NiFeOxHy with electron-deficient Ni2+ for oxygen evolution in mild media

NiFe-layered double hydroxide (NiFe–OH) is one of the most promising candidate materials for the oxygen evolution reaction (OER) in an alkaline electrolyte. However, it is difficult to be oxidized into Ni3+FeOOH active species with high valence Ni under mild conditions; thus, the activity under mild conditions is inferior. We report here that NiFe–OH is converted to amorphous NiFeOxHy (a3-NiFe-OH) with easily oxidized electron-deficient Ni2+ after pre-oxidation in an alkaline solution boosts the OER performance under mild conditions. The amorphous structure of a3-NiFe-OH also enlarges the electrochemically active area to expose more active sites. It merely needs an overpotential of 350 mV at 10 mA cm−2 in 0.1 M KHCO3 electrolyte. The corresponding Tafel slope is as low as 89 mV dec−1. This work affords a strategy for developing (near) neutral OER catalysts.