Unraveling the relationship between physicochemical properties of NiFeReOx catalysts and the correlated performance toward electrochemical oxygen evolution reaction

NiFeO_x catalysts with single site Re dopants exhibit much higher active and stability toward electrochemical oxygen evolution reaction (OER) compared to traditional NiFeO_x catalysts. Nevertheless, the relationship between physicochemical properties of NiFeReO_x catalysts and the correlated performance toward OER is unclear, which hampers to enhance the OER performance further. Herein, we prepared a series of NiFeReO_x catalysts with different physicochemical properties by treating them at different temperatures (up to 350 °C) and then evaluated their performance toward OER. The results show that heat treatment can convert all metal oxidation states to higher values as well as specific surface areas, which are believed to favor real active site generation and OER activity enhancement. A decrease in activity is observed with the temperature increase at the low current range, and the smallest overpotential of 248 mV at 10 mA cm⁻² is achieved with the pristine NiFeReO_x catalyst. In contrast, the heat-treated samples possess smaller Tafel slopes and lower charge transfer resistance likely due to enhanced intrinsic activity (from higher oxidation states) and conductivity, which facilitate the reaction kinetics and surpass the pristine sample at a large current density. Additionally, the sample treated at 350 °C exhibits a higher activity at 1000 mA cm⁻² (1.68 V vs. RHE compared to pristine sample of 1.92 V vs. RHE); however, it manifests a poorer stability compared to the pristine one due to the imbalance of reconstruction/transformations that occurred on the catalyst surface during OER operation. Our work unravels the relationship between physicochemical properties of NiFeReO_x catalysts and the correlated OER performance and provides valuable insights for designing NiFeReO_x catalysts with high activity and durability.