Catalytic Reactions in Direct Ethanol Fuel Cells

Kim, In; Han, Oc Hee; Chae, Seen Ae; Paik, Younkee; Kwon, Sung-Hyea; Lee, Kug‐Seung; Sung, Yung‐Eun; Kim, Hasuck

doi:10.1002/anie.201005745

Cited by 110 publications

(90 citation statements)

References 22 publications

(58 reference statements)

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“…Measurements of products from PEM-DEFCs have mainly been made by analyzing the anode exhaust solution only, 7,13,[23][24][25][26][27][28][29][30] which provides inaccurate results due to crossover of products to the cathode, and chemical oxidation of ethanol by the oxygen supplied to the cathode. 26,31 The latter problem can be avoided by using nitrogen and/or hydrogen at the cathode, 31 while the loss of products by crossover can be addressed by analysis of the cathode exhaust.…”

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confidence: 99%

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

Altarawneh

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

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2017

J. Electrochem. Soc.

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“…All electrochemical measurements were performed using a CH Instruments Model 760D workstation (Austin, TX, USA) in three electrodes configuration. The glassy carbon working electrode was utilized in a form of the disk of geometric area, 0.071 cm 2 . The reference electrode was the K 2 SO 4 -saturated Hg 2 SO 4 electrode, and the carbon rod was set as the counter electrode.…”

Section: Methodsmentioning

confidence: 99%

“…No oxidation of ethanol to products higher than acetaldehyde (e.g. CO 2 ) 58,62 are expected below 0.5 V. An important issue of the data of Figs. 4A and 4B is that the voltammetric responses are largely similar except that currents are ca.…”

Section: Microscopic Characterization Of Tio 2 Cnts and Cnt-supportedmentioning

confidence: 98%

“…Although ethanol (C 2 H 5 OH) is a model di-carbonic (ethyl) alcohol, its electrooxidation is much more complex when compared to the oxidation mechanism of mono-carbonic (methyl) alcohol. Indeed, methanol (CH 3 OH) can be readily oxidized to the final product, CO 2 , through the transfer of six electrons. 1 Due to high toxicity of methanol and its capability to undergo crossover through proton-conducting membranes to the cathodic compartments of fuel cells, intense research involving other small organic molecules including ethanol [2][3][4][5][6][7][8][9][10] has been recently pursued.…”

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Electroanalysis of Ethanol Oxidation and Reactivity of Platinum-Ruthenium Catalysts Supported onto Nanostructured Titanium Dioxide Matrices

Rutkowska

Kulesza

2015

J. Electrochem. Soc.

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This study concentrates on the development of catalytic materials capable of enhancing oxidation of ethanol particularly at low potentials, i.e. at conditions resembling operation of anodes in low temperature fuel cells. Indeed, the ethanol oxidation currents measured under voltammetric and chronoamperometric conditions have been significantly increased following dispersing bimetallic PtRu nanoparticle (∼4 nm) catalysts over TiO 2 (80% anatase, 20% rutile) nanostructures (∼20-30 nm) supported onto multi-walled carbon nanotubes. The improvement in activity is attributed not only to better dispersion of PtRu centers (some increase of active surface area) or improved (carbon-nanotube-assisted) propagation of electrons at the catalytic interface but also to the presence of hydroxyl groups and high mobility of protons at neighboring (to PtRu) TiO 2 . Further, specific interactions between TiO 2 and Pt or Ru metallic components are feasible. Importance of addition of TiO 2 is also evident from kinetic analysis based on measurements of steady-state currents at different concentrations. Ethanol is a renewable low-cost biofuel acting not only during simple combustion but also under electrochemical oxidation (catalytic) conditions thus becoming a reactant of potential importance to the technology of low-temperature direct-alcohol fuel cells. In principle, ethanol has high energy density, 29.7 kJ g −1 (23.3 kJ cm −3 ), moderate toxicity, and it exists as liquid at room temperature what allows its easier handling, transportation and storage. Although ethanol (C 2 H 5 OH) is a model di-carbonic (ethyl) alcohol, its electrooxidation is much more complex when compared to the oxidation mechanism of mono-carbonic (methyl) alcohol. Indeed, methanol (CH 3 OH) can be readily oxidized to the final product, CO 2 , through the transfer of six electrons.1 Due to high toxicity of methanol and its capability to undergo crossover through proton-conducting membranes to the cathodic compartments of fuel cells, intense research involving other small organic molecules including ethanol 2-10 has been recently pursued.If electrooxidation of ethanol proceeded ideally to carbon dioxide, the reaction would involve twelve electrons; under such conditions, the fuel cell (with an oxygen cathode) would theoretically produce the open circuit potential of 1.14 V. But complete oxidation of ethanol under electrochemical conditions is a complex reaction because the process would require cleavage of the strong C-C bond in the C 2 H 5 OH molecule.11-13 Consequently, the reaction rate is rather slow at ambient conditions, and typically acetaldehyde (two-electron oxidation) or acetic acid (four-electron oxidation) are formed during electrooxidations at common Pt-based (e.g. PtRu or PtSn) catalytic systems.Despite the unique ability of metallic platinum catalysts to break C-C bond in the ethanol molecule, Pt alloys with Ru or Sn tend to produce higher electrocatalytic currents than platinum itself. 14,15 Practical utility of bare Pt is largely limited by blocki...

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“…13,15,16 Labeling the specific sites of molecules with isotopes has made it easier to examine chemical reaction mechanisms. [17][18][19] Proton-deuteron exchange has been used to distinguish the surface sites and inner sites of proteins 4,20 and inorganic materials.…”

Section: 8-12mentioning

confidence: 99%

Deuterium Naturally Present in Solvent and Site-Specific Isotope Population of Deuterium-Enriched Solute

Hwang¹,

Han

Kim³

2013

Bulletin of the Korean Chemical Society

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As the concentration of aqueous CD 3 OH solutions was decreased, the OD peaks in 2 H NMR spectra grew relative to the CD 3 peaks. Isotope impurity for OH groups of CD 3 OH and deuterium naturally present in water contributed to the OD peaks. Using these peak area data, the site-specific isotope populations of isotope enriched chemicals were measured. In addition, the method using both 1 H and 2H NMR spectroscopy was demonstrated with neat CD 3 OH to measure the site-specific isotope populations. The results indicate that although it represents only ~0.015% of hydrogen isotopes, the deuterium naturally present in solvents cannot be ignored, especially when the concentration of deuterium-enriched solutes is varied. Proton/deuteron exchange between methyl and methyl/hydroxyl groups was confirmed to be negligible, while that among hydroxyl groups was detectable.

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Catalytic Reactions in Direct Ethanol Fuel Cells

Cited by 110 publications

References 22 publications

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

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

Electroanalysis of Ethanol Oxidation and Reactivity of Platinum-Ruthenium Catalysts Supported onto Nanostructured Titanium Dioxide Matrices

Deuterium Naturally Present in Solvent and Site-Specific Isotope Population of Deuterium-Enriched Solute

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