Electrocatalysis plays an essential role in diverse electrochemical energy conversion processes, and the searching for electrocatalysts based on earth-abundant metals is greatly important. Of particular interest are graphene-supported single atom catalysts (G-SACs) that integrate the merits of heterogeneous catalysts and homogeneous catalysts. Besides, the graphene support features a large surface area, high conductivity and excellent (electro)-chemical stability, making it a highly attractive substrate for supporting single atom electrocatalysts. Thus, a group led by Prof. Xiangfeng Duan from UCLA collaborated with researchers from BSRF reviewed the recent advancements in G-SACs for electrochemical energy conversion, from the synthetic strategies and identification of the atomistic structure to electrocatalytic applications in a variety of reactions, and finally conclude with a brief prospect on future challenges and opportunities. This review was published in the journal of Chem. Soc. Rev. on Oct. 21, 2019.

Pristine graphene is not a good support for G-SACs since most metal adatoms usually exhibit a rather low migration barrier and high mobility on pristine graphene even at room temperature. Therefore, the generation of defective sites or functionalization of graphene is generally required to create anchoring sites to stabilize metal atoms without the formation of metal aggregates. We summarized the synthetic strategies toward G-SACs, including pyrolysis and thermal activation (the precursors can be molecular/polymeric, GO or MOFs), electron/ion irradiation, ball milling, atomic layer deposition, photochemical reduction, and solution-phase synthesis.

The foundation for the establishment of the structure-to-activity linkage in G-SACs lies in the identification of the active site structure. Synchrotron X-ray absorption spectroscopy (XAS) is powerful to probe the coordination environment and the chemical state of the absorber in an element-selective way. Nonetheless, unambiguously extracting the exact atomistic and electronic structure by XAS remains neither trivial nor straightforward. Here we discussed the recent efforts in the employment of XAS for identifying the atomistic and electronic structure of the active sites in G-SACs. Then, we describe a global strategy for the structural identification by XAS that can reduce loose ends to a minimum, likely serving as a general guide for future studies facing the structural characterization of G-SACs.

We also summarized the recent progress in the applications of G-SACs in ORR, HER, OER, CO2RR, NRR and so on.

Finally, we pointed out that considerable challenges and opportunities remain for G-SACs from both fundamental and applied research perspectives. From the outset, the achievement of high metal loading in G-SACs with exclusive single atomic dispersion remains the most critical challenge for the field. Second, it remains difficult to correlate the exact structure configuration with the catalytic properties, which further precludes the establishment of design principles in optimizing the intrinsic activity of G-SACs. Lastly, there is little experimental insight into the metal–reactant and metal–support interactions in G-SACs under electrocatalytic conditions and a limited understanding of the mechanistic details of the reactions on the catalyst surface.

Graphene carbons as a support for single atom electrocatalysts and Schematic presentation of global XAS analysis strategy consisting of various EXAFS and XANES analysis approaches.

Article:

Huilong Fei, Juncai Dong, Dongliang Chen, Tiandou Hu, Xidong Duan, Imran Shakir,* Yu Huang* and Xiangfeng Duan*. Single atom electrocatalysts supported on graphene or graphene-like carbons. Chem. Soc. Rev., 2019, 48, 5207.