Electrochemical hydrogen storage capacities of Mg2Ni and MgNi alloys synthesized by mechanical alloying

Abstract

Mg2Ni and MgNi alloys were synthesized by the mechanical alloying and their electrochemical hydrogen storage characteristics were investigated. The XRD peaks indicated that MgNi alloy was mainly in the amorphous characteristics while Mg2Ni alloy was composed of mixture of amorphous and nano-crystalline structures. The development of the amorphous structure in MgNi alloy was very fast and the maximum storage capacity was reached at 15 h ball milling. The maximum storage capacity of Mg2Ni alloy was observable after at least 40 h ball milling. Both the initial discharge capacity and capacity retention rate of MgNi alloy were much greater than those of Mg2Ni alloy. This observation was mainly attributed to the relatively reversible charge/discharge behavior of MgNi alloy. The charge transfer resistance of Mg2Ni alloy was greater than that of MgNi alloy especially at the higher depths of discharges. The presence of free electro-catalytically active Ni particles on MgNi alloy surface was thought as the main reason for the facilitated hydrogen charge transfer reactions on this alloy.