Structural heterogeneity of single-atom catalysts and true active site generation via ligand exchange during electrochemical H2O2 production

Although often overlooked, single-atom catalysts inevitably contain heterogeneous active sites and their structures can further change under reaction conditions. Here, we conduct rigorous in situ X-ray absorp-tion spectroscopy with 1-10 wt% Pt on S-doped zeolite-templated carbon (SZTC) to elucidate their remarkable electrocatalytic H2O2 synthesis properties. SZTC with a curved polyaromatic framework and abundant sulfur functional groups can stabilize isolated Pt sites with up to 10 wt% Pt loading. Although all catalysts contain apparently identical Pt-S4 sites in their as-synthesized form, the Pt-specific activity increases rapidly with increasing Pt loading. It appears that Pt first forms inert Pt-S4 in SZTC and then forms labile Pt-S4 with increasing Pt loading. Upon contact with aqueous electrolytes, only the labile sites are converted to true active sites, Pt-S2(H2O)2, via ligand exchange with H2O. The results provide invaluable insights for understanding the heterogeneity and dynamic structural changes of single-atom catalysts. (c) 2023 Elsevier Inc. All rights reserved.