Effect of Varying Co Content in PtCo Nanoparticles on the Performance of PEM Fuel Cells

PtCo alloy catalysts are leading cathode candidates for PEMFC because of their relatively high activity and durability. Although it is known that during fuel cell operation the dissolution of Co results in loss of oxygen reduction reaction activity and that the migration of Co2+ into the membrane can have a negative impact on fuel cell high-current-density performance, the detailed mechanisms are unclear. Thus there are opportunities for PtCo alloy optimization to minimize these losses. Here, we focused on dealloyed PtCo catalysts with varying degrees of acid leaching in an attempt to vary the Pt-rich shell content while maintaining the Pt-to-Co core composition. While the specific activity of the catalyst decreased with reducing Co content, as expected, the high current fuel cell performance improved. Post-mortem analyses were done to quantify the amount of Co2+ in the membrane. Mathematical modelling was used to help interpret the voltage losses at high current density. We also employed newly developed nanobeam electron diffraction techniques to measure local crystal structure across the PtCo core-shell nanoparticles at subnanometer resolution. This allows us to correlate lattice strain relaxation and defect sites to the apparent catalyst kinetic activity. This work was partially supported by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy under grant DE-EE0007271.