A general approach to prepare composite films of metal–organic frameworks and graphene has been
developed. Films of copper(II)-based HKUST-1 and HKUST-1/graphene composites were grown
solvothermally on glassy carbon electrodes. The films were chemically tethered to the substrate by
diazonium electrografting resulting in a large electrode coverage and good stability in solution for
electrochemical studies. HKUST-1 has poor electrical conductivity, but we demonstrate that the addition
of graphene to HKUST-1 partially restores the electrochemical activity of the electrodes. The enhanced
activity, however, does not result in copper(II) to copper(I) reduction in HKUST-1 at negative potentials.
The materials were characterised in-depth: microscopy and grazing incidence X-ray diffraction
demonstrate uniform films of crystalline HKUST-1, and Raman spectroscopy reveals that graphene is
homogeneously distributed in the films. Gas sorption studies show that both HKUST-1 and HKUST-1/
graphene have a large CO2/N2 selectivity, but the composite has a lower surface area and CO2
adsorption capacity in comparison with HKUST-1, while CO2 binds stronger to the composite at low
pressures. Electron paramagnetic resonance spectroscopy reveals that both monomeric and dimeric
copper units are present in the materials, and that the two materials behave differently upon hydration,
i.e. HKUST-1/graphene reacts slower by interaction with water. The changed gas/vapour sorption
properties and the improved electrochemical activity are two independent consequences of combining
graphene with HKUST-1.