The Superior Electrical Conductivity and Anodic Stability of Vanadium-Doped Ti4O7

Abstract

The effectiveness of Magnéli phase titanium oxides (Ti n O2n−1, 4 ≤ n ≤ 10), promising alternatives to carbon-based materials in aqueous electrochemical technologies, is limited by their instability at strongly oxidizing electrode potentials. Ti4O7 and Ti5O9, the most electrically-conductive Ti n O2n−1, passivate in the harsh conditions demanded by fuel cells, batteries, and devices for the electrochemical treatment of water. Among other properties relevant to electrodes, doping of Ti n O2n−1 with transitional metals vanadium, chromium, and iron improves the oxidation stability as demonstrated by higher onset temperatures in the thermograms of doped Ti4O7 heated in air. To investigate the influence of doping on their anodic stability, disk electrodes of Ti4O7 doped with V, Cr, and Fe were investigated by electrochemical accelerated life testing (ALT). These disks, prepared by high-temperature H2 reduction of nominally 2 at% doped titanium(IV) oxide (TiO2), were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray fluorescence (XRF), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (PXRD), the 4-point probe method, cyclic voltammetry (CV), Tafel plot analysis, and electrochemical impedance spectroscopy (EIS). V- and Fe-doping are shown to improve the electrical conductivity and V-doping is demonstrated to improve the anodic stability as measured by the mean time-to-failure (TTF) during electrochemical ALT.