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

Abstract

The electroreduction of CO2 to value‐added chemicals such as CO is a promising approach to realize carbon‐neutral energy cycle, but still remains big challenge including low current density. Covalent organic frameworks (COFs) with abundant accessible active single‐sites can offer a bridge between homogeneous and heterogeneous electrocatalysis, but the low electrical conductivity limits their application for CO2 electroreduction reaction (CO2RR). Here, a 2D conductive Ni‐phthalocyanine‐based COF, named NiPc‐COF, is synthesized by condensation of 2,3,9,10,16,17,23,24‐octa‐aminophthalocyaninato Ni(II) and tert‐butylpyrene‐tetraone for highly efficient CO2RR. Due to its highly intrinsic conductivity and accessible active sites, the robust conductive 2D NiPc‐COF nanosheets exhibit very high CO selectivity (>93%) in a wide range of the applied potentials of −0.6 to −1.1 V versus the reversible hydrogen electrode (RHE) and large partial current density of 35 mA cm−2 at −1.1 V versus RHE in aqueous solution that surpasses all the conventional COF electrocatalysts. The robust NiPc‐COF that is bridged by covalent pyrazine linkage can maintain its CO2RR activity for 10 h. This work presents the implementation of the conductive COF nanosheets for CO2RR and provides a strategy to enhance energy conversion efficiency in electrocatalysis.

Conductive phthalocyanine-based metal-organic framework as a highly efficient electrocatalyst for carbon dioxide reduction reaction

“…As shown by the XANES curves in Figure 3a, the Ni absorption edge energy position of NiPc-Ni(NH) 4 is very close to that of the NiO, which suggests the valence state of Ni atom as +2 in both of the NiPc ligand and Ni(NH) 4 node [30], in alignment with the XPS result. Moreover, a weak pre-edge peak at around 8334 eV for NiPc-Ni(NH) 4 is observed, which corresponds to the dipole-forbidden but quadrupole-allowed transition from 1s to 3d [7]. Meanwhile, NiPc-Ni(NH) 4 shows a strong absorption peak at about 8340 eV similar to the reference sample NiPc, which is associated with the 1s to 4p electronic transition [7].…”

“…The space-filling structural model of NiPc-Ni(NH) 4 (Figure 1) shows 1D square channels with 1.78 nm, while running along the c direction with a distance of 0.34 nm between the stacking 2D conjugated layers. Therefore, the nitrogen atoms of the amino groups in NiPc-(NH 2 ) 8 ligands were successfully coordinated with Ni(II) ions in a square planar geometry, resulting in a fully π-conjugated 2D skeleton in NiPc-Ni(NH) 4 . In addition, no obvious peak corresponding to Ni nanoparticles (NPs) was observed in the PXRD patterns (Figure S1, Supporting Information online), implying that the Ni ions were not reduced during the synthesis process and the Ni species were in highly dispersed form.…”

“…Moreover, a weak pre-edge peak at around 8334 eV for NiPc-Ni(NH) 4 is observed, which corresponds to the dipole-forbidden but quadrupole-allowed transition from 1s to 3d [7]. Meanwhile, NiPc-Ni(NH) 4 shows a strong absorption peak at about 8340 eV similar to the reference sample NiPc, which is associated with the 1s to 4p electronic transition [7]. The results suggested that the Ni atoms in NiPc-Ni(NH) 4 adopt similar coordination configuration to NiPc with Ni-N 4 structure [35].…”

“…Thus, it is urgently desirable to reduce the CO 2 concentration to the normal level. The electrochemical conversion of CO 2 to valuable chemicals using renewable electricity is a promising alternative to realize carbon-energy balance and remit the environmental issues [2][3][4][5]. Among the electroreduction products, CO is considered as one of the important industrial feedstocks, which has been widely used for the Fischer-Tropsch synthesis to produce hydrocarbon liquid chemicals [6,7].…”

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

“…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.…”