A key challenge in proliferation of PEM fuel cells and water electrolyzers is their large loadings of platinum group metals (PGMs) that make them cost prohibitive. 3M's nanostructured thin film (NSTF) is a state-of-the-art PGM electrocatalyst material that has achieved some of the highest mass activity values for the oxygen reduction/evolution reactions while also showing some of the best fuel cell and water electrolyzer performance at low PGM loadings. However, the mesoscale geometry of the organic crystalline whisker supports used in NSTF has not been systematically tuned to examine how extended surface area structures effect electrochemical reactivity. This talk presents our work to investigate oxygen reduction reaction (ORR) kinetics, a model reaction, on systematically varied extended surface area mesoscale geometries prepared from self-assembled block copolymer templates. The block copolymer morphology is controlled by the ratio the blocks' volume fraction. The degree of polymerization for the block copolymer controls the periodic feature size (40 nm to 10 nm). Preliminary data in a rotating disk electrode with the new extended nanostructured thin films of platinum showed mass activity values of 0.35 A mgPt-1 to 0.46 A mgPt-1 at 0.9 V vs. RHE for the oxygen reduction reaction (ORR). The measured electro-chemically active surface area (ECSA) values obtained from hydrogen underpotential depositionwere 64 to 70 m2 gPt-1. The lower values hailed from lamellae morphology while the larger values corresponded to a cylindrical morphology. The measured mass activity values, which have no cobalt or nickel additives and are unoptimized, display competitive mass activity values for ORR.

Extended surface electrocatalyst supports for PGM thin films from self-assembled block copolymer templates

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