The cathode platinum loading has been significantly reduced from 0.4-0.8 mg_Pt/cm² to about 0.1 mg_Pt/cm², which meets the U.S. DOE’s target for 2020. However, at this low platinum loading, larger-than-expected mass-transfer polarization occurs at high current densities. Recent work proposed the enhancement of ionomer distribution via carbon support functionalization. In this study, two schemes of surface functionalization were investigated 1) diazotization of p-phenylenediamine and 2) amination of pre-oxidized carbon supports (Vulcan and Ketjen Black). N₂ adsorption, XPS, and sessile-drop method were used to verify and characterize the functionalization. Improvements of cell performance at high current densities were observed using 5 cm² MEAs. Scanning Transmission Electron Microscopy (STEM) coupled with Energy-dispersive X-ray Spectroscopy (EDX) were applied to characterize surface ionomer coverage.