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

Abstract

Self-organized TiO2 nanotube arrays (TiO2 Nts) for hydrogen evolution were successfully fabricated by electrochemical anodization in ethylene glycol-based electrolytes with various NH4F concentrations. Hydrogen production by photocatalytic water splitting was performed in a two-compartment photoelectrochemical (PEC) cell without any applied voltage. The effect of NH4F concentration on the morphological structure, PEC performance and hydrogen evolution of TiO2 samples were systematically investigated. TiO2 anodized with 0.50wt% of NH4F concentration for 60min exhibited highest hydrogen evolution of 2.53mLh−1cm−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 TiO2 nanotube arrays samples with the equal charge consumption (designated as TiO2 Nts-EC) were synthesized by controlling the anodization time in electrolytes containing different NH4F concentrations. Compared with TiO2 Nts prepared at the same NH4F concentration for 60min, hydrogen production and PEC properties of TiO2 Nts-EC samples have been obviously enhanced, especially for the sample prepared at 1.25wt% NH4F concentrations. Moreover, despite the difference of NH4F concentration in electrolyte, the TiO2 Nts-EC samples exhibit comparable PEC performances. These results indicated that the anodization charge-density play a crucial role in the hydrogen generation of TiO2 Nts. The results benefit the enhancement of the hydrogen production of TiO2 Nts.