Strain-Stabilized Metastable Face-Centered Tetragonal Gold Overlayer for Efficient CO₂ Electroreduction

Abstract

Synthesis of the unconventional phase of noble metal nanocrystals may create new opportunities in exploring intriguing physicochemical properties but remains challenging. In the research field of thin film growth, the interface strain offers a general driving force to stabilize the metastable phase of epitaxial film. Herein we extend this concept to the field of noble metal nanocrystals and report the solution synthesis of metastable face-centered tetragonal Au that has not been discovered before. The successful synthesis relies on the formation of intermetallic AuCu₃@Au core-shell structure, where the interface strain stabilizes the metastable <i>fct</i> Au overlayer. Compared with the face-centered cubic Au counterpart, the metastable <i>fct</i> Au shows greatly improved catalytic activity toward CO₂ reduction to CO. The density functional theory calculations and spectroscopic studies reveal that the metastable <i>fct</i> Au upshifts the <i>d</i>-band center, which lowers the energy barrier of key intermediate COOH* formation and thus facilitates the reaction kinetics.