The Role of Pore Diameter on Tuning the Hydrogen Storage Capacity of Yttrium Atom-Decorated Covalent Organic Frameworks: A Theoretical Study

The electronic structure and hydrogen storage properties of benzene-based covalent organic frameworks (COFs) with pore diameters of 0.53, 0.99, and 1.45 nm are studied using density functional theory calculations. The studied COFs show poor H₂ molecule adsorption properties. To enhance their H₂ molecule adsorption properties, Y atoms are decorated on the COFs with an average binding energy of about 5–6 eV per Y atom. Each Y atom of Y-decorated COFs, YCOF1, YCOF2, and YCOF3 effectively adsorbs six H₂ molecules with an average H₂ adsorption energy of −0.28, −0.34, and −0.35 eV per H₂ molecule, respectively. The H₂ molecule storage capacity of YCOF1, YCOF2, and YCOF3 is found to be 4.7%, 5.1%, and 6.5% with desorption temperatures of 358, 434, and 447 K, respectively. The findings show that a larger pore diameter provides more space for metal atom decoration and thereby increases the H₂ molecule adsorption capacity. The H₂ molecule adsorption weight percentage of YCOF3 meets the target H₂ molecule storage capacity suggested by the U.S. Department of Energy and Fuel Cells and Hydrogen Joint Undertaking (FCH-JU) in Europe.