Low-energy and solventless manufacturing of epoxy/expanded graphite bipolar plates

Abstract

Bipolar plates (BPs) based on a polymer matrix and carbon materials have lately been considered potential alternatives in fabricating polymer electrolyte fuel cell (PEFC) components. For widespread market adoption, utilizing minimal energy in the synthesis process and abstaining from harmful solvents is crucial. This study proposes an efficient, solventless method to address these limitations, emphasizing low-viscosity epoxy resin and high-expansion ratio graphite as critical parameters to fabricate highly conductive composites suitable for bipolar plate applications. To achieve this, high-quality expanded graphite (EG) was prepared using microwave heating, oxygen removal, and sieving for particle size control. The EG was then mixed with a commercial DGEBA-based resin in proportions of 40, 50, and 60 wt%, hot-molded at 110 °C with 4500 psi for 10 min, followed by post-curing at 130 °C, for an additional 10 minutes. The resulting composites were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), flexural strength testing, and in-plane electrical conductivity measurements. The properties obtained were compared with the requirements set by the U.S. Department of Energy (DOE). XRD and SEM revealed an amorphous, highly porous EG filler with limited dispersion, particularly at high EG concentrations, 60 wt%. Despite this, a remarkable electrical conductivity of 177.99 S cm⁻¹ was achieved at 60 wt% EG, without using any solvent or secondary filler, and most of the composites surpassed DOE's flexural strength requirement, 25 MPa. This methodology demonstrates a solventless approach for producing high-performance BPs composites that meet or exceed DOE's electrical and mechanical property requirements for PEFC applications.