Platinum electrodes carbon dioxide reduction

Numerous methods for the synthesis of salicyl alcohol exist. These involve the reduction of salicylaldehyde or of salicylic acid and its derivatives. The alcohol can be prepared in almost theoretical yield by the reduction of salicylaldehyde with sodium amalgam, sodium borohydride, or lithium aluminum hydride by catalytic hydrogenation over platinum black or Raney nickel or by hydrogenation over platinum and ferrous chloride in alcohol. The electrolytic reduction of salicylaldehyde in sodium bicarbonate solution at a mercury cathode with carbon dioxide passed into the mixture also yields saligenin. It is formed by the electrolytic reduction at lead electrodes of salicylic acids in aqueous alcoholic solution or sodium salicylate in the presence of boric acid and sodium sulfate. Salicylamide in aqueous alcohol solution acidified with acetic acid is reduced to salicyl alcohol by sodium amalgam in 63% yield. Salicyl alcohol forms along with -hydroxybenzyl alcohol by the action of formaldehyde on phenol in the presence of sodium hydroxide or calcium oxide. High yields of salicyl alcohol from phenol and formaldehyde in the presence of a molar equivalent of ether additives have been reported (60). Phenyl metaborate prepared from phenol and boric acid yields salicyl alcohol after treatment with formaldehyde and hydrolysis (61). 

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. 

Carbon Dioxide (C02). Figures 11.12 and 11.13 illustrate the electron-transfer reduction of C02 in Me2SO at gold, platinum, and mercury electrodes.18,19 Whereas the reduction at a gold electrode is a one-electron per C02 process on a voltammetric time scale, at mercury it is a sequential two-electron process. In both cases the overall reduction is two electrons per C02. The products for anhydrous conditions are C03 and CO, and with H20 present H0C(0)0-and HC(0)0 ... 

Electrochemical reduction of carbon dioxide at a platinum electrode in acetonitrile-water mixtures... 

CO2 reduction at metallic electrodes is generally poorly selective [151]. Monoelec -tronic reduction of carbon dioxide may occur at a platinum cathode in non-aqueous solvents, but at very negative potentials. Catalytic activation of CO2 has been described (e.g. at a cathode modified by a rhenium complex in a hydroorganic solvent) the observed conversions did correspond to the formation of CO and formic acid. In organic synthesis, CO2 was mainly used as an electrophile (toward electrogenerated anions from jt -acceptors or electrogenerated nucleophiles when adequate transition metals ions were present in situ) for the purpose of carboxylation. 

The most popular electrode materials for reduction are mercury, lead, titanium, and platinum. The choice of anode is limited because most metals are anodically corroded. In the laboratory, most of the electrodes are made of platinum, gold, or carbon. Exotic anodes such as lead dioxide or DSA (Dimensionally Stable Anode such as Ti/Ru02) have been developed for organic or chlorine electrochemistry. 

In the above reactions, the oxidation process takes place in the anode electrode where the methanol is oxidized to carbon dioxide, protons, and electrons. In the reduction process, the protons combine with oxygen to form water and the electrons are transferred to produce the power. Figure 9-1 is a reaction scheme describing the probable methanol electrooxidation process (steps i-viii) within a DMFC anode [1]. Only Pt-based electrocatalysts show the necessary reactivity and stability in the acidic environment of the DMFC to be of practical use [2], This is the complete explanation of the anodic reactions at the anode electrode. The electrodes perform well due to the presence of a ruthenium catalyst added to the platinum anode (electrode). Addition of ruthenium catalyst enhances the reactivity of methanol in fuel cell at lower temperatures [3]. The ruthenium catalyst oxidizes carbon monoxide to carbon dioxide, which in return helps methanol reactivity with platinum at lower temperatures [4]. Because of this conversion, carbon dioxide is present in greater quantity around the anode electrode [5]. 

Tomita Y, Hori Y (1998) Electrochemical reduction of carbon dioxide at a platinum electrode in acetonitrile-water mixtures. Advances in chemical conversions for mitigating carbon dioxide, Elsevier, Amsterdam, vol 114, pp 581-584... 

Catalytical activities have been claimed for copolymers arising from pyrrole and bithiophene with a small amount of dispersed platinum to be effective in the electrochemical oxidation of hydrogen, formic acid and methanol [245] the same catalytic effect was found for electrodes of 3-methyIPT with electrochemically deposited platinum and tin [246]. The reduction of tetracyano-p-quinodimethane and chloranil can be achieved at a glassy carbon electrode coated with 3-methylPT [247]. Phenol derivatives and carbon dioxide can be converted to salicylic acid derivatives on 3-hexylPT electrodes under irradiation in ethanolic solution [248]. This electrode material acts as a photocatalyst on irradiation with visible light, the luminescence is quenched by carbon dioxide as well as phenol. 

Lai-jcSr MnOs). Unlike its effect in fuel cells, platinum metal is not a very effective catalyst for metal-air batteries, especially for charging. Instead, silver has demonstrated high reduction efficiency and good stability. The most inexpensive catalyst is activated carbon, which has a very high surface area. For oxygen reduction in carbon-based air electrodes, manganese dioxide is the catalyst most extensively used. 

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