Optimizing the intermediates adsorbability and revealing the dynamic reconstruction of Co₆Fe₃S₈ solid solution for...

Co₉S₈ has been extensively studied as a promising catalyst for water electrolysis. Doping Co₉S₈ with Fe improves its oxygen evolution reaction (OER) performance by regulating the catalyst self-reconfigurability and enhancing the absorption capacity of OER intermediates. However, the poor alkaline hydrogen evolution reaction (HER) properties of Co₉S₈ limit its application in bifunctional water splitting. Herein, we combined Fe doping and sulfur vacancy engineering to synergistically enhance the bifunctional water-splitting performance of Co₉S₈. The as-synthesized Co₆Fe₃S₈ catalyst exhibited excellent OER and HER characteristics with low overpotentials of 250 and 84 mV, respectively. It also resulted in the low Tafel slopes of 135 mV dec^-1 for the OER and 114 mV dec^-1 for the HER. A two-electrode electrolytic cell with Co₆Fe₃S₈ used as both the cathode and anode produced a current density of 10 mA cm^-2 at a low voltage of only 1.48 V, maintaining high stability for 100 h. The results of in/ex-situ experiments indicated that the OER process induced electrochemical reconfiguration, forming CoOOH/FeOOH active species on the catalyst surface to enhance its OER performance. Density functional theory (DFT) simulations revealed that Fe doping and the presence of unsaturated coordination metal sites in Co₆Fe₃S₈ promoted H₂O and H* adsorption for the HER. The findings of this study can help develop a strategy for designing highly efficient bifunctional water splitting electrocatalysts.