Synthesis Of Novel Metal-organic Frameworks And Composite Membrane For Proton Conduction Application

In recent years,the proton-conductive properties of metal-organic framework compounds have been paid more attention,owing to their tunable pore structure,controllable guest molecule/ion,modifiable functional groups,and so on.With the development of proton exchange membrane fuel cell,MOFs in the field of proton exchange membrane applications began to be concerned about,MOFs proton conductivity is widely studied.We proceed from the simple synthesis of several MOFs materials,and gradually explored the application of these materials in the field of proton conduction,and concerned about the important factors:the stability of the material which impact its practical application.Then,we try to fabricate MOFs materials into a composite film,and take a step forward for the MOFs material practical application.In this paper,we used two kinds of organic ligands,one is based on chiral phosphonate ligands:D-H₃pmpc=（D）-1-（phosphono-methyl）piperidine-3-carboxylic acid and the other is a ligand with multi-phosphoric groups:phytic acid.We construct several new MOFs material,and from the following three aspects to investigate:First,we synthesized several new MOFs materials and studied their structure and proton conductivity.The solvothermal reaction of metal ions and D-H₃pmpc yield three phosphonate-based metal-organic coordination polymers,[Cu（D-Hpmpc）（CH₃OH）]_n（Compound 1）,[Cu（D-Hpmpc）]_n（Compound 2）,[Cd₂（D-pmpc H）（H₂O）₂Cl₂]_n（Compound 3）with diversified coordination fashions and dimensional features（D-H₃pmpc=（D）-1-（phosphono-methyl）piperidine-3-carboxylic acid）.Compound 1exhibits a right-handed helical chain with a pitch of 6.785?and interchain O–H???O hydrogen-bond.Compound 2 displays a chiral 2D network with（4,4）topology and 1D O–H???O hydrogen-bond chain.Compound 3 shows a non-interpenetrating diamondoid architecture and various hydrogen-bond interactions.Their chiralities are testified by vibrational circular dichroism spectroscopy and second-order nonlinear optical response measurements.Compared with compound 1 and 2,compound 3 has a high water stability,a moderate proton conductivity of 1.38×10^-4 S cm^-1 at 323K and⁹7%RH（relative humidity）and a lower activation energy of 0.14 eV.Second,MOFs as a new type of proton conductor have undergone rapid development due to available crystal structure and excellent film-forming ability.However,few MOFs for proton conduction have shown good chemical stability in the practical applications,mainly tolerance to water,acid,base and organic solvents,and even if they are stable,their stability have been roughly confirmed by powder X-ray diffraction（PXRD）.Herein,in the third chapter,we use D-H₃pmpc and Er to construct a chemical stable lanthanide oxalatophosphonate framework with proton conductivity（Compound 4）,and present an effective approach to analyze and evaluate chemical stability based on bulk phase and surface structure.More concretely,framework integrity,complete ratio（defects）,surface morphology and coordination environment have been characterized by using powder X-ray diffraction（PXRD）,inductively coupled plasma optical emission spectrometry（ICP-OES）,optical microscopy（OM）and X-ray photoelectron spectroscopy（XPS）.The results showed that compound 4 has very excellent stability.Finally the proton conduction ability test of different samples were carried out,the influence of different processing conditions on the conductivity were aslo compared.The study provides a new insight into understanding chemical stability from the materials themselves and a positive result for MOFs and their related materials in industrial applications.Finally,we explored how MOFs materials can be transformed from theoretical research to industrial applications in the field of proton conduction,and try to use MOFs and polymers to prepare composite membranes.Because the proton exchange membrane（PEM）is a key component of the proton exchange membrane fuel cells（PEMFCs）for clean energy applications.Recently,metal-organic frameworks（MOF）as well as its composite membranes with polymers as PEM have been one research focuse in this area.Herein,we describe the synthesis and proton-conductive properties of a novel hexaphosphate ester-based MOF,JUC-200,by the reaction of the inositol hexaphosphoric ligand（phytic acid）and Zn（II）.JUC-200 shows excellent water tolerance and acid resistance in pH=2.0 solution,and exhibits a proton conductivity of1.62×10^-3 S·cm^-1 at 80°C.Then,we fabricated the polymer composite membranes of poly（vinyl alcohol）（PVA）and JUC-200 as fillers with different mass percentage（X%,the membrane noted as JUC-200@PVA-X）.The measurement of proton conductivity on these membranes shows that JUC-200@PVA-10 benefits good proton conductivity of 1.25×10^-3 S·cm^-1 at 50°C.As far as we known,it is the first water-stable and acid-stable composite made of MOFs and polymer as proton exchange membranes.This research may make some contribution to the further development of MOFs in the field of the proton exchange membranes in fuel cells.