Structure Design And Performances Evaluations Of A Direct Methanol Fuel Cell Fed By Ultrasonic Atomization

With the progress of technology and improvement of people's lives, electronic devices such as smart phones are gradually becoming necessaries in people's life. A sharp increment in power consumption of the electronic products due to their plentiful functions. Conventional batteries are difficult to meet the requirements of the emerging electronic products because of their limited energy density. Direct methanol fuel cell(DMFC) as a new energy conversion equipment has been proposed and put in application.Although DMFC has been studied for more than two decades and the technology is mature, the catalyst poisoning and methanol permeation are still the seriously problems which barrier the widely applications of DMFC. For the methanol crossover, a method based on ultrasonic atomization of fuel supply has been presented in this paper. Combining with the methanol crossover and evaluation methods of cell performance, the experimental DMFC has been designed and manufactured, as well as the DMFC testing system. Based on the testing system, a LabVIEW testing program has been written and run. And the research of the cell performance based on ultrasonic atomization supply has been studied. In this paper, the main researching works include the following aspects:Firstly, according to the fact that the ultrasonic vibration can atomize the liquid fuel into tiny droplets, a new method based on ultrasonic atomization of fuel supply has been proposed in this paper. The new method can reduce the methanol crossover caused by the pressure of anode supplied with liquid and high concentration of methanol solution. And the DMFC structure and the ultrasonic atomization system has been designed and manufactured.Secondly, combining with the methanol crossover and evaluation methods of cell performance, a DMFC testing system has been completed. Through the theoretical analysis, a simple and single cell polarization performance testing methods has been proposed in this paper. And the low voltage polarization performance measurement system has been established; as well as the testing programs of the methanol permeate rate, open circuit voltage, and polarization performance based on LabVIEW.Thirdly, the methanol permeate rate, open circuit voltage and the polarization performance of DMFC supplied with ultrasonic atomization has been studied. The results show that when the vaporous methanol diffuses into the catalyst layer, the lower concentration of methanol solution which can reduce the concentration gradient on both sides of the electrolyte membrane, is formed on the surface of the anode catalyst,thus reducing the methanol crossover. The Mixed overpotential at the cathode becomes lower caused by low methanol crossover, thus improving the open circuit voltage of the DMFC. The performance of DMFC which is supplied with low concentration vaporous methanol is relatively low due to the lack of methanol participating in the reaction. When high concentration vaporous methanol is supplied to the DMFC, a large number of methanol diffuse to the cathode and generate mixed overpotential caused by the oxidizing reaction, thus reducing the cell performance.Finally, the results of methanol permeate rate, open circuit voltage and polarization performance of DMFC supplied with the ultrasonic atomization and with traditional liquid has been compared and analyzed. Results show that the methanol permeate rate of ultrasonic atomization is 1/2 of liquid supply, and the open circuit voltage is higher than 0.01 V. Compare with the best cell performance of two kinds of supply modes, the highest power of atomization supply with 4M methanol solution is 24.7mW which is little lower than 27.4mW of the power of liquid supply with 2M methanol solution. But, it can also be seen from the results that the atomization supply method can use a higher concentration methanol solution to obtain an equal power output, and can reduce methanol crossover. While, the method can also improve the fuel energy density and the utilization rate of fuel, thus increasing the using time of DMFC.