Computational investigation of liquid metal surface oxidation mechanism

Liquid metals (LMs) are promising catalytic materials due to their unique self-limiting oxide layers that significantly influence catalytic performance. However, the atomic-scale mechanisms governing oxide formation remain incompletely understood. We employed ab initio molecular dynamics (AIMD) simulations to investigate surface oxidation of three representative LM systems: gallium (Ga), eutectic gallium-indium (EGaIn), and tin-indium (SnIn). We elucidated the oxide layer characteristics in each system, showing O 2 molecules will approach the surface in a parallel orientation before adsorbing and dissociating preferentially over the base metal. Ga appears to form a self-limiting oxide layer where the oxygen is confined to the uppermost layer, forming an ultrathin 2D metal oxide network. EGaIn oxidation occurs preferentially with Ga, causing In atoms to segregate to the surface while remaining largely unoxidised. SnIn oxidation results in a thin oxide layer extending into the bulk, predominantly comprising In oxide with some Sn oxide. Electronic characterization revealed mixed ionic-covalent bonding, with EGaIn and SnIn exhibiting enhanced unoccupied states above the Fermi level. While the oxide thermodynamic stability causes surface passivation during the initial oxide formation, the kinetics of further oxidation is governed primarily by availability of reactive metal sites. These findings provide useful insights to help guide the rational design of LM-based catalysts.