Alcohol oxidation direct methanol fuel cells

The same group, in a previous work, reported on the realization of a hybrid anode electrode [197]. An appreciable improvement in methanol oxidation activity was observed at the anode in direct methanol fuel cells containing Pt-Ru and Ti02 particles. Such an improvement was ascribed to a synergic effect of the two components (photocatalyst and metal catalyst). A similar behavior was also reported for a Pt-Ti02-based electrode [198]. Another recent study involved the electrolysis of aqueous solutions of alcohols performed on a Ti02 nanotube-based anode under solar irradiation [199]. 

Fuels cells are of interest both from energetic and environmental considerations. When methanol is fed directly to an anode, as in Direct Methanol Fuel Cells , electric power is generated, making the devices suitable for small and lightweight uses [53], Alternative fuels such as polyhydric alcohols like ethylene glycol and glycerol are much less volatile and toxic, on the one hand, and electrochemically oxidizable on the other [54]. Therefore, the electrochemical oxidation of various polyhydric alcohols has been investigated in acidic as well as in alkaline conditions. 

Yang CC, Chien WC, Li YJ (2010) Direct methanol fuel cell based on poly(vinyl alcohol)/ titanium oxide nanotubes/poly(styrenesulfonic acid)(PVA/nt-Ti02/PSSA) composite polymer membrane. J Power Sources 195 3407-3415... 

In the first chapter, we introduce the concept of methanol economy, as an alternative to the most popular but still elusive hydrogen economy, and we also provide a brief historical description of fundamental research on electrochemical oxidation of methanol and the development of the first alkaline direct methanol fuel cells more than 60 years ago. The operating principles of PEM and alkaline direct alcohol fuel cells are analyzed, as well as their components, configuration, and operation modes, with a final remark on the state of the art of the technology. 

Yet, the most interesting results for ORR on Fe-Pd/WC catalyst are those obtained in the presence of alcohol. The electrode response for Fe-Pd/WC system in oxygen saturated acid has not been affected even at high concentrations of methanol, whereas the ORR on conventional catalyst Pt/C was completely restrained since the dominant reaction was basically methanol oxidation rally. Such results suggested that Pd-Fe/WC/C could be an excellent candidate for direct methanol fuel cell (DMFC) cathode because of its inert activity toward methanol oxidation as seen in Fig. 23.3. The utilization of a completely inert catalyst to methanol oxidation is one of the important criteria for DMFCs to operate at higher power densities since the issue of methanol crossover is unavoidable and can cause dramatic loss in cell performance, especially with common catalysts that are active... 

In fuel cells working with a liquid fuel, usually an alcohol such as methanol (a direct methanol fuel cell - DMFC), ethanol (a direct ethanol fuel cell - DEFC), glycerol (a direct glycerol fuel cell - DGEC), etc., in addition to the necessity to activate the ORR at the cathode, the alcohol oxidation reaction at the anode also involves a high overpotential. This high overpotential is mainly due to the formation, after dissociative adsorption of the alcohol at the catalyst surface, of poisoning species which block the catalytic surface the main one adsorbed is carbon monoxide. ... 

HjSO, but the magnitude of the current density was not affected largely up to a concentration of lOmmol dm . With 2-propanol, the current due to the alcohol oxidation was superimposed on the ORR current, and the potential shifted by approximately 0.5 V at 0.1 mol dm . Both 2-propanol and acetone are MEA components because 2-propanol is added to the catalyst ink, and acetone is produced by oxidation of 2-propanol on the platinum cathode. The effects are, however, not serious because their concentration is less than lOmmol dm . Methanol is used as a fuel in direct methanol fuel cells, and crossover through the polymer electrolyte membrane is known to cause a degradation of the ORR at the cathode, when the concentration of the fuel is as high as 5 mol dm . 

The direct methanol fuel ceU is a special form of low-temperature fuel cells based on PE technology. In the DMEC, methanol is direcdy electro-oxidized at the anode without the intermediate step of reforming the alcohol into a hydrogen-rich gas. Since hydrogen is the focus of this contribution this type is not further discussed. 

Among aU the alcohols, ethanol has being subject of extensive studies because it is a green fuel and can be easily obtained as biofuel. The schematic of direct ethanol fuel cell is presented in Fig. 4b, while Fig. 4c shows the onset on the oxidation potential of methanol and ethanol for different alloy catalyst. 

Fuel cells using directly liquid fuels are advantageous in this aspect. Methanol, formaldehyde (water solution), formic acid (water solution) and hydrazine are among fuels relatively easy to oxidize electrochemically. Alcohol and hydrocarbon with larger molecular weight are much harder to oxidize completely to C02- Other qualifications to be considered are price, availability, safety, energy density and ease of handling. 

In recent decades, direct alcohol fuel cells (DAFCs) have been extensively studied and considered as possible power sources for portable electronic devices and vehicles in the near future. The application of methanol is limited due to its high volatility and toxicity, although it is relatively easily oxidized to CO2 and protons. So other short chain organic chemicals especially ethanol, ethylene glycol, propanol, and dimethyl... 

Oxidation of Alcohols in a Direct Alcohol Fuel Cell The electrocatalytic oxidation of an alcohol (methanol, ethanol, etc.) in a direct alcohol fuel cell (DAFC) will avoid the presence of a heavy and bulky reformer, which is particularly convenient for applications to transportation and portable electronics. However, the reaction mechanism of alcohol oxidation is much more complicated, involving multi-electron transfer with many steps and reaction intermediates. As an example, the complete oxidation of methanol to carbon dioxide ... 

Hydrogen is a secondary fuel and, like electricity, is an energy carrier. It is the most electroactive fuel for fuel cells operating at low and intermediate temperatures. Methanol and ethanol are the most electroactive alcohol fuels, and, when they are electro-oxidized directly at the fuel cell anode (instead of being transformed in a hydrogen-rich gas in a fuel processor), the fuel cell is called a DAFC either a DMFC (with methanol) or a DEFC (with ethanol). 

Methanol is the most electro-reactive organic fuel, and, when it is electro-oxidized directly at the fuel anode (instead of to be transformed by steam reforming in a hydrogen-rich gas), the fuel cell is called a DMFC. More generally if the direct oxidation of a given fuel (alcohols, borohydrides, etc.)... 

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],... 

Ethanol is considered as the ideal fuel for the so-called direct alcohol fuel cells (DAFCs). This is because ethanol has a number of advantages over methanol it can be produced in a sustainable manner, easily stored and transported, and is less toxic or corrosive than methanol. The theoretical mass energy of ethanol is 8.0 kWh kg compared to 6.1 kWh kg" for methanol. The complete oxidation of ethanol releases 12 electrons per molecule its standard electromotive force E° q =1145V, is similar to that of methanol. 

Reviews on DEFC become available since 2006, describing the state of the art of catalysts for ethanol oxidation [31, 76, 77], while more recent works focused oti alkaline DEFC [78-80]. A comprehensive review on alkaline direct alcohol fuel cells was recently published by one of us [30] over viewing catalysts, membranes and cell performance of ADAFC fuelled with methanol, ethanol, and ethylene glycol. 

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