Direct electrocatalysts preparation

PtSn/C electrocatalysts prepared by different methods for direct ethanol fuel cell... 

Since the discovery of carbon nanotubes in the early 1990s [273] there has been emerging interest in their applicability as catalyst supports for low-temperature PEMFCs. Recently, Lee et al. reviewed the area of Pt electrocatalyst preparation techniques using carbon nanotubes and nanofibers as supports [274]. Here, the emphasis will be on the impact of novel nanostructured carbon supports (ordered mesoporous materials, nanotubes, and nanofibers) on the electrocatalytic activity with respect to direct fuel cell anodes. 

E.V. Spinace, L.A.l. do Vale, R.R. Dias, A.O. Neto, M. Linardi, 2006, RSn/C electrocatalysts prepar by different methods for direct ethanol fuel cell. Stud. Surf. Sci. Catal., 162,617-624. 

We have already referred to the Mo/Ru/S Chevrel phases and related catalysts which have long been under investigation for their oxygen reduction properties. Reeve et al. [19] evaluated the methanol tolerance, along with oxygen reduction activity, of a range of transition metal sulfide electrocatalysts, in a liquid-feed solid-polymer-electrolyte DMFC. The catalysts were prepared in high surface area by direct synthesis onto various surface-functionalized carbon blacks. The intrinsic... 

Q. Xin, Preparation of supported RRu/C electrocatalyst for direct methanol fuel cells, Electrochim. Acta 50, 2371-2376 (2005). 

For a long time, conventional alkaline electrolyzers used Ni as an anode. This metal is relatively inexpensive and a satisfactory electrocatalyst for O2 evolution. With the advent of DSA (a Trade Name for dimensionally stable anodes) in the chlor-alkali industry [41, 42[, it became clear that thermal oxides deposited on Ni were much better electrocatalysts than Ni itself with reduction in overpotential and increased stability. This led to the development of activated anodes. In general, Ni is a support for alkaline solutions and Ti for acidic solutions. The latter, however, poses problems of passivation at the Ti/overlayer interface that can reduce the stability of these anodes [43[. On the other hand, in acid electrolysis, the catalyst is directly pressed against the membrane, which eliminates the problem of support passivation. In addition to improving stability and activity, the way in which dry oxides are prepared (particularly thermal decomposition) develops especially large surface areas that contribute to the optimization of their performance. 

The direct electrochemical deposition methods for the preparation of electrocatalysts allow to localize the catalyst particles on the top surface of the carbon support, as close as possible to the solid polymer electrolyte and does not need heat (oxidative and/or reducing) treatment, as most of the chemical methods do, in order to clean the catalytic particles from surfactant contamination [27,28], This will prevent catalyst sintering due to the agglomeration of nanoparticles under thermal treatment. 

All the electrocatalysts are prepared as columnar surfaces (a preferential direction along y, as explained in Chapter 15), that is, d<< h, therefore, the potential or the current (depending on the electrochemical system) is generated mostly in the y direction. We can say... 

The overall objective is to develop new methods of preparing electrocatalysts, novel electrode structures, and new-low cost electrocatalysts that will result in overall cost reduction and improved performance of direct methanol fuel cells. 

One such reaction that has been studied is the electrocatalytic reduction of oxygen directly to water.The electrocatalysts for this process are often based on metal porphyrins and phthalo-cyanins. Thus a graphite eleetrode whose surface was modified by the irreversible adsorption of a cofacial dicobalt porphyrin dimer was able to reduce oxygen under conditions where the reduction did not occur on the bare electrode itself. Similarly, a catalytic chemically modified electrode for the oxidation of chloride to chlorine has been prepared where the active catalyst was reported to be a ruthenium dimer, [(bipy)2(0H)Ru 0Ru 0(bipy)2] , which was reduced to the corresponding [Ru -Ru ] dimer during the reaction. 

Case Study 1 Pt/Ru Carbon Three types of 30 wt.% PtsoRuso/Vulcan XC 72 electrocatalysts for Direct Methanol Oxidation Fuel Cells (DMFC) were prepared using Nl BetsH (Cat. 1), LiBetsH (Cat 2.), and Al(Me)3 (Cat 3.) for the co-reduction of Pt- and Ru-salts [169] ... 

In another work, Shukla and co-authors [27] studied the electrocatalytic activity of carbon-supported Pt-Au alloy catalysts, with different atomic ratios, to improve the oxygen reduction reaction (ORR) kinetics and methanol tolerance, in a direct methanol fuel ceU. The electrocatalysts were prepared by codeposition of Pt and Au nanoparticles onto a carbon support. 

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