Electrooxidation electrocatalysts for ethanol

Wang H, Xu CW, Cheng FL, Jiang SP (2007) Pd nanowire arrays as electrocatalysts for ethanol electrooxidation. Electrochem Commun 9(5) 1212-1216... 

PtSn/C electrocatalyts are claimed to be active electrocatalysts for ethanol electrooxidation and their performances depends greatly on the preparation procedure and Pt Sn atomic ratio. In this work, PtSn/C electrocatalysts with Pt Sn atomic ratios of 9 1, 3 1, 1 1 and 1 3 were prepared in water/ethylene glycol using electron beam irradiation. The obtained materials were characterized by EDX and XRD and tested for ethanol electro-oxidation in acid medium using chronoamperometiy. X-iay diffractograms of PtSn/C electrocatalysts showed typical face-centered cubic (fee) stractuie of Pt with average crystallite size of 2 nm and the presence of a Sn02 phase (cassiterite). PtSn/C electrocatalysts prepared with Pt Sn atomic ratios of 9 1 and 3 1 were more active for ethanol electro-oxidation than commercial PtSn/C BASF electrocatalyst. 

Although PtSn/C are the best binary electrocatalysts for the electrooxidation of ethanol, the main reaction products are acetic add (AA) and acetaldehyde (AAL). ... 

Several approaches to the designing of efficient electrocatalysts for the electrooxidation of ethanol have been reported. Some of them focused on the structure of the catalytic particles. For instance, by generating high-index faceted Pt particles, the catalytic activity and selectivity to COg of Pt/C can be improved.The same is true for PtNi/C catalysts.However, high-index planes are not stable in nanoparticles, hence the mass activity of those catalysts is low. Most studies, however, deal with bimetallic particles, typically Pt-M (M = W, Pd, Rh, Re, with PtSn... 

ELECTROCATALYSTS FOR THE ELECTROOXIDATION OF ETHANOL TABLE 3.1 Position and Assignment of the IR Bands of the Most Abundant Products and Intermediate Species Observed During Ethanol Electrooxidation in Acid Medium ... 

Although PtiRui/C is the best catalyst for methanol electrooxidation in DMFCs, it is not proved to be the best anode catalyst for ethanol electrooxidation. The addition of W and Mo can increase ethanol electrooxidation activity on the PtiRui/C catalyst. The I-V characteristics of single direct ethanol fuel cells show clearly that the PtiSni/C is a better anode catalyst than PtiRui/C and other carbon-supported bimetalhc Pt-based catalysts for DEFCs. From a practical point of view, PtiSni/C is the best electrocatalyst for DEFCs among these anode catalysts investigated here. 

PtSnCu/C electrocatalyst with Pt Sn Cu atomic ratio of 50 30 20 was prepared by borohydride reduction and the obtained material was further treated with nitric acid. The obtained material was characterized by EDX and XRD and tested for ethanol electrooxidation in acid medium using chronoamperometry. The X-ray diffractogram of as-synthesized PtSnCu/C electrocatalyst showed typical face-centered cubic (fee) stracture of Pt alloy and after acid treatment it was observed that the Pt (fee) stmemre was preserved. PtSnCu/C electrocatalyst acid-treated was more active for ethanol electro-oxidation than as-synthesized PtSnCu/C and PtSn/C electrocatalyts. 

Other electrocatalysts were considered for the electrooxidation of ethanol, such as rhodium, iridium or gold, " " leading to similar results in acid medium. The oxidation of ethanol on rhodium proceeds mainly through the formation of acetic acid and carbon monoxide. Two types of adsorbed CO are formed, i.e., linearly-bonded and bridge-bonded, in a similar amount, at relatively low potentials, then leading rapidly to carbon dioxide when the rhodium surface begins to oxidize, at 0.5-0.7 V/RHE. On gold in acid medium the oxidation reaction leads mainly to the formation of acetaldehyde. " " ... 

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],... 

Of the primary alcohols, a number of studies have investigated the electro-oxidation characteristics of ethanol, 2-propanol, and butanol. There have been several reviews on the electro-oxidation of these molecules on Pt, Au, and Pt/Au alloys. A number of trends have been observed for the electrooxidation of primary alcohols, including (i) the rate of electro-oxidation is dependent upon the pH of the solution, with R being the electrocatalyst in acidic media, (ii) the reactivity of the alcohols is governed by the position of the functional group on the backbone (primary alcohols are more reactive than secondary compounds, and tertiary alcohols show little reactivity), (iii) for the primary and secondary alcohols the first step in the dissociative adsorption... 

Takasu et al. [27] prepared a homogenized Pt-Ru/C electrocatalyst with a high-specific activity for methanol oxidation from carbon black and ethanolic solutions of Pt(NH3)2(N02)2 and RuN0(N03). The specific activity for methanol electrooxidation increased with an increase in the Pt/Ru particle size. The concept of larger particle size aiding in the activity of methanol oxidation was experimentally verified [28-33]. 

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 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... 

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

Most recently, PIml electrocatalysts were systematically studied for the electrooxidation of methanol and ethanol [108]. PIml was deposited on different substrates via the galvanic displacement of a Cu UPD monolayer, employing five single-crystal surfaces (Au(lll), Pd(lll), Ir(lll), Rh(lll), and Ru(OOOl))... 

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