American Chemical Society
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Flat-Band Potentials of Molecularly Thin Metal Oxide Nanosheets

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journal contribution
posted on 2016-04-22, 00:00 authored by Pengtao Xu, Tyler J. Milstein, Thomas E. Mallouk
Exfoliated nanosheets derived from Dion–Jacobson phase layer perovskites (TBAxH1–xA2B3O10, 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 (VFB) 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 VFB. The measured values of VFB 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.