Kim, Seulchan Yoon, Dogeun Chae, Jinwoong Kim, Hyeonwoo Hong, Jongsup Son, Ji-Won Lee, Jong-Ho Kang, Sungwoo Ji, Ho-Il 2026-03-25T05:00:20Z 2026-03-25T05:00:20Z 2026-03-24 2026-03 1754-5692 https://pubs.kist.re.kr/handle/201004/154443 The proton-coupled oxygen reduction reaction (PC-ORR) at protonic ceramic fuel cell (PCFC) cathodes involves multiple charges, which are proton, oxygen ion, and electron/electron hole, and its complexity has long impeded unambiguous identification of the reaction pathway and the rate-determining step (RDS). The difficulty is amplified by the prevailing practice of subjectively positing an a priori “most probable” pathway to infer the RDS—a procedure that heightens the risk of decisive bias and error. Consequently, mutually inconsistent pathways have been proposed for ostensibly the same reaction. Here, we present a generalized microkinetic framework that infers the RDS without prior pathway construction. Applying this approach, we resolve the RDS for two widely studied PCFC cathodes, PrBa0.5Sr0.5Co1.5Fe0.5O5+δ (PBSCF) and BaCo0.4Fe0.4Zr0.1Y0.1O3−δ (BCFZY). PBSCF is limited by vacancy-assisted O2 dissociation, whereas BCFZY is limited by a proton-coupled OH adsorbates formation step involving adsorbed atomic oxygen and bulk protons. While both exhibit sufficient proton transport and fast bulk diffusion such that surface reactions dominate porous cathode performance, the origin of the contrasting RDSs is traced to their different proton uptake/release mechanisms. English Royal Society of Chemistry Elucidating the proton-coupled oxygen reduction pathway in protonic ceramic fuel cells Article 10.1039/d5ee06170a 1 Energy & Environmental Science, v.19, no.5, pp.1715 - 1731 Energy & Environmental Science 19 5 1715 1731 Y scie scopus 001693157100001 2-s2.0-105030529088 Chemistry, Multidisciplinary Energy & Fuels Engineering, Chemical Environmental Sciences Chemistry Energy & Fuels Engineering Environmental Sciences & Ecology Article POWER-DENSITY SOFC CATHODE OXIDE PEROVSKITE SURFACE EXCHANGE HIGH-PERFORMANCE HYDRATION PRESSURE SRTIO3