Electrochemical and, more recently,
photoelectrochemical CO2 reductions have been widely investigated
to convert atmospheric
CO2 into other useful chemicals. However, understanding
the mechanism and selectivity of materials capable of reducing CO2 remains a challenge. Using plasmonic dendritic electrodes
of silver and cuprous oxide (Ag/Cu2O) and employing Raman
spectroelectrochemistry detection, we observe the selective photoelectroreduction
mechanism from CO2 to acetate as a value-added compound
instead of the more commonly reported products like methanol, ethylene,
or ethane. The selectivity, efficiency, and low overpotential (−0.4
V vs Ag/AgCl) in the CO2 reduction is favored by the basic
microenvironment, the semiconductor properties of the Cu2O, and the accumulation of hot electrons from the localized surface
plasmon resonance of the Ag nanostructure. Lateral surface interactions
between adsorbed CO species are the key to the formation of acetate.
The rate-determining step of the reaction is the single transfer of
an electron from the electrode to the CO2 molecule to reduce
it to the *CO2
– radical anion and subsequently
form adsorbed CO, which is a key intermediate in the formation of
the carbon–carbon bond during the reduction process.