Hierarchically Tailored Porous Carbon via Precursor Engineering for Dual-Redox Electrochemical Capacitors with Record-High Energy Density

Abstract

In energy storage systems utilizing redox reactions in the electrolyte (redox-enhanced electrochemical capacitors; redox ECs), electrode materials play a critical role: pore size distribution, free volume, and internal surface area directly impact the adsorption and diffusion of redox-active species at the electrode/electrolyte interface, thereby influencing overall energy storage capacity and efficiency. Importantly, achieving optimal full-cell performance requires tailored hierarchical pore architectures capable of accommodating structurally distinct redox-active species (catholytes and anolytes). Here, a streamlined precursor engineering strategy is presented to fabricate hierarchical, multi-scale porous carbon structures, providing a simplified alternative to conventional acid etching or resource-intensive pre-treatments. The porous carbon is engineered through thermal oxidation of precursor composites at moderate temperatures, combined with precise modulation of K2CO3 during activation. This approach yields a carbon material with a well-balanced pore structure, featuring a micropore volume of 0.74 cm3 g-1 and a mesopore volume of 1.64 cm3 g-1, and a specific surface area of 3,309 m2 g-1. When applied in a pentyl viologen/bromide dual redox EC, this system achieves a record-high energy density of 125 Wh kg-1. These findings highlight the significant relationship between pore structure and redox EC performance, offering valuable insights for advanced carbon materials in energy storage systems.