Understanding the influence of different porous microstructures derived from diverse drying methods of the cathode catalyst layer in PEMFC

Kurzfassung

The heart of the Polymer electrolyte membrane fuel cell (PEMFC) is the membrane electrode assembly (MEA), which consists of gas diffusion medium, active catalyst layer and polymer electrolyte membrane. The catalyst layer (CL) should enable high activity by large interface area and superior gas transport by effective porosity. It is established that transport limitations are significant for PEMFC performance, and it is reported that limited diffusion or accessibility of the reactant gas to the reaction site and poor water management are important. Catalyst-loaded membrane and gas diffusion medium in contact with the electrolyte allows the easy permeation of oxygen from the surrounding atmosphere and its subsequent reduction on supported electro-catalysts. Our group has introduced the freeze drying of CL prepared from suspensions that promotes the porosity of the catalytic layer and correspondingly improves the diffusivity and ionomer distribution [1]. To remove the solvent from the coating, drying step is essential. The major characteristic of freeze drying is removal of solvent by sublimation of the solid state. Thickness of the catalyst layer can also be controlled by controlling the catalyst ink composition in this drying method. Freeze drying of MEAs reduces the mass transport resistance by 20 %. In this work, we have investigated the influence of different drying techniques on microstructure of wet-coated electrodes and the structure performance relationship. We have also performed simulation into a transient 2D physical continuum-model to investigate the effect of the structural properties of the differently dried electrodes on cell performance. This modeling approach determines model parameters that describe a specific electrode structure through an optimization procedure which utilizes data from carefully planned experimental studies.