Hydrogen storage capabilities of ionothermally synthesized covalent triazine frameworks (CTFs)

Abstract

Covalent triazine frameworks (CTFs) represent an attractive new type of porous organic compounds demonstrating promising stability, nontoxicity, nitrogen functionalities and adjustable porosity. They have been greatly investigated in various applications; however, the hydrogen storage capacities of CTFs have been poorly described so far. Here, we present hydrogen storage capacities of a series of covalent triazine frameworks based on four different applied monomers (DCP, DCBP, mDCB and pDCB) synthesized via classical ionothermal route (ZnCl2, 400/600 °C). Among the synthesized CTFs, DCP shows the highest hydrogen storage capacity of 4.02 wt% at 20 bar, almost two times higher compared to the lowest value of 2.43 wt% for CTF DCBP. Furthermore, the CTF DCP outperforms with a H2 uptake of 2.95 wt% at 1 bar pressure and 77 K state-of-the-art 2D porous organic polymers and shows very high uptake capability within the reported porous polymer materials. The high hydrogen storage capability of DCP is correlated to the high nitrogen (N) content of 20.4 wt%, high fraction of pyridinic N-sites (50.3%), the largest defect structure, highest crystallinity and microporosity among the synthesized CTFs. The specific surface area (SSA) and the total pore volume (TPV) seem to not have an influential impact on the H2 storage capacity as the CTF DCP exhibits the highest H2 storage capacity with a SSA of 1737 m2 g−1 and a TPV of 0.9 cm3 g−1, the lowest values among the CTFs.