Black Nb₂O₅ nanorods with improved solar absorption and enhanced photocatalytic activity

Black titania, with greatly improved solar absorption, has demonstrated its effectiveness in photocatalysis and photoelectrochemical cells (PEC), inspiring us to explore the blackening of other wide band-gap oxide materials for enhanced performance. Herein, we report the fabrication of black, reduced Nb₂O₅ nanorods (r-Nb₂O₅), with active exposed (001) surfaces, and their enhanced photocatalytic and PEC properties. Black r-Nb₂O₅ nanorods were obtained via reduction of pristine Nb₂O₅ by molten aluminum in a two-zone furnace. Unlike the black titania, r-Nb₂O₅ nanorods are well-crystallized, without a core-shell structure, which makes them outstanding in photocatalytic stability. Substantial Nb⁴⁺ cation and oxygen vacancies (V_O) were introduced into r-Nb₂O₅, resulting in the enhanced absorption in both the visible and near-infrared regions and improved charge separation and transport capability. The advantage of the r-Nb₂O₅ was also proved by its more efficient photoelectrochemical performance (138 times at 1.23 V_RHE) and higher photocatalytic hydrogen-generation activity (13 times) than pristine Nb₂O₅. These results indicate that black r-Nb₂O₅ is a promising material for PEC application and photocatalysis.