Dynamic Proton Transfer Competition and pH-Dependent ORR Mechanism in γN-Modulated Fe-N-C Single-Atom Catalysts.

Area of Science:

• Electrochemistry
• Materials Science
• Computational Chemistry

Background:

• The oxygen reduction reaction (ORR) is crucial for alkaline fuel cells.
• Understanding proton transfer in Fe-N-C single-atom catalysts (SACs) is key but remains challenging.
• Existing models for proton supply via adsorbed water dissociation face kinetic limitations and competition from hydroxide ions.

Purpose of the Study:

• To elucidate the atomic-level proton supply and transfer mechanism in Fe-N-C SACs under neutral/alkaline conditions.
• To investigate the role of γN doping in modifying the proton supply pathway.
• To explore the influence of pH on the ORR kinetics and mechanism.

Main Methods:

• Density Functional Theory (DFT) calculations.
• Ab initio molecular dynamics (AIMD) simulations with an explicit water model.
• Investigation of Fe-N4 and γN-doped Fe-N4-γN2 SACs.

Main Results:

• Proposed a γN-mediated βC-modified proton supply mechanism.
• Identified two plausible proton transfer pathways: via βC-adsorbed ^#OH or a water-centered relay.
• Observed hydroxide ions abstracting protons from intermediates, potentially hindering the 4e- ORR pathway.

Conclusions:

• pH and γN doping synergistically influence ORR dynamics.
• The study provides an atomic-level mechanism for designing improved alkaline Fe-N-C SACs.
• Highlights the need to consider interfacial solvation and electrolyte ions in catalyst design.