CO2electro-reduction is a promising method for sustainable production of carbon fuels as well as valuable
chemicals. Herein, we investigated a direct electro-catalytic CO2conversion to CO by nanostructured gold
catalysts from the small nanoparticles to aggregated clusters to layered film. The selectivity of CO forma-tion was found to increase as the gold amount increased and it reached a saturation point of ∼78% (−0.59 V
vs. RHE) at the morphological transition from aggregated cluster to layered film. Furthermore, the ∼4 nm
gold nanoparticle exhibited a remarkable CO formation mass activity value at 166.1 A/g (−0.59 V vs. RHE)