Platinum Monolayer Perfection with the Assistance of Citric Acid in Galvanic Displacement Reaction

The slow kinetics of oxygen reduction reaction (ORR) is one of the main obstacles hindering the commercialization of low-temperature fuel cells.¹ Core-shell catalysts consisting of a Pd-based core and a Pt shell (Pt/Pd/C) showed higher Pt mass activity than commercial Pt/C catalysts due to a synergistic effect between the core and Pt shell and substantially complete utilization of Pt atoms.² The synthesis of a core-shell catalyst involves two main steps: (1) underpotential deposition (UPD) of a Cu monolayer on the surface of Pd nanoparticles; (2) displacement of the Cu atoms with Pt via a simple oxidation-reduction reaction: Cu + Pt²⁺ → Pt + Cu²⁺.  The challenges associated with production of core-shell catalysts in a large scale are the uniform deposition of a Pt overlayer on the Pd core during the displacement of Cu atoms.

Herein, we report our study on the production of core-shell catalysts at the gram scale by introducing citric acid in the Pt-Cu displacement reaction solution. It was found that the quality of the Pt monolayer shell could be significantly improved by adding citric acid.^3,4 In the presentation, we will discuss the role of citric acid in smoothing the Pt overlayer based on the experimental and density functional theory calculation results. The characterization and evaluation results of core-shell structures will be shown as well.

References

1. Electrocatalysis in Fuel Cells: A Non- and Low- Platinum Approach; Shao, M., Ed.; Springer: London, 2013.

2. Adzic, R. R.; Zhang, J.; Sasaki, K.; Vukmirovic, M. B.; Shao, M.; Wang, J. X.; Nilekar, A. U.; Mavrikakis, M.; Valerio, J. A.; Uribe, F. Topics in Catalysis 2007, 46, (3-4), 249-262.

3. Humbert, M.; Smith, B.; Wang, Q.; Ehrlich, S.; Shao, M., Electrocatalysis 2012, 3 (3-4), 29.

4. Shao, M. H., et al. Phys. Chem. Chem. Phys. 2013, 15, 15078