Methanol and ethanol electrooxidation

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

Methanol and Ethanol Electrooxidation on Bulk Platinum Electrode... 

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... 

Poisoning of platinum fuel cell catalysts by CO is undoubtedly one of the most severe problems in fuel cell anode catalysis. As shown in Fig. 6.1, CO is a strongly bonded intermediate in methanol (and ethanol) oxidation. It is also a side product in the reformation of hydrocarbons to hydrogen and carbon dioxide, and as such blocks platinum sites for hydrogen oxidation. Not surprisingly, CO electrooxidation is one of the most intensively smdied electrocatalytic reactions, and there is a continued search for CO-tolerant anode materials that are able to either bind CO weakly but still oxidize hydrogen, or that oxidize CO at significantly reduced overpotential. 

Chang SC, Leung LWH, Weaver MJ. 1990. Metal crystallinity effects in electrocatalysis as prohed hy real-time ETIR spectroscopy electrooxidation of formic acid, methanol, and ethanol on ordered low-index platinum surfaces. J Phys Chem 94 6013-6021. 

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]. 

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))... 

Ciszevski and Milczarek reported roughly similar oxidation onset potentials for methanol and ethanol in 0.1 M NaOH using Ni(II) tetrakis(3-methoxy-4-hydroxyphenyl) porphyrin film (poly-NiTMHPP). However, they explored catalytic oxidations up to 0.5 M methanol concentration [207]. Since the alcohol electrooxidation occurs at potentials more positive than the redox potential of Ni(III)/Ni(II) (i.e., Ni(III) is the electrocatalytically active form), a direction to improve the performance would be to find macrocycles that negatively shift the Ni(III)/Ni(II) potential. Another variant would be to develop mixed macrocycle catalysts by incorporating elements that promote OHad formation, since on Ni polymer films the methanol oxidation was strongly dependent on flie OH" concentration [207]. 

Pd) and the chemical energy is converted into electrical energy. Simple alcohols such as methanol, ethanol, 1,3-propanediol, 1,2-propanediol, buta-nediol, pentanediol, glycol and glycerol (GL) are used. Among them methanol and ethanol are popular. The catalyst used for electrooxidation are Pd-PEDOT [204] for C3-Aliphatic Alcohols, Pt-Pd-Au nano-catalyst [192] for ethanol oxidation, Pt and Pt-Ru dispersed in graphene-multiwalled CNT nanocomposites [188] for methanol oxidation. 

Verma, A. and Basu, S. Power from hydrogen via fuel cell technology, Chemical Weekly July 12 (2005d) 177-181. Verma, A., Sharma, S. and Basu, S. Electrooxidation study of methanol and ethanol in alkaline medium (2005e),... 

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],... 

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]. 

As mentioned above, the alcohol crossover from the anode to the cathode is a important problems to be overcome to improve the DAFC performance. This is due to the fact that the commonly used Pt-based cathode electrocatalysts are also active for the adsorption and oxidation of methanol [1]. So, in addition to the resulting mixed potential at the cathode, there is a decrease in the fuel utilization. Therefore, considering the above exposed reactions for the alcohol electrooxidation, and the features that govern the ORR electrocatalytic activity, as discussed in the Sect. 5.2, it is ready to conclude the importance of the modification of the active ORR electrocatalyst surfaces in order to inhibit the methanol or ethanol oxidative adsorption steps. In the next sections, some recent materials being developed to overcome the problems caused by the alcohol crossover will be presented. 

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