Dalton Trans
Beijing Spacecrafts Manufacturing Factory, Beijing 100094, PR China.
Published: November 2024
Proton-conducting metal-organic frameworks (MOFs) have attracted tremendous attention for their promising application in proton-exchange membrane fuel cells. Water clusters play an extremely important role in the proton-conduction process and affect the proton conductivity of host materials. To date, the close-packing effect of water clusters within pores on proton conductivity due to the amorphous structure of commercial proton-exchange membranes is unclear. Herein, we prepared two crystalline MOFs containing different water clusters, namely, [Sm(fum)(HO)]·3HO (Sm-fum-7HO) and [Er(fum)(HO)]·8HO (Er-fum-12HO) (Hfum = fumaric acid), and regulated their proton conductivities by changing the water clusters. As expected, Sm-fum-7HO showed a high proton conductivity of 6.89 × 10 S cm at 333 K and ∼97% RH because of the close packing of the water clusters within the pores triggered by a lanthanide contraction effect, outperforming that of Er-fum-12HO and some previously reported MOFs. Additionally, Sm-fum-7HO and Er-fum-12HO demonstrated high dielectric functions, reaching 2.22 × 10 and 1.42 × 10 at 10 Hz, respectively, making Er-fum-12HO a highly dielectric material. More importantly, broadband dielectric spectroscopy measurements indicated that there was a dielectric relaxation process in Er-fum-12HO with an activation energy of 0.59 eV. The present findings provide a better understanding of the crucial role of confined water clusters in proton conductivity and the novel phenomenon of the coexistence of proton conduction and dielectric relaxation in crystalline MOF materials.
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http://dx.doi.org/10.1039/d4dt01945h | DOI Listing |
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