2D and 3D phthalocyanine covalent organic frameworks for electrocatalytic carbon dioxide reduction

Dimensionality has great influence on the photo/electro-catalysts properties of covalent organic frameworks (COFs) because of the different electronic and porous structures. However, very rare attention has been paid on the dimensionality and function correlations of COF materials. In the present work, one new two-dimensional phthalocyanine COF, namely 2D-NiPc-COF, and one new three-dimensional phthalocyanine COF, namely 3D-NiPc-COF, were fabricated according to the imide reaction between tetraanhydrides of 2,3,9,10,16,17,23,24-octacarboxyphthalocyaninato nickel(II) with [2,2-bipyridine]-5,5-diamine and tetrakis(4-aminophenyl) methane, respectively. The crystalline structures of both COFs are verified by the powder X-ray diffraction analysis, computational simulation, and high resolution transmission electron microscopy measurement. Notably, 3D-NiPc-COF with dispersed conjugated modules has high utilization efficiency of NiPc electroactive sites of 26.8%, almost two times higher than the in-plane stacking 2D-NiPc-COF measured by electrochemical measurement, in turn resulting in its superior electrocatalytic performance with high CO2-to-CO Faradaic efficiency over 90% in a wide potential window, a large partial CO current density of −13.97 mA/cm2 at −0.9 V (vs. reversible hydrogen electrode) to 2D-NiPc-COF. Moreover, 3D-NiPc-COF has higher turnover number and turnover frequency of 5741.6 and 0.18 s-1 at −0.8 V during 8 h lasting measurement. The present work provides an example for the investigation on the correlation between dimensionality and electrochemical properties of 2D and 3D phthalocyanine COFs.