Direct Liquid-Feed Fuel Cells

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. 

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... 

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. 

Narayanan, S.R. Kindler, A. Jeffries-Nakamura, B. Chun, W. Frank, H. Smart, M. Surampudi. S. Halpert, G., Performance of PEM Liquid-Feed Direct Methanol-Air Fuel Cells , Electrochemical Society Proceedings Volume 95-23, 261 (1995). 

However, DMFCs do suffer some drawbacks such as lower electrical efficiency and higher catalyst loadings as compared to H2 fuel cells. Efforts should be continued on developing anode catalysts with improved methanol oxidation kinetics, cathode catalysts with a high tolerance to methanol, membranes with lower methanol permeation rates, and strategies to reduce the methanol crossover rate. Attention should also be given to other direct-feed fuel cells using other liquid fuels (such as formic acid). 

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. 

The meter is not suited to measure gas-liquid mixtures or low-pressure gases and develops high pressure drops when the gas velocity is high. To keep the tubes full, they should be installed in vertical pipes with an upward flow direction. Besides their relatively high cost, CMF limitations also include their relatively small sizes (up to 150 mm, or 6 in.), their vibration sensitivity, and the limitation of standard designs to 205°C (400°F) and special ones to 425°C (800°F). The Coriolis-based mass flowmeters are popular in fuel cell, fuel flow, reactor feed, and in other applications where mass flowmeters are needed. 

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