Effect of duplex surface treatment on electrochemical properties of AB3-type La0.88Mg0.12Ni2.95Mn0.10Co0.55Al0.10 hydrogen storage alloy

A new surface treatment technique, i.e. HF etching-Ni coating duplex surface treatment was applied to modify AB3-type La0.88Mg0.12Ni2.95Mn0.10Co0.55Al0.10 hydrogen storage alloy. Surface structure and electrochemical properties were investigated. SEM and EDS indicated that Ni deposited on the alloy surface, forming a porous Ni-rich layer. And thus initial activation ability and kinetics properties of the alloy electrode were improved significantly. The ratio C1st/Cmax increased from 68.0% to 89.3%, the middle discharge voltage is 0.025 V higher, the high rate dischargeability (HRD) was about 10% higher at a current density of 1080–1800 mA g−1, and the cycling stability was improved slightly after duplex surface treatment. In addition, the exchange current density I0, the limiting current density IL, the oxidation peak current and the peak area of cyclic voltammograms were also increased obviously after the duplex surface treatment.