Multiple synergistic effects of Zr-alloying on the phase stability and photostability of black niobium oxide nanotubes as efficient photoelectrodes for solar hydrogen production

Funding Sponsor

American University in Cairo

Author's Department

Energy Materials Laboratory

Third Author's Department

Physics Department

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https://doi.org/10.1016/j.apcatb.2021.119961

Document Type

Research Article

Publication Title

Applied Catalysis B: Environmental

Publication Date

6-15-2021

doi

10.1016/j.apcatb.2021.119961

Abstract

Niobium oxides exist in a plethora of metastable, stoichiometric, nonstoichiometric, and mixed phases, rendering the Nb-O systems very complicated and hard to study. These structures significantly differ in their catalytic activity, electrical conductivity, and photoresponse. Herein, we demonstrate the ability to selectively fabricate pure T-Nb2O5 via the addition of small amount of Zr as a phase stabilizer. Moreover, we were able to tune the photoactivity of the material via hydrogen annealing. The photoactivity and stability of the fabricated black Zr-doped Nb2O5 nanotubes were correlated with the nature of induced defects upon hydrogen annealing and Zr doping. The H2-treated nanotubes showed extraordinary and remarkable stability and photoactivity upon their use for solar water splitting. This was accompanied by a noticeable reduction in the bandgap energy from 3.23 eV to 2.5 eV, which is mainly correlated with the introduced oxygen vacancies within the lattice with a remarkable conductivity. Most importantly, the black-defective nanotubes exhibited a photocatalytic activity that is ∼ 65 times that of the air-annealed counterparts. The optimized photoanodes attained a hydrogen production rate of ∼ 496 μmol h−1 cm−2 in 1 M KOH, revealing increased charge carriers transport and separation. The Mott-Schottky and valence band XPS analyses confirmed the increased charge carriers’ concentration and the appropriate band positions of the fabricated black nanotubes relative to the redox potentials of the water.

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