The right kind of interior for multifunctional electrode architectures: carbon nanofoam papers with aperiodic submicrometre pore networks interconnected in 3D

Carbon nanoarchitectures are versatile platforms for advanced electrode structures in which the carbon edifice serves multiple simultaneous functions: a massively parallel 3-D current collector with an interpenetrating structural flow field that facilitates the efficient transport of electrons, ions, and molecules throughout the structure for further functionalization or high-performance electrochemical operation. We fabricate carbon nanofoam papers by infiltrating commercially available low-density carbon fiber papers with phenolic resin. The polymer-filled paper is ambiently dried and then pyrolyzed to create lightweight, mechanically flexible, and electronically conductive sheets of ultraporous carbon with an electronic conductivity characteristic of the paper support (20–200 S cm−1) rather than RF-derived carbon (typically 0.1–1 S cm−1). The resulting composites comprise nanoscopic carbon walls that are co-continuous with an aperiodic, 3-D interconnected network of mesopores (2 to 50 nm) and macropores (50 nm to 2 µm). Macropores sized at 100–300 nm have not been adequately explored in the literature and offer ample headspace to modify internal carbon walls, thereby introducing new functionality without occluding the interconnected void volume of the nanofoam. Increasing the viscosity of the polymer sol and matching the surface energetics of the carbon fibers and aqueous sol is necessary to avoid forming a standard carbon aerogel pore–solid structure, where the pores are sized in the micropore (<2 nm) and mesopore range. Carbon nanofoam papers can be scaled in x, y, and z and are device-ready electrode structures that do not require conductive additives or polymeric binders for electrode fabrication. This one class of nanofoams serves as a high-surface-area scaffold that can be segued by appropriate modification into multifunctional nanoarchitectures that improve the performance of electrochemical capacitors, lithium-ion batteries, metal–air batteries, fuel cells, and ultrafiltration.