Vacancy Control in TiNb2O7: Implications for Energy Applications

Rapid global electrification, including for transportation, has dramatically increased demand for long-lasting and faster-charging batteries. Titanium niobium oxide (TiNb2O7) is one of the most promising anode materials for high-power lithium-ion batteries (LIBs). However, the intrinsic low electronic conductivity of TiNb2O7 is a significant drawback. Herein, an almost 10 orders of magnitude increase in conductivity is achieved via reduction of TiNb2O7 in H2 at 900 °C. The observed dramatic increase in electron conductivity upon reduction is unprecedented and opens new possibilities to produce niobium-based conductive materials for next-generation energy storage. Upon extended reduction, TiNb2O7 converts into a distorted rutile TiNb2O6 structure, which can be reoxidized back into the crystallographic shear phase. In addition, TiNb2O7 can be thermally reduced in an inert atmosphere and reoxidized by CO2 with excellent oxygen exchange capacity. Thus, the TiNb2O7 Wadsley–Roth phase demonstrates outstanding potential for solar-driven thermochemical CO2 splitting at 1400 °C. These findings manifest that controlling defect chemistry paves the way for developing advanced materials for LIBs and solar-driven thermochemical fuel production.