Carbon Supported Pt-Co Alloy Nanoparticles As HOR and ORR Catalyst for PEM Fuel Cells

In a proton exchange membrane (PEM) fuel cell, a noteworthy part of the production cost is caused by the catalyst involving rare and costly noble metals. To meet the cost targets for the automotive PEMFC applications, the total Pt loading of state of the art membrane electrode assembly (MEA) has to be reduced from ~0.4 to 0.1 mg/cm². While on the anode side of the MEA, hydrogen oxidation reaction (HOR) is very fast in acidic media, high Pt loadings are needed to accelerate the very sluggish kinetics of the oxygen reduction reaction on the cathode side. This situation entirely turns if the environment changes from low to high pH values. For instance, in alkaline media the catalytic activity of the Pt for the HOR is insufficient and thus requires high Pt loadings, whereby the electro-activation of oxygen can occur on Pt-free catalyst materials [1]. A possible pathway to solve this issue is the implementation of bimetallic Pt-M (M = Co, Ru, Ni) alloy nanoparticles as electrocatalysts to reduce or substitute the Pt by maintaining the catalytic performance and durability [2-7]. Our approach is to tune carbon supported Pt-Co alloy nanoparticles as highly active and durable catalyst material for the HOR as well as for the ORR. We tailored the shape, size, structure, chemical composition and crystallinity of the Pt-Co particles by variation of the synthetic parameters. In particular, the structural arrangement of the Pt-Co nanoparticles was modified to form core-shell, Pt/Co-segregated or alloyed nanoparticles by using various synthetic and electrochemical conditions. The investigations of the electrocatalytic activity towards HOR and ORR on the modified Pt-Co nanoparticles were carried out by using a rotating disc electrode (RDE) setup in acidic and alkaline media. Furthermore, the structural properties and chemical composition of the Pt-Co nanoparticles were characterized by using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), CO pulse-chemisorption and X-ray diffraction (XRD). Controlling the atomic arrangement of the Pt-Co nanoparticles, superior catalytic activity for the HOR and ORR was achieved compared to commercially available Pt/C. Based on our results, we provide very promising pathways to tailor physical and electrochemical properties of the Pt-M alloy nanoparticles to boost the HOR and ORR activities for the PEM fuel cell. References: [1] H. A. Gasteiger, S. S. Kocha, B. Sompalli, and F. T. Wagner, Appl. Catal. B Environ. , 56 , 9–35 (2005) [2] Landsmann, D.A., Luczak, F.J., Handbook of Fuel Cells, vol. 4, Wiley, 2003, p.811 (Chapter 60). [3] V. Jalan and E. J. Taylor, J. Electrochem. Soc. , 130 , 2299–2302 (1983) [4] M. T. Paffett, J. G. Beery, and S. Gottesfeld, J. Electrochem. Soc. , 135 , 1431–1436 (1988) [5] F. Hasché, M. Oezaslan, and P. Strasser, J. Electrochem. Soc. , 159 , B24–B33 (2011). [6] M. Oezaslan and P. Strasser, J. Power Sources , 196 , 5240–5249 (2011) [7] M. Oezaslan, F. Hasché, and P. Strasser, J. Electrochem. Soc. , 159 , B444–B454 (2012)