Oxygen-Assisted Electrodeposition Of Zeolitic Imidazolate Frameworks

Permanently microporous metal-organic frameworks(MOFs)are a class of crystalline materials that are composed of metal ions(or clusters)linked with organic ligands.These hybrid materials have shown great potentials in many traditional applications such as gas storage,separations,and heterogeneous catalysis.MOFs are also emerging candidate materials in fields of energy storage and conversion,sensing,and electronics,where they usually exist in the form of films on a conductive substrate.Among the established methods for the preparation of MOF films,strategy based on electrochemical deposition is attractive with advantages such as mild reaction conditions,short reaction time,no special requirements for the surface modification of substrates,and capability in morphology and thickness controls.Nevertheless,reports on the cathodic deposition of MOFs are comparably fewer than those on their anodic deposition.The challenge arises from the higher reduction overpotentials of probases reported relative to those of some important metal ions,e.g.Zn(II),Co(II),and Cu(II),which contribute to the formation of most extensively studied MOFs.As a result,the cathodic deposition of these MOF materials are commonly accompanied with the plating of metals on the cathode.In addition,although the electrochemical deposition,in principle,enables more flexible controls over the formation reactions of MOFs,their potentiality on preparing MOF films with precisely tunable morphology and thickness has not been fully explored yet,which,however,is important for their applications in optical and electronic devices.Furthermore,the evaluation of porosity of the electrochemically prepared MOF films is lacking in most relevant reports.In this subject,we will introduce a new method of Oxygen-Assisted Electrodeposition of MOF_Related research works based ZIF(zeolitic imidazolate framework)include three aspects:(1)The reaction mechanism of oxygen-assisted Electrodeposition of ZIF-8 was systematically studied by cyclic voltammetry(CV).Our results show that the formation of ZIF-8 is achieved through a series of continuous electrochemical and chemical reactions.This includes the electrochemical reduction of O2 on the cathode surface and the deprotonation of O2-related Zn(Ⅱ)-imidazole complexes.Among them,the reduction of O2 is the only electrochemical reaction in the whole reaction process and the speed control step of the whole reaction process.(2)Based on the three-electrode system,the growth of ZIF-8 on different conductive substrates(HOPG,carbon fibers,FTO,ITO,Pt)was studied,the thickness of ZIF-8 film will increase and the size of crystals will be smaller as the voltage increasing.The thickness of ZIF-8 films will increase and the size of crystal will be larger as the reaction time increasing.By optimizing the reaction conditions,the morphology and thickness of ZIF-8 films were precisely controlled at the nanometer scale.(3)The feasibility of oxygen-assisted cathodic deposition method for the preparation of ZIF materials at two electrodes was studied and the applicability of this method to other ZIF materials was explored.Based on the two-electrode system,the ZIF-8 and ZIF-71 films can grow on different conductive substrates(HOPG,carbon fibers,FTO,ITO,Pt).