Solute-Induced Nonplanar Ice Growth Facilitates Space-Confined Polymerization for Two-Dimensional Polymer Sheets

While the ice-templating method has emerged as a powerful approach for fabricating complex architectures of various materials, the underlying mechanism has yet to be fully elucidated. Here, it's shown that dissolved solutes drive nonplanar ice crystal growth and generate interfacial boundaries where polymerization reactions can be space-confined. The ice crystal growth fronts are captured using in situ optical microscopy and observed to exhibit a sheath-like appearance, a result that is rationalized using constitutional supercooling theory. Building on these results, two-dimensional (2D) polymer sheets of poly(3,4-ethylenedioxythiophene) (PEDOT), polypyrrole (PPy), and polyaniline (PANI) with relatively high crystallinities are realized when micelles of sodium dodecyl sulfate are used to confine the oxidative polymerizations of the constituent monomers within the boundaries of the corresponding ice crystals. Supercapacitors (SCs) fabricated with the 2D PEDOT, PPy, and PANI sheets are found to exhibit high areal capacitances of 242.2, 640.9, and 648.2 mF cm^-2 at 0.2 mA cm^-2, respectively. Moreover, the SCs display remarkable cycling stabilities, i.e., 98.4%, 72.3%, and 81.6% of the respective initial capacitance values after 10 000 cycles at 10 mA cm^-2. These results advance the mechanistic understanding of the ice-templating technique and expand its potential utility in the rational design of hierarchically structured materials.