Two-Dimensional Polymer Synthesized <i>via</i> Solid-State Polymerization for High-Performance Supercapacitors

Two-dimensional
(2-D) polymer has properties that are attractive
for energy storage applications because of its combination of heteroatoms,
porosities and layered structure, which provides redox chemistry and
ion diffusion routes through the 2-D planes and 1-D channels. Here,
conjugated aromatic polymers (CAPs) were synthesized in quantitative
yield via solid-state polymerization of phenazine-based
precursor crystals. By choosing flat molecules (2-TBTBP and 3-TBQP)
with different positions of bromine substituents on a phenazine-derived
scaffold, C–C cross coupling was induced following thermal
debromination. CAP-2 is polymerized from monomers that have been prepacked
into layered structure (3-TBQP). It can be mechanically exfoliated
into micrometer-sized ultrathin sheets that show sharp Raman peaks
which reflect conformational ordering. CAP-2 has a dominant pore size of ∼0.8 nm; when applied
as an asymmetric supercapacitor, it delivers a specific capacitance
of 233 F g–1 at a current density of 1.0 A g–1, and shows outstanding cycle performance.