Enhanced platinum utilization efficiency of polymer-coated carbon black as an electrocatalyst in polymer electrolyte membrane fuel cells

The utilization efficiency of platinum (Pt) in polymer electrolyte membrane fuel cells (PEMFCs) needs to be increased to lower the cost of PEMFCs to facilitate their widespread commercialization. Here we developed a novel method to improve the Pt utilization efficiency by coating of polybenzimidazole (PBI) on the surface of the carbon support material; Vulcan. Electrochemical experiments revealed that Pt nanoparticle-loaded PBI-coated Vulcan (denoted as Vulcan/PBI/Pt) electrode possessed a much larger electrochemically active surface area (ECSA) compared with that of Pt nanoparticles directly deposited on Vulcan (Vulcan/Pt). The power density of the cell with Vulcan/PBI/Pt was 1.16 kW g⁻¹, which was ca. 20% higher than that of the control cell using Vulcan/Pt (0.97 kW g⁻¹). We considered that the higher Pt utilization efficiency of Vulcan/PBI/Pt than Vulcan/Pt resulted in such an enhanced ECSA and power density of the PBI-coated system. Two possible reasons were considered for the improvement; namely 1) the polymer layer prevented the loading of Pt nanoparticles into inaccessible micropores of Vulcan and 2) the polymer layer improved the coating homogeneity of Nafion ionomer, and thus improved the proton accessibility for Pt nanoparticles.