Based On Quantum Dot And Molecular-level Hybridization To Enhance The Proton Conduction And Methanol Barrier Property Of Nafion

This study proposes a functionalization stategy based on quantum dot(QD)and molecular-level hybridization,for precisely decorating nanophase of nanophase separation membrane.The 2-5 nm QD permits a molecular-level hybridization of Nafion,which can precisely assemble into different nanophase due to the matched structural size and chemical affinity.Then,in order to realize a uniform and continuous decoration of ionic nanophase of commercial Nafion,an in-situ molecular-level hybridization process(heat swelling adsorpotion-microwave assisted condensation)is developed.The mechanism of molecular-level hybridization has been analysed,the principle for manipulating membrane microstructure has been explored,then a new strategy for intensifying proton conduction and methanol barrier properties is proposed,in oder to offer some guidances to the hybrid material design & transfer/separation property intensification of nanophase separation membrane.The details are summarized as follows:(1)Controlling the oxidation degree and lateral size of graphene oxide(GO)by differing oxidation time and probe sonication time,and investigating the effect on nanophase separation structure and proton conduction property of Nafion hybrid membrane.It is found that,reducing the lateral size of GO could efficiently weaken the interference on nanophase separation of Nafion,thus maximizing the effect of organic-inorganic interface transfer channel on promoting proton conduction.However,the size of as-prepared smallest GO sheet is much larger than that of nanophase,so the incorporation of these species destroys the nanophase separation structure,leading to reduced mechanical properties and limited proton conduction enhancement.Based on these findings,a standard on filler selection for hybridizing nanophase separation membrane is proposed: an ideal filler for the hybridization of nanophase separation membrane should firstly possess matched structural size with nanophase.(2)Molecular-level hybridization of Nafion based on the matched structural size and chemical affinity of 2-5 nm QD.The mechanism of molecular-level hybridization is proposed: the hydrophilic polymer-like QD(PQD)generates strong electrostatic attraction with the hydrophilic –SO3H side chain of Nafion in casting solution,then automatically recognizes it and assembles into ionic nanophase driven by the side chain during DMAC evaporation;while the hydrophobic graphene oxide QD(GQD)generates strong interaction with the hydrophobic main chain of Nafion in casting solution,then assembles into backbone nanophase.PQD provides abundant ordered acid-base pairs in hybrid membrane,thus highly enhances the proton conduction property and H2/O2 fuel cell performances.Compared with control membrane,the maximum current density and power density of hybrid membrane are increased by 49% and 60%,respectively.(3)The development of in-situ molecular-level hybridization process(heat swelling adsorpotion-microwave assisted condensation)for uniform and continuous decoration of ionic nanophase of commercial Nafion.The presence of PQD network further enhances the proton conduction property and H2/O2 fuel cell performances of hybrid membrane.Compared with control membrane,the proton conductivity under 100% RH and 20% RH are enhanced by 100% and160%,respectively,the maximum current density and power density are both increased by almost one time.The presence of PQD network also efficiently regulates the free volume character and water state,hybrid membrane attains almost 12-times augment in proton/methanol transfer selectivity over control membrane.As as result,the maximum current density and power density of hybrid membrane in methanol fuel cell are increased by 96% and 94%,respectively.In addition,the mechanical property of hybrid membrane is also highly enhanced.