Construction Of Donor-acceptor Proton Transfer Sites And Performance Of Composite Proton Exchange Membrane

Proton exchange membrane(PEM),as the core component of Proton Exchange Membrane Fuel Cell(PEMFC),its performance directly determines the performance of the fuel cell.In low-humidity environments,most common PEMs face the problem that the proton conductivity is severely reduced due to water loss,so that the fuel cell cannot run for a long time.This study explores two key issues around the optimization of proton transfer sites and the construction of multi-stage transfer channels.Based on the strategy of constructing donor-acceptor proton transfer sites,three nanofillers with different functional groups were prepared:acid-base core-shell microspheres(PCSMs-MA@TAC),Acid-base double-shell halloysite nanotubes(DSNT-A@B)and phosphoric acid-loaded covalent triazine organic framework(H₃PO₄@CTFp).Functional fillers were embedded in the sulfonated poly ether ether ketone(SPEEK)matrix to prepare composite PEM.From the aspects of optimizing the proton carrier,constructing continuous transmission channels and coordinated optimization of the water environment in the membrane,the carrier mechanism and the hopping mechanism are jointly strengthened t to achieve efficient retention of proton conductivity under low humidity.The main research contents are as follows:1.Optimization of proton transfer sites and water environment in the membrane.The introduction of PCSMs-MA@TAC core-shell microspheres can form donor-acceptor double-group proton transfer sites(acid-base pairs)at the SPEEK/PCSMs interface,which provides a new low energy barrier pathway for proton hopping.The inner core sphere with high hydration energy carboxylic acid groups effectively slow the membrane's water loss under low humidity.Even when the RH is as low as 60%,the proton conductivity of the SPEEK/PCSMs-MA@TAC-10 composite membrane is still 67 m S/cm at 80°C,which is3.16 times higher than that of the SPEEK membrane.2.Construction of multi-stage transmission channels and optimization of proton transfer process.A continuous distillation-precipitation polymerization method was used to introduce an acidic shell layer rich in carboxylic acid groups and a basic shell layer rich in imidazole groups on the surface of HNTs,and incorporated them into SPEEK to prepare composite membranes.Two types of donor-acceptor dual-group transfer sites can be formed between the imidazole group of the DSNT-A@B outer shell and the-SO₃H group on the SPEEK and the-COOH group on the inner shell.Both provide low-energy barrier pathways for proton transfer,enabling proton transport in multi-stage channels.When the content is 5 wt%,the composite membrane reaches 0.336 S/cm at 80°C and 100%RH.Compared to the original membrane,its performance is improved by two times.3.Phosphoric acid molecules can be used as donor-acceptor single-group proton carriers,providing abundant proton hopping sites for proton transfer.The vacuum-assisted method(VAM)was used to extrude phosphoric acid molecules into the CTFp porous organic framework,achieving high loading of H₃PO₄ and low leakage rate of phosphoric acid.It was blended with SPEEK matrix to prepare composite membranes.The high concentration of H₃PO₄ stored in H₃PO₄@CTFp can form hydrogen bond networks in the membrane to provide a continuous transmission path for proton transfer.A transmission path with a low energy barrier can bring higher electrochemical performance to the composite membrane by enhancing proton hopping.At 30%RH,the maximum power density of batteries with SPEEK/H₃PO₄@CTFp-15 composite membrane is 68.9%higher than that of batteries with SPEEK blank membrane.