A benzimidazole-based covalent organic framework anchoring a single Pt atom
Hydrogen (H2) is a clean, carbon-free fuel with a high gravimetric energy density and is emerging as an attractive alternative to non-renewable fossil resources. Photocatalytic water splitting via semiconductors provides a promising economical and environmentally friendly route to convert unlimited solar energy into H2. The light-driven hydrogen evolution (HER) reaction involves light harvesting, charge separation and transport, and surface proton reduction. The slow reduction of protons at multi-electron interfaces usually occurs within milliseconds or longer, whereas the photoexcited state usually relaxes and returns to the ground state. through radiative or irradiative recombination in a few picoseconds. Formation of abundant long-lived electrons with timely transport to reactive sites for proton reduction is considered a major problem of HER but remains one of the challenges for designing photocatalysts.
Hydrogen (H2) is a clean, carbon-free fuel with a high gravimetric energy density and is emerging as an attractive alternative to non-renewable fossil resources. Photocatalytic water splitting via semiconductors provides a promising economical and environmentally friendly route to convert unlimited solar energy into H2. The light-driven hydrogen evolution (HER) reaction involves light harvesting, charge separation and transport, and surface proton reduction. The slow reduction of protons at multi-electron interfaces usually occurs within milliseconds or longer, whereas the photoexcited state usually relaxes and returns to the ground state. through radiative or irradiative recombination in a few picoseconds. Formation of abundant long-lived electrons with timely transport to reactive sites for proton reduction is considered a major problem of HER but remains one of the challenges for designing photocatalysts.
Co-catalysts are usually involved in HER to accelerate the transfer of electrons to protons. COF offers versatile affinities for modulating and stabilizing co-catalysts and maximizing their efficiency, especially for precious metal co-catalysts such as single atom Pt. Strategies such as pre-appointment, post-modification, and hybridization with other materials have been used to develop COF-based photocatalysts for HER. However, the function of COF relies heavily on building blocks, making synthesis and modulation of structures through important monomer designation. Although COFs are usually synthesized from highly symmetrical and rigid building blocks, the use of asymmetric monomers can greatly enrich the variety, physicochemical properties and functions of COFs. Nonetheless, the intrinsic mismatch between crystal isotropy and anisotropy of asymmetric building blocks poses a challenge in synthesis. While COF containing asymmetric monomers has been used in the fields of gas adsorption and fuel cells, it has not yet been applied in the fields of photocatalysis and metal supported catalysts, especially monoatomic catalysts.
Recently, a research team led by Prof. Yu Zhou and Prof. Jun Wang from Nanjing Tech University, China, reported the construction of a highly active covalent organic framework (COF) from an unusual benzimidazole monomer in a microwave-assisted solvothermal pathway. With a single atomic Pt site as cocatalyst, benzimidazole based COFs exhibit high HER levels up to 115 mmol g–1 H–1 and the replacement frequency is 4475.1 hours–1 under visible light irradiation. The above performance relies on the combined effect of the benzimidazole group and the COF framework, which, on the one hand, stabilizes the photogenerated electrons to extend the electron lifetime, and on the other hand, provides a strong host interaction that results in the creation of single atomic Pt sites and acceleration of electron transfer to Pt active site for proton reduction. This work demonstrates perspectives in the construction of electron stabilization and interfacial charge transfer pathways for HER processes, which can be achieved by the molecular-level design of COF-based organic semiconductors using structurally and functionally diverse asymmetrical building blocks. The results are published in Chinese Journal of Catalysis (https://doi.org/10.1016/S1872-2067(23)64422-5).
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About the Journal
Chinese Journal of Catalysis co-sponsored by the Dalian Institute of Chemical Physics, Chinese Academy of Sciences and Chinese Chemical Society, and currently published by the Elsevier group. This monthly journal publishes in English timely contributions of original and carefully reviewed manuscripts covering all areas of catalysis. This journal publishes Reviews, Accounts, Communications, Articles, Highlights, Perspectives and Viewpoints of high scientific value which help to understand and define new concepts in both fundamental problems and practical applications of catalysis. Chinese Journal of Catalysis ranks among the top two journals in Applied Chemistry with a current SCI impact factor of 12.92. The Chief Editor is Prof. Can Li and Tao Zhang.
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