AbstractHybrid supercapacitors (HSCs) comprising a battery‐type cathode and capacitive anode have recently become a research hotspot. Nevertheless, the low capacity utilization, poor kinetic behavior, and unstable structure of a single battery‐type oxide cathode restrict the overall performance of the device. Herein, the carbon quantum dots (CQDs) modified NiO/Co3O4 heterostructured flower‐like microspheres are constructed, and enhanced specific capacity, rate capability, and cycling performance are achieved when used as the cathode for HSCs. This is attributed to the fact that the modification of bifunctional CQDs as size regulators and conductive agents and the construction of heterostructure can not only improve the specific surface area and provide more electroactive sites, thereby enhancing the charge storage performance but also regulate the electronic structure and boost the interface charge transfer capability and electronic conductivity, thereby boosting the reaction kinetics and cycle stability. The enhanced electrochemical kinetic behavior is revealed by electrochemical kinetic analyses based on cyclic voltammetry, electrochemical impedance spectroscopy tests and density functional theory calculations. Meanwhile, the electrochemical reaction process and energy storage mechanism are illustrated by ex‐situ X‐ray diffraction and X‐ray photoelectron spectroscopy characterizations. Furthermore, an HSC is further constructed using the CQDs/NiO/Co3O4 heterostructured flower‐like microspheres as the cathode, simultaneously achieving high energy density (40.9 Wh kg−1), high power density (24 kW kg−1), and splendid cyclic stability (94.2% capacity retention after 5000 cycles at 10 A g−1). These synergistic modification strategies of bifunctional CQDs modification and heterostructure design provide a valuable direction for the design and development of HSCs with both high energy density and high power density.

Hybrid supercapacitors (HSCs) with large energy and power density have received increasing concern for their great potential in satisfying the requirements of energy storage systems. Nonetheless, the imbalanced kinetics between the sluggish battery-type cathode and the rapid capacitor-type anode make it difficult for HSCs to achieve high energy density at high power density. Herein, a novel N-doped carbon quantum dots/Ni-Co-Se (N- CQDs/Ni-Co-Se) hollow microspheres composite is synthesized via a facile hydrothermal approach using bifunctional CQDs as size regulators and conductive agents for the first time. Thanks to the synergism of highly conductive N-CQDs with rapid electron transfer and reduced-size hollow micro-/nanostructures contributing to the enhanced ion transport, the as-prepared battery-type N-CQDs/Ni-Co-Se hollow microspheres composite cathode exhibits admirable rate property. In-depth electrochemical kinetic analyses and density functional theory (DFT) calculations are utilized to elucidate the preeminent kinetic properties. Furthermore, a novel HSC is fabricated based on the N-CQDs/Ni-Co-Se hollow microspheres composite cathode with ultrafast electrochemical kinetics, displaying a high energy density of 23.1 Wh kg(-1) at a superb power density of 38.3 kW kg(-1). This encouraging work provides a good strategy to construct ultrahigh rate battery-type electrode materials with tunable size and component for simultaneously obtaining high energy/power density HSCs.

A graphene aerogel-based composite has recently been deemed as a prospective electrode material for advanced energy storage devices. Here, carbon quantum dots (CQDs) are simultaneously utilized as the conductive agents, intercalators, and stable links to boost the electrochemical property of graphene composite aerogels due to their many natural advantages. The threedimensional (3D) N, S dual-doped CQDs/reduced graphene oxide (rGO)/NiCo2S4 composite aerogel (N,S-CQDs/rGO/NiCo2S4) is first fabricated through a one-pot hydrothermal way and utilized as a supercapacitor cathode, exhibiting a large specific capacity of 162.6 mA h g(-1) at 1 A splendid rate property with 77.3% capacity retention at 50 A g(-1), and good cyclic stability with 87.5% capacity retention after 5000 cycles, which originates from the synergistic interaction of the 3D reticulation N,S-CQDs/rGO aerogel framework with excellent conductivity and structural stability and NiCo2S4 nanoparticles with abundant Faradaic redox reactions. Further, the resulting N,S-CQDs/rGO/NiCo2S4 cathode is coupled with the prepared N,S-CQDs/rGO anode to assemble a hybrid supercapacitor (HSC) device, manifesting a superior energy density (51.0 W h kg(-1)), an ultrahigh power density (14.4 kW kg(-1)), and good cyclic stability with 82.9% capacitance retention after 10,000 cycles. The present study offers a good strategy for designing and exploiting superior energy storage systems by utilizing the CQDs/rGO composite aerogel simultaneously as both the cathode and anode.

Constructing heterostructures can adjust the electronic structure and cause the interfacial charge redistribution to promote the reaction kinetics. Besides, metal selenides as emerging battery-type cathode materials for hybrid supercapacitors (HSCs) have recently attracted increasing interests. However, the reasonable design and fabrication of heterostructured bimetallic selenides hollow microspheres, especially the theoretical explanation of their electrochemical reaction processes and energy storage mechanisms, are scarcely explored. Herein, the heterostructured NiSe2/CoSe2 hollow microspheres are prepared via one-pot hydrothermal treatment and their energy storage mechanisms are proved with experimental and theoretical analyses. Meanwhile, the charge redistribution at the heterogeneous phase boundaries is authenticated by density functional theory (DFT) calculations. Benefiting from the abundant heterogeneous phase interfaces, unique hollow heterostructure and synergistic effect, the heterostructured NiSe2/CoSe2 hollow microspheres exhibit expected electrochemical properties, particularly admirable rate capability. Moreover, a HSC device is assembled based on the hetero-structured NiSe2/CoSe2 hollow microspheres cathode, displaying a superior energy density (53.7 Wh kg(-1)), an extremely high power density (26.1 kW kg(-1)) and a preeminent cycle stability. This work reveals the energy storage mechanisms of selenide and the charge redistribution of heterojunctions, which can provide a meaningful reference for constructing high-rate heterobimetallic selenide hollow microspheres with abundant phase boundaries.