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

Polychromium-oxo-deposited TiO (Cr O /TiO ) electrodes were fabricated by a simple electrochemical technique by using different TiO 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 Cr O layer with approximately 2-3 nm thickness was formed on the surface of the crystalline TiO particles. Upon visible-light irradiation of the electrodes, the photoanodic current based on water oxidation was generated at the Cr O /TiO electrodes. However, the wavelength (below 620 nm) for photocurrent generation at Cr O /TiO -rutile was longer than that (below 560 nm) at Cr O /TiO -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 TiO . This gives a quantitative account for the photocurrent generation based on interfacial charge transfer (IFCT) from Cr 3d of the deposited Cr O layer to the TiO CB. The photocurrent generated for Cr O /TiO -rutile was higher than that for Cr O /TiO -anatase, which is ascribed to 1) more effective Cr O deposition on the rutile particles, 2) a larger electrolyte/Cr O 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.