Study On Preparation Of Bipolar Plate And Water Management Of Three-dimensional Flow Field By SLM

Proton exchange membrane fuel cell(PEMFC)is an efficient and environmentally friendly energy supply device that directly converts hydrogen energy into electricity,and has been widely used in various important fields.Bipolar plate is the core component of PEMFC,and its material,flow field structure and forming process jointly determine the performance and cost of the battery.Choosing ideal material,simplifying forming process and optimizing flow field structure are the key steps for PEMFC commercialization.Therefore,this paper proposes a new idea and new process for preparing high-performance complex flow field structure by SLM technology.Firstly,based on the traditional two-dimensional grid flow field(SMFF)and mass transfer theory,a new flow field structure was designed,such as hindered logistics field(OMFF)and three-dimensional flow field(3D-GRI,3D-GRII and 3D-GRIII).Secondly,the bipolar plates with different flow field structures are prepared by SLM process.Then,assembled into a single battery,measured the output voltage under different current(constant current voltage measurement method),and draw the polarization curve;Finally,the three-dimensional models of single battery with different flow field structures were established for numerical simulation of water management.The differences in output characteristics of single battery with different flow field structures were comprehensively analyzed based on the numerical simulation and experimental results.The influence of the internal correlation among the airflow characteristics,liquid water distribution characteristics and current density distribution characteristics of the battery on the battery performance was mainly studied.The main conclusions are as follows:1.Obstacle logistics field(OMFF)is designed based on the traditional two-dimensional mesh flow field(SMFF).A three-dimensional single-cell simulation model was established to simulate the two-phase flow.The simulation results show that the performance of the three-dimensional flow field is significantly better than that of the two-dimensional flow field,especially the performance of 3D-GRIII is the best.2.The metal bipolar plate of PEMFC with complex flow field structure can be prepared by SLM process,which can ensure good forming accuracy and surface quality.When the laser power is 195w,the scanning speed is 1083mm/s and the scanning distance is 0.07mm,the forming height error is less than 3.4%,the length error is less than 1%and the surface roughness is less than 0.54μm.The forming results show that SLM has high process value and application potential,especially for the preparation of bipolar plates with high performance and complex structure flow field.3.The polarization tests of single cells with different flow field structures were carried out,and the polarization curves were plotted.The maximum power of OMFF,SMFF,3D-GR II and 3D-GR III was272.8m W/cm~2,387.9m W/cm~2,437.76m W/cm~2 and 451.44m W/cm~2,respectively.3D flow field shows excellent output performance.4.The numerical simulation analysis of water management for single battery with different flow field structures shows that in the two-dimensional flow field,one of the reasons why SMFF performance is better than OMFF is that it has a large contact area,so that it has high conductivity.On the other hand,the airflow characteristics and water distribution in SMFF are relatively uniform,so the battery is more stable and has higher performance.In the three-dimensional flow field,the flow of oxygen in3D-GR III is more stable and uniform,and is guided by the slope.The longitudinal diffusion occurs fully,which ensures the oxygen supply in the catalytic layer and improves the catalytic efficiency in various regions.Thus,the uniform distribution of gas/liquid phases is realized,and the gas distribution and water management ability of PEMFC are significantly improved.In summary,SLM can successfully prepare three-dimensional flow field with high performance and complex structure(e.g.,3D-GR III),and the performance of three-dimensional flow field bipolar plate single cell is significantly improved compared with the traditional two-dimensional flow field bipolar plate single cell.The power density is 451.44 m W/cm2at 0.55 V.The flow field of this structure can ensure the full and uniform diffusion of gas,and the water management ability is strong.Therefore,the battery has high performance and is more stable.