Preparation And Characterization Of Guanidinium-functionalized Graphene Oxide Hybrid Anion Exchange Membranes

Anion Exchange Membrane Fuel Cells(AEMFCs)has recently attracted tremendousattention due to its facile oxygen reduction in alkaline media,the usability of non-noble electro-catalysts and lower fuel crossover.As a critical component of AEMFCs,anion low ionic conductivity and inferior stability of AEMs are two major problems restricting practical application of AEMFCs.Therefore,modification of AEMs has become a research hotspot.The researches point out that the inorganic nanomaterials added into the membranes may lead to a great improvement in their ionic conductivity,mechanical strength and other electrochemical properties.In this dissertation,a series of AEMs were prepared by separating ion exchange groups and main chain,which contain guanidinium-functionalized graphene oxide as nanomaterial and un-quaternized,diethanolamine modified polysulfone(HPSf)as mian chain.Main contents are showed as following:(1)Firstly,single guanidinium-functionalized graphene oxide(GGO)was prepared by the reaction of graphene oxide,3-aminopropyltrimethoxysilane and 1-bromobutane.Then a series of HPSf-GGO membranes were prepared via(GGO)into HPSf,and the pure PSf-GGO composite membrane was also prepared as a comparative experiment.With the mass ratio of GGO increasing from 15% to 30%,a series of HPSf-GGO show good anti-swelling stability.In particular,HPSf-GGO-25% exhibits dimensional stability(7.3% swelling ratio at 30 o C),good compatibility and the highest conductivity(10.9 m S/cm),which is ca.38% higher than that of PSf-GGO-25% at similar IEC.However,excessive GGO loading,HPSf-GGO-30%shows the conductivity decreases and poor compatibility,which blocks the hydroxide ion transport.(2)Based on HPSf-GGO membranes,increasing the amount of ionic groups on graphene oxide is a direct way to improve the conductivity.Bi-guanidinium-functionalized graphene oxides(BGO)was prepared by the reaction of graphene oxide,1,6-diaminohexane and?-chloropropyltrimethoxysilane,then a series of HPSf-BGO hybrid membranes were prepared by incorporating BGO into HPSf.As the mass ratio of BGO increasing from 15% to 30%,the change curves of water uptake,swelling ratio and hydroxide conductivity rise first and then decrease.When BGO loading of 25%,HPSf-BGO membrane exhibits the highest water uptake(61.17%),but the SR is still below 9% at 30 o C.Meawhile by scanning electron microscopy and X-ray diffraction,BGO stacking did not occur appreciably in the matrix of HPSf due to good compatibility between them.And the conductivity of HPSf-BGO-25%(14.83 m S/cm)is 26.6% higher than that of HPSf-GGO-25% at the same loading.Additionally,the conductivity of HPSf-BGO-15%(IEC=0.81 mmol·g-1)is 61% higher than that of that of PSf-GGO-30%(IEC=0.89 mmol·g-1).When the BGO content increases,it leads to aggregation of the nano-fillers and the performance of HPSf-BGO drops rapidly.This is because excessive BGO may block water and hydroxide ion transport pathway.In this dissertation,different from most of conventional hybrid AEMs,a series of hybird membranes accomplish its hydroxide ion conduction solely by the nano-filler.And the improved hydrophilicity of main chain allows for better compatibility between GGO and polymer,and also gives higher water uptake,which is beneficial for facilitating ion transport and alleviating hydroxide attack.Our work provides a route to fabrication of hybrid AEMs with improved interface properties and well balanced conductivity and robustness.