Standard Reduction Potentials for Oxygen and Carbon Dioxide Couples in Acetonitrile and N,N‑Dimethylformamide

Standard Reduction Potentials for Oxygen and Carbon Dioxide Couples in Acetonitrile and N,N‑Dimethylformamide

Michael L. Pegis,† John A. S. Roberts,‡,∥ Derek J. Wasylenko,§,⊥ Elizabeth A. Mader,† Aaron M. Appel,*,‡ and James M. Mayer*,†

† Department of Chemistry, Yale University, PO Box 208107, New Haven, Connecticut 06520-8107, United States ‡ Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, P.O. Box 999 (K2-57), Richland, Washington 99352, United States § Department of Chemistry, University of Washington, Campus Box 351700, Seattle, Washington 98195-1700, United States

Inorg. Chem. DOI: 10.1021/acs.inorgchem.5b02136

Abstract:

A variety of next-generation energy processes utilize the electrochemical interconversions of dioxygen and water as the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). Reported here are the first estimates of the standard reduction potential of the O2 + 4e − + 4H+ ⇋ 2H2O couple in organic solvents. The values are +1.21 V in acetonitrile (MeCN) and +0.60 V in N,N-dimethylformamide (DMF), each versus the ferrocenium/ferrocene couple (Fc+/0) in the respective solvent (as are all of the potentials reported here). The potentials have been determined using a thermochemical cycle that combines the free energy for transferring water from aqueous solution to organic solvent, −0.43 kcal mol−1 for MeCN and −1.47 kcal mol−1 for DMF, and the potential of the H+ /H2 couple, − 0.028 V in MeCN and −0.662 V in DMF. The H+ /H2 couple in DMF has been directly measured electrochemically using the previously reported procedure for the MeCN value. The thermochemical approach used for the O2/H2O couple has been extended to the CO2/CO and CO2/CH4 couples to give values of −0.12 and +0.15 V in MeCN and −0.73 and −0.48 V in DMF, respectively. Extensions to other reduction potentials are discussed. Additionally, the free energy for transfer of protons from water to organic solvent is estimated as +14 kcal mol−1 for acetonitrile and +0.6 kcal mol−1 for DMF.

TOC:

The importance of being together; Coordination Number and effect on Catalysis

http://www.sciencemag.org/content/350/6257/164.summary

 

Science 9 October 2015:
Vol. 350 no. 6257 pp. 164-165
DOI: 10.1126/science.aad3716

• Perspective

Catalysis

The importance of being together

1. Ifan E. L. Stephens1,2,
2. Joseph S. Elias1,
3. Yang Shao-Horn*,1

+ Author Affiliations

1. ¹Electrochemical Energy Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
2. ²Department of Physics, Technical University of Denmark, DK-2800 Lyngy, Denmark.

Platinum catalyzes several chemical and electrochemical reactions that are central to humankind's use of energy, such as the electrochemical reduction of molecular oxygen, carbon monoxide oxidation, and the water-gas shift reaction to produce carbon dioxide and hydrogen from carbon monoxide and water. Two reports in the current issue provide insights into which platinum coordination number—defined as the number of nearest neighbors—may provide the highest catalytic activities for these reactions. On page 185, Calle-Vallejo et al. use the concept of generalized coordination numbers to show that concave atomic sites on a platinum single crystal are highly active for oxygen electroreduction (1). On page 189, Ding et al. use spectroscopic techniques to determine what role isolated Pt atoms play in CO oxidation and the water-gas shift reaction (2)