Construction of Donor–Acceptor Heterojunctions in Covalent Organic Framework for Enhanced CO₂Electroreduction

Abstract

Covalent organic frameworks (COFs) are promising candidates for electrocatalytic reduction of carbon dioxide into valuable chemicals due to their porous crystalline structures and tunable single active sites, but the low conductivity leads to unmet current densities for commercial application. The challenge is to create conductive COFs for highly efficient electrocatalysis of carbon dioxide reduction reaction (CO2RR). Herein, a porphyrin‐based COF containing donor–acceptor (D–A) heterojunctions, termed TT‐Por(Co)‐COF, is constructed from thieno[3,2‐b]thiophene‐2,5‐dicarbaldehyde (TT) and 5,10,15,20‐tetrakis(4‐aminophenyl)‐porphinatocobalt (Co‐TAPP) via imine condensation reaction. Compared with COF‐366‐Co without TT, TT‐Por(Co)‐COF displays enhanced CO2RR performance to produce CO due to its favorable charge transfer capability from the electron donor TT moieties to the acceptor Co‐porphyrin ring active center. The combination of strong charge transfer properties and enormous amount of accessible active sites in the 2D TT‐Por(Co)‐COF nanosheets results in good catalytic performance with a high Faradaic efficiency of CO (91.4%, −0.6 V vs reversible hydrogen electrode (RHE) and larger partial current density of 7.28 mA cm−2 at −0.7 V versus RHE in aqueous solution. The results demonstrate that integration of D–A heterojunctions in COF can facilitate the intramolecular electron transfer, and generate high current densities for CO2RR.

Conductive Phthalocyanine‐Based Covalent Organic Framework for Highly Efficient Electroreduction of Carbon Dioxide

“…These results indicated that the efficient electron transfer from the conjugated pyrazine units to the accessible nickel phthalocyanine active sites over the entire 2D ultrathin nanosheets plays a vital role in improving CO 2 RR activity. [69][70][71] The turnover frequencies (TOFs) for CO production were calculated on the basis of that all the loaded nickel phthalocyanine units in the NiPc-COF nanosheets were electrochemically active. As shown in Figures S10 of the Supporting Information, NiPc-COF presented a high TOF of 3772 h −1 at the applied potential of −1.1 V, exceeding most of the previously reported COF electrocatalysts (Table S5, Supporting Information), which highlights the superiority of the conductive 2D nanosheet structure to make a high degree of reactive sites work in boosting the activity for CO 2 RR.…”

Conductive Two‐Dimensional Phthalocyanine‐based Metal–Organic Framework Nanosheets for Efficient Electroreduction of CO2

“…[57] As shown in Figure S5, the main product of Ni 3 (HHTP) 2 is H 2 with selectivity of around 95 %t hroughout the testing range of À0.7 to À1.2 V, indicating that the NiO 4 node cannot catalyze the CO 2 RR and can be excluded as the active site in NiPc-NiO 4 for the CO 2 RR. Besides,p ure ketjen black and carbon paper electrode also only produce H 2 (Figures S6 and S7), while the ligand NiPc-OH shows certain activity toward the CO 2 RR, indicating that the active site in NiPc-NiO 4 is the NiN 4 sites of NiPc moiety.Thus,onthe basis of the NiPc motif as active site,the turnover frequency (TOF) of the NiPc-NiO 4 was calculated and summarized in Figure 3d.T he TOF of [29] CoCp 2 @MOF-545-Co, [30] PcCu-O 8 -Zn, [31] MOF-1992/CB, [32] Re-MOF film, [33] and Al 2 (OH) 2 TCPP-Co. [34] f) Stability of NiPc-NiO 4 at ap otential of À0.85 Vv ersus RHE for 10 h.…”

“…Conversion of CO 2 to value-added chemicals could help reduce the atmospheric CO 2 concentration and alleviate the dependence on fossil fuels.U sing electricity generated from renewable energy sources,C O 2 can be electrochemically reduced to energy-rich products such as carbon monoxide (CO), which is one of the most important feedstock to be used in the Fischer-Tropsch industrial process. [1][2][3][4][5] Over the past decades,v arious electrode materials for the conversion of CO 2 -to-CO have been explored, such as Au,A g, Cu metals, [6][7][8][9] metal complexes [10][11][12][13] and single-atom Fe,C o, Ni based catalysts, [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] metal-free carbons. [31][32][33] Nevertheless,i t still remains several challenges for the CO 2 electroreduction reaction (CO 2 RR), including low energy conversion efficiency,p oor selectivity and stability.T herefore,i ts till needs design and fabrication of highly active,s elective and robust electrocatalysts towards CO 2 RR.…”

“…Figure 3. a) LSV curves of NiPc-NiO 4 and NiPc-OH in CO 2 -, and Ar-saturated 0.5 MKHCO 3 .b )F aradaic efficiencies of CO, c) CO partial current density,d )turnover frequency for NiPc-NiO 4 and NiPc-OH. e) Comparison of the TOF and maximum CO partial current density with reported MOF catalysts, including Co-PMOF,[29] CoCp 2 @MOF-545-Co,[30] PcCu-O 8 -Zn,[31] MOF-1992/CB,[32] Re-MOF film,[33] and Al 2 (OH) 2 TCPP-Co [34]. f) Stability of NiPc-NiO 4 at ap otential of À0.85 Vv ersus RHE for 10 h.…”

Strategies for Improving the Catalytic Performance of 2D Covalent Organic Frameworks for Hydrogen Evolution and Oxygen Evolution Reactions

“…[67] Based on the influence of electron and hole mobility on HER catalytic activity, designing donor-acceptor (DÀ A) COFs has also received considerable attention from researchers. [68][69][70] For example, by the connection of electron-rich pyrene and electron-deficient thiazolo [5,4-d]thiazole, Wen group successfully synthesized a novel DÀ A COF (PyTz-COF) (Figure 9a). [71] The study showed PyTz-COF had an excellent ability for photoelectrochemical performance for HER.…”