Interplay between Collective and Localized Effects of Point Defects on Photoelectrochemical Performance of TiO2 Photoanodes for Oxygen Evolution

• Published in: Advanced materials interfaces 2023-12, Vol.10 (36), p.n/a
• Main Authors: Yang, Mengya, Cui, Junyi, Daboczi, Matyas, Law, Robert V., Luke, Joel, Kim, Ji‐Seon, Hankin, Anna, Eslava, Salvador
• Format: Article
• Language: English
• Subjects: Anatase; charge separation efficiency; Density; Electrolytic cells; Electromagnetic absorption; Electron paramagnetic resonance; Hydroxyl groups; light absorption; Oxidation; Oxygen; Photoanodes; Photoelectric effect; photoelectrochemical water splitting; Photoelectrons; Point defects; Titanium; Titanium dioxide; titanium dioxide photoanodes; Valence band; Water splitting
• ISSN: 2196-7350; 2196-7350
• DOI: 10.1002/admi.202300595

Among the various photoanode materials investigated for photoelectrochemical water splitting cells, TiO2 stands out due to its abundance, stability, and favorable valence band edge for water oxidation. In this study, the importance of introducing and combining oxygen and titanium vacancy point defects in anatase TiO2 photoanodes to improve their performance is unveiled, achieving a photocurrent density of 0.73 (±0.015) mA cm−2 at +1.23 VRHE under 100 mW cm−2 of simulated sunlight or 26.4 mA cm−2 at +1.23 VRHE under 100 mW cm−2 of 365 nm light. The characterization by X‐ray photoelectron spectroscopy, surface photovoltage, and electron paramagnetic resonance demonstrates that these oxygen and titanium vacancies can have both collective and localized positive effects on the material, leading to a narrowing of the bandgap, an increase in donor density, and an increase in hydroxyl groups on the surface of TiO2. These result in enhanced light absorption, conductivity, and photovoltage, as well as a more negative flat‐band potential and increase in hole flux to the semiconductor–electrolyte interface. These findings provide valuable insights into the role of point defects in modulating the properties of TiO2 and have important implications for the development of high‐performance TiO2‐based devices. The study presents a successful modification of anatase TiO2 photoanodes with point defects such as oxygen and titanium vacancies to have both collective and localized effects that boost their photoelectrochemical performance. The improved performance is due to enhanced light absorption, conductivity, and photovoltage, as well as a more negative flat‐band potential and increase in hole flux to the semiconductor–electrolyte interface.