Effect of Al, B, Ti and Zr additive elements on the electrochemical hydrogen storage performance of MgNi alloy

MgNi, Mg0.9(M)0.1Ni and Mg0.8(M)0.2Ni (M = Al, B, Ti, Zr) type alloys were synthesized by mechanical alloying and their electrochemical hydrogen storage characteristics were investigated. X-ray diffraction studies showed that although 15 h milling was enough to obtain amorphous/nano-crystalline MgNi alloy structure, the dissolution of all Ni in the main phase required at least 25 h milling. The discharge capacities of alloys were observed to increase sharply up to 15 h milling. Further increase up to 25 h did not cause change in the discharge capacities considerably. Titanium improved MgNi alloy discharge performance significantly. Although Al deteriorated the initial discharge capacity of MgNi alloy, it improved the alloy capacity retention rate. Despite the absence of any positive effect of B, Zr had limited positive effect on the alloy cyclic stability. It was estimated that up to 80% discharge level there was no considerable degradation by the anodic reaction in MgNi alloy since uncharged MgNi alloy stayed in the cathodic regime.

Research highlights
► In this research the effect of Al, B, Ti and Zr additive elements on the charge/discharge cyclic stability of MgNi hydrogen storage alloy was investigated by synthesizing Mg0.9(M)0.1Ni and Mg0.8(M)0.2Ni (M = Al, B, Ti, Zr) type alloys by mechanical alloying.
► The degradation behavior of MgNi alloy and the effect of additive elements on the degradation behavior of this alloy were also analyzed by electrochemical impedance spectroscopy technique.