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oai:figshare.com:article/33961288 2026-09-22T04:09:19Z category_1 category_4 category_915 category_24 category_272 category_873 category_39 category_64 category_135 portal_63 item_type_3 month_year_09_2026

Resolving Active-Site Heterogeneity in Fe–N–C Catalysts by Integrated Multimodal Spectroscopy and Simulation Jiayi Xu (2287153) Prajay Patel (4811796) Matthew E. Sweers (13150395) Esen E. Alp (4725867) Hoon Taek Chung (3254136) Piotr Zelenay (1455067) A. Jeremy Kropf (1440607) Deborah Myers (1327362) Cong Liu (66219) Biophysics Biochemistry Physical Sciences not elsewhere classified Evolutionary Biology Environmental Sciences not elsewhere classified Chemical Sciences not elsewhere classified Ecology Cancer Computational Biology temperature synthesis generates smaller pyridinic contribution oxygen reduction reaction density functional theory associated pyrrolic motif ray absorption spectroscopy integrated multimodal spectroscopy shell nitrogen coordination combine fe k axially coordinated fe orr ), yet 57 </ sup 4 </ sub spectroscopy simulations coordination beyond planar fe elucidate fe xas ), dft ), xanes features site structures site heterogeneity robust strategy resolving active pyrolyzed catalyst promising electrocatalysts local symmetry heterogeneous distribution edge x diverse population complex single best described atom catalysts air exposure Fe–N–C single-atom catalysts are among the most promising electrocatalysts for the oxygen reduction reaction (ORR), yet their atomic-scale structure remains difficult to resolve because high-temperature synthesis generates a diverse population of Fe sites. In this work, we combine Fe K-edge X-ray absorption spectroscopy (XAS), ⁵⁷Fe Mössbauer spectroscopy, density functional theory (DFT), and spectroscopy simulations to elucidate Fe-site structures before and after air exposure. The as-pyrolyzed catalyst is best described by a heterogeneous distribution of FeN₄ sites, dominated by a defect-associated pyrrolic motif with third-shell nitrogen coordination and a smaller pyridinic contribution. We show that coordination beyond the first shell strongly influences Fe–N bond distances, local symmetry, and XANES features. Air exposure converts square-planar Fe(II)-like sites into oxidized, axially coordinated Fe(III)-like species. Overall, this multimodal structure–spectroscopy framework provides a robust strategy for resolving active-site heterogeneity in complex single-atom catalysts. 2026-09-22T00:00:00Z Dataset Dataset 10.1021/acs.jpclett.6c02124.s002 https://figshare.com/articles/dataset/Resolving_Active-Site_Heterogeneity_in_Fe_N_C_Catalysts_by_Integrated_Multimodal_Spectroscopy_and_Simulation/33961288 CC BY-NC 4.0