Coupling ultrafine TiO2 within pyridinic-N enriched porous carbon towards high-rate and long-life sodium ion capacitors.

ABSTRACT

Coupling TiO2 within N-doped porous carbon (NPC) is essential for enhancing its Na+ storage performance. However, the role of different N configurations in NPC in improving the electrochemical performance of TiO2 is currently unknown. In this study, melamine is deliberately incorporated as a pore-forming agent in the self-assembly process of metal organic framework precursors (NH2-MIL-125(Ti)). This intentional inclusion of melamine leads to the one-pot and in-situ formation of highly active edge-N, which is vital for the development of TiO2/NPC with exceptional reactivity. Electrochemical performance characterization and density functional theory (DFT) calculation indicate that the interaction between TiO2 and pyridinic-N enriched NPC can effectively narrow the bandgap of TiO2/NPC, thereby significantly improving electron/ion transfer. Additionally, the abundant mesoporous channels, high N content and oxygen vacancies also contribute to the fast reaction kinetics of TiO2/NPC. As a result, the optimized TiO2/NPC-M, with high proportion of pyridinic-N (44.1 %) and abundant mesoporous channels (97.8 %), delivers high specific capacity of 282.1 mA h-1 at 0.05 A g-1, superior rate capability of 177.3 mA h-1 at 10 A g-1, and prominent capacity retention of 89.3 % over 5000 cycles even under ultrahigh 10 A g-1. Furthermore, the TiO2/NPC-M//AC sodium ion capacitors (SIC) device achieves a high energy density of 136.7 Wh kg-1 at 200 W kg-1. This research not only offers fresh perspectives on the production of high-performance TiO2-based anodes, but also paves the way for customizing other active materials for energy storage and beyond.