Current density transient response to variations in synthesis parameters during anodic growth of TiO2 nanotubes

Abstract

The field of TiO2 photo-electrode synthesis is fast-growing, due to the competitive performance of TiO2 in light-harvesting applications such as photo-electrochemical water splitting. Real-time monitoring of TiO2 nanotube array (NTA) synthesis is critical for reproducibility in a production chain of identical photo-electrodes. By analysing the transient stage of a current density signal, this work demonstrates the expected responses to changes in anodic voltage and electrolyte content. Seven titanium foil substrates were anodized in an anhydrous polar organic electrolyte mixed with NH4F as the etching agent. The current density increased with voltage and the first steady state of the transient, that indicates the onset of chemical dissolution, was reached earlier when using higher quantities of NH4F. Changes in film pore size and morphology of un-etched regions of the NTAs correlated with the growth parameters. A flowchart that can be used to formulate set points, in order to detect deviations from desired anodization parameters, and hence declare a sample rejected or otherwise, is proposed for applications requiring a closed-loop control system to accurately monitor the anodic growth of TiO2 in ethylene glycol + NH4F electrolytes.