Understanding the incorporating effect of Co2+/Co3+ in NiFe-layered double hydroxide for electrocatalytic oxygen evolution reaction

NiFe-layered double hydroxide (NiFe-LDH) has been widely accepted as promising catalyst candidates for the oxygen evolution reaction (OER). Recently, incorporating Co atoms in NiFe laminates has been recognized as an effective way to enhance the OER activity, but their roles have been rarely studied. Herein, density functional theory plus U (DFT + U) calculations are employed to evaluate the OER thermodynamics after introducing bivalent Co2+ or trivalent Co3+ and consequent sites sensitivity in NiFe-LDH catalyst. Generally, based on computational results, incorporation of Co2+/Co3+ into NiFe-LDH could modulate the electronic structure of metal sites and thus reducing their OER overpotential. Moreover, Co3+-doped NiFe-LDH has the lowest overpotential of η = 0.413 eV among the above proposed structure. This point was fully demonstrated by Co2+ and Co3+-incorporated NiFe-LDH nanosheets made by a co-precipitation method, by showing OER onset overpotential of 249 mV for Co3+-doped NiFe-LDH, 264 mV for Co2+-doped NiFe-LDH, which are 33 mV and 18 mV lower than that of pristine NiFe-LDH (282 mV), respectively. Such improved OER activity were attributed to the lowered overpotential at the *OOH formation step for Co2+-doped NiFe-LDH and the deprotonation step for Co3+-doped NiFe-LDH, which was the potential limiting step for their OER process. This work should be inspiring for future designing of more efficient NiFe-based oxygen evolution electrocatalysts.