3D Urchin-like Hierarchical Black TiO2 Hollow Nanospheres: A Highly Active and Stable Electrocatalyst for Water Oxidation in Alkaline and Neutral Media

Highly proficient, earth-abundant, long-term stable bifunctional electrocatalysts are very much desired for overall water splitting reactions. The present paper describes one such stable bifunctional electrocatalyst, 3D hollow nanostructured hierarchical hydrogenated TiO2 (H-TiO2) prepared by low-temperature treatment. The H-TiO2 electrocatalyst can catalyze oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) with a low overpotential of 270 and 128 mV at 10 mA cm–2 in alkaline media. Moreover, it exhibits an unusual catalytic activity in neutral electrolyte as well. The corresponding lower Tafel values indicate faster reaction kinetics on the H-TiO2 surfaces. When H-TiO2 is implemented as both the anode and cathode in a two-electrode system for overall water splitting in alkaline and neutral media, it only needs 1.57 and 2.11 V to reach a current density of 10 mA cm–2 and displays good durability for 12 h. The results suggest that Ti3+ and abundant oxygen vacancies in H-TiO2 favor HER and OER, which might originate from the enhanced electrical conductivity and rapid charge transfer rate due to the controlled interplay of the favoring factors. Thus, the present research work demonstrates a promising strategy for developing a highly efficient, stable, and carbon-free substitute for noble metal-based electrocatalysts for the overall water splitting in alkaline and neutral media.