PHOIBOS 150 HV NAP 1D-DLD

Ever since the invention of photoelectron spectroscopy, researchers have attempted to analyze materials under conditions
closely resembling their application environment. Near-Ambient Pressure X-ray Photoelectron Spectroscopy is a logical
development in this quest, since it allows for analyzing non-vacuum compatible samples in general, and phase boundaries,
such as solid|liquid or solid|gas interfaces, in particular. With the development of spectrometer systems compatible with
analysis pressures of up to 100 mbar, many novel experimental geometries have been realized since the early 2000s. Since
then, experimental capability and variety have further progressed through the proliferation of off-synchrotron laboratory
systems, and advanced sample environments to simulate material usage conditions. This progress has, e.g., enabled the
performance of operando spectroscopy during catalytic or electrochemical experiments. The present work gives, from an
instrumental point of view, a short overview over basic system design considerations and recent developments in the field.

M. Weidner and V. Streibel
表面と真空 Vol. 65, No. 3, pp. 133–138, 2022

n situ x-ray spectroscopies offer a powerful way to understand the electronic structure of the electrode–electrolyte interface under operating conditions. However, most x-ray techniques require vacuum, making it necessary to design spectro-electrochemical cells with a delicate interface to the wet electrochemical environment. The design of the cell often dictates what measurements can be done and which electrochemical processes can be studied. Hence, it is important to pick the right spectro-electrochemical cell for the process of interest. To facilitate this choice, and to highlight the challenges in cell design, we critically review four recent, successful cell designs. Using several case studies, we investigate the opportunities and limitations that arise in practical experiments.

J.-J. Velasco-Vélez, L. J. Falling, D. Bernsmeier, M. J Sear, P. C. J. Clark, T.-S. Chan, E. Stotz, M. Hävecker, R. Kraehnert, and A. Knop-Gericke
Juan-Jesús Velasco-Vélez et al 2021 J. Phys. D: Appl. Phys. 54 124003

Bismuth vanadate (BiVO₄) is an established n-type oxide semiconductor for photoelectrochemical oxygen evolution. Direct charge carrier recombination at the solid/liquid interface is a major cause of efficiency loss in BiVO₄-based devices. Intrinsic and extrinsic surface states (SSs) can act as electron and hole traps that enhance the recombination rate and lower the faradaic efficiency. In this study, we investigate the BiVO4/aqueous KPi interface using two types of samples. The samples were prepared at two different deposition and annealing temperatures (450 °C and 500 °C) leading to different morphologies and stoichiometries for the two samples. Both samples exhibit SSs in the dark that are passivated under illumination. In situ ambient pressure hard x-ray photoelectron spectroscopy experiments performed under front illumination conditions reveal the formation of a bismuth phosphate (BiPO₄) surface layer for the sample annealed at 450 °C, whereas the sample annealed at 500 °C exhibits band flattening without the formation of BiPO₄. These results imply that the light-induced formation of BiPO₄ may not be responsible for SS passivation. Our study also suggests that slight differences in the synthesis parameters lead to significant changes in the surface stoichiometry and morphology, with drastic effects on the physical-chemical properties of the BiVO₄/electrolyte interface. These differences may have important consequences for device characteristics such as long-term stability.

M. Favaro, I.Y. Ahmet, P. C. J. Clark, F. F. Abdi, M. J. Sear, R. van de Krol, and D. E. Starr
Marco Favaro et al 2021 J. Phys. D: Appl. Phys. 54 164001

We present a newly developed end-station at BESSY II dedicated to in situ Spectroscopic Analysis with Tender X-rays (SpAnTeX). The core of the end-station is a new SPECS PHOIBOS 150 HV NAP electron spectrometer. First, we show that the system has successfully achieved high electron transmission and detection efficiency under gas pressures up to 30 mbar and photon energies ranging between 200 eV and 10 keV. Second, using two features of this spectrometer (a new lateral resolution lens and a 3D delay line detector), we show that the endstation enables collection of the photoelectron spatial distribution under realistic working conditions (p ≥ 20 mbar) with a resolution better than 30 μm and the possibility to perform time resolved studies using a continuous tender X-ray source. We conclude by reporting an example of the possible experiments that can be performed using this new endstation using the Dip-and-Pull technique.

Although mainly focused on the characterization of solid/liquid interfaces using AP-HAXPES, the end-station can be used at soft X-ray beamlines for more traditional AP-XPS experiments. The Dip-and-Pull module also demonstrates good electrochemical performance. The wide pressure and photon energy range covered by this end-station also enables investigations of solid/solid, solid/gas, liquid/vapor and liquid/liquid interfaces at pressures up to 30 mbar with tender X-rays.

M. Favaro, P. C. J. Clark, M. J. Sear, M. Johansson, S. Maehl, R. van de Krol, and D.E. Starr
Surface Science
Volume 713, November 2021, 121903

This article presents an investigation of the sensing properties of chemiresistors based on Cu₂O/CuO core–shell nanowires containing p–p′ heterojunctions. The nanowires were synthesized by a conventional hydrothermal method and used for the detection of ethanol and nitrogen dioxide, reducing and oxidizing agents, respectively. To unravel the chemical processes connected with gas detection, an in situ approach was applied. This approach was based on near-ambient pressure X-ray photoelectron spectroscopy combined with simultaneous monitoring of sensor responses. The in situ measurements were performed during exposure to the analytes at a total pressure of 0.05–1.05 mbar and 450 K and were correlated with chemiresistor response measurements carried out at a standard pressure and under an ambient atmosphere. The study revealed that heterojunction treatment with ethanol vapors, accompanied by partial reduction of the nanowires, is the key step to obtaining chemiresistors with good sensing performance. While the untreated heterojunctions exhibited poor n-type sensing responses, the treated ones showed significantly improved p-type responses. The treated sensors were characterized by a stable baseline, high reversibility, detection limits estimated as 50 ppm for ethanol and 100 ppb for nitrogen dioxide, and with response times in tens of seconds. In all cases, we propose a band scheme of Cu₂O/CuO heterojunctions and a gas-sensing mechanism.
 

P. Hozák, M. Vorokhta, I. Khalakhan, K. Jarkovská, K. Jarkovská
J. Cibulková, P. Fitl, J. Vlček, J. Fara, D. Tomeček, M. Novotný, M. Vorokhta, J. Lančok, I. Matolínová, and M. Vrňata
J. Phys. Chem. C 2019, 123, 49, 29739–29749

Electrocatalysis is at the heart of our future transition to a renewable energy system. Most energy storage and conversion technologies for renewables rely on electrocatalytic processes and, with increasing availability of cheap electrical energy from renewables, chemical production will witness electrification in the near future1,2,3. However, our fundamental understanding of electrocatalysis lags behind the field of classical heterogeneous catalysis that has been the dominating chemical technology for a long time. Here, we describe a new strategy to advance fundamental studies on electrocatalytic materials. We propose to ‘electrify’ complex oxide-based model catalysts made by surface science methods to explore electrocatalytic reactions in liquid electrolytes. We demonstrate the feasibility of this concept by transferring an atomically defined platinum/cobalt oxide model catalyst into the electrochemical environment while preserving its atomic surface structure. Using this approach, we explore particle size effects and identify hitherto unknown metal–support interactions that stabilize oxidized platinum at the nanoparticle interface. The metal–support interactions open a new synergistic reaction pathway that involves both metallic and oxidized platinum. Our results illustrate the potential of the concept, which makes available a systematic approach to build atomically defined model electrodes for fundamental electrocatalytic studies.

F. Faisal, C.Stumm, M. Bertram, F. Waidhas, Y. Lykhach, S.Cherevko, F. Xiang, M. Ammon,
M. Vorokhta, B. Šmíd, T. Skála, N. Tsud, A. Neitzel, K. Beranová, K. C. Prince, S. Geiger,
O. Kasian, T. Wähler, R. Schuster, M. A. Schneider, V. Matolín, K. J. J.
Nature Materials volume 17, pages 592–598 (2018)