Ethanol electrooxidation

Using in situ spectroscopy the same authors revealed the roles of Sn and Ru as alloying elements. The rate of dissociative ethanol adsorption was lower on the 

On the same issue of product distribution, Iwasita and co-workers noted the ethanol concentration dependence [181-182], At ethanol concentrations below 0.05 M the yield of acetaldehyde on Pt at 0.5 V vs. RHE was virtually zero. Only for ethanol concentrations higher than 0.15 M did the yield of acetaldehyde exceed that of acetic acid [181]. 

Following up on half-cell experiments, it is of great interest to characterize the products obtained in direct ethanol fuel cells. Rousseau et al. investigated direct ethanol fuel cells employing Pt, PtSn (9 1 at. ratio), and PtSnRu (8.6 1 0.4) anode electrocatalysts supported on Vulcan XC72 prepared by the Bonnemann colloidal method (3 mg cm Pt content) [183]. 

There is now fairly conclusive evidence that PtSn performs better than PtRu, PtPd, PtRe, and PtW in direct ethanol fuel cell experiments, especially at temperatures equal to and above 343 K [185-186, 188-192]. Furthermore, the long-term stability of PtSn (9 1 at. ratio) was promising, as the cell voltage was virtually constant around 0.45 V for 240 min at 32 mA cm and 353 K [183]. 

The mass specific activities of the catalysts for ethanol electrooxidation are unfortunately quite low, between about 5 mW mg at 323 K and 9-11.5 mW mg at 353 K based on peak power outputs [183-184, 186]. Zhou et al. reported somewhat higher mass specific activities, reaching 23 mW mg at 333 K [188b]. Utilizing extended reaction zone anodes could also improve the mass specific activity (see also Section 4.3) [190]. 

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Wang H, Jusys Z, Behm RJ. 2004. Ethanol electrooxidation on a carbon-supported Pt catalyst Reaction kinetics and product yields. J Phys Chem B 108 19413-19424. 

In this chapter, two carbon-supported PtSn catalysts with core-shell nanostructure were designed and prepared to explore the effect of the nanostructure of PtSn nanoparticles on the performance of ethanol electro-oxidation. The physical (XRD, TEM, EDX, XPS) characterization was carried out to clarify the microstructure, the composition, and the chemical environment of nanoparticles. The electrochemical characterization, including cyclic voltammetry, chronoamperometry, of the two PtSn/C catalysts was conducted to characterize the electrochemical activities to ethanol oxidation. Finally, the performances of DEFCs with PtSn/C anode catalysts were tested. The microstmc-ture and composition of PtSn catalysts were correlated with their performance for ethanol electrooxidation. 

From the above experimental results, it can be seen that the both PtSn catalysts have a similar particle size leading to the same physical surface area. However, the ESAs of these catalysts are significantly different, as indicated by the CV curves. The large difference between ESA values for the two catalysts could only be explained by differences in detailed nanostructure as a consequence of differences in the preparation of the respective catalyst. On the basis of the preparation process and the CV measurement results, a model has been developed for the structures of these PtSn catalysts as shown in Fig. 15.10. The PtSn-1 catalyst is believed to have a Sn core/Pt shell nanostructure while PtSn-2 is believed to have a Pt core/Sn shell structure. Both electrochemical results and fuel cell performance indicate that PtSn-1 catalyst significantly enhances ethanol electrooxidation. Our previous research found that an important difference between PtRu and PtSn catalysts is that the addition of Ru reduces the lattice parameter of Pt, while Sn dilates the lattice parameter. The reduced Pt lattice parameter resulting from Ru addition seems to be unfavorable for ethanol adsorption and degrades the DEFC performance. In this new work on PtSn catalysts with more... 

Direct alcohol fuel cells (DAFC) are very attractive as power sources for mobile and portable applications. The alcohol is fed directly into the fuel cell without any previous chemical modification and is oxidized at the anode while oxygen is reduced at the cathode. Methanol has been considered the most promising fuel because it is more efficiently oxidized than other alcohols. Among different electrocatalysts tested in the methanol oxidation, PtRu-based electrocatalysts were the most active [1-3]. In Brazil ethanol is an attractive fuel as it is produced in large quantities from sugar cane and it is much less toxic than methanol. On the other hand, its complete oxidation to CO2 is more difficult than that of methanol due to the difficulty in C-C bond breaking and to the formation of CO-intermediates that poison the platinum anode catalysts. Thus, more active electrocatalysts are essential to enhance the ethanol electrooxidation [3],... 

An efficient ethanol electrooxidation catalyst should combine at least two features (i) high tolerance to CO and other intermediate species generated over the surface of the electrocatalyst during alcohol electrooxidation and (ii) ability to break the C-C bond of the ethanol molecule under mild conditions. The most relevant features for the designing of CO tolerant electrocatalysts have been described above namely, Pt modification with more oxophilic metals such as Ru, Mo or Sn renders the best electrocatalysts. This is because such oxophilic atoms promote the formation of -OfT. species (involved in the CO j oxidation reaction) at potentials that are more negative than that on pure Pt (Eq. 9.17). Among those, Sn-modified Pt electrocatalysts are the most active formulations. There is also widespread consensus that the PtsSn phase is the most active one in the CO reaction and early stages of the ethanol electrooxidation process. ... 

The addition of a third metal function (Ru, In, W) to PtSn/C catalysts has been reported to increase COg selectivity and/or improve the performance of ethanol electrooxidation in a single cell 133.155-160 context, the incorporation of Rh to the formula-... 

Simoes FC, dos Anjos DM, Vigier F, Leger JM, Hahn F, Coutanceau C, Gonzalez ER, Tremiliosi-Filho G, de Andrade AR, Olivi P, Kokoh KB (2007) Electroactivity of tin modified platinum electrodes for ethanol electrooxidation. J Power Sources 167 1-10... 

The ethanol oxidation on Pd electrocatalysts is dramatically affected by the pH of file aqueous ethanol solution no reaction occurs in acidic solutions, while the reaction is fast in alkaline solutions. Some raticmale for the origin of this pH effect on the ethanol oxidation to acetaldehyde has been provided by DFT calculations [111] (Fig. 8.8). DFT calculations show that in acidic media continued dehydrogenation of ethanol is difficult due to the lack of OH species to instantly remove hydrogen, which inhibits the ethanol electrooxidation. Conversely, both ethanol and sufficient OH can adsorb on Pd in alkaline media, leading to continuous ethanol electrooxidation. DFT calculations show that in acidic media continued... 

A mathematical model for DEFC was proposed by Pramanik and Basu describing different overpotentials [191]. The assumptions of their model are (i) the anode compartment considered as a well-mixed reactor, (ii) 1 bar pressure maintained both at the anode and cathode compartments, (iii) the transport processes are modelled in one dimension. The model accounts for Butler-Volmer-based descriptions of the ethanol electrooxidation mechanisms, diffusive reactants transport and ohmic losses at the electrode, current collector and electrode-current collector interfaces. The experiment data on current-voltage characteristics is predicted by the model with reasonable agreement and the influence of ethanol concentration and temperature on the performance of DEFC is studied by the authors (Fig. 8.19). 

Low-Platinum-Content Electrocatalysts for Methanol and Ethanol Electrooxidation... 

Methanol and Ethanol Electrooxidation on Bulk Platinum Electrode... 

Methanol electrooxidation and ethanol electrooxidation are complex reactions occurring in a pattern of parallel reaction pathways (Fig. 1.1) [5-14]. Although detailed reaction mechanisms remain obscure, a number of reaction intermediates and products have been identified by spectroscopic methods such as in situ Fourier transform infrared spectroscopy (FTIR), on-line differential electrochemical mass spectrometry (OEMS), and other techniques [6, 12-14]. 

Zhou ZY, Huang Z-Z, Chen D-J, Wang Q, Tian N, Sun S-G (2010) High-index faceted platinum nanocrystals supported on carbon black as highly ellicicmt catalysts for ethanol electrooxidation. Angew Chem Int Ed 49(2) 411-414... 

Del Colle V, Bema A, Tremiliosi-FUho G, Herrero E, Feliu JM (2008) Ethanol electrooxidation onto stepped surfaces modified by Ru deposition electrochemical and spectroscopic studies. Phys Chem Chem Phys 10 3766-3773... 

Camara GA, Lima RBD, Iwasita T (2004) Catalysis of ethanol electrooxidation by PtRu the influence of catalyst composition. Electrochem Commun 6(8) 812-815... 

Jiang L, Cohnenaresa L, Jusysa Z, Sunb GQ, Behma RJ (2007) Ethanol electrooxidation on novel carbon supported Pt/SnOx/C catalysts with varied Pt Sn ratio. Electrochim Acta 53 377-389... 

Zhou WP, Axnanda S, White MG, Adzic RR, Hrbek J (2011) Enhancement in ethanol electrooxidation by SnOx nanoislands grown on Pt(l 11) effect of metal oxide-metal intraface sites. J Phys Chem C 115 16467-16473... 

Li M, Marinkovic NS, Sasaki K (2012) In situ characterization of ternary Pt-Rh-Sn02/C catalysts for ethanol electrooxidation. Electrocatal 3 376-385... 

To improve the electrocatalytic activity of platinum and palladium, the ethanol oxidation on different metal adatom-modified, alloyed, and oxide-promoted Pt- and Pd-based electrocatalysts has been investigated in alkaline media. Firstly, El-Shafei et al. [76] studied the electrocatalytic effect of some metal adatoms (Pb, Tl, Cd) on ethanol oxidation at a Pt electrode in alkaline medium. All three metal adatoms, particularly Pb and Tl, improved the EOR activity of ft. More recently, Pt-Ni nanoparticles, deposited on carbon nanofiber (CNE) network by an electrochemical deposition method at various cycle numbers such as 40, 60, and 80, have been tested as catalysts for ethanol oxidadmi in alkaline medium [77]. The Pt-Ni alloying nature and Ni to ft atomic ratio increased with increasing of cycle number. The performance of PtNi80/CNF for the ethanol electrooxidation was better than that of the pure Pt40/CNF, PtNi40/CNF, and PtNi60/CNF. 

Fig. 5.4 Effect of the content of oxide in Pt/C and Pd/C catalysts for ethanol electrooxidation in 1.0 M KOH solution containing 1.0 M ethanol with a sweep rate of 50 mV s , Pt or Pd loading 0.3 mg cm . Reproduced from ref. [94]...

Xu CW, Cheng LQ, Shen PK, Liu YL (2007) Methanol and ethanol electrooxidation on Pt and Pd supported on carbon microspheres in afkaline media. Electrochtan Commun 9(5) 997-1001... 

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