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Nanoscale Electrodes by Conducting Atomic Force Microscopy: Oxygen Reduction Kinetics at the Pt|CsHSO_4 Interface

Louie, Mary W. and Hightower, Adrian and Haile, Sossina M. (2010) Nanoscale Electrodes by Conducting Atomic Force Microscopy: Oxygen Reduction Kinetics at the Pt|CsHSO_4 Interface. ACS Nano, 4 (5). pp. 2811-2821. ISSN 1936-086X.

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We quantitatively characterized oxygen reduction kinetics at the nanoscale Pt|CsHSO_4 interface at ~150 °C in humidified air using conducting atomic force microscopy (AFM) in conjunction with AC impedance spectroscopy and cyclic voltammetry. From the impedance measurements, oxygen reduction at Pt|CsHSO_4 was found to comprise two processes, one displaying an exponential dependence on overpotential and the other only weakly dependent on overpotential. Both interfacial processes displayed near-ideal capacitive behavior, indicating a minimal distribution in the associated relaxation time. Such a feature is taken to be characteristic of a nanoscale interface in which spatial averaging effects are absent and, furthermore, allows for the rigorous separation of multiple processes that would otherwise be convoluted in measurements using conventional macroscale electrode geometries. The complete current-voltage characteristics of the Pt|CsHSO_4 interface were measured at various points across the electrolyte surface and reveal a variation of the oxygen reduction kinetics with position. The overpotential-activated process, which dominates at voltages below -1 V, was interpreted as a charge-transfer reaction. Analysis of six different sets of Pt|CsHSO_4 experiments, within the Butler-Volmer framework, yielded exchange coefficients (α) for charge transfer ranging from 0.1 to 0.6 and exchange currents (i_0) spanning 5 orders of magnitude. The observed counter-correlation between the exchange current and exchange coefficient indicates that the extent to which the activation barrier decreases under bias (as reflected in the value of α) depends on the initial magnitude of that barrier under open circuit conditions (as reflected in the value of i_0). The clear correlation across six independent sets of measurements further indicates the suitability of conducting AFM approaches for careful and comprehensive study of electrochemical reactions at electrolyte-metal-gas boundaries.

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Haile, Sossina M.0000-0002-5293-6252
Additional Information:© 2010 American Chemical Society. Received for review January 14, 2010. and accepted April 08, 2010. Published online April 23, 2010. Funding for this project was provided by the Gordon and Betty Moore Foundation through the Caltech Center for Sustainable Energy Research and by the National Science Foundation through the Caltech Center for the Science and Engineering of Materials, a Materials Research Science and Engineering Center (DMR-052056). M.W.L. was supported in part through the NSF Graduate Research Fellowship Program. The authors thank Brian Sayers at Solartron Analytical and Dr. Shijie Wu at Agilent Technologies for assistance with instrumentation.
Funding AgencyGrant Number
Gordon and Betty Moore FoundationUNSPECIFIED
NSF Graduate Research FellowshipUNSPECIFIED
Subject Keywords:solid acid; scanning probe microscopy; microelectrode; impedance spectroscopy; cyclic voltammetry; fuel cells; electrode kinetics
Issue or Number:5
Record Number:CaltechAUTHORS:20100615-105421633
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Official Citation:Nanoscale Electrodes by Conducting Atomic Force Microscopy: Oxygen Reduction Kinetics at the Pt∣CsHSO4 Interface Mary W. Louie, Adrian Hightower, Sossina M. Haile ACS Nano 2010 4 (5), 2811-2821
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:18685
Deposited By: Tony Diaz
Deposited On:09 Jul 2010 21:54
Last Modified:03 Oct 2019 01:46

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