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Composite bipolar plates composed of conductivity fillers and resins are widely employed in stationary proton exchange membrane fuel cell (PEMFC) due to their high corrosion resistance in acidic environments. Phenol-formaldehyde resin is a commonly used adhesive in composite bipolar plates; while numerous benzene rings in phenol-formaldehyde resin result in the poor flexibility of composite bipolar plates. Embedding the flexible segment (–CHOH–CH 2 -O-) in the resin network structure of phenol-formaldehyde resin by copolymerization with epoxy resin is an effective method for improving the defects of phenol-formaldehyde resin. In this contribution, to tailor flexible-segment-rich (–CHOH–CH 2 -O-) resin network structure, the co-polymerization mechanism of phenol-formaldehyde resin and epoxy resin is investigated in detailed by in-situ Fourier Transform Infrared (FTIR), based on which an Alter-T strategy is proposed for flexible-segment-rich (–CHOH–CH 2 -O-) resin network structure during composite bipolar plates fabrication process. The obtained composite bipolar plates consisted of graphite and flexible-segment-rich resin network structure delivers improved flexural strength (86.97 MPa), electrical conductivity (203.22 S cm−1) and areal resistance (3.41 mΩ cm2) in comparison to previously reported composite bipolar plates with same components, which are also over the technical standard of the DOE. It is further demonstrated that enriching the flexible segment for improving the poor flexibility of resin network structure is of great importance to enhance the performance of the composite bipolar plates. A two-step alteration of temperature (Alter-T) strategy was proposed to tailor flexible-segment-rich (–CHOH–CH 2 -O-) in the resin network structure during polymerization, for improving the performance of CBP including mechanical properties and electrical conductivity. This approach provides a new insight of improving CBP performance by regulating resin network structure. [Display omitted] • Epoxy is embedded in the resin network structure of Phenol-Formaldehyde. • The resin network structure flexibility is improved by embedding flexible-segment. • The composite bipolar plates exhibit improved comprehensive performance. [ABSTRACT FROM AUTHOR]

Composite bipolar plates (CBP) composed of conductive carbon and flexible but insulated resin are considered promising skeletons in proton exchange membrane fuel cell (PEMFC) with the characteristics of desirable mechanical and electrical conductivity properties, as well as chemical stability. However, the paradox of mechanical and electrical properties caused by insulating resins limits the overall performance of the CBP. Recently, massive studies have been reported to develop high-performance practical CBP; while there is few detailed summarizations yet. This review covers the recent advances in materials and technologies of high-performance CBP comprehensively. First, the core materials supporting the electrical conductivity and mechanical properties are summarized in detail. Furthermore, the interaction between resins and carbon-based materials is analyzed carefully. Subsequently, the fabrication process and novel structure of CBP are reviewed. Finally, the existing challenges are also discussed, and several future research directions are proposed. Overall, this review can provide guidelines for selecting appropriate strategies for improved CBP in PEMFC. • The materials and technologies of composite bipolar plate are reviewed. • The core materials for electrical and mechanical properties are summarized. • The fabrication process and novel structure of CBP are reviewed. • Suggestions for future development of composite bipolar plate are discussed. [ABSTRACT FROM AUTHOR]

Composite bipolar plates (CBPs) are promising candidates in proton exchange membrane fuel cell (PEMFC) for achieving mechanical strength and electrical conductivity as well as chemical stability in acidic environments simultaneously. While widely-explored CBPs composed with Phenol-Formaldehyde (PF) resin as adhesive (donated as PF-CBP) deliver poor flexibility due to the numerous hard π-conjugation (benzene ring) in PF network structure, which is becoming the main bottleneck index and largely hindering the practical applications of CBP. Herein, we propose a co-polymerization method by introducing Epoxy (EP) into PF resin as adhesive for CBP (donated as PF-EP-CBP), by which abundant flexible segments (-CHOH-CH 2 -O-) from EP are demonstrated to be well embedded into the structure of PF resin for enhanced flexibility. The obtained PF-EP-CBP exhibits significantly improved flexural strength of 46.20 MPa, 1.57 times higher than pristine PF-CBP (29.58 MPa), which is also higher than the 2025 DOE targets (40 MPa). Moreover, the detailed areal specific resistance, thermal conductivity, H 2 permeability and corrosion behaviors are conducted systematically to support the single cell of PEMFC. The results provide a novel insight and convenient method on the adhesive tailoring by incorporating flexible linkers into resin network structure, which is of significance to drive the practical development of the CBPs in PEMFC fields. [Display omitted] • Epoxy is embedded in the resin network structure of Phenol-Formaldehyde. • The flexibility of resin network structure could be improved by embedding Epoxy. • The composite bipolar plates exhibit improved flexural strength of 46.20 MPa. [ABSTRACT FROM AUTHOR]