Electrochemical charge storage in hierarchical carbon manifolds

The use of hierarchical assemblies constituted from macroporous structures (e.g., reticulated vitreous carbon, RVC) where the internal pore area is covered with closely spaced nanostructures (e.g., carbon nanotubes, CNT) is proposed for substantially enhancing the energy density of electrochemical capacitors, while maintaining large charge/discharge rates. While the macroscale pores enable storage of substantial electrolyte volumes that would contribute through redox reactions to the energy density, the closely spaced nanostructures provide a large geometric area and capacitance in addition to enabling rate independent Faradaic charge storage via thin layer electrochemistry (TLE). A fifty fold increase in the double layer capacitance, in addition to increased Faradaic charge density - with potential for orders of magnitude improvement, was observed for the RVC-CNT electrodes, in comparison to the bare RVC foam electrode. It was seen that the hierarchical assembly enables the contribution from similar to 94% of the net volume of the wetted RVC-CNT electrode for active Faradaic charge storage. (C) 2015 Elsevier Ltd. All rights reserved.