Thermal Activation of a Copper-Loaded Covalent Organic Framework for Near-Ambient Temperature Hydrogen Storage and Delivery

Abstract

Copper(II) formate is efficiently incorporated into the pores of a 2D imine-based covalent organic framework (COF) via coordination with the phenol and imine groups. The coordinated metal ion is then reduced to Cu(I) with a thermal treatment that evolves CO2. After loading with hydrogen gas, the majority of H2 desorbs from the coordinatively saturated Cu(II) COF at temperatures < −100 °C. However, the activated Cu(I) COF retains adsorbed H2 above room temperature. Adsorption/desorption of H2 was highly reversible. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) strongly supports a molecular hydrogen interaction with Cu(I). A Kissinger analysis of variable ramp rate desorption experiments estimates the enthalpy of H2 desorption from Cu(I) at 15 kJ mol–1. The results represent an advance toward practical H2 storage and delivery in a lightweight, stable, and highly versatile material.