The Synergy of Cocatalysts and Covalent Organic Frameworks for Hydrogen Evolution

Abstract

Hydrogen (H2), the next-generation green fuel, can be obtained by the catalytic splitting of water using solar and electrochemical methods and a combination of both (photoelectrochemical). Among the various porous catalytic water reduction systems developed, covalent organic frameworks (COFs) based systems are emerging in recent times due to their structural ordering and facile tunability, high thermo-chemical stability, and permanent porosity. This review provides a detailed summary and analysis of COF-based photo-, electro-, and photoelectrochemical hydrogen evolution systems. Uniquely, it includes the journey from precious noble metal to earth-abundant molecular cocatalysts for the generation of H2 and their synergetic interaction with COFs. Moreover, the focus is on outlining the core concept of heterogeneous catalytic H2 evolution, measurement techniques, photophysical and physicochemical insights, and the relationship among key components of the overall process. Finally, the advantages and pitfalls of COFs as H2 evolution systems and the design principles for optimal catalytic efficiency are discussed. A dedicated outlook section is presented at the end to benefit researchers for future developments in this emerging field.

Expanding the horizons of covalent organic frameworks: sub-stoichiometric synthesis as an emerging toolkit for functional COFs

“…49–52 The field has also witnessed the utilization of unreacted sites, the introduction of non-interfering functional groups, and post-synthetic modifications that functionalize the pores or transform the linkages. 30,33,53 The functional versatility of such framework materials has led to various applications, including gas adsorption/separation, 54–57 host–guest chemistry, 58–61 sensing, 62–68 ion capture/transport, 69 catalysis, 70–76 and electrochemical applications. 77…”

“…[49][50][51][52] The eld has also witnessed the utilization of unreacted sites, the introduction of noninterfering functional groups, and post-synthetic modications that functionalize the pores or transform the linkages. 30,33,53 The functional versatility of such framework materials has led to various applications, including gas adsorption/separation, [54][55][56][57] host-guest chemistry, 58-61 sensing, [62][63][64][65][66][67][68] ion capture/transport, 69 catalysis, [70][71][72][73][74][75][76] and electrochemical applications. 77 Focussed research activities on COFs that started with the rst report via the formation of dynamic boroxine and boronate ester bonds have now been extended to seeded growth of 2D COFs, graphene nanoribbon 2D COFs, and recently to water harvesting frameworks.…”

Enhanced Photocatalytic Activity of Calix[4]arene-Based Donor–Acceptor Covalent Organic Frameworks by Dual Cocatalysts

“…(3) Construction of donor–acceptor (D–A) structures, one of the most efficient strategies to facilitate charge separation and transport. − This approach requires the selection of electron-deficient and electron-rich structural unit interconnections, and the difference in charge density formed by the two can have an effect on charge transport. Additionally, the D–A structure bestows a more suitable band gap and enhances the efficiency of separating electron–hole pairs, thereby facilitating photocatalytic energy conversion. − …”