Kinetics of the oxygen evolution reaction on NiSn electrodes in alkaline solutions

• Electrodeposited NiSn coatings were tested as anodes for oxygen evolution in 1 M NaOH at 25 °C.
• NiSn electrodes showed better apparent electrocatalytic activity compared to a pure Ni electrode.
• Improved catalytic performance of NiSn coatings was entirely ascribed to their high surface area.
• Opposite to Ni, NiSn anodes retained their initial activity after prolonged anodic polarization.

In order to examine the intrinsic catalytic activity and durability of the electrodeposited NiSn alloy electrodes and the electrodeposited Ni as a reference electrode material for the oxygen evolution reaction (OER) in alkaline solutions, a comparative investigation was performed. A series of NiSn electrodes were prepared by electrodeposition of NiSn alloys at different current densities onto a Ni40 mesh substrate. The surface morphology and chemical composition were studied by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The electrochemical surface characteristics were studied by cyclic voltammetry in order to find interdependence between the nickel oxy-hydroxide surface electrochemistry and the activity of the electrode for the OER. Quasi steady-state polarization measurements and electrochemical impedance spectroscopy (EIS) were used to determine kinetically significant parameters including the Tafel slopes and exchange current densities. Two well-defined Tafel slopes, the same for all investigated NiSn electrodes, were observed at the polarization curves, indicating that the OER was controlled by the same mechanism. It was demonstrated that any anodic polarization pretreatment led to a shift of the anodic and cathodic current peaks corresponding to the Ni(II)/Ni(III) redox transition towards cathodic potentials and, consequently, to some activation of the NiSn electrodes. The opposite behavior was obtained for the Ni electrode. Prolonged anodic polarization led to a loss of the initial catalytic activity of the Ni electrode, which was explained by the increase in the portion of γ-NiOOH at the Ni electrode surface. Among the investigated NiSn electrodes, the NiSn100 electrode, prepared by electrodeposition at the highest cathodic current density of −100 mA cm−2, exhibited the highest apparent catalytic activity for the OER, entirely due to surface roughness effects. Despite the fact that the NiSn electrodes did not exhibit better intrinsic catalytic activity than Ni, their high stability during the OER and acceptable apparent activity made them promising anodes for alkaline water electrolysis.