Effect of Surfactant for PTFE Binder Dispersion of Electrodes Prepared By Bar Coating Method in High Temperature Polymer Electrolyte Membrane Fuel Cell

Abstract

Polymer electrolyte membrane fuel cells (PEMFCs) are one of the most promising energy devices for both mobile and stationary applications due to their high energy conversion efficiency and low environment pollution. However, there are some problems to be solved. PEMFCs operating at low temperatures (below 80℃) based on Nafion require humidification and have low CO tolerance. To overcome this problem, high-temperature PEMFCs that operate up to 180℃ are being studied. High temperature PEMFCs does not require humidification, which simplifies the system and is highly resistant to CO. It also has the advantage of using waste heat. However, the cell performance of high-temperature PEMFCs is still much lower than that of low-temperature PEMFCs and needs to be increased for practical applications The reason for this is slow Oxygen Reduction Reaction (ORR) and limited transport of protons and reactants, especially in the presence of phosphoric acid in the catalyst layer. In the high-temperature PEMFCs, phosphoric acid acts as a proton conduction as an electrolyte and is a necessary element for electrochemical reactions at the triple phase boundaries. Therefore, if the amount of phosphoric acid in the catalyst layer is too small, it exhibits low electrochemical activity. If it is too much, the pore inside the catalyst layer is blocked to restrict the movement of the fuel, thereby reducing the number of triple phase boundaries and reducing the performance. Therefore, the amount and distribution of phosphoric acid and the formation of structural network pores in the catalyst layer are important. Thus, several polymeric binders have been introduced to perform this role. Among them, PTFE is known as the most promising binder. PTFE has hydrophobicity and high chemical stability. However, PTFE easily agglomerates and sinks immediately in the solvent due to its high hydrophobicity. Therefore, if an electrode is made of a catalyst slurry that does not properly disperse PTFE, uniform PTFE distribution in the catalyst layer cannot be expected. So, in the catalyst layer, there may be more or less parts of the specific part than the desired PTFE content. Therefore, it is not only difficult to form a proper phosphoric acid distribution and structural network of the catalyst layer, but also may affect the reproducibility of electrode manufacturing. In this study, the catalytic electrode was prepared by introducing a surfactant to disperse PTFE in the preparation of catalyst slurry. Single cell test was carried out using membrane electrode assembly made from this electrode. And the electrochemical and structural characterizations were compared. The details will be discussed in presentation.