Structurally Asymmetric Porous Carbon Materials with Ordered Top Surface Layers from Nonequilibrium Block Copolymer Self-Assembly
Sarah A. Hesse, Peter A. Beaucage, Detlef‐M. Smilgies, Ulrich Wiesner
Abstract
Inorganic materials with asymmetric pore structures provide increased accessibility and flux, making them attractive for applications in energy conversion and storage, separations, and catalysis. Non-equilibrium-based block copolymer structure-directed self-assembly approaches provide routes to obtaining such materials. We report a one-pot synthesis using the co-assembly and non-solvent-induced phase separation (CNIPS) of poly(isoprene)-b-poly(styrene)-b-poly(4-vinylpyridine) (ISV) triblock terpolymer and phenol formaldehyde resols. After heat-treatment, carbon materials with asymmetric pore structures result. They have a mesoporous top surface atop a porous support with graded porosity along the film normal. The walls of the macroporous support are also mesoporous, providing an additional structural hierarchy and increased specific surface area. We demonstrate how successfully navigating the pathway complexity associated with the nonequilibrium approach of CNIPS enables switching from disordered to ordered top surfaces in the as-made organic–organic hybrids and resulting carbon materials after thermal treatments. To that end, a combination of ex situ transmission small-angle X-ray scattering (SAXS) of the membrane dope solutions, in situ grazing-incidence SAXS (GISAXS) after dope solution blading and during solvent evaporation, and scanning electron microscopy (SEM) of the final membrane structures was used. We expect the final porous carbon materials exhibiting a combination of asymmetric, hierarchical pore structures and well-defined mesoporosity throughout the material to be of interest for a number of applications, including batteries, fuel cells, electrochemical double-layer capacitors, and as catalyst supports.