Nb Ions Induced Morphology and Enhanced Photoelectrochemical Functionalities from 3D Zn1-xNbxO Nanostructures

Abstract

Doping of niobium rare earth metal ions in ZnO based nanostructures are achieved by a simple chemical route for evaluating their photoelectrochemical conversion capabilities. The influence of dopant ions on the crystalline behavior and phase characteristics were studied in-depth using Raman spectroscopy and X-ray diffraction analysis. The crystalline size of the obtained pristine ZnO is 24 nm and the 5% Nb doped ZnO is 20 nm. The geometrical appearance of doped structures was inferred using high-resolution electron microscopic analysis. UV-absorbance spectra were comparatively studied and the corresponding band gap values of 3.10-3.02 eV were extracted using Tauc's plot. The evolution of multiple defects in the processed nanostructures was additionally investigated from the luminescence spectra. Mott-Schottky plots that represents the variation in capacitance as a function of applied voltage was used to evaluate the carrier density across respective nanostructures. Using electrochemical impedance spectroscopic results Nyquist plots were plotted for doped and undoped nanostructures to evaluate the nature and mechanism behind the charge transfer characteristics in the respective samples. The measured charge carrier concentration of pristine ZnO (0.3 x 10(20) cm(-3)) was several folds increased via 5% doping of Nb ions (3.7 x 10(20) cm(-3)). The processed nanostructures were then spin cast on transparent conducting substrates as photoanodes for photoelectrochemical (PEC) studies. NbxZn1-xO nanostructures made photoanodes exhibited a high photocurrent density of up to 0.651 mA cm(2) and was also very stable. The strong photocurrent readings showed that the type of metal ions had a big effect on how well the photoanode worked.