A Molecule Assembly Route to Simultaneously Detoxify Platinum Sites and Disentangle Reactant Transport Paths in Proton Exchange Membrane Fuel Cells

Abstract

Substantially reducing the platinum (Pt) usage is essential for large-scale application of proton exchange membrane fuel cells (PEMFCs), a key hydrogen-energy technology promising a carbon-neutral future. Currently, the low-Pt PEMFCs suffer from sluggish reaction and transport kinetics in the cathodic catalyst layers (CCLs) caused by the adsorption of perfluorinated sulfonic acid (PFSA) ionomers to Pt via the side chains and the accompanying uneven PFSA aggregation. Herein, we demonstrate, through detailed physical and electrochemical characterizations and molecular dynamics simulations, that β-cyclodextrin with a unique chemical and geometric structure can effectively address these issues through a molecule assembly route. On one side, β-cyclodextrin forms a hydrogen-bonded molecular assembly with PFSA, which effectively mitigates sulfonate poisoning to Pt, produces ordered hydrophilic domains for rapid proton transport, and at the same time increases the porosity crossing CCL. On the other side, the hydrophobic β-cyclodextrin nanocavities provide ideal O₂ diffusion paths. The thus formed CCL and Pt/ionomer interface with enriched catalytic sites, and well-segregated and ordered O₂ and proton transport channels, remarkably boost the fuel cell performance.