Synergistic Effect in a Metal–Organic Framework Boosting the Electrochemical CO₂ Overall Splitting

Abstract

It is a very important but still challenging task to develop bifunctional electrocatalysts for highly efficient CO 2 overall splitting. Herein, we report a stable metal−organic framework (denoted as PcNi-Co−O), composed of (2,3,9,10,16,17,23,24-octahydroxyphthalocyaninato)) ligands and the planar CoO 4 nodes, for CO 2 overall splitting. When working as both cathode and anode catalysts (i.e., PcNi-Co−O||PcNi-Co−O), PcNi-Co−O achieved a commercial-scale current density of 123 mA cm −2 (much higher than the reported values (0.2−12 mA cm −2 )) with a Faradic efficiency (CO) of 98% at a low cell voltage of 4.4 V. Mechanism studies suggested the synergistic effects between two active sites, namely, (i) electron transfer from CoO 4 to PcNi sites under electric fields, resulting in the raised oxidizability/reducibility of CoO 4 /PcNi sites, respectively; (ii) the energy-level matching of cathode and anode catalysts can reduce the energy barrier of electron transfer between them and improve the performance of CO 2 overall splitting.

A benzimidazole-linked bimetallic phthalocyanine–porphyrin covalent organic framework synergistically promotes CO2electroreduction

“…The chemical connectivity of the NiPc-CoPor-imi-COF was investigated by Fourier transform infrared radiation (FT-IR) and 13 C solid-state nuclear magnetic resonance ( 13 C ssNMR) spectroscopies. The FT-IR spectra revealed broad bands from 3385 to 3210 cm −1 that were assigned to the free N-H and hydrogenbonded N-H of the imidazole ring, respectively, 29,30 whereas the C]N stretching vibration was evident at 1605 cm −1 (Fig.…”

“…S5, ESI †). Because of the magnetic nature of the metal ions in the framework, the signals in 13 C NMR were broad. 33,34 Thermogravimetric analysis (TGA) indicated that NiPc-CoPor-imi-COF has a high thermal stability of up to 200 °C (Fig.…”

“…A particularly promising approach to overcome this problem is the integration of a second metal species in the framework, which could further enrich the active sites and improve catalytic activity. [10][11][12][13] Recently, pioneering studies have demonstrated that bimetallic catalysts could effectively activate CO 2 due to the synergy of the two metals. [14][15][16] However, the controlled xation of two kinds of catalytically active units into COFs to obtain bimetallic COFs still remains challenging.…”

The Microstructure–Activity Relationship of Metal–Organic Framework-Based Electrocatalysts for the Oxygen Evolution Reaction at the Single-Particle Level

“…Metal–organic frameworks (MOFs) and their derivatives have attracted a great deal of attention as promising electrocatalysts due to their diverse structures, high surface area, and tunable properties. − In these catalytic reactions, electronic modulation through surface-mounted transformations, structural rearrangements, and lattice strain often occurs, which leads to the formation of their derivatives. , Although these studies illustrated the importance of understanding these changes in the structure, a direct operando study monitoring the structure transformations of MOFs during reactions and their implications for OER activity is still lacking. − Additionally, to establish a link between the microstructure and activity also necessitates an operando characterization technique that can provide accurate structural information and intrinsic activity. Recently, substantial efforts have been made to exploit new characterization tools, but with limited successes.…”

“…5,6 In situ studies based on quartz crystal microbalance (QCM) and gas chromatography (GC) reveal accurate quantified information of the catalyst or product, with little molecular information. 2,5 Discovering new design principles for catalysts requires directly probing the structure and activity of the active sites. All kinds of catalysts, such as metals, metal oxides, and even nonmetals, are used as the form of particles exhibiting diverse shapes in a wide spectrum of sizes.…”