Eco-friendly synthesis of coal tar-derived oxygen-rich porous carbons for ultra-long-life zinc-ion hybrid supercapacitors

Zinc-ion hybrid supercapacitors (ZHSs) have emerged as a promising energy storage technology, combining the high energy density of batteries with the superior power density and cycling stability of supercapacitors. Nevertheless, the development of high-performance electrode materials for ZHSs remains a significant challenge. Herein, we report an environmentally friendly synthesis of oxygen-doped hierarchical porous carbons derived from coal tar, using calcium gluconate as a multifunctional template and K₂CO₃ as a mild activating agent. The optimized carbon cathode (MCK) possesses a high specific surface area up to 1067.6 m² g⁻¹ and an appropriate oxygen doping content of 6.05 at%, which collectively provide abundant active sites for Zn²⁺ storage and facilitate efficient ion transport pathways. As a result, the MCK cathode delivers a high specific capacity of 181.8 mAh g⁻¹ at 0.05 A g⁻¹, outperforming most previously reported carbon-based cathodes. Furthermore, it achieves impressive energy and power densities of 145.1 Wh kg⁻¹ and 13.9 kW kg⁻¹, respectively, along with exceptional cycling stability with 92.98 % capacity retention after 100,000 cycles. This work not only offers valuable insights into carbon material design but also demonstrates a scalable and green synthesis strategy for advanced energy storage applications.