Enhanced photoelectrochemical water splitting via hydrogenated TiO2 nanotubes modified with Cu/CuO species

Abstract

This study explores the collective influence of hydrogenation thermal treatment and the decoration of Cu/CuO onto TiO2 nanotubes (TiO2-NTs) concerning photoelectrochemical water splitting. To introduce point defects such as oxygen vacancies and Ti3+, electrochemically anodized Ti foils underwent hydrogenation in a 90 % Ar-10 % H2 atmosphere at 500 °C. Subsequently, Cu/CuO species were deposited on the hydrogenated TiO2-NTs through chemical decoration for varying stirring durations of 15, 30, 45, and 60 min. EPR analysis of the hydrogenated sample unveiled resonances at g-values distinct from the typical 1.997 signal associated with oxygen vacancies in TiO2-NTs, signifying the presence of Ti3+ and VO defects. Analysis via XPS identified Cu and CuO as the primary compositions of the decorated species on the hydrogenated TiO2-NTs. Additionally, SEM/EDS results showcased that longer stirring times, specifically 60 min., caused localized agglomeration of Cu/CuO species and TiO2-NTs breakage. The Cu/CuO-decorated hydrogenated TiO2-NTs exhibited enhanced absorption of visible light, leading to a band gap reduction to 2.09 eV after 45 min of Cu/CuO decoration. Notably, this particular sample demonstrated the highest photocurrent of 3.6 mA/cm2 and a photo-conversion efficiency of 2.48 % at 1.23 V vs. RHE. Overall, the presence of Cu/CuO species prolonged the lifetime of charge carriers, as evidenced by Nyquist plots and Mott-Schottky analysis. A schematic model is suggested based on the modified band gap of hydrogenated TiO2-NTs subsequent to Cu/CuO loading.