Polyacrylonitrile Derived Porous Carbon for Zinc‐Ion Hybrid Capacitors with High Energy Density

Abstract

Aqueous zinc‐ion hybrid capacitors (ZIHCs) attract widespread attention due to their excellent electrochemical performance, safety, and low cost. Here, a honeycomb‐like porous carbon is synthesized as the cathode of ZIHCs via facile pre‐oxidation in combination with an activation process. The pre‐oxidized porous carbon (PPC) displays a larger specific surface area and faster electrochemical kinetics compared to porous carbon without pre‐oxidation (PC), realizing a superior electrochemical performance. The PPC cathode can deliver a capacity of 238 mAh g−1 at 0.1 A g−1. Besides, the hybrid capacitors can achieve a high energy density of 193.6 Wh kg−1 at 76.6 W kg−1 and 109.5 Wh kg−1 at a maximum power density of 3981 W kg−1. More importantly, the hybrid capacitor exhibits a good cycling stability with a capacity retention of 83 % after 20000 cycles at a high current density of 2 A g−1. This cathode material – with an excellent electrochemical performance – could pave the way for application of ZIHCs.

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“…The galvanostatic charge-discharge curves in Figure 4b display quasi-isosceles triangle shapes exhibiting high symmetry, indicating excellent capacitive behavior on ZHC. [52,53] This observation is corroborated by Figure 4c, which shows that the Coulombic efficiency (CE) remains consistently $100%. The ZHC exhibits good recoverability, with the capacity decreasing from around 36.5 to 18.1 μAh cm À2 across a current density range of 100-1600 μA cm À2 .…”

“…The assembled ZHC achieved an open circuit voltage of 1.1 V, which is similar to other ZHCs that use aqueous electrolytes. [52,53] Figure 4a illustrates the cyclic voltammetry (CV) curves of ZHC from 0.7-1.4 to 0.7-1.7 V. A lower limit voltage of 0.7 V is established, corresponding to the minimum input voltage requirement for the PW5100 DC-DC converter with an output voltage ranging from 3.0 to 5.0 V. Any remaining power below the 0.7 V threshold is usually ineffective for most electronic devices. [54,55] In contrast, the upper limit voltage is set according to the theoretical high PCE region evaluated in Figure 3b.…”

“…This behavior is even comparable to the typical characteristics of other ZHCs with liquid electrolytes. [52,53] Such an outstanding performance is mainly attributed to the excellent infiltration of IE on evaporated zinc and spray-coated carbon electrodes (Figures S4-S6, Supporting Information). It should be noted that upon integration of the PSCs (0.18 cm 2 active area) and a 4 cm 2 ZHC, the generated photocurrent density is nearly equivalent to 400 μA cm À2 .…”

Recent progress on carbon materials for emerging zinc-ion hybrid capacitors

“…The assembled ZHCs achieved a high energy density of 130.1 W h kg −1 at 180.3 W kg −1 and a large power density of 7.8 kW kg −1 at 59 W h kg −1 under a relatively wide operating voltage of 0–1.8 V, as well as excellent cycling stability over 10 000 cycles at 10 A g −1 . Likewise, Fan et al 86 obtained porous honeycomb carbon (PPC) with a high SSA of 2926.4 m 2 g −1 by a pre-oxidation and KOH-activated process. Due to the interconnected structure of porous carbon, the Zn//PPC ZHCs displayed a high specific capacity of 238 mA h g −1 at 0.1 A g −1 , maximum energy density of 193.6 W h kg −1 at 76.6 W kg −1 and maximum power density of 3981 kW kg −1 at 109.5 W h kg −1 , together with a superior cycle life of up to 20 000 cycles with a capacity retention of 83% at 2 A g −1 (Fig.…”

Recent advances and future perspectives for aqueous zinc-ion capacitors

“…The highly reversible hydrogen and oxygen redox reactions of cathode materials during the charging and discharging processes originates from the chemical state variations of oxygen functional groups, together with the reversible (de)adsorption of hydrogen and zinc ions, contribute to the excellent specific capacitance of ZIC. Pre-oxidized PC derived from polyacrylonitrile delivered much higher specific capacitance than that of PC without oxidization, due to the introduced extra pseudocapacitance [42]. Reduced graphene oxide (rGO) with sufficient oxygen functional groups was explored as a cathode material for ZIC [43].…”