Oxygen enriched porous carbon nanoflakes enable high-performance zinc ion hybrid capacitors†

Zinc ion hybrid capacitors (ZIHCs) are expected to be one of the most promising energy storage devices due to their affordability, high level of safety, durability and exceptional electrochemical performance. However, the widespread applications of ZIHCs are often hindered by the low specific capacity and energy density of cathode materials. Faced with these challenges, we employed a template strategy to construct oxygen-doped porous carbon nanoflake (PCN) cathode materials with abundant defective sites as a potential candidate for the cathode material of ZIHCs. PCNs possess a substantial specific surface area of 1134 m² g⁻¹ with a hierarchical porous structure, and a high oxygen doping level of 19.0 at%, offering abundant active sites to enhance the storage capacity of PCN-based ZIHCs. Consequently, ZIHCs assembled from PCNs exhibit an extraordinary specific capacity of 179.3 mA h g⁻¹ at 0.1 A g⁻¹, excellent cycling stability with no obvious capacity decay over 5000 cycles even at 10 A g⁻¹, and an outstanding energy density of 116.7 W h kg⁻¹. Additionally, ex situ experiments were conducted to study the dynamic behaviors (adsorption/desorption) between zinc ions and anions of PCN-based electrodes during the charge and discharge process. This work highlights the importance of introducing rich oxygen-containing functional groups to carbon electrodes for constructing ZIHCs with outstanding performance.