Abstract
A nanostructured hybrid material consisting of TiO2 nanoparticles grown and stabilized on graphene oxide (GO) platelets, was synthesized and tested as nanofiller in a polymeric matrix of sulfonated polysulfone (sPSU) for the preparation of new and low-cost nanocomposite electrolytes for proton exchange membrane fuel cell (PEMFC) applications. GO-TiO2 hybrid material combines the nanoscale structure, large interfacial area, and mechanical features of a 2D, layered material, and the hygroscopicity properties of ceramic oxides, able to maintain a suitable hydration of the membrane under harsh fuel cell operative conditions. GO-TiO2 was synthetized through a new, simple, one-pot hydrothermal procedure, while nanocomposite membranes were prepared by casting using different filler loadings. Both material and membranes were investigated by a combination of XRD, Raman, FTIR, thermo-mechanical analysis (TGA and Dynamic Mechanical Analysis) and SEM microscopy, while extensive studies on the proton transport properties were carried out by Electrochemical Impedance Spectroscopy (EIS) measurements and pulse field gradient (PFG) NMR spectroscopy. The addition of GO-TiO2 to the sPSU produced a highly stable network, with an increasing of the storage modulus three-fold higher than the filler-free sPSU membrane. Moreover, the composite membrane with 3 wt.% of filler content demonstrated very high water-retention capacity at high temperatures as well as a remarkable proton mobility, especially in very low relative humidity conditions, marking a step ahead of the state of the art in PEMs. This suggests that an architecture between polymer and filler was created with interconnected routes for an efficient proton transport.
Highlights
Proton exchange membrane fuel cells (PEMFCs) are recognized worldwide as one of the most promising clean energy conversion technologies [1,2]. Owing to their high chemical-to-electrical energy conversion efficiency, and due to their zero-CO2 emission, proton exchange membrane fuel cell (PEMFC) are targeted as an energy source for electric vehicles, they are proposed for a wide range of applications, from portable to automotive and stationary
The state-of-the-art PEM is based on Nafion®, a perfluorosulfonic acid ionomer (PFSA), developed in the 1960s by Dupont, which is still, nowadays, the most used membrane both in fuel cell research and industry, since it combines high proton conductivity, excellent chemical stability, and good mechanical resistance
NanGomraatperhiaelsn2e020o,x1i0d, e157(2GO) was prepared according to the following procedure [41,42]: 10 g4 off18 graphite powder and 200 g of potassium chlorate powder were slowly added to a mixture of sulfuric aTvacnihpamgidednroaodfwrgaidonnnanuuasedicstlttfriGminciwnciOsaataatrgliscilprncyircdreieoadntn(cidrg4ctiiurd0efsi0codfttu(:ri24rawg1r00tei800anrd:oshmg2,o0cwafLme0on,nardmrstterhe1tiLsm8hefpud,uhpegsrsceeeaeqtrsdnivaupv,deteeeuwrnlctarycthalei)husv.t.eihesmTdelqhydebue)s.yserweTnepvahicotehcehurtearirddoilenintasbgitcmwyittlhilaepoeessdnomcwuwowriinixatanhdttsugeudrrccteiuohsteinnteniddtltmilouleindticdxhtaitewesundtpariileHtcileneeirdn=bautwano6nt.aht0diitc,leiuesartnt.hnibdlTedaleehtpwrdheHvafiwusi=ngnafiao6dtnler.e0oaGrr.,lulOys dried at room temperature
Summary
Proton exchange membrane fuel cells (PEMFCs) are recognized worldwide as one of the most promising clean energy conversion technologies [1,2]. The state-of-the-art PEM is based on Nafion®, a perfluorosulfonic acid ionomer (PFSA), developed in the 1960s by Dupont, which is still, nowadays, the most used membrane both in fuel cell research and industry, since it combines high proton conductivity, excellent chemical stability, and good mechanical resistance. Its high environmental impact, due to its content in fluorine atoms, and its elevated production costs are both issues that are driving the research toward alternative proton conductive ionomers [4]. In this regard, great efforts have been devoted to the development of non-fluorinated polymers (n-FPs) [5]. The incorporation of SiO2, ZrO2, TiO2, zeolites, zirconium hydrogen phosphonates, and Layered Doubled Hydroxide (LDH) materials has been demonstrated to remarkably improve the physico-chemical and mechanical properties of the resulting composite membranes, as well as the electrochemical behavior since the high acid surface area and hydrophilicity of such nanofillers usually favor the proton transport [20,21,22,23]
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