Structural Regulation of Coupled Phthalocyanine–Porphyrin Covalent Organic Frameworks to Highly Active and Selective Electrocatalytic CO₂ Reduction

Abstract

unsatisfactory conversion efficiency and product selectivity, and thus seeking novel electrocatalysts for highly active and selective CO 2 RR is a key issue. [7,8] Recently, carbon-based materials and complexes containing M-N 4 single-atom sites have been widely used as CO 2 RR electrocatalysts owing to their easy-tocontrol and highly exposed single-atom active sites. [9][10][11][12] Among them, metal phthalocyanines (MPcs) with unique M-N 4 units have been extensively used as efficient electrocatalyst since the metal center (M = Mn, Fe, Co, Ni, or Cu) has significant impact on the CO 2 RR performance. [13][14][15] For instance, it was reported that CoPc has a higher Faraday efficiency (99%) than the other MPcs at −0.80 V due to the moderate *CO binding energy at the Co active site, which is beneficial to the *COOH formation and the *CO desorption. [13] However, the poor intrinsic conductivity of such molecular catalysts usually results in low current density. [14,15] Although integrating these molecular catalysts with carbon substrate (e.g., carbon black, carbon nanotubes, or graphene) to form hybrid material can improve the conductivity, it is difficult to solve the uniformity of catalytic sites due to the molecular agglomeration, which usually cause an unsatisfactory CO 2 RR activity and stability. [16][17][18][19][20] Assembling the M-N 4 single-site molecules into covalent organic frameworks (COFs) or covalent organic polymers (COPs) is expected to be an ideal way since the catalytically active sites in such materials are usually separated by the linking units so as to expose more active sites, and the porous structure also allows rapid mass transport. [21][22][23][24][25][26][27][28][29] In addition to facilitating the mechanism research due to the well-defined metal center, those COFs/COPs also have some attractive features, such as controllable structure and pore size, good chemical stability, and easy composite with other materials. [30][31][32] Especially, the controllable pore size shows great application prospects in electrochemical and gas separation applications. [27,33] For example, when the phthalocyanine in CuPcF 8 -CoPc COF is replaced by naphthalocyanine, the pore size is enlarged from 1.1 to 1.3 nm, and thus the CO 2 RR activity was improved obviously. [27] Besides regulating the pore size, introducing electron-rich building blocks into COFs or COPs is also beneficial for the catalytic process. For example, porphyrin with electron-rich conjugated structure can transfer electrons to the catalytic Covalent organic frameworks (COFs) have been applied as potential electrocatalysts for CO 2 reduction reaction (CO 2 RR) due to their adjustable architecture and porous feature. Herein, tetraanhydrides of 2,3,9,10,16,17,23,24-octacarboxyphthalocyanine cobalt(II) (CoTAPc) are used as nodes to couple with 5,15-di(4-aminophenyl)-10,20-diphenylporphyrin (DAPor) or 5,15,10,20-tetrayl(4-aminophenyl)porphyrin (TAPor) via imidization reaction to fabricate novel coupled phthalocyanine-porphyrin Type 1:2 (CoPc-2...

Piperazine-Linked Metalphthalocyanine Frameworks for Highly Efficient Visible-Light-Driven H2O2 Photosynthesis

“…Unfortunately, the limited electronic absorption region below 600 nm for these COF photocatalysts associated with their small conjugated building blocks (e.g., biphenyl, triphenylamine, triazine, and pyrene) significantly hinders the further improvement of their overall photosynthesis performance due to the ineffective utilization of visible and near-infrared light. Fortunately, quite recently, 2D COFs with a fully conjugated structure, robust stability, high intrinsic electrical conductivity, and excellent light absorption capacity in the visible region have been fabricated from planar conjugated building blocks including porphyrin, phthalocyanine (Pc), and hexabenzocoronene via aromatic linkages. − Particularly, metallic Pc building blocks with M-N 4 coordination configuration have been revealed to act as efficient active sites for catalyzing various reactions as exemplified by the high selectivity and activity of CoPc toward 2e – ORR. − As a consequence, 2D CoPc-based COFs with a fully conjugated structure have been expected to be promising photocatalysts for H 2 O 2 photosynthesis.…”

Electronic Tuning of Active Sites in Bifunctional Covalent Organic Frameworks for Photoassisted CO2 Electrocatalytic Full Reaction

“…Covalent organic frameworks (COFs), a kind of famous porous crystalline frameworks that are constructed from periodically connected organic monomers by covalent bonds, − have received widespread attention in the fields of electro-/photocatalysis, sensing, gas storage/separation, energy storage, etc. With the inert high crystallinity and stability, large specific surface area, and small density, COFs are notable materials with tunable functionality originating from their molecularly designable constructs. − During past decades, COFs, especially that with metalloporphyrin or metallophthalocyanine counterparts, have been proven to be potential catalysts for the electrocatalytic CO 2 RR in the generation of products like CO, HCOOH, CH 4 or C 2 H 4 , etc. − Based on this, they might be desired candidates for the extended photoassisted CO 2 electroreduction coupling pollutant degradation owing to their superiority in flexible structure design that might fulfill the multirequirements (e.g., photo-sensitivity or electro-activity) of this powerful system. Therefore, we intend to study the possibility of COF-based catalysts as the bifunctional electrode catalysts with both photo-sensitive and electro-active units to explore the photoassisted CO 2 electroreduction coupling pollutant degradation, yet the applications of COFs in such systems have been rarely reported and remain a hot topic with daunting challenges to be explored.…”

Cobalt-phthalocyanine-modified two-dimensional cobalt hydroxide complexes for highly selective electrocatalytic reduction of CO2to CO

“…19 CoPc@MWCNT catalyst prepared from CoPc and MWCNT exhibited a high FE(CO) of over 95% at −0.80 V vs. RHE. 20 Therefore, the catalyst modified with CoPc can effectively promote the CO 2 RR to produce CO. 21–24 The metal center of metal phthalocyanine is considered the active site for the CO 2 RR. The direct electronic interaction between the metal center of phthalocyanine and the support would be beneficial to the electrocatalytic performance of CO 2 .…”