Proton-conducting Electrolyte Membranes Research Articles

Bilayer Cell Model and System Design of Highly Efficient Protonic Ceramic Fuel Cells

Protonic ceramic fuel cells (PCFCs) are promising devices for highly efficient next-generation fuel cell systems. PCFCs provide several benefits. Water formation at the cathode can improve fuel utilization. Also, lowering operation temperature using proton-conducting solid electrolyte membranes will enable a long lifetime and low system costs. On the other hand, ionic and electronic transport properties, i.e., proton, oxide ion, hole, and electron conductions, in PCFCs induce leakage current in electrolyte membranes and decrease energy conversion efficiency. Therefore, controlling the transport properties and designing cell structures to prevent them are important issues for developing highly efficient PCFCs. In this study, a comprehensive design approach was conducted from a bilayer cell to a PCFC system.It has been reported that bilayer electrolytes can improve the interface between cathode and electrolyte and also prevent nickel diffusion (1). Additionally, it has been reported that bilayer electrolytes can suppress leakage current by using a hole blocking layer (2, 3). Therefore, the use of bilayer electrolytes can help improve the efficiency and performance of PCFCs. In this study, a bilayer PCFC consisting of BaZr0.8Y0.2O3−δ (BZY) and BaZr0.1Ce0.7Y0.1Yb0.1O3−δ (BZCYYb) was modeled by considering the transport properties of each electrolyte. The main objective of the modeling was to determine the best cell design and operating conditions that maximize PCFC efficiency. Calculations were done by solving the set of integral equations described by Choudhury and Patterson (4) but extended for bilayer electrolytes (3) to obtain the cell potential, and the total and proton current densities.It was found that higher efficiencies were obtained when using a thin layer of BZY with a thicker layer of BZCYYb. The calculations suggest that the thin BZY layer acts as an electron-blocking layer. For example, leakage currents of less than 5% can be achieved by using a BZY(1 µm)|BZCYYb (19 µm). It was also found that the PCFC efficiency increased with decreasing temperature. Thus, higher efficiencies were obtained at 500°C than at 600°C.In addition, the energy conversion efficiency of a 5kW(DC)-class PCFC system was evaluated. In this study, the fuel in an anode was assumed to be hydrogen obtained by steam reforming of methane. Gas compositions in the streams of the PCFC system were calculated based on thermodynamic equilibrium at atmospheric pressure. The operating temperature of PCFC module was set as 500°C-600°C, and the external current density was assumed to be 300 mA/cm2. Here, the leakage current ratio was defined as a percentage of the leakage current to the total ion current density. The system efficiency was defined as an extracted power of the PCFC to the combustion heat of methane (25°C, LHV).The results are described as a standard case of 600°C as follows. A system efficiency of 69.5％ (LHV, DC) was attainable, assuming the cell voltage of 0.85 V, leakage current ratio of 1%, and fuel utilization of 94.2％. In this case, the steam-to-carbon ratio (S/C) was 2.5. In addition, a system efficiency of over 70％ (LHV, DC) was obtained under the cell voltage of 0.9 V, leakage current ratio of less than 5%, and fuel utilization of over 90％. Based on the above results, a cell design with bilayer electrolyte was discussed considering electrode/electrolyte materials and physical properties (e.g., transport number and conductivity). Acknowledgments This work was supported by a project, (JPNP20003), commissioned by the New Energy and Industrial Technology Development Organization (NEDO) and JSPS KAKENHI JP21H04938 and JP21J14251.

Pore-filling membrane containing solely zirconium phosphonates with high content through in-situ conversion

Organic-inorganic composite membranes are used in various applications, especially as proton-conducting electrolyte membranes for proton-exchange membrane fuel cells (PEMFCs). This study proposed a method to fill a flexible porous substrate solely with high amounts of inorganic (approximately 48 wt%) nano-zirconia precursor, surface-modified by acetylacetone (AcAc-Zr). AcAc-Zr can be converted to zirconium phosphate (ZrPi) in situ, and several other zirconium phosphonates, such as zirconium aminotris-methylene-phosphonate (ZrATMP) and zirconium 1-hydroxyethane-1,1-diphosphonate (ZrHEDP). Transmission electron microscopy-energy dispersive spectroscopy (TEM-EDS) analysis revealed that the pores were continuously filled with ZrPi, indicating that ZrPi has a percolated structure in the membrane, beneficial for their proton conduction. The proton conductivities of the membranes, including ZrPi, ZrHEDP, and ZrATMP, were sufficiently high, on the order of 1 mS cm−1 at 80 °C and 95% relative humidity.

Repeatable preparation of defect-free electrolyte membranes for proton-conducting fuel cells

Proton-conducting ceramic cells are promising devices for high-efficient energy conversion, while the preparation of defect-free electrolyte membranes is difficult and blocks their quick development. Here, a vacuum-assistant dip-coating method is developed to prepare defect-free BaCe0.4Zr0.4Y0.1Yb0.1O3-δ (BCZYYb4411) proton-conducting electrolyte membranes on porous anode (40 wt%BCZYYb4411 - 60 wt%NiO) substrates. Unlike the conventional dip-coating process, by using the vacuum-assistant dip-coating method, defects (like running through pinholes, cracks) that would cause gas leakage, short-circuit and low open-circuit voltage (OCV) in following electrochemical tests can be eliminated. By tuning the mass concentration of electrolyte powders in the coating slurry, thin electrolyte membranes with different thicknesses can be reproducibly prepared. Proton-conducting fuel cells (PCFCs) with BaCo0.4Fe0.4Zr0.1Y0.1O3-δ (BCFZY0.1) cathode show high OCV values closing to the theoretical value of 1.13 V at 600 °C, demonstrating that dense and defect-free electrolyte membranes are fabricated. The as-prepared PCFC with a 10-μm-thickness defect-free electrolyte membrane shows a high peak power density reaching up to 761 mW cm−2 at 650 °C and stability of more than 250 h at the current density of 200 mA cm−2 at 600 °C. All these results illustrate that the developed method is feasible to prepare dense and thin electrolyte membranes without defects for proton-conducting ceramic cells.

Perspectives on Technical Challenges and Scaling Considerations for Tubular Protonic-Ceramic Electrolysis Cells and Stacks

Proton-conducting ceramics (protonic ceramics) form the basis for applications that include intermediate-temperature (e.g., 500 °C–700 °C) fuel cells, electrolyzers, and membrane reactors. The electrolyte membranes are typically perovskites such as heterovalently doped barium cerates and zirconates (e.g., BaCe1−x−y Zr x Y y O3−δ , BCZY; and BaCe1−x−y−z Zr x Y y Yb z O3−δ , BCZYYb). Although the materials are dominantly proton conductors, they are mixed ionic-electronic conductors (MIEC) with oxygen-ion and small-polaron mobility. The present paper is concerned primarily with steam-electrolysis applications with the reactors using tubular cell configurations. An important advantage of the protonic-ceramic cells is that they can produce nearly dry hydrogen. Each tubular cell is comprised of a negatrode (electrolysis cathode), proton-conducting electrolyte membrane, and a positrode (electrolysis anode). The tubular cells are typically supported on the relatively thick (order of one millimeter) composite negatrode, with thin (order tens of microns) external membrane and positrode layers. The paper explores considerations for scaling from laboratory-based demonstrations to deployable technology.

Effect of humidification on the grain boundary conductivity and space-charge effects in yttrium-doped barium cerate

Yttrium-doped barium cerate (BCY) exhibits proton conductivity in the nominal absence of water (pH2O ≤ 10−4 atm) below 450 °C (J. Mater. Chem. A 7 (2019) 18,135–18142). Under these conditions, the well-known instability of this material against carbon dioxide and humidity can be minimized, potentially allowing its application even in hydrocarbon-based atmospheres. Nonetheless, electrochemical transport properties of grain boundaries of BCY are still not well understood. Hence, we compare specific grain boundary conductivity and space-charge properties of BaCe0·9Y0·1O3-δ (BCY10) in both wet and low humidity by means of impedance spectroscopy in the temperature range 100–300 °C. In H2, specific grain boundary conductivity increases in nominally dry conditions, while the bulk remains practically humidity independent. Conversely, in O2, both bulk and specific grain boundary conductivities are higher in wet. The space-charge properties highlight that low levels of humidity, pH2O ~10−4 atm, are sufficient to maintain functional performance, while providing enough stability. This work offers a significant advance to the knowledge of the transport properties of this family of materials at low temperatures, with special emphasis to conditions of low humidity, for potential future applications in proton-conducting electrolyte membranes.

Nanostructured Polymer Composite Electrolytes with Self-Assembled Polyoxometalate Networks for Proton Conduction

Nanostructured Polymer Composite Electrolytes with Self-Assembled Polyoxometalate Networks for Proton Conduction

Freestanding Dual-Gate Oxide-Based Neuromorphic Transistors for Flexible Artificial Nociceptors

A nociceptor is a type of sensory receptor with the ability to perceive noxious stimuli, which is very important for the survival and health of organisms. Several neuromorphic devices have been proposed to emulate this sensory receptor. The basic pain perception functions of a nociceptor can be emulated. However, those artificial nociceptors lack functional tunability and intelligent adaptability. Here, freestanding oxide-based neuromorphic transistors with dual-gate structures were fabricated on proton-conducting electrolyte membranes and used for flexible artificial nociceptor emulation. Such a freestanding biomimetic device can not only capture the pain perception functions to peripheral inputs. What is more, the modulation of pain sensitivity can be emulated in this device by the voltage applied on the second gate electrode. Our artificial nociceptors open a new avenue in the design of an artificial sensory system with sensory alarm function and intelligent adaptability.

(Invited) HT-PEM Fuel Cell Development for Product Definition and Scaleup

“High Temperature” Proton conducting Electrolyte Membrane (HT-PEM) fuel cells offer an attractive method of converting renewable energy carriers (e.g. methanol) to electricity, especially remotely and in transportation. A particular advantage is their ability to digest reformates containing a few % CO, thus not requiring high purity hydrogen.Membranes of polybenzimidazole (PBI) allow for operation in the 150-200 °C range, as they do not require liquid water for continuous moisturizing as do fluorinated polymer membranes. This temperature range is advantageous for the typically used Pt catalyst, as the passivation by CO is limited.A central challenge is cost reduction, with particular focus on Pt loading of electrodes. The critical trade-off is against lifetime and electrode performance while maintaining adequate tolerance to CO and fuel trace impurities. These limitations are sensitive to system and customer parameters via selection of fuel, reformer characteristics and operation mode.Results will be presented and discussed on single cell lifetime in the 10.000 h range; objectives and results in electrode development and Pt loading, as well as results on methanol slip testing, start-stop testing and testing at elevated pressure. Lessons from early upscaling will be shared.

Electrochemical sensors based on proton-conducting electrolytes for determination of concentration and diffusion coefficient of CO2 in inert gases

The monitoring of CO2 levels in gases has important environmental, technological and energy applications. In the present work, results of the fabrication and testing of an amperometric-type sensor based on a proton-conducting material for analysing the concentration of carbon dioxide (CO2) in inert gases at elevated temperatures are presented. The analysis consists in reading the limiting current values determined during preliminary tests, obtaining the calibration dependence on variation of CO2 concentration and further using it for the investigation of gas mixtures. Experimental results show that the sensor is able to precisely detect CO2 concentration ranging between ~2 and 14 vol% in a wet N2 atmosphere at an intermediate-temperature range (500–600 °C) with a response time of ~30 min. Moreover, the possibility of estimating diffusion coefficients for CO2–N2 mixtures is also demonstrated. These results open a new window for high-temperature electrochemical analysis of gas mixtures, when solid-state gas sensors and proton-conducting electrolyte membranes are jointly utilised.

(Invited) HT-PEM Fuel Cell Development for Product Definition and Scaleup

“High Temperature” proton conducting electrolyte membrane (HT-PEM) fuel cells offer an attractive method of converting renewable energy carriers (e.g. methanol) to electricity, especially remotely and in transportation. A particular advantage is their ability to digest reformates containing a few % CO, thus not requiring high purity hydrogen.Membranes of polybenzimidazole (PBI) allow for operation in the 150-200 °C range, as they do not require liquid-water for continuous moisturizing as do classical fluorinated polymer membranes. This temperature range is advantageous for the typically used Pt catalyst, as passivation by CO is limited.A central challenge is cost reduction, with particular focus on Pt loading of electrodes. The critical trade-off is against lifetime and electrode performance while maintaining adequate tolerance to CO and fuel trace impurities. These limitations are sensitive to system and customer parameters via selection of fuel, reformer characteristics and operation mode.Results will be presented and discussed on single cell lifetime in the 10.000 h range; objectives and results in electrode development and Pt loading, as well as results on methanol slip testing, start-stop testing and testing at elevated pressure. Lessons from early upscaling will be shared.

Spray Pyrolysis Strategy for Preparation of Cathode-Supported Protonic Ceramic Fuel Cells

Since the discovery of proton conducting ceramic materials many research efforts have been focused into overcoming processing difficulties that hinder long-term stability and high performance of protonic ceramic fuel cells (PCFCs). Notably, high processing temperatures exceeding 1600 °C are often required to meet the microstructural demand of a dense proton conducting electrolyte membrane [1-2]. At this temperature range most potential electrode materials are chemically incompatible and therefore preclude the fabrication of electrode supported structures. In addition, for barium-based electrolytes (e.g. BaZr1-xYxO3-d) barium loss is anticipated resulting in lower conductivities and formation of structural defects. To overcome this major challenge thin film deposition techniques can be employed[3-4].Spray pyrolysis is a cost effective and simple deposition technique for preparation of ultra-thin films (i.e.<5μm) enabling the reduction of operating and processing temperatures of fuel cells [5]. Microstructures and electrochemical performance of multi-layered thin film PCFCs fabricated at exceptional low temperatures of 950 °C, are investigated. Large area 5x5cm2 cathode substrates of (La0.8Sr0.2)0.95MnO3-d prepared by tape casting were used for mechanical support of the cells. To modify and reduce the surface porosity of the substrate Ce0.9Gd0.1O3-d was coated to facilitate the deposition of the BaZr0.9Y0.1O3-d (BZY) thin electrolyte. Subsequently, the anode electrode was sprayed in two stages comprised by a nano-porous layer of BZY and infiltrated Ni particles. Characterization of the cathode-supported PCFCs was performed by electrical measurements operating up to 600°C and scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX) techniques.[1] Shanwen Tao and John T.S. Irvine, Adv. Mater., 18, 1581-1584, (2006).[2] Peter Babilo and Sossina M. Haile, J. Am. Ceram. Soc., 88 2362-2368, (2005).[3] Kiho Bae et al., Adv. Energy Mater., 8, 1801315, (2018).[4] Georgios Tsimekas et al., ECS J. Solid State Sci. Technol.,6(8), P553-P560, (2017).[5] Georgios Tsimekas et al., ECS Trans., 70(1), 205-212, (2015).

Preparation and Properties of Hybrid Silane-crosslinked Sulfonated Poly(aryl ether ketone)s as Proton Exchange Membranes

A series of novel organic-inorganic hybrid proton-conducting electrolyte membranes with silane-crosslinked sulfonated poly(aryl ether ketone)(SC-SPAEK) networks was prepared via a simple procedure that includes solution casting and acid treatment. The organosilicon pendants of the silane-grafted SPAEK, which were expected to serve as coupling and crosslinking agents, were found to play a key role in the homogenous dispersion of inorganic particles and improved the performance of hybrid membranes. The hybrid membranes exhibited enhanced proton conductivity, and SC-SPAEK/TiO2-4 showed an extremely high proton conductivity of 0.1472 S/cm at 100 °C. The crosslinked hybrid membranes also demonstrated good chemical resistance, oxidative stability, and mechanical properties. The crosslinked hybrid membranes with excellent comprehensive performance may be a promising material for proton exchange membrane fuel cells.

Thermodynamic Insights for Electrochemical Hydrogen Compression with Proton-Conducting Membranes.

Membrane electrode assemblies (MEA) based on proton-conducting electrolyte membranes offer opportunities for the electrochemical compression of hydrogen. Mechanical hydrogen compression, which is more-mature technology, can suffer from low reliability, noise, and maintenance costs. Proton-conducting electrolyte membranes may be polymers (e.g., Nafion) or protonic-ceramics (e.g., yttrium-doped barium zirconates). Using a thermodynamics-based analysis, the paper explores technology implications for these two membrane types. The operating temperature has a dominant influence on the technology, with polymers needing low-temperature and protonic-ceramics needing elevated temperatures. Polymer membranes usually require pure hydrogen feed streams, but can compress H efficiently. Reactors based on protonic-ceramics can effectively integrate steam reforming, hydrogen separation, and electrochemical compression. However, because of the high temperature (e.g., 600 C) needed to enable viable proton conductivity, the efficiency of protonic-ceramic compression is significantly lower than that of polymer-membrane compression. The thermodynamics analysis suggests significant benefits associated with systems that combine protonic-ceramic reactors to reform fuels and deliver lightly compressed H (e.g., 5 bar) to an electrochemical compressor using a polymer electrolyte to compress to very high pressure.

Prospects and challenges of graphene based fuel cells

Abstract Novel characteristics of graphene have captured great attention of researchers for energy technology applications. Incorporation of graphene related hybrid and composite materials have demonstrated high performance and durability for fuel cell energy conversion devices. This article overviews graphene based materials for fuel cell technology applications such as electrodes additives, bipolar plates and proton conducting electrolyte membrane. The graphene dispersion over electrodes has revealed enhanced exposure of electrochemically active surface area for improved electro-catalytic activity towards fuel oxidation and oxidant reduction reactions. The issue of device stack durability and degraded performance due to corrosion of bipolar plates is discussed by incorporating graphene based materials. In proton exchange membrane devices, graphene as an electrolyte has shown an excellent performance towards high ionic conductivity and power density. The graphene incorporation in fuel cell devices has exhibited commendable performance and has bright future for commercial applications.

Highly-conductive proton-conducting electrolyte membranes with a low sintering temperature for solid oxide fuel cells

The microwave sintering strategy was for the first time adopted to prepare proton-conducting electrolyte membranes for solid oxide fuel cells. The preparation of a dense proton-conducting BaCe0.7Zr0.1Y0.2O3-δ (BCZY) electrolyte membrane can be achieved at 1200 °C with the microwave sintering method. In sharp contrast, a BCZY sample prepared at 1200 °C using the conventional thermal sintering method was found to be porous. In comparison with a dense BCZY sample prepared at 1400 °C using the conventional sintering method, the microwave-sintered BCZY electrolyte showed an improved proton conductivity, which is beneficial for fuel cell applications. Experimental results showed that the microwave sintering method enabled a homogenous elemental distribution and a suppression of barium evaporation, leading to the conductivity improvement in both bulk and grain boundaries. With the microwave sintered BCZY film as the electrolyte, a proton-conducting solid oxide fuel cell delivered a maximum power density of 838 mW cm−2 at 700 °C with an electrolyte film conductivity as high as 1.4 × 10−2 S cm−1. This study suggests that the microwave sintering method is a promising strategy to prepare electrolyte membranes at a relatively low temperature with high conductivity, which could advance the development of proton-conducting solid oxide fuel cells.

Synthesis, Characterization, and Alkaline Stabilities of p-(2-imidazoliumyl) Styrene-Grafted Anion-Conducting Electrolyte Membranes Prepared By Radiation-Induced Grafting for Fuel Cells

Anion-conducting electrolyte membrane fuel cells (AEMFCs) have attracted considerable interest due to their significant advantages over proton-conducting electrolyte membrane fuel cells (PEMFC). Because AEMFCs operate under alkaline environments, non-precious metals can be used as active catalysts (e.g. nickel, cobalt and iron) and electrochemical reactions are more facile than that in acidic medium.1) In recent years, we have developed imidazolium-type AEMs by radiation-induced grafting method and founded that copoly(N-vinylimidazolium/styrene)-grafted AEM shows moderate alkaline stability. However, the AEMs degraded via the β-elimination reaction and the ring opening reaction of C2 position.2) In this work, we synthesized p-(2-imidazoliumyl) styrene (2STZ)-grafted membrane (Pr-PrSTZ-AEM) to exclude β-hydrogen from the chemical structure and protect C2 position. The 2STZ monomer was synthesized from 4-vinylbenzyl chlorid)e via the 4-vinylbenzaldehyde. And then, the 2STZ was mono N-alkylated by sodium hydrate and propyl iodide in a standard manner to obtain propylated monomer (PrSTZ).3) Poly(ethylene-co-tetrafluoroethylene) (ETFE) films were irradiated with a 60Co γ-ray source (QST, Takasaki, Gunma, Japan) at room temperature in argon atmosphere with an absorption dose of 50 kGy. The pre-irradiated ETFE films were immediately immersed into the argon-purged monomer solution consisting of 50 vol% of PrSTZ in 1,4-dioxane for 1~16 h. The imidazole groups in the grafted-ETFE were N-alkylated by propyl iodide in a quantitative manner. The obtained Pr-PrSTZ-based AEMs (an iodide form) were immersed in 1M HCl and 1,4-dioxane (1 : 1 volume ratio) solution at 60 °C for 24 h to convert into a Cl- form, followed by the ion-exchange reaction in 1M KOH and 1,4-dioxane (1 : 1 volume ratio) solution at room temperature for 16 h to obtain Pr-PrSTZ-AEM (Scheme 1). The Pr-PrSTZ-based AEMs with IECexp. of 0.54~1.72 mmol/g were converted from the grafted membranes with grafting degrees of 18~98% by quantitative N-alkylation and ion-exchange reaction in more than 90% conversion. The prepared AEMs exhibited 7~78% of water uptakes and 50~181 mS/cm of ionic conductivities at 60°C (Figure 1). The alkaline stability of AEMs was evaluated by monitoring the change in conductivity of AEMs in 1M KOH at 80°C. The conductivity of AEM with a grafting degree of 47% decreased from 125 to 8 mS/cm after 600 h, whereas the conductivity of AEM with a grafting degree of 18% increased from 50 to 60 mS/cm after 600 h. This result indicates that the Pr-PrSTZ-based AEMs with the grafting degree of 18% has moderate ionic conductivity with surprised water uptake and quite high alkaline stability, comparing to copoly(N-vinylimidazolium/ styrene)-grafted AEMs. Therefore, the Pr-PrSTZ-based AEMs are expected as a promising membrane for highly alkaline durable fuel cells. Acknowledgement This work was supported by the Advanced Low Carbon Technology Research and Development Program (ALCA) from the Japan Science and Technology Agency (JST).

Anode-supported BaZr0.8Y0.2O3−δ membranes by tape casting and suspension spraying

Dense BaZr[Formula: see text]Y[Formula: see text]O[Formula: see text] (BZY) proton-conducting electrolyte membranes are successfully fabricated on NiO–BaZr[Formula: see text]Ce[Formula: see text]Y[Formula: see text]O[Formula: see text](NiO–BZCY) using tape casting combined with suspension spraying technique. The NiO–BZCY anode substrates were prepared by the tape-casting method and the BZY electrolyte membranes were prepared on the NiO-BZCY anodes by suspension spraying. The thermal decomposition of the anode green tape prepared by tape casting was investigated by thermogravimetry-differential thermal analysis while the phase structure and the morphology of the anode/electrolyte bi-layers were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). No obvious reaction was found between NiO and BZCY in anode substrates and gas-tight BZY membranes were achieved after co-sintering at 1450[Formula: see text]C. With Sm[Formula: see text]Sr[Formula: see text]CoO[Formula: see text]–Ce[Formula: see text]Sm[Formula: see text]O[Formula: see text](SSC–SDC) as the composite cathode, a maximum power density of 121 mW cm[Formula: see text] was obtained at 650[Formula: see text]C for the single cell with 23 [Formula: see text]m thick BZY electrolyte. Resistances of the tested cell were investigated under open circuit conditions at different operating temperatures by impedance spectroscopy.

Organic–inorganic hybrid proton-conducting electrolyte membranes based on sulfonated poly(arylene ether sulfone) and SiO2–SO3H network for fuel cells

A series of novel organic–inorganic hybrid proton exchange membranes (PEMs) were prepared from the sulfonated poly(arylene ether sulfone) with 4-amino phenyl pendant groups (Am-SPAES), (3-isocyanatopropyl) triethoxysilane (ICPTES), and 3-(trihydroxysilyl) propane-1-sulfonic acid with covalent bonds to form network using a sol-gel method. The obtained cross-linked hybrid membranes (Am-SPAES/I-SiO2-S) displayed excellent solvent resistance and thermal and mechanical stability. The Am-SPAES/I-SiO2-S membranes with cross-linking network exhibited a higher proton conductivity (0.043 S cm−1 at 20°C) than PEMs without covalent bonds (Am-SPAES/SiO2-S) and the swelling ratio maintained below 17.00% even at 100°C. Most importantly, all of the obtained membranes showed considerably lower methanol permeability than that of Nafion 117. In addition, the chemical structures and morphologies of the hybrid membranes were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy, respectively.

Effect of titanium doping on chemical and structural stability and electrical properties of proton-conducting solid electrolyte BaCe0.8Sm0.2O3−δ

In this study, the effects of Ti substitution for Ce on chemical and structural stability and electrical properties of proton-conducting solid electrolyte membrane BaCe0.8−xTixSm0.2O3−δ (BCST) are investigated. Our results show that both chemical and structural stability of the BCST samples in CO2 containing and moist atmospheres are remarkably enhanced with increasing the content of Ti which is higher electronegative than Ce. However, the proton conductivity of the sample decreases with increasing Ti content, which may be due to the increasing difficulty of lattice hydration and smaller grain size (corresponding to more grain boundaries) caused by Ti doping. The activation energy for proton migration increases with Ti content, which is mainly related with the weaker hydrogen bond. The results show that the BaCe0.75Ti0.05Sm0.2O3−δ has a great electrical conductivity (1.03×10−2Scm−1 at 650°C) and it also demonstrates good chemical and structural stability in CO2 and water containing atmospheres. Therefore, BaCe0.75Ti0.05Sm0.2O3−δ can be considered as a promising proton conducting electrolyte for intermediate temperature solid oxide fuel cells.

Water Uptake and Proton Conductivity in Porous Block Copolymer Electrolyte Membranes

We demonstrate that the water uptake and conductivity of proton-conducting block copolymer electrolyte membranes can be controlled systematically by the introduction of pores in the conducting domains. We start with a membrane comprising a mixture of homopolymer polystyrene (hPS) and a polystyrene-b-polyethylene-b-polystyrene (SES) copolymer. Rinsing the membranes in tetrahydrofuran and methanol results in the dissolution of hPS, leaving behind a porous membrane. The polystyrene domains in the porous SES membranes are then sulfonated to give a porous membrane with hydrophilic and hydrophobic domains. The porosity is controlled by controlling ϕv, the volume fraction of hPS in the blended membrane. The morphology of the membranes before and after sulfonation was studied by scanning transmission electron microscopy (STEM), electron tomography, and resonance soft X-ray scattering (RSoXS). The porous structures before and after sulfonation are qualitatively different. Water uptake of the sulfonated membranes i...