GRAPHENE-BENZOXAZINE COMPOSITES FOR AN APPLICATION AS BIPOLAR PLATES IN FUEL CELLS

Development of a suitable and efficient bipolar plate material for polymer electrolyte membrane fuel cell (PEMFC) is scientifically and technically important due to the critical demand on higher thermal properties, higher electrical conductivity and higher mechanical properties of this material. This research emphasizes on the development of highly filled graphene-polybenzoxazine composites and investigates thermal, electrical and mechanical properties of the obtained composites. The condition for the compression molding to produce highly filled graphene-polybenzoxazine composites was at temperature of 200 oC and a hydraulic pressure of 15 MPa for 3 hours to convince a fully cured composites. The compositions of graphene loading was achieved to be in the range of 10 to 60%wt. The densities of the obtained composites were linearly increased with graphene content and the values were determined to be 1.185-1.637 g/cm3 which followed the rule of mixture. The experimental results revealed that at the maximum graphene content of 60wt% (44.8vol%) filled in the polybenzoxazine, storage moduli at room temperature of the composites were considerably enhanced with the amount of the graphene i.e. from 5.9 GPa of the neat polybenzoxazine to about 25.1 GPa at 60wt% of graphene, which is about 322% improvement. The glass-transition temperatures (Tg) of the obtained composites were observed to be in the range of 174 to 188 oC for graphene-filled composites. The Tg values substantially increased with increasing the filler contents implying substantial interfacial interaction between the filler and the matrix. At the maximum loading of graphene in the composites, thermal conductivity as high as 8.0 W/mK is achieved for a graphene-filled polybenzoxazine. Furthermore, at the maximum graphene content of 60wt%, the flexural modulus and flexural strength of the composites were found to be as high as 18 GPa and 42 MPa, respectively. Water absorption of graphene filled-composite was relatively low with the value of only about 0.06% at 24 hours immersion. Additionally, electrical conductivity were measured to be 357 S/cm at maximum loading of graphene-filled composite. Consequently, the high thermal conductivity and the data on electrical conductivity and mechanical properties of graphene-filled polybenzoxazine composites indicated the values that highly satisfied the United States Department of Energy (DOE) requirements. Therefore, these graphene-filled composites based on polybenzoxazine are highly attractive for bipolar plates in PEMFC applications.