The formation of V-doped Ti4O7 hollow Magnéli phase with improved electrical conductivity and thermal stability

Abstract

Due to its excellent electrical conductivity and stable Magnéli phase structures, cermet Ti4O7 has emerged as one of the most promising materials in the fields of electrochemical application. However, the difficulties in creating high specific surface area structures, having room for conductivity enhancement when used as a conductive additive, and passivation forming TiO2 under sufficiently oxidizing conditions limit the development of Ti4O7 for practical applications. In this work, the V-doped Ti4O7 hollow spheres with improved electrical conductivity and thermal stability were synthesized by the three-step approach of solvothermal reaction, oxidative crystallization, and hydrogen reduction without any surfactant or template. The formation mechanism of hollow (Ti,V)4O7 was revealed by analyzing the valence evolution of V and comparing the morphology of Ti4O7. The conductivity of Ti4O7 and (Ti,V)4O7 was compared and contrasted as functions of pressure, demonstrating the superiority of (Ti,V)4O7 in terms of conductivity. Thermograms showed that the addition of V increased the complete oxidation temperature of Ti4O7. Moreover, the reason for the enhanced electrical conductivity and thermal stability of V-doped Ti4O7 was also revealed based on density functional theory (DFT) calculations.