Effects of surface treatment on electrochemical properties of AB3.8-type hydrogen storage alloy in alkaline electrolyte

The La0.8Mg0.2Ni3.2Co0.3Mn0.1Al0.2 has been treated by the HF and KF etching solution and Ni coating solutions with the different concentrations. The surface structure and the electrochemical properties of the untreated and the treated hydrogen storage alloys have been investigated in details. The results show that the surface oxide layer on the alloys is removed after fluoridation and the surface of the alloy powders becomes smooth with electroless Ni plating. The maximum discharge capacity of the alloy electrodes is increased from 359.5 mA h g(-1) (M1) to 370.1 mA h g(-1) (M5) and the cycling stability is improved slightly after the surface treatment. At a discharge current density of 900 mA g(-1), the high rate dischargeability (HRD) is enhanced from 38.3% (M1) to 77.0% (M5) and the M5 electrode still keeps at a high value of 55.9% at a discharge current density of 1500 mA g(-1). In addition, the exchange current density I (0) and the hydrogen diffusion coefficient D are also increased by the surface treatment.