Commercialization of semiconductor photoelectric devices has been limited by low photo-absorption efficiency and short lifetime of charge carriers due to fast charge recombination. Efforts to increase photo-absorption typically aim to lower the band gap of the semiconductor. WS2 is a promising material having a band gap of only 1.3 eV but unfortunately can be unstable in electrochemical aqueous environments. Recent results show that coating semiconductors with amorphous TiO2 (a-TiO2) can protect such semiconductors[1]. Holes may travel through the a-TiO2 to initiate oxidation reactions while electrons through the other semiconductor, which leads to increased charge separation. Key to this composite material is the a-TiO2, which must form a strong interface and allow fast hole mobility. Our experimental results show that a-TiO2 does indeed stabilize WS2 during photoelectrolysis of water. We have also simulated using density functional theory (DFT) interfaces between WS2 and TiO2. a-TiO2 structures were generated with a melt-and-quench approach, whereby the material is heated to high temperature then slowly cooled. Calculated band offsets between WS2 and a-TiO2 predict charge flow between the two materials. Other results have suggested that oxygen vacancies are key to efficient hole transport in a-TiO2[2]. We have accordingly simulated sub-stoichiometric a-TiOx (x = 2 to 1.7). Our results predict how the structure of a-TiO2 may affect its electrochemical and photocatalytic properties, and provide valuable insight on designing a-TiO2 composite materials. Our results also suggest whether a-TiO2 may be a viable replacement for crystalline TiO2. [1] S. Hu, M.R. Shaner, J. a Beardslee, M. Lichterman, B.S. Brunschwig, N.S. Lewis, Science. 344 (2014) 1005–9. [2] H.H. Pham, L.-W. Wang, Phys. Chem. Chem. Phys. 17 (2014) 541–50.

Synthesis and simulation of amorphous TiO2 for photoelectrochemical applications

251st National Meeting (2016)

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