Tunable oxygen vacancies in CeO2 nanorods via one-step NaBH4-assisted synthesis for enhanced visible-light photocatalytic water splitting

Abstract CeO 2 nanorod photocatalysts with systematically tuned oxygen vacancy concentrations were synthesized via a one-step NaBH 4 -assisted hydrothermal method to elucidate the role of defect engineering in photocatalytic water splitting. A series of reduced samples (Ce1–Ce5) and pristine CeO 2 were thoroughly characterized. Increasing NaBH 4 dosage induced XRD peak broadening with crystallite size reduction (5.37–4.44 nm) and a UV–Vis DRS red shift with bandgap narrowing (2.89–2.72 eV). Urbach energy increased (0.36–0.41 eV), reflecting mid-gap state formation. Raman, FTIR, and EPR (g ≈ 2.002) confirmed rising oxygen vacancy and Ce 3+ content, consistent with XPS, which revealed enhanced oxygen vacancy-related O 1s contribution (16.7–43%) and Ce 3+ fraction. Valence-band XPS and secondary electron cut-off showed band-edge shifts and reduced work function, promoting charge transfer. PL and TCSPC indicated prolonged carrier lifetimes in Ce3 (τ i − τ a = 1.1087 ns), while Ce4–Ce5 exhibited deep traps. CDB and S-parameter analyses identified Ce3 as optimal, balancing shallow and deep traps for efficient carrier dynamics. BET and BJH confirmed Ce3’s highest surface area (~ 1465 m 2 /g) and mesoporosity. Morphological analysis showed smooth rods (Ce, Ce1) evolving to porous, defect-rich rods (Ce2–Ce3) and partial amorphization (Ce4–Ce5). Ce3 delivered the highest H 2 evolution under visible light without sacrificial agents, highlighting the critical role of controlled oxygen vacancy engineering in advancing CeO 2 -based solar hydrogen production.