High efficiency electrochemical reduction of CO2 beyond the two-electron transfer pathway on grain boundary rich ultra-small SnO2 nanoparticles

Well crystallized and interconnected SnO2 nanoparticles (<5 nm) were synthesized via oxidation of exfoliated SnS2 sheets. The SnO2 nanoparticles exhibit a high total faradaic efficiency (FE) of 97% towards electrochemical reduction of CO2 at −0.95 V vs. the reversible hydrogen electrode (RHE). The main product ratio of CO/HCOO− which intrinsically correlates to the surface SnOx/Sn ratio variation varies with the applied potential. Beyond CO and HCOO− products formed via the two-electron transfer pathway, hydrocarbons and oxygenates are produced. The formation of hydrocarbon (CH4) versus oxygenate (C2H5OH) depends on the choice of electrolyte (KOH vs. KHCO3), both of which can reach a maximal faradaic efficiency of 10%. The distinctive grain boundary and exposed corner/step sites in the interconnected SnO2 nanoparticles contribute to the high FE of CO2 reduction and unique selectivity.