Titanium Dioxide Nanotubes as Model Systems for Electrosorption Studies.

Xian Li,Scott Pedu,Samantha Pustulka,Christiaan Richter,Patricia Taboada-Serrano,Thomas Close,Yuan Xue

doi:10.3390/nano8060404

Xian Li, Scott Pedu + Show 5 more

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https://doi.org/10.3390/nano8060404

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Abstract

Highly ordered titanium dioxide nanotubes (TiO2 NTs) were fabricated through anodization and tested for their applicability as model electrodes in electrosorption studies. The crystalline structure of the TiO2 NTs was changed without modifying the nanostructure of the surface. Electrosorption capacity, charging rate, and electrochemical active surface area of TiO2 NTs with two different crystalline structures, anatase and amorphous, were investigated via chronoamperometry, cyclic voltammetry, and electrochemical impedance spectroscopy. The highest electrosorption capacities and charging rates were obtained for the anatase TiO2 NTs, largely because anatase TiO2 has a reported higher electrical conductivity and a crystalline structure that can potentially accommodate small ions within. Both electrosorption capacity and charging rate for the ions studied in this work follow the order of Cs+ > Na+ > Li+, regardless of the crystalline structure of the TiO2 NTs. This order reflects the increasing size of the hydrated ion radii of these monovalent ions. Additionally, larger effective electrochemical active surface areas are required for larger ions and lower conductivities. These findings point towards the fact that smaller hydrated-ions experience less steric hindrance and a larger comparative electrostatic force, enabling them to be more effectively electrosorbed.

Highlights

The properties of charged interfaces and the electrosorption of ions on charged surfaces have a remarkable influence on the kinetics of various electrochemical processes, including those having technological importance such as water desalination and energy storage [1,2,3,4]
Electrosorption is a process where ions of opposite charge are immobilized within a region known as the electrical double layer (EDL), which forms in the vicinity of the electrolyte-electrode interface when a low direct current potential is applied [5,6]
The crystalline structure of the TiO2-NT electrode was a determinant factor of electrosorption capacity and charging rate for all ions studied in this work

Summary

Introduction

The properties of charged interfaces and the electrosorption of ions on charged surfaces have a remarkable influence on the kinetics of various electrochemical processes, including those having technological importance such as water desalination and energy storage [1,2,3,4]. Electrochemical capacitors (ECs) use the electric field in the EDLs established at the electrode-electrolyte interface to store electrical energy. The properties of the EDL crucially determine the ions that can be removed from aqueous solutions in CDI and the energy that can be stored in ECs. the characteristics of the EDL directly influence the outcome of electrochemical reactions by adding another “resistance” or providing more “housing” for electrostatic charge storage to the processes

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