Highly active O-, N-, and S-tridoped carbon spheres as electrode materials for efficient energy storage

Abstract

This work introduces a template-free approach for the direct activation of resorcinol–formaldehyde/thiourea polymer to synthesize O-, N-, and S-tridoped carbon spheres (TDCSs) and further discusses the effect of the ratio between thiourea and resorcinol on the electrochemical performances. The interconnected spherical morphology of TDCSs facilitates the formation of conductive networks, enabling electron transfer over shorter pathways, while the stacked porosity acts as ion reservoirs, promoting rapid ion diffusion. Additionally, the large surface area and high heteroatom content of the TDCSs enhance double-layer capacitance and provide additional pseudocapacitance. Consequently, the typical TDCS-2 electrode displays outstanding electrochemical performance, achieving a high specific capacitance of up to 319 F g⁻¹ at 0.2 A g⁻¹ and excellent long-term stability (92.4% retention after 10,000 cycles at 5 A g⁻¹) in 6 M KOH-loaded symmetric supercapacitor (KOH-SS). Moreover, the assembled KOH-SS demonstrates a noteworthy energy density of 11.08 Wh kg⁻¹ and a power density of 5000 W kg⁻¹. This study provides a straightforward and efficient method for fabricating heteroatoms doped carbon spheres for high-performance energy storage applications.