Atomically Dispersed Zn/Co–N–C as ORR Electrocatalysts for Alkaline Fuel Cells
Weixuan Xu, Rui Zeng, Michael Rebarchik, Alvaro Posada-Borbón, Huiqi Li, Christopher J. Pollock, Manos Mavrikakis, Héctor D. Abruña
Abstract
Hydrogen fuel cells have drawn increasing attention as one of the most promising next-generation power sources for future automotive transportation. Developing efficient, durable, and low-cost electrocatalysts, to accelerate the sluggish oxygen reduction reaction (ORR) kinetics, is urgently needed to advance fuel cell technologies. Herein, we report on metal–organic frameworks-derived nonprecious dual metal single-atom catalysts (SACs) (Zn/Co–N–C), consisting of Co–N 4 and Zn–N 4 local structures. These catalysts exhibited superior ORR activity with a half-wave potential ( E 1/2 ) of 0.938 V versus RHE (reversible hydrogen electrode) and robust stability (Δ E 1/2 = −8.5 mV) after 50k electrochemical cycles. Moreover, this remarkable performance was validated under realistic fuel cell working conditions, achieving a record-high peak power density of ∼1 W cm –2 among the reported SACs for alkaline fuel cells. Operando X-ray absorption spectroscopy was conducted to identify the active sites and reveal catalytic mechanistic insights. The results indicated that the Co atom in the Co–N 4 structure was the main catalytically active center, where one axial oxygenated species binds to form an O ads –Co–N 4 moiety during the ORR. In addition, theoretical studies, based on a potential-dependent microkinetic model and core-level shift calculations, showed good agreement with the experimental results and provided insights into the bonding of oxygen species on Co–N 4 centers during the ORR. This work provides a comprehensive mechanistic understanding of the active sites in the Zn/Co–N–C catalysts and will pave the way for the future design and advancement of high-performance single-site electrocatalysts for fuel cells and other energy applications.