Black Ti-P-O nanotubes with bulk-phase doping and surface oxygen-defective engineering as efficient bifunctional electrodes for photoelectrochemical water splitting and supercapacitors

Introduced of defects and bulk-phase doping is an effective method to enhance charge storage and transport, thereby enhancing performance of the titanium-based electrodes for photoelectrochemical (PEC) water splitting and supercapacitors (SCs). This research focused on improving the performance of TiO2 (TO) nanotube electrodes through the incorporation of P5+ doping, Ti3+ self-doping and the creation of oxygen vacancies. The black Ti-P-O (TPO) electrodes were successfully fabricated using a one-step phosphorization process, resulting in substantial enhancements in light absorption, electrical conductivity, and charge transfer efficiency. Electrochemical tests demonstrated that the photocurrent density of the TPO electrode reached 0.95 mA cm-2 at 1.23 V vs. RHE, showing a 1.2-fold increase compared to the pure TO electrode. Furthermore, I-t measurements under visible light revealed a 2.25-fold improvement in photocurrent density relative to the pristine TO. The TPO electrode also exhibited over four times greater capacitance, indicating superior performance in electrochemical energy storage with excellent rate capability. This work offers a robust approach for improving the light absorption, charge transfer, and energy storage characteristics of TO nanotube electrodes, advancing their potential applications in PEC water splitting and electrochemical energy storage technologies.