Study On Micro Direct Methanol Fuel Cell Anode Mass Transport Characteristics And Feul Support

As the portable and mobile electronic devices spread out rapidly,the technical requirements and market demands for high energy density micro-energy systems grow gradually,?DMFC,based on MEMS,becomes focus in mirco-energy technology because of its high energy density,simply operation,easy-stored fuel,long working hours,broad application prospects,etc.Currently,?DMFC has methanol premeation,low mass transfer efficiency,complex fuel-supply those problems,which leads to low output performances,thus it's hard to meet the market demands.The article raises a model including new anode and cathode flow field structrue and test its package using MEMS tech through establishing ?DMFC three-dimensional multi-physics coupling model and doing simulation analysis.This article also designs ?DMFC anode methanol fuel supply strutrue based on double-chamber,which is meaningful to protable ?DMFC system's practical development.A couping model of active ?DMFC with three-dimensional steady state and multiphysics was established in this work,an optimized design in anode internal mass transfer process and flow structrue also simulations in flow fields of point-based,gate,single serpentine and double serpentine were done respectively.It turns out that the best promances of single serpentine flow field appreas when opening rate is 47% and total long runner is 63.50 mm.In order to increase the pressure difference between different channels and to enhance the mass transfer efficiency of the catalytic layer,a novel tapered serpentine flow field is proposed with the constant effective size and the open ratio,the results showed that this structure is superior to the conventional structure described above.?DMFC plates are fabricated using MEMS bulk silicon processing tech in order to verify the simulation results.It is known that the maximum output power density of the new anode flow field structure ?DMFC is 15.41 m W/cm2,35% higher than the traditional structure and the anode mass transfer coefficient increased by 17.9% through comparing traditional-width single serpentine flow field and new tapered style ?DMFC output performance.The article also establishes a passive ?DMFC of three-dimensional steady-state multi-physics coupling model in order to study the impact of the anode and cathode structure passive ?DMFC performance.Simulation and experimental results show that the strip anode structure passive ?DMFC performs better and when the strip anode current collector plate openings is 56.71%,the battery showed the best performance.Focusing on self-respiratory ?DMFC cathodic oxygen mass transfer efficiency was low and its poor performance,the article put forward to a cathode current collector plates porous structure with a parallel channel.Such structure can effectively improve oxygen mass transfer and improve the battery performance,comparing with conventional structrue,by simulation of the cathode oxygen concentration,speed and current density simulation;taking adventage of micro-precision processing technology to achieve this kind of structure,the maximum output power density was 14.79 m W/cm2,tested at room temperature,considerably higher than the traditional porous structure.In order to improve the direct methanol fuel cell energy density,this paper designed an anode pure methanol fuel supply structure,which based on a dual-chamber structure of ?DMFC.The structure of the dual chamber,respectively,using for storing a low concentration of the methanol solution(low concentration chamber)and pure methanol(high concentration chamber),pure methanol solution slowly added to the low-concentration methanol solution diffusion through the barrier layer of the mass transfer between the two cavities.The structure circumvent the high concentration methanol solution directly in contact with the membrane electrode,effectively reducing methanol permeability.This fuel supply structure simulated the distribution of the mass transfer of methanol,verifying that pure methanol can supplement to low concentrations cavit respectively from the steady-state and transient model validation,and simulated the different mass transfer barrier layer structrue.Through testing on a variety of different structures of the mass transfer barrier layer's stable discharge time and the methanol concentration variation,thereby determining the optimal mass transfer barrier layer structure.It could be seen that the stable discharge time of multilayer film mass transfer barrier layer structure was greatly extended,from the experimental results.Meanwhile,through the measurement of the methanol concentration of the low concentration cavity,showing that it did not significantly increased,but kept at a suitable low concentration range and indicating that the feasibility of the passive ?DMFC pure methanol fuel supplied with such a double chamber structure.