Covalent Organic Frameworks Based Heterostructure in Solar‐To‐Fuel Conversion

Abstract

Photocatalytic reactions for fuel generation are crucial for the world's energy needs. Covalent‐Organic‐Frameworks (COFs) have been extensively studied as promising designable photocatalysts for these reactions due to their efficient visible‐light absorption, suitable energy‐band structure, facilitated intramolecular charge separation, and fast mass transfer. However, the activities of pristine COFs remain unsatisfactory, due to intermolecular charge recombination. Recently, COF‐based heterostructures, which combine COFs with metal‐sulfides, metal‐oxides, carbon materials, or MOFs, have attracted increasing attention for enhancing solar‐to‐fuel conversion efficiency by facilitating interfacial photo‐generated carrier separation, sensitizing wide‐gap semiconductors, and promoting surface redox reactions. Thus, a review of the state‐of‐the‐art progress of COF‐based heterostructure photocatalysts in reactions such as H2 evolution, CO2 reduction, O2 evolution, H2O splitting and CO2 splitting is crucial for the design of new photocatalysts to promote solar‐to‐fuel conversion. In this review, the COF‐based heterostructures photocatalysts are highlighted based on their synthesis, properties, and reasons for enhanced activities. Moreover, design principles are raised for such photocatalysts for each fuel generation reaction, based on insights into related research. Finally, this review is concluded by proposing future trends for COF‐based heterostructures photocatalysts, with attention to the design of COFs and supports, analyzing the photocatalytic reaction dynamics, together with considering practical applications.

Recent progress on covalent organic frameworks for photocatalytic hydrogen generationviawater splitting

“…Up to now, COFs have great potential for various applications, including gas adsorption and separation, sensing, heterogeneous catalysis, energy storage and other aspects. 32–39 Furthermore, numerous research findings have indicated that two-dimensional (2D) COFs possess excellent semiconductor properties and are a new type of superior photocatalysts, particularly for hydrogen generation via water splitting. As metal-free semiconductor photocatalysts, the advantages of 2D-COFs can be described as follows: first, one-dimensional nanopores with large surface area provide space for transport, action and transformation of matter, and also increase exciton utilization.…”

Selective Integrating Molecular Catalytic Units into Bipyridine-Based Covalent Organic Frameworks for Specific Photocatalytic Fuel Production

“…Utilizing solar energy, photocatalytic H 2 O splitting, and CO 2 reduction to produce energy-rich compounds is anticipated to offer a solution to the issues of fossil fuel shortages and global warming. − Due to their well-defined structure, definite catalytic mechanisms, and high product selectivity, molecular catalysts, especially noble-metal complexes, are widely used in the fields of H 2 evolution reaction (HER), − water oxidation, − and CO 2 reduction reaction (CO 2 RR). − However, the practical application of these noble-metal catalysts has been impeded by their limited reserves and high prices. The heterogenization of these homogeneous molecular catalysts is regarded as an effective approach to enhance their recycling efficiency, thereby reducing usage costs. − …”

Selective anchoring of Pt NPs on covalent triazine-based frameworks via in situ derived bridging ligands for boosting photocatalytic hydrogen evolution

“…4,5 Covalent organic frameworks (COFs) have attracted extensive attention as a promising candidate for H 2 production due to their visible light absorption, high stability and suitable conduction band position. 6,7 However, pure COFs still require the participation of noble metals (especially Pt with a high work function) as cocatalysts to show photocatalytic activity to promote charge separation. 8,9 Nevertheless, the high cost and high surface energy of Pt remain major hurdles, limiting its wide application.…”