NSF-DFG MISSION: Operando Surface X-ray Scattering Studies of Quasi-epitaxial Growth and Electrocatalysis at Liquid Gallium Electrodes

Liquid metals are fertile platforms for inorganic materials synthesis and design. Recently, room temperature liquid metals have proven uniquely suited for the electrochemical syntheses of novel nanomaterials, new compositions of matter, and potent (electro)catalysts. A critical factor in expanding the palette of materials chemistry possible with liquid metals is a clearer understanding of the structure of the interface with molecular solutions. With support from the Division of Chemistry at NSF and DFG, Dr. Maldonado at U Michigan, Dr. Ocko at Brookhaven National Lab in US and Dr. Magnussen at Kiel University in Germany will work together to define the microscopic details of the evolution of the liquid/liquid interface between metallic gallium (Ga) and water during electrochemical reactions. The successful completion of the proposed work will lead to the development of supported electrode platforms that enable smooth, thin liquid metal films that are amenable for more precise operando and electrocatalytic studies and that are applicable to any liquid metal composition. The students involved in the research project will have the opportunity to enhance students exposure to global research and practices. This work will advance the fundamental understanding of liquid metal/liquid electrolyte behaviors on two distinct fronts. First, the electrodeposition of various metals cations onto liquid Ga electrodes will be performed to examine the physicochemical and electrochemical factors at the interface relevant to observing quasi-epitaxial crystal growth. The atomistic details of quasi-epitaxy will be unraveled by operando X-ray reflectivity and grazing incidence X-ray diffraction. As an important prerequisite for these studies, the team 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. Second, the formation and activity of supported catalytically active liquid metal platforms based on Ga will be studied. The interplay of the interface structure of the liquid metal interfacial structure and the distribution and dynamics of isolated catalytic solute atoms will be determined for the case of hydrogen evolution and electrochemical CO2 reduction. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.