Conductive Network Enhancement in Polybenzoxazine‐Based Composite Bipolar Plates via Selective Localization of Carbon Black

ABSTRACT Polymer‐based proton exchange membrane fuel cell (PEMFC) composite bipolar plates (CBPs) typically contain over 80 wt% conductive filler to fulfill the conductivity requirement, limiting PEMFC lightweighting. Utilizing multi‐scale conductive fillers to optimize the conduction path is an effective strategy for enhancing filler efficiency. Herein, graphite flakes (GF) are selected as the primary conductive filler, and carbon black (CB) is used as the secondary filler to fabricate polybenzoxazine (PBA)‐based CBPs via dry dispersion method. The impact of GF size and content, and GF/CB filler ratio on the conductivity and various service properties of CBPs are investigated. Results demonstrate that smaller‐sized GF contributes to superior electrical performance. Owing to the selective distribution of CB within the PBA phase, the conductivity of PBA/GF/CB CBPs is substantially enhanced. At identical total filler loading, the binary PBA/GF CBP fails to meet the DOE target (100 S/cm), whereas the addition of 4 wt% CB brings the conductivity up to the DOE requirement (116.36 S/cm). Notably, the CBP containing 52 wt% GF and 8 wt% CB achieves the highest in‐plane conductivity (153.12 S/cm) as well as the maximum power density (673.13 mW/cm 2 ). Moreover, PBA/GF/CB CBPs also exhibit satisfactory flexural strength, thermal conductivity, corrosion resistance, and hydrophobicity.