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SummaryPlatinum and Pt alloy nanoparticles supported on carbon are the state of the art electrocatalysts in proton exchange membrane fuel cells. To develop a better understanding on how material design can influence the degradation processes on the nanoscale, three specific Pt/C catalysts with different structural characteristics were investigated in depth: a conventional Pt/Vulcan catalyst with a particle size of 3–4 nm and two Pt@HGS catalysts with different particle size, 1–2 nm and 3–4 nm. Specifically, Pt@HGS corresponds to platinum nanoparticles incorporated and confined within the pore structure of the nanostructured carbon support, i.e., hollow graphitic spheres (HGS). All three materials are characterized by the same platinum loading, so that the differences in their performance can be correlated to the structural characteristics of each material. The comparison of the activity and stability behavior of the three catalysts, as obtained from thin film rotating disk electrode measurements and identical location electron microscopy, is also extended to commercial materials and used as a basis for a discussion of general fuel cell catalyst design principles. Namely, the effects of particle size, inter-particle distance, certain support characteristics and thermal treatment on the catalyst performance and in particular the catalyst stability are evaluated. Based on our results, a set of design criteria for more stable and active Pt/C and Pt-alloy/C materials is suggested.

The efficiency of polymer electrolyte membrane fuel cells is strongly depending on the electrocatalyst performance, that is, its activity and stability. We have designed a catalyst material that combines both, the high activity for the decisive cathodic oxygen reduction reaction associated with nanoscale Pt alloys, and the excellent durability of an advanced nanostructured support. Owing to the high specific activity and large active surface area, the catalyst shows extraordinary mass activity values of 1.0 A mgPt(-1). Moreover, the material retains its initial active surface area and intrinsic activity during an extended accelerated aging test within the typical operation range. This excellent performance is achieved by confined-space alloying of the nanoparticles in a controlled manner in the pores of the support.

An understanding of the influence of structural surface features on electrocatalytic reactions is vital for the development of efficient nanostructured catalysts.G old is the most active and selective knowne lectrocatalyst for the reduction of CO 2 to CO in aqueous electrolytes.N umerous strategies have been proposed to improve its intrinsic activity. Nonetheless,the atomistic knowledge of the nature of the active sites remains elusive.W es ystematically investigated the structure sensitivity of Au single crystals for electrocatalytic CO 2 reduction. Reaction kinetics for the formation of CO are strongly dependent on the surface structure.U nder-coordinated sites,such as those present in Au(110) and at the steps of Au(211), show at least 20-fold higher activity than more coordinated configurations (for example,A u(100)). By selectively poisoning under-coordinated sites with Pb,w eh ave confirmed that these are the active sites for CO 2 reduction.