In this study, nanocrystals of a cerium-based metal–organic framework (Ce-MOF), Ce-MOF-808, are directly grown on the surface of carboxylic acid-functionalized carbon nanotubes (CNTs) by a facile one-step solvothermal synthesis method. Ce-MOF–CNT nanocomposites with various Ce-MOF-to-CNT ratios are synthesized, and their crystallinity, morphology, porosity, and electrical conductivity are examined. The redox-hopping and electrochemical behaviors of the pristine Ce-MOF in aqueous electrolytes are investigated, suggesting that the pristine Ce-MOF is electrochemically active but possesses a limited charge-transport behavior. As a demonstration, all the Ce-MOF, CNT, and nanocomposites are used as active materials for application in aqueous-based supercapacitors. The capacitive performance of the CNT can be significantly boosted with the help of redox-active Ce-MOF-808 nanocrystals.

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.

In this study, proton-conducting behaviors of a cerium-based metal–organic framework (MOF), Ce-MOF-808, its zirconium-based isostructural MOF, and bimetallic MOFs with various Zr-to-Ce ratios are investigated. The significantly increased proton conductivity (σ) and decreased activation energy (E a) are obtained by substituting Zr with Ce in the nodes of MOF-808. Ce-MOF-808 achieves a σ of 4.4 × 10–3 S/cm at 25 °C under 99% relative humidity and an E a of 0.14 eV; this value is among the lowest-reported E a of proton-conductive MOFs. Density functional theory calculations are utilized to probe the proton affinities of these MOFs. As the first study reporting the proton conduction in cerium-based MOFs, the finding here suggests that cerium-based MOFs should be a better platform for the design of proton conductors compared to the commonly reported zirconium-based MOFs in future studies on energy-related applications.

Electrically conductive nanocomposites composed of a zirconium-based metal−organic framework (MOF) and nanocarbons are synthesized by in situ growth of MOF nanocrystals in the presence of graphene nanoribbons (GNRs) or graphene oxide (GO). The electrical conductivity and porosity of the obtained MOF-based nanocomposites are highly tunable by adjusting the MOF-to-carbon ratio as well as the type of nanocarbons used during the synthesis. Redox-active manganese sites are thereafter decorated in the MOF structure in these nanocomposites to render redox hopping in MOF under electrochemical conditions, and the pseudocapacitive behaviors of these MOF−GNR and MOF−GO nanocomposites are investigated in aqueous electrolytes. With the electrical conductivity provided by nanocarbons and the high-density redox-active manganese sites supported by the porous framework, the Mndecorated nanocomposites exhibit better performances as the materials for pseudocapacitors than the pristine Mn-decorated MOF and nanocarbons.

In this study, metallic molybdenum nanoparticles confined in the nanopores of a zirconium-based MOF (Zr-MOF), MOF-808, are prepared by a self-limiting decoration of spatially isolated Mo(VI) sites on the hexa-zirconium nodes of MOF-808, followed by the electrochemical reduction of Mo(VI) to metallic Mo. The obtained pore-confined Mo exhibits reversible redox activity in a neutral aqueous electrolyte and serves as the pseudocapacitive material for negative electrodes. By introducing another MOF-based pseudocapacitive material that can be used for positive electrodes, a manganese-decorated Zr-MOF-carbon nanotube nanocomposite, as a demonstration, all-Zr-MOF-based asymmetric pseudocapacitors with an aqueous electrolyte are fabricated.