Ice templating synthesis of low-density porous Cu–C nanocomposites

Abstract

Controlled synthesis of porous metal–carbon nanocomposites is challenging. Here, we describe the fabrication of porous Cu–C nanocomposites by water-ice templating in an aqueous CuSO₄ solution with a suspension of graphene oxide and carbon nanotubes. Upon the crystallization of water, the salt and carbon constituents segregate at grain boundaries of water crystallites. Freeze drying (vacuum desiccation) is used to remove water, creating pores. Final Cu–C composites are obtained by thermally-induced reduction of graphene oxide and decomposition of CuSO₄. Pore walls in resultant Cu–C foams consist of a random network of reduced graphene oxide sheets and carbon nanotubes decorated with nearly spherical Cu nanoparticles with average diameters tunable in the range of ∼30–80 nm. With this approach, we demonstrate nanoporous Cu–C composites with an ultralow C matrix density of ≳5 mg cm⁻³ and controllable Cu loading in the range of ∼0–65 wt%. This versatile method could be extended to fabricate other nanoporous metal–carbon composites geared for specific applications. As an example, we demonstrate Ag–C nanocomposites by using AgNO₃ instead of CuSO₄.