ORALS

SESSION: ElectrochemistryWedPM1-R2	Amatore International Symposium on Electrochemistry for Sustainable Development
Wed Nov, 7 2018 / Room: Copacabana B (150/1st)
Session Chairs: Dongping Zhan; Session Monitor: TBA

15:15: [ElectrochemistryWedPM108]
Electrochemical Impedance Analysis of Oxygen Reduction Reaction Kinetics in HTPEMFCs
Panagiotis Giotakos¹ ; Stylianos G. Neophytides¹ ; ¹FORTH ICE-HT, University of Patras, Patras, Greece;
Paper Id: 396 [Abstract]

Even though Oxygen Reduction Reaction, (ORR), kinetics have been studied by many authors over several decades, [1-3], the electrochemical mechanism still remains an open subject of debate and research. Elucidating ORR kinetics is of paramount importance in advancing Fuel Cell technology, which in turn will result in faster commercialization and robust applications for a greener future. In this work we propose a microkinetic transition state multistep reaction mechanism for ORR which takes place inside the cathodic electrode of a High Temperature Polymer Electrolyte Fuel Cell, (HTPEMFC). ORR kinetics are analyzed by the means of Electrochemical Impedance Spectroscopy, (EIS), in the kinetic low current density, (lcd), regime of operation where ORR activation power losses are dominant. The corresponding impedance spectra contain a linear high frequency part feature and two arcs depending on the double layer capacitance, (Cdl), value. This high frequency linear part of the spectrum originates from the finite ionic, (H+), resistance in the catalyst layer. The high frequency arc, under which all charge transfer reaction steps appear, is directly related to the Cdl of the electrochemical interface, (EI), while the low frequency arc stems from the relaxation of the adsorbed surface reaction intermediates on the catalyst surface, which is caused by the depletion of OHad on the surface. Our proposed kinetic model provides two Tafel slopes in the low and high current density (hcd) regime equal to 60 (mV/dec) and 180 (mV/dec) respectively.

References:
[1] N.M. Markovic, T.J. Schmidt, V. Stamenkovic, P.N. Ross, Oxygen Reduction Reaction on Pt and Pt Bimetallic Surfaces: A Selective Review, Fuel Cells. 1 (n.d.) 105-116. doi:10.1002/1615-6854(200107)1:2<105::AID-FUCE105>3.0.CO;2-9.
[2] J.X. Wang, F.A. Uribe, T.E. Springer, J. Zhang, R.R. Adzic, Intrinsic kinetic equation for oxygen reduction reaction in acidic media: the double Tafel slope and fuel cell applications, Faraday Discuss. 140 (2008) 347-362; discussion 417-437. doi:10.1039/B802218F.
[3]J.A. Keith, G. Jerkiewicz, T. Jacob, Theoretical Investigations of the Oxygen Reduction Reaction on Pt(111), ChemPhysChem. 11 (2010) 2779-794. doi:10.1002/cphc.201000286