Investigations on the kinetics properties of the electrochemical reactions of MlNi3.55Co0.75 − xMn0.4Al0.3(Cu0.75P0.25)x (x = 0.0, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys

The effect of the multiple substitution of Cu–P for Co on the kinetics properties of the novel hydrogen storage alloys MlNi3.55Co0.75 − xMn0.4Al0.3(Cu0.75P0.25)x (x = 0.0, 0.1, 0.2, 0.3, 0.4) was investigated. The electrochemical impedance spectroscopy (EIS) method was applied to characterize the kinetics properties of the electrochemical reactions of the series composite alloys. It was found that the charge-transfer reaction resistance Rct decreased from 122.2 to 106 mΩ g and the exchange current density I0 increased from 210.1 to 242.2 mA g−1 with increasing Cu–P content. Moreover, the hydrogen transfer resistance Ra remarkably decreased from 149.1 to 17.23 mΩ g, and the hydrogen diffusion coefficient D increased from 1.01 × 10−11 to 7.01 × 10−11 cm2 s−1 with the increase of x from 0.0 to 0.4. The measurements revealed that the overall kinetics properties of the electrochemical reactions were improved as the multiple substitution, especially for the sample x = 0.4.

► The overall kinetics properties were improved as the substitution of Cu–P for Co.
► The charge-transfer resistance decreased and the exchange current density increased.
► The hydrogen transfer resistance remarkably decreased with increasing Cu–P content.
► The hydrogen diffusion coefficient increased with increasing Cu–P content.