the alloys. In nickel-plated alloys, MgNi₂ phase was detected, which may be the reason that electrochemistry reaction of electrode surface was easily carried through, and the circulating stability of the alloy was improved. The appearing of the high strength CuNi₄O phase and Mg₂Ni₃ phase in the composite plated alloys was the reason of the increment of the activation performance of the alloys and anti-oxidize performance. The results of SEM showed that after the composite plating, a fine globosity layer was appeared on the alloys surface, distributing uniformity, and the shape singleness. So the desquamation of oxidization-pulverization and aliquation of the lanthanon were prevented in the charge-discharge process of hydrogen storage alloys.