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.

Highly ordered ${\mathrm{TiO}}_{\mathrm{2}}$ nanowire (TN) arrays were prepared in anodic alumina membranes (AAMs) by a sol-gel method. The TNs are single crystalline anatase phase with uniform diameters around 60 nm. At room temperature, photoluminescence (PL) measurements of the TN arrays show a visible broadband with three peaks, which are located at about 425, 465, and 525 nm that are attributed to self-trapped excitons, F, and $F^{+}$ centers, respectively. A model is also presented to explain the PL intensity drop-down of the TN arrays embedded in AAMs: the blue PL band of AAMs arises from the $F^{+}$ centers on the pore walls, and the TNs first form in the center area of the pores and then extend to the pore walls.