Electrodic Properties and Surface Characteristics of Ni–V Alloys for Water Electrolysis Cathode Materials

Abstract

Abstract Hydrogen evolution reaction on a series of hydrogen absorbing Ni–V alloys, viz. Ni2V, NiV, and NiV3, before and after pretreatments with aq HF was studied in 1 M NaOH (1 M=1 mol dm−3) at 288–333 K by a galvanostatic overpotential transient technique. Results are related with the surface characteristics revealed by XPS techniques. It is concluded that the Ni in the Ni–V alloys is mainly responsible for their electrochemical properties and that the reaction proceeds via the Volmer-Tafel reaction route with mixed rate-determining characteristics: The activation heats are 7.7, 6.8, and kcal mol−1 (1 cal=4.184 J) for two elementary steps, Volmer and Tafel, and the overall reaction, respectively. The electrocatalytic activity of the Ni–V alloys, particularly NiV3, is drastically enhanced through the treatment with aq HF, and this is in parallel with the formation of porous Ni layers on their surface, namely the increase of the effective surface area. Potentiality of the alloys for water electrolysis cathode materials is indicated by a higher electrocatalytic activities of the Ni–V alloys over ordinary Raney nickel electrodes. Hydrogen absorbability of the alloys was also investigated: NiV3 stored hydrogen up to [H]/[M]=≤0.3 after a cathodic polarization at about −400 mV hydrogen overpotential, but that in Ni2V or NiV was far smaller.