Water-Insoluble Copper Complexes As Electrocatalysts for CO₂ Reduction

The electrochemical reduction of carbon dioxide (CO 2 R) constitutes a promising CO 2 utilization technology, allowing the production of valuable fuels and chemicals by using electrical energy from renewable sources. Nevertheless, poor selectivity and high required overpotentials hamper practical applications of the CO 2 R, which highlights the need for the development of more efficient electrocatalysts. Different copper-based materials have been extensively studied as electrocatalysts for CO 2 R. Particularly, copper complexes exhibited interesting properties under operational conditions: many of them undergo structural modifications (e.g. changes in oxidation state and/or coordination number), which potentially affect activity, selectivity and stability. Interestingly, some complexes exhibit reversible restructuring under specific conditions, which can be an interesting property to reach higher stability. In this presentation, we will show the results obtained for the electrocatalysis of water-insoluble copper complexes for the CO 2 R. The activity, selectivity and stability of both [Cu(bzimpy)Cl 2 ] and [Cu(pyrben) 2 (NO 3 )]NO 3 were investigated in K 2 SO 4 0.1 mol L -1 (CO 2 sat.) under different electrochemical conditions. Here, bzimpy and pyrben stand for 2,6-bis(2-benzimidazolyl)pyridine and 2-(2-pyridyl)benzimidazole, respectively. Qualitative EC-MS (Electrochemistry Coupled to Mass Spectrometry) analysis evidenced that both complexes are active for CO 2 reduction and that product distribution changes according to the applied potential. Quantitative gas chromatography measurements revealed that, at -1.24 V vs. RHE, [Cu(bzimpy)Cl 2 ] promotes the formation of H 2 , CO, CH 4 and C 2 H 4 with faradaic efficiencies of 26, 3.4, 9.2 and 31%, respectively. On the other hand, [Cu(pyrben) 2 (NO 3 )]NO 3 shows FE values of 24, 8.8, 15 and 24% for H 2 , CO, CH 4 and C 2 H 4 , respectively. After 1.6 h of electrolysis, the former exhibited stable current and FE of ~42% towards ethylene formation.