The conductive network optimization of composite graphite plates and its morphological analysis

The improvement of the conductivity and mechanical properties of composite graphite bipolar plates is critical for the performance optimization of proton exchange membrane fuel cells (PEMFC). However, it is difficult to achieve the balance of the conductivity and mechanical properties. An important element is that the resin deposits between graphite layers, resulting in weakened interconnection between the graphite layers, and this structure feature is directly related to the graphite and resin mixing process. In this study, a continuous conductive network was established to optimize the performance of composite graphite plates by developing the infiltration methods, which involved graphite plates preforming and resin infiltration (FGP-I). The conductive network was constructed preferentially through the preforming of graphite plates, which decreased the adverse effects of resin on the graphite connection during the mixing process. The conductivity of FGP-I was 322.64 S/cm at a resin content of 25 wt%, which was higher than that of the composite graphite plate made from the mixture of graphite and resin (FGP-M). The flexural strength of FGP-I was 86.95 MPa, higher than 57.97 MPa for FGP-M and 22.66 MPa for the flexible graphite infiltrated plates. And its helium permeability was 1.1*10-6 cm3·cm−2·s−1. The cross-section analysis and the density measurement confirmed that FGP-I possessed a more sufficient graphite conductive network and less structural defect, which were crucial factors to improve the composite plate performance. FGP-I was a viable candidate for composite bipolar plate preparation because the preparation method was straightforward and favorable to the balanced improvement of electrical conductivity and mechanical properties.