Titanium Oxycarbides: Formation, Properties and Application in Electrocatalysis

Abstract

Carbon modified titania (TiOC) is a promising material that could substitute carbon based electrocatalyst supports in proton-exchange membrane fuel cells, whose durability is limited by corrosion of the carbon electrode. A considerable number of recently published studies report on the synthesis of planar TiOC model systems for fundamental electrocatalysis studies at low pH via a carbothermal treatment of compact anodic TiO2 films on polycrystalline Ti substrates. Parameter studies have been performed, in which TiOC films were prepared at different synthesis temperatures between 550°C and 1050°C. Through combination of microscopic, (micro-)spectroscopic and diffractometric analysis tools, the influences of annealing temperature and Ti substrate texture on the physicochemical properties of the prepared TiOC films have been investigated. Electrochemical experiments in combination with in situ X-ray photoelectron spectroscopy, as well as operando carburization studies under UHV conditions yielded a fundamental understanding of the conversion mechanism of compact anodic TiO2 to oxycarbide (TiO1−xCx) phases and of their subsequent reoxidation in air and under anodic polarization in acidic electrolyte. TiOC electrodes, synthesized at different annealing temperatures, have been studied with electrochemical techniques to assess their electrical conductivity at the electrode/electrolyte interface and their stability against passivation/corrosion under anodic polarization in acidic electrolytes. Pt nanoparticles deposited on TiOC films and on a glassy carbon (GC) electrode have been investigated in terms of their activity towards the electrochemical ethanol oxidation reaction (EOR) and in terms of their electrochemical stability in 1.0M HClO4 at room temperature and in concentrated H3PO4 at temperatures between 25°C and 80°C. Compared to Pt/GC, the Pt/TiOC system yields higher EOR current densities. Several features in the electrochemical response of Pt/TiOC point to a synergistic effect of the support on the EOR activity. This review summarizes the key results of the studies on compact TiOC films that have been published so far to provide an overview of the current understanding of the properties of these interesting model systems for electrocatalysis studies.