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The study on the methanol crossover in a DMFCLai, Jhih-jia 09 September 2008 (has links)
In this experiment, we are going to discuss the possibility of zero methanol crossover to the cathode target within the capacity of DMFC electrode and with proper methanol supply.
After various trials, it is found that electrospray can be used to reduce fuel demand. The methanol will be consumed immediately within the electrode capacity. The methanol solution is volatile. As a result, the actual amount of electricity generated will never accord with the input. If we supply the electrode with methanol by direct contact using infusion pump, the volatility will be reduced. The total power generated then accords with the amount of methanol input. Although only low methanol concentration is supported currently, it¡¦s hoped that the crossover problem can be solved completely. In the electrode design, we try to take away the carbon cloth from the anode and leave the catalyst layer. By this way, the methanol is in touch with the catalyst. Such change is good for this experiment.
In our study, following difficulties are found:
(1) Methanol input
(2) The impact of volatility in electrospray
(3) When supplying fuels to the surface of electrode, the reaction size is too small.
More attentions should be paid in the future cell design.
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Development and understanding of new membranes based on aromatic polymers and heterocycles for fuel cellsLi, Wen 20 October 2009 (has links)
Direct methanol fuel cells (DMFC) are appealing as a power source for portable
devices as they do not require recharging with an electrical outlet. However, the DMFC
technology is confronted with the high crossover of methanol fuel from the anode to the
cathode through the currently used Nafion membrane, which not only wastes the fuel but
also poisons the cathode platinum catalyst. With an aim to overcome the problems
encountered with the Nafion membrane, this dissertation focuses on the design and
development of new polymeric membrane materials for DMFC and a fundamental
understanding of their structure-property-performance relationships.
Several polymeric blend membranes based on acid-base interactions between an
aromatic acidic polymer such as sulfonated ploy(ether ether ketone) (SPEEK) and an
aromatic basic polymer such as heterocycle tethered poly(sulfone) (PSf) have been
explored. Various heterochylces like nitro-benzimidazole (NBIm), 1H-Perimidine
(PImd), and 5-amino-benzotriazole (BTraz) have been tethered to PSf to understand the influence of pKa values and the size of the hetrocycles. The blend membranes show
lower methanol crossover and better performance in DMFC than plain SPEEK due to an
enhancement in proton conductivity through acid-base interactions and an insertion of the
heterocycle side groups into the ionic clusters of SPEEK as indicated by small angle Xray
scattering and TEM data. The SPEEK/PSf-PImd blend membrane shows the lowest
methanol crossover due to the larger size of the side groups, while the SPEEK/PSf-BTraz
blend membrane shows the highest proton conductivity and maximum power density.
To further investigate the methanol-blocking effect of the heterocycles, N,N’-Bis-
(1H-benzimidazol-2-yl)-isophthalamide (BBImIP) having two amino-benzimidazole
groups bonded to a phenyl ring has been incorporated into sulfonated polysulfone (SPSf)
and SPEEK membranes. With two 2-amino-benzimidazole groups, which could greatly
increase the proton transfer sites, and three phenyl rings, which are compatible with the
aromatic polymers, the BBImIP/SPSf and BBImIP/SPEEK blend membranes show
suppressed methanol crossover and increased fuel cell performance in DMFC.
Novel sulfonated copolymers based on poly(aryl ether sulfone) (SPS-DP) that
exhibit low methanol crossover have been synthesized and explored as a methanol-barrier
center layer in a multilayer membrane configuration having SPEEK as the outer layers.
These multilayer membranes exhibit better performance in DMFC than plain SPEEK and
Nafion 115 membranes due to suppressed methanol crossover.
To address the issue of incompatibility between the new hydrocarbon-based
membranes synthesized and the Nafion ionomer used in the catalyst layer in fabricating
membrane-electrode assemblies (MEAs), the MEAs have been fabricated with the
SPEEK membranes and 10 to 30 % SPEEK ionomer in the catalyst layer. These MEAs
exhibit better performance in DMFC compared to the MEAs fabricated with the SPEEK
membranes and Nafion ionomer in the catalyst layer due to lower interfacial resistance. / text
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Design and development of a methanol concentration controller for fuel cellsViljoen, Marius 09 September 2010 (has links)
Thesis (M. Tech.) (Engineering: Electrical, Dept.: Electronic Engineering))--Vaal University of Technology, 2008. / The demand for higher efficiency, sustainability and cleaner power sources increases daily. A Direct Methanol Fuel Cell is a power source that can be applied for small to medium household appliances and office equipment. It can ideally be used for operating appliances like notebook computers on remote sites where no electrical power is available.
One of the problems in methanol fuel cells is methanol crossover. Methanol crossover occurs when methanol is not completely used in the process of generating electrons, and a certain percentage of the methanol is wasted. Crossover may damage the proton exchange membrane of the fuel cell and reduce the efficiency of a DMFC. Literature reviews were done and suggestions from other writers are discussed on how to reduce methanol crossover. This research focuses primarily on the fact that crossover can be controlled by controlling the methanol / water concentration.
A prototype methanol controller was built with an ultrasonic sensor for detecting the density of the methanol/water mixture and a sensor for the temperature of the mixture; this was done because the density of the mixture is dependant on the temperature and the concentration. The controller was calibrated to determine the amount per volume of water and methanol which enables the controller to control the percentage of methanol in the water. The prototype also had the feature built in to adjust the mixture in order to enable the study on the effects of crossover. A data logger function was added to store collected data on a personal computer for the study on methanol and water.
It was observed that the sensor was sensitive enough and was able to produce 1% increments of the level of methanol concentration in the water provided the temperature was stable. A methanol controller was successfully built to ensure the correct volume of methanol. / Telkom Centre of Excellence
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