Morphology-controlled Au nanostructures for efficient and selective electrochemical CO₂ reduction

Electrochemical conversion of CO₂ has been considered as a promising method for producing value-added chemicals. Here, we report a systematic study on the formation of Au nanostructures via electroreduction of anodic Au(OH)₃ for selective CO production by an electrochemical CO₂ reduction reaction (CO₂RR). First, we demonstrate the influence of electrochemical process parameters on the formation of Au nanostructures and Au(OH)₃. The Au nanostructure morphologies can be tuned into either pore-like or pillar-like structures by controlling the anodic potential and/or reduction current density. This distinctive morphology is associated with the electric-field-assisted transport of Au³⁺ at/near the Au(OH)₃/Au interface. Additionally, we report the catalytic activity of the morphology-controlled Au nanostructures in the CO₂RR. Both Au nanostructures exhibit significantly higher CO selectivity at a low overpotential than the untreated Au film due to the high density of grain boundaries which can assist with faster stabilization of the CO₂^- intermediate. In particular, the pore-like structures have a higher CO selectivity than the pillar-like ones at 280 mV overpotential although the pillar-like Au nanostructures have a higher CO selectivity and CO producing current density at high overpotentials. This potential-dependent CO₂RR performance of the two different Au nanostructures is discussed.