Cyclic Voltammetry As an Activation Method of TiO2 Nanotube Arrays for Improvement of Photoelectrochemical Water Splitting Performance

A facile and eco-friendly method for activating anodic TiO2 nanotubes (TNTs) by cyclic voltammetry (CV) is proposed, and photoelectrochemical properties of CV-activated TNTs are compared with those of non-activated TNTs and of TNTs activated by hydrogen-thermal reduction. EPR and luminescence studies show that the pristine samples demonstrate rather large content of paramagnetic and luminescing defects, while hydrogenation and CV-activation lead to the different type of rearrangement of defects. TNTs activated by CV-Na2SO4 demonstrate significantly improved photocurrent density (2.25 mA cm(-2)) in comparison with that of the hydrogen treated and pristine ones (0.93 mA cm(-2) and 0.31 mA cm(-2)) under NUV-irradiation at 0.2 V (RHE). Enhanced photoactivity of Na2SO4-activated TNTs correlates with higher luminescence quantum yield, lowest paramagnetic defects content and larger decay time of the luminescence. Thus, a decrease in the content of defects is an important factor that reduces the non-radiative recombination of charge carriers. The activation-induced redistribution of surface and bulk defects in nanotubes explains the increased photoelectrochemical activity of TiO2-based anodes. Cyclic voltammetry has been proved to be a reliable method to increase the efficiency of TNTs in PEC water splitting.