An accurate and general local electronic structural descriptor for oxygen reduction on metal surface alloys: Potential of breaking scaling relationship and application to PtZn ones with superior activity

Abstract

Metal alloys and metal surface alloys are important ways to improve oxygen reduction activity and reduce economic costs. Due to the decline of symmetry of alloys, prediction of surface catalytic site activity by traditional structural and electronic descriptors faces a great challenge. Thus, it is important and urgent to develop a suitable and general descriptor to quickly identify the catalytic activity of surface sites for designing novel alloy catalysts and improving the computational efficiency. Herein, oxygen reduction on PtZn surface alloys with Zn substrate is selected as an example to search for suitable descriptors and high ORR activity materials. A local electronic structural descriptor for surface alloys, which includes charge states of the active sites and the nearby sites is developed. In addition, the contribution of each part of charge states to the adsorption intensity can be clearly known according to the descriptor. Comparing with traditional descriptors, this descriptor exhibits superior accuracy in predicting the binding strength of *OH and *OOH and ORR activity of PtZn surface alloys. Accordingly, the ORR activity of PtZn surface alloys at different Zn concentrations in sublayer (Pt@Pt1−xZnx@), are systematically examined. Both DFT and descriptor predication prove its high ORR activity in a large range of Zn concentrations: Pt@Pt1-xZnx@ shows better or comparable activity than Pt(111) at x = 1/9 ∼ 4/9, or 5/9 ∼ 7/9, respectively, and the corresponding calculated exchange current rate constants are 0.84 ∼ 7.69, 0.10 ∼ 0.60 mA cm−2, respectively. Combining with their stability verified by formation energy, vacancy formation energy, segregation energy and AIMD, the PtZn surface alloy will be a promising ORR catalyst. Furthermore, our proposed descriptor also indicates the broken of scale relationship for ORR, implying possible extremely high ORR activity in other metal alloys and its popularity application.