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. 

Recent advances on materials and technologies of composite bipolar plate for proton exchange membrane fuel cell

Sustainable elastomers derived from renewable biobased resources with excellent mechanical properties and varied functions are highly pursued to substitute traditional petroleum-based polymers yet challenging due to their limited macroscopic performance. In this work, we designed a series of wholly biobased cellulose-graft-poly(vanillin acrylate-co-tetrahydrofurfuryl acrylate) (Cell-g-P(VA-co-THFA) copolymer elastomers with cellulose as the rigid backbone, sustainable VA derived from lignin and soft THFA derived from hemicellulose as the hard and soft segments in the rubbery side chains. Moreover, the grafted side chains can be cross-linked to introduce an additional dynamic network structure via Schiff-base chemistry between the aldehyde and amino groups. The mechanical properties of Cell-g-P(VA-co-THFA) copolymer elastomers, including tensile strength, extensibility, elasticity, and toughness can be facilely manipulated by the VA/THFA feed ratio, cellulose content, and cross-linking density. These Cell-g-P(VA-co-THFA) copolymer elastomers are thermally stable and possess outstanding adhesion behavior and prominent UV-shielding performance. Besides dramatically enhanced mechanical properties, the cross-linked Cell-g-P(VA-co-THFA) counterparts exhibit remarkable shape memory behavior. This work provides a robust and convenient strategy for developing strong and versatile sustainable elastomers with different application demands by integrating different biomass feedstocks via elaborate molecular design. 

Wholly sustainable graft copolymers derived from cellulose, lignin, and hemicellulose for high-performance elastomers, adhesives, and UV-blocking materials

Integrating mechanical robustness with efficient healability under mild conditions is an inevitable requirement for the commercial development of self-healing ionomers. This work reveals that the resonance isomerization effect can be adopted to construct vigorous ionic networks in ionomers. As a proof of concept, 4-(alkylamino) pyridine (DMAP) and its derivatives are selected to react with bromobutyl rubber (BIIR) to fabricate BIIR ionomers. The ionized DMAP moieties manifest a resonance isomerization effect, leading to stronger ionic interactions, larger regular ionic aggregations, and more obvious microphase separation. Benefiting from the resonance isomerization effect, the BIIR ionomers in our work possess superior tensile strength (21 MPa) and toughness (92 MJ/m3), exceeding those of the existing BIIR-based materials. Moreover, the plasticizing effect of the alkyl substituent group on the DMAP-based derivatives can be further used to tailor the ionic cluster relaxation, thereby overcoming the compromise between mechanical performance and self-healing ability. Despite the dynamic network, the self-healing BIIR ionomers show a high gas barrier property which is very close to that of covalently crosslinked BIIR, enabling their potential to be used in next-generation repairable automobile tires. This work will expand the toolbox of ionic bond chemistry and afford an effective molecular design approach for optimizing mechanical and self-healing properties simultaneously. 

Mechanically Robust and Healable Bromobutyl Rubber Ionomer via Designing the Resonance Isomerization Effect

Olefin block copolymers (OBCs), which exhibit improved mechanical and thermal properties over conventional random copolymers, are high-performance polyolefin materials with promising applications in cutting-edge fields. Herein, we reported a series of isotactic polypropylene (iPP)-based OBCs with both high melting temperatures (Tms) and tunable mechanical properties, prepared via coordinative chain transfer polymerization, using a dimethyl(pyridylamido)hafnium/[Ph3C][B(C6F5)4]/AliBu3 catalytic system. The prepared OBCs were composed of a semicrystalline iPP segment with Tm > 146 °C and a propylene/α-olefin copolymer segment with comonomer content up to 17 mol %. The block microstructure of the OBCs was confirmed by gel permeation chromatography along with cross-fractionation chromatography. By properly tuning the block length and block composition, these OBCs exhibited tunable mechanical properties ranging from tough plastics (breaking strength reaching 26 MPa, elongation at break reaching 1170%) to ductile elastomers (breaking strength reaching 14 MPa, elastic recovery reaching 84%). The synthetic strategy of iPP-based OBCs in this study not only provides insights for academic research on block copolymers but also reveals great potential in the industrialization of high-value-added polyolefin materials. 

Efficient Preparation of Isotactic Polypropylene-Based Block Copolymers with Tunable Mechanical Properties: From Thermoplastics to Elastomers

Synthesis, Characterization of Polyethylene Ionomers and Their Antibacterial Properties

Because of their superior mechanical properties, excellent processability, reusability, and recyclability, thermoplastic elastomers (TPEs) have attracted considerable research attention. For random polyolefin-based TPEs, because the high crystallinity contributes to the high strength while decreasing the elastic recovery, the management of the tradeoff between the strength and stretchability is a critical challenge. Therefore, in this study, an elastomer was prepared based on a dual-cross-linking strategy by combining physical cross-links originating from polyolefin crystallinity and dynamic ionic cross-linking to resolve the tradeoff between the tensile strength and elastic recovery. First, ethylene/5-iodomethyl-2-norbornene/1-hexene terpolymers were synthesized with reactive iodine atoms, and the active sites were then transformed into a series of imidazolium-based ionomers bearing methane sulfonate (CH3SO3–), trifluoromethanesulfonate (CF3SO3–), or bis(trifluoromethane)sulfonimide (Tf2N–) counteranions via ionization and ion exchange. The interaction intensities between counteranions and imidazolium ions varied depending on the counteranion type. The ionomers containing CH3SO3– showed the highest tensile strength of up to 13.7 MPa, and those containing Tf2N– presented a favorable strain-at-break of up to 624%. The tensile properties were modulated over a broad range by changing the counteranion type and content. Moreover, because cross-links were generated by both ionic interactions and polyethylene crystallinity, the ionomers displayed excellent elastic recovery of up to 96%. 

High-Performance Polyethylene-Ionomer-Based Thermoplastic Elastomers Exhibiting Counteranion-Mediated Mechanical Properties

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High-Performance Polyethylene-Ionomer-Based Thermoplastic Elastomers Exhibiting Counteranion-Mediated Mechanical Properties