Overall Water Splitting with Room-Temperature Synthesized NiFe Oxyfluoride Nanoporous Films

A room-temperature synthesis of NiFe oxyfluoride (NiFeOF) holey film, using electrochemical deposition and anodic treatments, has been developed in this work. The developed room-temperature synthetic route can preserve the fine nanoporous structure inside the holey film, providing high surface area and abundant reaction sites for electrocatalytic reactions. Both computational and experimental studies demonstrate that the developed NiFeOF holey film with highly porous structure and metal residuals can be used as a high-efficiency and bifunctional catalyst for overall water splitting. Simulation result indicates that the exposed Ni atom on the NiFeOF surface serves as the active site for water splitting. Fe doping can improve the catalytic activity of the Ni active site due to the partial charge-transfer effect of Fe³⁺ on Ni²⁺. Electrochemical performance of the NiFeOF catalyst can be experimentally further enhanced through improved electrical conductivity by the residual NiFe alloy framework inside the holey film. The synergistic combination of NiFeOF holey film properties results in a highly efficient electrochemical catalyst, showing overall water splitting.