Electro-Oxidation of Oxygenated Molecules

The use of simple organic compounds, such as methanol, 1. formaldehyde, 2, and formic acid, 3 have been deemed attractive for fuel cell applications due to several advantages, which include the fact that they are easy to store and handle, and they possess high energy densities. Another attractive feature of these types of fuels Is that they can be generated from 

Other potential oxygenated hydrocarbon fuels include C -Cs molecules which include one or more C-C bonds include tetrahydrofuran, Ui, 1.3,-dioxolane.  

ethylene carbonate, 12, ethanol, oxalic acid. 13. glyoxylic acid, 14, 

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Electro-oxidation of Oxygenated Molecules in Fuel Cells... 

This chapter attempts to provide a critical review of the work carried out on alkaline fuel cell, which directly uses hydrogen rich liquid fuel and oxygen or air as an oxidant. The subjects covered are electrode materials, electrolyte, half-cell analysis and single cell performance in alkaline medium. Koscher et al. (2003) brought out elaborate review work on direct methanol alkaline fuel cell. Earlier Parsons et al. (1988) reviewed literature on anode electrode where, the oxidation of small organic molecules in acid as well as in alkaline conditions was considered. A review work on electro-oxidation of boron compounds was done by Morris et al. (1985). However, in this chapter use of three specific fuels, e.g., methanol, ethanol and sodium borohydride in alkaline fuel cell is discussed. 

Oxygen electroreduction/ EDAX, XRD NixCo3 04 spinel KOH solution Electro-deposition of oxide films by spraying on Ni foil The ratio of oxygen molecules reduced via the direct 4e pathway with respect to those reduced via indirect 2+2 electron pathway depends on x. The ratio is maximum for X = 0 and 0.6 < x < 1.2 Heller-Ling etal. (1997)... 

Gupta et al. (2004) studied the cyclic voltammograms (Fig. 10) of ethanol electro-oxidation behavior on CuNi, CuNi/Pt and CuNi/PtRu alloys electro-catalysts in 0.5 M NaOH solution. Fig. 10 (a) shows a steady rise of the anodic peak current for the CuNi/Pt electro-catalyst. The peak current increases substantially from F to the 50 scan. Fig. 10 (b) shows the increase in reaction kinetics for ethanol electro-oxidation when Ru is added in the alloy. They have detected the presence of acetaldehyde and CO2 (as carbonate) with CuNi/PtRu electro-catalyst Authors found carbonate ions because of the cleavage of C—C bond of ethanol molecule. The temperature of ethanol electro-oxidation was not mentioned although the experimental work was done at room temperature. Tripkovic et al. (2001) studied the electro-oxidation of methanol, ethanol, -propanol and n-butanol (C[—C4 alcohol) in alkaline solution at the Pt (111) and vicinal stepped planes Pt (755) and Pt (332). The nature of the oxygen-containing species as well as their role in the alcohol oxidation is proposed. A dual path reaction mechanism as shown by eqs. (4) and (5) is proposed based on the assumptions that RCOa is a reactive intermediate of the main reaction path, while CO2 is a product of the poisoning species oxidation in a parallel reaction path. 

The improved electro-oxidation behavior observed with the C-8 and C-12 acid coated electrodes might be attributed to (i) the higher concentration of sulfonic acid groups present in the electrocatalytic layer of the C-8 acid and C-12 acid coated electrode, (ii) enhanced diffusion of reactants and products, and/or (iii) the enhanced wettability" at the catalytic site of oxidation facilitating hydrocarbon adsorbtion. These results are in accordance with earlier findings where the addition of C-8 acid was observed to significantly enhance the ease of oxidation of various oxygenated molecules. 

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