Study On Thermally Driven Passive Direct Methanol Fuel Cell

With the rapid development of science and technology,more and more small portable electronic devices are pouring into the market and entering thousands of households.Under this development situation,fuel cell,as a new energy source with high energy density,high energy conversion efficiency,low pollution,and renewable,has become one of the traditional power supply alternatives.Compared to active fuel cell,passive direct methanol fuel cell(DMFC)is more compact,simpler,less expensive,and more energy efficient,these advantages make it more suitable for portable devices and small electric systems.However,since the passive DMFC does not have an additional supplementary fuel,the output performance is bound to decrease with the fuel cell long-term operation.If a high concentration of methanol solution is used at the anode in order to increase the energy density,it will cause serious methanol permeation problems.Therefore,designing a new type of fuel supply device to maintain the stability of the passive DMFC for a long time is of great significance for the development of fuel cell.This paper is aimed at researching on passive DMFC to improve the problem that fuel cell can not provide stable output for a long time due to anode fuel limitation.Several factors that affect the output voltage of DMFC during electrochemical reaction were analyzed,and the relationship between total methanol consumption and current density was derived by the formula.The finite element analysis software was used to simulate the structure of the thermally driven fuel supply device.The heat distribution and velocity fieldsimulation results demonstrated the rationality of the structure of the flat-plate type thermally driven fuel supply device with the porous wick and the grid-shaped heating groove layered.A passive DMFC with an effective area of 1cm~2 was fabricated,including the fabrication of membrane electrodes and the assembly of current collectors and end plates.According to the simulation results,a flat type thermally driven fuel supply device was designed.In the device,the liquid methanol was injected from the top of the device so that the porous wick was in a state of infiltration.The thermally driven fuel supply device utilized heat energy at the bottom and caused phase change of methanol.Methanol steam directly escaped from the bottom of the porous wick to provide a continuous supply of methanol steam.A thermally driven passive DMFC system was set up in the project to test and analyze the influence of operating temperature and current density.The output stability under different operating conditions was evaluated by performing a long-term constant current discharge test on the system.It was found that within a certain range,with a higher operating temperature of the thermally driven fuel supply device and lower current density of the fuel cell,the system had a more stable output and longer working time.The thermally driven passive DMFC system can greatly alleviate the problem of fuel cell performance degradation caused by anode fuel consumption,which achieved the design goal.