Pegis Michael L, Roberts John A S, Wasylenko Derek J, Mader Elizabeth A, Appel Aaron M, Mayer James M
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.
Inorg Chem. 2015 Dec 21;54(24):11883-8. doi: 10.1021/acs.inorgchem.5b02136. Epub 2015 Dec 7.
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.
多种下一代能源过程利用氧气和水的电化学相互转化作为氧还原反应（ORR）和析氧反应（OER）。本文报道了在有机溶剂中O2 + 4e(-) + 4H(+) ⇋ 2H2O电对标准还原电位的首次估算值。在乙腈（MeCN）中该值为 +1.21 V，在N，N - 二甲基甲酰胺（DMF）中为 +0.60 V，均相对于各自溶剂中的二茂铁鎓/二茂铁电对（Fc(+/0)）（本文报道的所有电位均如此）。这些电位是通过一个热化学循环测定的，该循环结合了将水从水溶液转移到有机溶剂中的自由能，在MeCN中为 -0.43 kcal mol(-1)，在DMF中为 -1.47 kcal mol(-1)，以及H(+)/H2电对的电位，在MeCN中为 - 0.028 V，在DMF中为 -0.662 V。DMF中的H(+)/H2电对已使用先前报道的测定MeCN值的方法进行了电化学直接测量。用于O2/H2O电对的热化学方法已扩展到CO2/CO和CO2/CH4电对，在MeCN中分别得到 -0.12和 +0.15 V的值，在DMF中分别为 -0.73和 -0.48 V。讨论了对其他还原电位的扩展。此外，质子从水转移到有机溶剂的自由能在乙腈中估计为 +14 kcal mol(-1)，在DMF中为 +0.6 kcal mol(-1)。
