Electrochemical study to explore the capacitance properties of the TiO₂/solution interface

In this study, we employed classic electrochemical techniques including cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) to perform electrochemical characterization on atomic-level single-crystal TiO₂ electrodes and extract capacitive and resistive properties of single-crystal TiO₂ electrode/solution interface in KCl and KCl/K₃PO₄ at various pH levels. The lattice structure and crystal appearance were characterized using X-ray diffractometry (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy to facilitate the in-depth exploration of heterogeneous reaction dynamics and theory. Furthermore, this study aimed to verify and improve the theory and application of capacitance at the single-crystal TiO₂ electrode/solution interface. The electrochemical measurements indicate that, in the same pH, the presence of PO₄³⁻ significantly increases the total capacitance (C_T), outer capacitance (C_O), electrical double-layer capacitance (C_dl), and diffusion layer capacitance (C_diff) at single-crystal TiO₂ electrode/solution interface. This enhancement is attributed to the direct interaction between PO₄³⁻ and the single-crystal TiO₂ electrode surface, leading to the specific adsorption of PO₄³⁻ on the electrode surface, revealing higher current and stronger electrochemical activity in the interaction between TiO₂ and PO₄³⁻. Additionally, our XPS results indicate the adsorption of PO₄³⁻ on the single-crystal TiO₂ electrode surface. The interaction of PO₄³⁻ with the TiO₂ surface demonstrates increased hydrophilicity and enhanced adsorption capacity through mechanisms such as ligand exchange or cation bridging, thereby augmenting the C_dl at the single-crystal TiO₂ electrode/solution interface.