A Theoretical and Computational Study of H$_2$ Physisorption on Covalent Organic Framework Linkers and Metalated Linkers: A Strategy to Enhance Binding Strength

TL;DR

This study uses computational methods to analyze how chelating transition metals in covalent organic frameworks can enhance hydrogen storage by increasing binding strength, providing insights for designing better storage materials.

Contribution

It introduces a detailed computational analysis of H$_2$ physisorption on metal-chelated COF linkers, highlighting the potential for improved hydrogen storage capacity.

Findings

Most complexes have binding enthalpy > 10 kJ/mol, suitable for practical storage.

Dispersion and electrostatic interactions dominate the physisorption process.

Metal chelation enhances H$_2$ binding strength in COFs.

Abstract

Hydrogen is deemed as an attractive energy carrier alternative to fossil fuels, and it is required to store for many applications. Physisorption is one of the promising ways to store H$_2$ for its practical applications. Covalent Organic Frameworks (COFs) are promising candidates for H$_2$-storage due to high porosity, surface area and tunable characteristics. To improve the hydrogen physisorption in the COFs, the chelation of transition metals (TM) in the building blocks of the framework has been studied by using first principle-based density functional theory (DFT) method. Here, we report total 96 H$_2$ complexes made of six different COF linkers and chelated with the Sc, Ti and V atoms interacting with up to H$_2$ molecules. The molecular interactions between physisorption H$_2$ and these Sc-, Ti- and V-chelated linkers have been explored in detail. The binding enthalpy of the most complexes is higher than ~10 kJ/mol, which is the basic requirement for practical H$_2$-storage. In the total interaction energy (between physisorption H$_2$ and chelated linkers), the dispersion and electrostatic interactions are dominant. This study is essential in finding out the more efficient COF linkers for practical H$_2$ storage. It can also help to improve the uptake of existing porous materials for H$_2$ storage. The present study paves a way to design transition metal chelated COFs for an effective H$_2$-storage and the knowledge gained from this study is expected to provide some inspiration for developing the corresponding experiments.