Self-synergistic cobalt catalysts with symbiotic metal single-atoms and nanoparticles for efficient oxygen reduction

Abstract

The design of highly active noble metal-free oxygen reduction reaction (ORR) catalysts is of paramount importance for current energy conversion and storage devices, such as fuel cells, but challenges remain due to the sluggish kinetics and mismatched adsorption of oxo-species. Here, we present a new type of self-synergistic Co catalyst consisting of symbiotic Co single-atoms and nanoparticles (S/Co-SA–NPs) for use as a highly efficient ORR catalyst. The well-designed S/Co-SA–NP catalyst exhibits a record ORR activity with an excellent half-wave potential (E_1/2) of 0.925 V and a large kinetic current density (J_k) of 122.57 mA cm⁻² at 0.85 V, which is tens of times that of benchmarking Pt/C catalyst. Using advanced operando electrochemical impedance and synchrotron infrared spectroscopies, we observe that the self-synergistic Co sites can effectively optimize *OOH adsorption at low driven overpotentials and promote the crucial *O intermediate to emerge on the Co sites during the ORR process, which suggests a fast four-electron mechanistic pathway for the ORR.