Hydrogen adsorption on hydrogen storage alloy surface and electrochemical performances of the MlNi4.0Co0.6Al0.4 alloy electrodes before and after surface treatment

The surfaces of the hydrogen storage alloy powders (MlNi4.0Co0.6Al0.4) before and after surface treating were analyzed by X-ray photoelectron spectroscopy (XPS), electron probe micro-analysis (EPMA), inductively coupled plasma spectroscopy (ICP). It was found that a Ni-rich surface layer was produced and the specific surface area was augmented by the surface treatment with a hot 6 M KOH or 6 M KOH+0.02 M KBH4 solution due to the preferential dissolution of Al and the etching of the hot alkaline solution. The effect of the surface treatments on the hydrogen adsorption on the alloy surface was for the first time evaluated by means of the thermal desorption spectroscopy (TDS). It was found that the surface treatments enhanced the hydrogen adsorption on the alloy surfaces and produced new adsorption states. The untreated alloy had only one hydrogen adsorption peak at about 400 K. There were two hydrogen adsorption states at about 540 and 630 K on the surface of the alloy treated with 6 M KOH. In the case of the alloy treated with 6 M KOH+0.02 M KBH4 three hydrogen adsorption peaks were observed at about 390, 540 and 630 K, respectively. The results of electrochemical measurements showed that the treated alloy electrodes exhibited higher exchange current density for the hydrogen electrode reaction than the untreated hydrogen alloy. After the surface treatment, the hydrogen adsorption enhancement on the treated alloy surface facilitated the hydrogen electrode reaction process on the alloy electrodes and results in good activation and low polarization resistance.