In Situ Rapid Formation of a Nickel–Iron-Based Electrocatalyst for Water Oxidation

If an oxygen evolution reaction (OER) catalyst is expected to be more durable, especially under conditions of thin-layer catalysts or strong gas evolution, it will ideally function in a self-repair mode. In earlier studies, the electrochemical fabrications of Ni–Fe oxide catalysts were exclusively carried out by cathodic reduction of Ni­(II) and Fe­(III,II) in an individual solution that is different from the alkaline media commonly used for the OER. The procedure does not suggest that the dissolution/corrosion of the film catalysts could be countered by continual catalyst formation during the OER. Herein, we report a highly active NiFeOx catalyst by in situ rapid (3–15 min) anodic deposition of Ni­(II) and Fe­(III,II) in concentrated carbonate solution. At a transparent indium tin oxide (ITO) electrode, the conformal deposition of NiFeO x (7–11-atom layer) results in a very low optical loss (5–8%) with activity comparable to that of other planar NiFeO x films. Extension to a 3D nickel foam produces a hierarchical coating of grasslike structure. With few added Ni­(II) and Fe­(III) atoms to counter the film dissolution/corrosion, the catalyst can deliver a stable current density of 100 mA/cm2 at an overpotential of only 260 mV in alkaline media. This example of a NiFeO x catalyst forms during in situ OER and operates by a self-repair mode, highlighting a truly important feature for the practical application of this state of the art OER electrocatalyst.