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

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 alkyl-ferrocene 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.