Polymer electrolyte membrane (PEM) fuel cells are promising devices for electrochemical energy conversion due to their high-efficiency, high-power density, and benign by-products. A major challenge facing the catalyst layer in PEM fuel cells is the high cost of Pt, which is currently the only single-metal catalyst capable of overcoming the slow kinetics of the oxygen reduction reaction at the PEM cathode. I will discuss our approach in addressing this challenge, which we have attacked in two ways: 1) by fabricating efficient, low Pt loading catalyst layers via pulse potential deposition (PPD) of nanoparticles and 2) by adapting our PPD method to produce bimetallic PtCo nanoparticles, which demonstrate a 2-fold enhancement in peak power density over pure Pt nanoparticles. Using PPD, we are able to control the size, morphology and loading of platinum nanoparticles from H2[Pt(OH)6] by controlling the deposition parameters such as the pulse potential, the pulse width and the duty cycle. We have deposited Pt nanoparticles on amorphous carbon supports with high surface area and high catalytic activity. Electrodes fabricated from PPD Pt nanoparticles display increased fuel cell performance compared to commercial electrodes with up to an order of magnitude less Pt. We have also found that by incorporating a very small amount of the non-precious metal Co to produce PtCo bimetallic nanoparticles results in increased catalytic activity. Fuel cell electrodes utilizing PPD PtCo nanoparticles at the cathode showed a 2-fold enhancement in peak power density compared to a cathode with PPD Pt-only nanoparticles. This improvement was achieved with the incorporation of only ~0.5 atom % Co; or only a single Co atom in a 2nm PtCo nanoparticle. X-ray absorption spectra indicate that Co is intercalated into the Pt fcc lattice, resulting in charge transfer from Co to Pt and a Pt-Co bond length contraction. The resulting change in the electronic structure of the PtCo nanoparticle is responsible for the enhanced catalytic activity. I will discuss how this enhanced activity is influenced by extrenal fields and the type of non-precious metal incorporated into the lattice such as Co or Ni.

Highly efficient Pt and PtCo nanoparticle catalysts prepared by electrochemical deposition for PEM fuel cells

2019 Spring National Meeting

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