High Ammonia Adsorption in MFM-300 Materials: Dynamics and Charge Transfer in Host-Guest Binding.

Ammonia (NH) is a promising energy resource owing to its high hydrogen density. However, its widespread application is restricted by the lack of efficient and corrosion-resistant storage materials. Here, we report high NH adsorption in a series of robust metal-organic framework (MOF) materials, MFM-300(M) (M = Fe, V, Cr, In). MFM-300(M) (M = Fe, V, Cr) show fully reversible capacity for >20 cycles, reaching capacities of 16.1, 15.6, and 14.0 mmol g, respectively, at 273 K and 1 bar. Under the same conditions, MFM-300(V) exhibits the highest uptake among this series of MOFs of 17.3 mmol g. neutron powder diffraction, single-crystal X-ray diffraction, and electron paramagnetic resonance spectroscopy confirm that the redox-active V center enables host-guest charge transfer, with V being reduced to V and NH being oxidized to hydrazine (NH). A combination of inelastic neutron scattering and DFT modeling has revealed the binding dynamics of adsorbed NH within these MOFs to afford a comprehensive insight into the application of MOF materials to the adsorption and conversion of NH.