Black Ti–Nb–P–O Nanotubes with Bulk-Phase Doping and Surface Oxygen Defective Engineering for High-Performance Symmetric Supercapacitors

Abstract

Structural modulation with defective engineering designing is a potential approach for the facilitating electrical conductivity and electrochemical activity of Ti-based oxide. Herein, we develop a blackened codoping system (denoted as black Ti–Nb–P–O) with bulk-phase Nb/P codoping and surface oxygen vacancy (Vo) self-doping through in situ anodization of Ti–Nb alloy with one-step phosphorization process. Electrochemical measurements combined with microstructure analysis and density functional theory (DFT) calculations further revealed that the blackened codoping indeed significantly promoted the carrier density, electrical conductivity, diffusion kinetics, and hydrophilicity of electrode materials. The black Ti–Nb–P–O nanotube arrays exhibited a remarkable areal capacitance of 36.60 mF cm–2 at 0.1 mA cm–2, which was approximately 91.5 times higher than that of pristine TiO2 (0.40 mF cm–2). Besides, the electrode realized superior rate capability (80.75% capacitance retention with the scan rate increased from 10 to 100 mV s–1) and impressive cycling stability (84.00% capacitance retention after 5000 cycles). Furthermore, the assembled symmetric supercapacitors owned a wide potential window (2 V) and performed exceptional energy density (4.32 mWh cm–3) at high power density (186.92 mW cm–3). This work involving bulk-phase Nb/P codoping with surface oxygen defective engineering may help provide an effective strategy to improve areal capacitance of Ti-based nanostructures for enhanced electrochemical energy storage.