Preparation And Study Of Rapid COFs Proton Electrolytes And Flexible COFs Proton Exchange Membranes

In the face of increasingly depleted fossil energy,countries around the world are developing efficient and sustainable energy technologies.Currently,popular new energy sources include fuel cells,solar cells,nuclear power and lithium batteries.There are many types of fuel cells,among which proton exchange membrane fuel cells have the advantages of high conversion efficiency,environmental protection,and quick start at lower temperatures.Moreover,more and more researchers are paying attention to the research and development of proton exchange membrane fuel cells.The proton fuel cell is composed of five components:a proton exchange membrane?PEM?,a cathode catalytic layer?CaCL?,an anode catalytic layer?AnCL?,a cathode gas diffusion layer?CaGDL?,and an anode gas diffusion layer?AnGDL?.Among them,proton exchange membrane is the most important component.The most widely used one is the perfluorosulfonic acid polymer represented,such as Nafion.However,large-scale applications are limited due to its high fuel permeability and expensive cost.Covalent Organic Framework?COFs?is a new type of crystalline porous polymer with periodic strucure,which has high designability and periodicity.And its high specific surface area and light weight make it widely used in many fields.However,it has not been reported in terms of ion conduction,especially proton conduction.This paper first demonstrates a simple and versatile COFs modification strategy that converts COFs into proton conductors with high electrical conductivity.We chose COF-1 and COF-2 with imine groups as model materials,and in order to further verify the versatility of this method,we also selected a class of amorphous porous polymers?PCP-1?for research.Through the lithiation and sodium treatment of the COFs skeleton,abundant Li⁺or Na⁺sites can be introduced inside the COFs,and the conductivity of the material after ionization is obviously improved,from¹0^-88 S cm^-1 to¹0^-2 S cm^-1.It is found that the hydrophilicity of the material after ionization is significantly improved.The water vapor adsorption test data shows that the water adsorption amount is increased by about 3 times.The proton activation energy of the material after ionization is calculated to be less than 0.4 eV,which is consistent with the Grotthus conduction mechanism.In addition,based on the calculation of the diffusion coefficient,we found that the diffusion coefficient of water molecules in ionized COFs decreased significantly.In order to further understand the mechanism,we carried out corresponding simulation calculations and found that hydrophilic Li⁺and Na⁺can promote the formation of a large and dense hydrogen bond network in the water molecules inside the COFs,thus greatly increasing the conduction rate of protons in COFs.We chose COF-1 and COF-2 with imine groups,and in order to further verify the versatility of our method,we chose another PCP-1 porous polymer for research.Ionized COFs and PCP were prepared by reacting COFs and PCP with NaH and LiH in DMSO.It was found that after ionization,the conductivity was significantly improved from¹0^-8 S cm^-1 to¹0^-2 S.cm^-1.After ionization,the hydrophilicity of the material increased significantly,and the water vapor adsorption test data showed that the water adsorption amount increased by about 3 times.According to the test of constant humidity and temperature conductivity,the proton migration activation energy is less than 0.4 eV,which follows the Grotthus Mechanisam.In order to further study the mechanism,we carried out simulation calculations and found that the hydrogen bond density in COFs increased significantly after ionization,and according to the calculation of diffusion coefficient,it was found that the diffusion coefficient of water molecules in ionized COFs decreased significantly due to alkali.The effect of the high ionic potential of the metal.Finally,according to the in-situ infrared test in high humidity and low humidity environment,it is found that there are more free protons in high humidity,which is good for proton conduction.In addition,in view of the fact that COFs materials are insoluble and infusible nature of the COFs material makes it difficult to process.,we have developed a novel COFs organic gel composite strategy to construct COFs films with high proton conductivity.Using the characteristics of spontaneous gelation of pyrrole and phosphoric acid,COFs and small molecule gel monomers are gelled in situ to obtain flexible and mechanically strong COFs films.The advantage of this strategy is that the organic gel film we choose not only provides a certain mechanical strength,but also has a rich hydrogen bond network inside and thus has good proton conductivity.The resulting COF-containing composite film thus has a proton conductivity of up to1.31?10^-1 S cm-1?at 313 K and 98%relative humidity?,which is the highest reported value of the proton film based on COFs.We further applied this membrane to a fuel cell system using commercial Pt/C as a catalyst.The test results show that the open circuit voltage of the battery is 0.93 V,and it can be stable for up to 5 hours;the output power density can reach⁵4 mW cm^-2?room temperature condition?.