Rice husk-derived carbon materials for aqueous Zn-ion hybrid supercapacitors

High-performance rice husk-derived carbonaceous electrode materials for aqueous zinc-ion hybrid supercapacitors (ZHSCs) were prepared via a simplistically one-step molten salt carbonization process in molten eutectic Na2CO3-K2CO3 at 750, 850 and 950 °C. ZHSC assembled by Zn foil as an anode and carbon material prepared at 850 °C as a cathode delivers 149.8, 120.1, 108.7, 100.3, 89.3, 80.7 and 69.8F g−1 from 0.2 to 20 A g−1 in 3 mol L−1 Zn(CF3SO3)2 aqueous solution with a rate performance of 47 % capacitance retention. It exhibited energy (power) density with 58.6 Wh kg−1 (167.8 W kg−1) at 0.2 A g−1 and power (energy) density with 10.0 kW kg−1 (9.7 Wh kg−1) at 20 A g−1 as well as excellent cyclic stability with 95.8 % capacitance retention and coulombic efficiency of 99.9 % after 3005 charge-discharge cycles at 2 A g−1. The relationship between structure and electrochemical energy storage performance is also discussed with performance depending on the synergistic effect of porous structure, specific surface area, electrical conductivity and heteroatom doping of rice husk-derived carbon materials.