Real-time FTIR spectroscopy as an electrochemical mechanistic probe

Leung, Lam-Wing H.; Chang, Si‐Chung; Weaver, Michael J.

doi:10.1016/0022-0728(89)85078-8

Cited by 149 publications

(83 citation statements)

References 43 publications

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“…More than 75% of the ethanol and acetaldehyde adsorbate, the exact value depends on the adsorption potential, are oxidized in the low potential region (below 0.85 V), while the remaining fraction can only be oxidized in the high potential region, above 0.85 V. The number of electrons for the oxidation of the adsorbate to CO 2 is slightly lower than, or approximately, 2.5 in all cases except the very negative adsorption potentials. This agrees with findings from IR experiments on massive bulk Pt electrodes, which shows that adsorbed CO is formed during the adsorption of ethanol and acetaldehyde [5,10,11,13,14,20,26]. Hence, adsorption of both molecules on Pt/C is predominantly dissociative.…”

Section: Discussionsupporting

confidence: 90%

“…This anodic current, which increases for more positive potentials, indicates continuous oxidation of ethanol at these potentials. It is most likely to be oxidized to acetaldehyde and acetic acid, as supported by DEMS [1,2,4,5,7,10,18,20] and in-situ IR measurements [26]. Therefore, the charge collected upon ethanol adsorption at potentials positive of 0.21 V cannot be related to ethanol adsorption alone and is not reliable for quantitative evaluation.…”

Section: Chronoamperometric Transients During Adsorption Of Ethanol mentioning

confidence: 97%

“…The average number of electrons lies between 2.2 and 2.4 for n l , except for adsorption at 0.16 V. This is close to the value of 2.0, which would be expected for CO oxidation. Likewise, IR experiments have proven that adsorbed CO is formed during ethanol adsorption [10,11,13,14,26] high potential region the electron yields are much higher, between 3 and 6. This indicates that the origin of the high potential peak is the complete oxidation of (partly oxidized) adsorbed hydrocarbons, in agreement with previous findings for ethanol adsorbate stripping on bulk Pt and porous Pt electrodes [4,19,20].…”

Section: Oxidation and Reduction Of Ethanol Adsorbate On Pt/vulcanmentioning

confidence: 97%

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Ethanol and Acetaldehyde Adsorption on a Carbon‐Supported Pt Catalyst: A Comparative DEMS Study

Wang

Jusys

Behm³

2004

Fuel Cells

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The adsorption of ethanol and acetaldehyde on carbon Vulcan supported Pt fuel cell catalyst and the electrochemical desorption of the adsorption products were studied, using electrochemical measurements and differential electrochemical mass spectrosmetry (DEMS), under continuous flow conditions. Faradaic current adsorption transients at different constant adsorption potentials, which also include CO adsorption for comparison, show pronounced effects of the adsorption potential and the nature of the reactant molecule. Acetaldehyde adsorption is much faster than ethanol adsorption at all potentials. Pronounced Had induced blocking effects for ethanol adsorption are observed at very cathodic adsorption potentials, < 0.16 V, while for acetaldehyde adsorption this effect is much less significant. Comparison of the adsorption charge for CO adsorption with the H‐upd charge allows differentiation between H‐displacement and double‐layer charging effects. Continuous bulk oxidation is observed for both reactants at potentials > 0.31 V; for acetaldehyde adsorption, increasing bulk reduction is found at low potentials. Based on the electron yield per CO2 molecule formed and on the similarity with the CO stripping characteristics the dominant stable adsorbate is CO, coadsorbed with smaller amounts of (partly oxidized) hydrocarbon decomposition fragments, which are also oxidized at higher potentials (> 0.85 V) and which can be reductively desorbed as methane or, to a very small extent, as ethane. The presence of small amounts of adsorbed C2 species and the oxidative dissociation of these species in the main CO oxidation potential range is clearly demonstrated by increased methane desorption after a potential shift to 0.85 V. The data demonstrate that the Pt/Vulcan catalyst is very reactive for C‐C bond breaking upon adsorption of these reactants.

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Section: Discussionsupporting

confidence: 90%

Section: Chronoamperometric Transients During Adsorption Of Ethanol mentioning

confidence: 97%

Section: Oxidation and Reduction Of Ethanol Adsorbate On Pt/vulcanmentioning

confidence: 97%

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Ethanol and Acetaldehyde Adsorption on a Carbon‐Supported Pt Catalyst: A Comparative DEMS Study

Wang

Jusys

Behm³

2004

Fuel Cells

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“…Improving the further oxidation of acetaldehyde within the fuel cell is therefore of considerable interest for technical applications. Previous studies on acetaldehyde oxidation, however, are scarce and mostly deal with Pt electrodes [5][6][7][8][9][10][11][12][13][14]. First results on the performance of modified Pt and Pt alloy electrodes were reported in [6,15].…”

Section: Introductionmentioning

confidence: 99%

Electrooxidation of acetaldehyde on carbon-supported Pt, PtRu and Pt3Sn and unsupported PtRu0.2 catalysts: A quantitative DEMS study

2006

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The oxidation of acetaldehyde on carbon supported Pt/Vulcan, PtRu/Vulcan and Pt 3 Sn/Vulcan nanoparticle catalysts and, for comparison, on polycrystalline Pt and on an unsupported PtRu 0.2 catalyst, was investigated under continuous reaction and continuous electrolyte flow conditions, employing electrochemical and quantitative differential electrochemical mass spectroscopy (DEMS) measurements. Product distribution and the effects of reaction potential and reactant concentration were investigated by potentiodynamic and potentiostatic measurements. Reaction transients, following both the Faradaic current as well as the CO 2 related mass spectrometric intensity, revealed a very small current efficiency for CO 2 formation of a few percent for 0.1 M acetaldehyde bulk oxidation under steady-state conditions on all three catalysts, the dominant oxidation product being acetic acid. Pt alloy catalysts showed a higher activity than Pt/Vulcan at lower potential (0.51 V), but do not lead to a better selectivity for complete oxidation to CO 2 . C-C bond breaking is rate limiting for complete oxidation at potentials with significant oxidation rates for all three catalysts. The data agree with a parallel pathway reaction mechanism, with formation and subsequent oxidation of CO ad and CH x, ad species in the one pathway and partial oxidation to acetic acid in the other pathway, with the latter pathway being, by far, dominant under present reaction conditions.

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“…[15] Behm and co-workers [1] performed a thorough investigation on the selectivity under a wide range of conditions and employing a wide range of morphologies, and they convincingly showed that platinum catalysts exhibit selectivity towards CO 2 in the region of 0.5-7.5 %, which is far short of the selectivity needed for economic implementation of the technology. This problem has proven difficult to surmount empirically.…”

mentioning

confidence: 99%

Origin of Low CO₂ Selectivity on Platinum in the Direct Ethanol Fuel Cell

et al. 2012

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The direct ethanol fuel cell (DEFC) represents one of the most exciting future clean energy solutions in modern research, because ethanol can be sustainably produced from biomass, is relatively nontoxic and, most importantly, has a high energy density. [1][2][3][4][5][6][7][8] The exceptional energy density is due to the transfer of 12 electrons from ethanol during complete electrochemical oxidation (as opposed to six electrons from methanol or two from hydrogen). The practicality of such a device is contingent on its ability to selectively catalyze the total oxidation of ethanol to CO 2 . [9,10] However, the CO 2 selectivity in the current ethanol fuel cells is very low, and the main products are acetic acid (resulting in the transfer of only four electrons) and acetaldehyde (only two electrons) in most systems reported. [11][12][13] Herein, we address the origin of low CO 2 selectivity in the DEFC, arguably the most important question to be answered in the field, using first-principles calculations.The pioneering work on DEFCs can be traced back to the 1950s, [14] but it was not until later that the selectivity was comprehensively investigated with IR spectroscopy showing CO 2 to be a minor product.[15] Behm and co-workers [1] performed a thorough investigation on the selectivity under a wide range of conditions and employing a wide range of morphologies, and they convincingly showed that platinum catalysts exhibit selectivity towards CO 2 in the region of 0.5-7.5 %, which is far short of the selectivity needed for economic implementation of the technology. This problem has proven difficult to surmount empirically. Recent work has made significant progress in terms of activity and selectivity, [2] but further improvements are required. Theoretical studies have made considerable advances [2,[16][17][18] and identified the platinum monoatomic step as the most likely site for total ethanol oxidation and concluded that the close-packed surfaces are unsuitable. [17] Despite the extensive experimental and theoretical work that has been carried out, the inhibiting factors in CO 2 formation remain unclear. There are good reasons for this: 1) the catalytic reactions occur on solid surfaces in the presence of a solvent, resulting in a system that is complex to understand at the molecular level; and 2) electrocatalysts operate at an applied potential (i.e. bearing charge), leading to more complications. Hence, it is extremely difficult to characterize the molecular-level surface processes by using experimental techniques, and it is also a huge computational challenge to realistically model the system. Without a clear understanding of the issue, strategies to overcome the problem remain limited to trial and error.Although the selectivity problem has been identified, a fundamental understanding of the low CO 2 selectivity observed is still missing. In fact, the low selectivity of CO 2 in ethanol fuel cells is in contrast to the general consensus in chemistry: CO 2 is significantly more stable than the major products acetic...

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Real-time FTIR spectroscopy as an electrochemical mechanistic probe

Cited by 149 publications

References 43 publications

Ethanol and Acetaldehyde Adsorption on a Carbon‐Supported Pt Catalyst: A Comparative DEMS Study

Ethanol and Acetaldehyde Adsorption on a Carbon‐Supported Pt Catalyst: A Comparative DEMS Study

Electrooxidation of acetaldehyde on carbon-supported Pt, PtRu and Pt3Sn and unsupported PtRu0.2 catalysts: A quantitative DEMS study

Origin of Low CO₂ Selectivity on Platinum in the Direct Ethanol Fuel Cell

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Real-time FTIR spectroscopy as an electrochemical mechanistic probe

Cited by 149 publications

References 43 publications

Ethanol and Acetaldehyde Adsorption on a Carbon‐Supported Pt Catalyst: A Comparative DEMS Study

Ethanol and Acetaldehyde Adsorption on a Carbon‐Supported Pt Catalyst: A Comparative DEMS Study

Electrooxidation of acetaldehyde on carbon-supported Pt, PtRu and Pt3Sn and unsupported PtRu0.2 catalysts: A quantitative DEMS study

Origin of Low CO2 Selectivity on Platinum in the Direct Ethanol Fuel Cell

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Origin of Low CO₂ Selectivity on Platinum in the Direct Ethanol Fuel Cell