Quinones are attractive redox-active starting materials due to their excellent electron transfer kinetics and outstanding redox reversibility, while amines featuring high electron-pair donicity reinforce the redox behavior of quinones and simultaneously introduce redox groups themselves. Herein, a novel quinone-amine route is designed to fabricate N, O codoped porous carbon nanospheres (PCNs) by direct carbonization–activation of a quinone-amine polymer which serves as an “all-in-one” precursor for the carbon source and self-dopant. The synthesis features simplicity, high efficiency and scale-up potential, based on the polymerization of p-benzoquinone and 3,3′-diaminobenzidine in ethanol under mild conditions, without any template, complicated technique or tedious procedure. PCNs integrate the superiorities of uniform spherical geometry, superior pore structure, and ultrahigh surface area and N/O content. A typical PCN electrode exhibits a high capacitance (376 F g⁻¹ at 0.5 A g⁻¹ in a three-electrode system) in KOH electrolyte. The assembled supercapacitor based on the PCN electrode and KOH electrolyte delivers a capacitance of 72.5 F g⁻¹ and an energy output of 6.5 W h kg⁻¹. More importantly, a constructed symmetric supercapacitor using an ionic liquid gel electrolyte gives an ultrahigh energy density up to 65.8 W h kg⁻¹, along with superb cycling stability. This study presents a more convenient and competitive route to design functionalized carbons for highly efficient energy storage.

Significantly boosting the energy densities of supercapacitors without compromising their power densities is of paramount importance for practical applications, but still faces great challenges. Herein, we report an ultrahigh-energy-density solid-state supercapacitor enabled by synergistical design of a N, O co-doped honeycomb porous carbon (HPC) electrode and an ionogel electrolyte. HPC is synthesized through the co-assembly of melamine/formaldehyde with silica spheres, and shows an ultrahigh surface area (2379 m² g⁻¹) coupled with a 3D interconnected macro-, meso- and microporous structure, and high-level redox-active N/O dopants (6.90 and 10.17 wt%). Benefiting from such merits, the HPC electrode yields an extremely high capacitance of 533 F g⁻¹ at 0.5 A g⁻¹ in an alkaline electrolyte, together with superior cycling stability with 92.1% capacitance retention after 20 000 cycles at 5 A g⁻¹. HPC assembled supercapacitors deliver energy outputs of 12.8 and 26.6 W h kg⁻¹ using KOH and Na₂SO₄ electrolytes, respectively. More attractively, a HPC-fabricated all-solid-state symmetric device based on the use of a well-designed, polymer-gel supported ionic liquid electrolyte achieves an ultrahigh energy density of 94.1 W h kg⁻¹, which is the highest value among those of previously reported supercapacitors of the same type, and an excellent cycling stability (91.5% retention over 10 000 cycles). This study highlights promising prospects of developing solid-state energy storage systems of high energy-power supply.

Zn-ion hybrid capacitors, with a large-capacity Zn anode (battery-type) integrated with a capacitive cathode, hold great potential to relieve the unsatisfactory energy-to-power ratio of aqueous supercapacitors. The research into cathode design is expected to bridge the capacity gap between the two electrodes without sacrificing the inherent power/cycling superiorities but is still in its infancy. In this work, robust O/N-decorated porous carbon cathodes were derived by the in situ calcination of conjugated polyamides, wherein the solvent-guided strategy was applied to shape the carbon nanoarchitecture for the activation of Zn storage sites. After optimizing the solvent–precursor interactions, the packed particle architecture (C_DMF) ultimately exposed ample electrosorption platform up to 1656 m² g⁻¹, and O/N dopants (15.77 wt%) promoted interfacial Zn adsorption by lowering the energy barrier for C–O–Zn bonding. Further experimental evaluations revealed that the CO species on the robust C_DMF framework tended to boost reversible chemical adsorption to form C–O–Zn bondings while maintaining durable charge transfer, which minimized capacity loss even at high rates. As a result, the aqueous C_DMF//Zn capacitor achieved a large capacity of 180 mA h g⁻¹, an ultrahigh energy density of 106.7 W h kg⁻¹ and an excellent power output of 13.4 kW kg⁻¹, as well as 91.1% capacity retention over 300 000 cycles. This design strategy gives an appealing insight into the subtle fabrication of high-performance carbon cathodes and highlights their applicability towards practical Zn-based energy storage in the future.

The key concern in constructing high-energy supercapacitors is maximizing the electrode capacitance and the cell voltage. However, the current research usually addresses this issue by designing advanced electrodes or seeking high-potential electrolytes separately, instead of both. Herein, we demonstrate a two-pronged design of ternary-doped carbon electrodes and a high-voltage “water-in-salt” (WIS) gel electrolyte to support advanced aqueous-based solid-state supercapacitors. The fabrication of N/S/O multidoped carbons is quite straightforward, involving a facile benzoquinone/sulfourea polymerization and a common carbonization/activation procedure, which avoid sophisticated technique/conditions and/or time-consuming synthetic routes. The carbons feature an extraordinary surface area, high content of heteroatoms, and improved surface wettability. A highly porous gel polymer is introduced as a supporting matrix for the WIS to design a 2.3 V gel-type electrolyte, in pursuit of a new record high-energy aqueous solid-state supercapacitor of 37.7 W h kg⁻¹, with excellent temperature robustness in the range of 0–80 °C. Furthermore, an assembled flexible device delivers a stable energy output of 34.3 W h kg⁻¹ and demonstrates great flexibility with 91.6% energy retention even in a bending state of 180°. This study presents an electrode/electrolyte cooperative effect to unlock the energy potential of aqueous flexible solid-state supercapacitors.

N/O self-doped hollow carbon nanorods (HCNs) with micro/mesoporous walls are fabricated based on a new deep-eutectic-solvent that serves as an all-in-one precursor, self-template, and self-dopant agent. The carbon-based supercapacitor using an ionic liquid electrolyte exhibits a high energy density of 116.5 W h kg⁻¹ with excellent long-term cycling performance.