Electrochemical and photoelectrochemical study on exfoliated Nb 3O 8 nanosheet

Abstract

Transition metal oxide nanosheet of Nb 3O 8 was synthesized by delaminating a layered host compound of KNb 3O 8. Ultrathin two-dimensional morphology, about 1 nm thickness vs. submicrometer lateral size, was revealed by atomic force microscopy. The colloidal nanosheets were assembled layer-by-layer with polycation onto an indium-tin-oxide (ITO)-coated glass electrode via sequential adsorption technique. UV–vis absorption spectra in the assembly process showed the linear enhancement of absorbance at 270 nm per deposition cycle, indicating the successful formation of multilayer composite films, which can be converted into polymer free films upon exposure to UV light. The cyclic voltammogram of resulting Nb 3O 8 nanosheet film electrodes exhibited reduction/oxidation (Nb 4+/Nb 5+) peaks at −1.2 V (vs. Ag/Ag +) attributable to insertion and deintercalation of Li + ions into and from the nanosheet galleries. The reaction (reduction/oxidation) ratio of the electroactive Nb atom in Nb 3O 8 nanosheet was calculated to be 6.3% by integrating a charge transfer in a sweep range of +1.0 to −1.9 V. The Nb 3O 8 nanosheet electrode generated anodic photocurrent in response to UV illumination. Analysis on the photocurrent action spectrum indicated that Nb 3O 8 nanosheet is an indirect transition-type semiconductor with bandgap energy of 3.58 eV. The flat-band potential was estimated to be −1.32 V vs. Ag/Ag + from the applied potential dependence.