CO2 Capture and Electrochemical Reduction of Low-Concentration CO2 Using a Re(I)-Complex Catalyst in Ethanol

Abstract

Direct reduction of low-concentration CO₂ from exhaust gases (3–13%) is important for CO₂ utilization technologies because CO₂ condensation processes require high energy consumption and cost. The Re(I) ethoxide complex fac-[Re(bpy-CH₂OH)(CO)₃(OEt)] (bpy-CH₂OH = 4,4′-bis(hydroxymethyl)-2,2′-bipyridine), which is formed in an EtOH solution containing a base, efficiently captured CO₂ to form the carbonate-ester complex fac-[Re(bpy-CH₂OH)(CO)₃(OCOOEt)] (Re(OCOOEt)) under both 10% and 100% CO₂ atmospheres. In an EtOH solution containing 1,1,3,3-tetramethylguanidine (TMG) as the base, the electrocatalytic CO₂ reduction reaction proceeded by Re(OCOOEt) with high CO selectivity, Faradaic efficiency, and durability even under a 10% CO₂ atmosphere. This high electrocatalysis was retained in the presence of water in the solution up to 2.8 M (5 vol %). On the other hand, the electrocatalytic CO₂ reduction reaction did not proceed efficiently in the absence of TMG under 10% CO₂. The mechanistic studies and investigation suggest that the formation of the carbonate-ester complex in advance is necessary for the highly efficient electrocatalytic reduction of low-concentration CO₂ in EtOH.