[Mo3S13] To understand the mechanism of action of the photoabsorber materials and the co-catalyst under realistic conditions such as applied bias, under illumination and in an electrolyte solution, near ambient pressure X-ray photoelectron spectroscopy (NAPXPS) can be utilized. Operating with tender X-rays (~4000 eV), this technique investigates the solid-liquid interface at pressure levels of a few millibars, with the differentially pumped electron analyzer withstanding roomtemperature water vapor pressure inside the analysis chamber. Samples with amorphous molybdenum sulfide were highly hydrophilic, stabilizing a thick water film (thickness above 40 nm), which made studies of the solid-liquid interface with NAPXPS impossible. NAPXPS observations deemed the molybdenum sulfide cluster samples suitable, given their stability and minimal hydrophilicity. NAPXPS measurements were designed not only to understand the catalysts' behavior on the surface but also to investigate the charge carrier dynamics of Sb2Se3 films through surface photovoltage, which manifests as a change in binding energy. However, no discernible effects or changes were observed at different potentials and between dark and illuminated conditions. Nevertheless, NAPXPS provided valuable insights into the stability of the molybdenum sulfide clusters as catalysts. The NAPXPS endstation at the Swiss Light Source (SLS) at the Paul Scherer Institute (PSI) has a chamber capable of operating up to 30 mbar. In this endstation, it is possible to position a beaker containing an aqueous electrolyte solution just below the inlet cone of the analyzer. After being immersed in the electrolyte, the sample can be set up in a standard three-electrode arrangement to perform in-situ cyclic voltammetry. By employing appropriate reduction-oxidation cycles through electrochemical processes, welldefined surface preparations can be accomplished, resulting in atomically pristine surfaces. The sample can be moved in front of the analyzer cone, maintaining a short distance (600 µm) from the orifice leading to the differentially-pumped lens optics. In instances involving hydrophilic surfaces, sustaining a continuous water film with a few tens of nanometers thickness is feasible, which allows probing of the liquid-solid interface when using tender X-rays (3-5 keV). With Qel = charged flowed during chronopotentiometry (C), n = 2 (number of electrons), F = Faraday constant = 96485.33 (C mol -1 ). The samples were irradiated with one sun with a white LED, and a potential of -0.2 V versus RHE (chronoamperometry, CA) was applied for specified times. Afterwards, the hydrogen gas was measured. Inserting the measured peak area into the calibration curve gives the hydrogen produced in mol (N).