Researchers develop hydrogen-bonded organic frameworks based electrochromic film

(Nanowerk News) Electrochromic (EC) materials have been widely applied in the fields such as smart window, information storage, electronic display, and dynamic mirror. Hydrogen-bonded organic frameworks (HOFs) is well suited to explore new EC materials without introducing unnecessary components.
In a study published in Angewandte Chemie International Edition ("An Electrochromic Hydrogen-Bonded Organic Framework Film"), the research group led by Prof. CAO Rong and LIU Tianfu from Fujian Institute of Research on the Structure of Matter (FJIRSM) of the Chinese Academy of Sciences developed an EC HOFs film with long cycle life, facile modification, easy recycling and regeneration prepared via electrophoretic deposition (EPD) rapidly and facile.
The researchers first prepared the nanosized rod crystalline HOFs, PFC-1 via self-assembly of the ligand in a mixture solvent of N,N-Dimethylformamide (DMF) and water at room temperature. Then they fabricated the corresponding HOFs films with different thickness via EPD method by changing the deposition voltage of 15-90V.
The as-prepared film was used as EC materials. From the cyclic voltammogram (CV) characterizations, nano-PFC-1 film showed an anodic peak potential of 1.23 V and a cathodic peak potential of 1.19 V (vs. Ag/AgCl), accompanied with the color change from yellow to blue-violet. The CV analysis with variable scan rates proved that during the chromic process, the kinetics is capacitance-dominant kinetics of the EC chemistry.
To verify the EC mechanism, the researchers conducted the in-situ UV-vis, Raman and electron paramagnetic resonance (EPR) spectra at different potentials. The results proved that the EC performance of HOFs film originated from the redox nature of the pyrene moieties of the ligands.
Through post-synthetic modification (PSM) method due to the -COOH group from the HOFs, the researchers obtained the Fe ions, the EC groups. Compared with the pristine HOFs film, the prepared [email protected] composite films exhibited more color change. The HOFs film can be regenerated by the facile process of elution, recrystallization and re-EPD.
Besides, the researchers designed and prepared an EC device with HOFs film on fluorine-doped tin oxide (FTO) as the working electrode, blank FTO as the counter electrode, and between which filled with electrolyte exhibiting the similar EC behavior.
This study provides a new method for the HOFs film fabrication and the corresponding device.
Source: Chinese Academy of Sciences
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