Abstract
The understanding of the relationship between the chemical structure and the hydrophilic structure is crucial for the designing of high-performance PEMs. Comparative studies in typical Nafion and sulfonated poly (ether ether ketone) (SPEEK) were performed using a combined experimental and theoretical method. SPEEK showed suppressed fuel crossover and good mechanical property but low water uptake, weak phase separation, and inadequate proton conductivity. Molecular dynamics (MD) simulation approaches were employed to get a molecular-level understanding of the structure–property relationship of SPEEK and Nafion membranes. In SPEEK membranes, the local aggregation of hydrophilic clusters is worse, and much stronger electrostatic interaction between Os–Hh was verified, resulting in less delocalized free H3O+ and much lower DH3O+. In addition, the probability of H2O–H3O+ association varied with water content. Particularly, SPEEK exhibited much lower H9O4+ probability at various relative water contents, leading to lower structural diffusivity than Nafion. Eventually, SPEEK possessed low vehicular and structural diffusivities, which resulted in a low proton conductivity. The results indicated that the structure of hydrated hydronium complexes would deform to adapt the confining hydrophilic channels. The confinement effect on diffusion of H2O and H3O+ is influenced by the water content and the hydrophilic morphologies. This study provided a new insight into the exploration of high-performance membranes in fuel cell.
Highlights
Proton exchange membrane fuel cell (PEMFC) is a type of renewable and sustainable electricity generation technology with the advantage of high efficiency and zero emission [1,2,3]
Perfluorosulfonic acid (PFSA) ionomers, in particular Nafion, composed of a hydrophobic polytetrafluoroethylene (PTFE) backbone with pendant hydrophilic side chains terminated by a sulfonic acid, are the most widely used benchmark proton exchange membrane (PEM) materials because of good stability and high proton conductivity [6,7,8]
Where Wwet are the weight of the wet membranes, Wdry are the weight of the dry membranes, Mw is the molecular weight of water (18 g mol−1), and EW is equivalent weight of Nafion (1100 g eq−1) and SPEEK (657 g eq−1) in this study
Summary
Proton exchange membrane fuel cell (PEMFC) is a type of renewable and sustainable electricity generation technology with the advantage of high efficiency and zero emission [1,2,3]. Perfluorosulfonic acid (PFSA) ionomers, in particular Nafion, composed of a hydrophobic polytetrafluoroethylene (PTFE) backbone with pendant hydrophilic side chains terminated by a sulfonic acid, are the most widely used benchmark PEM materials because of good stability and high proton conductivity [6,7,8]. They are limited by their low operation temperature, high cost, and high fuel crossover [9,10,11]. TThheenn,, MMDD ssiimmuullaattiioonnss wweerree eemmppllooyyeedd ttoo pprroovviiddee iinnssiigghhttss iinnttoo eexxppeerriimmeennttaallllyy oobbsseerrvveedd pphheennoommeennaa aanndd ggeett aa mmoolleeccuullaarr--lleevveell uunnddeerrssttaannddiinnggoof fthethheydhryodprhoilpichisltircucstturruecatunrdeparontdonpcrhoatroanctecrhisatriacsctienrNistaificsoninandNSaPfiEoEnKamndemSbPraEnEeKs. mTheemlobcraanl aesg.gTrehgealtoiocanl oafghgyredgraotpiohniliocfchluysdtreorps hainlidc tchluesstteartseaonfdhythderastteadtecoofmhpylderxaetsedwceoremipnlveexsetsigwateerde. iEnvveensttuigaaltley,dt.heEpvreonttounaldlyiff, utshioen pabroiltiotines,diinfcfulusdioinng avbeihliitciuesla, r ianncdlusdtirnugctuvreahl idciuffluarsivaitnides, sintruNcatufiroanl danifdfuSsPivEiEtiKes,minemNbarfaionnesawnderSePcEoEmKpmareemd.branes were compared
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