Experimental and computational studies on oxygen functionalization of covalent triazine frameworks for enhanced hydrogen storage

Abstract

We report the hydrogen (H2) storage performance of an oxygen-functionalized covalent triazine framework (O-CTF) measured at 77 K and up to 20 bars. The O-CTF was synthesized using a carboxylic acid-functionalized carbonitrile monomer via an ionothermal nitrile trimerization reaction. Despite its lowered specific surface area (599 m2/g vs. 756 m2/g) compared to CTF-1, O-CTF exhibited an enhanced H2 storage capacity of 4.34 wt.% at 20 bars, nearly 1.61 times as high than the 2.69 wt.% H2 storage capacity of CTF-1. Furthermore, O-CTF demonstrated a notable H2 storage capacity of 2.19 wt.% at 1 bar and 77 K, emphasizing its competitive performance among other porous polymeric materials. The superior H2 uptake performance of O-CTF, as demonstrated by density-functional theory (DFT) calculations performed using the M06-2X-D3/def2-TZVPD method, was attributed to its high heteroatom content, especially the presence of oxygen. Compared to CTF-1 with nitrogen as the heteroatom (18.97 wt.%), the high oxygen and nitrogen contents (27.16 and 11.83 wt.%, respectively) of O-CTF resulted in additional accessible adsorption sites, enhancing the electrostatic/dispersion interaction with H2 molecules and increasing the adsorption capacity.