Black Phosphorus Quantum Dot-Sensitized TiO2 Nanotube Arrays with Enriched Oxygen Vacancies for Efficient Photoelectrochemical Water Splitting

Photon absorption, charge separation and transportation, and charge-induced reactions at the active sites are the main crucial factors involved in the photoelectrochemical (PEC) water splitting. Herein, a combination of black phosphorus quantum dot (BPQD) sensitization and defect engineering strategies is employed to optimize the PEC performance of one-dimensional TiO2 nanotube array (NTA) photoanodes. The as-prepared TiO2–x/BP electrode exhibits a strong photocurrent density under simulated solar light irradiation, which is almost ∼3 times higher than that of bare TiO2. Specifically, the photocurrent increment of TiO2–x/BP is even larger than the sum of TiO2–x and TiO2/BP, verifying the synergistic effect of oxygen vacancies and BPQD sensitization. The maximum photoconversion efficiency of TiO2–x/BP is as high as 0.35%, while the value of TiO2 NTAs is calculated to be 0.13%. The results reveal that oxygen vacancies and BPQDs in the TiO2–x/BP composite not only facilitate the charge separation and transportation but also enhance the activity and quantity of reactive sites for water oxidation. The present strategy might open new routes to develop high-performance photoelectrodes for water splitting.