The Berlin Joint Lab for Electrochemical Interfaces, BElChem: A Facility for In-situ and Operando NAP-XPS and NAP-HAXPES Studies of Electrochemical Interfaces at BESSY II

Vol. 35, No. 3, 2022, Synchrotron radiation newS Technical RepoRT The Berlin Joint Lab for Electrochemical Interfaces, BElChem: A Facility for In-situ and Operando NAP-XPS and NAP-HAXPES Studies of Electrochemical Interfaces at BESSY II DaviD E. Starr,1 MichaEl hävEckEr,2,3 axEl knop-GErickE,2,3 Marco Favaro,1 SiMonE vaDilonGa,1 MarcEl MErtin,1 GErD rEicharDt,1 Jan-SiMon SchMiDt,1 Frank SiEwErt,1 robErt Schulz,1 JEnS viEFhauS,1 chriStian JunG,1 anD roEl van DE krol1 1Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Berlin, Germany 2Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany 3Max-Planck-Institut für Chemische Energiekonversion, Mülheim, Germany Introduction The Berlin Joint Lab for Electrochemical Interfaces (BElChem) is located at the BESSY II synchrotron in Berlin, Germany, and co-run by the Fritz-Haber-Institut, the Max-Planck-Institut of Chemical Energy Conversion and the Helmholtz-Zentrum Berlin. BElChem focuses on providing a molecular-level description of (photo)electrochemical interfaces that are of high relevance for solar fuel production and renewable energy storage. The CO 2 reduction reaction (CO2RR) and the oxygen evolution reaction (OER) are of particular current interest. In BElChem, near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and near-ambient pressure hard X-ray photoelectron spectroscopy (NAP-HAXPES) will be used for the in-situ and operando interrogation of the electronic structure and chemical composition of catalytically active solid/gas and solid/liquid interfaces. BElChem will also enable heterogeneous catalytic reactions, such as oxidation and hydrogenation reactions, to be investigated. The BElChem facility consists of two beamlines with two endstations in two separate hutches and an additional sample preparation/ chemical lab. One beamline, the undulator beamline U49/2 PGM (plane grating monochromator), covers the soft X-ray energy range, whereas the other dipole magnet sourced beamline, BElChem-DCM, with a double crystal monochromator (DCM), covers the tender X-ray energy range. Combined, the BElChem beamlines cover a photon energy range nominally from 90 eV to 10 keV. Each endstation has its own electron spectrometer. The endstation frame is composed of two separate parts. On one part, the electron spectrometer is mounted and, on the other, the analysis chamber is mounted. This allows the easy exchange of experimental modules and the ability for users of BElChem to provide tailor-made modules targeting the sample environment relevant for their in-situ or operando measurement. The BElChem facility provides the opportunity to study electrochemical interfaces with two general approaches. Due to the high surface sensitivity and short mean free paths of low kinetic energy photoelectrons generated with soft X-rays, a suitable method to explore the electrode/electrolyte interface with XPS during a (photo)electrochemical reaction is needed. At BElChem, these types of measurements are carried out using dedicated electrochemical cells or setups, and generally make use of thin membranes with arrays of holes that are either open or covered with graphene, to separate the electrochemical cell from the vacuum environment. Different types of cells are available, and which cell is most appropriate will be determined by the properties of the sample and the desired experimental conditions [1]. Using tender X-rays can produce photoelectrons with higher kinetic energies than soft X-rays, facilitating the investigation of buried interfaces. At the BElChem-DCM beamline, two approaches are used to study electrified solid/liquid interfaces. With the dip-and-pull method, thin electrolyte films, on the order of a few tens of nanometers, cover the electrode surface, and tender X-ray photoemission is used to study the buried solid/electrolyte interface [1, 2]. (Photo)electrochemical reactions can also be investigated in situ using a 3-electrode H-cell [3]. The NAPHAXPES measurements are carried out such that both the X-ray excitation and electron detection occur through a thin electrolyte film. In both cases, the simultaneous detection of the activity of the electrode, product analysis, and measurement of the electrode’s chemical composition and electronic structure enables structure-function relationships to be established.