Highly Nitrogen-Doped Carbon Microtubes via Confined Carbonization of g-C3N4 for Enhanced Potassium-Storage Performance

Abstract

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.