Research On Key Technologies In Packaging For Micro Direct Methanol Fuel Cell

Micro direct methanol fuel cell (μDMFC) is one of the most promising power source candidates for applications in portable electronic devices in the future. It has become a research focus throughout the world. However, there are still many bottlenecks which should be solved beforeμDMFC is put into use. Among these problems, packaging has comprehensive impact on the output performance ofμDMFC. This thesis investigated some key technologies aboutμDMFC packaging.The effect of compression pressure on the mass transfer and contact resistance of gas diffusion layer (GDL) was studied first in this thesis. Deformation of GDL and methanol concentration grads at the interface between GDL and catalyst layer (CL) were calculated under different compression pressure. The results show that the lower the compression pressure, the smaller the methanol concentration grads at the interface between GDL and CL, and the more uniform the methanol distribution. The smaller the methanol concentration grads, the higher the performance ofμDMFC. However, the lower the compression pressure, the higher the contact resistance between the GDL and current collector. So, there is an optimal compression pressure forμDMFC.The influence of load history and cathode feeding mode on the performance ofμDMFC was investigated. Based on a special designed integrated platform for packaging and measurement ofμDMFC, the effect of compression pressure on the performance of theμDMFC was systematically studied. The results show that the optimal compression pressure is 1 MPa when the cell was assembled for the first time in forced convection mode of cathode. The optimum compression pressure for the DMFC depends on the loading history. The optimal pressure is lower by an order of magnitude when theμDMFC is compressed again in this thesis. Feeding mode ofμDMFC cathode also has impact on the optimal pressure. The optimal pressure decreases to 0.5 MPa when the cell operates in air-breathing mode.The effect of current collector structure and feature size on the mass transfer and contact resistance of GDL were also investigated in this paper. The methanol concentration at the interface between GDL and CL was calculated under three current collectors with the same open ratio and different flow field feature size. The contact resistances between the GDL and current collectors were measured. The results indicate that the methanol concentration grads under flow field with spot flow field of 1mm diameter is smallest among the three flow fields. The contact resistance between the GDL and current collector with spot flow field of 1mm diameter is also the smallest among the three current collectors. Based on the above results, package structure of high polymer forμDMFC was designed and fabricated. The experimental results confirm thatμDMFCs packaged by UV resin and epoxy are feasible.AμDMFC stack with passive fuel-CO2 self-circulation system was developed and packaged according to the aforementioned optimal compression pressure. The fuel and CO2 in anode ofμDMFC can circulate in order without parasitic power consumption. The relationship of the fuel concentration and discharge current, discharge time is deduced. The peak power density of the stack reached 16.9 mW·cm-2 in passive feeding mode. TheμDMFC stack successfully powered a sensor node for 39 hours, which demonstrates the practical values of the stack.