A new endstation to perform operando chemical analysis at solid–liquid interfaces by means of ambient pressure x-ray photoelectron spectroscopy (APXPS) is presented. The endstation is located at the Swiss Light Source and can be attached to the soft x-ray in situ spectroscopy beamline (X07DB) for solid–gas type experiments and to a tender x-ray beamline (PHOENIX I) for solid–liquid interface experiments. The setup consists of three interconnected ultrahigh vacuum chambers: one for sample preparation using surface science techniques, the analysis chamber for APXPS experiments, and an entry-lock chamber for sample transfer across the two pressure regimes. The APXPS chamber is designed to study solid–liquid interfaces stabilized by the dip and pull method. Using a three-electrode setup, the potential difference across the solid-electrolyte interface can be controlled, as is demonstrated here using an Ir(001) electrode dipped and pulled from a 0.1M KOH electrolyte. The new endstation is successfully commissioned and will offer unique opportunities for fundamental studies of phenomena that take place at solid–liquid interfaces and that are relevant for fields such as electrochemistry, photochemistry, or biochemistry, to name a few.

Photo-electro-chemical (PEC) water splitting represents a promising technology towards an artificial photosynthetic device but many fundamental electronic processes, which govern long-term stability and energetics are not well understood. X-ray absorption spectroscopy (XAS), particularly its high energy resolution fluorescence-detected (HERFD) mode, emerges as a powerful tool to study photo-excited charge carrier behavior under operating conditions. The established thin film device architecture of PEC cells provides a well-defined measurement geometry, but it puts many constraints on conducting operando XAS experiments. So far, operando cells have not been developed that enable to concurrently measure highly intense X-ray fluorescence and photo-electro-chemical current without experimental artifacts caused by O₂ and H₂ bubbles formation. Moreover, we are missing a standardized thin film exchange procedure. Here, we address and overcome the instrumental limitations for operando HERFD-XAS to investigate photo- and electrochemical thin film devices. Our cell establishes a measurement routine that will provide experimental access to a broader scientific community, particularly due to the ease of sample exchange. Our operando photo-electro-chemical cell is optimized for the HERFD-XAS geometry and we demonstrate its operation by collecting high-resolution Fe K-edge spectra of hematite (α-Fe₂O₃) and ferrite thin film (MFe₂O₄, M= Zn, Ni) photoelectrodes during water oxidation.<br>

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The role of the perovskite lattice oxygen in the oxygen evolution reaction (OER) is systematically studied in the PrBaCo2O5+δ family. The reduced number of physical/chemical variables combined with in‐depth characterizations such as neutron dif‐fraction, O K‐edge X‐ray absorption spectroscopy (XAS), electron energy loss spectroscopy (EELS), magnetization and scanning transmission electron microscopy (STEM) studies, helps investigating the complex correlation between OER activity and a single perovskite property, such as the oxygen content. Larger amount of oxygen vacancies appears to facilitate the OER, possibly contributing to the mechanism involving the oxidation of lattice oxygen, i.e., the lattice oxygen evolution reaction (LOER). Furthermore, not only the number of vacancies but also their local arrangement in the perovskite lattice influences the OER activity, with a clear drop for the more stable, ordered stoichiometry.

The perovskite-type oxide Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) is known as a highly active and stable oxygen evolution reaction (OER) electrocatalyst composited out of non-noble metals. The possibility of using the scalable flame spray synthesis (FSS) technique for the production of BSCF nanoparticles intensified the interest in this material for a future application in an alkaline water electrolyzer. A possible scale-up would require the optimization of the synthesis parameters to maximize the production rate. To further understand the influence of the synthesis parameters of the tunable FSS on the OER activity of BSCF, a systematic study was carried out by producing BSCF with different total metal concentrations (CTM), flow rates of the precursor solution (FRPS) and of the dispersion gas (FRDG). This study reveals that all three parameters have a direct impact on the OER activity of BSCF—measured in a rotating disc electrode (RDE) setup—due to the controllability of the initial Co and Fe oxidation state—indicated by X-ray absorption spectroscopy (XAS) measurements—and with that also of the oxygen vacancy concentration in the as-synthesized BSCF. This controllability enables the optimization of the OER activity of BSCF and emphasizes the importance of having Co in a lower initial oxidation state for reaching a high electrocatalytic performance.