Catalytic methanol electrooxidation

Pt-Ru anodes for methanol electrooxidation The catalytically most active samples are highly dispersed and contain, as indicated by the Mossbauer data, a mixture of two Ru(IV) species... 

The catalytic properties of a Pt/Sn combination were observed on different kinds of electrode materials alloys [90], electro co-deposits of Pt and Sn [89, 90], underpotential deposited tin [42] or a mixture of tin oxide and platinum deposited on glass [95], All different materials present a marked influence on methanol electrooxidation. 

J. Luo, M. M. Maye, Y. Lou, L. Han, M. Hepel, and C. J. Zhong, Catalytic activation of core-shell assembled gold nanoparticles as catalyst for methanol electrooxidation, Catal. Today 77,127-138 (2002). 

Also, the catalytic ability of Zn electrode modified by Pt-doped nickel hexacyanoferrate for methanol electrooxidation was investigated [480]. 

The high dispersity inside the nano-honeycomb matrix and the high surface area of the nanopartides leads to very good electrocatalytic activity. The electrocatalytic activities of nanosized platinum particles for methanol, formic add and formaldehyde electrooxidation have been recently reported [215]. The sensitivity of the catalyst particles has been interpreted in terms of a catalyst ensemble effect but the detailed microscopic behaviour is incomplete. Martin and co-workers [216] have demonstrated the incorporation of catalytic metal nanopartides such as Pt, Ru and Pt/Ru into carbon nanotubes and further used them in the electrocatalysis of oxygen reduction, methanol electrooxidation and gas phase catalysis of hydrocarbons. A related work on the incorporation of platinum nanopartides in carbon nanotubes has recently been reported to show promising electrocatalytic activity for oxygen reduction [217]. 

The electrochemical oxidation of methanol has been extensively studied on pc platinum [33,34] and platinum single crystal surfaces [35,36] in acid media at room temperature. Methanol electrooxidation occurs either as a direct six-electron pathway to carbon dioxide or by several adsorption steps, some of them leading to poisoning species prior to the formation of carbon dioxide as the final product. The most convincing evidence of carbon monoxide as a catalytic poison arises from in situ IR fast Fourier spectroscopy. An understanding of methanol adsorption and oxidation processes on modified platinum electrodes can lead to a deeper insight into the relation between the surface structure and reactivity in electrocatalysis. It is well known that the main impediment in the operation of a methanol fuel cell is the fast depolarization of the anode in the presence of traces of adsorbed carbon monoxide. 

Many efforts have been undertaken to enhance the electrocatalytic performance of catalytic reactions that have technological importance. The case of organic fuel electrooxidation is a major point for study, especially the possibility of achieving long-term, less-polluting fuel cells. In the case of methanol electrooxidation, the reaction occurs by a self-poisoning mechanism, so it is clear that the catalysts performances must be improved to impede the formation of carbon... 

Carbon-supported bimetallic or even ternary catalysts are of increasing interest in electrocatalytic reactions such as methanol oxidation. In this sense, the preparation routes are of pristine importance in determining the catalytic performance. As an example, it has been shown that Pt/Rn/Ni = 5 4 1 nanoparticles have a higher catalytic activity for methanol electrooxidation than does Pt/Ru = 1 1... 

It is worth noting that the remarkable effect described for the carbon support porosity on the metal utilization factor and hence on the specific electrocat-alytic activity in methanol electrooxidation was only observed when the catalysts were incorporated in ME As and measured in a single cell. The measurements performed for thin catalytic layers in a conventional electrochemical cell with liquid electrolyte provided similar specific catalytic activities for Pt-Ru/C samples with similar metal dispersions but different BET surface areas of carbon supports [223]. The conclusions drawn from measurements performed in liquid electrolytes are thus not always directly transferable to PEM fuel cells, where catalytic particles are in contact with a solid electrolyte. Discrepancies between the measurements performed with liquid and solid electrolytes may arise from (1) different utilization factors (higher utilization factors are usually expected in the former case), (2) different solubilities and diffusion coefficients, and (3) different electrode structures. Thus, to access the influence of carbon support porosity... 

Wang Z, Yin G, Zhang J. Sun Y, Shi P (2006) Co-catalytic effect of Ni in the methanol electrooxidation on Pt-Ru/C catalyst for direct methanol fuel cell. Electrochim Acta 51 5691-5697... 

The role of organometallie eomplexes as co-catalysts with Pt for methanol electrooxidation was mentioned earlier. Can they also act alone and replace Pt completely For the anodic oxidation of methanol, ethanol, and formic acid, studies looking at CO oxidation by various porphyrin complexes with Ir, Rh, and Co in aqueous electrolytes (both acid and alkaline) are relevant [90, 203, 204]. The mechanism proposed by Shi and Anson for the activity Co-octaethylporphyrin considers the oxidation of Co(II) to Co(III) in conjunction with coordination of CO to the Co(III) centres, followed by nueleophilic H2O attack leading to catalytic oxidation forming CO2 (see Equations 4.15-4.18) [90]. 

Attwood, P.A., McNicol, B.D., Short, R.T. Van, A.J.A. Platinum on carbon fiber paper catalysts for methanol electrooxidation. Part 1. Influence of activation conditions on catalytic activity. J. Chem. Soc., Faraday Trans. 1 76 (1980), pp. 2310-2321. 

He, D., Yang, L., Kuang, S., and Cai, Q. (2007) Fabrication and catalytic properties of Pt and Ru decorated Ti02 CNTs catalyst for methanol electrooxidation. Electrochemistry Communications, 9, 2467-2472. 

For methanol oxidation (2 M in 1 M H2SO4), cyclic voltammograms were obtained at the as-deposited diamond, the as-deposited diamond/Pt, 60 x 500 nm/Pt and the 400 nm x 3 pm/Pt electrodes (Fig. 19.8). At an as-deposited diamond film, no methanol oxidation was observed diamond is known to have low activity for methanol oxidation. In the case of the nonporous diamond/Pt electrode, a large anodic peak was observed at ca. 0.9 V, attributable to methanol oxidation. The Pt containing film is known to be electroactive for methanol electrooxidation [30, 31]. The Pt nanoparticles supported on the diamond electrode provide the catalytic activity for methanol oxidation in acid solution. The oxidation current for the 400 nm x 3 pm/ Pt electrode (ca. 7.0 mA cm2, geometric) was greatly enhanced compared to the as-... 

In addition to these different types of alloys, some studies were also devoted to alternatives to platinum as electrocatalysts. Unfortunately, it is clear that even if some catalytic activities were observed, they are far from those obtained with platinum. Nickel tungsten carbides were investigated, but the electrocatalytic activity recorded for methanol oxidation was very low. Tungsten carbide was also considered as a possible alternative owing to its ability to catalyze the electrooxidation of hydrogen. However, it had no activity for the oxidation of methanol and recently some groups showed that a codeposit of Pt and WO3 led to an enhancement of the activity of platinum. ... 

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