The effect of anodizing temperature on the oxygen evolution reaction activity of anodized FeNiCo alloy in alkaline electrolyte

This study investigates the oxygen evolution reaction (OER) activity of the FeNiCo alloy anodized at several temperatures in a fluoride-containing ethylene glycol electrolyte. When the alloy is anodized at 10 V, the OER activity in KOH electrolyte is highly enhanced on the alloy anodized at 15 and 20 °C, at which non-uniform film growth proceeds. The fraction of the locally thick film regions increases with anodizing time, enhancing the OER activity. Only thin porous films are formed at ≥30 °C even though the anodizing current is high because of the promotion of film dissolution at high electrolyte temperatures. Because of the thickness limitation, the OER activity is relatively low when the anodic films are formed at ≥30 °C. A good correlation is found between the OER activity and the electric double-layer capacitance; thicker porous anodic films enhance the OER activity. The anodic film formed at each temperature consists of a rutile-type (FeNiCo)F2 phase, but in KOH electrolyte, it is converted readily to an oxyhydroxide phase, which is OER active. A ∼2 μm-thick film obtained under the optimum anodizing condition reduces the overpotential of OER to 245 mV at 10 mA cm–2 in 1.0 mol dm–3 KOH electrolyte.