Valence Photoelectron and Auger-Emission Spectroscopy from the Solid-Aqueous Solution Interface under Operando Photochemical Conditions

• Applicant: Dr. Robert Seidel
• Subject Area: Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: from 2016 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 319327379

• Final Report Year: 2024

Final Report Abstract

Solar energy is our inexhaustible, natural energy source and plays a central role in meeting the future global energy demand, which is steadily increasing due to population growth and rising demand for clean energy production. One of the most important challenges, in addition to efficient energy generation, is storing this energy in so-called solar fuels, where energy is stored in chemical bonds. This is analogous to natural photosynthesis, in which plants convert sunlight, water, and CO2 into usable forms of energy. One of the most promising, technically feasible processes that will eventually replace conventional energy generation relying on non-renewable resources is water splitting at catalytic surfaces using sunlight and/or an applied voltage. Technically, this can be achieved with a (photo)electrochemical cell, which consists of an aqueous electrolyte, a semiconductor anode exposed to sunlight, and a metal cathode. Two fundamental reactions determine water splitting: the formation of molecular oxygen, O2, at the photoanode, and the formation of hydrogen gas, H2, at the cathode. The focus of this project was the X-ray spectroscopic investigation of the first of these two reactions at the electrolyte-anode interface, particularly the application of (resonant) Auger and valence electron spectroscopy to understand the electronic structure of this interface. Using novel and innovative measurement techniques, such as liquid microjet technology, graphene-covered membrane electrode setups under operando conditions, and near-ambient pressure photoelectron spectroscopy on condensed water layers on electrodeposited semiconductor layers, essential mechanisms occurring during (photo)electrocatalytic water splitting were elucidated at the atomic level. The catalyst systems under investigation included iron-based oxides (Fe2O3) and mixed oxides (Fe0.75Ni0.25Ox), as well as oxygen-free Fe-N-C catalysts and cobalt oxide and titanium dioxide nanoparticles in aqueous or electrolytic solution. The results obtained in this project provide new insights into the differently catalytically active interfaces studied and significantly contribute to their rational optimization and the development of future concepts for improved (solar) energy conversion.

Publications

• Advances in liquid phase soft-x-ray photoemission spectroscopy: A new experimental setup at BESSY II. Review of Scientific Instruments, 88(7).
  Seidel, Robert; Pohl, Marvin N.; Ali, Hebatallah; Winter, Bernd & Aziz, Emad F.
  
• Molecular species forming at the α-Fe2O3 nanoparticle–aqueous solution interface. Chemical Science, 9(19), 4511-4523.
  Ali, Hebatallah; Seidel, Robert; Pohl, Marvin N. & Winter, Bernd
  
• Electronic structure of aqueous-phase anatase titanium dioxide nanoparticles probed by liquid jet photoelectron spectroscopy. Journal of Materials Chemistry A, 7(12), 6665-6675.
  Ali, Hebatallah; Seidel, Robert; Bergmann, Arno & Winter, Bernd
  
• In-Situ X-ray Spectroscopy of the Electric Double Layer around TiO2 Nanoparticles Dispersed in Aqueous Solution: Implications for H2 Generation. ACS Applied Nano Materials, 3(1), 264-273.
  Ali, Hebatallah; Golnak, Ronny; Seidel, Robert; Winter, Bernd & Xiao, Jie
  
• Photoelectron spectra of alkali metal–ammonia microjets: From blue electrolyte to bronze metal. Science, 368(6495), 1086-1091.
  Buttersack, Tillmann; Mason, Philip E.; McMullen, Ryan S.; Schewe, H. Christian; Martinek, Tomas; Brezina, Krystof; Crhan, Martin; Gomez, Axel; Hein, Dennis; Wartner, Garlef; Seidel, Robert; Ali, Hebatallah; Thürmer, Stephan; Marsalek, Ondrej; Winter, Bernd; Bradforth, Stephen E. & Jungwirth, Pavel
  
• Reversible Water-Induced Phase Changes of Cobalt Oxide Nanoparticles. ACS Nano, 14(11), 15450-15457.
  Hein, Dennis; Wartner, Garlef; Bergmann, Arno; Bernal, Miguel; Roldan, Cuenya Beatriz & Seidel, Robert
  
• Spectroscopic evidence for a gold-coloured metallic water solution. Nature, 595(7869), 673-676.
  Mason, Philip E.; Schewe, H. Christian; Buttersack, Tillmann; Kostal, Vojtech; Vitek, Marco; McMullen, Ryan S.; Ali, Hebatallah; Trinter, Florian; Lee, Chin; Neumark, Daniel M.; Thürmer, Stephan; Seidel, Robert; Winter, Bernd; Bradforth, Stephen E. & Jungwirth, Pavel
  
• Insights into the electronic structure of Fe–Ni thin-film catalysts during the oxygen evolution reaction using operando resonant photoelectron spectroscopy. Journal of Materials Chemistry A, 11(15), 8066-8080.
  Wartner, Garlef; Hein, Dennis; Bergmann, Arno; Wendt, Robert; Roldan, Cuenya Beatriz & Seidel, Robert
  
• The Metal-Oxide Nanoparticle–Aqueous Solution Interface Studied by Liquid-Microjet Photoemission. Accounts of Chemical Research, 56(13), 1687-1697.
  Ali, Hebatallah; Winter, Bernd & Seidel, Robert
  
• Operando X-ray absorption spectroscopy of Fe–N–C catalysts based on carbon black and biomass-derived support materials for the ORR. Sustainable Energy & Fuels, 8(10), 2309-2320.
  Wartner, Garlef; Müller-Hülstede, Julia; Trzesniowski, Hanna; Wark, Michael; Wagner, Peter & Seidel, Robert