Exploration of Oxygen Reduction Reaction Catalyzed by FePPc and Pz-FeTPr Conjugated Organic Polymer: Insights From Grand-Canonical Density Functional Theory

This report examines the oxygen reduction reaction (ORR) catalyzed by iron-polyphthalocyanine (FePPc) and pyrazine-linked iron-coordinated tetrapyrrole (Pz-FeTPr) conjugated organic polymer (COP) catalysts, utilizing grand-canonical density functional theory (GC-DFT) and microkinetic (MK) simulations. The computed half-wave potential for AA stacking FePPc under alkaline conditions is in strong agreement with experimental findings. The ORR mechanism for AA stacking FePPc is characterized by the ^*O₂ mechanism ($O_2{\to }^{\ast }{O}_2{\to }^{\ast }OOH{\to }^{\ast }O{\to }^{\ast }OH\to H_{2}O$), with the Fe site serving as the active site. In the case of Pz-FeTPr, the ORR mechanism is similarly governed by the ^*O₂ mechanism, with the Fe site remaining the active site at lower potentials (less than 0.5 V_RHE, vs reversible hydrogen electrode). However, at higher potentials (greater than 0.5 V_RHE), the Fe site becomes obstructed by $O_2^{-}$, resulting in a shift of the active site from the Fe site to a neighboring C site (designated as type A3). The corresponding ORR mechanism at the C site is denoted as $O_2^{-}$ mechanism ($O_2\to O_2^{-}{\to }^{\ast }{O}_2^{-}\to {}^{\ast }\mathrm{OOH}\to {}^{\ast }O\to {}^{\ast }\mathrm{OH}\to H_{2}O$). This mechanism yields a calculated half-wave potential that aligns well with experimental observations. The mechanisms identified for FePPc and Pz-FeTPr can be substantiated by the Raman signals detected in experimental studies.