NSF-DFG MISSION: Operando surface X-ray scattering studies of quasi-epitaxial growth and electrocatalysis at liquid gallium electrodes

• Applicant: Professor Dr. Olaf Magnussen
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 541739330

Liquid metals have received substantial interest in recent years for applications in materials synthesis and catalysis, because they are capable of solvating inorganic solutes of technological interest and often exhibit a tendency for surface enrichment of these solutes. These properties enable facile crystal growth and surface reactions of catalytically active atomic solutes within the liquid metal matrix. In the proposed project, the Michigan and Kiel groups will apply their joint expertise in this area to studies of liquid gallium (Ga) electrodes in aqueous alkaline solution by in situ/operando surface X-ray scattering techniques. These methods can provide unique atomic scale data on liquid-liquid phase boundaries, which will be utilized to clarify the role of the interface structure in electrochemical metal growth and electrocatalytic processes. First, we will investigate the electrodeposition of Pb, Bi, and Pd on liquid Ga. Recent experiments by the Michigan group indicate that in these systems flat metal (Pb, Bi) and intermetallic (PdGa5) crystallites with defined orientation along the surface normal are formed. This deposit morphology suggests a quasi-epitaxial growth that is steered by ultra-thin two-dimensional precursor layers formed at the interface in the initial stages of deposition. The atomistic details and mechanisms of this process will be unraveled by operando X-ray reflectivity and grazing incidence X-ray diffraction. Second, we plan to study the formation and activity of Ga-based electrocatalysts, prepared by electrodeposition of these metals. The interplay of the interface structure of these liquid metal catalysts and their catalytic properties will be determined for the case of hydrogen evolution on Pd/Ga and electrochemical CO2 reduction on Bi/Ga. As an important prerequisite for these studies, we will investigate the interface structure of liquid Ga in metal-free aqueous base electrolyte as a function of potential and pH, focusing in particular on the presence and structure of Ga surface oxide layers. Furthermore, we will develop smooth Ga thin film electrodes for improved operando and electrocatalytic studies.

• DFG Programme: Research Grants
• International Connection: USA
• Partner Organisation: National Science Foundation (NSF)
• Co-Investigator: Privatdozentin Dr. Bridget Murphy
• Cooperation Partners: Professor Dr. Stephen Maldonado; Dr. Ben Ocko