Abstract
Electrochemical reduction of carbon dioxide is a clean and highly attractive strategy for the production of organic products. However, this is hindered severely by the high negative potential required to activate carbon dioxide. Here, we report the preparation of a copper-electrode onto which the porous metal–organic framework [Cu2(L)] [H4L = 4,4′,4″,4′′′-(1,4-phenylenebis(pyridine-4,2,6-triyl))tetrabenzoic acid] can be deposited by electro-synthesis templated by an ionic liquid. This decorated electrode shows a remarkable onset potential for reduction of carbon dioxide to formic acid at −1.45 V vs. Ag/Ag+, representing a low value for electro-reduction of carbon dioxide in an organic electrolyte. A current density of 65.8 mA·cm−2 at −1.8 V vs. Ag/Ag+ is observed with a Faradaic efficiency to formic acid of 90.5%. Electron paramagnetic resonance spectroscopy confirms that the templated electro-synthesis affords structural defects in the metal–organic framework film comprising uncoupled Cu(II) centres homogenously distributed throughout. These active sites promote catalytic performance as confirmed by computational modelling.
Highlights
Electrochemical reduction of carbon dioxide is a clean and highly attractive strategy for the production of organic products
The metal–organic framework (MOF) was synthesised by a conventional solvothermal reaction [denoted as Cu2(L)-t]31, which crystallised in much larger octahedralshaped crystals of several microns in size (Supplementary Fig. 4)
We have electrochemically prepared the Cu2(L)-e/Cu electrode through controllable growth of MOF nanoparticles onto a Cu-foam support
Summary
Electrochemical reduction of carbon dioxide is a clean and highly attractive strategy for the production of organic products. We report the preparation of a copperelectrode onto which the porous metal–organic framework [Cu2(L)] [H4L = 4,4′,4′′,4′′′-(1,4phenylenebis(pyridine-4,2,6-triyl))tetrabenzoic acid] can be deposited by electro-synthesis templated by an ionic liquid This decorated electrode shows a remarkable onset potential for reduction of carbon dioxide to formic acid at −1.45 V vs Ag/Ag+, representing a low value for electro-reduction of carbon dioxide in an organic electrolyte. The resultant electrode, Cu2(L)-e/Cu, shows excellent activity for the reduction of CO2 to formic acid with an onset potential of −1.45 V vs Ag/Ag+ for production of formic acid, a Faradaic efficiency (FEHCOOH) reaching 90.5% at −1.8 V vs Ag/Ag+ and a current density of 65.8 mA·cm−2 Side reactions, such as H2 evolution and reduction of Cu(II) sites, are effectively hindered at low potentials, and the catalytic mechanism has been studied by electron paramagnetic resonance (EPR) spectroscopy and density functional theory (DFT) calculations
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