Abstract
Understanding the molecular mechanism of proton conduction is crucial for the design of new materials with improved conductivity. Quasi-elastic neutron scattering (QENS) has been used to probe the mechanism of proton diffusion within a new phosphonate-based metal–organic framework (MOF) material, MFM-500(Ni). QENS suggests that the proton conductivity (4.5 × 10–4 S/cm at 98% relative humidity and 25 °C) of MFM-500(Ni) is mediated by intrinsic “free diffusion inside a sphere”, representing the first example of such a mechanism observed in MOFs.
Highlights
Functionalization of the organic linker in metal−organic framework (MOF) materials PalOlo3wHs2)th,1e0−p1e2raionddicthienitrroindturicntsioicnpoofroasciitdyicengarbolueps sth(ee.lgo.a, dSiOng3Hof, additional protonic molecules within the pore,[13−15] to yield decorated materials with improved proton conductivity
Pulsed field gradient (PFG) NMR is capable of measuring the dynamics of specific species in materials containing intrinsic structural defects
Quasi-elastic neutron scattering (QENS) has been used to investigate the intrinsic mechanism of proton diffusion within MFM-500(Ni), and this study suggests that the proton conduction in MFM-500(Ni) is mediated by the model of “free diffusion inside a sphere” rather than “jump diffusion between sites”
Summary
Quasi-elastic neutron scattering (QENS) has been used to investigate the intrinsic mechanism of proton diffusion within MFM-500(Ni), and this study suggests that the proton conduction in MFM-500(Ni) is mediated by the model of “free diffusion inside a sphere” rather than “jump diffusion between sites”. The difference in the conductivities between these isostructural materials probably correlates to the bond strength between coordinated water molecules and the metal cations, as suggested by the TGA plots and solid-state UV/vis absorption spectra (see SI). These values are comparable to those recently reported for MOFs functionalized with phosphonic acid groups under similar conditions. QENS data of MFM-500(Ni) recorded under humid conditions confirm that the proton diffusion remains as “free diffusion inside a sphere” with the same diffusion distance r = 2.25 Å (Figure S12).
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