Electrochemical study to explore the capacitance properties of the TiO 2 /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 TiO 2 electrodes and extract capacitive and resistive properties of single-crystal TiO 2 electrode/solution interface in KCl and KCl/K 3 PO 4 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 TiO 2 electrode/solution interface. The electrochemical measurements indicate that, in the same pH, the presence of PO 4 3− 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 TiO 2 electrode/solution interface. This enhancement is attributed to the direct interaction between PO 4 3− and the single-crystal TiO 2 electrode surface, leading to the specific adsorption of PO 4 3− on the electrode surface, revealing higher current and stronger electrochemical activity in the interaction between TiO 2 and PO 4 3− . Additionally, our XPS results indicate the adsorption of PO 4 3− on the single-crystal TiO 2 electrode surface. The interaction of PO 4 3− with the TiO 2 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 TiO 2 electrode/solution interface.