Electric double-layer synthesis of a spongelike, lightweight reticular membrane

Electrochemical polymer synthesis usually forms dense films bound to the electrode. We report a single-step synthesis of large-area, ultrathin (~70-nanometer) polymeric membranes with a luffa-like, reticular cross-linked network with low density (0.5 grams per cubic centimeter). This particular membrane forms within an electric double layer in water constructed by voltage application without supporting electrolytes—in which deprotonated resorcinol and an aldehyde react three-dimensionally with a self-termination mechanism—and is spontaneously released when the voltage bias is removed. Initially rigid with a Young’s modulus of 8.9 gigapascals, this membrane reversibly regains flexibility (0.5 gigapascals) upon wetting and can be used as a large-area membrane for separations. Its shape-persistent carbonization made it possible to yield ultrathin (~22-nanometer) nanoporous carbon membranes.