The electrochemical hydrogen storage performances of Mg_xCo_100-x (x = 40, 45, 50, 55, 60, 63) body-centered cubic alloys and their Pd-doped system

In this work, a serial of Mg-Co binary alloys with body-centered cubic (BCC) phase were prepared for anode materials of Ni-MH hydrogen storage battery system. TEM/SAED analyses on binary Mg-Co alloys demonstrated that their grains were all in nano-size (∼5 nm) with BCC structure. Electrochemical tests found that, with increase of the concentration of Mg in alloys, theoretical charge-discharge capacities would increase accordingly, discharge kinetics (exchange current densities and hydrogen diffusion abilities) were improved as well. However, the tested capacity will attain a maximum value (325 mAh g^-1) at the point of Mg₅₅Co₄₅ and deteriorate subsequently with continuous increase of Mg content, which was possibly due to the optimized lattice parameter value and Mg corrosion. The increase of Co concentration in the binary alloys effectively inhibited the corrosion of the electrodes. On the basis of Mg-Co binary alloys, the Pd-doped ternary alloys with BCC structure were also prepared by means of ball milling. These alloys possess greatly enhanced discharge capacities (280-500 mAh g^-1) from binary ones. It shows that with increase of the Mg content, the discharge capacities of Mg-Co-Pd ternary alloys will increase monotonously. The additional Pd also improved cycle stabilities, kinetics, and corrosion potentials of the alloys, which was beneficial to improving the properties of Mg-Co hydrogen storage electrodes.