Single-Source Alkoxide Precursor Approach to Titanium Molybdate, TiMoO₅, and Its Structure, Electrochemical Properties, and Potential as an Anode Material for Alkali Metal Ion Batteries

Abstract

Transition-metal oxide nanostructured materials are potentially attractive alternatives as anodes for Li ion batteries and as photocatalysts. Combining the structural and thermal stability of titanium oxides with the relatively high oxidation potential and charge capacity of molybdenum(VI) oxides was the motivation for a search for approaches to mixed oxides of these two metals. Challenges in traditional synthetic methods for such materials made development of a soft chemistry single-source precursor pathway our priority. A series of bimetallic Ti-Mo alkoxides were produced by reactions of homometallic species in a 1:1 ratio. Thermal solution reduction with subsequent reoxidation by dry air offered in minor yields Ti₂Mo₂O₄(OMe)₆(OⁱPr)₆ (<b>1</b>) by the interaction of Ti(OⁱPr)₄ with MoO(OMe)₄ and Ti₆Mo₆O₂₂(OⁱPr)₁₆(iPrOH)₂ (<b>2</b>) by the reaction of Ti(OⁱPr)₄ with MoO(OⁱPr)₄. An attempt to improve the yield of <b>2</b> by microhydrolysis, using the addition of stoichiometric amounts of water, resulted in the formation with high yield of a different complex, Mo₇Ti_7+<i>x</i>O_31+<i>x</i>(OⁱPr)_8+2<i>x</i> (<b>3</b>). Controlled thermal decomposition of <b>1</b>-<b>3</b> in air resulted in their transformation into the phase TiMoO₅ (<b>4</b>) with an orthorhombic structure in space group <i>Pnma</i>, as determined by a Rietveld refinement. The electrochemical characteristics of <b>4</b> and its chemical transformation on Li insertion were investigated, showing its potential as a promising anode material for Li ion batteries for the first time. A lower charge capacity and lower stability were observed for its application as an anode for a Na ion battery.