Flat-Band Potentials of Molecularly Thin Metal Oxide Nanosheets

• Published in: ACS applied materials & interfaces Vol. 8; no. 18; pp. 11539 - 11547
• Main Authors: Xu, Pengtao, Milstein, Tyler J, Mallouk, Thomas E
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 11.05.2016
• Subjects: flat-band potential; perovskite; water splitting; semiconductor; layered metal oxide; nanosheets
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/acsami.6b02901

Exfoliated nanosheets derived from Dion–Jacobson phase layer perovskites (TBA x H1–x A2B3O10, A = Sr, Ca, B = Nb, Ta) were grown layer-by-layer on fluorine-doped tin oxide and gold electrode surfaces. Electrochemical impedance spectra (EIS) of the five-layer nanosheet films in contact with aqueous electrolyte solutions were analyzed by the Mott–Schottky method to obtain flat-band potentials (V FB) of the oxide semiconductors as a function of pH. Despite capacitive contributions from the electrode–solution interface, reliable values could be obtained from capacitance measurements over a limited potential range near V FB. The measured values of V FB shifted −59 mV/pH over the pH range of 4–8 and were in close agreement with the empirical correlation between conduction band-edge potentials and optical band gaps proposed by Matsumoto ( J. Solid State Chem. 1996, 126 (2), 227–234). Density functional theory calculations showed that A-site substitution influenced band energies by modulating the strength of A–O bonding, and that subsitution of Ta for Nb on B-sites resulted in a negative shift of the conduction band-edge potential.