Niobium-tungsten bimetal oxides have received wide attention due to their excellent lattice properties. In this work, Nb18W16O93 (NbWO) with a tetragonal tungsten bronze structure was synthesized by simple hydrothermal method. NbWO was modified to provide high specific surface area via combining with hollow carbon nanotubes. Meanwhile, NbWO grows along the tube wall of carbon nanotubes, thus buffering the volume effect of NbWO particles. Also, the migration distance of Li-ion is effectively shortened, as well as the improved ion transfer efficiency and the reaction kinetics. In addition, carbon tube can enhance conductivity of NbWO, contributing to outstanding charge storage capacity and rate energy. Precisely, NbWO@C as electrode possesses large specific capacity (249.6 F g-1 at 0.5 A g-1) and good rate performance (55.9 % capacity retention from 0.5 A g-1 to 2 A g-1). The aqueous Li-ion capacitor presents the advantages of high safety, low cost and good environmental friendliness. An asymmetric aqueous capacitor AC//NbWO@C, based on "water-in-salt" electrolyte with high concentration lithium acetate, exhibits a large energy density of 43.2Wh kg-1 and a power density of 9 kW kg-1. Generally, NbWO@C as anode materials shows superior application perspective.

The green synthesis of biomass multifunction carbon is a major research direction within the carbon field. In this work, double-ion codoped two-dimensional (2D) carbon nanosheets, derived from biomass by recyclable boric acid templates, are prepared as supercapacitor electrode materials. Here, biomacromolecules from pomacea canaliculata egg (an exotic invasive species in China) self-assemble uniformly on the surface of H 3 BO 3 plates by hydrogen bonding, thus forming a precursor with a sandwich structure. Subsequently, gas from the H 3 BO 3 pyrolysis further inflates the resultant carbon material to 2D-shaped ultrathin nanosheets and also to acquire the carbon material (NBC) after simple water-washing. NBC has the following advantages: (1) N, B codoping changes the electron distribution of the carbon lattice, enhancing the electrochemical activity and conductivity; (2) abundant and uniformly distributed active sites are produced on the carbon nanosheet surface due to the full contact between boric acid (as both the template and doping source) and the biomass precursor; (3) the reagent used in this work (H 3 BO 3 ) can be recycled and used repeatedly without pollution to the environment, achieving the closed-loop usage of chemical reagents. Compared with the traditional alkaline activation method, this work has a better prospect in view of material stability, preparation difficulty, and environmental protection. In terms of performance, the NBC//NBC delivers an energy density of 8.2 Wh kg −1 and a maximum power density of 2500 W kg −1 . Besides, NBC//NBC preserves about 92.3% high specific capacitance after 10 4 cycles, meaning its splendid stability.

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