Controlled Pt Coverage for Extended Thin Film Catalyst ORR Studies via Templated Gas Phase Synthesis

Platinum-based materials are currently the most effective catalysts for the oxidation reduction reaction (ORR) in acidic medium for PEM fuel cells. However, the high cost of platinum, and the associated cost due to the low durability of Pt nanoparticles (NP), makes them commercially cost prohibitive to date. Therefore, the efficient use of Pt and its improved durability are essential to achieving commercialization in PEM fuel cells. The development of extended thin films has provided promise for addressing these issues.(1,2,3) In this study, we take a templating approach to achieve morphological control of the extended surface catalyst. By choosing a sacrificial template with appropriate surface energy for gas phase platinum deposition we can produce a controlled catalyst layer deposited film. Here, anodized aluminum oxide (AAO) templates are used in conjunction with atomic layer deposition (ALD) of Pt to produce the controlled catalyst layer. The advantage of the AAO template is in its ability to control the size and shape of the deposited platinum layer by providing a deposition surface with satisfactory wetting properties. This more appropriate surface energy (as compared to direct deposition onto carbon) allows for the platinum to be deposited as nanoparticles with controllable high spatial density while avoiding large aggregation phenomena. By varying the number of ALD cycles deposited into the AAO pores, the platinum loading can be systematically controlled. The pores are subsequently back-filled with carbon via chemical vapor deposition to stabilize the particles on a supporting conductive backbone. Once the solid carbon core is supporting the platinum layer, the template can be easily removed via etching. Figure 1 shows the resulting uniform coverage and morphology of the Pt NPs on the carbon surface produced by this technique. The particle size and distribution are determined with high-resolution transmission electron microscopy. CO stripping and ORR results will be shown to characterize the performance of the catalyst. Correlation of the electrochemical performance to the thickness and continuity of Pt deposition will provide fundamental insight into the effectiveness of the extended catalyst surfaces. Figure 1. TEM images of extended surfaces of Pt NPs supported on carbon backbone show A) discrete particles and B) uniform morphology.