Tuning the performance of composite bipolar plate for proton exchange membrane fuel cell by modulating resin network structure

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-CH₂-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, H₂ 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.