Alleviating the Misalignment of Fe Single Sites Relative to Triple-Phase Interfaces to Achieve High Performance Fuel...

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Single-atom catalysts (SACs) like Fe─N─C are promising alternatives to platinum in proton exchange membrane fuel cells (PEMFCs).
• Low atomic efficiency due to poor site accessibility at triple-phase interfaces (TPIs) hinders SAC performance in real cells.
• Optimizing catalyst layer structure to enhance reactant-accessible single sites is critical for advancing SACs in PEMFCs.

Purpose of the Study:

• To design a catalyst layer structure that increases the density of reactant-accessible single sites for Fe─N─C SACs in PEMFCs.
• To investigate the role of hierarchical porosity and tuned surface hydrophilicity in activating TPIs.
• To improve the overall performance and durability of PEMFCs utilizing Fe─N─C SACs.

Main Methods:

• Fabrication of hierarchical porous Fe─N─C_pot catalysts with controlled surface hydrophilicity.
• Coarse-grained molecular dynamics (MD) simulations to model catalyst layer structure and ion transport.
• Combinatory spectroscopic techniques to confirm mass transfer channel formation.

Main Results:

• Macropores and tuned hydrophilicity act as "on-switches," facilitating Nafion/water domain penetration and alleviating transport bottlenecks for O₂ and H₃O⁺.
• The engineered structure creates continuous mass transfer channels, increasing Fe site utilization by 80%.
• Achieved a peak power density (P_max) of 1581 mW cm^-2 and maintained 63% performance after 60,000 accelerated stress tests (AST).

Conclusions:

• A tailored catalyst layer structure, achieved through hierarchical porosity and surface chemistry, effectively activates TPIs in PEMFCs.
• This approach significantly enhances the utilization efficiency and durability of single-atom catalysts.
• Establishes a design rule linking pore hierarchy and surface chemistry to TPI activation for improved fuel cell performance.