Electrochemical incorporation of heteroatom into surface reconstruction induced Ni vacancy of NiO nanosheet for enhanced water oxidation.

Surface reconstruction of non-oxide oxygen evolution reaction (OER) electrocatalysts has been intensively studied to improve their catalytic performances. However, further modification of the reconstructed active surfaces for better catalytic performances has not been reported. In this work, NiSe nanorods are prepared on nickel foam (NiSe@NF) as the pre-catalyst for electrochemical OER. It is revealed that non-stoichiometric NiO nanosheets with abundant Ni vacancies (NiO) are formed on the surfaces of NiSe nanorods (NiO/NiSe@NF) via in-situ electrochemical oxidation. Furthermore, the OER performances are obviously improved after heteroatom Fe is incorporated electrochemically into NiO nanosheets ((FeNi)O/NiSe@NF). For OER to have a current density of 20 mA cm in 1 M KOH solution, the as-prepared (FeNi)O/NiSe@NF electrode only needs an overpotential of 268 mV. Density functional theory (DFT) calculations reveal that the formation of Ni vacancy can increase the free energy of *OH. More importantly, the incorporation of heteroatom Fe into Ni vacancy can significantly decrease the free energy of *O, which enables Fe-NiO to have the lowest theoretical overpotential for OER in this work. The present work provides a facile and universal strategy to modify the reconstructed active oxides' surfaces for higher electrocatalytic performances.