PEM fuel cell electrocatalyst durability measurements

Electrode material durability is an important factor in limiting the commercialization of polymer electrolyte membrane fuel cells (PEMFCs). PEMFCs typically use carbon supported nanometer sized Pt and/or Pt alloy catalysts for both anode and cathode. Electrocatalyst surface area loss is due to the growth of platinum particles. Particle size growth is accelerated by potential cycling whether due to artificial potential cycling or by cycling during fuel cell operation. Catalysts were analyzed by X-ray diffraction (XRD) to determine the degree of electrocatalyst sintering. Cathode Pt particle size growth is a function of temperature, test length and potential. The largest increase in cathode Pt particle size was observed during potential cycling experiments and increased with increasing potential. During single cell durability testing, the cathode catalyst particle size grew from about 1.9 to 3.5 nm during the drive cycle experiments over 1200 h of testing. This extent of growth was greater than that observed during steady-state testing, where the particles grew to 2.6 nm at 900 h and 3.1 nm over 3500 h. During cycling measurements, catalyst coarsening rates exhibited a linear increase with temperature. Low relative humidity decreased platinum particle growth, but substantially increased carbon loss. Carbon corrosion of the electrode catalyst layer was found to increase with increasing potential and decreasing humidity.