@inproceedings{RichterLichtermanHuetal., author = {Richter, Matthias and Lichterman, Michael F. and Hu, Shu and Crumlin, Ethan J. and Axnanda, Stephanus and Favaro, Marco and Drisdell, Walter S. and Hussain, Zahid and Brunschwig, Bruce S. and Liu, Zhi and Lewis, Nathan S. and Lewerenz, Hans-Joachim}, title = {Experimental Approach for Determining Semiconductor/liquid Junction Energetics by Operando Ambient Pressure X-ray Photoelectron Spectroscopy}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, pages = {S. 409}, abstract = {The performance of a photoelectrochemical solar cell depends strongly on the electrochemical nature of the semiconductor/electrolyte junction [1]. Operando Ambient Pressure X-ray photoelectron spectroscopy investigation of semiconductor/liquid junctions provides quantitative understanding of the energy bands in these photoelectrochemical solar cells [2, 3, 4]. We demonstrate how OAP-XPS may be used to determine these relationships for semiconductor/liquid systems. The data can be analyzed to determine the energy relationship between the electronic energy bands in the semiconductor electrode and the redox levels in the solution. The major conditions for semiconductor-electrolyte contacts including accumulation, depletion, and Fermi-level pinning are observed, and the so-called flat-band energy can be determined. [1] Science 344 (2014) 1005; [2] Sci Rep 5 (2015) 9788; [3] Ener Sci 8 (2015) 2409; [4] J Electrochem Soc 162 (2016) H1}, language = {en} } @inproceedings{LichtermanRichterHuetal., author = {Lichterman, Michael F. and Richter, Matthias and Hu, Shu and Crumlin, Ethan J. and Axnanda, Stephanus and Favaro, Marco and Drisdell, Walter S. and Hussain, Zahid and Brunschwig, Bruce S. and Liu, Zhi and Lewis, Nathan S. and Lewerenz, Hans-Joachim}, title = {Probing the TiO2/Liquid Interface of a Photoelectrochemical Cell by X-Ray Photoelectron Spectroscopy}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, pages = {S. 414}, abstract = {Amorphous TiO2 coatings can stabilize semiconductor photoanodes such as Si, GaAs, and GaP that are otherwise unstable in aqueous media [1]. Using tender X-rays with their substantially increased inelastic mean free scattering length of photoelectrons and using the classical three-electrode potentiostatic arrangement allows one to follow of the influence of the applied potentials on the semiconductor electrode energetics such as band bending and band edge shifts directly [2, 3]. The observed shifts in binding energy with respect to the applied potential have directly revealed rectifying junction behavior on semiconducting samples. Accumulation, depletion and Fermi level pinning were observed. Additionally, the non-linear response of the core level binding energies to changes in the applied electrode potential has revealed the influence of defect-derived electronic states on the Galvani potential across the complete cell. [1] Science 344 (2014) 1005; [2] Sci Rep 5 (2015) 9788; [3] Ener \& Env Sci 8 (2015) 2409}, language = {en} } @inproceedings{RichterLichtermanHuetal., author = {Richter, Matthias and Lichterman, Michael F. and Hu, Shu and Crumlin, Ethan J. and Axnanda, Stephanus and Favaro, Marco and Drisdell, Walter S. and Hussain, Zahid and Brunschwig, Bruce S. and Liu, Zhi and Lewis, Nathan S. and Lewerenz, Hans-Joachim}, title = {An Electrochemical, resonant Photoemission and Ambient Pressure-X-ray Photoelectron Spectroscopic Investigation of Si/TiO2/Ni/Electrolyte Interfaces}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, pages = {S. 414}, abstract = {Photoelectrochemical cells based on semiconductor-liquid interfaces provide a method of converting solar energy to electricity or fuels. Recently, we have demonstrated operational systems that involved stabilized semiconductor-liquid junctions [1]. The electrical and spectroscopic properties of the TiO2/Ni protection layer system have been investigated in contact with electrolyte solutions [2, 3, 4]. From the response of the photoelectron binding energies to variations in applied potential the energetics of the solid/electrolyte interface are elucidated. The degree of conductivity depended on the chemical state of the Ni on the TiO2 surface. The combinations of these techniques provide a powerful tool for the investigation of hybrid electrode/solution contacts. [1] Science 344 (2014) 1005; [2] Sci Rep 5 (2015) 9788; [3] Ener \& Env Sci 8 (2015) 2409; [4] J Electrochem Soc 162 (2016) H1}, language = {en} } @misc{MoralesTschammerPożarowskaetal., author = {Morales, Carlos and Tschammer, Rudi and Pożarowska, Emilia and Kosto, Julia and Villar-Garcia, Ignacio J. and P{\´e}rez-Dieste, Virginia and Favaro, Marco and Starr, David E. and Kapuścik, Paulina and Mazur, Michał and Wojcieszak, Damian and Domaradzki, Jarosław and Alvarado, Carlos and Wenger, Christian and Henkel, Karsten and Flege, Jan Ingo}, title = {Hydrogen sensing via heterolytic H₂ activation at room temperature by atomic layer deposited ceria}, series = {ChemSusChem : chemistry, sustainability, energy, materials}, volume = {18}, journal = {ChemSusChem : chemistry, sustainability, energy, materials}, number = {13}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1864-5631}, doi = {10.1002/cssc.202402342}, pages = {1 -- 13}, abstract = {Ultrathin atomic layer deposited ceria films (\<20 nm) are capable of H2 heterolytic activation at room temperature, undergoing a significant reduction regardless of the absolute pressure, as measured under in-situ conditions by near ambient pressure X-ray photoelectron spectroscopy. ALD-ceria can gradually reduce as a function of H2 concentration under H2/O2 environments, especially for diluted mixtures below 10 \%. At room temperature, this reduction is limited to the surface region, where the hydroxylation of the ceria surface induces a charge transfer towards the ceria matrix, reducing Ce4+ cations to Ce3+. Thus, ALD-ceria replicates the expected sensing mechanism of metal oxides at low temperatures without using any noble metal decorating the oxide surface to enhance H2 dissociation. The intrinsic defects of the ALD deposit seem to play a crucial role since the post-annealing process capable of healing these defects leads to decreased film reactivity. The sensing behavior was successfully demonstrated in sensor test structures by resistance changes towards low concentrations of H2 at low operating temperatures without using noble metals. These promising results call for combining ALD-ceria with more conductive metal oxides, taking advantage of the charge transfer at the interface and thus modifying the depletion layer formed at the heterojunction.}, language = {en} }