Formic acid oxidation on Platinum

A generally accepted dual-path mechanism for formic acid oxidation on platinum was proposed by Capon and Parsons [90] and continuously revised by the new spectroscopic insights mainly due to the discussion of the nature of the poison species. According to the current accepted mechanism, the direct path of FAO occurs via a reactive intermediate described... 

Seland F, Tunold R, Harrington DA (2008) Impedance study of formic acid oxidation on platinum electrodes. Electrochim Acta 53 6851-6864... 

Fig. 33 Niquist piot for formic acid oxidation on platinum, obtained at -t-740 mV versus SHE, that is, in the region of the positive siope of i[f>) (compare Fig. 7), showing an inductive loop and negative faradic impedance 0.1 M HCOONa/0.033 M H2SO4, indicating a dynamic instability [131, 132], as already mentioned under Sect. 5.2.5.1.

Clavilier J, Parsons R, Durand R, Lamy C, Leger JM. 1981. Formic acid oxidation on single crystal platinum electrodes. Comparison with polycrystalline platinum. J Electroanal... 

Femandez-Vega A, Feliu JM, Aldaz A, Clavilier J. 1991. Heterogeneous electrocatalysis on well-deflned platinum surfaces modifled by controlled amounts of irreversibly adsorbed adatoms Part IV. Formic acid oxidation on the Pt(lll)-As system. J Electroanal Chem 305 229-240. 

Lovic JD, Tripkovic AV, Gojkovic SL, Popovic KD, Tripkovic DV, Olszewski P, Kowal A (2005) Kinetic study of formic acid oxidation on carbon-supported platinum electrocatalyst. J Electroanal Chem 581 294—302... 

A more direct motivation for studies of carbonaceous adlayers comes from the recent finding that formic acid oxidation can occur through a hydrocarbon residue formed by formic acid itself on platinum [2]. One implication from this study is that carbonaceous residues could be present in other electrocatalytic reactions, perhaps influencing them in some way, but otherwise remaining quite difficult to detect. 

Figure 6 Peak turnover rates (reactions per bare platinum atom per second) for formic acid oxidation on Pt(lll) as a function of carbon coverage. The data were obtained from cyclic voltammograms (squares - positive sweep circles -negative sweep) at 50 mV/s in 0.1 mol/dm HCOOH plus 0.1 mol/dm HCIO. The lines are guides to the eye.

Figure 4.35. Chronopotentiometry of formic acid oxidation on Pd, PdPt (prepared by the polyol method), and Pt. 10 M HCOOH - 0.1 M H2SO4, 293 K, 100 mA cm l Catalyst load 6 mg cm . The Pd Pt atomic ratios are listed [174], (Reproduced by permission of ECS— The Electrochemical Society, from Blair S, Lycke D, lordache C. Palladium-platinum alloy anode catalysts for direct formic acid fuels.)...

Paladds L, Wieckowski A. A catal5dic study of formic acid oxidation on preferentially oriented platinum electrodes. Cat Lett 1989 3 143-58. 

Fig. 61. Steady-state current-potential curves of formic acid oxidation on platinized platinum in XM HCOOH-1-0.5 M HjSO at 25°C.

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. 

Many examples of this type of reaction are known the decomposition of arsine the decomposition of phosphine on surfaces of glass, f porcelain, J silica the decomposition of formic acid vapour on a variety of different surfaces— glass, platinum, rhodium, titanium oxide, and others the decomposition of nitrous oxide on the surface of gold Tf the decomposition of sulphuryl chloride on the surface of glass the decomposition of hydrogen iodide on the surface of platinum ff the decomposition of hydrogen selenide on the surface of selenium. J J A general discussion... 

Fig. 44 Comparison between experimental ( ) and theoretical currents for formic acid oxidation versus the fraction of platinum surface blocked by the adatom on three different electrodes (a) Bi/Pt(lll),...

Besides methanol and ethanol, only a few other small molecules (HCOOH, HCHO, CO), have been oxidized at electron conducting polymer electrodes modified by incorporation of platinum microparticles. The first study on formic acid oxidation at Pt particles dispersed in a PAni matrix was carried out, as early as 1986, by Gholamian et al. [57], They found that the incorporation of 100 pg cm of Pt into PAni was sufficient to enhance considerably the oxidation rate of formic acid (ten-fold increase). The cyclic voltammograms recorded with 0.5 M HCOOH in 0,5 M H2SO4 displayed an enhanced oxidation current particularly for the first oxidation peak at 0.2 V/SCE, attributed to the oxidation of the weakly adsorbed intermediate (reactive species). The second peak, at 0.6 V/SCE, attributed to the oxidation of the strongly chemisorbed... 

Methanol is the typical fuel with one carbon (Cl) atom for fuel cells. Methanol was one of the first small molecules chosen to study the oxidation on platinum group metals in the very early beginning of electrocatalysis. In that time, the oxidation of other Cl molecules such as formic acid and formaldehyde (interest in CO oxidation came latter with the oxidation of reformatted gases) were investigated as a model oxidation because their elementary steps were supposedly present in the mechanism of methanol oxidation. From the point of view of CO2 emission, methanol has, among the other small molecules, the highest energy production per unit of produced... 

In Sects. 2.1 and 2.2 of this chapter the mechanism of methanol oxidation on platinum was discussed. This section is dedicated to clarify the impact of the main Pt-alloys, as already mentioned in Sects. 2.2.3 and 2.2.4, on the kinetics of the most relevant oxidative steps belonging to the MOR mechanism. Baring this in mind, the CO oxidation, the last step for complete methanol oxidation, is analyzed as well as the oxidation of other MOR intermediates such as formic acid and formaldehyde. 

The interest in formic acid oxidation (FAO) rose up in the 1970s with the aim of shedding light on the mechanism of methanol oxidation beyond the commercial interest in direct formic acid oxidation in fuel cells [90]. The FAO in acid solution was extensively investigated on surfaces of platinum [91-100] The FAO on other pure metallic surfaces seems to have been restricted to the palladium surface [98, 101-104]. In the 1980s, the remarkable contribution was done by the studies on the influence of the ad-atom in the activity of the platinum electrode [91—94]. In the 1990s, superficial spectroscopic techniques were employed to describe the electrochemical mechanism on palladium surface [98, 101—103] as well as platinum surface [97, 98, 105]. In the last 10 years, there was a triplication of publications about the FAO, specially driven by the use of nanoparticles. 

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