Silver Nanoparticles with Surface-Bonded Oxygen for Highly Selective CO₂ Reduction

The surface electronic structures of catalysts need to be carefully engineered in CO 2 reduction reaction (CO 2 RR), where the hydrogen evolution side reaction usually takes over under a significant overpotential, and thus dramatically lowers the reaction selectivity. Surface oxides can play a critical role in tuning the surface oxidation state of metal catalysts for a proper binding with CO 2 RR reaction intermediates, which may significantly improve the catalytic activity and selectivity. Here, we demonstrate the importance of surface-bonded oxygen on silver nanoparticles in altering the reaction pathways and improving the CO 2 RR performances. A comparative investigation on air-annealed Ag (Air-Ag) catalyst with or without the post-treatment of H 2 thermal annealing (H 2 -Ag) was performed. In Air-Ag, the subsurface chemically bonded O species (O–Ag δ+ ) was identified by angle resolved X-ray photoelectron spectroscopy and X-ray absorption spectroscopy techniques, and contributed to the improved CO selectivity rather than H 2 in CO 2 RR electrolysis. As a result, though the maximal CO Faradaic efficiency of H 2 -Ag is at ∼30%, the Air-Ag catalyst presented a high CO selectivity of more than 90% under a current density of ∼21 mA/cm 2 .