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

The surface electronic structures of catalysts need to be carefully engineered in CO2 reduction reaction (CO2RR), 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 CO2RR 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 CO2RR 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 delta+) 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 CO2RR electrolysis. As a result, though the maximal CO Faradaic efficiency of H-2-Ag is at similar to 30%, the Air-Ag catalyst presented a high CO selectivity of more than 90% under a current density of similar to 21 mA/cm(2).