The microfluidic fuel cell (MFC) is a promising microscale power source. Unlike conventional micro fuel cells which use physical barriers (commonly proton-exchange membranes), MFCs exploit the co-laminar nature of multi-stream flow in microchannels to segregate the reactants. Therefore, the membrane-related problems are eliminated; the fabrication is simplified and the cost is reduced. In this thesis, both modeling and experimental studies have been carried out to investigate the fundamentals of MFC systems and innovative design of MFCs for enhanced performance. Special attention is placed on the porous electrodes.
A dimensionless model was developed first to evaluate the effects of important operating and design parameters on the cell performance via multi-parametric sensitivity analysis. The dimensionless nature of the model not only brings the benefit of computational efficiency but also enables high versatility as a single set of modeling analysis can interpret a wide range of MFCs in terms of fuel properties, physical dimensions and scales. This dimensionless model was then used to analyze the working mechanisms of porous electrodes in the MFC systems. Partial modification of the porous electrode in the electrochemical active region was investigated to achieve a balance between performance and cost.
To further validate the feasibility of the partial modification design, a two dimensional model was set up for simulating an all-vanadium MFC with multi-layer flow-through electrodes. This novel electrode configuration provides flexibility for selecting appropriate electrode materials so as to accommodate different needs in different layers of the porous electrode. Partial modification of the porous electrode is thus easily realized. In the experiment, a proof-of-concept cell is assembled. Cell performance measured under different electrode configurations reveals that maximum power density is achieved when the electrodes are modified in the electrochemical active region. The finding is consistent with the modeling results.
Besides, effective design principles for the current collectors in MFCs were derived based on three-dimensional modeling analysis. The current collectors and the external circuit, which are commonly ignored in previous modeling studies, are included in the present modeling domain. Systematic parametric analysis shows that the current collector position is the most influential factor. This finding was further validated in an experimental study. Based on the results, design rules were derived for the current collector in MFCs.
This study contributes to the thorough understanding on the underlying fundamentals in MFC with porous electrodes and provides useful guidance for the design optimization to enhance the cell performance. Future research tasks in the MFC field are also recommended.