AC Impedance study to evaluate the MEA characteristics in a passive mode DMFC mini-stack (Contributo in atti di convegno)

Type
Label
  • AC Impedance study to evaluate the MEA characteristics in a passive mode DMFC mini-stack (Contributo in atti di convegno) (literal)
Anno
  • 2009-01-01T00:00:00+01:00 (literal)
Alternative label
  • V. Baglio; A. Stassi; F.V. Matera; H. Kim; V. Antonucci; A.S. Aricò (2009)
    AC Impedance study to evaluate the MEA characteristics in a passive mode DMFC mini-stack
    in 215th Meeting of The Electrochemical Society, San Francisco, CA, 24-29/05/2009
    (literal)
Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#autori
  • V. Baglio; A. Stassi; F.V. Matera; H. Kim; V. Antonucci; A.S. Aricò (literal)
Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#affiliazioni
  • CNR-ITAE Seoul National University, Department of Chemistry, Seoul 151-747, South Korea (literal)
Titolo
  • AC Impedance study to evaluate the MEA characteristics in a passive mode DMFC mini-stack (literal)
Abstract
  • Direct methanol fuel cells (DMFCs) are becoming an important area of research for application in portable electronic devices, such as notebook computers, personal digital assistants (PDAs), music systems and cellular telephones due to their advantages in terms of high energy density (when a concentrated methanol solution is used), simplicity, easy and fast recharging. Yet, in order to be commercially viable, it is necessary to eliminate power losses from auxiliaries, i.e. the pump and the fan that are usually used to feed methanol and air into the stack. Nowadays, passive mode DMFCs are receiving increasing attention due to th eir advantages of operating without any external devices for feeding methanol and breathing air into the cells. Oxygen diffuses into the cathode side from ambient air without any help of external devices, such as a pump or fan, due to an air-breathing action of the cell. The gradient of oxygen partial pressure is directly formed by oxygen consumption. The methanol solution, stored in the reservoir attached to the anode compartment, also diffuses into the anode driven by a concentration gradient between the reservoir and anode as a consequence of electrochemical consumption of methanol. Thus, passive DMFCs can potentially result in high reliability, low cost, high fuel utilization and high energy density, which are in favor of portable equipments in future electronic devices . Significant efforts are presently devoted to develop new concepts of DMFC stacks [1, 3] in order to miniaturize the device; yet, limited attention is focused on the optimization of electrode structures for a suitable mass transport of reactants in passive mode stack. Nowadays, direct methanol fuel cell electrodes mainly consist of gas diffusion electrodes similar to those used in H2-fuelled proton exchange membrane fuel cells (PEFCs). One of the most used configurations consists of a macroporous layer, which is a carbon cloth or paper; this is the conductive support onto which the microporous gas diffusion layer and thereafter the catalytic layer are deposited. In most electrode configurations, the gas diffusion layer is formed by olytetrafluoroetylene (PTFE) and Carbon black; whereas, the composite catalytic layer consists of carbon supported Pt or Pt alloy catalysts and Nafion ionomer. Such an electrode structure was originally developed for operation at about 80°C since the development of DMFC for transportation was historically considered to provide the ain perspectives for large-scale application of such devices. In low temperature liquid-fuelled DMFCs finalized to the development of portable systems, this electrode configuration suffers from mass-transport limitations. These constraints mainly occur at the anode side due to the low diffusion coefficient of methanol in water and the release of carbon dioxide gas bubbles. DMFCs are generally operated with aqueous methanol solution at different concentrations; therefore, in order to ensure a better reactant distribution and supply, good hydrophilicity is required for the anode side. Whereas, for the cathode, hydrophobic properties are necessary to avoid the flooding of the electrode in particular for low temperature operations using a high methanol concentration at the anode. In this work we have evaluated by impedance measurements the effect of MEA configurations on the performance of a monopolar mini-stack operating at ambient te mperature, under conditions close to the practical application (high methanol concentration at the anode, passive mode, air breathing). (literal)
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