Hydrogen Storage with Spectroscopic Identification of Chemisorption Sites in Cu-TDPAT via Spillover from a Pt/Activated Carbon Catalyst

Abstract

Hydrogen spillover to the Cu-TDPAT (TDPAT = 2,4,6-tris(3,5-dicarboxylphenylamino)-1,3,5-triazine) metal–organic framework is probed with adsorption measurements, ex situ characterization techniques, and density functional theory (DFT) calculations. At 1 bar and 300 K, hydrogen chemisorption to Pt/AC/Cu-TDPAT exceeds that expected for physisorption by 8-fold, which is attributable to both catalyst insertion and the creation of structural defects. Hydrogenation of (a) the Cu–O–C bond of the Cu paddlewheel, (b) the sp2 N heterocycle, and (c) the secondary amine is demonstrated with ex situ spectroscopy. Exothermic (with respect to H2) hydrogenation at the Cu–O–C bond of the paddlewheel is substantiated by DFT. However, hydrogenated Cu–O–C is metastable, as evidence for dissociation is found at higher temperature (i.e., 473 K H2). DFT calculations demonstrate hydrogenation of the N groups may occur exothermically only for a charged ligand, suggestive that defects may contribute to hydrogen chemisorption. At high pressure, slow adsorption rates and material instability render the material unsuitable for practical hydrogen storage applications.