Fabrication of nano-carbon cages via molten salt CO2 electrolysis for high-performance symmetrical supercapacitor

Abstract

Utilizing greenhouse gas CO₂ as the feedstock to prepare carbon-based electrode materials for energy storage system presents significant potential for both renewable energy storage and carbon mitigation. However, this approach remains technically challenging. Herein, we report the fabrication of oxygen-enriched nano-carbon cages with hierarchically porous structure via molten salt CO₂ electrolysis. Electrochemical results demonstrate that these nano-carbon cages exhibit an ultrahigh specific capacitance of 334 F g⁻¹ at 1 A g⁻¹ in alkaline electrolyte, along with exceptional electrochemical stability, retaining 100 % after 10000 cycles at 20 A g⁻¹. Furthermore, the symmetrical supercapacitors assembled with these nano-carbon cages deliver energy densities of 9.7 and 14.9 Wh kg⁻¹ in alkaline and neutral electrolyte, respectively, still ranking the highest level among carbon materials of the same kinds and highlighting their practical application potentials. Theoretical calculations and electrochemical assessments collectively reveal that the synthesis of nano-carbon cages is primarily driven by the controlled generation of CO, which acts as a pore-forming agent and facilitates the creation of hierarchically porous structure. This work offers a feasible route for converting CO₂ into valuable carbon materials, simultaneously providing a viable alternative to traditional energy storage materials.