Electrocatalysts Derived from Copper Complexes Transform CO into C2+ Products Effectively in a Flow Cell

Electrochemical reactors that electrolytically convert CO2 into higher-value chemicals and fuels often pass a concentrated hydroxide electrolyte across the cathode. This strongly alkaline medium converts the majority of CO2 into unreactive HCO3- and CO32- byproducts rather than into CO2 reduction reaction (CO2RR) products. The electrolysis of CO (instead of CO2) does not suffer from this undesirable reaction chemistry because CO does not react with OH-. Moreover, CO can be more readily reduced into products containing two or more carbon atoms (i. e., C2+ products) compared to CO2. We demonstrate here that an electrocatalyst layer derived from copper phthalocyanine (CuPc) mediates this conversion effectively in a flow cell. This catalyst achieved a 25 % higher selectivity for acetate formation at 200 mA/cm(2) than a known state-of-art oxide-derived Cu catalyst tested in the same flow cell. A gas diffusion electrode coated with CuPc electrolyzed CO into C2+ products at high rates of product formation (i. e., current densities >= 200 mA/cm(2)), and at high faradaic efficiencies for C2+ production (FEC2+; >70 % at 200 mA/cm(2)). While operando Raman spectroscopy did not reveal evidence of structural changes to the copper molecular complex, X-ray photoelectron spectroscopy suggests that the catalyst undergoes conversion to a metallic copper species during catalysis. Notwithstanding, the ligand environment about the metal still impacts catalysis, which we demonstrated through the study of a homologous CuPc bearing ethoxy substituents. These findings reveal new strategies for using metal complexes for the formation of carbon-neutral chemicals and fuels at industrially relevant conditions.

Automated summary

In this study, a copper phthalocyanine catalyst layer was used to successfully electrolyze CO2 into high-value chemicals and fuels. Compared to traditional CO2 electrolysis, CO electrolysis can produce products containing two or more carbon atoms more efficiently. These findings provide new strategies for the development of sustainable carbon-neutral chemicals and fuels.