Composition of electrosorbed methanol

Biegler, T.

doi:10.1021/j100851a031

“…Kazarinov et al (19), $*e using a radiotracer technique, have shown that the oxidation of CH3OH, HCHO, and HCOOH, in both acid and alkaline electrolytes, results in the formation of C OH intermediates. This is in agreement with the results of Wieckowski (20), Breiter (21), Biegler (22), and Capon and Parsons (7). Vassilyev et al (23) showed how C OH could arise from a whole variety of organic molecule oxidations.…”

Section: Hcooh + Cooh-> C(oh)2 + Co= + H + E [7]supporting

confidence: 92%

Oxidation of HCOOH and CH 3 OH on Platinum Modified by Foreign Metal Adatoms in 85% Phosphoric Acid

Adžić

¹

,

O’Grady

²

,

Srinivasan

³

1981

J. Electrochem. Soc.

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The use of underpotentially deposited metal atoms as electrocatalysts suggests a promising route for enhancing the kinetics of oxidation of organic fuels. The electro-oxidation of formic acid and methanol was studied on underpotentially deposited metal atoms on platinum in 85% phosphoric acid. The rates of these reactions were greatly improved. Due to adsorption of phosphate ions, formic acid oxidation rates on underpotentially deposited metal atoms are lower than in perchloric acid. The electrocatalytic activity of the investigated underpotentially deposited metals for formic acid oxidation follows the order Pb > Bi > TI: for methanol oxidation during the cathodic scan the rates are higher for lower lead concentrations, which is probably due to lower concentration of adsorbed lead and/or oxide. It is proposed that the enhanced reaction rates with underpotentially deposited metal atoms are due to inhibition of hydrogen adsorption and hence of formation of poisoning intermediates such as COH.The interest in the more efficient use of organic fuels has increased considerably after the energy crisis of 1973. For this reason, the attention of a number of electrochemists has focused on electrochemical energy conversion including the direct oxidation of organic molecules. The oxidation reactions of HCOOH and CI-I3OtI are of particular interest because these molecules are potential fuels for fuel cells and represent "model molecules" for reactions which serve as a basis for studies of more complex ones. It was recently shown (1-3) that foreign metal adatoms have a striking catalytic effect on these reactions on several noble metals in 1M HC104. In this work, the results obtained for the oxidation of formic acid and of methanol on platinum modified by foreign metal adatoms in 85% tI3PO4, which is one of the most attractive electrolytes for practical fuel cells, are reported. ExperimentalThe measurements were made in a three-compartment Pyrex cell. The working electrode was 2 cm 2 Pt foil. The counterelectrode was also Pt, while the reversible hydrogen electrode served as the reference. The working electrode was first polished to obtain a mirror finish, washed, cleaned with 1:1 volume ratio H2SO4-HNO~, and then rinsed with triply distilled water.The acid was purified using essentially the procedure of Ferrier et al. (4) and Huang et al. (5). H~O~ was added to reagent grade 85% H3PO4 (Mallinckrodt) and this solution was heated to 90~ until gas evolution ceased. The acid was then heated to 160~ to reduce the water content and destroy any remaining traces of H202. The water content was adjusted and the acid was preelectrolyzed for 24 hr. ResultsUnderpotential deposition of Pb, Bi, and T1 on Pt in 85% HsPO4.-- Figure 1 shows the underpotential deposition (UPD) of Pb. This metal was added in the form of perchlorate, which introduced some HC104 and H~O * Electrochemical Society Active Member.

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“…The effect of C 0 2 on the current-potential behaviour was studied by conducting the experiments described above under an atmosphere of COa, rather than argon. C 0 2 is electro inactive at the potentials of interest, but reacts with an intermediate of the H+ reduction, namely adsorbed H ', to give an adsorbed 'reduced' C 0 2 species (Giner 1963;Brummer 1966;Breiter 1967;Biegler 1968;Breiter 1968;Brummer & Cahill 1968;Kamath & Hira Lai 1968;Brummer & Cahill 1969;Stonehart 1973;Sobkowski & Czerwinski 1974Andreev et at. 1982;Beden et at.…”

Section: (Ii) Amperometric Measurements O F H+mentioning

confidence: 99%

The dissolution of calcite in aqueous solution at pH < 4: kinetics and mechanism

Compton

¹

,

Unwin

²

1990

Phil. Trans. R. Soc. Lond. A

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The requirements of any experimental investigation of a reaction, such as dissolution or precipitation, at the solid-liquid interface are delineated, and it is shown that no previously adopted experimental method successfully meets all of these criteria. A new strategy for studying such reactions is therefore proposed, and described specifically for the dissolution kinetics of calcium carbonate in acidic aqueous solution. This technique involves locating a calcite crystal in part of one wall of a rectangular duct, through which reactant flows under laminar conditions, and positioning either an amperometric or potentiometric detector electrode immediately adjacent to and downstream of the crystal. The rate of the reaction at the crystal surface is then followed by measuring the concentration of the reactant or products reaching the electrode as a function of solution flow rate. In this way both transport (to the crystal and detection system) and the surface topography of the crystal are defined and controllable, and, most importantly, the concentrations interrogated by the detector electrode are those pertaining at the crystal surface and not the bulk values, which are those probed with other (previous) methods. A mechanistic model for the dissolution reaction at pH < 4, H + + CaCO 3 → C a 2 + + HCO 3 − , is developed, and it is recognized that half-, first- and second-order reactions in surface H + constitute possible candidate heterogeneous processes. The model also takes the following homogeneous (solution) reactions into account: HCO 3 − + H + ⇌ H 2 C O 3 ⟶ k H 2 C O 3 C O 2 + H 2 O , K H 2 C O 3 = a H + a HCO 3 − / a H 2 C O 3 The backward implicit finite difference method is used to provide theory for the proposed flow cell experiment. Specifically this relates the rate of an n th order process at the crystal surface to the transport-limited current at an amperometric detector electrode, as a function of solution flow rate and cell-crystal-electrode geometry. The computational method selected allows both the full parabolic velocity profile and any value of n to be considered. The validity of the numerical approach is checked by invoking the Lévêque approximation (linearizing the parabolic velocity profile) and solving the problem analytically for n = 0 and 1. The numerical method is extended so that both parallel heterogeneous and homogeneous reactions are covered, specifically so that theory describing the mechanistic model can be derived as related to the flow cell experiment. The design and construction of the necessary experimental apparatus is described, along with experiments devised to prove the validity of the experimental approach. The results of flow cell dissolution experiments carried out with 0.25–1.0 mM HCl solutions are presented, and it is shown for the first time that the reaction between H + and calcite is not transport-controlled. Assuming k H 2 C O 3 = 20 s − 1 and K H 2 C O 3 = 3.06 × 1 0 − 4 M , a best fit to the data is obtained for a first-order heterogeneous process with a rate constant of (0.043 ± 0.015) cm s -1 .

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“…In fact, the reverse is the case except in the approach to steady state (Figures 1-4 Composition of -Type. We have discussed the literature concerning the likely composition of "reduced C02"-similar to O-type11•30-in recent publications.31 •32 The basic controversy concerns whether that species is [33][34][35] or is not31•36 similar to adsorbed CO.…”

Section: The Journal Of Physical Chemistrymentioning

confidence: 99%

Adsorption and oxidation of hydrocarbons on noble metal electrodes. VIII. Composition of adsorbed methane and rate-limiting step in the overall methane to carbon dioxide reaction

Taylor¹,

Brummer²

1969

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Composition of electrosorbed methanol

Cited by 35 publications

References 2 publications

Oxidation of HCOOH and CH 3 OH on Platinum Modified by Foreign Metal Adatoms in 85% Phosphoric Acid

Oxidation of HCOOH and CH 3 OH on Platinum Modified by Foreign Metal Adatoms in 85% Phosphoric Acid

The dissolution of calcite in aqueous solution at pH < 4: kinetics and mechanism

Adsorption and oxidation of hydrocarbons on noble metal electrodes. VIII. Composition of adsorbed methane and rate-limiting step in the overall methane to carbon dioxide reaction

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