A Solid-Solution Approach for Redox Active Metal–Organic Frameworks with Tunable Redox Conductivity

Abstract

Systematically tuning the conductivity of metal−organic frameworks (MOFs) is key to synergizing their attractive synthetic control and porosity with electrochemical attributes useful in energy and sensing technologies. A priori control of charge transfer is possible by exploiting the solid-solution properties of MOFs together with electronic self-exchange enabled by redox pendants. Here we introduce a new strategy for preparing redox-active MOF thin-film electrodes with finely tuned redox pendant content. Varying the ratios of alkylferrocene containing redox-active and inactive links during MOF synthesis enabled the fabrication of electrodes with tunable redox conductivity. The prepared MOF electrodes display maximum electron conductivity of 1.10 mS m −1 , with crystallographic and electrochemical stability upon thousands of redox cycles. Electroanalytical studies demonstrated that the conductivity follows solution-like diffusion-controlled behavior with nonlinear electron diffusion coefficients consistent with charge hopping and percolation models of spatially fixed redox centers. Our studies create new prospects in the design and synthesis of redox-active MOFs with targeted properties for the design of advanced electrochemical devices.

Transport Phenomena: Challenges and Opportunities for Molecular Catalysis in Metal–Organic Frameworks

“…Notably, Cottrell behavior has been repeatedly observed for these systems (the transient current after a large potential step is proportional to t –1/2 ). 28 − 30 , 34 , 49 − 51 …”

J-dimer emission in interwoven metal–organic frameworks

“…What is unique about this mixture is that the links are isostructural, 5,6 and contain complex moieties that can be easily incorporated at varying concentrations, resulting in isoreticular materials that behave like substitutional solid-solutions (SSS) of organic molecules. We previously demonstrated this concept, 7,8 by incorporating highly uorescent and redox active groups, allowing us to observe changes in bulk physical properties directly related to the active link and its concentration in the MOF. In contrast, crystalizing the organic components by themselves into purely organic solid solutions (not within a MOF matrix), brings the challenges that are associated with organic crystals, such as a lack of predictability in structure and type of intermolecular interactions present, phase separation, and loss of molecular properties.…”

Functionalizing MOF with Redox-Active Tetrazine Moiety for Improving the Performance as Cathode of Li–O 2 Batteries

“…Electrochemical impedance spectroscopy (Figure 3c) reveals that the Tz-Mg-MOF-74-based cathode has higher electrochemical activity compared with the Ben-Mg-MOF-74, which is attributed to the synergy of the redox activity and the close packing of the Tz moieties. 36 Besides, the almost identical pore sizes and O 2 capture capabilities of Ben-Mg-MOF-74 and Tz-Mg-MOF-74 (Figures 3d and 3e) imply that the presence of redox-active Tz is decisive for the enhanced performance of the corresponding cathode.…”