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Title: Mechanisms of Two-Electron and Four-Electron Electrochemical Oxygen Reduction Reactions at Nitrogen-Doped Reduced Graphene Oxide

Abstract

Doped carbon-based systems have been extensively studied over the past decade as active electrocatalysts for both the two-electron (2e ) and four-electron (4e ) oxygen reduction reactions (ORRs). However, the mechanisms for ORR are generally poorly understood. Here, we report an extensive experimental and first-principles theoretical study of the ORR at nitrogen-doped reduced graphene oxide (NrGO). We synthesize three distinct NrGO catalysts and investigate their chemical and structural properties in detail via X-ray photoelectron spectroscopy, infrared and Raman spectroscopies, high-resolution transmission electron microscopy, and thin-film electrical conductivity. ORR experiments include the pH dependences of 2e versus 4e ORR selectivity, ORR onset potentials, Tafel slopes, and H/D kinetic isotope effects. These experiments show very different ORR behavior for the three catalysts, in terms of both selectivity and the underlying mechanism, which proceeds either via coupled proton–electron transfers (CPETs) or non-CPETs. Reasonable structural models developed from density functional theory rationalize this behavior. The key determinant between CPET vs non-CPET mechanisms is the electron density at the Fermi level under operating ORR conditions. Regardless of the reaction mechanism or electrolyte pH, however, we identify the ORR active sites as sp 2 carbons that are located next to oxide regions. This assignmentmore » highlights the importance of oxygen functional groups, while details of (modest) N-doping may still affect the overall catalytic activity, and likely also the selectivity, by modifying the general chemical environment around the active site.« less

Authors:
ORCiD logo [1]; ORCiD logo [2];  [3];  [4]; ORCiD logo [5]; ORCiD logo [6]; ORCiD logo [7];  [8]; ORCiD logo [4]; ORCiD logo [3]; ORCiD logo [2]; ORCiD logo [2]; ORCiD logo [5]
  1. Univ. of California, Berkeley, CA (United States). Dept. of Chemical and Biomolecular Engineering; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Energy Storage and Distributed Resources Division; Kangwon National Univ., Samcheok (Korea). Dept. of Advanced Materials Engineering
  2. Stanford Univ., CA (United States). SUNCAT Center for Interface Science and Catalysis; SLAC National Accelerator Lab., Menlo Park, CA (United States)
  3. Hanyang Univ., Seoul (Korea). Dept. of Organic and Nano Engineering
  4. Sookmyung Women’s Univ., Seoul (Korea). Dept. of Chemical and Biological Engineering
  5. Univ. of California, Berkeley, CA (United States). Dept. of Chemical and Biomolecular Engineering; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Energy Storage and Distributed Resources Division
  6. Korea Advanced Inst. Science and Technology (KAIST), Daejeon (Korea, Republic of)
  7. Korea Research Inst. of Chemistry Technology (KRICT), Daejeon (Korea, Republic of)
  8. Kangwon National Univ., Samcheok (Korea). Dept. of Advanced Materials Engineering
Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
OSTI Identifier:
1605369
Grant/Contract Number:  
AC02-76SF00515; 2016R1A6A1A03013422; 2016R1A6A3A03012382; CBET-1604927
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
ACS Catalysis
Additional Journal Information:
Journal Volume: 10; Journal Issue: 1; Journal ID: ISSN 2155-5435
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; electrocatalysis; oxygen reduction reaction; mechanism; selectivity; pH; kinetic isotope; nitrogen-doped reduced graphene oxide

Citation Formats

Kim, Hyo Won, Bukas, Vanessa J., Park, Hun, Park, Sojung, Diederichsen, Kyle M., Lim, Jinkyu, Cho, Young Hoon, Kim, Juyoung, Kim, Wooyul, Han, Tae Hee, Voss, Johannes, Luntz, Alan C., and McCloskey, Bryan D. Mechanisms of Two-Electron and Four-Electron Electrochemical Oxygen Reduction Reactions at Nitrogen-Doped Reduced Graphene Oxide. United States: N. p., 2019. Web. doi:10.1021/acscatal.9b04106.
Kim, Hyo Won, Bukas, Vanessa J., Park, Hun, Park, Sojung, Diederichsen, Kyle M., Lim, Jinkyu, Cho, Young Hoon, Kim, Juyoung, Kim, Wooyul, Han, Tae Hee, Voss, Johannes, Luntz, Alan C., & McCloskey, Bryan D. Mechanisms of Two-Electron and Four-Electron Electrochemical Oxygen Reduction Reactions at Nitrogen-Doped Reduced Graphene Oxide. United States. https://doi.org/10.1021/acscatal.9b04106
Kim, Hyo Won, Bukas, Vanessa J., Park, Hun, Park, Sojung, Diederichsen, Kyle M., Lim, Jinkyu, Cho, Young Hoon, Kim, Juyoung, Kim, Wooyul, Han, Tae Hee, Voss, Johannes, Luntz, Alan C., and McCloskey, Bryan D. Mon . "Mechanisms of Two-Electron and Four-Electron Electrochemical Oxygen Reduction Reactions at Nitrogen-Doped Reduced Graphene Oxide". United States. https://doi.org/10.1021/acscatal.9b04106. https://www.osti.gov/servlets/purl/1605369.
@article{osti_1605369,
title = {Mechanisms of Two-Electron and Four-Electron Electrochemical Oxygen Reduction Reactions at Nitrogen-Doped Reduced Graphene Oxide},
author = {Kim, Hyo Won and Bukas, Vanessa J. and Park, Hun and Park, Sojung and Diederichsen, Kyle M. and Lim, Jinkyu and Cho, Young Hoon and Kim, Juyoung and Kim, Wooyul and Han, Tae Hee and Voss, Johannes and Luntz, Alan C. and McCloskey, Bryan D.},
abstractNote = {Doped carbon-based systems have been extensively studied over the past decade as active electrocatalysts for both the two-electron (2e–) and four-electron (4e–) oxygen reduction reactions (ORRs). However, the mechanisms for ORR are generally poorly understood. Here, we report an extensive experimental and first-principles theoretical study of the ORR at nitrogen-doped reduced graphene oxide (NrGO). We synthesize three distinct NrGO catalysts and investigate their chemical and structural properties in detail via X-ray photoelectron spectroscopy, infrared and Raman spectroscopies, high-resolution transmission electron microscopy, and thin-film electrical conductivity. ORR experiments include the pH dependences of 2e– versus 4e– ORR selectivity, ORR onset potentials, Tafel slopes, and H/D kinetic isotope effects. These experiments show very different ORR behavior for the three catalysts, in terms of both selectivity and the underlying mechanism, which proceeds either via coupled proton–electron transfers (CPETs) or non-CPETs. Reasonable structural models developed from density functional theory rationalize this behavior. The key determinant between CPET vs non-CPET mechanisms is the electron density at the Fermi level under operating ORR conditions. Regardless of the reaction mechanism or electrolyte pH, however, we identify the ORR active sites as sp2 carbons that are located next to oxide regions. This assignment highlights the importance of oxygen functional groups, while details of (modest) N-doping may still affect the overall catalytic activity, and likely also the selectivity, by modifying the general chemical environment around the active site.},
doi = {10.1021/acscatal.9b04106},
url = {https://www.osti.gov/biblio/1605369}, journal = {ACS Catalysis},
issn = {2155-5435},
number = 1,
volume = 10,
place = {United States},
year = {2019},
month = {11}
}

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