Platinum/carbon black (Pt/C) catalysts trapped in epichlorohydrin-cross-linked chitosan are used to prepare cathode electrocatalysts for PEM fuel cells H2/O2. The effects of epichlorohydrin content (0–12 g), operating temperatures (40–80 C), and relative humidity (50–100% RH) on fuel cell performance are investigated. The optimal amount of epichlorohydrin of 4 g (Pt/C–4–Chi) results in a uniform distribution of Pt particles on the carbon black support and a sufficient number of chitosan cross-links in the catalyst that can both hold the three-phase boundary in place and simultaneously decrease the degree of swelling of the chitosan chains in humidified conditions. The optimal epichlorohydrin content in combination with the optimal operating conditions of 40 C and 100% relative humidity produce the best fuel cell performance (lowest activation overvoltage and ohmic overvoltage), compared to the unmodified catalyst and the other catalysts modified. Under optimal operating conditions, the voltage stability of the fuel cell containing Pt/C–4–Chi in continuous operation for 30 hours is comparable to that of the cell containing the unmodified catalyst. Fuel cell performance is highly dependent on the relative humidity of the cells which enhances proton transfer in the cells.1. IntroductionAt the cathode, the slow electrochemical reaction (i.e. oxygen reduction reaction) and poor proton and electron transport reduce the performance of H2/O2 proton exchange membrane fuel cells (PEMFCs) by increasing the activation overvoltage or loss of activation [1] . This problem can be overcome by increasing the operating temperature [2], but too high a temperature reduces the humidity of the membrane, which can increase the...... middle of the paper ......ochemistry: application to cell fuel, Doctoral Thesis, Department of Materials Science and Engineering, Stanford University, USA, 2004.[20] B. Gou, WK Na, B. Diong, Fuel Cells: Modeling, Control and Applications, in: Power Electronics and Applications Series, CRC Press, USA, 2009.[21] X.-Z. Yuan, H. Wang in: J. Zhang (ed.), PEM Fuel Cell Electrocatalysts and Catalyst Layers: Fundamentals and Applications, Springer, London, 2008.[22] S. Song, G. Wang, W. Zhou, X. Zhao, G. Sun, Q. Xin, S. Kontou, P. Tsiakaras, J. Power Sources 140 (2005) 103-110.[23] IE Pacios, MJ Molina, MR Gómez-Antón, IF Piérola, J. Appl. Polim. Sci. 103 (2007) 263–269.[24] C. Song, J. Zhang in: J. Zhang (ed.), PEM Fuel Cell Electrocatalysts and Catalyst Layers: Fundamentals and Applications, Springer, London, 2008.[25] Q. Yan, H. Toghiani, J. Wu, J. Energy sources 158 (2006) 316−325.