Solar water splitting for hydrogen production has been regarded as an effective way to solve the worldwide energy and environment crisis. How to improve the quantum conversion efficiency of visible-light is the key problem in this field, and is very important for accelerating the industrial application of photoelectrochemical (PEC) water splitting. However, the development of visible-light water splitting is now hindered by the short diffusion length and high recombination rate of the visible-light excited photocarriers in the PEC materials. To solve this problem, the researchers of Qinghua Liu, Jingfu He, and Tao Yao leaded by Prof. Shiqiang Wei in National Synchrotron Radiation Laboratory (NSRL) of Hefei used the synchrotron radiation X-ray absorption spectroscopy (XAFS) technique to study the local atomic and electronic structures of low dimensional nanostructure PEC materials, and disclosed the influence of surface distortion on the diffusion route of photogenerated carriers, and made a significant process in the visible-light PEC water splitting. In experiment, the researchers designed a composite Fe2TiO5/TiO2 nanotube arrayed structure through coating a narrow band gap semiconductor of Fe2TiO5 on the surface of highly ordered TiO2 nanotube arrays. An effective separate interface for photocarriers was formed between the surfaces of Fe2TiO5/TiO2, which could successfully transfer the photocarriers in bulk TiO2 to the surface active reaction cites. As a result, the quantum conversion efficiencies for the visible light in the range of 400 to 600 nm were significantly enhanced to above 40% and the total energy conversion efficiency was improved to 2.7%. Experimental characterizations including XAFS technique revealed that the improved PEC performance is attributed to the “vectorial-hole-transfer” channel between the Fe2TiO5 and TiO2 surface. This result is published on Nature Comms. 5, 5122 (2014), which enriches peoples’ comprehension of using energy band engineering to improve the visible light PEC water splitting and provides some new hints for manipulation of the performance of transition metal oxide PEC materials.

Structure and performance representation of Fe2TiO5-TiO2 nanotube array.