Chapter 4 - 4. Main Cell Components, Materials Properties and Processes

Abstract

This chapter describes the main cell components, materials properties, and processes of fuel cells. The heart of a fuel cell is a polymer, proton-conductive membrane. On both sides of the membrane there is a porous electrode. The electrodes must be porous because the reactant gases are fed from the back and must reach the interface between the electrodes and the membrane, where the electrochemical reactions take place on the catalyst surface. The multilayer assembly of the membrane sandwiched between the two electrodes is commonly called the membrane electrode assembly or MEA. A fuel cell membrane must exhibit relatively high proton conductivity, must present an adequate barrier to mixing of fuel and reactant gases, and must be chemically and mechanically stable in the fuel cell environment. The protonic conductivity of a polymer membrane is strongly dependent on membrane structure and its water content. The first step corresponds to uptake of water by solvation by the ions in the membrane; whereas the second step corresponds to water that fills the pores and swells the polymer. The key to improving the polymer electrolyte membrane (PEM) fuel cell performance is in increasing Pt utilization in the catalyst layer. A gas diffusion layer in PEM fuel cells provides a pathway for reactant gases from the flow field channels to the catalyst layer, allowing their access to the entire active area.