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Title: Molecular Cobalt Catalysts for O 2 Reduction: Low-Overpotential Production of H 2 O 2 and Comparison with Iron-Based Catalysts

Abstract

A series of mononuclear pseudo-macrocyclic cobalt complexes have been investigated as catalysts for O2 reduction. Each of these complexes, with CoIII/II reduction potentials that span nearly 400 mV, mediate highly selective two- electron reduction of O2 to H2O2 (93–99%) using decamethylferrocene (Fc*) as the reductant and acetic acid as the proton source. Kinetic studies reveal that the rate exhibits a first- order dependence on [Co] and [AcOH], but no dependence on [O2] or [Fc*]. A linear correlation is observed between log(TOF) vs. E1/2(CoIII/II) for the different cobalt complexes (TOF = turnover frequency). The thermodynamic potential for+ O2 reduction to H2O2 was estimated by measuring the H /H2 open-circuit potential under the reaction conditions. This value provides the basis for direct assessment of the thermodynamic efficiency of the different catalysts and shows that H2O2 is formed with overpotentials as low as 90 mV. These results are compared with a recently reported series of Fe-porphyrin complexes, which catalyze four-electron reduction of O2 to H2O. The data show that the TOFs of the Co complexes exhibit a shallower dependence on E1/2(MIII/II) than the Fe complexes. This behavior, which underlies the low overpotential, is rationalized on the basis of the catalytic rate law.

Authors:
 [1]; ORCiD logo [2]; ORCiD logo [2]; ORCiD logo [1]
  1. Department of Chemistry, University of Wisconsin−Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
  2. Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Energy Frontier Research Centers (EFRC) (United States). Center for Molecular Electrocatalysis (CME)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1411919
Report Number(s):
PNNL-SA-129979
Journal ID: ISSN 0002-7863; KC0307010
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of the American Chemical Society; Journal Volume: 139; Journal Issue: 46
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Wang, Yu-Heng, Pegis, Michael L., Mayer, James M., and Stahl, Shannon S. Molecular Cobalt Catalysts for O 2 Reduction: Low-Overpotential Production of H 2 O 2 and Comparison with Iron-Based Catalysts. United States: N. p., 2017. Web. doi:10.1021/jacs.7b09089.
Wang, Yu-Heng, Pegis, Michael L., Mayer, James M., & Stahl, Shannon S. Molecular Cobalt Catalysts for O 2 Reduction: Low-Overpotential Production of H 2 O 2 and Comparison with Iron-Based Catalysts. United States. doi:10.1021/jacs.7b09089.
Wang, Yu-Heng, Pegis, Michael L., Mayer, James M., and Stahl, Shannon S. Tue . "Molecular Cobalt Catalysts for O 2 Reduction: Low-Overpotential Production of H 2 O 2 and Comparison with Iron-Based Catalysts". United States. doi:10.1021/jacs.7b09089.
@article{osti_1411919,
title = {Molecular Cobalt Catalysts for O 2 Reduction: Low-Overpotential Production of H 2 O 2 and Comparison with Iron-Based Catalysts},
author = {Wang, Yu-Heng and Pegis, Michael L. and Mayer, James M. and Stahl, Shannon S.},
abstractNote = {A series of mononuclear pseudo-macrocyclic cobalt complexes have been investigated as catalysts for O2 reduction. Each of these complexes, with CoIII/II reduction potentials that span nearly 400 mV, mediate highly selective two- electron reduction of O2 to H2O2 (93–99%) using decamethylferrocene (Fc*) as the reductant and acetic acid as the proton source. Kinetic studies reveal that the rate exhibits a first- order dependence on [Co] and [AcOH], but no dependence on [O2] or [Fc*]. A linear correlation is observed between log(TOF) vs. E1/2(CoIII/II) for the different cobalt complexes (TOF = turnover frequency). The thermodynamic potential for+ O2 reduction to H2O2 was estimated by measuring the H /H2 open-circuit potential under the reaction conditions. This value provides the basis for direct assessment of the thermodynamic efficiency of the different catalysts and shows that H2O2 is formed with overpotentials as low as 90 mV. These results are compared with a recently reported series of Fe-porphyrin complexes, which catalyze four-electron reduction of O2 to H2O. The data show that the TOFs of the Co complexes exhibit a shallower dependence on E1/2(MIII/II) than the Fe complexes. This behavior, which underlies the low overpotential, is rationalized on the basis of the catalytic rate law.},
doi = {10.1021/jacs.7b09089},
journal = {Journal of the American Chemical Society},
number = 46,
volume = 139,
place = {United States},
year = {Tue Nov 07 00:00:00 EST 2017},
month = {Tue Nov 07 00:00:00 EST 2017}
}