Potassium-ion batteries are a promising alternative to lithium-ion batteries. However, it is challenging to achieve fast charging/discharging and long cycle life with the current electrode materials because of the sluggish potassiation kinetics. Here we report a soft carbon anode, namely highly nitrogen-doped carbon nanofibers, with superior rate capability and cyclability. The anode delivers reversible capacities of 248 mAh g^–1 at 25 mA g^–1 and 101 mAh g^–1 at 20 A g^–1, and retains 146 mAh g^–1 at 2 A g^–1 after 4000 cycles. Surface-dominated K-storage is verified by quantitative kinetics analysis and theoretical investigation. A full cell coupling the anode and Prussian blue cathode delivers a reversible capacity of 195 mAh g^–1 at 0.2 A g^–1. Considering the cost-effectiveness and material sustainability, our work may shed some light on searching for K-storage materials with high performance.

Graphene quantum dots (GQDs) have various alluring properties and potential applications, but their large-scale applications are limited by current synthetic methods that commonly produce GQDs in small amounts. Moreover, GQDs usually exhibit polycrystalline or highly defective structures and thus poor optical properties. Here we report the gram-scale synthesis of single-crystalline GQDs by a facile molecular fusion route under mild and green hydrothermal conditions. The synthesis involves the nitration of pyrene followed by hydrothermal treatment in alkaline aqueous solutions, where alkaline species play a crucial role in tuning their size, functionalization and optical properties. The single-crystalline GQDs are bestowed with excellent optical properties such as bright excitonic fluorescence, strong excitonic absorption bands extending to the visible region, large molar extinction coefficients and long-term photostability. These high-quality GQDs can find a large array of novel applications in bioimaging, biosensing, light emitting diodes, solar cells, hydrogen production, fuel cells and supercapacitors.

Efficient full-color fluorescent carbon quantum dots are synthesized by acid reagent engineering for white light–emitting devices.

Highly blue luminescent carbon nanoparticles with photo-luminescence quantum yields of 31.6%–40.6% were prepared by a one-step pyrolytic route from ethylenediamine-tetraacetic acid salts and a unique emission that is strongly dependent on pH, solvent, spin, and excitation wavelength was observed.