@misc{RichterChengCrumlinetal., author = {Richter, Matthias R. and Cheng, Wen-Hui and Crumlin, Ethan J. and Drisdell, Walter S. and Atwater, Harry A. and Schmeißer, Dieter and Lewis, Nathan S. and Brunschwig, Bruce S.}, title = {X‑ray Photoelectron Spectroscopy and Resonant X‑ray Spectroscopy Investigations of Interactions between Thin Metal Catalyst Films and Amorphous Titanium Dioxide Photoelectrode Protection Layers}, series = {Chemistry of Materials}, volume = {33}, journal = {Chemistry of Materials}, number = {4}, issn = {0897-4756}, doi = {10.1021/acs.chemmater.0c04043}, pages = {1265 -- 1275}, abstract = {The use of electrochemistry, X-ray photoelectron spectroscopy, and resonant X-ray spectroscopy has unlocked the paradox of interfacial hole conduction through amorphous TiO2 (a-TiO2) to deposited Ni, Ir, and Au metal catalysts. Although electrocatalysts for the oxygen-evolution reaction derived from metallic Ir and Ni have mutually similar overpotentials in alkaline media, Si/a-TiO2/Ir interfaces exhibit higher overpotentials than Si/a-TiO2/Ni interfaces. The data allow formulation of full band energy diagrams for n-Si/a-TiO2/metal interfaces for M = Ni, Ir, or Au. Although both Ni and Ir produce band bending in a-TiO2 favoring hole conduction, only Ni creates multiple states within the a-TiO2 band gap at the a-TiO2/Ni interface, which produces a quasi-metallic interface at the a-TiO2/Ni junction. Au, however, produces a flat-band interface that limits hole conduction without any new band gap states.}, 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 = {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{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} } @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} } @misc{ErikssonHahlinAxnandaetal., author = {Eriksson, Susanna K. and Hahlin, Maria and Axnanda, Stephanus and Crumlin, Ethan J. and Wilks, Regan G. and Odelius, Michael and Eriksson, Anna I. K. and Liu, Zhi and {\AA}hlund, John and Hagfeldt, Anders and Starr, David E. and B{\"a}r, Marcus and Rensmo, H{\aa}kan and Siegbahn, Hans}, title = {In-situ probing of H₂O effects on a Ru-complex adsorbed on TiO₂ using ambient pressure photoelectron spectroscopy}, series = {Topics in Catalysis}, volume = {59}, journal = {Topics in Catalysis}, number = {5}, issn = {1022-5528}, doi = {10.1007/s11244-015-0533-3}, pages = {583 -- 590}, language = {en} }