Development of Mass-Production-Scale High Performance and Reliable Catalyst Coated Membrane (CCM) for PEMFC Via Optimized Electrode Slurry for Direct Coating Process

Abstract

The mass production of polymer electrolyte membrane fuel cells (PEMFCs) requires a reduction in the materials cost. The most costly component of a PEMFC is the membrane electrode assembly (MEA), which contains the precious metal catalyst, platinum. Most related research is focused on cost-reduction of the catalysts, or cost-reduction of the proton exchange membranes (PEMs), and little fundamental research has focused on alternative MEA manufacturing routes as a means of cost-reduction. The MEAs are generally manufactured by decal transfer method. The decal transfer method necessitates coating wider catalyst layers to address alignment tolerance stack up and membrane shrinkage issues at lamination. The costs of existing processes are too high and not scalable and the film quality can be too low for long life. In order to support large scale manufacturing, alternative methods for MEA fabrication are imperative. Available fabrication techniques, such as direct coating by brushing, screen printing, spraying and reactive spray deposition. The direct coating method is more simple and efficient than indirect coating process, decal transfer method and has no risk of uneven and incomplete transfer of catalyst in the catalyst layer (CL). Furthermore, it also produces a higher MEA performance than the conventional decal transfer method due to an easier controllability of the CL thickness as well as a better ionic connection between the CLs and the membrane resulted from a strong attachment of the solvent on the membrane. However, the direct coating of electrode slurry onto the membrane has a critical problem that the membrane has a high tendency to swell or wrinkle with a contact of many solvents in the electrode slurries, which could give rise to the deformation of the CL by fast volume changes of the membrane. Therefore, the optimization of electrode slurry and control of dry process is very important in the direct coating method for the high quality MEA fabrication. Additionally, the effects of direct roll-to-roll coating conditions on the electrode structure and PEMFC performance are poorly understood in many systems. This provides a detailed protocol and materials for the fabrication of reproducible, high-performance, mass-production-scale catalyst coated membranes (CCMs) through implementation of an advance slot-die coating approach of the CLs directly onto PEMs. And this work is to investigate the influence of direct coating parameters on CCM structure and performance, with a particular focus on the slot-die system because of its ability to produce very high performance CCMs at low initial capital cost, particularly at mass-production-scale. The CCMs were analyzed by scanning electron microscopy (SEM) to assess surface morphology, as well as cross-section thickness and porosity. The performance of these CCMs was tested in PEMFCs with standard protocols and their resistance during PEMFC testing was studied by electrochemical impedance spectroscopy. Figure 1. (a) Procedure of direct roll-to-roll coating process, and (b) catalysts coated membrane. Figure 1