Hydrophobicity Optimization of Cathode Catalyst Layer of Proton Exchange Membrane Fuel Cell

Hao-Jie Chen, Hubei Key Laboratory of Electrochemical Power Sources, Department of Chemistry, Wuhan University, Wuhan 430072, China
Mei-hua Tang, Hubei Key Laboratory of Electrochemical Power Sources, Department of Chemistry, Wuhan University, Wuhan 430072, China
Sheng-Li Chen, Hubei Key Laboratory of Electrochemical Power Sources, Department of Chemistry, Wuhan University, Wuhan 430072, China

Abstract

Hydrophobicity of the cathode catalyst layers (CCLs) crucially determines the performance of proton exchange membrane fuel cells (PEMFCs) by affecting the transport of O2 and liquid water. In this regard, polytetrafluoroethylene (PTFE) is usually used as a hydrophobic additive to facilitate the oxygen and water transport in CCLs. So far, there remains lacking systematic effort to optimize the addition methods of PTFE in CCLs and the mechanisms behind. In this work, we study the effects of the approaches of PTFE addition and its distribution on the mass transport of O2 and the proton conduction in CCLs by using a number of electrochemical characterization methods and contact angle tests. First, it is found that the direct addition of PTFE molecules is a better way than adding the PTFE-modified carbons to improve the electrochemical properties of CCLs, since the latter causes an increase in the proton transport resistance, whereas the direct molecule addition results in obviously improved O2 transport without affecting the proton conduction. In addition, the gradient distribution of PTFE in CCLs, more specifically, adding PTFE near the interface between CCL and gas diffusion layer (GDL), yields higher catalyst utilization than the homogeneous distribution of PTFE due to the lower oxygen transport resistance.