Formic acid, electrocatalytic oxidation

Park I-S, Lee K-S, Yoo SJ, Cho Y-H, Sung Y-E (2010) Electrocatalytic properties of Pd clusters on Au nanoparticles in formic acid electro-oxidation. Electrochim Acta 55 4339 345... 

Conteol over the reaction pathway was also observed in electrocatalytic reactions. In electeocatalytic formic acid oxidation, there are two pathways by which formic acid is oxidized dehydration (HC00H H20-i-C0) and dehydrogenation (HC00H H2-hC02). The dehydration pathway generates surface-poisoning CO... 

Interest in fuel cells has stimulated many investigations into the detailed mechanisms of the electrocatalytic oxidation of small organic molecules such as methanol, formaldehyde, formic acid, etc. The major problem using platinum group metals is the rapid build up of a strongly adsorbed species which efficiently poisons the electrodes. 

The use of adatoms of foreign metals obtained by imderpotential deposition on the platinum surface is another convenient method for investigating the effect of a promoter on the electrocatalytic properties of platinum. However, the effect of adatoms in this case has been shown to be not as effective for electrooxidation of methanol as for the oxidation of other organic molecules such as formic acid adatoms of tin, however, showed a positive effect on the rate of methanol oxidation. ... 

For the Pt(llO) electrode, there are some contradictory results regarding its catalytic performance compared with Pt(lOO) some studies indicate that the activity is higher for Pt(llO), whereas others suggest the opposite [Chang et al., 1990 Clavilier et al., 1981 Lamy et al., 1983]. The differences are probably associated with different surface states of the Pt(l 10) electrode. The acmal surface strucmre of the Pt(llO) electrode is strongly dependent on the electrode pretreatment. Since formic acid oxidation is a surface-sensitive reaction, different electrocatalytic behavior can be obtained for the same electrode after different treatments. 

Sun SG, Clavilier J, Bewick A. 1988. The mechanism of electrocatalytic oxidation of formic acid on Pt(lOO) and Pt(lll) in sulphuric acid solution An EMIRS study. J Electroanal Chem 240 147-159. 

Samjeske G, Miki A, Ye S, Osawa M. 2006. Mechanistic study of electrocatalytic oxidation of formic acid at platinum in acidic solution by time-resolved surface-enhanced infrared absorption spectroscopy. J Phys Chem B 110 16559-16566. 

The electrocatalytic oxidation of methanol was discussed on page 364. The extensively studied oxidation of simple organic substances is markedly dependent on the type of crystal face of the electrode material, as indicated in Fig. 5.56 for the oxidation of formic acid at a platinum electrode. 

Both the data on hydrogen adsorption and formic acid oxidation show pronounced structural sensitivity, thus confirming a paramount role of surface structure in electrocatalytic reactions. It can be concluded that each crystallographic orientation represents a distinct electrochemical (chemical) entity. The investigation of stepped surfaces seems to be necessary to reach an understanding of these systems on a molecular level. Hydrogen adsorption shows dependences on the terrace orientation, step orientation, and step density. All the... 

Thymidine-specific depyrimidination of DNA by this and other Ru(lV) 0x0 complexes, e.g. electrocatalytically by [Ru(0)(py)(bpy)2] Vaq. formate buffer was studied and related to their Ru(IV)/Ru(ll) redox potentiis [664]. Oxidation of formate and of formic acid to CO by stoich. aT-[Ru(0)(py)(bpy)2] Vwater was studied kinetically, and a two-electron hydride transfer mechanism proposed [665]. 

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... 

In acidic medium, the electrocatalytic oxidation of glyoxal on platinum in the potential range 1 to 1.5 V/RHE leads mainly to formic acid (60%) and CO (40%). With lead adatoms, it becomes possible to oxidize glyoxal between 0.4 and 1.0 V/RHE leading mainly to CO2 formation (46%), while the selectivity towards, glyoxylic acid is sensibly increased (28%). At pH=7 and 1,9 V/RHE, the main oxidation product is formic acid (99%). Otherwise, in acidic medium the oxidation is more selective towards glyoxylic acid (70%), when the applied potential is in the range of 1.80 to 2.13 V/RHE. 

Similar reaction pathways have also been found for the oxidation of dimethyl sulfide to dimethyl sulfoxide and dimethyl sulfoxide to dimethyl sulfone by [Ru(bpy)2(py)(0)]2+ with respective rate constants of 17.1 and 0.13 M l s"1 in MeCN at 298 K (48). The complex [Ru(bpy)2 (py)(0)]2+ has also been used electrocatalytically for the oxidation of alcohols, aldehydes, alkenes, and aromatics (23, 49). The kinetics of oxidation of formic acid/formate ion by [Ru(bpy)2(py)(0)]2 +, with a large kinetic isotope effect [ HC02-/ADCo2- = 19 (25°C, /r = 1.0 M)], has been reported (50). A two-electron hydride transfer has been suggested for the oxidation of HC02 by [Ru(bpy)2(py)(0)]2+. A similar mechanism has also been suggested for the oxidation of alcohols (51) and aromatics (52) by [Ru(bpy)2(py)(0)]2+ and other related Ru(IV) oxo complexes (28,... 

Chen, W. Kim, J. Xu. L-P. Sun, S. Chen, S. Langmuir-Blodgett Thin Films of Fe Ptso Nanoparticles for the Electrocatalytic Oxidation of Formic Acid. J. Phys. Chem. C2007, 111,13452-13459. 

The electrocatalytic oxidation of many small organic molecules was carried out at Pt-based catalysts dispersed in an ECP, particularly that of Cl molecules (formic acid, formaldehyde, and methanol). 

The oxidation of formic acid was one of the first electrocatalytic oxidations at ECP modified by platinum particles, which was studied by Gholamian et al. [27]. They observed that the incorporation of O.lmgcm of Pt into a PAni film enhanced greatly the oxidation rate of formic acid (10 times enhancement). They evaluated the optimum film thickness (around 1 pm) for a maximum enhancement of the oxidation current. They also determined the resistance profile of the PAni film correlatively to the catalytic activity of the Pt particles and found that the maximum electroactivity occurs within the conducting potential window of the polymer. However, this correlation is not definitively established since they do not determine the conductivity of the PAni film in the presence of Pt particles, which must be higher than in the absence of the metallic particles. 

With the development of fuel cells, electrocatalytic oxidation of small organic molecules, such as methanol or formic acid, has attracted great interest recently (Rice et al., 2003). Ethanol oxidation to acetaldehyde can be performed by means of the reactions ... 

Figure 10.8 Tafel plots of the electrocatalytic oxidation of 0.1 M formic acid in 0,1 M HCIO4 at different platinum-based alloy electrodes dispersed in a polyaniline film and containing 0,1 mg cm of platinum (—) Pt (---) Pt-Ru (...) Pt-Sn (—) Pt-Ru-Sn. (Reprinted with permission from ref 69)...

Park, S., Y. Xie, and M.J. Weaver, Electrocatalytic pathways on carbon-supported platinum nanoparticles Comparison of particle-size-dependent rates of methanol, formic acid und formaldehyde electrooxidation. Langmuir, 2002. 18(15) pp. 5792-5798 Vinodgopal, K., M. Haria, D. Meisel, and P. Kamat, Fullerene-based carbon nanostructures for methanol oxidation. Nano Letters, 2004. 4(3) pp. 415 18 Sun, N.X. and K. Lu, Physical Review B, 1997. 54 pp. 6058... 

It has been observed that the rate of electrocatalytic oxidation of formic acid at R electrodes can be enhanced significantly by the incorporation of adatoms, such as Pb, Bi, Tl, and Cd. The most significant enhancement has been seen with Pb adatoms, which were shown to be accompanied by a dramatic decrease in the poisoning phenomena on R. ° A similar type of behavior has been observed with systems based on Pt/Cdg, Pt/TI and Pt/Biads, although to a lesser extent. One of the most plausible explanations given rationalizing the improved characteristics of electro-oxidation in the presence of adatoms was proposed by Shibata and Motoo ° who invoke a... 

PANI-NTs synthesized by a template method on commercial carbon cloth have been used as the catalyst support for Pt particles for the electro-oxidation of methanol [501]. The Pt-incorporated PANl-NT electrode exhibited excellent catalytic activity and stabUity compared to 20 wt% Pt supported on VulcanXC 72R carbon and Pt supported on a conventional PANI electrode. The electrode fabrication used in this investigation is particularly attractive to adopt in solid polymer electrolyte-based fuel cells, which arc usually operated under methanol or hydrogen. The higher thermal stabUity of y-Mn02 nanoparticles-coated PANI-NFs on carbon electrodes and their activity in formic acid oxidation pomits the realization of Pt-free anodes for formic acid fuel cells [260]. The exceUent electrocatalytic activity of Pd/ PANI-NFs film has recently been confirmed in the electro-oxidation reactions of formic acid in acidic media, and ethanol/methanol in alkaline medium, making it a potential candidate for direct fuel cells in both acidic and alkaline media [502]. 

V. Selvaraj, M. Alagar, and K. S. Kumar, Synthesis and characterization of metal nanopar-ticles-decorated PPY-CNT composite and their electrocatalytic oxidation of formic acid and formaldehyde for fuel cell applications, Appl. Catalysis B, 75, 129-138 (2007). 

The electrochemical oxidation of small molecules such as methanol, formaldehyde and formic acid on Pt and Pd electrodes has received considerable attention because of the potential of these molecules as fuels for low temperature fuel cells. Samjeske et al. described the electrocatalytic oxidation of formaldehyde at an electrode made from a 50-nm Pt film deposited on a single-reflection hemicylindrical Si IRE under constant current (galvanostatic) and potential sweep conditions by time-resolved SEIRA spectroscopy." ... 

The investigation on the electrochemical epitaxial growth of palladium on gold and platinum singlemonolayer coverage of palladium on Pt(lll) electrode by the immersion technique for the first time [74]. Llorca and coworkers investigated the irreversibly adsorbed palladium on Pt(hiJ) in acidic solution [75] and reported that electrocatalytic activity for the oxidation of formic acid on the Pt(lOO) electrodes vras improved drastically by the palladium-adlayer modification, while that on the Pt(lll) electrode was not greatly affected by the Pd-modification [76]. However, it is difficult to prepare an ultrathin film of palladium with various thickness by the immersion technique, and STM observation of the atomic structure of these surfaces is not available yet. 

The electrocatalytic behavior of the thin palladium layers deposited on Au(hkl) surfaces for hydrogen adsorption/absorp-tion [77, 80], oxygen reduction [79], oxide formation/reduction [80], copper UPD [33, 77], electrochemical oxidation of formic acid [84] as well as formaldehyde [80] has been investigated in detail. These electrocatalytic activities depended significantly on the surface structure and thickness of the ultrathin palladium layers [80, 84]. 

Sensse A, Gatermann K, Eiswirth M (2005) Analytic solution for the electrocatalytic oxidation of formic acid. J Electroanal Chem 577 35-46... 

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