3D N and O co-doping hierarchical porous carbon with ultrahigh surface area as cathode material for high-performance zinc-ion hybrid capacitor

Aqueous zinc-ion hybrid capacitors (ZIHCs) have garnered significant attention due to their cost-effectiveness, safety, and high theoretical capacity. However, the use of carbon-based materials in ZIHCs faces challenges such as electrolyte ion and pore size mismatching, inadequate infiltration between electrolyte and electrode, and limited surface active sites and defects, all of which impede the device's ability to achieve optimal energy density and electrochemical performance. To address these issues, a three-dimensional N and O co-doping hierarchical porous activated carbon (3DNOHC) with an ultrahigh specific surface area of 3477.69 m2 g-1 is synthesized through the direct calcination of nitrilotriacetic acid sodium salt precursor followed by a chemical activation process. Density functional theory calculations demonstrate that the N/O co-doping of activated carbon significantly enhances the ion adsorption/desorption capabilities on the surface of the materials, thereby improving their kinetic and electrochemical properties. The structural changes in zinc metal anodes and 3DNOHC cathodes during charging/discharging are investigated using ex situ XRD and ex situ Raman tests. Due to its abundant porous structure and active sites, the 3DNOHC-6 sample exhibits rapid ion transport and impressive electrochemical performance in ZIHCs. In particular, the 3DNOHC-6//Zn device demonstrates a high reversible capacity of 171/102 mA h g-1 at 0.2/10 A g-1 and an outstanding energy density of 137 Wh kg-1@160 W kg-1. Moreover, it exhibits excellent capacity retention of 80% at 5 A g-1 after 45 000 cycles. This study serves as a valuable reference for the development of activated carbon cathode materials for aqueous hybrid capacitors aiming for high energy/power density.