Pore size distribution and specific pore volume in the catalyst layer of polymer electrolyte membrane fuel cells were modified by controlling the temperature during the catalyst layer fabrication. Raising the temperature of the gas diffusion layer where the platinum catalyst is coated facilitated evaporation of the solvent in the catalyst ink and induced a large pore volume especially in the secondary pore. Fuel cell electrodes with large amounts of pores exhibit 30% improved single cell performance. The microstructure and electrochemical properties of electrodes were investigated by field emission scanning electron microscopy, mercury intrusion porosimetry, electrochemical impedance spectroscopy, and current-voltage polarization measurement. The results indicate that increased volume of the secondary pore reduces the mass transfer resistance and improves the performance. (c) 2007 Elsevier Ltd. All rights reserved.