Surface properties of Ga–Cu based liquid-metal alloys: impact of Cu dilution, topography, and alloy liquefaction

We studied the surface properties of Ga-Cu based liquid metal alloys - a promising material system for supported catalytically active liquid metal solutions (SCALMSs). The impact of Cu dilution in the (liquid) Ga matrix is in-detail investigated by X-ray and UV photoelectron spectroscopy (XPS/UPS) and machine-learned-force field (ML-FF) calculations. With decreasing Cu content, microscopic and macroscopic Ga-Cu model samples exhibit a shift of the Cu 2p core level line to higher binding energies (<i>E</i> _b) as well as a correspondingly shifted and narrowed d-band with respect to pure Cu, which we ascribe to site isolation. To study the property evolution of Ga-Cu at SCALMS reaction conditions, <i>i.e.</i>, where Cu is present in liquid Ga, additional XPS measurements were performed between 100 and 500 °C. The observed Cu 2p shift to lower <i>E</i> _b is tentatively ascribed to changes in the local environment with increasing temperature, <i>i.e.</i> bond elongation, which is corroborated by ML-FF simulations; the increased Cu surface content at low temperatures is attributed to the presence of crystallized Cu-rich intermetallic compounds, as evidenced by transmission electron microscopy images. In an attempt to generalize the findings for filled d-band transition metals (TMs) in liquid Ga, first results on Ga-Ag and Ga-Au model systems are presented. The observed insights may be another step of paving the way for an insight-driven development of low-temperature melting liquid metals for heterogeneous catalysis.