Carbon-based Single Atom Catalysts for Tailoring ORR Pathway: A Concise Review

Carbon-based single-atom catalysts (C-SACs), featured with flexible, well-defined atomic geometry and superior electrical conductivity, have experienced a rapid development in the last decade and proved unique opportunities in selective oxygen reduction reaction (ORR) electrocatalysis via direct 4e- pathway or alternative 2e- pathway for sustainable energy conversion and chemical synthesis. This concise review summarizes recent experimental efforts aiming at tailored selectivity, activities and derived progressive guidelines for catalyst design. First, the current exploration and development of synthetic methodologies of diverse C-SACs for ORR is briefly outlined. Then we present a key overview on structure-dependent catalytic selectivity and activity properties, in particular emphasizing on the microenvironment modulation of single-atom active sites from the aspects of regulating the central metal atoms, coordination environment and support properties. Besides, the dual active sites enabled synergistic catalysis for breaking conventional scaling relation are also highlighted. Finally, the current remaining challenges in C-SACs for ORR and related perspectives are proposed to shed some light on the further developments toward industrialization in the future.