PEM Fuel Cell Catalyst Layers and MEAs

Proton exchange membrane fuel cells (PEMFCs) have attracted intensive attention as a result of their applicability to transportation systems and portable electronic products [1]. The important challenges in PEMFC research arise in the catalyst layers (CLs) because these are complex and heterogeneous. The catalyst layers need to be designed so as to generate high rates of the desired reactions and minimize the amount of catalyst necessary for reaching the required levels of power output. To meet the goal, the following requirements need to be considered: (1) large three-phase interface in the CL, (2) efficient transport of protons, (3) easy transport of reactant and product gases and removal of condensed water, and (4) continuous electronic current passage between the reaction sites and the current collector. A CL with a thickness around several micrometers is a critical component of a PEMFC and requires more elaborate treatment [2]. The CL is in direct contact with the membrane and the gas diffusion layer (GDL), as shown in Figure 7.1. It is also referred to as the active layer [3]. Gottesfeld and Zawodzinski provided a good overview of the CL structure and functions [4]. The overall CL performance depends on all these critical factors and is therefore essential to identify the electrode structures and operation conditions. In this section, the functions and the technical impacts of the CLs will be described.