Real-Time Monitoring Reveals Stability of Gallium Nanoparticles beyond the Thermodynamic Reduction Potential of Their Oxide Skin under CO2 Reduction Conditions

Gallium (Ga)-based liquid metals have garnered increasing attention in applications across different disciplines. Soft electronics and electrocatalysis benefit from the intriguing potential-dependent properties of Ga-based liquid metals, which include high conductivity, fluid-like properties, and a dynamic native oxide skin. Yet, the connection between the applied potential and the compositional and structural evolution of liquid metals remains underexplored at the nanoscale. This study investigates the real-time dynamic behavior of Ga nanoparticles (NPs) under applied potential and CO₂ electrocatalytic conditions, as one representative example. In situ electrochemical liquid phase transmission electron microscopy provides a picture of the local phenomena occurring at increasingly higher cathodic potentials. Notably, the NPs remain stable up to −0.9 V_RHE, which is more negative than the thermodynamic reduction potential of the native oxide skin surrounding the metallic liquid Ga core, which is around −0.56 V_RHE. Capillary-driven contact and necking between adjacent particles eventually relaxing into larger spherical particles become evident only at −1.2 V_RHE. Our results reveal that kinetics governs the stability of the oxide shell and, thus, of the liquid droplets. These findings elucidate the interplay between electrochemical potential and oxide shell dynamics, providing a mechanistic framework for understanding interfacial dynamics in liquid metal electrocatalysts and beyond.