In the developments of the polymer membrane electrolyte fuel cells (PEMFCs), strategic design of their catalysts layer is a key to improve the performance and durability. Especially, interfacial structure of the electrocatalysts constructed by carbon support, platinum (Pt)-based nanoparticles and polymer electrolyte so called ionomer dominates the performance. It is known that the surface coverage of the ionomers onto the carbon-supported Pt nanoparticles generates overpotentials in the catalyst layer. To avoid this, an ionomer-free electrocatalyst is developed by functionalized surface of carbon supports, in which the support is covalently grafted to benzenesulfonic acid to facilitate the proton conduction on the carbon surface and Pt nanoparticles are attached to the acid-grafted carbon support. In single-cell measurements, although the ionomer-free electrocatalyst exhibits larger proton resistance than a conventional ionomer-based electrocatalyst, higher activity at low (<0.01 A cm−2) and high (>1.7 A cm−2) current densities were achieved owing to increased oxygen reduction reaction activity and decreased oxygen diffusion resistance, respectively. Elimination of the ionomer reduces both the interfacial overpotential as well as diffusion overpotential of the oxygen.
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