Bromine anion mediated epitaxial growth of core–shell Pd@Ag towards efficient electrochemical CO2 reduction

Noble-metal core–shell nanostructures are promising electrocatalysts for CO2 reduction thanks to their interfacial configurations which are beneficial for electrocatalytic kinetics, but are severely limited to a few couples that require tiny lattice mismatches (<3%) between two metals for classical epitaxial growth. Herein, non-classical epitaxial growth mediated by bromine anions (Br−) is proposed to surmount the thermodynamic limitation of largely mismatched Ag and Pd lattices (5.012%), resulting in core–shell Pd@Ag cubes that are unavailable via conventional strategies. As evidenced, Br− strongly bonded on the surface of Pd seeds serves as a buffer layer (possibly AgBr) to relieve interfacial strains and enable the epitaxial growth of Ag lattices. Due to interfacial electron-transfer, the engineered Ag sites enhance efficient CO2 reduction to CO (faradaic efficiency ∼85% at −0.8 V vs. RHE in 0.5 M KHCO3), superior to the counterparts of Pd octahedrons, Ag nanoparticles and Pd–Ag nanoalloys. Providing new insights into the epitaxial growth of core–shell nanocrystals, this study is anticipated to inspire new design strategies for active and selective electrocatalysts.