Effect of Dispersing Solvents of Ionomer Binder Solutions in Catalyst Inks on Performance and Durability of Membrane-Electrode Assembly

Abstract

Proton exchange membrane fuel cells (PEMFCs) is currently considered as a potential next-generation alternative energy technology because of the high energy density and high abundance of hydrogen in nature. However, many issues still exist to be improved in terms of performance and durability for the wide use of PEMFCs as a clean and efficient power system. One of the most important parts in PEMFCs is membrane-electrode assembly (MEA) which provides the electrochemical reactions at electrode where fuel/oxidant (gas), hydrated ions (liquid) and electron (solid) co-exist (so called triple phase boundary), the permeation of fuel and/or oxidant gas and the drainage of water product. In MEA, water and IPA based Nafion dispersion is the most widely used as the ionomer binder for conduction of hydrated ions, formation of pores and adhesion of solid catalyst. The structure of electrodes in MEA could be significantly determined by characteristics of ionomer binder solutions where polymer dispersion interacts with solvent. Upon the structure of the electrodes formed by agglomerates of catalyst and ionomer binder with different size, it has reported that MEA performance and durability would be highly affected. The former could be achieved by reducing overvoltages, and the latter by reducing electrode cracking (i.e., well adhesion of catalyst by ionomer). Electrode structure of MEA, including the Pt-ionomer interface, is determined when electrodes are solidified from catalyst inks during a drying step. Thus, the properties of the solvent system in catalyst inks play an important role in determining the electrode structure in MEA. A fundamental understanding of the phenomenological outcome from the relationship between morphology and property for perfluorosulfonic acid (PFSA) membranes is crucial in obtaining high power and durable MEA. In this study ion and liquid water behavior in PFSA membranes formed from different dispersing solvents were investigated with ionomer particle sizes, solvent viscosity, solvent dielectric constants and distribution which cause various morphology. In addition, MEAs with different electrodes prepared by different ionomer binder solutions were investigated in terms of I-V polarization, cyclic voltammetry, electrochemically-active surface area (ECSA), and chemical stability. Acknowledgment This work was supported by the New and Renewable Energy of the Korea Institute of Energy Technology Evaluation and Planning(KETEP) granted financial resource from the Ministry of Trade, Industry & Energy, Republic of Korea (No. 20173010032100).