Construction And Proton Conduction Of Anderson-type Polyoxmetable-based Metal-organic Coordination Polymers

Proton exchange membrane fuel cell?PEMFC?has been recognized as the most promising candidate for green energy because of its high power density and ultra-low emission.The development of electrolyte materials exhibiting durable,high proton conductivity is one of the primary technological barriers that must be overcome for the next generation of PEMFCs.Among them,the introduction of polyoxometalates with extremely high proton mobility and oxygen-enrichment as inorganic building units into various coordination polymers will be the key to the construction of crystalline materials with high proton conductivity.On this basis,we adopted Anderson-type polyoxometallate Na₅[IMo₆O₂₄]·3H₂O as the inorganic building unit,pyridine-4-carboxylic acid as the organic ligand,lanthanide series and alkaline earth metal ions as the metal center successfully obtained a series of polyoxometallate-based metal organic coordination polymers and reasonably completed the following work:In this work,we successfully prepared a series of polyoxometalate?POM?-based metal-organic coordination polymer:[?C₆NO₂H₅?₄(C₆NO₂H_4.875)₂Ln_3.25?H₂O?_19.5][IMo₆O₂₄]₂·3H₂O?Ln=Pr?PLP-1?,Nd?PLP-2?,Sm?PLP-3??by using protection raw materials:rare earth salt,pyridine-4-carboxylic acid,and Anderson type POM Na₅[IMo₆O₂₄]·3H₂O.They captured a?H₂O?_19.5 cluster in a 1D channel along the c axis.?H₂O?_19.5 clusters can form a rich hydrogen bond network,which not only promote the formation of 3D supramolecular structure but also provide an effective way for proton transfer.Therefore,the proton conductivity was studied with PLP-1 as an example.AC impedance analysis showed that the conductivity of PLP-1 was up to 1.48 x 10^-3 S cm^-1 at 353 K and 97%RH.In addition,the proton conductivity of this series of compounds at 333 K and without water was 2.3 x 10^-3 S cm^-1,which was completely attributed to the presence of?H₂O?_19.5 clusters in the framework.However,when the temperature is higher than 343 K,the proton conductivity of PLP-1reduces due to the volatilization of most of the water in the?H₂O?_19.59.5 clusters.Therefore,we used aminated graphene oxide?HGO?as a substrate to further synthesize the composite material?PLP-1@HGO?to improve its water retention and water stability.The conductivity of PLP-1@HGO reached 1.44 x 10^-3 S cm^-11 at 353 K and 97%RH.We used alkaline earth metal ions Sr²⁺instead of lanthanide metal ions,and obtained an example of a novel high-water-stability metal-organic coordination polymer with a suitable conventionalaqueoussolutionsynthesisstrategy:[Sr?C₆NO₂H₆?₂?C₆NO₂H₅??H₂O?₃(IMo₆O₂₄)Na?H₂O?]·2H₂O?PAP-1?.The compound revealed an effective proton transport pathway associated with sodium ions and their adsorbed water.At 358 K,97%RH,AC impedance analysis shows that PAP-1 has a high proton conductivity is 6.2 x 10^-2 S cm^-1,which is comparable to most high proton conducting MOFs.At the same time,the compound is also a material with high water stability that can be stably present in boiling water at 120oC for 3 days,and its structure has not changed.