High Current Density Oxygen Evolution in Carbonate Buffered Solution Achieved by Active Site Densification and Electrolyte Engineering

High current density reaching 1 A cm(−2) for efficient oxygen evolution reaction (OER) was demonstrated by interactively optimizing electrolyte and electrode at non‐extreme pH levels. Careful electrolyte assessment revealed that the state‐of‐the‐art nickel‐iron oxide electrocatalyst in alkaline solution maintained its high OER performance with a small Tafel slope in K‐carbonate solution at pH 10.5 at 353 K. The OER performance was improved when Cu or Au was introduced into the FeO( x )‐modified nanostructured Ni electrode as the third element during the preparation of electrode by electrodeposition. The resultant OER achieved 1 A cm(−2) at 1.53 V vs. reversible hydrogen electrode (RHE) stably for 90 h, comparable to those in extreme alkaline conditions. Constant Tafel slopes, apparent activation energy, and the same signatures from operando X‐ray absorption spectroscopy among these samples suggested that this improvement seems solely correlated with enhanced electrochemical surface area caused by adding the third element.