Visualization Experiment And Optimization On Performance In Direct Liquid Fuel Cells

As a promising power source with high energy density for the portable electronic devices, the development of direct methanol fuel cell(DMFC) is hindered by some inherent issues,such as methanol crossover, slow kinetic rate of methanol oxidation, anodic gas-liquid double phase flow issue and thermal management for the DMFC stack. In order to solve or relive these issues, a series of related research has been carried out.During electrochemical reaction in a DMFC, water is produced in the cathode from oxygen reduction reaction and CO2 is produced in the anode from methanol oxidation reaction by products. Produced CO2 in the anode catalyst layer is basically in gas phase and typically removed through the anode channel out of the cell. During this CO2 removal process, it is known that CO2 gas brings on a strong two-phase flow in the anode channel as shown, which causes a large pressure drop along the anode channel and makes study of DMFC difficultly. In order to maintain steady cell operation, produced CO2 should be removed out of the cell.We tried to solve these issues in the DMFC by making the visualization device and introducing the magnetic field inside the DMFC. This paper is divided into two aspects. Firstly, this paper uses the visualization techniques to study the real situation in the anode flow field of the DMFC and analysis the influence of operating parameters and flow field conditions on the performance of the cell. Secondly, removal of CO2 bubble from the anode catalyst was promoted by combining the magnetic field with the passive DMFC. The concrete results are as follows:(1) In order to observe the situation of the CO2 bubbles in the anode flow channel of the DMFC by using the visualization technology. With the increase of the discharge current, we found that the increase number of CO2 bubbles in the anode flow channel, polymerization, growth and formation of discontinuous gas bomb blocking anode diffusion layer phenomenon periodically。We observed the effect of the operation conditions on the effective area of 9cm2 of DMFC. It included the mass transport of methanol、the concentration of methanol、the temperature of methanol and the type of the flow field. We also find the optimum value and analyze the reasons in each of the operation conditions. The experimental results will be helpful to understand the anode CO2 gas discharge mechanism and provided a reference for the improvement of flow field and optimizing the operation of the operation conditions. It is to achieve the stable and efficient operation of DMFC eventually.(2) For the first time, a novel approach was proposed to promote CO2 removal from the anode catalyst layer of a liquid-fed passive direct methanol fuel cell(DMFC) by introducing Lorentz force via magnetic field integrating. Due to the promoted removal of CO2 micro-bubble, the physical block of triple-phase boundary in the anode catalyst layer was reduced evidently. CO2 removal was promoted through introducing forced convection around the CO2 bubbles which can be proved by the mathematical calculations. Performance of the vapor-fed DMFC, in where no CO2 bubble existing in the anode, did not change by the magnetic field, also indicated that the enhanced performance of the liquid-fed magnetic-coupled DMFC was resulted from the promotional CO2 removal. A 12.5% enhancement in maximum power density was obtained for the liquid-fed DMFC by combining the magnetic field. This work reported a simple method to relieve the micro double-phase issue in the anode of DMFC. This method also provides a novel tactics for double-phase issue solving.