Steady-State Electrochemistry Isolates Electron Hopping from Counterion Diffusion-Migration in Planar MOF Films

Current methods for measuring electron-hopping diffusion coefficients of planar metal-organic framework (MOF) films typically use transient potential-step experiments, assuming a simple diffusional response. However, these experiments induce a net flux of counter ions, resulting in an electric field and transport by electromigration, which can impair the accuracy of the measurement. To remedy this, we employ an alternative method based on steady-state cyclic voltammetry. By adding a mobile redox acceptor molecule to the electrolyte, the additional cross reaction between the film and the acceptor mimics a source-drain electrode configuration, generating a steady state with negligible counter ion flux. Additionally, we construct a bespoke physical model and derive an analytical expression to correct the current response for any electric field effects. Overall, this method effectively isolates the diffusional response from ionic diffusion-migration and electric field effects. We expect these results will improve the accuracy of experimentally determined electron-hopping rates of electroactive MOF films.