Hydrogen electrode formic acid

Eor formic acid oxidation, 182 Eor methanol oxidation, 189, 350-351 Eor oxygen reduction, 18-20, 276-277, 297, 364-365, 522, 534, 538 Theoretical Standard Hydrogen Electrode, 58-60, 101... 

More recently, Ikeda et a/.108 have examined C02 reduction in aqueous and nonaqueous solvents using metal-deposited p-GaP and p-InP electrodes under illumination. Metal coatings on these semiconductor electrodes gave much improved faradaic efficiencies for C02 reduction. In an aqueous solution, the products obtained were formic acid and CO with hydrogen evolution at Pb-, Zn-, and In-coated electrodes, while in a nonaqueous PC solution, CO was obtained with faradaic efficiencies of ca. 90% at In-, Zn-, and Au-coated p-GaP and p-InP, and a Pb coating on a p-GaP electrode gave oxalate as the main product with a faradaic efficiency of ca. 50% at -1.2 V versus Ag/AgCl. 

The use of a biofuel cell type electrode for BOD-determination has been described by Karube et al. [29]. The current generated by the biofuel cell results from the oxidation of hydrogen and formic acid produced from organic compounds by Clostridia under anaerobic conditions. 

Many investigators have actively studied the electrochemical reduction of C02 using various metal electrodes in organic solvents because these solvents dissolve much more C02 than water. With the exception of methanol, however, no hydrocarbons were obtained. The solubility of C02 in methanol is approximately 5 times that in water at ambient temperature, and 8-15 times that in water at temperatures below 0°C. Thus, studies of electrochemical reduction of C02 in methanol at —30°C have been conducted.148-150 In methanol-based electrolytes using Cs+ salts the main products were methane, ethane, ethylene, formic acid, and CO.151 This system is effective for the formation of C2 compounds, mainly ethylene. In the LiOH-methanol system, the efficiency of hydrogen formation, a competing reaction of C02 reduction, was depressed to below 2% at relatively negative potentials.152 The maximum current efficiency for hydrocarbon (methane and ethylene) formation was of 78%. 

Similarly, the kinetics and mechanism of C02 reduction to formic acid has been studied by Vassiliev et al. over a wide range of metal electrodes with high or moderate hydrogen overpotentials (e.g., Cu, Sn, In, Sb, Bi, In, Zn, Pb) [48]. The best... 

When Bandi and Kuhne studied the reduction of C02 to methanol at mixed Ru02 + Ti02 electrodes (ratio 3 1) produced by coating titanium foil [65], in a C02-saturated KHC03 solution at a current density of 5 mA cm 2, only minimal C02 reduction was observed. However, the addition of electrodeposited Cu led to faradaic efficiencies of up to 30% for methanol at potentials of approximately -0.972V (versus SCE). Trace amounts of formic acid and ethanol were also observed. In this case, the rate-limiting step was surmised to be the surface recombination of adsorbed hydrogen and C02 to yield adsorbed COOH". 

Some anaerobic bacteria such as Escherichia coli and Clostiridium butyricum produce hydrogen from formic acid. Therefore, determination of formic acid is possible by using Clostridium butyricum and a fuel cell type electrode(9). 

V versus SCE [64], The cathodic limiting reaction is hydrogen evolution, thus forming the acid anion as the coproduct. The apparent electrochemical window of acetic acid is about 4 V [63], whereas that of formic acid is around 1 V [49], For methanol and ethanol, there are reports on limiting cathodic potentials around -2 V versus mercury pool electrode [65], and their accessible electrochemical window is around 2 V. The cathodic limiting reactions are probably hydrogen evolution and an alkoxide formation. 

The quinhydrone electrode has been adapted for pH measurements in non-aqueous media, such as alcohols, acetone, formic acid, benzene and liquid ammonia. For the determination of hydrogen ion activities in solutions in pure acetic acid a form of quinhydrone electrode involving tetrachloroquinone (chloranil) and its hydroquinone has been used. ... 

The lead-impregnated electrodes produced formic acid with 100% current efficiency at 115 mA/cm and a potential of -1.8 V vs. SCE, at room temperature and atmospheric pressure. The electrodes bonded with indium and tin produced formic acid at rates comparable with those on lead electrodes, but small concentrations of carbon monoxide were also produced. The evolution of hydrogen was also more significant on these electrodes. 

The rate of hydrogen evolution varies with solution composition and in particular with pH. It is higher at neutral pH values than at acidic pH, which is not consistent with that observed on Pt. The kinetics may also greatly change due to the adsorption of solution species or presence of solid phases on the surface. For example, hydrogen evolution in H2SO4 on illuminated p-Si is inhibited by addition of formic acid in the solution due to the chemisorption of HCOOH on the electrode surface. ... 

CO2 reduction proceeds readily to formic acid on most metal electrodes, and formic acid reduction proceeds most rapidly on electrodes with high hydrogen overvoltage such as lead, tin, and indium this appears to be related to the stability of intermediates (22, 23). 

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