Effects of media and electrode materials on the electrochemical reduction of dioxygen

Abstract

Cycllc voltammetry has been used to measure the extent of superoxlde Ion solvatlon (and consequent shift In the redox potentlal for the 02/02-couple) In acetonltrlle, dlmethylformamlde, pyridine, and dlmethyl sulfoxide. A parallel study of the reverslblllty of the 02/01 couple as a function of electrode materlal has been made for platinum, gold, mercury, and glassy carbon In acetonltrlle. The results Indicate that surface Interactions between superoxide Ion and metal-electrode surfaces occur. Additional studies of the reductlon of oxygenIn the presence of protic substrates and metal salts confirm that Lewis aclds promote the disproportkmatlon of superoxide Ion. I n the presence of electrophlles (e.g., CCI, and esters) the reduction current for dioxygen Is enhanced because of rapid nucleophlllc reactlons by 4-, which result In regeneration of 02.Although the electrochemical reduction of dioxygen to superoxide ion in aprotic solvents has been known since 1965 (1-5), the effects of media and electrode material have not been addressed in any systematic study. An early study (6) established that activated metal electrodes in aqueous media catalyze the reduction of O2 to water at a reduction potential characteristic of the particular metal. In contrast, at passivated metal electrodes the reduction of 02, which is independent of electrode material and pH, yields H202 via a one-electron mechanism with facile disproportionation of the 0,-intermediate (7). Three recent reviews discuss the redox chemistry and electrochemistry of dioxygen (8-10).The general view has been that the electrochemistry of O2 in aprotic media also is independent of media and electrode materials, and that only protic contaminants promote the rapid disproportionation of the 02-product to H202 and 0 2 . For a test of this conclusion the present study has been undertaken to compare the effects of various media and electrode materials on the reduction potential, reversibility, and overall electron stoichiometry for the cyclic voltammetry of dioxygen. EXPERIMENTAL SECTIONInstrumentation. The cyclic voltammetric measurements were made with either a Princeton Applied Research Model 173/ 175/179 potentiostat/universal programmer/electronic integrator or a universal potentiostat/amperostat that was constructed from operational amplifiers (11). The electrochemical cell (Brinkman) included (a) a platinum-foil auxiliary electrode that was isolated from the bulk solution by a glass tube with a medium frit, (b) a Ag/AgCl reference electrode in a glass tube closed with a cracked sofbglaas tip that contained aqueous Me4NCl (concentration was adjusted to obtain a potential of 0.000 V vs. SCE) (12), (c) a luggin capillary that contained the bulk electrolyte solution and the reference electrode (the capillary tip was placed within 1 mm of the working electrode surface), (c) inlet/outlet tubes for gas dispersion in the solution or over its surface, and (d) the working electrode. The latter was either a Beckman Model 39273 platinum-inlay electrode (area, 0.23 cm2) or on...

Experimental and Computational Analysis of the Solvent‐Dependent O2/Li+‐O2− Redox Couple: Standard Potentials, Coupling Strength, and Implications for Lithium–Oxygen Batteries

“…Abraham and co-workers [13,14,18] have suggested that the stability of Li + -O 2 À increases with solvent donor number (DN), which is a measure of the solvation enthalpy of the Lewis acid SbCl 5 in a given solvent . [19] This concept is supported by recent work, [12] which reports that increasing solvent DN leads to increased [20] while the Li + /Li potential decreases with increasing Li + solvation (Figure 1 b). These trends are consistent with reports that the reversible potential of O 2 /TBA…”

“…[23] Figure 1 b and previous work. [20,21] Figure 2 a shows cyclic voltammograms (CVs) obtained in O 2 -saturated dimethylsulfoxide (DMSO), 1,2-dimethoxyethane (DME), acetonitrile (MeCN), and dimethyl acetamide (DMA)-based electrolytes, which contained TBA + and Me 10 Fc. Similar measurements were performed in dimethyl formamide (DMF; Supporting Information, Figure S2).…”

Rotating Ring-Disc Electrode Investigation of the Aprotic Superoxide Radical Electrochemistry on Multi-Crystalline Surfaces and Correlation with Density Functional Theory Modeling: Implications for Lithium-Air Cells

“…3b. This was similar to the potential at which Sawyer et al 39 reported oxidation peaks in the presence of protons (from added HClO 4 ) and also close to the potential at which oxidation peaks were observed with the addition of water. 44 The voltage range from 1.85 V to 4.35 V covered the operating range of Li-air cells wherein the discharge and charge plateaus were found to occur at ∼2.5 V and ∼4 V respectively.…”

Rate Constants of Hydroperoxyl Radical Addition to Cyclic Nitrones: A DFT Study

“…Conventional transition state theory (TST) was utilized to estimate the rates for spin-adduct formation at 298 K. 35 The conventional TST rate equation in the thermodynamic formulation as a function of temperature is as follows: (1) In Equation 1, T is the absolute temperature, h is Planck's constant, k B is Boltzmann constant, and ΔG ≠ 0 is the free energy barrier height relative to reactants at infinite separation. The temperature dependent factor Γ(T) represents quantum mechanical tunneling and is accounted for by the Wigner approximation: 36 (2) in which ν i is the imaginary vibrational frequency representing the TS barrier's curvature.…”

“…6 In vivo rat heart studies show that the ischemic period (a condition by which the tissues or organs are deprived of blood flow) and immediate reperfusion have enhanced oxygen radical production 7,8 and are accompanied by ischemia-induced acidosis. 9 These two processes by which O 2 •-can be generated under acidic conditions may have detrimental consequences, resulting in oxidative damage to cellular systems as HO 2 • is a stronger oxidizer than O 2 •-(E o ′ = 1.06 and 0.94 V, respectively). 5…”