Effect of surface treatments on microstructure and electrochemical properties of La–Ni–Al hydrogen storage alloy

Abstract

Surface treatment by the fluorination treatment with an aqueous solution of KF and HF with a little addition of KBH 4 followed by electroless Ni–P plating has been carried out to modify the surface structure and electrochemical properties of the La–Ni–Al hydrogen storage alloy. The results of scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) show that a Ni-rich and Al-poor layer forms after fluorination treatment. The electroless plating results in the precipitation of the nanometer-scale Ni–P particles with homogeneous distribution on the alloy surface. Both the treatments contribute to an increase in exchange current density, a decrease in charge-transfer resistance and the facility of hydrogen diffusion within the bulk alloy, leading to significant improvements on high rate dischargeability (HRD) of the alloy. The alloy treated by the composite treatment of the fluorination treatment and the following electroless plating possesses best overall electrode performance.