Zirconium-Based Metal–Organic Framework Nanocomposites Containing Dimensionally Distinct Nanocarbons for Pseudocapacitors

Abstract

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.

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

“…Preparation of pellets and thin films : For measuring electrical conductivity, the pellets of PANI, UiO‐66‐NH 2 , and PANI/UiO‐66‐NH 2 were prepared by following the reported procedure [12d, 26, 30] . Briefly, the sample was packed into a 7 mm die set and wetted with 40 μL of acetone.…”

“…For electrochemical measurements, the drop‐casting process was utilized to fabricate thin films modified on fluorine‐doped tin oxide (FTO) conducting glass substrates [12d, 30] . An FTO substrate (7 Ω/sq., 3 cm×1.5 cm) was first washed by sonicating in soapy water, ethanol, and acetone for 5 min, sequentially.…”

Metal−Organic Frameworks toward Electrochemical Sensors: Challenges and Opportunities

“…Thus, it should be noted that within such composites, redox hopping or moderate electrical conduction in the MOF phase is still necessary during the electrochemical processes so that the active sites presented within the pore structure of MOF can be electrochemically utilized. For example, in our recent study, a Zr‐MOF decorated with redox‐active manganese sites that allow redox hopping in MOF was grown on the 1D graphene nanoribbons or 2D graphene oxide . The resulting electrochemical performance of the MOF‐carbon composite with the electrical conductivity provided by nanocarbons and the high‐density redox‐active manganese sites supported by the porous framework was found to outperform those of the pristine nanocarbons and MOF decorated with redox‐active sites.…”

Electrochemical Evolution of Pore-Confined Metallic Molybdenum in a Metal–Organic Framework (MOF) for All-MOF-Based Pseudocapacitors

“…However, the electrically insulating nature of most MOFs strongly limits their use in electrochemical applications. − For example, the Zr-MOF thin films installed with high-density and spatially dispersed molybdenum-based redox-active sites were found to show very limited electrochemical activity due to the sluggish charge transport between the redox-active sites . Recently, some published studies have used nickel- and cobalt-based MOFs in supercapacitors with KOH as the electrolytes. − To utilize water-stable MOFs in supercapacitors, strategies such as the design of electrically conductive MOFs − and the use of conductive MOF-based composites − have been proposed, but the examples are relatively rare. A more common alternative strategy is to convert MOFs to conductive MOF-derived carbons or metal oxides for charge-storage purposes. − …”

“…In this study, molybdenum­(VI) redox-active sites were first decorated on the hexa-zirconium nodes of a Zr-MOF, MOF-808 (see Figure a), by a self-limiting solvothermal deposition in MOFs (SIM) technique. ,,, Thereafter, the thin film of the obtained material (Mo-SIM-MOF-808) deposited on a conducting substrate was subjected to electrochemical reduction to generate electrochemically active metallic molybdenum confined in the pores of MOF crystals (Mo@MOF-808; see Figure b). The rigid and water-stable Zr-MOF framework is supposed to prevent the electrochemically induced agglomeration of metallic nanoparticles during the electrochemical operations in aqueous electrolytes, as found in the previous example for copper .…”