Electrochemical Oxide Growth on Nickel and Commercial Nickel Alloys: Influence of Chromium and Molybdenum

Abstract

Nickel-chromium-molybdenum (NiCrMo) alloys are well-known for having exceptional corrosion resistance, but their electrocatalytic properties have not been extensively studied. In this paper, the development of electro-active nickel-oxyhydroxide (NiOOH) phases and kinetics of the oxygen evolution reaction (OER) have been examined on alloys G35, B3, and C276 in alkaline electrolyte at 25 °C. Reproducible oxide layers were grown by potential cycling between 0.85 and 1.52 V vs RHE up to 600 cycles, and the transition between Ni(OH)2 and NiOOH was monitored by cyclic voltammetry throughout. Onset potentials, Tafel slopes, and turnover frequencies (TOF) were measured at OER overpotentials between 270 and 390 mV. Alloys with dissimilar Cr:Mo ratios had significantly higher electrochemical surface area and increased γ-NiOOH formation, suggesting higher metal dissolution rates. The equal Cr:Mo concentration alloy and pure Ni developed a primarily β-NiOOH surface, and had 1.8–2.0 times larger TOF values than those containing significant γ-NiOOH. The NiCrMo alloys required smaller overpotentials (54–80 mV) to produce 10 mA cm−2 of OER current, and had comparable Tafel slopes to pure Ni. The findings here indicate a β-NiOOH-developed surface to be more OER-active than a γ-NiOOH-developed surface, and suggest certain NiCrMo alloys have promise as OER electrocatalysts.