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 ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:msup><mml:mo>→</mml:mo> <mml:mo>∗</mml:mo></mml:msup> <mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:msup><mml:mo>→</mml:mo> <mml:mo>∗</mml:mo></mml:msup> <mml:mi>O</mml:mi> <mml:mi>O</mml:mi> <mml:mi>H</mml:mi> <mml:msup><mml:mo>→</mml:mo> <mml:mo>∗</mml:mo></mml:msup> <mml:mi>O</mml:mi> <mml:msup><mml:mo>→</mml:mo> <mml:mo>∗</mml:mo></mml:msup> <mml:mi>O</mml:mi> <mml:mi>H</mml:mi> <mml:mo>→</mml:mo> <mml:msub><mml:mi>H</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>O</mml:mi></mml:mrow> <mml:annotation>${{\rm{O}}_2} \to ^*{O_2} \to ^*OOH \to ^*O \to ^*OH \to {H_2}O$</mml:annotation></mml:semantics> </mml:math> ), 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msubsup><mml:mi>O</mml:mi> <mml:mn>2</mml:mn> <mml:mo>-</mml:mo></mml:msubsup> <mml:annotation>$O_2^ - $</mml:annotation></mml:semantics> </mml:math> , resulting in a shift of the active site from the Fe site to a neighboring C site (designated as type A3). The corresponding ORR mechanism at the C site is denoted as <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msubsup><mml:mi>O</mml:mi> <mml:mn>2</mml:mn> <mml:mo>-</mml:mo></mml:msubsup> <mml:annotation>$O_2^ - $</mml:annotation></mml:semantics> </mml:math> mechanism ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mo>→</mml:mo> <mml:msubsup><mml:mi>O</mml:mi> <mml:mn>2</mml:mn> <mml:mo>-</mml:mo></mml:msubsup> <mml:msup><mml:mo>→</mml:mo> <mml:mo>∗</mml:mo></mml:msup> <mml:msubsup><mml:mi>O</mml:mi> <mml:mn>2</mml:mn> <mml:mo>-</mml:mo></mml:msubsup> <mml:mo>→</mml:mo> <mml:mrow><mml:msup><mml:mrow></mml:mrow> <mml:mo>∗</mml:mo></mml:msup> <mml:mi>OOH</mml:mi></mml:mrow> <mml:mo>→</mml:mo> <mml:mrow><mml:msup><mml:mrow></mml:mrow> <mml:mo>∗</mml:mo></mml:msup> <mml:mi>O</mml:mi></mml:mrow> <mml:mo>→</mml:mo> <mml:mrow><mml:msup><mml:mrow></mml:mrow> <mml:mo>∗</mml:mo></mml:msup> <mml:mi>OH</mml:mi></mml:mrow> <mml:mo>→</mml:mo> <mml:msub><mml:mi>H</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>O</mml:mi></mml:mrow> <mml:annotation>${{\rm{O}}_2} \to O_2^ - \to ^*O_2^ - \to {\rm{^*OOH}} \to {\rm{^*O}} \to {\rm{^*OH}} \to {{\rm{H}}_2}{\rm{O}}$</mml:annotation></mml:semantics> </mml:math> ). 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.