Wide-bandgap semiconductors are of high interest for photochemical reactions such as water splitting. However, so far most studies only considered reactions in water. Recently, it was shown that UV light illumination enhances... [ view full abstract ]
Wide-bandgap semiconductors are of high interest for photochemical reactions such as water splitting. However, so far most studies only considered reactions in water. Recently, it was shown that UV light illumination enhances oxygen incorporation in Fe-doped SrTiO3 (Fe:STO) [1] and therefore also changes its composition. Moreover, under UV light the usage of Fe:STO in a zirconia based solid state electrochemical cell leads to a battery type voltage [2]. An investigation of the basic mechanisms and the arising effects is presented.
After several hours at 400 °C under UV light, a blackening of Fe:STO single crystals is observed. The colour change is attributed to an increasing electron hole and a decreasing VO concentration. Van der Pauw measurements support this interpretation by showing an enhanced conductivity of blackened compared to native Fe:STO single crystals. The time dependence of the sample’s resistance decline under UV light is further investigated by electrochemical impedance spectroscopy (EIS). When heating blackened specimens above 300 °C, without UV exposure, oxygen is released and the oxygen vacancy concentration increases again. Consequently, incorporation of oxygen due to UV irradiation is reversible and a switch between different steady states determined by the kinetics of oxygen incorporation and release has been accomplished.
[1] R. Merkle, R.A. De Souza, and J. Maier, Optically Tuning the Rate of Stoichiometry Changes: Surface-Controlled Oxygen Incorporation into Oxides under UV Irradiation, Angewandte Chemie International Edition 40(11) (2001) 2126-2129.
[2] G. Walch, B. Rotter, G.C. Brunauer, E. Esmaeili, A.K. Opitz, M. Kubicek, J. Summhammer, K. Ponweiser, and J. Fleig, A Solid Oxide Photoelectrochemical Cell with UV Light-Driven Oxygen Storage in Mixed Conducting Electrodes, Journal of Materials Chemistry A 5(4) (2017) 1637-1649.
