Proton Conductivity Measurements Research Articles

Structure, Luminescent Sensing and Proton Conduction of a Boiling-Water-Stable Zn(II) Metal-Organic Framework.

A novel Zn(II) metal-organic framework [Zn4O(C30H12F4O4S8)3]n, namely ZnBPD-4F4TS, has been constructed from a fluoro- and thiophenethio-functionalized ligand 2,2′,5,5′-tetrafluoro-3,3′,6,6′-tetrakis(2-thiophenethio)-4,4′-biphenyl dicarboxylic acid (H2BPD-4F4TS). ZnBPD-4F4TS shows a broad green emission around 520 nm in solid state luminescence, with a Commission International De L’Eclairage (CIE) coordinate at x = 0.264, y = 0.403. Since d10-configured Zn(II) is electrochemically inert, its photoluminescence is likely ascribed to ligand-based luminescence which originates from the well-conjugated system of phenyl and thiophenethio moieties. Its luminescent intensities diminish to different extents when exposed to various metal ions, indicating its potential as an optical sensor for detecting metal ion species. Furthermore, ZnBPD-4F4TS and its NH4Br-loaded composite, NH4Br@ZnBPD-4F4TS, were used for proton conduction measurements in different relative humidity (RH) levels and temperatures. Original ZnBPD-4F4TS shows a low proton conductivity of 9.47 × 10−10 S cm−1 while NH4Br@ZnBPD-4F4TS shows a more than 25,000-fold enhanced value of 2.38 × 10−5 S cm−1 at 40 °C and 90% RH. Both of the proton transport processes in ZnBPD-4F4TS and NH4Br@ZnBPD-4F4TS belong to the Grotthuss mechanism with Ea = 0.40 and 0.32 eV, respectively.

Development of proton conductive polymer electrolytes composed of sulfonated poly(ether ether ketone) and Brønsted acidic ionic liquid (1-methylimidazolium tetrafluoroborate)

This article relates to the synthesis, characterization and dielectric measurements of solid polymer electrolytes, derived from the ionic interaction of sulfonated poly(ether ether ketone) (sPEEK) and a Brønsted acidic ionic liquid (1-methylimidazolium tetrafluoroborate, [Hmim][BF4]) for electrochemical applications. The efficiency of the interaction was examined by incorporating different amounts of ionic liquid (IL) with the sulfonated polymer matrices having three different degrees of sulfonation (DS). The polymer matrices and composite electrolytes were systematically characterized with 1H NMR, FT-IR, SEM, TGA and DMA. Anhydrous proton conductivity and dielectric measurements were studied in detail with varying temperature and frequencies. The presented analyzes revealed that sPEEK1.0–2 sample (2.50–3.51 × 10–1 Sm−1 at 380–450 K) exhibited maximum proton conductivity and thermomechanical stability under anhydrous environment. Dielectric measurements also provided results confirming proton conductivity measurements. Furthermore, sPEEK1.0–2 composite membrane exhibited higher glass transition temperature and reasonable storage modulus value (Tg = 157 °C; E′ = 0.22 GPa) compared to IL-doped sPEEK membranes presented in the literature. The work herein opens new prospects for the as-synthesized materials to use as a solid polymer electrolyte for electrochemical applications such as high temperature proton exchange membrane fuel cells (HT-PEMFC) in a wide temperature range.

Proton exchange composite membranes comprisingSiO2, sulfonatedSiO2, and metal–organic frameworks loaded inSPEEKpolymer for fuel cell applications

AbstractProton exchange membrane fuel cell (PEMFC) is a promising technology that offers a clean and efficient renewable energy source. The hybrid SiO2, sulfonated SiO2(SSiO2), and metal–organic framework‐5 (MOF‐5) incorporated sulfonated poly (ether ether ketone) (SPEEK) ternary composite membranes are fabricated using dry phase inversion technique for PEMFC. The membrane performance is evaluated in terms of water uptake, ion exchange capacity, methanol permeability, and proton conductivity (PC) measurements. The morphological study of fabricated membranes was carried out using scanning electron microscopy and atomic force microscopy analysis. The mechanical stability is strengthened up to 30–40%, and the PC gets enhanced with the incorporation of MOF‐5, achieving simultaneous improvement in proton conduction and membrane stability. The PC of the ternary SPEEK/SSiO2/MOF‐5 membrane is 3.69 × 10−3S cm−1, 32% more than the neat membrane. A significant increase in selectivity of 23% is observed by incorporating SSiO2and MOF‐5 fillers when compared with the neat membrane. The synergistic effect of MOF‐5 and SSiO2in the ternary membrane has significantly improved water retention and proton conductivity. The functional SO3H groups of SiO2and MOF‐5 bonded via acid–base electrostatic interactions with the SPEEK; enhances proton conduction accompanied by suppressing the methanol penetration through membranes.

수소-산소 연료 전지용 나노물질 첨가 고분자 전해질 막

The solid electrolyte membrane for a hydrogen-oxygen fuel cell was prepared and investigated from the potential of sulfonated poly(ether ether ketone) (SPEEK) embedded together with montmorillonite (MMT). Acid hydrophilized poly(ether ether ketone) (PEEK) and MMT with varying sulfonation levels of 25-70% prepared through solvent casting were investigated for their performance. The nuclear magnetic resonance (1H NMR) spectra at 7.5 ppm affirmed the occurrence of sulfonation reaction, and its degree was studied by both 1H NMR and titration method. The reaction time was varied to achieve sulfonation levels from 25 to 70%. The effect of incorporation of pristine and sulfonated MMT into SPEEK was examined. The membranes, prepared using solvent casting technique, were involved for water uptake over the wide range of temperature, thermal stability, and proton conductivity measurements. The cross-sectional surface arrangement of the membrane and clay dispersion was deliberated using SEM. The proton exchange membrane fuel cell (PEMFC) single cell’s tests revealed that sulfonated PEEK membrane demonstrated service performance comparable to that of Nafion, as validated using MATLAB software.

Light-Responsive Proton Conductor: Record High Gain of Proton Conductivity Achieved by Photoinduced Electron-Transfer Strategy

Light-Responsive Proton Conductor: Record High Gain of Proton Conductivity Achieved by Photoinduced Electron-Transfer Strategy

New isoreticular phosphonate MOFs based on a tetratopic linker.

The tetratopic linker 1,1,2,2-tetrakis(4-phosphonophenyl)ethylene (H8TPPE) was used to synthesize the three new porous metal-organic frameworks of composition [M2(H2O)2(H2TPPE)]·xH2O (M = Al3+, Ga3+, Fe3+), denoted as M-CAU-53 under hydrothermal reaction conditions, using the corresponding metal nitrates as starting materials. The crystal structures of the compounds were determined ab initio from powder X-ray diffraction data, revealing small structural differences. Proton conductivity measurements were carried out, indicating different conductivity mechanisms. The differences in proton conductivity could be linked to the individual structures. In addition, a thorough characterization via thermogravimetry, elemental analysis, IR-spectroscopy as well as N2- and H2O-sorption is given.

Site-Specific Proton Dynamics in Indium-Doped Tin Pyrophosphate

Tin pyrophosphates are solid-state materials that have been proposed for use as proton conductors in intermediate-temperature fuel cells. However, protons must be added synthetically as these materials do not contain structural protons. Protonation via indium doping results in two NMR-resolvable proton signals that correspond to hydrogen-bonded interstitial protons at phosphate tetrahedral and metal octahedral sites. These sites were assigned by using 1H NMR spectroscopy, allowing for site assignment based on the assumption that protons occupying the octahedral sites are more mobile. The full width at half-maximum and longitudinal relaxation were measured to assess proton mobility. Exchange spectroscopy showed that intersite proton exchange (needed for long-range proton transport) is enhanced by increased indium doping up to 20%. Activation energies calculated from proton exchange and proton conductivity measurements suggest that indium doping does not affect the mechanism of proton conduction in these materials: hopping between octahedral and tetrahedral sites. The increased proton conductivity is instead attributable to increased proton concentration.

Analysis of proton and electron transport impedance of a PEM fuel cell in H2/N2 regime

AbstractAnalytical expressions for impedance of proton and electron transport in the cathode catalyst layer of a PEM fuel cell operating in H/N regime are derived. In the high–frequency range, the dependence of imaginary part of impedance on is a straight line with the slope depending on the cathode catalyst layer (CCL) proton and electron conductivity. The characteristic frequencies of proton and electron transport associated with the double layer charging are close to each other (denoted below as ). The frequency in the cathodes of various type may differ by three orders of magnitude. DRT spectrum of CCL impedance in H2/N2 regime shows two peaks located at the frequencies and . The second frequency of electron transport in the CCL is about four times higher than . Analytical results can be used for simultaneous measurement of proton and electron conductivity of PEMFC cathodes using electrochemical impedance spectroscopy.

Measurement of Proton Conductivity and Water Diffusivity of Nafion Membrane at Subzero Temperatures

Water management is critical for the high performance of proton exchange membrane fuel cells (PEMFCs). The knowledge of PEM properties such as water content, proton conductivity, and water diffusivity is necessary for water management. In literature, PEM properties are very well documented at temperatures above room temperatures but at subzero temperatures PEM properties are scarcely reported. The acquisition of PEM properties at sub-zero temperatures is very important to the quick start-up of fuel cell electric vehicles in below freezing conditions.The objective of this study is to obtain the water transport characteristics of a membrane at subzero temperatures for automotive applications. In this study, three different properties of a Nafion membrane are quantified: water content, proton conductivity, and water diffusivity.In sub-zero condition at different RHs, the membrane water content and proton conductivity were quantified from gravimetric and electrochemical measurements. A novel measurement technique using segmented cell and methodology were established to estimate water diffusion coefficient as a function of water content and temperature (see figure below). Further, particular to the Nafion membrane, an empirical relationship between water diffusivity and water content in temperature range of 243K to 303K was developed. Figure 1

Direct Measurement of Proton Conductivity in the Catalyst Layer of PEFC

I ntroduction Since the commercialization of FCVs, PEFCs have attracted attention. For further improvement of the efficiency, raising the operating temperature is focused as one possible solution. We have been studying higher temperature and low humidity operation, and have found that decrease in ionomer’s proton conductivity enhances degradation of the cathode and there is a correlation between the proton conductivity of ionomers in the cathode and PEFC’s durability [1, 2]. Even though the proton conductivity within the cathode is important, such proton conductivity has not been directly measured. Therefore, in this study, we investigated a method of directly measuring proton conductivity in the cathode layer. Experimental By referring to a common method of making MEAs, electrocatalyst layers were prepared by spraying the slurry containing 46%Pt/KB (TEC10E50E) and three different ionomers (Nafion, AquivionD72, and AquivionD83) on the Nafion membrane (Nafion 212). The I/C was kept 0.72 and 0.76 for Nafion and Aquivion, respectively. Then, another Nafion membrane was placed further on the sprayed electrocatalyst layer. The size of electrocatalyst layer and Nafion membranes were 30 mm×10 mm and 35 mm×14 mm, respectively, as shown in Fig. 1(a). Here, the catalyst layer was smaller than the membrane for the catalyst layer not to contact with Pt electrode of the holder shown in Fig. 1(b) even after hot-pressing. Two carbon papers adhered by carbon paste were put between the membrane and Pt electrode. With this holder, impedance was measured in the nitrogen or hydrogen atmosphere by applying DC or AC (10 mV, 0.1 mA, 32 MHz~10 Hz). Measurements were performed under 80oC-RH100% and 105oC-RH57% as a common operating condition and a low humidity condition, respectively. Results and discussion The proton conductivity was calculated based on the impedance. Measuring impedance in nitrogen atmosphere with AC, the movement of electrons within the electrocatalyst layer cannot be excluded completely. If Nafion ionomer within the electrocatalyst layer forms a condensed thin film, the thickness will be 1.25 μm based on the mass and density of Nafion ionomer, resulting in 0.0025 Ω. However, in reality, Nafion ionomer spreads out through the catalyst layer and results in higher resistance. In this study, the obtained resistance for the catalyst layer with Nafion ionomer was 0.031 Ω, which was more than ten times larger. Larger resistance is reasonable at this moment, but again there is high possibility of including electron conductivity within the catalyst layer. Therefore, in the next step, we tried to apply DC. Since the reaction with low overvoltage was desired for this measurements, DC was applied under hydrogen atmosphere where the reaction is reversible and its overvoltage is small. We’ll report the results obtained by applying DC under the hydrogen atmosphere.

Experimental measurement of proton conductivity and electronic conductivity of membrane electrode assembly for proton exchange membrane fuel cells

Charge transport processes involving the proton migration and electron transfer for different parts of membrane electrode assemble (MEA) play an essential role for developing the novel electrode and enhancing the electrochemical performance towards proton exchange membrane fuel cells (PEMFCs). However, the coupled charge transport processes make it difficult for evaluating proton conductivity and electronic conductivity of different parts in MEAs under operation conditions of fuel cells. Here in this work, we propose an experiment approach for separating the electronic conductivity and proton conductivity of different components of MEA at the operating conditions of PEMFCs. This approach involves two different measuring devices, which both consist of electron or proton conducting layers, sealing layers and sample layer, followed by tailoring the thickness of sample layers and via electrochemical impedance spectroscopy (EIS) to quantity the electronic conductivity and proton conductivity of different layers. These experiment results show the great potential in the development of different components of MEA.

Measurement of Proton Conductivity and Water Diffusivity of Nafion Membrane at Subzero Temperatures

Objective of this study is to obtain the water transport characteristics of Nafion at subzero temperature for automotive application. To achieve this objective, three different properties of the membrane are quantified: water content, proton conductivity, and diffusivity. Water content is computed from measuring the difference in weight between the dry membrane and humidified membrane at each relative humidity and subzero temperature. To measure the weight a special environmental cell was developed and integrated with the microbalance. To quantify the proton conductivity and the water diffusivity, a conductivity measurement electrochemical cell with segmented electrode is designed and fabricated to measure the high frequency resistance across the membrane at test conditions. An equation is developed for water content in terms of relative humidity and temperature. Equations for proton conductivity and water diffusion coefficient are presented in terms of water content and temperature. These equations are developed from experimental data obtained between 243K and 303K at different relative humidity.

Electron and proton conductivity of Fe-N-C cathodes for PEM fuel cells: A model-based electrochemical impedance spectroscopy measurement

Impedance spectra of a PEM fuel cell with three Fe-N-C cathodes have been measured under the H2/N2 testing regime. The spectra have been fitted using a recently developed physics-based impedance model, which takes into account finite proton (σp) and electron (σe) conductivity of the oxygen-free cathode catalyst layer. Fitting allowed to extract numerical data for σp, σe, the double layer capacitance, and the inductance of cables used for measuring impedance spectra. The values of σp and σe are close to what previously found for standard Pt/C electrodes, which is found for the first time using PGM-free catalysts. The method enables simultaneous measurement of reference proton and electron conductivity of PEMFC cathode.

Stability of Ionic-Covalently Cross-Linked PBI-Blended Membranes for so2 electrolysis at Elevated Temperatures

In this study, the effect of component composition on the chemical stability of the developed ionic-covalently cross-linked PBI-blended membrane concept from earlier studies for application in SO2 electrolysis at elevated temperatures (>100 °C) is further investigated. Three different acid-base ratios were studied by blending a partially fluorinated sulfonated arylene main-chain polymer (SFS) with polybenzimidazole (F6PBI) and a partially or non-fluorinated bromo-methylated polymer (BrPAE). In addition two different alkylated imidazoles (EMIm and TMIm) were included as quaternization agents. Accordingly, twelve different PBI-blended membranes were used in this study. The suitability of these membranes for SO2 electrolysis at elevated temperatures was determined in terms of i) the H2SO4 stability (80 wt% H2SO4 at 100 °C for 120 hours), (ii) the oxidative stability (Fenton’s test, FT) and (iii) the organic solvent stability (extraction in N,N-Dimethylacetamide). Membranes were characterized in terms of the percentage weight, the ion exchange capacity (IEC) and the thermal stability (TGA-FTIR) changes, before and after the various treatments. Although all blended membrane types were sufficiently stable during H2SO4 treatment, proton conductivity measurements indicated that the blends containing only partially fluorinated blend components displayed superior stability (better compatibility) as well as conductivity. Cell voltages showed an improvement of up to 190 mV for operations at 120 °C compared to earlier studies conducted at 80 °C for similar PBI-blended membranes. It was established that both chemically stable and conductive PBI-blended membranes, suitable for SO2 electrolysis above 100 °C, could be obtained by varying the composition of selected polymer components.Figure 1: Schematic of the ionic-covalently cross-linking concept for the blend membranes (black – BrPAE, purple – F6PBI, blue – EMIm, and brown - sPPSU). Figure 1

Stability of ionic-covalently cross-linked PBI-blended membranes for SO2 electrolysis at elevated temperatures

In this study, the effect of component composition on the chemical stability of the developed ionic-covalently cross-linked PBI-blended membrane concept from earlier studies for application in SO2 electrolysis at elevated temperatures (>100 °C) is further investigated. Three different acid-base ratios were studied by blending a partially fluorinated sulfonated arylene main-chain polymer (SFS) with polybenzimidazole (F6PBI) and a partially or non-fluorinated bromo-methylated polymer (BrPAE). In addition two different alkylated imidazoles (EMIm and TMIm) were included as quaternization agents. Accordingly, twelve different PBI-blended membranes were produced in this study. The suitability of these membranes for SO2 electrolysis at elevated temperatures was determined in terms of i) the H2SO4 stability (80 wt% H2SO4 at 100 °C for 120 h), (ii) the oxidative stability (Fenton's test, FT) and (iii) the organic solvent stability (extraction in N,N-Dimethylacetamide). Membranes were characterized in terms of the percentage weight, the ion exchange capacity (IEC) and the thermal stability (TGA-FTIR) changes, before and after the various treatments. Although all blended membrane types were sufficiently stable during H2SO4 treatment, proton conductivity measurements indicated that the blends containing only partially fluorinated blend components displayed superior stability (better compatibility) as well as conductivity. Cell voltages showed an improvement of up to 190 mV for operations at 120 °C compared to earlier studies conducted at 80 °C for similar PBI-blended membranes. It was established that both chemically stable and conductive PBI-blended membranes, suitable for SO2 electrolysis above 100 °C, could be obtained by varying the composition of selected polymer components.

Incorporation of titanium pyrophosphate in polybenzimidazole membrane for medium temperature dry PEFC application

In the interest of adopting acid-modified metal oxide additives in polymer electrolyte membrane fuel cell membrane, titanium pyrophosphate (TiP2O7) was synthesized via direct modification of TiO2-P25 with 85% orthophosphoric acid (stochiometric ratio of P/Ti = 2.0) using a modified synthesis path and calcined at 600 °C for 5 h. Low amounts of TiP2O7 (1 and 2 wt%) were successfully introduced into polybenzimidazole (PBI), upon confirmation by FT-IR and SEM-EDS. The obtained membranes were doped with 8 mol phosphoric acid doping level (PADL) prior to proton conductivity measurement under dry condition from 160 to 50 °C. Among the measurements, the highest conductivity was obtained by PBI with 1 wt% TiP2O7, which was 3.85 mScm−1 at 160 °C, followed by PBI with 2 wt% TiP2O7 (2.69 mScm−1). Both samples exhibited higher conductivity compared to PBI with 2 wt% TiO2 (2.03 mScm−1) and pristine PBI (1.53 mScm−1). For the fuel cell performance under the same condition, PBI with 2 wt% TiP2O7 achieved a maximum power density of 580 mWcm−2 at 160 °C, outperformed PBI with 2 wt% TiO2 (524 mWcm−2), PBI with 1 wt% TiP2O7 (497 mWcm−2) and pristine PBI 454 mWcm−2. Acid leaching test and long term stability evaluation with 0.2 Acm−2 constant current density test revealed that TiP2O7 inherited the acid retention ability of TiO2 while the pyrophosphate group significantly improved the proton conductivities of composite membrane.

Proton Conductivity through Polybenzimidazole Composite Membranes Containing Silica Nanofiber Mats.

The quest for sustainable and more efficient energy-converting devices has been the focus of researchers′ efforts in the past decades. In this study, SiO2 nanofiber mats were fabricated through an electrospinning process and later functionalized using silane chemistry to introduce different polar groups −OH (neutral), −SO3H (acidic) and −NH2 (basic). The modified nanofiber mats were embedded in PBI to fabricate mixed matrix membranes. The incorporation of these nanofiber mats in the PBI matrix showed an improvement in the chemical and thermal stability of the composite membranes. Proton conduction measurements show that PBI composite membranes containing nanofiber mats with basic groups showed higher proton conductivities, reaching values as high as 4 mS·cm−1 at 200 °C.

Synthesis, crystal structure and possible proton conduction of Fe(H2PO4)2F

A new iron fluorophosphate compound, Fe(H2PO4)2F, was synthesized by a solvent-less method at low temperatures. Its structure was determined from single crystal X-ray diffraction. Fe(H2PO4)2F was found to have a 3-dimensional structure built up by parallel chains of corner-sharing octahedra. This novel compound crystallizes in a tetragonal I4/mcm space group with the following lattice parameters: a = b = 9.01870(10) Å and c = 7.8058(2) Å. Further characterization of the material was conducted by TGA and Mössbauer spectroscopy. Proton conductivity measurements under dry condition revealed activation energies of Ea = 0.43 eV (along c-axis) and Ea = 0.41 eV (along a-axis) with corresponding room-temperature conductivities 2.6 × 10−7 S cm−1 and 5.8 × 10−8 S cm−1.

Probing Acetonitrile Solvation in Perfluorsulfonate Ion Exchange Membrane By in-Situ FTIR

In-situ FTIR is a successful tool to study water absorption and interactions within the Perfluorsulfonate Ion Exchange Membrane (PFSA)(1–4). The versatility of the technique can reveal in-depth information related to proton transport in PFSA, including proton dissociation and solvation. Another desirable feature is that experiments under controlled water content(λ) is also possible. Studies of PFSA membranes equilibrated with different λ was fundamental to understand membrane behavior(5). The volatile nature of acetonitrile and many organic solvents adds to the inaccuracy of many classic membrane characterization methods. To overcome this, techniques tailored for membrane incorporated with organic solvents are necessary. In this study, acetonitrile and lithiated PFSA were chosen to revisit the in-situ IR technique. The goal of this work is to examine acetonitrile’s role in membrane swelling and to create a ‘slow-motion picture’ of how acetonitrile molecules behave upon being imbibed into the membrane, especially at low λ. The vibrational signal of cyanide group (~2250 cm-1)does not overlap with other signals from the membrane and is known to respond to dipole interactions by shifting to higher wavenumber(6). This feature makes an acetonitrile-swollen system an even more favorable candidate for in-situ IR study compared to its aqueous counterpart. For studying proton transport in membrane, initial water buildup in membrane yields a weak and broad signal, making the already obscure -OH stretching region even more complicated to analyze. Without interference from hydrogen bonding, lithium ion solvation with cyanide can be clearly observed. Coupled with monitoring -SO3- area, it is totally feasible to simultaneously see both cation dissociation from membrane (Fig.1A) and cation solvation in solvent (Fig.1B) in a real-time manner to compare with fully swollen state. Acknowledgement We gratefully acknowledge the support of this work by the U.S. Department of Energy, Office of Electricity Delivery and Energy Reliability (Dr. Imre Gyuk). We also thank 3M for providing membranes. References Elabd YA, Baschetti MG, Barbari TA. Time-resolved Fourier transform infrared/attenuated total reflection spectroscopy for the measurement of molecular diffusion in polymers. J Polym Sci Part B Polym Phys. 2003;41(22):2794–807.Hallinan DT, Elabd YA. Diffusion of Water in Nafion Using Time-Resolved Fourier Transform Infrared−Attenuated Total Reflectance Spectroscopy. J Phys Chem B. 2009 ;113(13):4257–66.Hallinan DT, Elabd YA. Diffusion and Sorption of Methanol and Water in Nafion Using Time-Resolved Fourier Transform Infrared−Attenuated Total Reflectance Spectroscopy. J Phys Chem B. 2007 ;111(46):13221–30.Kunimatsu K, Bae B, Miyatake K, Uchida H, Watanabe M. ATR-FTIR Study of Water in Nafion Membrane Combined with Proton Conductivity Measurements during Hydration/Dehydration Cycle. J Phys Chem B. 2011 21;115(15):4315–21.Zawodzinski TA, Derouin C, Radzinski S, Sherman RJ, Smith VT, Springer TE, et al. Water Uptake by and Transport Through Nafion® 117 Membranes. J Electrochem Soc. 1993 ;140(4):1041–7.Barthel J, Buchner R, Wismeth E. FTIR Spectroscopy of Ion Solvation of LiClO4 and LiSCN in Acetonitrile, Benzonitrile, and Propylene Carbonate. J Solut Chem. 2000 ;29(10):937–54. Figure.1A: SO stretching shift due to solvation; Figure.1B: Normalized CN stretching area upon acetonitrile buildup in the membrane. Blue dashline indicates corresponding fully swollen state. Figure 1

Thickness Dependence Impact on Proton Transport Proton Properties of Nafion® Thin-Film on Platinum Model Electrode

Introduction Improving oxygen reduction reaction (ORR) activity of cathode catalyst is required for wide spread of polymer electrolyte fuel cells. Because ORR occurs at the three-phase-boundary among the cathode catalyst, ionomer and oxygen gas, understanding the impact the ionomer on the cathode catalyst is important to achieve the high performance PEFCs. Especially, the structure of the ionomer on the cathode is strongly influenced by humidity, thickness, annealing treatment [1-3]. In this study, we examined the proton conductivity the Nafion® thin-film with various thickness from 5 to 200 nm. The correlation between structure and proton conductivity of the Nafion on Pt electrode was discussed. Experimental For proton conductivity measurements, Nafion thin-films were prepared on interdigitated array of gold electrodes on SiO2 substrate by soaking the electrode on Nafion dispersion. For GISAXS measurements, Nafion thin-films were prepared on Pt sputtered P doped-silicon substrates by spin casting of Nafion dispersion. Proton conductivity under humidity was measured by applying an alternating potential of amplitude 100 mV over a frequency 7 MHz to 0.01 Hz. GISAXS measurements were performed under humidity in beamline BL40B2 at SPring-8, Japan. Results and Discussion In the Nafion thin-films with thickness more than 50 nm, EIS results indicated that the hydrophilic domains grew gradually as the thickness increases. In contrast, the hydrophilic domains, which works as the protonic path, grows larger with increase of the thickness, leading to reduce the activation energy of proton conductivity. According to GISAXS, the hydrophilic domain disappears in the Nafion thin-film with thickness less than 50 nm. These results indicate that the structure of Nafion thin-film drastically changes with the thickness. It is anticipated that the proton conductivity of the in-plane in the Nafion film is larger than that of the out-of-plane because the hydrophilic domain of the in-plane grows larger than that of the out-of-plane. The anisotropy of the ordered structure in the Nafion thin-film is enhanced by the interaction between the ionomer and substrate. These results indicate that the proton conductivity in the Nafion is largely influenced by the amount of the hydrophobic domain. Acknowledgments This research is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO). Reference: [1] A. Kusoglu, D. Kushner, D. K. Paul, D. Karan, M. Hickner, A. Weber, Adv. Funct. Mater., 24, 4763 (2014) [2] D. K. Paul, H. K. Shim, J. B. Giorgi, K. Karan, J. Polym. Sci. B Polym. Phys., 54, 1267 (2016) [3] D. K. Paul, R. McCreery, K. Karan, J. Electrochem. Soc., 161, F1395 (2014)