The Direct Alcohol Fuel Cell (DAFC) is an ideal candidate for many portable applications because of its extended-life per refueling and its low weight as compared to a conventional battery. In this type of fuel cell, either direct methanol fuel cell (DMFC) or direct ethanol fuel cell (DEFC), alcohol is not reformed into hydrogen gas but is used directly in a very simple manner. Its low operating temperature of 30-100C is ideal for micro to miniature sizes. One of the leading benefits of a DAFC is that the fuel can be stored in its liquid state, and has the potential to be delivered by passive means, making all the power produced available for external work. One of the major issues with designing a DAFC is controlling the amount of alcohol crossover. Alcohol crossover is alcohol that diffuses through the membrane and reacts at the cathode catalyst layer.
Intellectual Merit: The primary goal of the proposed work is to develop basic fundamental knowledge which is lacking and essential for design and development of passive miniature DAFC with an efficient thermal-fluids management system to replace existing batteries At present, effective passive DAFC design is restricted by the lack of detailed knowledge of the physical processes of multiphase, multi-component transport phenomena within these devices, both in the fuel delivery system and the fuel cell. The goal is to develop a detailed physical non-isothermal model including a 2D-3D numerical simulation, and compare it to the proposed detailed experimental results. The transient model addresses: crossover, fuel delivery, water and thermal management issues. In our view, this research represents the leading edge in the exciting future of portable passive fuel cells.
The proposed analysis simulates transport in the liquid and gas phases separately through a multi-fluid model approach. An appropriate statistical distribution function is needed to create the local pore properties, as well as the continuous phase limitation, which directly relates to connectivity of the pores. The model should also employ the energy equation, which is important in passively operated fuel cells, since no forced convection effects are available to keep the cell operating at a nearly constant temperature. None of the existing multiphase models take into account the local variability of porous properties or the irreducible saturation limits, including the effect of continuous/discontinuous phase limitation, in the liquid and vapor phases. Most importantly, presently there is no non isothermal multiphase physical model for the prediction of various processes in vapor feed passive DAFC systems.
Broader Impacts: The fundamental research on transport phenomena in mico/minature DAFCs in this proposal can benefit the advancement of larger DAFC systems used for transportation applications and some stationary applications. The work will be disseminated to through education of both graduate and undergraduate students and continued workshops in the fuel cell area.
