Chemical and electronic structure analysis of a SrTiO 3 (001)/ p -Ge (001) hydrogen evolution photocathode
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Research Letter
Chemical and electronic structure analysis of a SrTiO3 (001)/p-Ge (001) hydrogen evolution photocathode Kelsey A. Stoerzinger and Yingge Du, Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, 902 Battelle Blvd, Richland WA 99352, USA Steven R. Spurgeon, Energy and Environment Directorate, Pacific Northwest National Laboratory, 902 Battelle Blvd, Richland WA 99352, USA Le Wang, Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, 902 Battelle Blvd, Richland WA 99352, USA Demie Kepaptsoglou, SuperSTEM, SciTech Daresbury Campus, Daresbury, WA44AD, UK; Jeol Nanocentre, University of York, Heslington, York, YO10 5BR, UK; Department of Physics, University of York, Heslington, York, YO10 5BR, UK Quentin M. Ramasse, SuperSTEM, SciTech Daresbury Campus, Daresbury, WA44AD, UK; School of Chemical and Process Engineering, University of Leeds, Leeds, LS2 9JT, UK; School of Physics, University of Leeds, Leeds, LS2 9JT, UK Ethan J. Crumlin, Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA Scott A. Chambers, Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, 902 Battelle Blvd, Richland WA 99352, USA Address all correspondence to Kelsey A. Stoerzinger and Scott A. Chambers at [email protected]; [email protected] (Received 22 January 2018; accepted 2 March 2018)
Abstract Germanium is a small-gap semiconductor that efficiently absorbs visible light, resulting in photoexcited electrons predicted to be sufficiently energetic to reduce H2O for H2 gas evolution. In order to protect the surface from corrosion and prevent surface charge recombination in contact with aqueous pH 7 electrolyte, we grew epitaxial SrTiO3 layers of different thicknesses on p-Ge (001) surfaces. Four-nanometer SrTiO3 allows photogenerated electrons to reach the surface and evolve H2 gas, while 13 nm SrTiO3 blocks these electrons. Ambient pressure x-ray photoelectron spectroscopy indicates that the surface readily dissociates H2O to form OH species, which may impact surface band bending.
Introduction The direct conversion of solar energy to chemical fuels is a tantalizing route to store renewable energy. By employing photocatalysts to split water into H2 and O2 gas,[1,2] solar energy can be stored in H2 fuel, subsequently combined with O2 to produce water and electricity in a cycle free of CO2 emissions. A “Z-scheme”[3,4] separates the two constituent reactions—the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER)—so that they occur on separate electrodes, thus decoupling the requirements of band gap and the energy of photoexcited carriers in materials design. Typical oxide photoanodes used to drive the OER have large band gaps,[5–7] and can thus absorb high-energy photons in a photoelectrochemical (PEC) device, allowing low-energy photons to pass through to the photocathode, which drives the HER. One semiconductor with attractive light-absorption properties is Ge. In c
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