Abstract
In this paper, a micro-droplets fuel supply system has been developed for direct methanol fuel cells (DMFCs) by piezoelectric actuation. Compared with common serpentine flow plate, this new fuel supply mode can improve fuel usage rate and power density while lower down carried fuel volume and fuel crossover issue in DMFCs. A micro droplets device with various concentration of fuel supply was tested and expected to find the most suitable fuel supplying mode. PZT ceramic was used to actuate droplets. A syringe needle tip was fixed 0.2-0.5mm above the piezo actuator surface to provide fuel for atomizing into 4-5μm droplets. The droplet size was much smaller than Si-based nozzle. Methanol mixture in tank transported by micro pump would be broken by piezoelectric actuation into droplets and sprayed onto the anode of DMFCs directly. Air at cathode was introduced convectively by a fan, and the cell was operated at room temperature. When the device was setup, various concentration of the fuel was supplied to the cell. The results showed that methanol mixture reaching 6M is the optimized concentration for the cell. Compared to the circulatory system, micro-droplets system, could greatly improve power density at the same condition (60 Celsius). On the other hand, the voltage fluctuated more drastically in micro-droplets system, and it enables the usage of higher concentration methanol fuel (5M) relative to circulatory flow system (2M), resulting in a higher peak power density at 32.5mW*cm-2 than that (20.5mW*cm-2) of the circulatory system at 0.4V.