Research On Preparation And Properties Of Graphite/Vinyl Ester Resin Composites

Bipolar plate is one of the key components of proton exchange membrane fuel cell(PEMFC), which plays an important part in the whole battery weight and cost. Therefore, developing high performance and low cost of bipolar plate materials have come into the spotlight of PEMFC presently.In this study, graphite was chosen as a conductive filler and thermosetting vinyl ester resin (VER) as a binder matrix. Differential scanning calimetry (DSC) was used to study the curing behavior of graphite/VER composites at different scanning rates. The influences of resin content, graphite types, different proportion of the spherical graphite and flake graphite as conductive fillers, carbon black content, vacuum moulding, molding pressure and curing temperature on the micro structure,electrical, mechanical properties and thermal stability of the graphite/VER composite bipolar plate were researched.The results showed that the calculation of apparent activation energies (Ea) and reaction order(n) for VER and graphite/VER composite system were as follows:46.15kJ/mol,79.82kJ/mol;0.950,0.951. The addition of graphite improved the resin’s apparent activation energy, but had almost no effect on the reaction order. The curing average exothermic heat(△H) of the composites was decreased about17%than the pure VER system, thus, the curing degree of the resin was reduced to a certain extent; postcure phenomenon was almost non-existent in the composite system. Theoretical curing temperature parameters such as Gelling temperature(Tgel≈70.5℃), curing temperature(Tcure≈104.6℃) and post-treating temperature(Ttrear≈187.2℃) were obtained by extrapolating,which provided theory basis for graphite/VER composite bipolar plate’s curing.The best comprehensive properties of graphite/VER composite bipolar plates could be prepared when take the following conditions:use vacuum moulding; choose the mixture which spherical graphite to flake graphite is3:7(w/w) as conductive filler; keep VER resin content20wt%～25wt%and carbon content3wt%～4wt%; moulding pressure for6MPa;curing temperature procession80℃-0.5h,120℃-1h,160℃～0.5h. At the temperature around300℃, there was only1%weight loss, which indicated that the graphite/VER composite bipolar plate could completely used in the PEMFC operating environment; Spherical graphite/VER composite bipolar plate had better mechanical performances than Spherical graphite/GCPI composite plate and SCHUNK plate.