Electrolytic reduction of oxygen

M.E. Poever and B.S. White, Electrolytic reduction of oxygen in aprotic solvents the superoxide ion. Electrochim. Acta. 11, 1061-1067 (1966). 

Peover ME, White BS. Electrolytic reduction of oxygen in aprotic solvents the... 

A novel electrochemical process for the production of alkaline hydrogen peroxide has been developed by Dow. The process employs a monopolar cell to achieve an electrolytic reduction of oxygen in a dilute sodium hydroxide solution. 

The Huron-Dow Process. The Huron-Dow (H-D) process is a refinement of the cathodic reduction of oxygen in an alkaline electrolyte yielding low strength hydrogen peroxide directiy. Earlier attempts reHed on neutralizing the excess caustic or forming insoluble metal peroxides (92). The two reactions involved are... 

Ghromium(II) Compounds. The Cr(II) salts of nonoxidizing mineral acids are prepared by the dissolution of pure electrolytic chromium metal ia a deoxygenated solution of the acid. It is also possible to prepare the simple hydrated salts by reduction of oxygen-free, aqueous Cr(III) solutions using Zn or Zn amalgam, or electrolyticaHy (2,7,12). These methods yield a solution of the blue Cr(H2 0)g cation. The isolated salts are hydrates that are isomorphous with and compounds. Examples are chromous sulfate heptahydrate [7789-05-17, CrSO 7H20, chromous chloride hexahydrate... 

Reduction of oxygen is one of the predominant cathodic reactions contributing to corrosion. Awareness of the importance of the role of oxygen was developed in the 1920s (19). In classical drop experiments, the corrosion of iron or steel by drops of electrolytes was shown to depend on electrochemical action between the central relatively unaerated area, which becomes anodic and suffers attack, and the peripheral aerated portion, which becomes cathodic and remains unattacked. In 1945 the linear relationship between rate of iron corrosion and oxygen pressure from 0—2.5 MPa (0—25 atm) was shown (20). 

Any chemical (such as zinc hydroxide) that suppresses the reduction of oxygen to hydroxyl ion. A cathodic inhibitor suppresses that part of the electrolytic corrosion process at the cathodic sites on a metal surface. 

Vogel WM, Baris JM. 1977. Reduction of oxygen on platinum black in acid electrolytes. Electrochim Acta 22 1259-1263. 

Being thermally decomposed onto the surface of carbon, this complex is expected to form very small catalytically active NiCo204 spinel centers. Thus, we have studied the catalytic activity of the products of pyrolysis at different temperatures toward two electrochemical reactions -reduction of oxygen in alkaline electrolyte and intercalation of lithium into carbons in aprotic electrolyte of Li-ion battery. To our knowledge, the catalytic effect of the metal complexes in the second reaction was not yet considered in the literature. 

The electrodes in the direct methanol fuel cell (DMFC) (i.e. the anode for oxidising the fuel and the cathode for the reduction of oxygen) are based on finely divided Pt dispersed onto a porous carbon support, and the electro-oxidation of methanol at a polycrystalline Pt electrode as a model for the DMFC has been the subject of numerous electrochemical studies dating back to the early years ot the 20th century. In this particular section, the discussion is restricted to the identity of the species that result from the chemisorption of methanol at Pt in acid electrolyte. This is principally because (i) the identity of the catalytic poison formed during the chemisorption of methanol has been a source of controversy for many years, and (ii) the advent of in situ IR culminated in this controversy being resolved. 

H.J. Forman and I. Fridovich, Electrolytic univalent reduction of oxygen in aqueous solution demonstrated with superoxide dismutase. Science. 175, 339 (1972). 

For the study of the electrocatalytic reduction of oxygen and oxidation of methanol, our approach to the preparation of catalysts by two-phase protocol " provides a better controllability over size, composition or surface properties in comparison with traditional approaches such as coprecipitation, deposition-precipitation, and impregnation. " The electrocatalytic activities were studied in both acidic and alkaline electrolytes. This chapter summarizes some of these recent results, which have provided us with further information for assessing gold-based alloy catalysts for fuel cell reactions. 

Figure 4. Some mechanisms thought to govern oxygen reduction in SOFC cathodes. Phases a, and y refer to the eiectronic phase, gas phase, and ionic phase, respectiveiy (a) Incorporation of oxygen into the buik of the electronic phase (if mixed conducting) (b) adsorption and/or partial reduction of oxygen on the surface of the electronic phase (c) bulk or (d) surface transport of or respectively, to the oJy interface, (e) Electrochemical charge transfer of or (f) combinations of and e , respectively, across the aJy interface, and (g) rates of one or more of these mechanisms wherein the electrolyte itself is active for generation and transport of electroactive oxygen species.

The first chelate found to be electrocatalytic was cobalt phthalocyanine x>, which functions as an oxygen catalyst in alkaline electrolytes. Soon afterwards we were able to show 3,4,10,11) -that several phthalocyanines are also active in commercially important, sulfuric acid containing media. A comparison of various central atoms showed that activity increased in the order Cu Ni iron phthalocyanine, the nature of the carbon substrate plays a very important part FePc is more active on a carbon substrate with basic surface groups than on one with acid surface groups3). This property is however specific to phthalocyanines (Pc). 

Many complexes are unstable in 4.5 N H2SO4, which is used as electrolyte in the fuel cell, even at room temperature. Where tiffs was the case, measurements were carried out in potassium carbonate/potassium bicarbonate buffer solution (pH 9.3). We were thus able to determine the reactivity of a wide range of substances, in particular for the catalytic reduction of oxygen. 

Cobalt pkthalocyanine as catalyst in alkaline electrolyte. Jasinski 1 2> was the first to show that CoPc in alkaline solution showed a pronounced activity for the cathodic reduction of oxygen. The compound was mixed with powdered nickel in a ratio of 1 10 w/w and pressed into a stainless steel tube (geometrical surface of the electrode 0.5 cm2). The tube served for both current conduction and gas supply. 

Transition-metal -phthalocyanines as catalysts in acid medium. To prevent carbonate formation by the carbon dioxide in the air or that produced by oxidation of carbonaceous fuels, an acid electrolyte is necessary hence it is important to find electrocatalysts for an acid medium. Independently of Jasinski, we were soon able to show 3>4> that under certain conditions the reduction of oxygen in dilute sulfuric acid proceeded better with phthalocyanines on suitable substrates than with platinum metal. The purified phthalocyanines were dissolved in concentrated sulfuric acid and precipitated on to the carbon substrate by addition of water. This coated powder was made into porous electrodes bound with polyethylene and having a geometrical surface of 5 cm2 (cf. Section 2.2.2.1.). The results obtained with compact electrodes of this type are shown in Fig. 6. 

Fig. 17. Activity of various catalysts for the reduction of oxygen. (Electrolyte 4.5 N H2SO4)...

To do this, it may be helpful to plot the derivative dE/di as a function of 1/i, deducing from it the coefficients a and b. One can then calculate the value of E0 from the initial curves, (b) Establish theoretically the law E =JQn i). Find from the experimental data the resistance of the electrolyte / p, the product OCj n2, and (he exchange current density for the reduction of oxygen, (c) Calculate the maximum current and maximum power of the cell, (d) What electrode surface would be necessary to obtain twice the normal power of the cell You are given ... 

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