Key Takeaways & Executive Findings
- •• • Graphite-based bipolar plates (GBPs) constitute approximately 70% of stack volume/weight and 30% of stack cost, making material and process optimization critical for commercial PEMFC viability. • • The review identifies that graphite particle size, morphology, and surface characteristics directly influence electrical conductivity and mechanical strength; for instance, larger flake sizes enhance conductivity but reduce mechanical integrity, necessitating a balance. • • Filler type (e.g., CNTs, carbon black, graphene oxide, carbon fibers) and content are pivotal; multiscale filler design can achieve synergistic improvements, with specific formulations enabling electrical conductivity above 100 S/cm and flexural strength exceeding 40 MPa. • • Molding processes (injection vs. compression molding) and resin content optimization are key to reducing gas permeability below 10^-6 cm^3/(cm^2·s) while maintaining corrosion resistance, meeting DOE 2025 targets.
Abstract
Graphite-based bipolar plates (GBPs) are critical components in proton exchange membrane fuel cells (PEMFCs), offering excellent electrical and thermal conductivity, corrosion resistance, and durability. However, their inherent brittleness and porous structure lead to inadequate mechanical strength and high gas permeability, limiting practical application and large-scale manufacture. This review summarizes recent advances in GBP fabrication, focusing on the effects of graphite raw materials, polymer matrices, conductive and reinforcing fillers, and molding processes on GBP performance. The relationships among graphite particle size, morphology, surface characteristics, filler dispersion, interfacial bonding, resin content, and the electrical conductivity, mechanical strength, gas permeability, and corrosion resistance of GBPs are discussed. The effects of material composition, microstructure, and processing conditions on overall performance are analyzed. Trade-offs between electrical conductivity, mechanical strength, gas permeability, corrosion resistance, and processability are highlighted. Strategies for improving performance are summarized, including optimization of graphite raw materials, multiscale filler design, interfacial regulation, resin-content optimization, and improvements in molding processes.
1. Introduction
Proton exchange membrane fuel cells (PEMFCs) represent a promising clean energy technology, converting hydrogen and oxygen into electricity with only water and heat as byproducts. However, the bipolar plate, a key component that constitutes roughly 70% of stack volume and weight and 30% of stack cost, remains a bottleneck for commercial deployment. Traditional graphite plates offer excellent electrical and thermal conductivity and corrosion resistance but suffer from brittleness and porosity, leading to inadequate mechanical strength and high gas permeability. These deficiencies hinder their practical application and large-scale manufacturing, as they cannot withstand the clamping forces and gas-tightness requirements of real-world fuel cell stacks.
This review addresses these challenges by systematically analyzing recent advances in graphite-based bipolar plate (GBP) fabrication. It focuses on the interplay between graphite raw materials, polymer matrices, conductive and reinforcing fillers, and molding processes. The authors critically examine how graphite particle size, morphology, and surface characteristics, along with filler dispersion and interfacial bonding, affect key performance metrics such as electrical conductivity, mechanical strength, gas permeability, and corrosion resistance. By highlighting the trade-offs among these properties and processability, the review provides a roadmap for optimizing material composition and processing conditions to achieve high-performance, cost-effective GBPs suitable for commercial PEMFC applications.
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Wang Dengke, Lu Wei, Yang Peiyong, Chai Maorong (2026). Progress on graphite-based bipolar plates for use in proton exchange membrane fuel cells. New Carbon Materials. https://doi.org/10.1016/S1872-5805(26)61117-1
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Frequently Asked Questions
What are the primary failure mechanisms of graphite-based bipolar plates under fuel cell operating conditions, and how do material properties mitigate them?
The primary failure mechanisms include mechanical fracture due to brittleness, gas leakage through pores, and corrosion in acidic environments. The review indicates that optimizing graphite particle size and morphology, along with resin content, can enhance flexural strength and reduce gas permeability. For instance, using larger flake graphite improves conductivity but may reduce strength; thus, a balance is needed. Incorporating reinforcing fillers like carbon fibers can increase mechanical integrity without significantly compromising conductivity.
How do different molding processes (injection vs. compression molding) affect the final properties of graphite-based bipolar plates, and which is more suitable for large-scale production?
Injection molding offers higher production rates and complex geometries but may lead to filler orientation and residual stress, affecting conductivity and strength. Compression molding typically yields better filler dispersion and higher density, improving electrical and mechanical properties, but is slower. The review suggests that process optimization, including premixing and wet/dry mixing, can mitigate drawbacks. For large-scale production, injection molding is favored for speed, but compression molding may be necessary to meet stringent performance targets.
What are the trade-offs between electrical conductivity and mechanical strength in graphite-based bipolar plates, and how can they be balanced?
Increasing graphite content enhances electrical conductivity but reduces mechanical strength due to poor interfacial bonding and increased porosity. The review highlights that using a hybrid filler system (e.g., graphite with carbon nanotubes or carbon black) can create conductive networks at lower filler loadings, preserving mechanical properties. Additionally, optimizing resin content and curing conditions can improve interfacial adhesion, achieving conductivity above 100 S/cm and flexural strength above 40 MPa, meeting DOE targets.
How does the choice of polymer matrix (thermoset vs. thermoplastic) influence the performance and processability of graphite-based bipolar plates?
Thermoset resins like epoxy and phenolic offer high strength and chemical resistance but are brittle and require longer curing times. Thermoplastics like polypropylene and PVDF provide better processability and recyclability but may have lower thermal stability. The review indicates that the matrix affects resin content optimization and interfacial bonding. For high-temperature PEMFCs, thermosets are often preferred, while thermoplastics are suitable for lower-cost, high-volume production.
What are the current challenges in scaling up the production of graphite-based bipolar plates to meet commercial fuel cell demands, and what strategies are proposed?
Challenges include achieving consistent quality, reducing cycle times, and lowering cost. The review suggests that improvements in molding processes, such as injection molding with optimized filler dispersion, can increase throughput. Additionally, using low-cost graphite sources and optimizing resin content can reduce material costs. Multiscale filler design and interfacial regulation are proposed to enhance performance without increasing filler loading, thus improving cost-effectiveness.
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