Direct Liquid-Feed Fuels

State-of-the-art DMFCs have not been considered for use in vehicles, except small vehicles, because of the lower efficiency and power density. In addition, a carbon-free fuel would be preferable for use in FC-powered vehicles. Alternative fuels, oxidation catalysts, reaction medium, electrolyte membranes, and electrode preparation have been evaluated to obtain optimal DLFCs. L-Ascorbic acid (AA), widely known as vitamin C, has been proposed as a novel fuel that does not require the use of an anode catalyst metal. DLFCs that use ethanol and D-glucose as renewable biofuels have been studied and developed using an anion exchange membrane (AEM). Hydrazine fuel cells were reconsidered for use in transportation based on the application of recent PEMFC technology. A novel anode catalyst for NaBILj oxidation is also described. 

DLFCs can use a cation exchange membrane (CEM) or an anion exchange membrane as an electrolyte, the principles of which are shown in Fig. 6.1a and b. DLFCs that use acidic and alkaline reaction media correspond to the CEM and AEM types, respectively. Perfluorinated sulfonic acid membranes, that is, Nafion , are typical CEMs, in which a countercation of sulfonate can be exchanged for another 

1 Schematic diagram of conventional CEM-type (a) and AEM-type (b) DLFCs. 

2 Cell voltage (a) and power density (b) versus current density plots of DAAFCs with Vulcan XC72 ( ), Ke enblack EC (A), KetjenblackECbOOJD (B), and Black Pearls 2000 (V) (0.3 mg/cm ) and Pd Black ( ) (3 mg/cm ) at room temperature and atmospheric pressure. (Reprinted with permission from Elsevier (2006). Copyright 2006 Elsevier [11].) 

The anodic reaction (Eq. (6.1)) is the same as the metabolic conversion of AA, and the hydrolysis of DH A A can also occur in vivo. These product analyses confirmed that DAAFCs are very safe power sources in which both the fuel and evolved products are harmless. 

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Narayanan, S., Surampudi, S., and Halpert, G., Direct liquid-feed fuel cell with membrane electrolyte and manufacturing thereof, US 5,945,231 (to California Institute of Technology), (August 31, 1999). 

Demlrcl UB (2007) Direct liquid-feed fuel cells thermodynamic and environmental concerns. J Power Sources 169 239-246... 

Demirci UB (2009) How green are the chemicals used as liquid fuels in direct liquid-feed fuel cells Environ Int 35 626-631... 

Demirci UB (2007) Theoretical means for searching bimetallic alloys as anode electrocatalysts for direct liquid-feed fuel cells. J Power Sources 173 11-18... 

The conventional electrochemical reduction of carbon dioxide tends to give formic acid as the major product, which can be obtained with a 90% current efficiency using, for example, indium, tin, or mercury cathodes. Being able to convert CO2 initially to formates or formaldehyde is in itself significant. In our direct oxidation liquid feed fuel cell, varied oxygenates such as formaldehyde, formic acid and methyl formate, dimethoxymethane, trimethoxymethane, trioxane, and dimethyl carbonate are all useful fuels. At the same time, they can also be readily reduced further to methyl alcohol by varied chemical or enzymatic processes. 

In contrast to the electrolyte membranes mentioned above, PSSA-PVDF membranes have high conductivities at low temperatures (25-90 °C), low methanol permeability rates, and have been successfully operated in low temperature direct methanol, liquid-feed fuel ceils. In the present study, the methanol permeability and ionic conductivity of PSSA-PVDF membranes have... 

The current-voltage response of a 2 x 2 direct oxidation liquid-feed fuel cell operated with TMM, investigated over a range of concentrations, and with methanol under similar conditions is compared and illustrated in Fig 1.42. 

Argyropoulos P, Scott K, Taama WM (2000) Hydrodynamic modeling of direct methanol liquid feed fuel cell stacks. J Appl Electrochem 30 899-913... 

The schematic diagram of the liquid-feed direct methanol fuel cell (DMFC) is shown in Figure 13.1. 

Figure 13.1. Liquid-feed direct methanol fuel cell.

Z. G. Shao, 1. M. Hsing, H. Zhang, and B. Yi. Influence of anode diffusion layer on the performance of a liquid feed direct methanol fuel cell by AC impedance spectroscopy. International Journal of Energy Research 30 (2006) 1216-1227. 

Methanol is one of the few alcohols that can be fed directly into a fuel cell and can be converted electrochemically at the anode. The DMFC can be fed with a gaseous or liquid fuel feed. The liquid DMFC generally uses a diluted methanol in water mixture (ty pically 1-2 molar) and only a fraction of the methanol is used at the anode (Collins, 2001). The DMFC, like an ordinary battery, provides DC electricity according to the following half reactions. 

In this paper we report on factors which affect the conversion of fuel nitrogen to TFN in laboratory jet-stirred combustors which serve to simulate the primary zone in a gas turbine. The independent variables in the experiments were fuel type (aliphatic isooctane vs. aromatic toluene), equivalence ratio (fuel-to-oxygen ratio of combustor feed divided by stoichiometric fuel-to-oxygen ratio), average gas residence time in the combustor, and method of fuel injection into the combustor (prevaporized and premixed with air vs. direct liquid spray). Combustion temperature was kept constant at about 1900K in all experiments. Pyridine, C5,H5N, was added to the fuels to provide a fuel-nitrogen concentration of one percent by weight. 

E) Liquid fuel obtained in the first stage i.e. Depolymerisation, can be directly utilized as fuel for DG sets, thereby generating electricity through a nonconventional waste plastic source, for applications such as agricultural pumps, as well as producing, boiler fuels, marine fuel, fuel oil and input feed for petroleum refineries. Gaseous fuel can be utilized as domestic or industrial fuel. 

Microfabrication processes have been used successfully to form micro-fuel cells on silicon wafers. Aspects of the design, materials, and forming of a micro-fabricated methanol fuel cell have been presented. The processes yielded reproducible, controlled structures that performed well for liquid feed, direct methanol/Oj saturated solution (1.4 mW cm ) and direct methanol/H O systems (8 mA cm" ). In addition to optimizing micro-fuel cell operating performance, there are many system-level issues to be considered when developing a complete micro power system. These issues include electro-deposition procedure, catalyst loading, channel depth, oxidants supply, and system integration. The micro-fabrication processes that have... 

M.K. Ravikumar and A.K. Shula, Effect of methanol crossover in a liquid-feed polymer-electrolyte direct methanol fuel cell, J. Electrochem. Soc., 1996, 143, 2601-2606. 

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