Defect-Rich Metallic Titania (TiO1.23)—An Efficient Hydrogen Evolution Catalyst for Electrochemical Water Splitting

As a promising alternative hydrogen evolution electro-catalyst to platinum, a classical and earth-abundant "titania" is investigated. Herein, the paradigm of electro-inactive titania has been surmounted by exploiting defect engineering as a tool, which tailors the local atomic structure of nonconductive titania via electrochemical cathodization strategy. The enhanced electro-conducting properties along with favorable surface energetics for Hads of reduced titania (TiO1.23) ensures ultrafast HER kinetics. Because of the proximity with the benchmark Pt, the reduced titania exhibits excellent HER catalytic activity in an acidic electrolyte by exhibiting low onset potential of 75 mV versus RHE and a Tafel slope of 88 mV·dec–1, and it demonstrates 10 mA·cm–2 at a potential of 198 mV versus RHE. Furthermore, the cathodization process also endows "magic effects" by effectively exposing the (111) close-packed plane with extravagant texture coefficient and makes the structure more thermodynamically stable. The long-term durability studies (5000 cycles of cyclic sweeping, 40 h of static polarization) confirm the extremely stable HER catalytic activity of TiO1.23. These findings suggest that by tuning oxygen vacancies in the lattice and its concomitant cumulative strained configuration, reduced titania can be an effective HER electro-catalyst for electrochemical water splitting.