Ardra Ajith, A. Surya Mary, Priya S. Nair, K. Arjun, Sadasivan Shaji, and Rachel Reena Philip | High-performance self-doped TiO2 nanotube electrodes for supercapacitor applications | Journal of Energy Storage (2025)

https://doi.org/10.1016/j.est.2025.117649

Nanoarchitectured TiO₂ is a benchmark material for electrochemical energy storage. Modifications like doping, metal decoration, and hybridization have helped in enhancing its efficiency. The present study introduces self-doped TiO₂ nanotube electrodes (TNTAs), fabricated through a cost-effective electrochemical anodization followed by reduction in a water bath. These TNTA electrodes constituted of a mixture of brookite and TiO₂(B), achieve record-high performance among TiO₂ electrodes when specific capacitance, energy density (ED), and power density (PD) are considered collectively. The electrode, self-doped for 5 s in 0.5 M Na₂SO₄ manifests an areal/gravimetric specific capacitance of 665.85 mFcm⁻² /1459.26 Fg⁻¹ at a scan rate of 10 mVs⁻¹ and a maximum ED of 121.76 Whkg⁻¹ and a PD of 4.57 kWkg⁻¹. The electrode shows good cycling stability, retaining 103 % of their capacitance after 500 cycles, 98 % after 800 cycles, and 80 % after 1600 cycles. Extending the self-doping duration to 10s enhances the ED and PD to 197.86 Whkg⁻¹ at 2.9 kWkg⁻¹ whereas increasing the molarity of the doping solution to 1.0 M increases them to 240.09 Whkg⁻¹ at 4.9 kWkg⁻¹ respectively. The exceptional performance of these specially fabricated electrodes arises from the synergy of intercalative and surface pseudocapacitive charge storage, rapid ion diffusion, low interfacial resistance, and a high concentration of oxygen vacancies and Ti³⁺ species. A symmetric supercapacitor with the TNTA has achieved a remarkable areal/gravimetric specific capacitance of 417.97 mFcm⁻² /916.27 Fg⁻¹ at 1.3 mA cm⁻² in a 2 V potential window and a high ED of 509 Whkg⁻¹ at a PD of 2.9 kWkg⁻¹.