Oxygen Reduction Reaction at Binary and Ternary Nanocatalysts Based on Pt, Ni and Au
Authors: Lankiang Styven , Berndt Johannes , Baranton Stève , Caillard Amaël , Brault Pascal , Coutanceau Christophe 
Published: February 2020

Improving design and/or reducing noble metal content in electrocatalysts for fuel cell electrodes while maintaining and/or increasing proton exchange membrane fuel cell (PEMFC) performance in terms of durability and power density are crucial challenges for PEMFC mass market applications. A possible way consists in combining noble metals (Pt, Pd, Au ...) and non-noble metals for preparing binary and ternary nanocatalysts.

The formation of platinum alloys with transition metals such as Ni, Co, Fe, Cr represents a promising way for improving the activity of Pt-based catalysts [1-3].  Pt based alloys have indeed often demonstrated higher electrocatalytic activity towards ORR than pure platinum.

However, while non-noble metals are interesting from a cost reduction point of view, their presence may involve lower stability of the catalyst than that of pure platinum due to their dissolution [4.5], which leads to a loss of performances in PEMFC. Au addition was proposed to improve durability of the nanocatalysts [6-9].

On the other hand, the atomic structure and morphology [10] also play very important roles in the electrocatalytic efficiency for ORR.

In this context, the present study aims at systematically comparing the catalytic activity and the selectivity towards the ORR of binary and ternary catalysts based on Pt, Ni, Co and Au in order to determine the best atomic ratio for this reaction, in terms of kinetics current density and of number of exchanged electrons per oxygen molecule reduced. For this purpose, monometallic (Pt/C), binary (PtxNi10-x/C and PtxCo10-x/C) and ternary (PtxAuyNiz/C and PtxAuyCoz/C) nanocatalysts supported on carbon Vulcan XC-72 have been first synthesized by a wet chemical method and comprehensively characterized. The morphologies, compositions and structures of the particles were characterized by physical methods (transmission electron microscopy, X-ray diffraction and atomic absorption), whereas metal loadings on the carbon support was determined by thermogravimetric analysis. Electrochemical active surface areas and surface compositions were estimated by cyclic voltammetry. Electrocatalytic activity, selectivity and durability of catalysts were studied by the rotating disc (Figure 1) and rotating ring disc electrodes.

After having determined the best atomic ratios for the different metals, i. e. Pt7Ni3, Pt6Ni2Au2/C and Pt5Ni1.7Au3.3/C, plasma sputtering method was use to prepare alloyed PtxAuyNiz/C and Auy@PtxNiz core-shell electrodes with ultra-low metal loadings (10 µgmetal cm-2). This method is indeed very convenient for controlling the materials loading, composition and structure by controlling the physical parameters of deposition. The electrocatalytic behavior of these different electrode structures was evaluated and compared to that of chemical catalysts.

Acknowledgement:

The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant agreement #325327 (SMARTCat project). 

Reference

[1] M.T. Paffet, J.G. Beery, S. Gottesfeld, J. Electrochem. Soc. 135 (1988) 1431–1436.

[2] C. Wang, M. Chi, D. Li, D. van der Vliet, G. Wang, Q. Lin, J. F. Mitchell, K. L. More, N. M. Markovic, V. R. Stamenkovic, ACS Catal. 1 (2011) 1355–1359.

[3] T. Toda, H. Igarashi, H. Uchida, M. Watanabe, J. Electrochem. Soc. 146 (1999) 3750–3756.

[4] M. Watanabe, K. Tsurumi, T. Mizukami, T. Nakamura, P. Stonehart, J. Electrochem. Soc. 141 (1994) 2659–2668.

[5] C.F. Yu, S. Koh, J.E. Leisch, M.F. Toney, P. Strasser, Faraday Discuss. 140 (2009)

283–296.

[6] D.F. Yancey, E.V. Carino, R.M. Crooks, J. Am. Chem. Soc. 132 (2010) 10988–10989.

[7] J. Zhang, K. Sasaki, E. Sutter, R.R. Adzic, Science 315 (2007) 220–222.

[8] K. Sasaki, H. Naohara, Y. Cai, Y.M. Choi, P. Liu, M.B. Vukmirovic, J.X. Wang, R.R.

Adzic, Angew. Chem. Int. Ed. 49 (2010) 8602–8607.

[9] V. Tripkovic, H.A. Hansen, J. Rossmeisl, Tejs Vegge, Phys. Chem. Chem. Phys. 17 (2015) 11647–11657.

[10] D. Alloyeau, C. Mottet, C. Ricolleau, Nanoalloys, London: Springer-Verlag; 2012.

Figure 1