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

Ammonia (NH3) 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 NH3 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-III, Cr) show fully reversible capacity for >20 cycles, reaching capacities of 16.1, 15.6, and 14.0 mmol g(-1), respectively, at 273 K and 1 bar. Under the same conditions, MFM-300(V-IV) exhibits the highest uptake among this series of MOFs of 17.3 mmol g(-1). In situ 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-IV being reduced to V-III and NH3 being oxidized to hydrazine (N2H4). A combination of in situ inelastic neutron scattering and DFT modeling has revealed the binding dynamics of adsorbed NH3 within these MOFs to afford a comprehensive insight into the application of MOF materials to the adsorption and conversion of NH3.

Automated summary

A series of robust metal-organic framework materials show high NH3 adsorption capacity, with V-IV exhibiting the highest uptake. The redox-active V center enables charge transfer between host and guest, leading to the oxidation of NH3 to hydrazine. The combination of in situ techniques and modeling provides insights into the binding dynamics of adsorbed NH3 within these MOFs.