Design of Electroactive Metal-Organic Framework-Based Thin Films via a Gel Precursor Method

Electroactive metal-organic frameworks (MOFs) are considered as a promising porous platform for constructing a wide variety of electrochemical schemes. Nevertheless, traditional methods for preparing MOF thin-film electrodes often rely on polymeric binders that tend to suffer from poor film homogeneity and potentially compromise device performance. Hence, full realization of such systems into practical applications will necessitate the development of simple, binder-free, and scalable MOF thin film deposition techniques. In this work, we demonstrate that a Zr-based MOF gel (UIO-66) could act as a binder-free precursor ink for the drop-casting of homogeneous and conformal MOF thin films with a controllable thickness. Moreover, taking advantage of the high density of missing linker defects present in the UIO-66 gel precursor, we were able to engender MOF electroactivity via installation of a high concentration of ferrocene redox-active shuttles within the MOF pores. Furthermore, reversible switching of the ferrocene/ferrocene⁺ redox state resulted in controlled bias-induced MOF film permselectivity, as confirmed by a scanning electrochemical microscopy analysis. Thus, these results present an approach for the design of MOF-based thin films with adjustable, potential-stimuli electrochemical gating capabilities, which could be found to be useful for regulation of electrocatalytic reactions.