The work aims to fabricate a well-defined core-shell nanostructure consisting of TiO2 nanotube arrays filled with Cu2O nanorods and to comprehensively investigate the multiple factors that affect the filling process. Through the application of a carefully controlled cathodic polarization treatment combined with an optimized pulse electrodeposition technique, Cu2O was successfully deposited into the interior of the TiO2 nanotube arrays, ultimately achieving a 100% filling rate throughout the entire nanotube length. A systematic analysis was conducted to elucidate the effects of several critical variables, including the choice of electrochemical deposition method, the specific pulse potential deposition parameters, and the composition of the electroplating solution, on the efficiency and completeness of Cu2O incorporation within the TiO2 nanotube channels.
By implementing a precise cathodic polarization step prior to deposition, the intrinsic electrical conductivity of the internal barrier layer of the TiO2 nanotube arrays was selectively enhanced. This polarization treatment created a distinct conductivity gradient between the inner barrier layer and the outer nanotube wall, which in turn promoted preferential nucleation of Cu2O at the closed bottom of the nanotube arrays. Following nucleation, Cu2O progressively deposited along the axial direction of the TiO2 nanotube arrays, propagating from the bottom toward the open top and ultimately forming a continuous core-shell architecture with a complete 100% filling rate. It was observed that the electrochemical deposition method, the fine-tuned pulse deposition parameters, and the electrolyte formulation collectively exerted significant effects on the final filling morphology of Cu2O within the TiO2 nanotube arrays. Among these, the pulse potential deposition method proved to be the most effective, as the intermittent potential application generated a higher instantaneous deposition current density, accelerated the nucleation kinetics of Cu2O, and decreased the critical nucleus radius, thereby ensuring dense and uniform filling.
Furthermore, as the cathodic pulse potential shifted toward more negative values, the number of deposition pulse cycles increased, and the ratio of cathodic to anodic pulse widths was adjusted upward, both the nucleation rate and the overall deposition time of Cu2O within the TiO2 nanotube arrays were substantially enhanced. These variations induced a clear microstructural evolution of the filled arrays, which underwent distinct transitional stages, including an initial no-filling state, partial filling, complete filling, and eventually overfilling when deposition exceeded the nanotube capacity. In addition, the characteristics of the electroplating solution played a vital role: increasing the main salt concentration, lowering the pH, and elevating the electrolyte temperature all promoted a higher nucleation rate of Cu2O, which drove the microstructure through the same sequence of partial to complete and overfilling states.
The overall results demonstrate that the successful filling of Cu2O nanorods into TiO2 nanotube arrays is primarily governed by the one-dimensional electrical conductive properties of the TiO2 nanotube arrays, while the deposition process parameters serve as secondary critical affecting factors. For the TiO2 nanotube arrays with different aspect ratios, the combined effects of cathodic polarization, the selected electrochemical deposition approach, the optimized pulse deposition parameters, and the electrolyte composition must be carefully balanced to achieve a high and uniform filling rate of Cu2O within the TiO2 nanotube arrays. These findings provide valuable insights into the rational design of core-shell nanostructures for functional applications in energy conversion, photocatalysis, and sensing technologies.
Key words
TiO2 nanotube arrays /
Cu2O /
filling rate /
core-sheath structure /
electrochemical deposition /
affecting factors
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Funding
National Natural Science Foundation of China (42276216, 52301087); Fujian Province University-Industry Collaborative Innovation Project (2023H6028); Education and Scientific Research Project for Middle-aged and Young Teachers of Fujian Province, China (Science and Technology Category) (JAT231049); Natural Science Foundation of Fujian Province, China (2023J01783)
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