Coulombic surface dipole trapping ionomer for efficient proton exchange membrane fuel cells.

Uniform ionomer distribution and controlled sulfonate adsorption are critical for low-Pt-loading proton exchange membrane fuel-cell membrane electrode assemblies (MEAs), especially at high current density. In conventional Pt/C catalysts, differences between Pt and carbon surfaces promote sulfonate adsorption on Pt and ionomer aggregation on carbon, thereby limiting proton and oxygen transport. Here we show that a single Co atom dipole layer covering Pt/C (SCDC-Pt) regulates the catalyst-ionomer interface through electrostatic attraction between positively charged Co sites and sulfonate groups. The resulting MEA delivers a peak power density of 1.4 W cm-2 and only 26 mV loss at 0.8 A cm-2 after 30,000 square-wave cycles, compared with 0.86 W cm-2 and 75 mV loss for commercial Pt/C under identical conditions. Operando characterization and simulations indicate that surface dipoles promote a more uniform ionomer distribution, suppress sulfonate poisoning of Pt, and stabilize the Pt structure. Electrochemical diagnostics show lower apparent sulfonate coverage ( ~ 8%) and local O2 transport resistance (38.6 S m-1) than those of commercial Pt/C ( ~ 20% and 48.1 S m-1).