New insight into the pathways of methanol oxidation

Batista, Eduardo Augusto Caldas; Malpass, Geoffroy Roger Pointer; Motheo, Artur J.; Iwasita, T.

doi:10.1016/j.elecom.2003.08.010

Cited by 126 publications

(129 citation statements)

References 15 publications

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“…A noticeably different trend in the m/z 60:44 ratio is observed for the cyclic voltammograms recorded in perchloric acid: compared to sulfuric acid, the selectivity of Pt(100) and especially Pt(110) towards the direct oxidation pathway is enhanced, while Pt(111) is less active towards the direct pathway in perchloric acid compared to that in sulfuric acid. This observation is in agreement with results from Batista et al [45], who found that on Pt(111) the pathway producing adsorbed CO is inhibited in the presence of H 2 SO 4 . This enhanced selectivity of the direct oxidation pathway in sulfuric acid was explained as follows: adsorption of methanol via the C-atom and subsequent dehydrogenation to CO ad requires several neighboring Pt sites, while adsorption of methanol as methoxy and subsequent dehydrogenation to formaldehyde requires only a single vacant surface site [40,41].…”

Section: Methanol Electrooxidation On Ptsupporting

confidence: 93%

Mechanisms of Carbon Monoxide and Methanol Oxidation at Single-crystal Electrodes

et al. 2007

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The electrochemical oxidation of carbon monoxide and methanol on single-crystal noble metal electrodes has been studied using cyclic voltammetry, chronoamperometry, in situ FTIR spectroscopy, online electrochemical mass spectrometry, and theoretical methods. The oxidation of CO was found to be enhanced by steps and defects. Furthermore, the surface diffusion rate was found to have a significant influence on the kinetics of the oxidation process: for high diffusion rates, such as the oxidation of CO on platinum, the kinetics can be described by a mean field model, while for low diffusion rates, such as CO oxidation on rhodium in sulfuric acid, a nucleationand-growth model was found to be more suitable. Voltammetric and mass spectrometric measurements on the oxidation of methanol on platinum indicate that steps enhance the overall reaction rate. In general, the selectivity towards the direct oxidation pathway through soluble intermediates was found to be higher in the absence of strongly adsorbing anions. In both perchloric and sulfuric acid, this selectivity was also found to increase with increasing step density. In sulfuric acid, Pt(111) shows the highest relative contribution for the direct pathway of all surfaces studied in that electrolyte. Based on these results, a detailed reaction scheme for the electrochemical oxidation of methanol is presented.

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Section: Methanol Electrooxidation On Ptsupporting

confidence: 93%

Mechanisms of Carbon Monoxide and Methanol Oxidation at Single-crystal Electrodes

et al. 2007

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“…However, more recent studies of the mechanism of the methanol oxidation on Pt in HClO 4 and H 2 SO 4 media (cf. e.g., [120,121]) indicate the existence of even three parallel routes, differing with the nature of the intermediate: CO ads , HCHO, and HCOOH. The products of methanol oxidation include not only CO 2 since the intermediates HCHO and HCOOH can diffuse away from the electrode.…”

Section: Galvanostatic Conditionsmentioning

confidence: 97%

Temporal Instabilities in Anodic Oxidation of Small Molecules/Ions at Solid Electrodes

Orlik

2012

Monographs in Electrochemistry

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Oscillations and multistability in oxidation processes at solid electrodes are important for several reasons. First, they were reported for species that are (or can appear) important in chemical engineering of fuels, including the fuel cells: hydrogen, carbon monoxide, formaldehyde, formic acid/formate ions, 2-propanol, 1-butanol, hydrazine, or ethylene glycol. It can be useful to know how to avoid instabilities involving these species or, on the contrary, to profit from them. Second, electrooxidation of these molecules exhibits rich variety of nonlinear dynamic behaviors which can be treated in a model way for the sake of generalization. Third, some of these processes, under appropriate conditions, can become a source of spatial or spatiotemporal patterns on electrodes which phenomena only recently gained satisfactory explanation and description. In this chapter, we shall summarize the temporal phenomena associated with the oxidation of the above-mentioned molecules, while pattern formation will be discussed in separate Chap. 2 of volume II.Current research data indicate that such processes should be qualified as electrocatalytic, i.e., the electrode surface is actively engaged in the kinetics of the electron transfer reaction, usually involving the process taking place via the adsorbed intermediate. As in the case of other types of electrochemical oscillators, one can observe the evolution of the understanding of the source of chemical instabilitiesfrom early, sometimes oversimplified explanations oriented exclusively on the properties of the electrode/electrolyte interface toward more recent concepts, involving the analysis of the system's stability in terms of nonlinear dynamics. In particular, oscillations under galvanostatic conditions could be understood only recently in terms of the concept of the HN-NDR oscillator [1] (cf. Chap. 3).The anodic oxidation of H 2 on Pt electrode is an electrocatalytic process, in which the electron transfer is preceded by the adsorption of H 2 molecule on the active surface site. Hence, the oscillatory course of this process can be associated M. Orlik, Self-Organization in Electrochemical Systems I, Monographs in Electrochemistry,

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“…So far, formaldehyde (HCHO), formic acid (HCOOH), formate (HCOO À ) and methyl formate (HCOOCH 3 ) were identified as soluble intermediates which conduct the discussion on the pathways of methanol oxidation. In case the first stripped hydrogen of the adsorbed methanol originates from the hydroxyl, the resulting adsorbed species, H 3 CO ad (methoxide), eliminates a second hydrogen from methoxy, forming formaldehyde which then desorbs [4]. In case the first eliminated hydrogen proceeds from methoxy group, CH 2 OH ad (hydroxymethyl) is the adsorbed intermediate whose further dehydrogenation would lead to formaldehyde and formic acid formation.…”

Section: The Oxidation Of Methanol On Platinummentioning

confidence: 98%

Catalysts for Methanol Oxidation

González

Mota-Lima

2013

Direct Alcohol Fuel Cells

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Methanol electroxidation proceeds via a multistep reaction. Herein, mechanisms of reaction and reaction rates of sub-set of the mechanism on different surfaces are discussed. Platinum is a reasonable catalyst for the first methanol electroxidation steps (dehydrogenation), but not for the last (CO electroxidation). Hence, alloying Platinum with a second metal was used as a strategy to enhance the rate of the last step. Accordingly, enhanced rates of CO electroxidation are attained by modifying the bonding energy of the adsorbate to the catalyst or by promoting the formation of oxygenated species at lower overvoltage. Finally, new perspectives on the field of methanol catalysts are commented including the search for catalysts that promote early onset of oscillations, i.e. under lower overvoltage. IntroductionMethanol is the typical fuel with one carbon (C1) 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 C1 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 CO 2 emission, methanol has, among the other small molecules, the highest energy production per unit of produced

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New insight into the pathways of methanol oxidation

Cited by 126 publications

References 15 publications

Mechanisms of Carbon Monoxide and Methanol Oxidation at Single-crystal Electrodes

Mechanisms of Carbon Monoxide and Methanol Oxidation at Single-crystal Electrodes

Temporal Instabilities in Anodic Oxidation of Small Molecules/Ions at Solid Electrodes

Catalysts for Methanol Oxidation

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