Effect of the coat layer thickness on the electrochemical activity and fine structure of TaOx/Ti electrodes

Abstract

TaOx/Ti electrodes with various coating layers were prepared through the thermal decomposition method and were characterized with electrochemical activity tests including cyclic voltammetry (CV) and Mott–Schottky analysis. CV test results revealed that the electrochemical activity of the TaOx/Ti electrode increased with the decreasing number of coating layers. A Mott–Schottky study revealed that the TaOx/Ti electrode was of p–n type, whereas the TaOx powder prepared using the same procedure was of n-type. The carrier density of the TaOx/Ti electrode also decreased with the increasing number of TaOx coat layers. X-ray absorption fine structure (XAFS) and density functional theory (DFT) calculations were used to interpret this phenomenon. XAFS results revealed that the Ta–O structure was seriously distorted close to the Ti substrate. The shift in the white-line peak position during the X-ray near-edge structure (XANES) analysis showed that oxygen vacancies and Ta(IV) were present in the TaOx/Ti electrode. Furthermore, results indicate that the oxygen vacancy concentration decreased with the increasing number of TaOx coating layers. A Tinear-edge x-ray absorption fine structure (NEAXFS) analysis of the Ti L-edge found that Ti existed on the surface of the TaOx/Ti electrode, and its concentration decreased with the increasing thickness of the TaOx coating. Density functional theory (DFT) results revealed that oxygen vacancies could be introduced into the TaOx coating and were present adjacent to the tantalum atoms around the doping Ti atoms.