Light-Driven Hydrogen Evolution Assisted by Covalent Organic Frameworks

Abstract

Covalent organic frameworks (COFs) are crystalline porous organic polymers built from covalent organic blocks that can be photochemically active when incorporating organic semiconducting units, such as triazine rings or diacetylene bridges. The bandgap, charge separation capacity, porosity, wettability, and chemical stability of COFs can be tuned by properly choosing their constitutive building blocks, by extension of conjugation, by adjustment of the size and crystallinity of the pores, and by synthetic post-functionalization. This review focuses on the recent uses of COFs as photoactive platforms for the hydrogen evolution reaction (HER), in which usually metal nanoparticles (NPs) or metallic compounds (generally Pt-based) act as co-catalysts. The most promising COF-based photocatalytic HER systems will be discussed, and special emphasis will be placed on rationalizing their structure and light-harvesting properties in relation to their catalytic activity and stability under turnover conditions. Finally, the aspects that need to be improved in the coming years will be discussed, such as the degree of dispersibility in water, the global photocatalytic efficiency, and the robustness and stability of the hybrid systems, putting emphasis on both the COF and the metal co-catalyst.

Enhanced Photocatalytic Activity of Hyper‐Cross‐Linked Polymers Toward Amines Oxidation Coupled with H2O2 Generation through Extending Monomer's Conjugation Degree

“…Porous organic polymers (POPs), including covalent organic frameworks (COFs), covalent triazine frameworks (CTFs), conjugated microporous polymers (CMPs), hyper‐cross‐linked polymers (HCPs) and polymers of intrinsic microporosity (PIMs), are a series of porous materials which are composed by various organic monomer by strong covalent bond [7] . Owing to their advantages of wide light‐absorption range, tunable optical bandgaps as well as favorable mass transfer capacity, POPs have been widely used in photocatalytic organic synthesis, [8] H 2 production, [9] CO 2 reduction, [10] and organic pollutants degradation [11] . Compared with other POPs, HCPs have been considered to be excellent candidates for practical photocatalysts because of their merits, such as easy to synthesis, low cost, high stability and high visible light response capability [12] .…”

1,3,5-Triazine and dithienothiophene-based conjugated polymers for highly effective photocatalytic hydrogen evolution

“…1 Unquestionably, the rational design of photocatalysts is the crucial point for high hydrogen evolution reactivity. [2][3][4][5][6][7] Numerous inorganic semiconducting materials including metal oxides [8][9][10] and metal sulfides [11][12][13][14] have been explored as photocatalysts for the hydrogen evolution reaction (HER), but most of the inorganic photocatalysts showed low absorption in the visible light region, which limits their practical application. In recent years, organic semiconductors featuring extended delocalized π-electrons have been started to be used for PHP investigation.…”

Visible-light-induced photocatalytic reductive carbonylation of nitroarenes using formic acid as a hydrogen source over a water-dispersible CTF-based palladium catalyst

“…[23][24][25][26][27] Covalent organic frameworks (COFs) have exhibited outstanding visible-light-driven hydrogen evolution activity due to their advantages of low density, tunable band gaps, wide light-harvesting ability, porous structure nature, and delocalized π-bonds. [28][29][30] However, the recombination rate of photogenerated electronhole pairs is still very high in single-component COFs. In recent years, to improve the separation and migration of photogenerated electron-hole pairs and the transfer of photoinduced electrons in hydrogen evolution reactions, the introduction of a second semiconductor with proper band positions into covalently bonded COF heterostructures has been proved to be a feasible way that also improves the photocatalytic performance.…”