Characterization of Interfacial Charge-Transfer Photoexcitation of Polychromium-Oxo-Electrodeposited TiO2 as an Earth-Abundant Photoanode for Water Oxidation Driven by Visible Light

Polychromium‐oxo‐deposited TiO2 (CrIIIxOy/TiO2) electrodes were fabricated by a simple electrochemical technique by using different TiO2 basal electrodes (anatase, rutile, and mixed polymorphic phases P25) as earth‐abundant photoanodes for visible‐light‐driven water oxidation. The high‐resolution transmission electron microscopy (HR‐TEM) observation illustrated that an CrIIIxOy layer with approximately 2–3 nm thickness was formed on the surface of the crystalline TiO2 particles. Upon visible‐light irradiation of the electrodes, the photoanodic current based on water oxidation was generated at the CrIIIxOy/TiO2 electrodes. However, the wavelength (below 620 nm) for photocurrent generation at CrIIIxOy/TiO2‐rutile was longer than that (below 560 nm) at CrIIIxOy/TiO2‐P25 by 60 nm, which is in agreement with the difference (0.2 eV) in the conduction band (CB) edge energy between rutile and anatase TiO2. This gives a quantitative account for the photocurrent generation based on interfacial charge transfer (IFCT) from Cr 3d of the deposited CrIIIxOy layer to the TiO2 CB. The photocurrent generated for CrIIIxOy/TiO2‐rutile was higher than that for CrIIIxOy/TiO2‐anatase, which is ascribed to 1) more effective CrIIIxOy deposition on the rutile particles, 2) a larger electrolyte/CrIIIxOy interface for water oxidation as a result of smaller rutile particles (ca. 30–40 nm) compared with larger P25 particles (ca. 40–80 nm), and 3) more effective use of visible light owing to the low energy IFCT transition of rutile. Earth‐abundant photoanode for water splitting: Polychromium‐oxo‐deposited TiO2 (CrIIIxOy/TiO2) electrodes were fabricated by a simple electrochemical technique by using different TiO2 basal electrodes (anatase, rutile, and mixed polymorphic phases P25) as earth‐abundant photoanodes. Visible‐light‐driven water oxidation was achieved based on interfacial charge transfer (IFCT) from Cr 3d of the CrIIIxOy layer to the TiO2 conduction band.