Effect of NH4F concentration and controlled-charge consumption on the photocatalytic hydrogen generation of TiO2 nanotube arrays

Abstract Self-organized TiO 2 nanotube arrays (TiO 2 Nts) for hydrogen evolution were successfully fabricated by electrochemical anodization in ethylene glycol-based electrolytes with various NH 4 F concentrations. Hydrogen production by photocatalytic water splitting was performed in a two-compartment photoelectrochemical (PEC) cell without any applied voltage. The effect of NH 4 F concentration on the morphological structure, PEC performance and hydrogen evolution of TiO 2 samples were systematically investigated. TiO 2 anodized with 0.50 wt% of NH 4 F concentration for 60 min exhibited highest hydrogen evolution of 2.53 mL h −1 cm −2 and maximum photoconversion efficiency of 4.39%. Based on the above results and the different current-time curves during anodization processes, another series of TiO 2 nanotube arrays samples with the equal charge consumption (designated as TiO 2 Nts-EC) were synthesized by controlling the anodization time in electrolytes containing different NH 4 F concentrations. Compared with TiO 2 Nts prepared at the same NH 4 F concentration for 60 min, hydrogen production and PEC properties of TiO 2 Nts-EC samples have been obviously enhanced, especially for the sample prepared at 1.25 wt% NH 4 F concentrations. Moreover, despite the difference of NH 4 F concentration in electrolyte, the TiO 2 Nts-EC samples exhibit comparable PEC performances. These results indicated that the anodization charge-density play a crucial role in the hydrogen generation of TiO 2 Nts. The results benefit the enhancement of the hydrogen production of TiO 2 Nts.