The Fabrication of Pd Single Atoms/Clusters on COF Layers as Co-catalysts for Photocatalytic H₂ Evolution

Abstract

The particle size of co-catalysts significantly affects the activity of semiconductors in photocatalysis. Herein, we report that the photocatalytic H 2 evolution (PHE) activity of a visible light responsive covalent organic framework (COF) layer supported on SiO 2 nanoparticles was greatly promoted from 47.7 to 85.5 μmol/h by decreasing the particle size of the Pd co-catalyst from 3.3 nm to single atoms/clusters. A PHE rate of 156 mmol g COF −1 h −1 and apparent quantum efficiency up to 7.3% were achieved with the Pd SAs/Cs cocatalyst. The relationship between the activity of Pd in H 2 dissociation, proton reduction, and PHE rate suggests that the promotion effect of Pd SAs/Cs is mainly attributed to their enhancement in charge separation of COF layers rather than proton reduction. Furthermore, a photoactive film was fabricated and steady production of H 2 was achieved under visible light irradiation and static conditions. The optimization of the particle size of co-catalysts provides an efficient method for enhancing the photocatalytic activity of semiconductors.

Visible-Light-Driven Production of Solar Fuels Catalyzed by Nanosized Porphyrin-Based Metal–Organic Frameworks and Covalent–Organic Frameworks: A Review

“…In all cases, there is a very small decrease in productivity within a cycle, and versus cycling, while the PXRD data indicate stability of the framework. The second one concerns the best photocatalytic rate mentioned within this review: 156 mmol g –1 h –1 (H 2 evolution) . This rate is also associated with the smallest NP (3.3 nm), which is composed of a SiO 2 particle covered with a composite built upon single Pd atoms spread inside a COF.…”

“…As polypyrrolic species, BODIPY and porphyrins are structurally related and absorb strongly in the visible spectrum, which confers them and their related materials an optical advantage. However, the best reported rate to our knowledge is 156 mmol g –1 h –1 and belongs to an ultrasmall yellow Pd-containing cocatalyst (3.3 nm) inserted inside a 2D-COF covering an SiO 2 particle …”

“…The second one concerns the best photocatalytic rate mentioned within this review: 156 mmol g −1 h −1 (H 2 evolution). 211 This rate is also associated with the smallest NP (3.3 nm), which is composed of a SiO 2 particle covered with a composite built upon single Pd atoms spread inside a COF. In this case, the diffusion of materials into and out of the particle is very fast because steric hindrance is minimal.…”

“…However, best reported rate to our knowledge is 156 mmol g −1 h −1 and belongs to an ultrasmall yellow Pd-containing cocatalyst (3.3 nm) inserted inside a 2D-COF covering an SiO 2 particle. 211 The TONs and TOFs are also crucial parameters of any catalytic process. For nanosized porphyrin-based MOFs and COFs (Table 1), the best TON and TOF values are TON = 49479, 152 TON = 24508, 166 and TOF = 12500 h −1 .…”

Metalated covalent organic frameworks: from synthetic strategies to diverse applications

“…The more relevant literature on metalated COF-based photocatalysts for the HER is summarized in Table 6 to facilitate comparison of their properties and to provide information for designing new materials. 204,250,351,352,364,376,580,581,583,585,586,591,592…”