On the Activity of Electrospun Tantalum Doped SnO2 for Durable ultra-Low PGM Fuel Cell Cathodes

Abstract

Despite the advances in the development of Proton Exchange Membrane Fuel Cells (PEMFCs), some locks still need to be lifted before they are deployed on a large scale: i) Reduce the amount of platinum group metals (PGM) used in the electrodes by increasing the mass activity of the supported catalyst.ii) Improve durability of the electrodes by replace the conventional carbon support In particular, for the cathode side, carbon blacks (e.g. Vulcan XC-72) are conventionally used as a support materials for Pt and Pt-alloy nanoparticles. These materials exhibit high electric conductivity, controlled chemical properties, and high surface area that are of interest in PEMFCs application as electrocatalyst supports. However, carbon blacks are oxidized at the high voltage experienced at the cathode side (e.g. in stop/start conditions) leading to PEMFC major failure due to support corrosion leading to catalyst particles sintering or detachment [1,2]. Alternative supports based on tin oxide have attracted research interest due to their high corrosion resistance and promotion of activity for oxygen reduction reaction (ORR)[3]. The drawback is their low electrical conductivity, that in this work was tackled by doping with tantalum. Ta-doped SnO2 conducting fibers were synthetized by electrospinning followed by calcination [4] (Figure 1). This support was catalyzed with platinum nanoparticles prepared by a microwave-assisted polyol method and characterized for their physico-chemical and electrocatalytic properties towards ORR. In particular, stability to voltage cycling at high potential was evaluated by ex situ electrochemical analysis. A very significant mass activity of 470 A / gPt has been reached with 7.4wt.% of Pt homogenously deposited onto Ta-doped SnO2 nanofibers [5,6]. In addition, improved electrochemical stability was demonstrated with the retention of 70 % of the mass activity up to 10000 cycles from 1 to 1.6 V/RHE. Figure 1: SEM micrograph of 1%at. Ta-doped SnO2 nanofibers. References C. Meier, C. Galeano, I. Katsounaros, A. a. Topalov, A. Kostka, F. Schüth, K. J. J. Mayrhofer, ACS Catal. 2012, 2, 832–843. Yu, H. Li, H. Wang, X.-Z. Yuan, G. Wang, M. Pan, J. Power Sources 2012, 205, 10–23. Savych, S. Subianto, Y. Nabil, S. Cavaliere, D. Jones and J. Rozière, Chem. Chem. Phys. 2015, 17, 16970-16976 . Cavaliere, I. Jiménez-Morales, G. Ercolano, I. Savych, D. Jones and J. Rozière, ChemElectroChem 2015, 2, 1966-1973. Senoo, K. Taniguchi, K. Kakinuma, M. Uchida, H. Uchida, S. Deki, and M. Watanabe, ElectroChem. Commun. 2015, 51, 37–40. Jiménez-Morales, S. Cavaliere, D. Jones, and J. Rozière, Phys. Chem. Chem. Phys. 2018, 20, 8765–8772 . Figure 1