For the fresh Ag200 catalyst, Ag is the main element detected up to the highest sputter dose. The detected small fluorine intensity originates from the PTFE substrate (Fig. ). After 24 hours of CO2RR using the Ag200 catalyst (Fig. ), it can be seen for the first few sputter-cycles a large amount of K is present. Oxygen is also present at the surface with its intensity decreasing with the sputter depth. This is in line with the XPS measurements, concerning the penetration of the KHCO3 electrolyte in the catalyst's surface. A tiny amount of Cu was also detected, which is most likely a contamination from the prolonged catalytic tests (minor leakage of Cu from tapes or wires), which still can be detected with LEIS.