Electrodeposition of Zn-Terephthalate Metal-Organic Framework Thin Films

Electrochemical self-assembly (ESA) of metal-organic framework (MOF) thin films of Zn2+ ions and terephthalic acids (TPA) in a layered structure and with a composition of Zn3(OH)4(TPA)•6H2O was made possible by addition of TPA into the bath for electrodeposition of ZnO, namely, O2-saturated aqueous solution of ZnCl2. The deposition of Zn-TPA MOF, however, resulted in a strong passivation of the electrode towards O2 reduction to limit the electrochemical growth. Interestingly, chemical precipitation of Zn-TPA MOF was found to take over the film growth to achieve a thickness of about 2 µm in the extended electrolysis, in spite of the negligibly small current. Due to decrease of TPA concentration in the solution bulk, the electrode finally recovered the activity for the O2 reduction, which, however, resulted in the electrodeposition of ZnO to be overlaid on the Zn-TPA MOF. The electrodeposited Zn-TPA MOF was well adherent to the substrate.