Construction Of Proton Transfer Channel Formed By Acid-base Pair And Optimization Of The Channel Microenvironment

As an emerging energy, proton exchange membrane fuel cell (PEMFC), whichconverts chemical energy into electrical energy, has attracted considerable attentionsdue to the features of high efficiency and non-polluting. For PEMFC, the corecomponent is proton exchange membrane (PEM). The proton conductivity of PEMexerts a crucial influence on the performances of the fuel cell. It has beendemonstrated that continuous proton transfer pathways and suitable proton transfersites are the basis for the proton transfer through PEM. The one-or two-dimensionalmaterials with high aspect ratio have unique advantages in constructing continuouspathways, and the acid–base pairs formed by acidic and basic groups could act aslow-barrier proton transfer sites. Based on hybridization theory, continuous protontransfer pathways were constructed in this thesis by embedding the modifiednano-tube/sheet into membrane matrix. In such a way, suitable proton transfer sitesare incorporated in the resulting hybrid membrane. These two factors conferenhanced proton conductivity on the hybrid membrane. Moreover, the method andtheory about process intensification of proton conduction in PEM were proposed byinvestigating the influence of membrane microstructure on the mode and efficiencyof proton conduction. The details were summarized as follows:(1) Owning to the high aspect ratio, halloysite nanotubes (HNTs) were chosen forconstructing continuous proton transfer pathways. In this study, the surface of HNTswas modified by a polymer layer bearing numerous sulfonic acid groups. Then, thesulfonated halloysite nanotubes (SHNTs) were incorporated into sulfonatedpoly(ether ether ketone)(SPEEK) to prepare the hybrid membranes. Afterwards, thestudy of proton transfer mode and mechanism were performed throughcharacterizations and measurements of the hybrid membranes. It was found that theproton conductivity of SPEEK/S4HNT-10membrane was0.0245S/cm,61%higherthan that of SPEEK control membrane at25oC and100%RH. The result indicatedthat the incorporation of SHNTs significantly enhanced the proton conductivity ofthe membranes by continuous and efficient transfer pathways. (2) Inspired by the bioadhesion mechanism, HNTs modified by polydopaminelayer with numerous amino and imino groups (dopamine-modified HNTs, DHNTs)was synthesized and then embedded into SPEEK to prepare hybrid membranes. Theproton transfer modes and mechanisms of the membranes were explored bycharacterizing and measuring systematically of the hybrid membranes. It was foundthat the SPEEK/DHNT-30membrane gived the highest conductivity ca0.018S/cmat25oC and100%RH. The result indicated that the acid-base pairs formed by basicgroup within polydopamine layer and sulfonic acid group within SPEEK phaseconstructed low-barrier transfer pathways on the SPEEK-DHNT interfacial domains.Consequently, the proton conductivity was enhanced after DHNTs incorporation.(3) Owning to the high surface area, graphene oxide (GO) was chosen forconstructing continuous proton transfer pathways. In this study, the hybridmembranes were prepared by filling the sulfonated GO (SGO) into chitosan (CS)matrix. It was found that the hydrated proton conductivity of CS/S4GO-2membranewas0.0267S/cm at25oC, and the anhydrous proton conductivity was10.894mS/cm at120oC, which were2.28and1.19times of CS control membrane underthe same condition, respectively. The results indicated that the acid-base pairsformed by sulfonic acid group within SGO and basic group within CS chainsconstructed long-range ordered pathways. The presence of these efficient pathwaysyielded an obvious enhancement of proton conductivity to the hybrid membranes.Additionally, these acid-base paired pathways could allow fast proton transfer viaGrotthuss mechanism under anhydrous condition, resulting in a high anhydrousproton conductivity for the hybrid membranes.