Formic Acid electrode processes

Overall, we demonstrated electrode potential- and time-dependent properties of the atop CO adsorbate generated from the formic acid decomposition process at three potentials, and addressed the issues of formic acid reactivity and poisoning [Samjeske and Osawa, 2005 Chen et al., 2003,2006]. There is also a consistency with the previous kinetic data obtained by electrochemical methods the maximum in formic acid decomposition rates was obtained at —0.025 V vs. Ag/AgCl or 0.25 V vs. RHE (cf. Fig. 12.7 in [Lu et al., 1999]). However, the exact path towards the CO formation is not clear, as the main reaction is the oxidation of the HCOOH molecule ... 

Anastasijevic NA, Baltruschat H, Heitbaum J. 1989. DBMS as a tool for the investigation of dynamic processes Galvanostatic formic acid oxidation on a Pt electrode. J Electroanal Chem272 89-100. 

The processes classified in the third group are of primary importance in elucidating the significance of electric variables in electrosorption and in the double layer structure at solid electrodes. These processes encompass interactions of ionic components of supporting electrolytes with electrode surfaces and adsorption of some organic molecules such as saturated carboxylic acids and their derivatives (except for formic acid). The species that are concerned here are weakly adsorbed on platinum and rhodium electrodes and their heat of adsorption is well below 20 kcal/mole (25). Due to the reversibility and significant mobility of such weakly adsorbed ions or molecules, the application of the i n situ methods for the surface concentration measurements is more appropriate than that of the vacuum... 

Electrodes modified by underpotential deposition of metal were subjected as electrocatalysts to reduction of oxygen,oxidation of formic acid, and other processes in which polycrystalline metal substrates were used (see review in Ref. 151). Electrocatalysis of single-crystal electrodes modified by underpotential deposition was also investigated, as reviewed by Ad2iC. ... 

A large body of work has been published and recently reviewed on spectroscopic evidence of the adsorption and transformation of formic acid on Pt and Pt alloy surfaces according to reactions (34) and (35) [130,131]. Pt was found to interact weakly up to a potential of 0.2 V/RHE. Above this electrode potential, both reaction pathways were found to be present. Reaction (34) was estabhshed as the dominant process with reaction (35) being the site-blocking side reaction. On Ru, however, formic acid reacted distinctly differently. Here formic acid decomposition into surface COads was found to be very pronounced even at very low electrode potentials. 

The EOTR between the organic compound (R) and the hydroxyl radicals take place at the electrode surface (both adsorbed) according to a Langmuir-Hinshelwood type mechanism. This process has been extensively studied mainly for fuel cell applications. However, as it has. been reported in Sect. 1.2, it is limited for simple Ci organic compounds (methanol, formic acid). Furthermore, there are problems with electrode deactivation due to CO chemisorption on the electrode active sites. 

The chemical reaction scheme (F1)-(F4) was translated into a mathe-matical model. The variables of the model are formic acid concentration in the reaction plane, Cp, the coverages of the electrode with carbon monoxide, 0co> and with OH, Gqh, and the electrode potential, ( )dl- In contrast to some previously proposed models, the pH in the reaction plane was assumed to be constant and entered only the reaction constants for a given bulk solution acidity. The concentration of the radical species COOHad was adiabatically eliminated because its oxidation is by far the fastest process of the scheme. The resulting equations read ... 

Value added products, such as the reduction of oxalic acid to glyoxylic acid, are nowadays developed at an industrial scale (BASF—Badische Anilin und Soda-Fabriken). This process uses non-precious metals such as lead. This electrode material reduces carbon dioxide to formic acid in an aqueous medium and to oxalic acid in an organic solvent. This approach can be used to develop environmentally friendly value added products from abundant anthropogenic carbon dioxide. 

Zhang M, Wilde CP (1995) The influence of organic adsorbates on the UPD process. Oxidation of formic acid at UPD lead-modified platinum electrodes. J Electroanal Chem 390 59-68... 

The results obtained in this work are related mainly with the high rates for the reduction process achieved with this kind of electrodes. With Co phthalocyanine electrodes the only significant products were CO and H2 and the results are highly dependent on the potential used for the electrolysis experiments. Other important factor described by the authors was the amounts of carbon monoxide and hydrogen produced from sample to sample, reflecting probably variations in the exact composition of different Co phthalocyanines electrodes. For Mn, Cu, and Zn impregnated electrodes both formic acid and hydrogen were produced. 

Assuming mass transport processes as negligible for simplicity, the rate controlled by the rate-determining step of net reaction 67 will depend upon the relative electrode potential, the bulk concentration of formic acid, and the coverage with chemisorbed carbonaceous species. A similar statement holds for The value of the open-circuit potential L/op is determined by Eq. 69. On the potential scale it is located [15] between the Uo value of reaction 67 and 68 under standard conditions. 

Examples of delicate, unstable dissolved analytes with sluggish response were formaldehyde, methanol and formic acid [27]. Their reactirai on Pt was not influenced by thermal convection, indicating that the oxidation processes are controlled by surface reactions and not by mass transport. The oxidatimi current signals were significantly improved at a heated electrode. Oxidation current increments of more than tenfold were obtained for a 56 K temperature rise. Increased temperatures favour the enhancement of the main oxidation reaction as weU as the decrease of the overvoltage for the formation of adsorbed reactive OH species oti platinum. 

During galvanostatic oxidation of formic acid on a rhodium electrode periodic changes in potential were observed under certain conditions [6, 55]. Periodic effects have also been described in electrochemical oxidation processes [62, 187, 188]. It has been suggested that the potential fluctuations may be due to periodic formation and oxidation of an adsorbed layer of organic substances on the electrode [55]. 

Plaque fluids can be isolated by high-speed centrifugation and analysed by, for example, capillary electrophoresis and ion chromatography. Certain species, such as H+ and F, are usually determined by ion-selective electrodes. The main inorganic anions are chloride and Pi, whilst short-chain organic acids include lactic, acetic, propionic, succinic, formic, pyruvic and butyric acids. The main cationic components are ammonium, potassium, magnesium and Ca. Although it cannot be concluded that any individual component plays a key role in the caries process, studies have shown that some components are more related to caries susceptibility than others. 

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