Potassium-ion hybrid capacitors (PIHCs) shrewdly combine a battery-type anode and a capacitor-type cathode, exhibiting an energy density close to that of potassium ion batteries and a comparable power density of supercapacitors. However, the rosy scenario is compromised by the sluggish kinetics in the PIHCs device. Herein, the kinetics enhanced nitrogen-doped hierarchical porous hollow carbon spheres (NHCS) are synthesized and successfully applied to PIHCs. As for the K half-cell, NHCS anchored with sodium alginate delivers excellent electrochemical performance. Further evaluation shows that the binder can significantly affect the potassium storage performance of NHCS by adjusting the coatability and ionic conductivity of the NHCS anode. Moreover, kinetic analysis and density functional theory calculations reveal the origin of the superior electrochemical properties of NHCS. As expected, an advanced PIHC device is assembled with a NHCS anode and an activated NHCS cathode, demonstrating an exceptionally high energy/power density (114.2 Wh kg −1 and 8203 W kg −1 ), along with a long-life capability. The successful construction of high-performance PIHCs in this work opens a new avenue for the development and application of PIHCs in the future.

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Potassium-ion hybrid capacitors (PIHCs) have attracted tremendous attention because their energy density is comparable to that of lithium-ion batteries, whose power density and cyclability are similar to those of supercapacitors. Herein, a pomegranate-like graphene-confined cucurbit[6]uril-derived nitrogen-doped carbon (CBC@G) with ultra-high nitrogen-doping level (15.5 at%) and unique supermesopore-macropores interconnected graphene network is synthesized. The carbonization mechanism of cucurbit[6]uril is verified by an in situ TG-IR technology. In a K half-cell configuration, CBC@G anode demonstrates a superior reversible capacity (349.1 mA h g −1 at 0.1 C) as well as outstanding rate capability and cyclability. Moreover, systematic in situ/ex situ characterizations, and theory calculations are carried out to reveal the origin of the superior electrochemical performances of CBC@G. Consequently, PIHCs constructed with CBC@G anode and KOH-activated cucurbit[6]uril-derived nitrogen-doped carbon cathode demonstrate ultra-high energy/power density (172 Wh kg −1 /22 kW kg −1) and extraordinary cyclability (81.5% capacity retention for 5000 cycles at 5 A g −1). This work opens up a new application field for cucurbit[6]uril and provides an alternative avenue for the exploitation of high-performance PIHCs.

Transition-metal selenides (TMSe) incorporate reversible multielectron Faradaic reactions that can deliver high specific capacitance. Unfortunately, they usually exhibit actual capacitance lower than their theoretical value and suffer from sluggish kinetics, which do not satisfy the demands of hybrid supercapacitors (HSCs), due to poor electron-transmission capability and inferior ion-transport rate. Herein, a kind of hollow biphase and bimetal cobalt nickel perselenide composed of metastable marcasitetype CoSe 2 (m-CoSe 2 ) and stable pyrite-type NiCoSe 4 (p-NiCoSe 4 ) is synthesized with metal glycerol alkoxide as precursors by regulating the Ni/Co ratios. This unique hollow biphase structure and bimetallic synergistic effect serves to boost electrontransmission capability and accelerate the ion/electron transfer rate, delivering an excellent specific capacitance of 1008 F g −1 at 0.5 A g −1 and a high discharge rate capability of 859 F g −1 at 20 A g −1 . The capacitance remains around 80% of the initial capacitance after 5000 cycles. Consequently, a HSC based on the cobalt nickel perselenide cathode and a hierarchical porous carbon anode reveals a maximum energy density of 34.8 W h kg −1 and a maximum power density of 7272 W kg −1 . This polymorphic bimetallic phase engineering provides an advanced and effective guidance for TMSe with high electrochemical properties.

However, the inferior energy density of SCs (typically < 5 Wh kg −1) severely restricts their widespread application in large-scale energy storage. [3-5] Based on the evaluation criterion of energy density, the energy density of SCs is proportional to the specific capacity and the square of the operating voltage of the device. [3,6] Therefore, in principle, the key to construct high energy density SCs lies in the electrode material with superb intrinsic characteristics and the electrolyte with high voltage window that is highly matched with the electrode material. To date, many kinds of active materials, such as transition metal hydroxides/oxides, phosphates, and carbon-based materials have been developed as electrode materials for SCs. [7-12] Among them, compounds based on the Faraday reaction tend to possess superior theoretical specific capacity, but due to poor intrinsic conductivity, sluggish kinetics, and collapse-prone structure, the key parameters such as rate capability and cyclability are unsatisfactory. [2,13] As a versatile SCs electrode material, carbon-based materials based on reversible ion adsorption/desorption not only integrate high specific capacity, excellent rate capability, and outstanding cycling performance, but also compatible with various electrolyte systems such as aqueous, organic, and ionic liquid. [14,15] In view of energy storage characteristics, pore structure plays the most vital role in electrochemical properties of carbon-based materials. [16,17] In the inherent cognition, micropores provide active sites to store charge, mesopores contribute channels to promote ion diffusion and transfer, and macropores act as ion buffers. [18,19] However, since the small-sized micropores (d <0.5 nm) are ioninaccessible, as well as the charge storage efficiency of smallsized mesopores (d <4 nm) is comparable to that of micropores, the specific capacity of carbon-based material is not always linearly related to the micropore volume. [2,20-22] Therefore, the active site contributors should be defined as ion-accessible micropores and small-sized mesopores. In view of this, the ideal carbonbased materials for SCs should be a hierarchical porous carbon (HPC), in which the ion-accessible micropores and small-sized mesopores are dominated and supplemented by a reasonable proportion of supermesopores (d >4 nm). The intrinsic properties of carbon-based material and the voltage window of electrolyte are the two key barriers to restrict the energy density of carbonbased supercapacitors (SCs). Herein, a cucurbit[6]uril-derived nitrogen-doped hierarchical porous carbon (CBCx) with unique pore structure characteristics is synthesized and successfully applied to construct SCs based on different electrolyte systems. Owing to narrow pore size distribution (0.5-4 nm), colossal ion-accessible pore volume, prominent supermesopore volume, and reasonable heteroatom configuration, the CBCx-based SCs demonstrate excellent electrochemical performances with high operating voltages in two distinct systems. The optimal SCs...