Stability of van der Waals FePX ₃ materials (X: S, Se) for water-splitting applications

Abstract The interaction of high-quality transition metal trichalcogenides (TMTs) single crystals FePX ₃ (X: S, Se) with water molecules is studied using near-edge x-ray absorption fine structure (NEXAFS) and x-ray photoelectron spectroscopy (XPS) in a wide range of temperature and partial pressure of H ₂ O. The physisorption nature of interaction between H ₂ O and FePX ₃ is found at low temperatures and relatively small concentrations of water molecules, that is supported by the DFT results. When temperature of the FePX ₃ samples and partial pressure of H ₂ O are increased, the interaction at the interface is defined by two competing processes—adsorption of molecules at high partial pressure of H ₂ O and desorption of molecules due to the increased surface mobility and physisorption nature of interaction. Our intensive XPS/NEXAFS experiments accompanied by DFT calculations bring new understanding on the interaction of H ₂ O with surface of a new class of 2D materials, TMTs, pointing to their stability and reactivity, that is important for further applications in different areas, like sensing and catalysis.