| As one of the core components of proton exchange membrane fuel cell(PEMFC),bipolar plate has good electrical conductivity,thermal conductivity,mechanical properties,chemical stability and low processing cost.The preparation of bipolar plate with excellent comprehensive performance not only improves the performance and service life of PEMFC,but also plays a crucial role in promoting the commercial development and mass preparation of PEMFC.Graphite composite bipolar plate combines some advantages of metal materials and graphite materials,which is the most promising bipolar plate to meet the standards of the DEPARTMENT of Energy of the United States and be prepared on a large scale.This paper focuses on the irreconcilable relationship between mechanical properties and electrical conductivity of graphite composite bipolar plate,mainly from the following aspects of work and research:(1)Polyimide(PI),polyether ether ketone(PEEK)and polyether imide(PEI)were selected to prepare and study the comprehensive properties of expanded graphite composite bipolar plates.The resin was analyzed by TG-DSC and FTIR to establish the optimal preparation process of composite bipolar plate,and the composite bipolar plate was prepared by molding.The influence of resin type and content on the comprehensive performance of composite bipolar plate was studied.The results show that PEEK resin has the best comprehensive performance.The electrical conductivity of composite bipolar plate decreases with the increase of resin content,and the bending strength increases with the increase of resin content.When PEEK resin is 40%,the composite bipolar plate has the best comprehensive performance,with plane conductivity of 165.8 S/cm,contact resistance of 9.64 mΩ·cm~2 and bending strength of 38.65 MPa,all of which can meet the standards of THE US Department of Energy.(2)The PI and PEEK blend system was constructed by blending PI resin with PEEK resin,and the expanded graphite composite bipolar plate was prepared by using PI resin and PEEK resin blend as adhesive.PEEK resin is a bridge connecting expanded graphite and PI resin,which makes the polymer resin evenly distributed between expanded graphite and improves the comprehensive performance of composite bipolar plate.The flexible ether bond in PEEK resin increases the toughness of graphite composite bipolar plate.The experimental results show that when PI:PEEK=1.25,the composite bipolar plate has the best comprehensive performance,with plane conductivity of 181.8 S/cm,contact resistance of6.73 mΩ·cm~2 and flexural strength of 48.37 MPa.FPEEK resin was prepared by modification before polymerization,and pi-FPEEK composite bipolar plate was prepared by adding FPEEK according to the characteristics of PI-PEEK blend system.The experimental results show that the addition of fluorine atom greatly enhances the hydrophobic performance of the composite bipolar plate,the maximum contact Angle is 123.6°,and the addition of FPEEK also slightly improves the conductivity and flexural strength of the composite bipolar plate.(3)Carbon nanofibers were deposited on the surface of expanded graphite particles by chemical vapor deposition,and the effects of different CVD process conditions and commercial carbon nanofibers on the comprehensive properties of composite bipolar plates were comparatively studied.The experimental results show that the improvement effect of carbon nanofibers synthesized by CVD method on composite bipolar plate is obviously better than that of commercial carbon nanofibers,indicating that in-situ growth of carbon nanofibers by CVD can effectively avoid the agglomeration phenomenon of carbon nanofibers.With the increase of CVD temperature,the diameter and length of carbon nanofibers deposited on expanded graphite surface will increase,and the comprehensive performance of composite bipolar plate will improve.The composite anode prepared with 2%CVD carbon nanofibers at 700℃has the best performance,with plane conductivity of245.6 S/cm,contact resistance of 3.71 mΩ·cm~2,bending strength of 54.84MPa,compacting density of 1.79 g/cm~3 and contact Angle of 125.7°. |
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