[2,1,3]-Benzothiadiazole-Spaced Co-Porphyrin-Based Covalent Organic Frameworks for O₂ Reduction

Abstract

Designing N-coordinated porous single-atom catalysts (SACs) for the oxygen reduction reaction (ORR) is a promising approach to achieve enhanced energy conversion due to maximized atom utilization and higher activity. Here, we report two Co(II)-porphyrin/ [2,1,3]-benzothiadiazole (BTD)-based covalent organic frameworks (COFs; Co@ rhm -PorBTD and Co@ sql -PorBTD), which are efficient SAC systems for O2 electrocatalysis (ORR). Experimental results demonstrate that these two COFs outperform the mass activity (at 0.85 V) of commercial Pt/C (20%) by 5.8 times (Co@ rhm -PorBTD) and 1.3 times (Co@ sql -PorBTD), respectively. The specific activities of Co@ rhm -PorBTD and Co@ sql -PorBTD were found to be 10 times and 2.5 times larger than that of Pt/C, respectively. These COFs also exhibit larger power density and recycling stability in Zn–air batteries compared with a Pt/C-based air cathode. A theoretical analysis demonstrates that the combination of Co-porphyrin with two different BTD ligands affords two crystalline porous electrocatalysts having different d-band center positions, which leads to reactivity differences toward alkaline ORR. The strategy, design, and electrochemical performance of these two COFs offer a pyrolysis-free bottom-up approach that avoids the creation of random atomic sites, significant metal aggregation, or unpredictable structural features.

Single-Atom Catalysts on Covalent Organic Frameworks for Energy Applications

“…Recently, Bhunia et al reported two Co(II) COFs, Co@rhm-PorBTD and Co@sql-PorBTD, by compensating for the porphyrinic units with two different benzothiadiazole groups to introduce heteroatoms S and N (Figure 8a). 55 Highly crystalline structures were confirmed by PXRD patterns (Figure 8b) and TEM images. Their ORR performances were tested by cyclic voltammetry (CV) and linear-sweep voltammetry analyses.…”

“…39 For example, COFs using different monomers may result in different packing densities when anchoring atomic metals, which is critical for catalytic performance. 55 However, due to monomer solubility, sometimes COF structures cannot be synthesized directly and require post-treatments such as linkage interconversion. Taking the example of imine linkages, they can be transformed into amide, amine, thioazole, oxazole, quinoline, and protonated imine linkages through oxidation, reduction, molten sulfur, monomer exchange, protonation, etc., respectively.…”

“…Donor−acceptor pairs. 55,73 Copyright 2023 American Chemical Society and copyright 2023 American Chemical Society. Metal microenvironment.…”

Benzothiadiazole and its derivative-based sp2 carbon-conjugated covalent organic frameworks for photocatalytic hydrogen generation

“…Benzothiadiazole is one of the representative electron-deficient groups and has been widely used to synthesize frameworks, such as COFs 40–45 and metal–organic frameworks (MOFs). 46 For example, benzothiadiazole-based 2D imine-linked COFs were reported by Liu et al as efficient heterogeneous photocatalysts for organic transformation under visible light.…”

“…39 Besides these aforementioned applications, Liu et al synthesized sp 2 c-and imine-linked COFs using a three-component synthesis method, which exhibits higher hydrogen production activity compared with two-component COFs. 7 Benzothiadiazole is one of the representative electrondeficient groups and has been widely used to synthesize frameworks, such as COFs [40][41][42][43][44][45] and metal-organic frameworks (MOFs). 46 For example, benzothiadiazole-based 2D imine-linked COFs were reported by Liu et al as efficient heterogeneous photocatalysts for organic transformation under visible light.…”