Enhancing Co–O Covalency by Low Electronegativity Anion-Induced Charge Rebalance in a (Co,Fe)S<sub>2</sub>/Co<sub>3</sub>O<sub>4</sub> Composite for Efficient Oxygen Evolution Reaction
Meiyan Jiang, Shuting Li, Yuan Zhang, Xiyang Wang, Jianrong Zeng, Xiaotian Wu, Xiaotian Wu, Lu Yao, Qian Zhu, Zhiyu Shao, Xiaofeng Wu, Xiaofeng Wu
Abstract
The metal–oxygen covalency is the most advanced descriptor to understanding the relationship between the electronic structure and oxygen evolution reaction (OER) properties of oxide catalysts; however, its regulation strategy by an anion is very limited. Herein, we demonstrated that the Co–O covalency can be enlarged by introducing a second phase of disulfide (Co,Fe)S 2 coupled on the spinel Co 3 O 4 . The S and O with different electronegativity coordinated simultaneously with transition metal ions at the composite interface of (Co,Fe)S 2 /Co 3 O 4, which brings the oxygen charge shifting toward the metal ions. The strengthened covalency and the charge rebalance between oxygen and metal ions are observed directly by X-ray photoelectron spectroscopy and X-ray absorption spectroscopy, which are further confirmed by the calculated O 2p band center upshift to the Fermi level based on the density functional theory. The reinforced Co–O covalency resulted in an OER overpotential reduction of more than 100 mV compared to the pristine one. This work provides a rational way to enhance the metal–oxygen covalency by constructing a composite phase for elevating the intrinsic OER activity of the catalyst, which may be extendable to other oxides.