Ethanol electrooxidation on a carbon-supported Pt catalyst at elevated temperature and pressure: A high-temperature/high-pressure DEMS study

Sun, Shi‐Gang; Halseid, M. Chojak; Heinen, Martin; Jusys, Z.; Behm, R. Jürgen

doi:10.1016/j.jpowsour.2009.01.073

Cited by 116 publications

(116 citation statements)

References 60 publications

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“…7 Using 0.1 M ethanol at 0.58 V, they found the overall activation energy to be 41 kJmol −1 and the CO 2 activation energy 67 kJmol −1 . They attributed the observed increase in CO 2 efficiency at lower ethanol concentrations to transport effects.…”

Section: Resultsmentioning

confidence: 99%

“…The values are rather high, being ∼0.4 eV for the former and ∼0.7 eV for the latter in ref. 7 for example. In ref 7 Behm et al discuss earlier effective activation energy determinations from other labs, noting that they were smaller, and that they are affected by the complexity of having many individual reactions and mass transport effects.…”

Section: Temperature-dependency Of Reaction Mechanisms and Products-mentioning

confidence: 99%

See 1 more Smart Citation

Mechanisms for Ethanol Electrooxidation on Pt(111) and Adsorption Bond Strengths Defining an Ideal Catalyst

Asiri

Anderson

2014

J. Electrochem. Soc.

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Ethanol electrooxidation on the Pt(111) electrode has been studied with computational theory. Using a solvation model and a modified Poison-Boltzmann theory for electrolyte polarization, standard reversible potentials for forming 17 reaction intermediates in solution were calculated with density functional theory. Reversible potentials for adsorbed intermediates were then determined by inputting calculated adsorption energies into a linear Gibbs energy relationship. A path to CO 2 was found where surface potentials were low and close to the calculated 0.004 V reversible potential for the 12 electron oxidation of ethanol. An exception was the 0.49 V potential for forming the OH(ads) from H 2 O(l), this being required for oxidation of CO(ads) and RH(ads) intermediates. The surface potentials show that acetyl, OCCH 3 (ads) forms at small positive potentials and decomposes to CH(ads), CH 3 (ads), and CO(ads), which poison the surface at these potentials. Energy losses due to non-electron transfer reaction steps are small and cause a small shift in the reversible potential for the 12 electron oxidation. Values for adsorption bond strengths over a perfect catalyst were determined. It is concluded that on an ideal catalyst most intermediates will adsorb more weakly and OH more strongly than on Pt(111). Unlike a fossil fuel, ethanol is renewable and can be produced from biomass. Compared to methanol, ethanol is less toxic. The specific energy density of ethanol is high (8.0 kWh/kg). It is liquid, which makes it easy to store and transport. These advantages make the direct ethanol fuel cell (DEFC) a promising green energy source. However, commercialization of DEFC is hindered by the slow inefficient electrooxidation reaction of ethanol on platinum. Platinum is active as the anode electrocatalyst in hydrogen fuel cells but is much less active for ethanol oxidation. Theoretical understanding of the failures of platinum will establish the specific steps during the electrooxidation which present the challenges. As shown in this paper, some of these challenges can be overcome by using electrocatalysts where reaction intermediates have specific adsorption energies to the active site. Designing materials with these properties is the goal for electrocatalyst development.The complete electrochemical oxidation reaction which takes place at the anode surface produces twelve electrons, twelve protons, and carbon dioxide:The 4 Thus, the overpotential for oxidation is about 300 mV-400 mV under typically employed conditions of study.However, the oxidation is not complete, and several final oxidation products have been observed over platinum electrodes. Iwasita's on-line differential electrochemical mass spectroscopy (DEMS) mea- * Electrochemical Society Active Member.z E-mail: aba@po.cwru.edu surements identified acetaldehyde, OCHCH 3 , forming at potentials greater than about 0.3 V and identified CO 2 forming at potentials greater than about 0.5 V.2 Fourier transform infrared (FTIR) spectroscopy provided evidence for the functional g...

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Section: Resultsmentioning

confidence: 99%

Section: Temperature-dependency Of Reaction Mechanisms and Products-mentioning

confidence: 99%

Mechanisms for Ethanol Electrooxidation on Pt(111) and Adsorption Bond Strengths Defining an Ideal Catalyst

Asiri

Anderson

2014

J. Electrochem. Soc.

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“…A detailed understanding of the reaction mechanism and in particular of the rate-limiting step(s) in EOR under continuous reaction conditions is of critical importance for the design of highly active catalysts [11,12]. Although numerous experimental studies using Fourier transform infrared spectroscopy (FTIR) [13][14][15][16][17][18][19][20][21][22][23][24][25][26] or differential electrochemical mass spectrometry (DEMS) [27][28][29][30][31][32][33][34][35][36][37], as well as theoretical studies [38][39][40][41][42][43][44][45] have been conducted to understand the EOR process, a detailed mechanism of EOR remains unclear or even contradictory. Nevertheless, a so-called dual-pathway (C1 and C2) mechanism has been largely agreed upon: the C1 pathway proceeds via adsorbed carbon monoxide (COads) intermediate to form CO2 (or carbonate in alkaline solutions) by delivering 12 electrons, and the C2 pathway mainly leads to the formation of acetic acid (or acetate in alkaline solutions) by delivering four electrons and/or acetaldehyde by delivering two electrons.…”

Section: Introductionmentioning

confidence: 99%

Recent Advances on Electro-Oxidation of Ethanol on Pt- and Pd-Based Catalysts: From Reaction Mechanisms to Catalytic Materials

2015

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Abstract:The ethanol oxidation reaction (EOR) has drawn increasing interest in electrocatalysis and fuel cells by considering that ethanol as a biomass fuel has advantages of low toxicity, renewability, and a high theoretical energy density compared to methanol. Since EOR is a complex multiple-electron process involving various intermediates and products, the mechanistic investigation as well as the rational design of electrocatalysts are challenging yet essential for the desired complete oxidation to CO2. This mini review is aimed at presenting an overview of the advances in the study of reaction mechanisms and electrocatalytic materials for EOR over the past two decades with a focus on Pt-and Pd-based catalysts. We start with discussion on the mechanistic understanding of EOR on Pt and Pd surfaces using selected publications as examples. Consensuses from the mechanistic studies are that sufficient active surface sites to facilitate the cleavage of the C-C bond and the adsorption of water or its residue are critical for obtaining a higher electro-oxidation activity. We then show how this understanding has been applied to achieve improved performance on various Pt-and Pd-based catalysts through optimizing electronic and bifunctional effects, as well as by tuning their surface composition and structure. Finally we point out the remaining key problems in the development of anode electrocatalysts for EOR. OPEN ACCESSCatalysts 2015, 5 1508

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“…However, there have been relatively few studies of product distributions for ethanol oxidation at elevated temperatures, in either liquid electrolytes or PEM cells. Sun et al 22 conducted a comprehensive DEMS study of CO 2 production at a carbon supported Pt (Pt/C) electrode in aqueous sulfuric acid over a temperature range of 23-100…”

mentioning

confidence: 99%

Product Distributions and Efficiencies for Ethanol Oxidation in a Proton Exchange Membrane Electrolysis Cell

Altarawneh

Pickup

2017

J. Electrochem. Soc.

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The stoichiometry, efficiency, and product distribution for ethanol oxidation in fuel cell hardware has been determined at 80 • C for commercial Pt/C, PtRu/C and PtSn/C anode catalysts. The amounts of ethanol consumed and acetic acid and acetaldehyde produced were determined by proton NMR spectroscopy while CO 2 was measured with a non-dispersive infrared CO 2 monitor. The Pt/C catalyst was most selective for the complete oxidation of ethanol to CO 2 at all potentials and therefore produced the highest number of electrons per ethanol molecule (stoichiometry). Consequently, it would provide the highest efficiency for a fuel cell, and for an electrolysis cell at high current densities. However, PtRu/C provided much higher currents at low overpotentials and therefore better electrolysis efficiency than Pt/C at low current densities. The main product at the PtRu/C catalyst was acetic acid, with ≥ 86% conversion at potentials ≥ 0.35 V vs. a dynamic hydrogen electrode. The PtSn/C catalyst also provided high yields of acetic acid (65-75%), with substantial production of CO 2 (26-27%) at high potentials. The electrochemical oxidation of ethanol in cells with proton exchange membrane (PEM) electrolytes is of central importance to the development of energy technologies based on bio-ethanol. PEM-based direct ethanol fuel cell (DEFC) 1,2 power systems are potentially one of the best alternatives to internal combustion engines, 3 although their efficiencies will need to be increased significantly. Alternatively, ethanol electrolysis cells (EEC) can be used to produce hydrogen. [4][5][6] In an EEC, ethanol is oxidized at the anode and protons are reduced to hydrogen at the cathode. In a DEFC, ethanol is oxidized at the anode and oxygen is reduced to water at the cathode. The attraction of these technologies arises from their high theoretical efficiencies and the perception that emissions will be low. However, the incomplete oxidation of ethanol at all known catalysts currently results in low efficiency cells and large amounts of byproducts.2 To achieve high energy efficiencies in EECs and DEFCs the faradaic efficiency (ε F ) for the electrochemical oxidation of ethanol to carbon dioxide (Eq. 1) must be high.2,7 However, in practice low yields of CO 2 have generally been reported, with the major products being acetaldehyde (Eq. 2) and acetic acid (Eq. 3).The faradaic efficiency is the ratio of the average number of electrons transferred per molecule of ethanol (n av ) to the maximum of 12 for the complete oxidation to CO 2 (ε F = n av /12). It is determined by the product distribution according to Eq. 4,where n i is the number of electrons transferred to form product i and f i is the fraction of ethanol converted to product i. The importance of n av in determining the efficiency of ethanol oxidation technologies makes product analysis of central importance in the development of better anode catalysts. 9Although there have been many advances in the electrochemical performances (voltage efficiency) of ethanol oxidation catalysts...

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Ethanol electrooxidation on a carbon-supported Pt catalyst at elevated temperature and pressure: A high-temperature/high-pressure DEMS study

Cited by 116 publications

References 60 publications

Mechanisms for Ethanol Electrooxidation on Pt(111) and Adsorption Bond Strengths Defining an Ideal Catalyst

Mechanisms for Ethanol Electrooxidation on Pt(111) and Adsorption Bond Strengths Defining an Ideal Catalyst

Recent Advances on Electro-Oxidation of Ethanol on Pt- and Pd-Based Catalysts: From Reaction Mechanisms to Catalytic Materials

Product Distributions and Efficiencies for Ethanol Oxidation in a Proton Exchange Membrane Electrolysis Cell

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