A Facile Route to Efficient Water Oxidation Electrodes via Electrochemical Activation of Iron in Nickel Sulfate Solution

The oxygen evolution reaction (OER) is an important half reaction in many electrochemical energy conversion processes, such as water splitting and carbon dioxide reduction. However, new, scalable and more efficient synthetic methods to inexpensive OER electrocatalysts are currently needed in order to develop water electrolyzers and carbon dioxide reduction cells on large scale. To this end, we here report efficient free-standing FeNi-based electrocatalysts for OER derived from iron, one of the most Earth-abundant metals, by a facile potential cycling synthetic method in an aqueous NiSO4 solution. The optimized catalyst requires a low overpotential of 236 mV to catalyze OER with a current density of 10 mA/cm2 in 1.0 M KOH solution. More importantly, this free-standing water-oxidation electrode can maintain a current density of 100 mA/cm2 for more than 72 h. During the course of the electrochemical activation, both cathodic reduction and anodic oxidation are found to play important roles in the surface reconstruction of metallic iron into electrocatalytically active FeNi-based bimetallic hydroxide nanosheet arrays for OER electrocatalysis. This inexpensively fabricated OER electrode prepared from iron has a great potential to reduce the overall cost of water electrolyzers and other related renewable energy systems.