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Published on: February 10, 2021
Nanoscale electrodes by conducting atomic force microscopy: oxygen reduction kinetics at the Ptmid R:CsHSO4 interface
Mary W Louie1, Adrian Hightower, Sossina M Haile
1Department of Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA.
This study quantifies oxygen reduction kinetics at the nanoscale Platinum:Cesium acid sulfate (Pt:CsHSO4) interface using advanced AFM techniques. Results reveal positional variations in reaction rates and a counter-correlation between charge transfer parameters, highlighting nanoscale interface characterization benefits.
Area of Science:
- Electrochemistry
- Materials Science
- Nanotechnology
Background:
- Understanding oxygen reduction reaction (ORR) kinetics is crucial for electrochemical devices.
- Nanoscale interfaces present unique electrochemical behaviors compared to macroscale systems.
- Characterizing ORR at the Pt:CsHSO4 interface informs catalyst and electrolyte design.
Purpose of the Study:
- To quantitatively characterize ORR kinetics at the nanoscale Pt:CsHSO4 interface.
- To investigate the influence of overpotential on ORR processes.
- To explore the spatial variability of ORR kinetics across the interface.
Main Methods:
- Conducting atomic force microscopy (AFM) combined with AC impedance spectroscopy and cyclic voltammetry.
- Nanoscale electrochemical measurements at approximately 150°C in humidified air.
- Analysis using the Butler-Volmer framework to determine charge transfer parameters.
Main Results:
- ORR at the Pt:CsHSO4 interface involves two distinct processes, one exponentially and one weakly dependent on overpotential.
- Interfacial processes exhibit near-ideal capacitive behavior, indicative of nanoscale effects.
- Significant spatial variations in ORR kinetics were observed across the electrolyte surface.
- Charge transfer analysis revealed exchange coefficients (α) from 0.1 to 0.6 and exchange currents (i0) spanning five orders of magnitude.
- A counter-correlation between exchange current and exchange coefficient was identified.
Conclusions:
- Nanoscale AFM provides rigorous separation of electrochemical processes, absent in macroscale measurements.
- The observed counter-correlation suggests a relationship between activation barrier magnitude and its change under bias.
- Conducting AFM is suitable for comprehensive studies of electrochemical reactions at electrolyte-metal-gas interfaces.
