Selective Formation of Polyaniline Confined in the Nanopores of a Metal–Organic Framework for Supercapacitors

Abstract

In this study, a strategy that can result in the polyaniline (PANI) solely confined within the nanopores of a metal–organic framework (MOF) without forming obvious bulk PANI between MOF crystals is developed. A water‐stable zirconium‐based MOF, UiO‐66‐NH2, is selected as the MOF material. The polymerization of aniline is initiated in the acidic suspension of UiO‐66‐NH2 nanocrystals in the presence of excess poly(sodium 4‐styrenesulfonate) (PSS). Since the pore size of UiO‐66‐NH2 is too small to enable the insertion of the bulky PSS, the quick formation of pore‐confined solid PANI and the slower formation of well dispersed PANI:PSS occur within the MOF crystals and in the bulk solution, respectively. By taking advantage of the resulting homogeneous PANI:PSS polymer solution, the bulk PANI:PSS can be removed from the PANI/UiO‐66‐NH2 solid by successive washing the sample with fresh acidic solutions through centrifugation. As this is the first time reporting the PANI solely confined in the pores of a MOF, as a demonstration, the obtained PANI/UiO‐66‐NH2 composite material is applied as the electrode material for supercapacitors. The PANI/UiO‐66‐NH2 thin films exhibit a pseudocapacitive electrochemical characteristic, and their resulting electrochemical activity and charge‐storage capacities are remarkably higher than those of the bulk PANI thin films.

Cerium-Based Metal–Organic Framework Nanocrystals Interconnected by Carbon Nanotubes for Boosting Electrochemical Capacitor Performance

“…As shown in Figure S14, its area capacitance remains 71% of its initial value after 2000 cycles of the charge–discharge processes. Table S2 shows a partial list of MOF-based materials that have been reported for supercapacitors along with their capacitive performances. ,,− Compared to most reported MOF-based materials, Ce-MOF-808–20CNT exhibits a higher or comparable area capacitance.…”

Proton-Conductive Cerium-Based Metal–Organic Frameworks

“…However, it is then crucial to ensure that the crystallinity of the tested MOF can be preserved after pressing it into the pellet. Pressures of 50–200 MPa were commonly used to prepare the MOF pellets, ,, and in our previous studies, a pressure of 115 MPa was used for preparing pellets of other Zr-MOFs. − , Thus, pellets of Zr-MOF-808, Ce-MOF-808, and bimetallic MOF-808 were first prepared with a load of 0.5 ton, i.e ., a pressure of 115 MPa. XRD patterns of the resulting pellets were thereafter collected.…”

“…The pellets of Zr-MOF-808, Ce-MOF-808, and bimetallic MOF-808 were prepared by the following procedure to measure their electrical conductivities and proton conductivities; a similar protocol has been used to prepare both Zr-MOF pellets and Ce-MOF pellets in our previous studies. − Approximately 15 mg of MOF powder was packed into a 7 mm die set and pressed into a pellet by a minipellet press (Specac). The load of the minipellet press used here was set as 0.1 ton; this pressure is lower than that used in our previous studies, as discussed in the text regarding Figure later.…”

“…The electrical conductivities of the pelletized Zr-MOF-808, Ce-MOF-808, and bimetallic MOF-808 were measured by two-probe current–voltage ( I – V ) measurements. Following the same procedure reported in our recently published studies for other Zr-MOFs as well as Ce-MOF-808, − the MOF pellet was sandwiched between two metallic plates, and the I – V curve of the pellet after drying under vacuum overnight was then collected on a CHI6273E electrochemical workstation (CH Instruments Inc.) at 25 °C.…”

Microporous MOF as nanogen facilitating diffusion-coupled charge transfer near the percolation threshold in a polyaniline pseudo-supercapacitor

“…A recent study also demonstrated the efficient confinement of PANI chains within the pores of UiO-66-NH 2 , with a positive impact on the stability of the PANI chains observed upon extended cycling. 32 Attempts were also successfully made to link the observed enhancement to the intrinsic microporosity of the MOFs and the electrical conductivity of the PANI. 33 However, a deeper understanding of the underlying mechanism for this observed synergy is still lacking.…”