Formic acid anodic oxidation

When formic acid is oxidized directly at the anode as the fuel, the fuel cell is called a direct formic acid fuel cell (DFAFC). The anode, the cathode, and the overall reactions are expressed by Reactions 1.7,1.8, and 1.9, respectively. Since the formic acid oxidation does not require water, highly concentrated formic acid can be used. 

Considerable effort was directed toward finding efficient co-catalysts or promoters that, together with Pt, could enhance the rate of anodic oxidation of methanol and formic acid. The oxidation of ethanol received comparatively less attention in the 1970s and 1980s, most likely due to the more complex electrode kinetics and catalysis imposed by the C-C bond. 

Wolter O, Willsau J, Heitbaum J. 1985. Reaction pathways of the anodic oxidation of formic acid on platinum evidenced by oxygen-18 labeling—A DEMS study. J Electrochem Soc 132 1635-1638. 

OH/oxide species. At potentials anodic of 1 V, incomplete oxidation of formaldehyde to formic acid is activated, while methanol oxidation is almost completely hindered. This reflects an easier oxidation of the C-H group in the aldehyde than in the alcohol. For the negative-going scan, where the COadouble-peak stmcture in the current efficiency. 

Finally, we have discussed the effect of incomplete Cj oxidation product formation for fuel cell applications and the implications of these processes for reaction modeling. While for standard DMFC applications, formaldehyde and formic acid formation will be negligible, they may become important for low temperature applications and for microstructured cells with high space velocities. For reaction modeling, we have particularly stressed the need for an improved kinetic data base, including kinetic data under defined reaction and transport conditions and kinetic measurements on the oxidation of Ci mixtures with defined amounts of formaldehyde and formic acid, for a better understanding of cross effects between the different reactants at an operating fuel cell anode. 

Methoxypiperazine-2,5-diones have been obtained by the formic acid cyclization of the corresponding linear peptides (91T563). The latter were obtained by electrochemical oxidation of normal dipeptides (Scheme 4). The electrolysis was performed in MeOH-lithium perchlorate (0.1 M) containing NaCl at a platinum anode and was found to be totally regiose-lective. 

The conditions encountered in studying the stability of catalysts under electrochemical load are very complicated. Stability depends strongly on the potential and on the nature of the working substance. For example, pure CoTAA, when used as an oxygen catalyst at potentials of about 800 mV, is active only for a period of some hours. If, however, it is used in the anode for the oxidation of formic acid at 350 mV, it will give more than 6 months (4000 hours ) continuous service under the same conditions. 

In the first cycle, there is superimposed on this change of valency an irreversible oxidation of the molecule, in which about two electrons are lost. This could, for example, involve the formation of a dication. It is obviously the species so formed that catalyzes so excellently the subsequent anodic oxidation of formic acid (broken curve, measured with 1 M HCOOH). 

These properties make CoTAA a good catalyst for the anodic oxidation of formic acid. Economic application of this catalyst is, however, not anticipated because formic acid is not economically attractive as a fuel. It is certainly possible to prepare electrodes containing a mixture of tungsten carbide and CoTAA as catalyst, with the tungsten carbide catalyzing the first stage of the oxidation of CH2O to HCOOH, and the CoTAA the further oxidation of HCOOH to CO 2, but this possibility does not offer any more favorable prospects. Economic application of CoTAA will only come into question when cheap catalysts are available for the partial oxidization of methanol to formaldehyde or formic acid. 

This section addresses the role of chemical surface bonding in the electrochemical oxidation of carbon monoxide, CO, formic acid, and methanol as examples of the electrocatalytic oxidation of small organics into C02 and water. The (electro)oxidation of these small Cl organic molecules, in particular CO, is one of the most thoroughly researched reactions to date. Especially formic acid and methanol [130,131] have attracted much interest due to their usefulness as fuels in Polymer Electrolyte Membrane direct liquid fuel cells [132] where liquid carbonaceous fuels are fed directly to the anode catalyst and are electrocatalytically oxidized in the anodic half-cell reaction to C02 and water according to... 

Anodic oxidation of 6- and 7-pteridone, using electrolysis at a controlled potential, gave pteridine-6,7-dione in 95-100% yield.409 Under controlled-potential electrolysis conditions pteridine-6,7-dione is oxidized to the bridgehead diol, which undergoes rearrangement, further oxidation, and hydrolysis, yielding tetraketopiperazine, oxamide, urea, oxamic acid, ammonia, formaldehyde, formic acid, and C02-... 

A diagram of the microbial sensor is illustrated in Figure 2. When the sensor was inserted into a sample solution containing formic acid, formic acid permeated through the porous Teflon membrane. Hydrogen, produced from formic acid by butyricum, penetrated through the Teflon membrane, and was oxidized on the platinum anode. As a result, the current increased until it reached a steady state. The steady state current depended on the concentration of formic acid. The steady state current was obtained within 20 min. 

Figure 15 Evolution of (a) acetic acid, (b) formic acid, and (c) oxalic acid concentrations, and (d) ICE during the anodic oxidation of 500 mL of 0.16 mol dm-3 acetic acid in 1 mol dm 3 H2S04 at 30°C on a 50-cm2 Si/diamond anode. The applied current is 30 mA cm2. (From Ref. 44.)...

The thin semiconductor particulate film prepared by immobilizing semiconductor nanoclusters on a conducting glass surface acts as a photosensitive electrode in an electrochemical cell. An externally applied anodic bias not only improves the efficiency of charge separation by driving the photogenerated electrons via the external circuit to the counter electrode compartment but also provides a means to carry out selective oxidation and reduction in two separate compartments. This technique has been shown to be veiy effective for the degradation of 4-chlorophenol [116,117], formic acid [149], and surfactants [150] and textile azo dyes [264,265]. 

While these experiments, which were carried out without giving a theoretical insight into the nature of the electrochemical reaction, yielded almost all the possible oxidation products in the oxidation of methyl alcohol, Elbs and Brunner 2 have discovered a method which gives 80% of the current yield in formaldehyde. This is exactly the substance which could not be proven present up to that time among the electrolytic oxidation products of methyl alcohol. Elbs and Brunner electrolyzed an aqueous solution of 160 g. methyl alcohol and 49 to 98 g. sulphuric acid in a litre. They employed a bright platinum anode in an earthenware cylinder, using a current density of 3.75 amp.1 and a temperature of 30°. Only traces of formic acid and carbonic acid and a little carbon monoxide, aside from the 80 per cent, of formaldehyde, were formed. Plating the platinum anode with platinum decreased the yield of formaldehyde at the expense of the carbon dioxide. With an anode of lead peroxide the carbon dioxide exceeded the aldehyde. 

Acetone, acetic acid, formic acid, and carbonic acid are formed. The oxidation takes place more easily than in the case of the primary alcohols, and yields up to 70% acetone, which, however, is readily oxidized further. In alkaline electrolytes the alcohols are converted at the anode into complicated condensation products of the aldehydes. 

An analogous description can be given for the oxidation of various organic compounds. For instance, Morrison and co-workers [156, 157] have investigated quantitatively the oxidation of formic acid at n-ZnO and found a doubling of the anodic photocurrent upon addition of HCOOH. They interpreted this result in terms of the reaction... 

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