Abstract
The effect of the catalyst synthesis method on the location of platinum nanoparticles on a high surface area Ketjenblack is investigated with respect to the high current density performance in low loaded proton exchange membrane fuel cells (PEMFC). Catalysts were prepared using various synthetic methods to deposit platinum nanoparticles at different locations on the carbon surface, e.g. inside or outside the pores of the primary particle. Transmission electron microscopy (TEM) suggested, that the Pt-particle deposition can be controlled to be preferentially on the outer carbon surface or within the pores. Electrochemical characterization was performed in thin-film rotating disk electrode (RDE) setup as well as in 5 cm2 single cell MEA tests. Although the carbon support was identical for all catalysts, the one with more Pt particles deposited on the outer carbon surface performed superior at high current which was attributed to a lower oxygen mass transport resistance. From the presented data, it can be concluded that not only the type or the surface area of the carbon black support affects the fuel cell performance, but that the synthesis approach is an additional parameter to tune the fuel cell performance at high current density.
Highlights
One of the challenges for fuel cell electric vehicles (FCEVs) to become cost-competitive with internal combustion engines is the reduction of the platinum catalyst loading
The effect of the synthesis method for the deposition of Pt nanoparticles on a high surface area Ketjenblack carbon support with respect to the electrochemically active surface area (ECSA), the oxygen reduction reaction (ORR) mass activity, and the fuel cell performance of the resulting catalysts was investigated
For catalysts prepared by a polyol synthesis method, strong evidence is supported that Pt particles were predominantly deposited on the external Ketjenblack support surface, as indicated by Transmission electron microscopy (TEM) images and by an analysis of the ORR activity
Summary
Characterization of carbon supports and catalysts.—Elemental analysis and X-ray photoelectron spectroscopy (XPS) was utilized to determine the bulk and surface composition of the Ketjenblack support before and after the functionalization procedure. The catalysts prepared by the polyol reduction method showed a significant amount of platinum particles on the edges of the carbon (examples marked by red circles in Figures 2a and 2b), which suggests a considerable amount of Pt particles to be located on the outside of the carbon black Based on these observations, a simplified sketch of the platinum particle distribution on the primary carbon black is proposed in Figures 2e and 2f. The electrochemically active surface area determined from HUPD for the Pt/KBIW and Pt/KBTKK was found to be ≈79–83 m2/gPt (see Table III) These values are consistent with previously reported values for high surface area carbon black supports.[13,28,29] Significantly lower ECSA values of ≈66–69 m2/gPt were found for the catalysts prepared by the polyol method.
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