a composite bipolar plate for a proton exchange membrane fuel cell is prepared as follows : a ) melt compounding a polypropylene resin and graphite powder to form a melt compounding material , the graphite powder content ranging from 50 wt % to 95 wt % based on the total weight of the melt compounding material and the polypropylene resin being a homopolymer of propylene or a random copolymer of propylene and ethylene , butylenes or hexalene , wherein 0 . 01 - 15 wt % of polymer - grafted carbon nanotubes by an acyl chlorination - amidization reaction , based on the weight of the polypropylene resin , are added during the compounding ; and b ) molding the melt compounding material from step a ) to form a bipolar plates having a desired shaped at 100 - 250 ° c . and 500 - 4000 psi .