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Title: Insights into proton-coupled electron transfer mechanisms of electrocatalytic H2 oxidation and production

Abstract

The design of molecular electrocatalysts for H2 oxidation and production is important for the development of alternative renewable energy sources that are abundant, inexpensive, and environmentally benign. Recently nickel-based molecular electrocatalysts with pendant amines that act as proton relays for the nickel center were shown to effectively catalyze H2 oxidation and production. We developed a quantum mechanical approach for studying proton-coupled electron transfer processes in these types of molecular electrocatalysts. This theoretical approach is applied to a nickel-based catalyst in which phosphorous atoms are directly bonded to the nickel center and nitrogen atoms of the ligand rings act as proton relays. The cataly c step of interest involves electron transfer between the nickel complex and the electrode as well as intramolecular proton transfer between the nickel and nitrogen atoms. This process can occur sequentially, with either the electron or proton transferring first, or concertedly, with the electron and proton transferring simultaneously without a stable intermediate. The heterogeneous rate constants are calculated as functions of overpotential for the concerted electron-proton transfer reaction and the two electron transfer reactions in the sequential mechanisms. Our calculations illustrate that the concerted electron-proton transfer standard rate constant will increase as the equilibrium distance between themore » nickel and nitrogen atoms decreases and as the nitrogen atoms become more mobile to facilitate the contraction of this distance. This approach assists in the identification of the favored mechanisms under various experimental conditions and provides insight into the qualitative impact of substituents on the nitrogen and phosphorous atoms. This research was supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under FWP 56073.« less

Authors:
 [1];  [1];  [1];  [1]
  1. Pennsylvania State Univ., University Park, PA (United States)
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1054440
Report Number(s):
PNNL-SA-84797
Journal ID: ISSN 0027-8424; KC0307010
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Volume: 109; Journal Issue: 39; Journal ID: ISSN 0027-8424
Publisher:
National Academy of Sciences, Washington, DC (United States)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; hydrogen evolution; heterogeneous catalysis; PCET

Citation Formats

Horvath, S., Fernandez, L. E., Soudackov, A. V., and Hammes-Schiffer, S. Insights into proton-coupled electron transfer mechanisms of electrocatalytic H2 oxidation and production. United States: N. p., 2012. Web. doi:10.1073/pnas.1118333109.
Horvath, S., Fernandez, L. E., Soudackov, A. V., & Hammes-Schiffer, S. Insights into proton-coupled electron transfer mechanisms of electrocatalytic H2 oxidation and production. United States. doi:10.1073/pnas.1118333109.
Horvath, S., Fernandez, L. E., Soudackov, A. V., and Hammes-Schiffer, S. Mon . "Insights into proton-coupled electron transfer mechanisms of electrocatalytic H2 oxidation and production". United States. doi:10.1073/pnas.1118333109.
@article{osti_1054440,
title = {Insights into proton-coupled electron transfer mechanisms of electrocatalytic H2 oxidation and production},
author = {Horvath, S. and Fernandez, L. E. and Soudackov, A. V. and Hammes-Schiffer, S.},
abstractNote = {The design of molecular electrocatalysts for H2 oxidation and production is important for the development of alternative renewable energy sources that are abundant, inexpensive, and environmentally benign. Recently nickel-based molecular electrocatalysts with pendant amines that act as proton relays for the nickel center were shown to effectively catalyze H2 oxidation and production. We developed a quantum mechanical approach for studying proton-coupled electron transfer processes in these types of molecular electrocatalysts. This theoretical approach is applied to a nickel-based catalyst in which phosphorous atoms are directly bonded to the nickel center and nitrogen atoms of the ligand rings act as proton relays. The cataly c step of interest involves electron transfer between the nickel complex and the electrode as well as intramolecular proton transfer between the nickel and nitrogen atoms. This process can occur sequentially, with either the electron or proton transferring first, or concertedly, with the electron and proton transferring simultaneously without a stable intermediate. The heterogeneous rate constants are calculated as functions of overpotential for the concerted electron-proton transfer reaction and the two electron transfer reactions in the sequential mechanisms. Our calculations illustrate that the concerted electron-proton transfer standard rate constant will increase as the equilibrium distance between the nickel and nitrogen atoms decreases and as the nitrogen atoms become more mobile to facilitate the contraction of this distance. This approach assists in the identification of the favored mechanisms under various experimental conditions and provides insight into the qualitative impact of substituents on the nitrogen and phosphorous atoms. This research was supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under FWP 56073.},
doi = {10.1073/pnas.1118333109},
journal = {Proceedings of the National Academy of Sciences of the United States of America},
issn = {0027-8424},
number = 39,
volume = 109,
place = {United States},
year = {2012},
month = {4}
}