The cathodic material plays an essential role in oxygen reduction reaction for energy conversion and storage systems. Titanium dioxide, as a semiconductor material, is usually not recognized as an efficient oxygen reduction electrocatalyst owning to its low conductivity and poor reactivity. Here we demonstrate that nano-structured titanium dioxide, self-doped by oxygen vacancies and selectively exposed with the high-energy {001} facets, exhibits a surprisingly competitive oxygen reduction activity, excellent durability and superior tolerance to methanol. Combining the electrochemical tests with density-functional calculations, we elucidate the defect-centred oxygen reduction reaction mechanism for the superiority of the reductive {001}-TiO2−x nanocrystals. Our findings may provide an opportunity to develop a simple, efficient, cost-effective and promising catalyst for oxygen reduction reaction in energy conversion and storage technologies.

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TiO2 is a typical semiconductor and has been extensively used as an effective photocatalyst for environmental pollution control. But it could not be used as an electrochemical reductive catalyst because of its low electric conductivity and electrocatalytic activity. In this work, however, we demonstrate that TiO2 can act as an excellent cathodic electrocatalyst when its crystal shape, exposed facet and oxygen-stoichiometry are finely tailored by the local geometric and electronic structures. The defect-engineered TiO2-x single crystals dominantly exposed by high-energy {001} facets exhibits a high cathodic activity and great stability for electrochemical reduction of nitrobenzene, a typical refractory pollutant with high toxicity in environment. The single crystalline structure, the high-energy {001} facet and the defective oxygen vacancy of the defect-engineered TiO2-x single crystals are found to be mainly responsible for their cathodic superiority. With the findings in this work, a more practical non-Pd cathodic electrocatalyst could be prepared and applied for electrocatalytic reduction of refractory pollutants in water and wastewater, and extend the promising applications of TiO2 in the fields of environmental science.