Study On Covalent Organic Framework Modified Nanofibers/Perfluorosulfonic Acid-Based Proton Exchange Membrane

Proton exchange membrane（PEM）is the core component of proton exchange membrane fuel cell（PEMFC）.Perfluorosulfonic acid（PFSA）has excellent proton conductivity and is the most widely used in PEM.However,PFSA is rich in hydrophilic ionic groups,and the size expansion and shrinkage are accompanied by the process of water absorption and dehydration,which is easy to cause the catalytic layer to peel off from the PEM.The introduction of polymer nanofibers can improve the dimensional stability of membranes,but taking both proton conductivity and dimensional stability into consideration is a bottleneck that needs to be broken through.Covalent organic frameworks（COFs）have the characteristics of large specific surface area,tunable molecular structure,and structural stability,which are expected to improve the stability of membranes while constructing efficient proton transport channels.Therefore,in this thesis,an in-situ growth method is designed,and the mixed solution of phenolic monomer and polyacrylonitrile（PAN）for synthesizing COF is electrospun to synthesize COFs with different structures on the surface of nanofibers.The following researches are carried out:（1）COF（TpPa-SO₃H）containing sulfonic acid group is grown in situ on PAN fiber,and the ratio of COF monomer to PAN and the influence of synthesis conditions on the structure of COF were studied.TpPa-SO₃H@PAN nanofibers are introduced into PFSA matrix to study the effect of COF on the properties of composite membranes.The introduction of nanofibers improves the dimensional stability of the composite membrane,and at the same time increases the concentration of sulfonic acid groups at the interface between the nanofibers and the PFSA matrix,thereby improving the proton conductivity.Among them,the PFSA/TpPa-SO₃H@PAN-5 composite membrane has the best proton conductivity,reaching 260.8 m S·cm^-1 at 80°C.Compared with the PFSA membrane,the proton conductivity is increased by 36.7%,and the area swelling ratio is decreased by8.2%.（2）By adjusting the monomer type of COF,COF（TpPa-（SO₃H-Py））with both acid and base groups is grown in situ on nanofibers.The generated COF was fibrous in three-dimensional direction and form a proton transport network.By adjusting the ratio of Pa-SO₃H and Pa-Py in the reaction solution,the loading of TpPa-（SO₃H-Py）on the nanofiber surface is controlled.The content of acid and base groups in the TpPa-（SO₃H-Py）@PAN structure and the influence rule of composite membrane performance are studied.The proton conductivity of the PFSA/TpPa-（SO₃H:Py=10:10）@PAN composite membrane can reach 202.3 m S·cm^-1 at 80°C and 100%RH,which is 6%higher than that of the PFSA membrane,and the area swelling rate is reduced by 25.8%.At 80°C and 95%RH,the through-plane proton conductivity of the composite membrane can reach 96.67 m S·cm^-1,which is 1197.6%higher than that of the PFSA membrane.After soaked at 80°C for 312h,the conductivity of the PFSA/TpPa-（SO₃H:Py=10:10）@PAN composite membrane decreases by only 1.6%.