Unraveling Fundamental Descriptors for the Structural and Morphological Degradation of Pt Nanoparticles on Indium Tin Oxide Using in Situ Techniques

Abstract

Enhancing stability of cathode catalysts for PEMFC applications under operating conditions is of great importance because state-of-art supports for nanoparticular Pt electrocatalysts suffer from carbon corrosion especially during start-stop procedure. Metal oxides have been proven to be viable alternatives because of their corrosion resistance and observed strong metal support interaction which is thought to enhance activity as well as stability of the catalyst [1-3]. Tin-based oxides excel by their thermal stability as well as high conductivity and are therefore promising candidates as alternative fuel cell support materials [4]. But the structural evolution of Pt-based nanoparticles under electrochemical conditions on oxides is still unknown. On high surface area carbon it has been shown by using in-situ SAXS studies that Pt nanoparticles grow due to Ostwald ripening and a dissolution/redeposition mechanism decreasing the electrochemical active surface area (ECSA) [5]. Here, we report on metal oxide supported Pt nanoparticles focussing on the structural evolution under electrochemical potential cycling applied to mimic fuel cell operating conditions. The Pt nanoparticles were synthesized using a solvothermal route and deposited on Indium Tin Oxide (ITO) resulting in homogenously distributed particles with well defined size. The electrocatalysts were extensively tested with respect to long-term electrochemical stability in order to investigate its potential as alternative carbon-free support material. We determined the evolution of crystal structure, composition, crystallite size and particle size distribution of the oxide support and the Pt nanoparticles by using in situ XRD and ASAXS. Additionally, we were able to follow the dissolution of the catalyst components during the electrochemical protocol using SFC ICP-MS setup. We can show that in case of ITO the size of Pt nanoparticles increases only slightly, whereas the mass-based catalytic activity decreases primarily due to changes of the support. Furthermore, our results show that we are able to unravel fundamental aspects of morphological degradation of Pt nanoparticles on non-carbon supports under electrochemical conditions. These results will help to understand stability determining properties of oxide supports leading to enhanced cathode electrocatalysts for a PEMFC. [1] A. Kumar, V. Ramani, J. Electrochem. Soc. 2013, 160, F1207-F15. [2] A. Lewera, L. Timperman, A. Roguska, N. Alonso-Vante, J. Phys. Chem. C 2011, 115, 20153-59. [3] T.T.H. Van, C.J. Pan, J. Rick, W.N. Su, B.J. Hwang, J. Am. Chem. Soc. 2011, 133, 11716-24. [4] H.-S. Oh, H.N. Nong, P. Strasser, Adv. Funct. Mater. 2015, 25, 1074-81. [5] X. Tuaev, S. Rudi, V. Petkov, A. Hoell, P. Strasser, Acs Nano 2013, 7, 5666-74.