A Controllable Synthesis of Pt-Based Electrocatalyst for the Oxygen Reduction Reaction of PEMFC with High Pt Utilization

Abstract

Proton exchange membrane fuel cells (PEMFCs) are characterized with many advantages including high power density, low operating temperature (~80 oC), quick start-up and quick match to shifting demands for power, and regarded as a very promising technology for powering transportation and stationary applications1. However, the kinetics of the cathodic oxygen reduction reaction (ORR) in PEMFCs is sluggish and the most efficient material is platinum (Pt) that is rare on the earth and has a prohibitive cost. To make PEMFCs economically available, it is imperative to maximize the utilization of Pt or rather noble metal by improving catalyst layer’s mass transport of reactants and products, and by increasing noble-metal-mass activities toward the ORR in cathode. One of the strategies to improve mass transport in cathode is to thin the catalyst layer through developing high-content and high-dispersion Pt electrocatalysts. However, it is difficult to prepare Pt supported catalysts with a high Pt content because of the agglomeration of Pt nanoparticles. It was reported that the commercial Pt/VC catalysts had a particle size of 2.0 nm in Pt(10 wt%)/VC, 3.2 nm in Pt(30 wt%)/VC, and 8.8 nm in Pt(60 wt%)/VC2. Although great efforts have been made to improve traditional methods, such as impregnation method and colloidal method, it remains very challenging to find an economical and controllable way to synthesize Pt/VC electrocatalysts with a high Pt content for the ORR in PEMFCs. This can be attributed to several facts, including the poor size control, the contaminants from stabilizer residue, tedious procedures and so on. In this work, we propose a simple and controllable approach to deposit highly-dispersed Pt nanoparticles on Vulcan XC-72 carbon black. The as-synthesized Pt/VC possesses a high Pt content as well as high-dispersion Pt NPs via controlling the nucleation and growth process, and was investigated as the cathodic catalyst in PEMFC. Ideally highest Pt utilization with an extraordinary Pt-mass activity has been achieved by the Pt-monolayer-shell electrocatalysts which possess monoatomic thick Pt shells on noble-metal substrates3. However, the noble-metal-mass activities for these Pt-monolayer-shell electrocatalysts were also compromised, since the noble-metal substrates are quite essential for fabricating such electrocatalysts. In this regard, with the highest Pt utilization, improving the non-Pt noble-metal utilization in the substrates is critical for developing the Pt-monolayer-shell electrocatalysts. In this work, a surfactant-based, composition- and size-tunable method has been demonstrated to synthesize the monodispersed Pd-Ni as the substrates for fabricating the carbon-supported Pd-Ni@Pt nanospheres with Pt monolayer shells. And an excellent balance among activity, durability and noble-metal utilization was acquired. Acknowledgements This work was supported in part by National Natural Science Foundation of China (Grant No. 21373135 and 21533005) and Science Foundation of Ministry of Education of China ( Grant No. 413064). Reference 1. M.L. Perry, F.T. Fuller, J Electrochem Soc, 149 S59-S67 (2002). 2. B. L. Gratiet, H. Remita, G. Picq, M. Delcourt, J Catal, 164, 36 (1996). 3. (a) J. Zhang, M. B. Vukmirovic, Y. Xu, M. Mavrikakis, R. R. Adzic, Angewandte Chemie International Edition, 44 2132-2135, (2005); (b) M. Shao, K. Shoemaker, A. Peles, K. Kaneko, L. Protsailo, J Am Chem Soc, 132 9253-9255, (2010). (c) J. X. Wang, H. Inada, L. Wu, Y. Zhu, Y. Choi, P. Liu, W. P. Zhou, R. R. Adzic, J Am Chem Soc, 131,17298( 2009) .