Effect of Hydrophobicity of Catalyst Layer for Gas Diffusion Electrode at High Temperature Proton Exchange Membrane Fuel Cells

Abstract

The high-temperature proton exchange membrane fuel cell (HT-PEMFC) is operated between 120 ℃ and 180 ℃, so it has higher CO tolerance than the low-temperature proton exchange membrane fuel cell. However, since HT-PEMFC is operated at dehydrating condition, the Nafion which has high proton conductivity in high humid condition can’t be used at electrodes. Therefore, the electrodes consist of not only catalysts and polymer binders but phosphoric acid (PA) due to proton conductivity. At performance of the membrane electrode assembly (MEA), PA distribution in electrodes is important in forming three-phase interface, and it is determined by the hydrophobicity of the polymer binder. In this study, we compared the hydrophobicity of the electrode and MEA performance depending on the type of binder and the presence of additives. First, we compared the electrodes with PVDF and PTFE binder that were made by spraying method. In addition, changes in presence or absence of PA were also compared. The PTFE electrode had higher hydrophobicity than the PVDF electrode, which affected the MEA performance and charge transfer resistance (Rct). And adding PA decreased ohmic resistance (Rohm) and proton resistance (Rpro) but increased Rct. Second, we compared the electrode with PPO-MPA and PPO-HPA binder made by bar coating method and change in presence or not of vinylphosphonic acid (VPA). The PPO-HPA electrode had higher hydrophobicity and MEA performance than the PPO-MPA electrode. However, adding VPA made the Rohm increased because of growing the interface resistance. Therefore, the hydrophobicity enhanced the MEA performance and decreased the Rct value.