Effect of a polybenzimidazole coating on carbon supports for ionomer content optimization in polymer electrolyte membrane fuel cells

Abstract

Optimizing the ionomer/carbon (I/C) ratio in the catalyst layer (CL) of polymer electrolyte membrane fuel cells (PEMFCs) is vital for maximizing PEMFC efficiency. In this study, the effect of the I/C ratio for a platinum (Pt) catalyst loaded on a polybenzimidazole (PBI)-coated Vulcan (Vulcan/PBI/Pt) is compared with a conventional Pt catalyst on Vulcan (Vulcan/Pt). Furthermore, this study determines that a CL comprising Vulcan/PBI/Pt with an I/C = 0.2 exhibits the highest maximum power density (750 mW cm−2), while that of a CL having Vulcan/Pt is calculated to be 610 mWcm−2 at I/C = 0.6. Effective interactions between ionomer and the PBI-coated Vulcan enables stable ionomer coating and high proton conductivity, even at very low I/C ratios. At such low I/C ratios, the O2 diffusion coefficient of Vulcan/PBI/Pt CL is improved by 51% when compared to Vulcan/Pt CL with an I/C = 0.6. Cross-sectional scanning electron microscopy images further reveal that Vulcan/PBI/Pt CLs possess better pore connectivity than those of Vulcan/Pt. Hence, it concludes that the proposed PBI coating approach is advantageous and significant breakthrough to fabricate highly efficient CLs by improving both proton conduction and O2 diffusion simultaneously with lower ionomer contents.