Effect of Inner Catalyst Layer with PTFE Binder on Performance of High Temperature Polymer Electrolyte Membrane Fuel Cells

Abstract

Recently, high temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) have attracted much attention due to their tolerance to carbon monoxide and simple water management in the system level. HT-PEMFCs mostly use polybenzimidazole membrane doped with phosphoric acid (PA) as electrolyte. Therefore, uniform distribution of PA through a whole MEA plays a critical role in determining fuel cell performance. Distribution of PA in a MEA does not only depend only on properties of membrane such as a doping level of PA in membrane but also on gas diffusion layer(GDE) characteristics, especially the structure of the catalyst layer (CL). At present, the CL for HT-PEMFCs is typically composed of platinum catalyst and a polymeric binder. The polymeric binder maintaining the integrity of CL has an influence on mechanical stability of CL and the PA distribution within MEA. There have been many studies to explore the characteristics of different binders such as polytetrafluoroethylene(PTFE), polybenzimidazole(PBI) and polyvinylidenefluoride(PVDF). As previously described by Huaneng Su et al., PVDF has a good affinity with PA which leads to quick distribution of PA, on the other hand hydrophobic PTFE reduce PA leaching.[1] In this study, dual structured CLs with two different binders(PVDF and PTFE) by controlling the contents in catalyst layer are fabricated to investigate the influence of the wettability of CL surface in terms of fuel cell perfoemance. The properties of these CL were evaluated by structure characterization and electrochemical analysis. At ambient pressure and 150oC, the GDEs with PTFE binder exhibit the highest power density (383mW/cm2) with H2/air which may result from highly hydrophobic CL, leading to improved mass transport. It was suggested that the change in ratio of two binders with different wettabilities respectively had an impact on small arc on EIS.