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. 2024 Jul 8;29(13):3239.
doi: 10.3390/molecules29133239.

Encapsulation of Imidazole into Ce-Modified Mesoporous KIT-6 for High Anhydrous Proton Conductivity

Agata Tabero  1 , Aldona Jankowska  1 , Adam Ostrowski  2 , Ewa Janiszewska  1 , Jolanta Kowalska-Kuś  1 , Agnieszka Held  1 , Stanisław Kowalak  1
Affiliations

Encapsulation of Imidazole into Ce-Modified Mesoporous KIT-6 for High Anhydrous Proton Conductivity

Agata Tabero et al. Molecules. .

Abstract

Imidazole molecules entrapped in porous materials can exhibit high and stable proton conductivity suitable for elevated temperature (>373 K) fuel cell applications. In this study, new anhydrous proton conductors based on imidazole and mesoporous KIT-6 were prepared. To explore the impact of the acidic nature of the porous matrix on proton conduction, a series of KIT-6 materials with varying Si/Al ratios and pure silica materials were synthesized. These materials were additionally modified with cerium atoms to enhance their Brønsted acidity. TPD-NH3 and esterification model reaction confirmed that incorporating aluminum into the silica framework and subsequent modification with cerium atoms generated additional acidic sites. UV-Vis and XPS identified the presence of Ce3+ and Ce4+ in the KIT-6 materials, indicating that high-temperature treatment after cerium introduction may lead to partial cerium incorporation into the framework. EIS studies demonstrated that dispersing imidazole within the KIT-6 matrices resulted in composites showing high proton conductivity over a wide temperature range (300-393 K). The presence of weak acidic centers, particularly Brønsted sites, was found to be beneficial for achieving high conductivity. Cerium-modified composites exhibited conductivity surpassing that of molten imidazole, with the highest conductivity (1.13 × 10-3 S/cm at 393 K) recorded under anhydrous conditions for Ce-KIT-6. Furthermore, all tested composites maintained high stability over multiple heating and cooling cycles.

Keywords: Brønsted acid centers; KIT-6 porous materials; cerium modification; imidazole; proton conductivity.

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Conflict of interest statement

The authors declare no conflicts of interest. The funders had no role in the design of the study, in the collection, analyses, or interpretation of data, in the writing of the manuscript, or in the decision to publish the results.

Figures

Figure 1
Figure 1
PXRD patterns of KIT-6 matrices with different Si/Al ratio: 25; 50; 100; 200; and infinity.
Figure 2
Figure 2
N2 adsorption/desorption isotherms (A) and pore size distribution (B) of KIT-6 materials.
Figure 3
Figure 3
FTIR spectra of selected H-KIT-6 and Ce-KIT-6 samples with different Si/Al ratio.
Figure 4
Figure 4
UV-Vis spectra of selected Ce-KIT-6 materials before (A) and after calcination at 673 K (B).
Figure 5
Figure 5
TEM images of H-KIT-6 (100) (A) and Ce-KIT-6 (100) (B) samples.
Figure 6
Figure 6
XPS spectrum of the Ce3d core level of Ce-KIT-6 (100).
Figure 7
Figure 7
Temperature dependence of conductivity measured during the second cooling cycle for imidazole and imidazole-containing H-KIT-6 composites of various Im loading.
Figure 8
Figure 8
Temperature dependence of conductivity measured during the second cooling cycle for imidazole and imidazole-containing Ce-KIT-6 composites of various Im loading.
Figure 9
Figure 9
Temperature dependence of conductivity for the H-KIT-6 (100) 0.40 Im composite recorded for two heating–cooling cycles.
Figure 10
Figure 10
Temperature dependence of conductivity for the Ce-KIT-6 (100) 0.40 Im composite recorded for two heating–cooling cycles.
Figure 11
Figure 11
Temperature dependence of conductivity and activation energies for H-KIT-6 composites with different Si/Al ratios measured during the second cooling cycle.
Figure 12
Figure 12
Temperature dependence of conductivity and activation energies for Ce-KIT-6 composites with different Si/Al ratios measured during the second cooling cycle.
Figure 13
Figure 13
Conductivity values of selected composites determined at 393 K for second cooling cycle.
Figure 14
Figure 14
Correlation of conductivity values of selected composites determined at 393 K for second cooling cycle with acetic acid (HAc) conversion.
See this image and copyright information in PMC

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