Layer-by-layer growth of ferrocene decorated metal–organic framework thin films and studies of their electrochemical properties

Abstract

As electroactive metal–organic frameworks (MOFs) become the centerpiece of many emerging applications in electrocatalysis, energy storage/conversion and electronics, the ability to grow high-quality of electroactive MOF thin films and understanding the mechanism of charge transport in the frameworks are crucial. Herein, we demonstrate that the use of ferrocene pendant biphenyl dicarboxylate (bpdc-Fc) ligand allows the successful growth of redox-active surface-attached MOFs (SURMOFs) [Cu2(bpdc-Fc)2dabco] SURMOF, on self-assembled monolayers (SAMs) functionalized surfaces by layer-by-layer (LBL) deposition method. The nature of the SAMs significantly affects the morphologies and electrochemical properties of [Cu2(bpdc-Fc)2dabco] SURMOFs owing to their different ability to coordinate Cu2 dimmer. The purine-based SAMs offer excellent anchoring sites for the nucleation of MOF crystals leading to dense films with good electrochemical properties. On the contrary, sparse MOF nanocrystals with poor electrochemical properties were obtained on pyridine-based SAMs. A redox hopping mechanism accompanied by anion diffusion was proposed to explain the different redox properties of [Cu2(bpdc-Fc)2dabco] SURMOFs on SAMs. This work has potential to contribute to rational design and growth of novel MOFs for the applications in ionic conductors, electrocatalysts, energy storage devices and electrochemical sensors.