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Enhanced photoelectrochemical behavior of H-TiO₂ nanorods hydrogenated by controlled and local rapid thermal annealing

: Wang, X.; Estrade, S.; Lin, Y.; Yu, F.; Lopez-Conesa, L.; Zhou, H.; Gurram, S.K.; Peiro, F.; Fan, Z.; Shen, H.; Schäfer, L.; Bräuer, G.; Waag, A.

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Nanoscale research letters : NRL 12 (2017), Art. 336, 9 pp.
ISSN: 1931-7573
ISSN: 1556-276X
Journal Article, Electronic Publication
Fraunhofer IST ()
H-TiO₂ core-shell nanorods; hydrogenation; rapid thermal annealing; TEM / EELS; optical absorption; PEC property

Recently, colored H-doped TiO₂ (H-TiO₂) has demonstrated enhanced photoelectrochemical (PEC) performance due to its unique crystalline core—disordered shell nanostructures and consequent enhanced conduction behaviors between the core-shell homo-interfaces. Although various hydrogenationapproaches to obtain H-TiO₂ have been developed, such as high temperature hydrogen furnace tube annealing, high pressure hydrogen annealing, hydrogen-plasma assisted reaction, aluminum reduction and electrochemical reduction etc., there is still a lack of a hydrogenation approach in a controlled manner where all processing parameters (temperature, time and hydrogen flux) were precisely controlled in order to improve the PEC performance of H-TiO₂ and understand the physical insight of enhanced PEC performance. Here, we report for the first time a controlled and local rapid thermal annealing (RTA) approach to prepare hydrogenated core-shell H-TiO₂ nanorods grown on F:SnO₂ (FTO) substrate in order to address the degradation issue of FTO in the typical TiO₂ nanorods/FTO system observed in the conventional non-RTA treated approaches. Without the FTO degradation in the RTA approach, we systematically studied the intrinsic relationship between the annealing temperature, structural, optical, and photoelectrochemical properties in order to understand the role of the disordered shell on the improved photoelectrochemical behavior of H-TiO₂ nanorods. Our investigation shows that the improvement of PEC performance could be attributed to (i) band gap narrowing from 3.0 to 2.9 eV; (ii) improved optical absorption in the visible range induced by the three-dimensional (3D) morphology and rough surface of the disordered shell; (iii) increased proper donor density; (iv) enhanced electron–hole separation and injection efficiency due to the formation of disordered shell after hydrogenation. The RTA approach developed here can be used as a suitable hydrogenation process for TiO₂ nanorods/FTO system for important applications such as photocatalysis, hydrogen generation from water splitting and solar energy conversion.