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Title: Graphite-Conjugated Acids Reveal a Molecular Framework for Proton-Coupled Electron Transfer at Electrode Surfaces

Abstract

Proton-coupled electron-transfer (PCET) steps play a key role in energy conversion reactions. Molecular PCET reactions are well-described by “square schemes” in which the overall thermochemistry of the reaction is broken into its constituent proton-transfer and electron-transfer components. Although this description has been essential for understanding molecular PCET, no such framework exists for PCET reactions that take place at electrode surfaces. Herein, we develop a molecular square scheme framework for interfacial PCET by investigating the electrochemistry of molecularly well-defined acid/base sites conjugated to graphitic electrodes. Using cyclic voltammetry, we first demonstrate that, irrespective of the redox properties of the corresponding molecular analogue, proton transfer to graphite-conjugated acid/base sites is coupled to electron transfer. We then show that the thermochemistry of surface PCET events can be described by the pKa of the molecular analogue and the potential of zero free charge (zero-field reduction potential) of the electrode. Finally, this work provides a general framework for analyzing and predicting the thermochemistry of interfacial PCET reactions.

Authors:
 [1]; ORCiD logo [1]; ORCiD logo [1]
  1. Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
Publication Date:
Research Org.:
Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
OSTI Identifier:
1510160
Alternate Identifier(s):
OSTI ID: 1515187
Grant/Contract Number:  
SC0014176
Resource Type:
Published Article
Journal Name:
ACS Central Science
Additional Journal Information:
Journal Name: ACS Central Science; Journal ID: ISSN 2374-7943
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Jackson, Megan N., Pegis, Michael L., and Surendranath, Yogesh. Graphite-Conjugated Acids Reveal a Molecular Framework for Proton-Coupled Electron Transfer at Electrode Surfaces. United States: N. p., 2019. Web. doi:10.1021/acscentsci.9b00114.
Jackson, Megan N., Pegis, Michael L., & Surendranath, Yogesh. Graphite-Conjugated Acids Reveal a Molecular Framework for Proton-Coupled Electron Transfer at Electrode Surfaces. United States. doi:10.1021/acscentsci.9b00114.
Jackson, Megan N., Pegis, Michael L., and Surendranath, Yogesh. Wed . "Graphite-Conjugated Acids Reveal a Molecular Framework for Proton-Coupled Electron Transfer at Electrode Surfaces". United States. doi:10.1021/acscentsci.9b00114.
@article{osti_1510160,
title = {Graphite-Conjugated Acids Reveal a Molecular Framework for Proton-Coupled Electron Transfer at Electrode Surfaces},
author = {Jackson, Megan N. and Pegis, Michael L. and Surendranath, Yogesh},
abstractNote = {Proton-coupled electron-transfer (PCET) steps play a key role in energy conversion reactions. Molecular PCET reactions are well-described by “square schemes” in which the overall thermochemistry of the reaction is broken into its constituent proton-transfer and electron-transfer components. Although this description has been essential for understanding molecular PCET, no such framework exists for PCET reactions that take place at electrode surfaces. Herein, we develop a molecular square scheme framework for interfacial PCET by investigating the electrochemistry of molecularly well-defined acid/base sites conjugated to graphitic electrodes. Using cyclic voltammetry, we first demonstrate that, irrespective of the redox properties of the corresponding molecular analogue, proton transfer to graphite-conjugated acid/base sites is coupled to electron transfer. We then show that the thermochemistry of surface PCET events can be described by the pKa of the molecular analogue and the potential of zero free charge (zero-field reduction potential) of the electrode. Finally, this work provides a general framework for analyzing and predicting the thermochemistry of interfacial PCET reactions.},
doi = {10.1021/acscentsci.9b00114},
journal = {ACS Central Science},
number = ,
volume = ,
place = {United States},
year = {2019},
month = {5}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
DOI: 10.1021/acscentsci.9b00114

Citation Metrics:
Cited by: 7 works
Citation information provided by
Web of Science

Figures / Tables:

Figure 1 Figure 1: (a) Partial square scheme for the molecular proton-coupled electron-transfer (PCET) reaction M−B +H+ + e→M−BH+. The horizontal leg represents the thermochemistry of the proton-transfer step, determined by the p$K$a of the proton acceptor and the pH of the solution. The vertical leg represents the thermochemistry of the electron-transfermore » step, determined by the reduction potential of the protonated molecule, M−BH+, in the absence of proton transfer. The diagonal represents the thermochemistry of the overall reaction, which is the sum of the two legs. (b) Partial square scheme for PCET at a GCC−COOH site. The p$K$a in the horizontal leg is taken as that of a molecular phenazine analogue, and the vertical leg is grayed out because the parameter defining it was unknown prior to this work. (c) Partial square scheme for a PCET reaction to form a bond at a Pt surface. The horizontal and vertical legs of the scheme defining these legs were unknown prior to this work.« less

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