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Title: Elucidating the Dynamic Nature of Fuel Cell Electrodes as a Function of Conditioning: An ex Situ Material Characterization and in Situ Electrochemical Diagnostic Study

Abstract

To increase the commercialization of fuel cell electric vehicles, it is imperative to improve the activity and performance of electrocatalysts through combined efforts focused on material characterization and device-level integration. Obtaining fundamental insights into the ongoing structural and compositional changes of electrocatalysts is crucial for not only transitioning an electrode from its as-prepared to functional state, also known as 'conditioning', but also for establishing intrinsic electrochemical performances. Here, we investigated several oxygen reduction reaction (ORR) electrocatalysts via in situ and ex situ characterization techniques to provide fundamental insights into the interfacial phenomena that enable peak ORR mass activity and high current density performance. A mechanistic understanding of a fuel cell conditioning procedure is described, which encompasses voltage cycling and subsequent voltage recovery (VR) steps at low potential. In particular, ex situ membrane electrode assembly characterization using transmission electron microscopy and ultra-small angle X-ray scattering were performed to determine changes in carbon and Pt particle size and morphology, while in situ electrochemical diagnostics were performed either during or after specific points in the testing protocol to determine the electrochemical and interfacial changes occurring on the catalyst surface responsible for oxygen transport resistances through ionomer films. The results demonstrate that the voltagemore » cycling (break-in) step aids in the removal of sulfate and fluoride and concomitantly reduces non-Fickian oxygen transport resistances, especially for catalysts where Pt is located within the pores of the carbon support. Subsequent low voltage holds at low temperature and oversaturated conditions, i.e., VR cycles, serve to improve mass activities by a factor of two to three, through a combined removal of contaminants, surface-blocking species (e.g., oxides), and rearrangement of the catalyst atomic structure (e.g., Pt-Pt and Pt-Co coordination).« less

Authors:
ORCiD logo [1];  [2];  [2];  [2];  [1];  [3];  [3];  [3];  [4]; ORCiD logo [1]
  1. National Renewable Energy Lab. (NREL), Golden, CO (United States)
  2. Argonne National Lab. (ANL), Argonne, IL (United States)
  3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
OSTI Identifier:
1578259
Report Number(s):
NREL/JA-5900-74853
Journal ID: ISSN 1944-8244
Grant/Contract Number:  
AC36-08GO28308
Resource Type:
Accepted Manuscript
Journal Name:
ACS Applied Materials and Interfaces
Additional Journal Information:
Journal Volume: 11; Journal Issue: 48; Journal ID: ISSN 1944-8244
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
30 DIRECT ENERGY CONVERSION; fuel cell; electrocatalyst; conditioning; electrochemical diagnostics; kinetics; oxygen transport resistances

Citation Formats

Kabir, Sadia, Myers, Deborah J., Kariuki, Nancy, Park, Jaehyung, Wang, Guanxiong, Baker, Andrew, Macauley, Natalia, Mukundan, Rangachary, More, Karren L., and Neyerlin, Kenneth C. Elucidating the Dynamic Nature of Fuel Cell Electrodes as a Function of Conditioning: An ex Situ Material Characterization and in Situ Electrochemical Diagnostic Study. United States: N. p., 2019. Web. doi:10.1021/acsami.9b11365.
Kabir, Sadia, Myers, Deborah J., Kariuki, Nancy, Park, Jaehyung, Wang, Guanxiong, Baker, Andrew, Macauley, Natalia, Mukundan, Rangachary, More, Karren L., & Neyerlin, Kenneth C. Elucidating the Dynamic Nature of Fuel Cell Electrodes as a Function of Conditioning: An ex Situ Material Characterization and in Situ Electrochemical Diagnostic Study. United States. doi:10.1021/acsami.9b11365.
Kabir, Sadia, Myers, Deborah J., Kariuki, Nancy, Park, Jaehyung, Wang, Guanxiong, Baker, Andrew, Macauley, Natalia, Mukundan, Rangachary, More, Karren L., and Neyerlin, Kenneth C. Wed . "Elucidating the Dynamic Nature of Fuel Cell Electrodes as a Function of Conditioning: An ex Situ Material Characterization and in Situ Electrochemical Diagnostic Study". United States. doi:10.1021/acsami.9b11365.
@article{osti_1578259,
title = {Elucidating the Dynamic Nature of Fuel Cell Electrodes as a Function of Conditioning: An ex Situ Material Characterization and in Situ Electrochemical Diagnostic Study},
author = {Kabir, Sadia and Myers, Deborah J. and Kariuki, Nancy and Park, Jaehyung and Wang, Guanxiong and Baker, Andrew and Macauley, Natalia and Mukundan, Rangachary and More, Karren L. and Neyerlin, Kenneth C.},
abstractNote = {To increase the commercialization of fuel cell electric vehicles, it is imperative to improve the activity and performance of electrocatalysts through combined efforts focused on material characterization and device-level integration. Obtaining fundamental insights into the ongoing structural and compositional changes of electrocatalysts is crucial for not only transitioning an electrode from its as-prepared to functional state, also known as 'conditioning', but also for establishing intrinsic electrochemical performances. Here, we investigated several oxygen reduction reaction (ORR) electrocatalysts via in situ and ex situ characterization techniques to provide fundamental insights into the interfacial phenomena that enable peak ORR mass activity and high current density performance. A mechanistic understanding of a fuel cell conditioning procedure is described, which encompasses voltage cycling and subsequent voltage recovery (VR) steps at low potential. In particular, ex situ membrane electrode assembly characterization using transmission electron microscopy and ultra-small angle X-ray scattering were performed to determine changes in carbon and Pt particle size and morphology, while in situ electrochemical diagnostics were performed either during or after specific points in the testing protocol to determine the electrochemical and interfacial changes occurring on the catalyst surface responsible for oxygen transport resistances through ionomer films. The results demonstrate that the voltage cycling (break-in) step aids in the removal of sulfate and fluoride and concomitantly reduces non-Fickian oxygen transport resistances, especially for catalysts where Pt is located within the pores of the carbon support. Subsequent low voltage holds at low temperature and oversaturated conditions, i.e., VR cycles, serve to improve mass activities by a factor of two to three, through a combined removal of contaminants, surface-blocking species (e.g., oxides), and rearrangement of the catalyst atomic structure (e.g., Pt-Pt and Pt-Co coordination).},
doi = {10.1021/acsami.9b11365},
journal = {ACS Applied Materials and Interfaces},
number = 48,
volume = 11,
place = {United States},
year = {2019},
month = {11}
}

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This content will become publicly available on November 6, 2020
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