Synthesis And Proton Conduction Properties Of Organic Amine Derivatives Based On Keggin-Type Polyoxometalates

Proton-exchange membrane fuel cells?PEMFCs?as an important branch of energy development have attracted much attention,and proton exchange membrane?PEM?is the core component of PEMFCs.At present,the widely used perfluorosulfonic acid Nafion membrane exhibits high proton conductivity up to 0.13 S cm^-1 at 75?and 100%relative humidity?RH?;however,high cost and environmental risk limit its application,complex microstructures and multiphase problems make it difficult to clearly understand the relationship between structure and proton conductivity.Therefore,in order to explore low cost and environmentally friendly PEM with high proton conductivity which could simultaneously revealing the relationship between its structure and proton conduction properties remains a challenge.The introduction of small functional guest molecules that provide mobile protons to modify POM to obtain crystalline materials with simple structure and desired proton conductivity provides the possibility to demonstrate a clear proton conduction process and the relationship between structure and properties.Two new supramolecular proton conductors?C₃N₆H₆?₄H₄[SiW₁₂O₄₀]·6H₂O?1?and?C₃N₆H₆?₃H₃[PW₁₂O₄₀]?2?based on Keggin-type polyoxometalate anions have been successfully synthesized by conventional aqueous evaporation method.In compounds 1 and 2,protonated melamine is connected with[SiW₁₂O₄₀]^4-and[PW₁₂O₄₀]^3-by supramolecular forces such as hydrogen bonding,respectively,to form 3D hydrogen bond organic frameworks.Highly ordered structure and continuously stable hydrogen bond network can result in high proton conductivity.As the temperature rises,the proton conductivity of Compounds 1 and 2 can reach 1.59 mS·cm^-1 and 47.6 mS·cm^-1 at 85?and 97%RH.Interestingly,although protonated melamine interacts with POMs possessing the same structure and the experimental methods are consistent,there is no crystallization water in 2,but there are 6 crystal waters in 1,which affect the formation of hydrogen bond networks and change the humidity dependence.Compound 2 without crystal water can achieve rapid proton conduction at high temperature and ambient humidity.The optimized proton conductivity was observed to be 2.47 x 10^-4 S·cm^-1 at 100?and 65%RH.