Oxygen transport is a serious limiting factor on the performance of polymer electrolyte fuel cells (PEFCs). In the present study, without modification of either the chemical structure of the ionomer or the Pt surface, the oxygen transport resistance in ionomer films (R-CL,R-film) was successfully mitigated via a newly developed electrospray (ES) catalyst layer (CL) preparation. We prepared the CL according to two different ionization modes [positive ionization mode (ESP) and negative ionization mode (ESN)] and ionomer/carbon mass ratios (I/C) of 0.3 and 0.7. The ionomer morphology revealed differences according to the ionization mode, as analyzed by scanning transmission electron microscopy. Spherical and dendritic ionomer morphologies were observed resulting from ESP and ESN, respectively. To quantitatively estimate R-CL,R-film values, limiting current measurements were used. Consequently, the CL prepared by ESN exhibited the lowest R(CL,film )value compared to that for the conventional pulse-swirl-spray (PSS) method and ESP (I/C 0.3 PSS, 61; ESP, 94; ESN, 40 s(-1); and I/C 0.7 PSS, 68; ESP, 66; ESN, 46 s m(-1)). Moreover, the difference in the ionomer morphology not only influenced the mass activity at low current density but also helped to implement superior performance at high current density. Therefore, it was confirmed that the decreased thickness of the ionomer film covering the surface of the catalyst with ESN decreased R-CL,R-film by a factor of 1.5 and, as a result, improved the overall PEFC performance by the same factor.