Maximizing Electroactive Sites in a Three-dimensional Covalent Organic Framework for Significantly Improved Carbon Dioxide Reduction Electrocatalysis.

Synthesis of functional 3D COFs with irreversible bond is challenging. Herein, 3D imide-bonded COFs were constructed via the imidization reaction between phthalocyanine-based tetraanhydride and 1,3,5,7-tetra(4-aminophenyl)adamantine. These two 3D COFs are made up of interpenetrated pts networks according to powder X-ray diffraction and gas adsorption analyses. CoPc-PI-COF-3 doped with carbon black has been employed to fabricate the electrocatalytic cathode towards CO2 reduction reaction within KHCO3 aqueous solution, displaying the Faradaic efficiency of 88-96% for the CO2-to-CO conversion at the voltage range of -0.60~-1.00 V (vs. RHE). In particular, the 3D porous structure of CoPc-PI-COF-3 enables the active electrocatalytic centers occupying 32.7% of total cobalt-phthalocyanine subunits, thus giving a large current density (jCO) of -31.7 mA cm-2 at -0.90 V. These two parameters are significantly improved than the excellent 2D COF analogue (CoPc-PI-COF-1, 5.1%&21.2 mA).