Preparation And Proton Conductivity Of Carboxylate MOFs And MOGs

The proton exchange membrane fuel cell has become a research hotspot to deal with energy and environmental problems,and the proton exchange membrane（PEM）plays a key role as its core component.In order to obtain PEM materials with excellent performance,the selection of proton conductor and the modification of membrane materials have been studied.In this paper,two kinds carboxylic organic ligands{1,4-（3,5-dicarboxyphenyl）terephthalamide（H₄L¹）and 1,3-（3,5-dicarboxyphenyl）isophthalamide（H₄L²）}were synthesized,and they were used to prepare three kinds of metal-organic frameworks（MOFs）and four kinds of metal-organic gels（MOGs）.The MOGs-composite membranes were prepared by solution casting.The proton conduction and mechanism of MOFs,MOGs and MOGs-composite membranes were explored.The details are as follows:1.Preparation of carboxylate MOFs.First,two kinds carboxylic organic ligands,H₄L1 and H₄L2,were synthesized,and then three kinds of MOFs were prepared by the interaction between ligands and metals under solvothermal conditions.The MOFs were characterized by X-ray single crystal diffraction,IR,TGA,PXRD,and their proton conduction were investigated.The results show that MOF1 has a 3D porous frame structure and its maximum proton conductivity is 6.57×10^-3 S·cm^-1（98%RH,363 K）.The structural simulation shows that MOF2 has a 3D supramolecular structure connected by hydrogen bonds.The AC impedance results show that the maximum proton conductivity of MOF2can reach 7.40×10^-3 S·cm^-1（98%RH,367 K）,which is higher than many currently reported MOFs materials.At 98%RH and 368 K,the maximum proton conductivity of MOF3reaches 1.48×10^-3 S·cm^-1.The above results show that the three MOFs are good proton-conducting materials.2.Preparation of carboxylate MOGs.Four kinds of MOGs,Co-MOG,Cd-MOG,Cu-MOG and Zn-MOG,were prepared by using H₄L¹ and H₄L² with transition metals,respectively.They were characterized by IR,TGA,PXRD,and their proton conduction were explored.The results show that the maximum proton conductivities of Co-MOG and Cd-MOG are 1.35×10^-3S·cm^-1（368 K）and 1.05×10^-3S·cm^-1（358 K）at 98%RH,respectively.And the activation energies are 0.09 e V and 0.23 e V,indicating that they follow the Grotthuss mechanism in the process of proton conduction.The maximum proton conductivities of Cu-MOG and Zn-MOG are 2.20×10^-3S·cm^-1（98%RH,368 K）and1.22×10^-3S·cm^-1（98%RH,363 K）with activation energies of 0.24 e V and 0.15 e V,respectively,indicating that they obey the Grotthuss mechanism in the process of proton conduction.3.Preparation of MOGs-composite membranes.MOGs were mixed with polymer（SPPO,SPEEK）to obtain a series of composite membrane materials by solution casting method.The water uptake,swelling ratio,ion exchange capacity and oxidative stability of all composite membranes were investigated.The results of AC impedance test show that SPPO composite membranes have excellent proton conductivity at 98%RH and 348 K,and the maximum proton conductivities of Co-MOG@SPPO-3 and Cu-MOG@SPPO-3 reach3.13×10^-1 S·cm^-1 and 1.79×10^-1 S·cm^-1,respectively.At 98%RH and 348 K,SPPEK series composite membranes also show good proton conductivity.And the maximum proton conductivities of Cd-MOG@SPEEK-3 and Zn-MOG@SPEEK-3 are 7.53×10^-2 S·cm^-1 and1.27×10^-1 S·cm^-1,respectively.