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Conductive epoxy composites are of great interest due to their applications in electronics. They are usually made by mixing powdered conductive fillers with epoxy. However, the conductivity of the composite is limited by the low filler content because increasing filler content causes processing difficulties and reduces the mechanical properties of the epoxy host. We describe here the use of ultra-stiff graphene foams (uGFs) as three-dimensional (3D) continuous conductive fillers for epoxy resins. The powder metallurgy method was used to produce the dense uGFs monoliths that resulted in a very high filler content of 32 wt % in the uGF–epoxy composite, while the density of epoxy was only increased by 0.09 g/cm3. The composite had an electrical conductivity of 41.0 ± 6.3 S/cm, which is among the highest of all of the polymer-based composites with non-conductive polymer matrices and comparable with the conductive polymer matrices reported to date. The compressive modulus of the composite showed a remarkable improvement of >1700% compared to pure epoxy. We have demonstrated that the 3D uGF filler substantially improves the conductivity and reinforces the polymer matrix with a high filler content while retaining a density similar to that of the epoxy alone.

Here we show that a versatile binary catalyst solution of Fe3O4/AlOxnanoparticles enables homogeneous growth of single to few-walled carbon nanotube (CNT) carpets from three-dimensional carbon-based substrates, moving past existing two-dimensional limited growth methods. The binary catalyst is composed of amorphous AlOxnanoclusters over Fe3O4crystalline nanoparticles, facilitating the creation of seamless junctions between the CNTs and the underlying carbon platform. The resulting graphene-CNT (GCNT) structure is a high-density CNT carpet ohmically connected to the carbon substrate, an important feature for advanced carbon electronics. As a demonstration of the utility of this approach, we use GCNTs as anodes and cathodes in binder-free lithium-ion capacitors, producing stable devices with high-energy densities (∼120 Wh kg–1), high-power density capabilities (∼20,500 W kg–1at 29 Wh kg–1), and a large operating voltage window (4.3 to 0.01 V).