Highly nitrogen-doped carbon microtubes via confined carbonization of g-C₃N₄ for enhanced potassium-storage...

Defect-rich nanostructured anode materials such as g-C₃N₄-derived carbons offer high storage capacity and long cycling stability because of their abundant active K-ion storage sites, fast diffusion dynamics, and small volume changes during cycling. Herein, we report defect-rich, ultrahigh N-doped carbon microtubes (DN-CMTs), prepared by carbonizing the g-C₃N₄ hollow microtubes with a polydopamine (PDA) capsule. The optimized sample, carbonized at 700 °C with a g-C₃N₄/dopamine (DA) mass ratio of 2 : 1 (DN-CMT-2/1-700), presents a large BET surface area of 238.5 m² g^-1 and a high nitrogen doping of ∼17.71 at%. As a result, it delivers a stable reversible capacity of 618.9 mAh g^-1 at 0.05 A g^-1 and retains 313.9 mAh g^-1 after 1000 cycles at 1 A g^-1, as well as the highest first-cycle coulombic efficiency in the series. More importantly, a series of CV, GITT, and ex situ Raman measurements show pseudocapacitive-dominated K-ion storage with fast K-ion diffusion, as abundant defects and ultrahigh N-doping provide numerous active sites for potassium-ion storage. This study offers a novel perspective and methodology for developing nanostructured carbon anode materials with abundant defects for high-capacity and long-life potassium storage.