The development of solid-state proton-conducting materials with high conductivity that operate under both anhydrous and humidified conditions is currently of great interest in fuel-cell technology. A 3D metal-organic framework (MOF) with acid-base pairs in its coordination space that efficiently conducts protons under both anhydrous and humid conditions has now been developed. The anhydrous proton conductivity for this MOF is among the highest values that have been reported for MOF materials, whereas its water-assisted proton conductivity is comparable to that of the organic polymer Nafion, which is currently used for practical applications. Unlike other MOFs, which conduct protons either under anhydrous or humid conditions, this compound should represent a considerable advance in the development of efficient solid-state proton-conducting materials that work under both anhydrous and humid conditions.
A metal–organic framework (MOF) having superprotonic conductivity, MOF‐808, is prepared by modulating the binding mode of the sulfamate (SA) moieties grafted onto the metal clusters. The activation of the SA‐grafted MOF‐808 at 150 °C changes the binding mode of the grafted SA from monodentate to bridging bidentate, thus converting the neutral amido (‐S−NH2) moiety of the grafted SA to the more acidic cationic sulfiliminium (‐S=NH2+) moiety. Further, the acidic sulfiliminium moiety of MOF‐808‐4SA‐150 results in more efficient proton conduction than the amido moiety of MOF‐808‐4SA‐60. At 60 °C and 95 % relative humidity, MOF‐808‐4SA‐150 is found to have a proton conductivity of 7.89×10−2 S cm−1, which is more than 30‐times higher than that of MOF‐808‐4SA‐60. Moreover, this superprotonic conductivity is well maintained over 1000 cycles of conductivity measurements and for similar cyclic measurements each day for seven days.
The development of solid‐state proton‐conducting materials with high conductivity that operate under both anhydrous and humidified conditions is currently of great interest in fuel‐cell technology. A 3D metal–organic framework (MOF) with acid–base pairs in its coordination space that efficiently conducts protons under both anhydrous and humid conditions has now been developed. The anhydrous proton conductivity for this MOF is among the highest values that have been reported for MOF materials, whereas its water‐assisted proton conductivity is comparable to that of the organic polymer Nafion, which is currently used for practical applications. Unlike other MOFs, which conduct protons either under anhydrous or humid conditions, this compound should represent a considerable advance in the development of efficient solid‐state proton‐conducting materials that work under both anhydrous and humid conditions.
Chimeric metal–organic frameworks (CMOFs) composed
of symmetry-mismatched
inorganic and organic building blocks are rare because the interconnections
between these blocks are topologically demanding. Herein, an MOF with
symmetry-matched building blocks is used as a self-template for the
template-assisted synthesis of CMOFs. Specifically, the post-synthetic
transformation of the [Zn4O(COO)6] clusters
in the self-templating MOF into the [Fe3
IIIO(COO)6]+ clusters with symmetry-mismatched trigonal prismatic
site symmetry affords isoreticular CMOFs while maintaining the template
morphology and crystallinity. The framework strain of CMOFs due to
the symmetry-mismatched linkages between their building blocks is
reduced by modulating the conformation of organic building blocks
with torsional degrees of freedom. The further transformation of [Fe3
IIIO(COO)6]+-based CMOFs
through redox-facilitated metal exchange using Cr2+ ions
yields highly stable isostructural CMOFs containing [Cr3
IIIO(COO)6]+ clusters and exhibiting
stabilities in strongly acidic and moderately basic media comparable
to those of prototypical [Cr3
IIIO(COO)6]+-based MOFs with symmetry-matched building blocks. These
results hold significant potential and highlight the vast opportunities
for revisiting well-known yet fragile MOFs built upon the zinc acetate
clusters.
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