Oxygen Vacancies Unfold the Catalytic Potential of NiFe-Layered Double Hydroxides by Promoting Their Electronic Transport for Oxygen Evolution Reaction

Oxygen vacancies (Ov) engineering has demonstrated tremendous power to expedite electrocatalytic kinetics for oxygen evolution reaction (OER). The mechanism is elusive, and most of them were attributed to the decoration or creation of active sites. Here, we report the critical role of superficial Ov in enhancing the electronic transport, thereby unfolding the catalytic potential of NiFe-layered double hydroxides for OER. We reveal that the superficial Ov engineering barely regulates the intrinsic catalytic activities but lowers the charge transport resistances by more than one order of magnitude. Loading-dependent electrochemical analysis suggests that the superficial Ov engineering intensively modulates the utilization rate of electronically accessible active sites for OER catalysis. By correlating catalytic activities to charging capacitances of CΦ (related to the absorption of reaction intermediates), we unveil a linear dependence, which indicates switchable catalysis on electronically accessible active sites. Based on the unified experimental and theoretical analysis of the electronic structures, we propose that the superficial Ov imposes electron donation to the conductive band of NiFeOOH, thereby enabling the regulation of electronic transport to switch on/off OER catalysis. The switch effect holds fundamental and technical implications for understanding and designing efficient electrocatalysts.