Sulfonate-Functionalized Two-Dimensional Metal–Organic Framework as a “Dispersant” for Polyaniline to Boost Its Electrochemical Capacitive Performance

Polyaniline (PANI) is a conducting polymer with remarkable electrochemical performance for supercapacitors. On the other hand, materials with sulfonate groups, such as polystyrenesulfonate and Nafion, are commonly used as the dispersants to spatially separate the polymeric chains of PANI by means of the electrostatic interaction between the aniline unit and the negatively charged sulfonate. Herein, a two-dimensional (2D) zirconium-based metal–organic framework (MOF) with enriched sulfonate-based ligands postsynthetically coordinated onto its nodes, ZrBTB–SO3 (BTB = 1,3,5-tri(4-carboxyphenyl)benzene), is utilized as the dispersant during the in situ polymerization of aniline; composites with various ratios between PANI and ZrBTB–SO3 are thus synthesized. For comparison, the pristine 2D MOF without sulfonate groups is also subjected to the in situ polymerization to synthesize the PANI@ZrBTB composite. Crystallinity, porosity, morphology, elemental composition, and electrical conductivity of each composite are examined. These PANI-based materials are thereafter cast on the electrodes as thin films to investigate their electrochemical capacitive performances in acidic aqueous electrolytes. With the help of the negatively charged sulfonate-functionalized 2D MOF sheets as the dispersant, the resulting PANI in the composite can achieve a specific capacitance of 515 F/g at a charge–discharge current of 0.5 mA/cm2, which is much higher than those achieved by the pristine PANI (230 F/g), PANI@ZrBTB (137 F/g), and the physical mixture of PANI and ZrBTB–SO3 (130 F/g). Findings here open numerous opportunities for utilizing such water-stable and sulfonate-functionalized 2D MOFs to spatially disperse various conducting polymers and boost their performances in a range of applications.