Zinc-ion hybrid supercapacitors with hierarchically N-doped porous carbon electrodes and ZnSO4/ZnI2 redox electrolyte exhibit boosted energy density

Zinc-ion hybrid capacitors (ZIHCs) with high energy density is commercial need as energy storing devices, but facile preparation is still a challenge. Herein, we proposed a combined strategy for preparation of ZIHCs with high performance. For this purpose, a nanoemulsion assembly approach with Pluronic F127 as structure-directing agent, 1, 3, 5-trimethylbenzene as pore-expanding agent, polydopamine as carbon and nitrogen source, was used to synthesize hierarchically N-doped porous carbon spheres (N-HNCSs). The optimized sample of N-HNCS-1 exhibited uniform size of 150 nm, hierarchically porous structure, large surface area (705.46 m 2 g −1 ), and N-doping amount of 6.51 %. These properties were beneficial for the transportation of the electrolyte ions resulted in that the N-HNCS-1 electrode displayed superior electrochemical performance with specific capacity of 142 mAh g −1 . Furthermore, the Zn//ZnSO 4 + ZnI 2 //N-HNCS-1 ZIHCs achieves an exceptionally high energy density of 347.7 Wh kg −1 , which is 3-fold higher than that of Zn//ZnSO 4 //N-HNCS-1 ZIHCs. To elucidate this outstanding performance, we investigate the mechanisms involved, including Zn 2+ deposition/stripping, SO 4 2- /I - adsorption/desorption, Zn 4 SO 4 (OH) 6 ⋅0.5 H 2 O precipitation/dissolution, and redox reactions relating to iodine ions . The incorporation of ZnI 2 redox-electrolyte significantly enhanced the energy density by providing prominent pseudocapacitance via the faradaic reaction. Therefore, the high performance of Zn//ZnSO 4 + ZnI 2 //N-HNCS-1 ZIHCs is attributed to the introduction of nitrogen (N) species, advantageous 3D carbonaceous framework, and redox reactions triggered by adding zinc iodide (ZnI 2 ) into the aqueous zinc sulfate (ZnSO 4 ) electrolyte. This groundbreaking research opens up possibilities for the development of high-energy ZIHCs, and advancements in energy storage technology.