(575ae) Principles of Fabricating High Performance Catalyzed Membranes for Proton-Exchange-Membrane (PEM) Fuel Cells

Based on the fundamental understanding of the membrane properties, we present an improved methodology for membrane-electrode-assembly (MEA) fabrication, wherein the catalyst ink is directly coated on the Nafion membrane in order to increase the interfacial contact between the catalyst layer and the electrolyte, thus enhancing the catalyst utilization. A key issue in the fabrication of catalyzed membranes via spraying of catalyst ink is that Nafion swells making it difficult to deposit a uniform film without cracking or warping. Thus, the properties of the solvent used in the catalyst ink such as polarity and di-electric constant are thoroughly investigated.

We have systematically investigated the effect of cation-exchange, to convert the membrane into Li+, Na+, K+ and Cs+ form, on the fabrication protocol. Membrane sorption was found to decrease in the order Li+ > Na+ > K+ > Cs+, with the increase in size of the counter ion due to a corresponding decrease in ion hydration capacity. This also increases the membrane Young's modulus, thus preventing it from swelling or distorting following catalyst application, improving adhesion between the catalyst ink and the membrane surface, and thereby, reducing the likelihood of electrode structure delamination. The morphology of the MEA thus developed, was studied using EDX and SEM, which reveals that thin and uniform catalyst layer can be fabricated, thus reducing ohmic losses. The catalyst loading can be further reduced without affecting the fuel cell performance and exceeding the performance of commercial MEA.