Facile Strategy of Directing Metal–Organic Frameworks into Hollow Nanostructures by Halide Ions

The rapid development of metal–organic frameworks (MOFs) enables the widespread potentials in catalysis, adsorption, separation/purification, and energy storage, but new re-engineering options with enhanced functions offer exciting opportunities. However, the conversion strategies to MOF derivatives in the solution-based scheme mainly involve the wet chemical reactions, for which the cation etching/exchange normally plays the vital role. Here, we report a facile and effective strategy of tuning MOFs into various hollow nanostructures by using the halide anions. The ZIF-67 MOFs would be modulated into the core–shell or completely hollow nanostructures through controlling the solvents, ions, and reaction times. The outer shell of the derivatives was the layered cobalt hydroxides without any additional metal elements from the added salts, in contrast to the cation etching strategy. Upon comparison with the pristine ZIF-67, the hollow Co(OH)2 exhibits better hydrogen evolution reaction activity with a low overpotential of 216 mV at a current density of 10 mA cm–2 and also long-term electrochemical stability. The underlying conversion mechanism by the halide anions was discussed. The finding provides a critical insight into the design and control of complex MOF-derived hollow nanostructures without foreign metal impurities, retaining the original frameworks but possessing multiple advanced functions.