Research On Copper-based Modified Bipolar Plate For Proton Exchange Membrane Fuel Cell

Proton Exchange Membrane Fuel Cell(PEMFC)is a new type of power generation device that can directly convert chemical energy into electrical energy.Because of its high combined heat and power efficiency(>70%),fast start-up,low operating temperature,high power density,and only water byproduct,it has been widely studied.As a key component of PEMFC,the bipolar plate plays an important role in blocking the anode and cathode,conducting electrons,supporting the Membrane Electrode Assembly(MEA),discharging by-product water,and equally dividing hydrogen and oxygen.Due to the traditional graphite bipolar plate having the disadvantages of high mechanical processing difficulty and difficulty in preparation,the commercial development of PEMFC is restricted.The proposal of the metal bipolar plate solves this problem.Copper metal has much higher electrical and thermal conductivity than graphite,which has a positive impact on cell output performance.In addition,it is easier to process complex flow field shapes on the surface of the copper bipolar plate to reach the uniform distribution of fuel and remove by-product water.In this paper,by summarizing the latest domestic and foreign research progress in two aspects of metal bipolar plate and flow field design,the corrosion situation of copper-based modified bipolar plate under simulated PEMFC conditions is explored;in view of the influence of the channel shape on the flow field performance,The traditional parallel flow field and the serpentine flow field were optimized,and the two-dimensional enhanced drainage parallel flow field,the multi-turn serpentine flow field,and the threedimensional semi-closed block flow field were designed;combined with numerical simulation and experimental results,the copper-based modification was verified applicability of bipolar plates to PEMFC.The main research work and innovations of this paper are as follows:(1)Preparation and corrosion mechanism of copper-based modified bipolar platesAccording to research,it is found that when the pretreated copper foil is buried in natural flake graphite powder for one hour at 900°C,graphite coating will grow on the surface of the copper foil.The coating can increase the corrosion potential of bare in a simulated PEMFC working environment and is higher than the anode working potential.This puts the copper-graphite composite in a cathodic protection state at the anode of the fuel cell and avoids the production of metal ions.The 4h potentiostatic polarization test results show that compared with the substrate,the corrosion current density of the coppergraphite composite material is not only reduced by an order of magnitude but also can quickly reach a stable state.In addition,the interface contact resistance value under 1.4Mpa is 18.4 mΩ·cm~2,which is also better than most metal bipolar plates.(2)Design of two-dimensional enhanced drainage parallel flow field and multi-turn serpentine flow field and research on convective mass transfer mechanismCross flow under-rib can improve the distribution of fuel and by-product water under-rib,and affect the cell output performance.Based on the parallel flow field and the serpentine flow field,the two-dimensional enhanced drainage parallel flow field and the multi-turn serpentine flow field are innovatively designed.By the analysis of the numerical simulation results,the two flow fields have significant under-rib cross flow phenomenon.The two designs not only improve the distribution of fuel and water in the active area,but also obtain a pressure drop loss much lower than the traditional flow field.The polarization curve also shows that the designed flow field improves the cell output performance.(3)Three-dimensional semi-closed block flow field design and research on the enhanced mass transfer mechanism3D block flow field design has become a research hotspot in recent years.Due to the complicated manufacturing process,the research often stayed in the simulation.In this paper,through single-channel modeling,the influence mechanism of semi-closed block distribution and spacing on cell performance are studied.When the block spacing is 10mm(one side block),the net power density can reach 0.81W/cm~2.Compared with the full block(0.53W/cm~2),there is a significant improvement.Subsequently,the 3D block is placed in a traditional parallel flow field for simulation and experimental verification.Under the optimal experimental conditions,the maximum power density of the parallel block flow field is increased by 46.3% compared with the traditional parallel flow field.It further proves that the semi-closed block is suitable for the development of PEMFC flow field design.(4)Fuel cell single-cell assembly and output performance testCombining the above research results,we assembled a pure graphite bipolar plate single-cell,a copper anode-graphite cathode bipolar plate single cell,and conducted a single-cell experiment using the 840 Fuel Cell System.The test results not only verified the usability of the copper-based modified bipolar plate in PEMFC but also verified the actual performance of the different flow fields we designed.By the comparison of HFR,we found that the difference between the copper-based graphite bipolar plate and the pure graphite bipolar plate is very small,which proves the stability of the Cu-graphite bipolar plate under the actual working conditions of PEMFC.In addition,as the stoichiometric ratio increases,the cell output performance is improved.In summary,this article has conducted a systematic study on the severe corrosion of metal bipolar plates in the PEMFC environment and flow field design.We have prepared a copper-graphite bipolar plate at a low cost.Electrochemical tests and experiments have verified the usability of the composite material.In addition,the two-dimensional enhanced drainage parallel flow field and the multi-turn serpentine flow field under-rib cross flow enhancement method were innovatively proposed;the three-dimensional semiclosed block structure enhanced mass transfer mechanism was studied;the simulation and experimental results verified the design applicability of the flow field in PEMFC.This provides a reference meaning for the metal bipolar plate in the commercial development of PEMFC.