Polyelectrolyte membrane PEM and fuelcell catalyst studies using a miniaturized PEM fuel cell test fixture
Authors: Creager Stephen , Bukola Saheed , Smith Rhett 
Published: June 2019

Advances in catalyst and electrolyte materials for hydrogen fuel cells are driving performance gains and cost reductions that are helping to bring hydrogen fuel-cell technology to market. Research on new materials is always a combination of synthesis and characterization, where characterization must eventually include incorporation of materials into an operating fuel cell. It is at this stage that research on leading-edge new materials often stalls, because conventional fuel-cell tests require relatively large amounts of material, e.g. several grams of a new catalyst and tens to hundreds of grams of ionomer, corresponding to many tens of square centimeters of membrane area, are required to run a comprehensive set of tests as is necessary to assure reproducibility and examine behavioral trends. These amounts of material are often not available in early-stage synthetic work, which means that characterization uses other approximate approaches, e.g. rotating disk electrode (RDE) voltammetry to study catalyst activity, with true fuel-cell testing often being delayed until syntheses may be scaled up. This situation is unfortunate because approximate tests often do not adequately screen materials. It would be desirable to run preliminary fuel-cell tests at an early stage to gain a better idea of materials properties before making decisions regarding which materials to scale up. This contribution will present our recent work building and using a miniature PEM fuel-cell test fixture that uses only very small amounts of material to conduct a true solvent-free fuel-cell test. The cell is fabricated from a conventional compression-style fitting and uses 5/8 inch diameter graphite or metal rods for gas delivery and for making electric contact with the electrodes. Membrane-electrode assemblies (MEAs) are made from 3/4-inch diameter PEM disks, typically cut from Nafion ionomer membrane, onto which carbon-cloth-based electrodes are bonded by hot pressing. Electrode diameters range from 1/8 to 3/8 inch. The presentation will include recent published work demonstrating reproducibility and select MEA characterization data, including in-situ voltammetry to assess electrochemically active surface area (ECSA) of catalysts and polarization curve measurements that are easily obtained using conventional linear sweep voltammetry with a conventional laboratory potentiostat. This situation is in contrast to conventional fuel-cell testing that requires specialized instrumentation with passage of very large currents, e.g. tens of amperes. Very recent work using the cells in hydrogen pump configuration will also be presented. This configuration is particularly useful for measuring resistances to proton transport through ionomers in the direction through the membrane plane, in contrast to most measurements which focus on in-plane resistance, because it is easier to measure. Very recent work on the synthesis and properties of new tetra-aryl-phosphonium (TAP) alkaline ionomers which are expected have high alkaline stability and to be good hydroxide-ion conductors, and on the effect of single graphene layers embedded in Nafion membranes on proton and other ion conduction through the Nafion membranes, will also be presented.