PtCo/C catalysts with narrow particle size distribution improve high current density operation in PEM fuel cells

The design of catalysts with stable and finely dispersed platinum on the carbon support is key in controlling the performance of fuel cells. In the present work, an intermetallic PtCo/C catalyst with a narrow particle size distribution synthesized via double-passivation galvanic displacement is demonstrated. The catalyst exhibits an improved high-current-density performance in single-cell low-temperature fuel cell tests. TEM and XRD confirm a significantly narrowed particle size distribution for the catalyst particles in contrast to commercial benchmark catalysts (Umicore PtCo/C 30 and 50 wt%). Only about 10 % of the mass fraction of PtCo particles show a diameter larger than 8 nm, whereas up to > 35 % for the reference systems. This directly results in a considerable increase in electrochemically active surface area (96 m² g-1 vs. < 70 m² g-1). In addition, a higher fraction of these finely distributed PtCo nanoparticles are anchored on the carbon surface compared to the industrial benchmarks where nanoparticles are located inside the carbon pores. Single-cell tests confirm this finding by a significantly improved performance, especially at high current densities (~ 1 W cm-2 at 0.55 V under H2/air, 50 % RH, 250 kPaabs) and even with lower Pt loading (0.25 mgPt cm-2) compared to the commercial reference (< 0.9 W cm-2 at the same potential and the given conditions) with a higher Pt loading (0.4 mgPt cm-2). Lastly, reducing the cathode catalyst loading from 0.4 to 0.25 mg cm-² resulted in a power density drop at application-relevant 0.7 V of only 4 % for the novel catalyst, compared to the 10 % and 20 % for the Umicore reference catalysts with 30 wt% and 50 wt% PtCo on carbon.