Reticular Electronic Tuning of Porphyrin Active Sites in Covalent Organic Frameworks for Electrocatalytic Carbon Dioxide Reduction

Abstract

The electronic character of porphyrin active sites for electrocatalytic reduction of CO to CO in a two-dimensional covalent organic framework (COF) was tuned by modification of the reticular structure. Efficient charge transport along the COF backbone promotes electronic connectivity between remote functional groups and the active sites and enables the modulation of the catalytic properties of the system. A series of oriented thin films of these COFs was found to reduce CO to CO at low overpotential (550 mV) with high selectivity (faradaic efficiency of 87%) and at high current densities (65 mA/mg), a performance well beyond related molecular catalysts in regard to selectivity and efficiency. The catalysts are stable for more than 12 h without any loss in reactivity. X-ray absorption measurements on the cobalt L-edge for the modified COFs enable correlations between the inductive effects of the appended functionality and the electronic character of the reticulated molecular active sites.

Opportunities of Covalent Organic Frameworks for Advanced Applications

“…Initially, a model COF material (COF-366-Co) by the imine condensation of 5,10,15,20-tetrakis(4-aminophenyl)porphinato]cobalt [Co(TAP)] with 1,4-benzenedicarboxaldehyde (BDA) was synthesized for electrocatalysis studies (Figure 6). Subsequently, the performance of the catalysts was further systematically tuned by modification of the reticular structure and the current density for CO formation increases from 45 mA mg −1 for COF-366-Co, to 46 mA mg −1 for COF-366-(OMe) 2 -Co, and up to 65 mA mg −1 for COF-366-F-Co. [34] The development of robust heterogeneous chiral catalysts that can perform asymmetric reactions with high efficiency and superb enantiomeric selectivity is of great importance. [33] More significantly, COF-366-Co showed greater than 10% enhancement in CO 2 to proton selectivity over the molecular Co(TAP).…”

“…Sci. [34] Copyright 2018, American Chemical Society. a) Design and synthesis of metalloporphyrin-derived 2D covalent organic frameworks.…”

Catalytic Mechanisms and Design Principles for Single‐Atom Catalysts in Highly Efficient CO2 Conversion

“…To date, the electrocatalysts have confronted severe bottlenecks issue: poor selectivity about various accessory products in CO 2 conversion process, and loss of efficiency toward competing hydrogen evolution. [7][8][9][10] This type of catalysts contains M-N-C moiety with single atoms and is common in building metalorganic frameworks (MOFs), [11] covalent organic frameworks (COFs) [12] with transition metal macrocyclic clusters, such as porphyrin, phthalocyanine, and tetraazannulene, as well as metal-doped carbon materials [13] (e.g., graphene, carbon nanotubes, fullerene). [5,6] Therefore, CO 2 RR is much more complex than other energy-related electrochemical reactions such as oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), and it is still a great challenge to design and synthesize electrocatalytic materials with higher product selectivity and catalytic activity for CO 2 RR.…”

“…[7][8][9][10] This type of catalysts contains M-N-C moiety with single atoms and is common in building metalorganic frameworks (MOFs), [11] covalent organic frameworks (COFs) [12] with transition metal macrocyclic clusters, such as porphyrin, phthalocyanine, and tetraazannulene, as well as metal-doped carbon materials [13] (e.g., graphene, carbon nanotubes, fullerene). [7][8][9][10] This type of catalysts contains M-N-C moiety with single atoms and is common in building metalorganic frameworks (MOFs), [11] covalent organic frameworks (COFs) [12] with transition metal macrocyclic clusters, such as porphyrin, phthalocyanine, and tetraazannulene, as well as metal-doped carbon materials [13] (e.g., graphene, carbon nanotubes, fullerene).…”

An Integrated Design with new Metal‐Functionalized Covalent Organic Frameworks for the Effective Electroreduction of CO2

“…[10][11][12][13] With al arge surface/mass ratio, COFs display much higherc apacities compared to commercial used carbon-based and zeolite sorbents. [5,14,15] By using cobalt-functionalized porphyrin and biphenyl dicarboxaldehyde as building blocks, Lin et al synthesized two COFs as catalysts for the CO 2 reduction, with both showing excellent turnovern umbers and turnoverf requenciesi naqueous solvent.M eantime, the COFs retain their activity after twenty-four hours without degradation, suggesting the good long-term stability of COFs. [5,14,15] By using cobalt-functionalized porphyrin and biphenyl dicarboxaldehyde as building blocks, Lin et al synthesized two COFs as catalysts for the CO 2 reduction, with both showing excellent turnovern umbers and turnoverf requenciesi naqueous solvent.M eantime, the COFs retain their activity after twenty-four hours without degradation, suggesting the good long-term stability of COFs.…”