Sustained Solar H₂ Evolution from a Thiazolo[5,4-d]thiazole-Bridged Covalent Organic Framework and Nickel-Thiolate Cluster in Water

Abstract

Solar hydrogen (H 2 ) evolution from water utilizing covalent organic frameworks (COFs) as heterogeneous photosensitizers has gathered significant momentum by virtue of the COFs’ predictive structural design, long-range ordering, tunable porosity, and excellent light-harvesting ability. However, most photocatalytic systems involve rare and expensive platinum as the co-catalyst for water reduction, which appears to be the bottleneck in the development of economical and environmentally benign solar H 2 production systems. Herein, we report a simple, efficient, and low-cost all-in-one photocatalytic H 2 evolution system composed of a thiazolo[5,4- d ]thiazole-linked COF ( TpDTz ) as the photoabsorber and an earth-abundant, noble-metal-free nickel-thiolate hexameric cluster co-catalyst assembled in situ in water, together with triethanolamine (TEoA) as the sacrificial electron donor. The high crystallinity, porosity, photochemical stability, and light absorption ability of the TpDTz COF enables excellent long-term H 2 production over 70 h with a maximum rate of 941 μmol h –1 g –1 , turnover number TON Ni > 103, and total projected TON Ni > 443 until complete catalyst depletion. The high H 2 evolution rate and TON, coupled with long-term photocatalytic operation of this hybrid system in water, surpass those of many previously known organic dyes, carbon nitride, and COF-sensitized photocatalytic H 2 O reduction systems. Furthermore, we gather unique insights into the reaction mechanism, enabled by a specifically designed continuous-flow system for non-invasive, direct H 2 production rate monitoring, providing higher accuracy in quantification compared to the existing batch measurement methods. Overall, the results presented here open the door toward the rational design of robust and efficient earth-abundant COF–molecular co-catalyst hybrid systems for sustainable solar H 2 production in water.

Design, Synthesis and Characterization of Nickel‐Functionalized Covalent Organic Framework NiCl@RIO‐12 for Heterogeneous Suzuki–Miyaura Catalysis

“…[16] For this reason,m ore recent studies concerning COF applicationshave become an active area of research in organic chemistry. [37][38][39][40] Their first application in catalysis was reported in 2011b y Ding et al [2] with the robusti ncorporation of Pd II into the 2D imine-based scaffold LZU1 material. The resultant Pd/COF-LZU1 material was applied in Suzuki-Miyaura cross-coupling reactions.…”

Homolytic versus Heterolytic Hydrogen Evolution Reaction Steered by a Steric Effect

“…The viability of a hydrogen‐based energy society is depended on efficient and durable production of hydrogen . Recent efforts have resulted in the identification of many molecular catalysts for hydrogen evolution . Despite these achievements, however, understanding and further controlling reaction processes are still highly challenging .…”

Improved Photoreduction of CO2 with Water by Tuning the Valence Band of Covalent Organic Frameworks

“…Covalent organic frameworks (COFs), with high stability, large series of components, easy synthesis, modification, adjustable amplitude, etc., have emerged as a promising material class for the photoreduction of CO 2 . There have been many reports on the use of COFs as photocatalysts . However, photocatalysis using COFs alone, without the help of sacrificial agents and co‐catalysts, has rarely been reported to photoreduce CO 2 .…”