The selectivity of CO2 electroreduction (CO2ER) is strongly dependent on the nature of the catalyst. Among the single metals which show CO2ER activity , In and Sn are mainly HCOO -producers, while Cu shows a unique ability to reduce CO2 into a wide range of products including C1 compounds (CO, HCOO -and CH4) and C2+ hydrocarbons (C2H4, C2H5OH, and others), typically as an undesirable mixture. A variety of approaches, including surf ace nanostructuring , and tuning the electronic structure by modifying with a second metal, have been introduced to direct the selectivity of Cu towards a specific product. Several recent studies revealed that modulating the Cu surf ace with another metal, such as In or Sn, is an ef f ective strategy to tune selectivity towards either CO or HCOO -at relatively low overpotentials. Luo et al. , Rasul et al. and Zhu et al. reported high CO f aradaic efficiency (>85% CO FE) at Cu surf aces modified with In nanoparticles. On the other hand, other researchers developed Cu-In bimetallic electrocatalysts with high FE f or HCOO - (>85%). Many other studies revealed a similar behavior f or Cu-Sn systems, where researchers reported Cu-Sn catalysts with high FE towards either CO or HCOO -. For instance, Li et al. investigated CO2ER on Cu/SnO2 core-shell nanoparticles with various Sn shell thickness, finding the selectivity to strongly depend on said thickness, with thicker Sn shells showing Sn-like activity with high HCOO -selectivity (FE ~90%), while thinner shell exhibited a high CO selectivity (FE ~93%). Moreover, our recently published work reported a similar behavior f or Cu nanowires coated with ultrathin SnOx layers grown using atomic layer deposition, and detailed X-ray spectroscopic investigation revealed differing Sn speciation (i.e. oxidation state) between the COand HCOO --selective catalysts.