Journal
ACS CATALYSIS
Volume 6, Issue 2, Pages 1345-1353Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acscatal.5b02817
Keywords
photocatalytic water splitting; photoelectrochemical cell; TiO2 nanotubes; photonic crystals; photonic bandgap; electrochemical anodization
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Funding
- Regione Lombardia
- Cariplo Foundation within the SmartMatLab Centre project [2013-1766]
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Two series of self-assembled TiO2 nanotube (NT) arrays were grown by electrochemical anodization on a metallic titanium substrate with different anodization times and applied potentials in HF-containing ethylene glycol electrolyte solutions and postcalcined at 450 degrees C. The obtained thin films were characterized by FESEM, XRD, and UV-vis-NIR DRS analyses and tested as photoanodes in incident photon to current efficiency (IPCE) measurements and in a two-compartment photoelectrochemical cell (PEC) for separate H-2 and O-2 production. The photocatalytic performance of the NT arrays significantly increased with an increase in the potential applied during anodization (i.e., with increasing the NT inner diameter) and the incident angle of the light. IPCE measurements revealed that such unexpected behavior is due to a red shift of the activity threshold that allows harvesting and converting a larger portion of the solar spectrum. This phenomenon is ascribed to the parallel shift of the photonic band gap position originated by the intrinsic photonic crystal properties and demonstrates the important role played by ordered hierarchical structures in improving the photocatalytic performance of NT arrays by confining and manipulating light.
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