(495j) Blocking the Ionomer Sulfonate Groups Via Controlling Pt Nanoparticles on the Mesoporous Carbon Support for Membrane Electrode Assembly

In recent decades, extensive research has focused on developing high-performance platinum (Pt)-based catalysts for polymer electrolyte membrane fuel cells (PEMFCs). These efforts have significantly enhanced Pt activity toward the oxygen reduction reaction (ORR), particularly in rotating disk electrode tests. However, these improvements are not fully translated to membrane electrode assembly (MEA) performance, where higher interfacial and transport resistances create a noticeable performance gap between the two evaluation methods. Among several contributing factors, strong adsorption of the sulfonate group (-SO₃^-) in Nafion^® ionomer onto the Pt surface has been identified as a key limitation. This undesired interaction increases mass transport resistance, occupies active Pt sites, and decreases overall mass activity. To address this challenge, it is crucial to minimize direct contact between Pt surfaces and ionomer sulfonate groups.

In this study, we introduce a mesoporous carbon support-based strategy to physically block an adsorption of the sulfonate groups in ionomer and improve catalyst performance at the MEA level. Graphitic acetylene black carbon (ca. 120 m² g^-1) was thermally activated in air to create a high-surface-area (∼440 m² g^-1) mesoporous structure. Pt nanoparticles (1.5–3.5 nm) were uniformly dispersed within the mesopores, allowing partial shielding from the ionomer. This configuration effectively reduced sulfonate interaction and enhanced catalyst utilization. The resulting catalysts demonstrated improved electrochemical stability and significantly enhanced MEA performance, validating the mesoporous-blocking concept for next-generation PEMFC catalyst layers.