Improving the contact properties of CdS-decorated TiO2 nanotube arrays using an electrochemical/thermal/chemical approach

Abstract

Decoration of TiO 2 nanotube films (TiO 2 nanotube arrays (TNAs)) with CdS nanoparticles has been pursued for a broad range of applications that goes from solar cells to biological sensors. In most synthesis methods, the scale-up of devices has been challenging due to the poor contact at the chalcogenide/oxide interface. In this work, we validate the electrochemical/thermal/chemical route as a superior strategy to sensitize TNAs with CdS nanoparticles when compared with conventional methods. The process consisted of (i) electrodeposition of cadmium on TNAs to ensure strong bonding between TiO 2 and Cd precursor particles, (ii) air annealing of Cd-decorated TNAs to thermally oxidize cadmium to cadmium oxide, and (iii) total sulfurization of cadmium oxide to obtain CdS in an hexagonal phase matching that of TNAs. X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) analyses indicated the complete transformation of cadmium precursor particles into CdS and a good surface coverage of the internal/ external walls of TNAs. When compared to samples prepared by successive ionic layer adsorption and reaction (SILAR), electrochemical impedance spectroscopy data revealed the improvement of the electrical properties of the TNA matrix due to the sulfurization process and a lower contact resistance at the CdS/TNA interface. These improvements explain the superior photoelectrochemical response of CdS/TNA photoelectrodes obtained by the electrochemical/thermal/ chemical route.

A Facile Route to Synthesize a TiNT-RuO2 Electrocatalyst for Electro-Generated Active Chlorine Production

“…4c. This eec has been previously reported for the analysis of electrodes based on TiO 2 nanostructures, 33,[36][37][38] where R s is the solution resistance, R f is the charge transport resistance in the internal film (TiNTs or TiNT-RuO 2 ), and R ct is the charge transfer resistance between the electrode surface and the electrolyte. Q sc and Q dl are constant phase elements (CPE) associated with the space charge capacitance and the double layer capacitance, respectively.…”

“…Thus, the peaks associated with the anatase phase diminished when the GIXRD geometry was used owing to the presence of large agglomerates of the deposited phases (i.e., CdS) on top of TiO 2 nanotubes. 33 Likewise, the crystal structure of TiO 2 (pdf 00-021-1272) in the TiNT-RuO 2 was predominantly the anatase phase as previously discussed, indicating that RuO 2 loading does not change the crystal structure of the TiNTs. 34 Thus, three small peaks at 2θ = 28.0°, 35°, and 54°were measured, corresponding to (110), (011), and (211) diffraction planes of RuO 2 , respectively (tetragonal structure) (pdf 00-040-1290).…”

Pulse-Plating Electrodeposition of Metallic Bi in an Organic-Free Aqueous Electrolyte and Its Conversion into BiVO4 To Improve Photoelectrochemical Activity toward Pollutant Degradation under Visible Light

“…This indicates that there is a higher charge transfer resistance when a potential is not applied in the materials, which considerably decreases upon the application of 0.9 V versus Ag/AgCl for the substrate and PE. In order to obtain the corresponding value of this resistance and the one associated with the FTO and catalyst, the experimental EIS data were fitted by using ZView software, employing the equivalent electric circuit displayed in Figure c, where R s , R f , and R ct are resistances related to the electrolyte, film, and charge transfer, respectively; whereas Q sc and Q dl are constant phase elements associated with the space charge capacitance and double layer capacitance, respectively. − The fitted curves are shown in Figure c, and the values obtained from the fitting are displayed in Table . Although R f is higher for the FTO-BiVO 4 electrode compared with the FTO at 0.9 V versus Ag/AgCl in the dark, R f considerably decreases for the PE at the same potential but under illumination, suggesting that the conductivity of the electrode is improved when the catalyst is photoactivated.…”

The Effect of the Heating Rate on Anatase Crystal Orientation and Its Impact on the Photoelectrocatalytic Performance of TiO2Nanotube Arrays

“…37 This phenomenon displaced the OCP of the semiconductor toward more negative values, as an indirect measure of the energy level of electrons in the semiconductor under illumination, depending on the type of illumination and the test electrolyte. 37 Then, the 10-min interruption of illumination relaxed the semiconductor and thus electrons could recombine or be transferred toward the solution, substrate conductor or trap states, 38 which would define their approximation to the stabilization potential in the dark. The OCP measurements in Figure 6 clearly show a greater displacement of the potential under illumination for films with a lower degree of crystal orientation, that is, for films treated at 10 and ∞ • C min −1 .…”