Carbon-supported catalysts with atomically dispersed metal sites for oxygen electroreduction: present and future perspectives

Carbon-supported catalysts with atomically dispersed metal sites, also known as “single-atom catalysts (SACs)”, have attracted enormous attention for the oxygen reduction reaction (ORR) due to their theoretical maximal atom utilization and superior catalytic activity. Two common strategies to achieve high electrocatalytic performance for SACs are to enhance the intrinsic activity by modulating the electronic structure of active sites and to incorporate more single active sites by increasing the metal loading. In this review, we have summarized the key advances in ORR electrocatalysis of carbon-supported heterogeneous catalysts with atomically dispersed metal sites during the past decade, mainly focusing on the modulation of the electronic structure and the elevation of metal loading, and the operando/ex situ characterization techniques of the electronic structure evolution of SACs during the ORR process have also been highlighted. Meanwhile, the underlying formation mechanism of SACs has also been discussed in detail for both “bottom-up” and “top-down” approaches. Finally, the current challenges and future perspectives of carbon-supported SACs for ORR-related energy devices have been outlined. Hopefully, this timely review will provide an insightful roadmap for the future research of SACs.