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Abstract

The synthesis of TiO₂ nanostructures with visible light absorption is critical for realizing low-cost and efficient photoelectrochemical hydrogen generation from water splitting. In this work, we report an Ar-NH₃-Ar treatment method capable to generate Ti₃₊ species in anodic self-ordered TiO₂ nanotube arrays for the synthesis of substoichiometric TiO₂ nanotube arrays. The presence of Ti₃₊ is verified by XPS, EPR and EDS measurements while no detectable N is observed in the material. The modified TiO₂ exhibits a 5-fold enhancement in photocurrent compared to pristine TiO₂ at 1.23V vs. RHE due to the increased absorption of the solar spectrum. For the 4-h treated sample, a photocurrent of 1 mAcm₋₂ is obtained at 1.18V vs. RHE, owing to the reduced flat band potential and the increased density of charge carriers evaluated using EIS measurements. The photocatalytic activity can be further optimized by increasing the layer thickness, leading also to a cathodic shift of the onset potential. Furthermore, the modified TiO₂ remains intact in air for no less than 1 week. This enhancement in photo-catalytic activity is proven to be closely relevant to the Ti₃₊ induced by the Ar-NH₃-Ar treatment.