Facile Synthesis of Transition-Metal-Doped (Fe, Co, and Ni) CuS/CuO/CS Nanorod Arrays for Superior Electrocatalytic Oxygen Evolution Reaction

Electrochemical water splitting is a promising way to produce sustainable, renewable, and clean H2 fuel. The anodic half-reaction of electrochemical water splitting, oxygen evolution reaction (OER) lowers the overall efficiency of the system due to this four-electron process with sluggish reaction kinetics. The state-of-the-art catalysts for OER are based on precious metals (Ru and Ir). In this article, transition-metal-doped (Fe, Co, and Ni) CuS/CuO nanorod arrays on copper sheet (CS) substrates were synthesized for the first time via the facile solvothermal method, and the electrocatalytic activity of the synthesized material toward OER in alkaline media was investigated. Fe-doped CuS/CuO/CS showed superior electrochemical performance with an overpotential of only 340 mV at 10 mA/cm2 current density. The OER performance of the material was compared with the state-of-the-art catalyst for RuO2/CS. The overpotential of RuO2/CS was 320 mV at 10 mA/cm2 current density which is only 20 mV lower than the state-of-the-art catalyst. The enhancement of the OER activity was obtained by valence regulation upon doping Fe3+ and Fe2+ into CuS/CuO/CS nanorod arrays (NAs). The charge transfer resistance was lowered from 10.2 Ω/cm2 for pristine CuS/CuO/CS NA to 1.2 Ω/cm2 upon Fe doping. The electrochemically active surface area was increased from 36 to 51 cmECSA2 upon Fe doping. The Fe-doped CuS/CuO/CS shows an exceptionally high turnover frequency (TOF) of 0.68 s–1. The catalyst was stable up to 1000 cycles of OER over 10 h. The increase in electrical conductivity, increase in electrochemically active surface area (ECSA), and creation of defect sites leading to preferential absorption of OH– upon Fe doping led to enhanced OER activity of Fe–CuS/CuO/CS. This is the first report of an Fe-doped CuS/CuO/CS nanoarray that shows superior OER activity with high TOF and excellent stability.