Effect of electroless nickel coating on the electrochemical hydrogen storage characteristics of Al and Zr including Mg-based alloys

Mg2Ni, Mg1.5Al0.5Ni, Mg1.5Zr0.5Ni and Mg1.5Al0.2Zr0.3Ni alloys were synthesized by the mechanical alloying and the effect of electroless Ni coatings on the electrochemical hydrogen storage characteristics of these alloys were investigated. X-ray diffraction studies showed that the Ni particles formed on the alloy surface during the electroless coating resulted in the formation of two new broad Ni peaks. The application of the Ni coating improved the capacity retention rates of all the alloys. This improvement was attributed to the hydrogen diffusion pathways provided by the external Ni particles. The capacity retention of the coated Mg2Ni alloy was relatively lower than those of the coated Al and Zr including alloys. This observation was assumed to arise from the contribution of the underlying electrocatalytically active Ni sites formed as a result of the dissolution of the disseminated Al and Zr oxides throughout the Mg(OH)2 layer to the alloy capacity retention rate. The electrochemical impedance spectroscopy experiments indicated that the Ni crystals nucleated during the electroless coating make the alloy surface more catalytic for the electrochemical charge transfer reactions.