In situ scanning tunneling microscopy studies of carbonate-induced restructuring of Ag-decorated Cu(100) electrodes

Ag-decorated Cu electrocatalysts are of great interest for electrochemical CO₂ reduction, because of an increased yield of multi-carbon products. Here, we present studies of well-defined AgCu electrodes by in situ scanning tunneling microscopy. These bimetallic model electrocatalysts are prepared by electrodepositing submonolayer Ag coverages on Cu(100) in 0.1 M H₂SO₄, resulting in monolayer islands with a hexagonal quasi-Ag(111) atomic lattice. Upon exchanging the solution at potentials in the double layer range to 0.1 M KHCO₃, pronounced Ag island restructuring towards anisotropic shapes, the nucleation and growth of new islands, and a strong reduction in surface mobility are observed. In addition, high-resolution images reveal a highly disordered molecular adlayer, contrary to the case of Ag-free Cu(100) electrodes. These observations can be explained by interactions of metal adatoms with adsorbed (bi)carbonate and show that Ag redispersion on Cu electrocatalysts may occur even in the absence of CO₂ reduction.