Ionic Covalent Organic Frameworks in Adsorption and Catalysis

The ion extraction and electro/photo catalysis are promising methods to address environmental and energy issues. Covalent organic frameworks (COFs) are a class of promising template to construct absorbents and catalysts because of their stable frameworks, high surface areas, controllable pore environments, and well-defined catalytic sites. Among them, ionic COFs as unique class of crystalline porous materials, with charges in the frameworks or along the pore walls, have shown different properties and resulting performance in these applications with those from charge-neutral COFs. In this review, current research progress based on the ionic COFs for ion extraction and energy conversion, including cationic/anionic materials and electro/photo catalysis is reviewed in terms of the synthesis strategy, modification methods, mechanisms of adsorption and catalysis, as well as applications. Finally, we demonstrated the current challenges and future development of ionic COFs in design strategies and applications.

Elaborate Modulating Binding Strength of Intermediates via Three-component Covalent Organic Frameworks for CO2 Reduction Reaction

The catalytic performance for electrocatalytic CO2 reduction reaction (CO2RR) depends on the binding strength of the reactants and intermediates. Covalent organic frameworks (COFs) have been adopted to catalyze CO2RR, and their binding abilities are tuned via constructing donor-acceptor (DA) systems. However, most DA COFs have single donor and acceptor units, which caused wide-range but lacking accuracy in modulating the binding strength of intermediates. More elaborate regulation of the interactions with intermediates are necessary and challenge to construct high-efficiency catalysts. Herein, the three-component COF with D-A-A units was first constructed by introducing electron-rich diarylamine unit, electron-deficient benzothiazole and Co-porphyrin units. Compared with two-component COFs, the designed COF exhibit elevated electronic conductivity, enhanced reducibility, high efficiency charge transfer, further improving the electrocatalytic CO2RR performance with the faradic efficiency of 97.2 % at -0.8 V and high activity with the partial current density of 27.85 mA cm-2 at -1.0 V which exceed other two-component COFs. Theoretical calculations demonstrate that catalytic sites in three-component COF have suitable binding ability of the intermediates, which are benefit for formation of *COOH and desorption of *CO. This work offers valuable insights for the advancement of multi-component COFs, enabling modulated charge transfer to improve the CO2RR activity.

Solvent Effects on Metal-free Covalent Organic Frameworks in Oxygen Reduction Reaction

Binding water molecules to polar sites in covalent organic frameworks (COFs) is inevitable, but the corresponding solvent effects in electrocatalytic process have been largely overlooked. Herein, we investigate the solvent effects on COFs for catalyzing the oxygen reduction reaction (ORR). Our designed COFs incorporated different kinds of nitrogen atoms (imine N, pyridine N, and phenazine N), enabling tunable interactions with water molecules. These interactions play a crucial role in modulating electronic states and altering the catalytic centers within the COFs. Among the synthesized COFs, the one with pyridine N atoms exhibits the highest activity, with characterized by a half-wave potential of 0.78 V and a mass activity of 0.32 A mg-1, which surpass those from other metal-free COFs. Theoretical calculations further reveal that the enhanced activity can be attributed to the stronger binding ability of *OOH intermediates to the carbon atoms adjacent to the pyridine N sites. This work sheds light on the significance of considering solvent effects on COFs in electrocatalytic systems, providing valuable insights into their design and optimization for improved performance.

Quantitative Construction of Boronic-Ester Linkages in Covalent Organic Frameworks for the Carbon Dioxide Reduction

Covalent organic frameworks (COFs) have been utilized for catalyzing the reduction of carbon dioxide (CO2RR) due to their atomic metal centers and controllable pore channels, which are facilitated by different covalent bonds. However, the exploration of boron-based linkages in these catalytic COFs has been limited owing to potential instability. Herein, we present the construction of boronic ester-linked COFs through nucleophilic substitution reactions in order to catalyze the CO2 RR. The inclusion of abundant fluorine atoms within the frameworks enhances their hydrophobicity and subsequently improves water tolerance and chemical stability of COFs. The content of boron atoms in the COF linkages was carefully controlled, with COFs featuring a higher density of boron atoms exhibiting increased electronic conductivity, enhanced reductive ability, and stronger binding affinity towards CO2 . Consequently, these COFs demonstrate improved activity and selectivity. The optimized COFs achieve the highest activity, achieving a turnover frequency of 1695.3 h-1 and a CO selectivity of 95.0 % at -0.9 V. Operando synchrotron radiation measurements confirm the stability of Co (II) atoms as catalytically active sites. By successfully constructing boronic ester-linked COFs, we not only address potential instability concerns but also achieve exceptional catalytic performance for CO2 RR.