Bimetallic electrocatalyst and magnetically improved oxygen reduction reaction in PEFC

NORES PONDAL, FEDERICO J.; GUILLET, NICOLAS; FRANCO, ALEJANDRO A.

Montreal

Conferencia; 219th ECS Meeting; 2011

Electrochemical Society

Bimetallic electrocatalyst and magnetically improved oxygen reduction reaction in PEFC Federico J. Nores-Pondal, Nicolas Guillet, Alejandro A. Franco. Laboratoire de Composants pour les Piles à Combustible  et Electrolyseurs, et de Modélisation (LCPEM)/ DEHT/ LITEN/ DRT/  Commissariat à l’Energie Atomique (CEA)  17, Rue des Martyrs - 38054 Grenoble Cedex 9 (France) e-mail: federico.nores-pondal@cea.fr                 Polymer electrolyte fuel cells (PEFCs) have long been touted as clean and efficient alternatives to traditional power sources such as combustion engines and batteries. Some key points for the development and commercial viability of PEFCs are the cost and the performance of the Membrane-Electrode assembly (MEA).                 Recent international efforts allowed a clear reduction in the MEA platinum content without significant performance losses, but one of the main performance limitations remain related to the sluggish kinetics of oxygen reduction reaction (ORR). A direct and intrinsic way to improve ORR kinetics is the development of more active electrocatalysts, which is essential for widespread adoption of PEFCs technology (1). However, another recent and promising way is the improvement of the ORR by the presence of a magnetic field which favours the diffusion of oxygen to the cathode by means of the Kelvin force (2, 3).                 In the present work both strategies were addressed, first, new catalysts for ORR and hydrogen oxidation reaction (HOR) were developed, and secondly, some preliminary studies of the effect of a magnetic field on the ORR were performed. Pt (HOR) and Pt:Co (75:25 at.%) (ORR) catalysts supported on carbon Vulcan XC-72R were synthesized by liquid phase chemical methods. Structural and electrochemical characterizations of the prepared nanoparticles were performed. The former included transmission electron microscopy (TEM), X-ray powder diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS); and the later consisted in performance evaluation in half and single PEFCs of an MEA entirely made with the catalysts synthesized in this work. Evaluation of the magnetic field effect on the ORR was performed by applying an external magnetic field gradient in the half-PEFC configuration and by introducing magnetic microparticles in the electrodes of a PEFC. An optimized distribution of magnetized particles in the electrode has been proposed by the CEA/LCPEM multiscale kinetic model “MEMEPhys” (4, 5), and was used as a guide for preparing the magnetic electrodes.                 Results obtained were promising, the catalysts synthesized achieved performances similar to commercial ones (~ 1 gPt/kW). The chemical methods used have proved to be simple, low temperature and low cost methods to produce highly active electrocatalysts. The improvement of the ORR in the presence of an external magnetic field was confirmed, as can be observed for the higher ORR currents in Figure 1, while the first preliminary tests in full cells with magnetic microparticles showed no improvement. This poor performance of the particles was attributed to their corrosion in the acidic environment of PEFC electrode. A proper protection of the magnetic microparticles against corrosion, remains a key challenge for an improved ORR using magnetically modified electrodes. This constitutes the current strategy followed in this work and experiments are being carried out to find the most suitable anticorrosive protection. Figure 1: Chronoamperometry tests at different potentials, performed on an MEA in a half Fuel-Cell configuration, with (solid line) and without (dash line) the presence of an external magnetic field gradient, built by a permanent magnet (0.4 T) placed beside the MEA. In all cases the initial quantity of oxygen is the same and is consumed along the time, reaching a near zero current at the end of experiment. References: 1. F. J. Nores-Pondal, I.M. J. Vilella, H. Troiani, M. Granada, S. R. de Miguel, O. A. Scelza and H. R. Corti, Int. J. Hydrgen Energy, 34, 8193 (2009). 2. T. Okada, N.I. Wakayama, L. Wang, H. Shingu and J. Okano, T. Ozawa, Electrochim. Acta, 48, 531 (2003). 3. D. C. Dunwoody, W. L. Gellett and J. Leddy, Abstract presented to the 207th ECS Meeting (2006). 4. A.A. Franco, C. Nayoze, C. Roux and D. Marsacq, international patent no. FR 2848341 A1 20040611 (French) WO 200454018 A1 20040624 (French), (2002). 5. A.A. Franco, P. Schott, C. Jallut and B. Maschke, Fuel Cells, 7, 99 (2007).