At the heart of polymer membrane fuel cells and electrolyzers is a membrane electrode assembly (MEA), comprising of an ion-conducting membrane sandwiched between two gas diffusion electrodes. The porous gas diffusion electrode structure consists of electrocatalyst dispersed on a high surface area conductive support, held together with an ion-conducting polymer that serves as a binder. It has been long established that optimal electrochemical kinetics is achieved when a three-phase interface between the membrane, the electrode and the reactant gas is optimized. Only catalyst located in this region is electrochemically active.
A review of the membrane electrode assembly from the perspective of polymer science is provided in “Fuel Cell Catalyst Layers” Chem. Mater., Invited perspective commemorating 25th year of Chemistry of Materials, 2014, 26 (1), 381–39. Here, it is noted that the polymeric ionomer plays a vital role in PEM fuel cell device technology, not simply as the membrane that transports protons and water from one electrode to another, but as the binder and transport medium responsible for electrochemical activity within the catalyst layer. This review examines critical features of the catalyst layer ionomer. It highlights the current understanding of interactions of ionomer in catalyst inks, where the microstructure of the catalyst layer is largely formed, and in the catalyst layer itself.
Our MEA fabrication facilities at Simon Fraser University include a suite of automated systems for catalyst layer deposition such as screen printing, spray coating, decal transfer for catalyst coated gas diffusion layers or catalyst coated membranes.
Several research projects aimed at understanding and advancing fuel cell technology are on-going. One such project investigates the interplay between the PEM, active catalyst area, and catalyst utilization at membrane/GDE interfaces. This requires in depth knowledge of the microstructure and nanostructure of the various components, which are examined using a variety of techniques – including SEM and TEM as illustrated below
SEMs and TEMs of MEA and catalyst layer. Increasing magnification (left to right)
Membrane-electrode-assembly fabrication suite.