Time-Engineered Hydrothermal Nb2O5 Nanostructures for High-Performance Asymmetric Supercapacitors

Abstract

Precise control over nanostructure evolution is critical for optimizing the electrochemical performance of pseudocapacitive materials. In this work, Nb2O5 nanostructures were synthesized via a time-engineered hydrothermal route by systematically varying the reaction duration (6, 12, and 18 h) to elucidate its influence on structural development, charge storage kinetics, and supercapacitor performance. Structural and surface analyses confirm the formation of phase-pure monoclinic Nb2O5 with a stable Nb5+ oxidation state. Morphological investigations reveal that a 12 h reaction time produces hierarchically organized Nb2O5 architectures composed of nanograin-assembled spherical aggregates with interconnected porosity, providing optimized ion diffusion pathways and enhanced electroactive surface exposure. Electrochemical evaluation demonstrates that the NbO-12 electrode delivers superior pseudocapacitive behavior dominated by diffusion-controlled Nb5+/Nb4+ redox reactions, exhibiting high areal capacitance (5.504 F cm(-2) at 8 mA cm(-2)), fast ion diffusion kinetics, low internal resistance, and excellent cycling stability with 85.73% capacitance retention over 12,000 cycles. Furthermore, an asymmetric pouch-type supercapacitor assembled using NbO-12 as the positive electrode and activated carbon as the negative electrode operates stably over a wide voltage window of 1.5 V, delivering an energy density of 0.101 mWh cm(-2) with outstanding durability. This study establishes hydrothermal reaction-time engineering as an effective strategy for tailoring Nb2O5 nanostructures and provides valuable insights for the rational design of high-performance pseudocapacitive electrodes for advanced energy storage systems.