Highly redox-active oligomers between graphene sheets as ultrahigh capacitance/rate and stable electrodes for supercapacitors

Organic electrodes have emerged as promising candidates for supercapacitors due to their sustainability, structural diversity, and high electrochemical activity. However, the intrinsic poor electronic conductivity and solubility in electrolytes impede their further applications. Herein, we propose a facile strategy for the synthesis of pyrogallic (PG) oligomer confined in-between graphene layers (FRGO) as high-performance electrodes for supercapacitors. The PG oligomer exhibits both physiochemical properties of small molecules and organic polymers, such as fast reaction kinetics and structural stability in aqueous electrolyte. Conjugated sp² carbon plane with abundant electroactive groups (-OH and -C=O) possess high electrochemical activity and construct fast electron transfer tunnels crossing the longitudinal graphene layers. Accordingly, FRGO delivers an excellent rate performance (835 F g⁻¹ at 0.5 A g⁻¹, 233 F g⁻¹ at 200 A g⁻¹) and ultra-long cycle stability. The symmetric supercapacitor exhibits an ultra-high energy density of 82.4 Wh kg⁻¹ at 300 kW kg⁻¹, dramatic power density of 90 kW kg⁻¹ at 4 Wh kg⁻¹, and remarkable stability of 90% retention after 20000 cycles. This work may open a new window for the rational design of organic oligomers in energy storage and conversion fields.