Intermediate Temperature Proton Research Articles

Recent Progress of Crystalline Porous Frameworks for Intermediate-Temperature Proton Conduction.

Proton exchange membranes (PEMs), especially for work under intermediate temperatures (100-200 °C), have attracted great interest because of the high CO toleration and facial water management of the corresponding proton exchange membrane fuel cells (PEMFCs). Traditional polymer PEMs faced challenges of low stability and proton carrier leaking. Crystalline porous materials, such as metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), are promising to overcome these issues contributed by nanometer-sized channels. Herein we summarized the recent development of MOF/COF-based intermediate-temperature proton conductors. The strategies of framework engineering and pore impregnation were introduced in detail for raising proton conductivity. The proton-conducting mechanism was described as well. This spotlight will provide new insight into the fabrication of MOF/COF proton conductors under intermediate-temperature and anhydrous conditions.

Synthesis of Yttrium Doped Barium Zirconate/Cerate Electrolyte Materials and Densification Using Conventional and Cold-Sintering Processes

Compared to high temperature solid oxide electrolysis cell, usually based on Yttrium stabilized Zirconia electrolytes, intermediate temperature proton conducting electrolysis cell, allows the production of water free hydrogen and a better chemical stability. Proton conducting perovskite materials, such as Barium Indates, Zirconates or Cerates are nearly commercial electrolytes for such devices. At intermediate temperature and under humid atmosphere, hydration process allows diffusion of protonic charges. Such electrolyte material combines a low thermal expansion coefficient and a high protonic conductivity. and The Zirconium rich material BaZr0.7Ce0.2Y0.1O3-δ that shows a conductivity around 10-2 S.cm-1 at 500°C will be compared to the Cerium rich BaZr0.3Ce0.6Y0.1O3-δ material that shows conductivities around 10-4 S.cm-1 at the same temperature.

Intermediate-Temperature Proton Exchange Membranes Based on Cerium Ultraphosphate Composited with Polybenzimidazole

This paper reports the rational fabrication and structural, thermal, mechanical and electrochemical characterization of a new type of intermediate-temperature (IT) polymer-inorganic composite (PIC) proton exchange membranes (PEMs) that are made of cerium ultraphosphate (CeP5O14—CUP) as the solid-state proton conductor composited with a high-temperature (HT) polybenzimidazole (PBI) as the polymeric binder. Flexible PBI-CUP PIC membranes with the thickness of ∼135 μm and CUP mass fraction of up to 75% were prepared by solution-casting without additional acid-doping (e.g., phosphoric acid). The proton conductivity of the fabricated IT-PIC-PEMs was up to 5.80 × 10−2 S cm−1 as measured from a prototype IT PEM fuel cell (PEMFC) operated at 200 °C in the humidified hydrogen and air environment. This type of IT-PIC-PEMs also demonstrated sufficient mechanical strength and flexibility, excellent thermal stability (up to 350 °C), and very good durability of the proton conductivity (within the test duration of 500 h). The present experimental study shows the promising future of the IT-PIC-PEMs for applications in various IT electrochemical processes including IT-PEMFCs, IT-electrolyzers, etc.

Developing a Unique Hydrogen-Bond Network in a Uranyl Coordination Framework for Fuel Cell Applications.

Crystalline materials with persistent high anhydrous proton conductivity that can be directly used as a practical electrolyte of the intermediate-temperature proton exchange membrane fuel cells for durable power generation remain a substantial challenge. The present work proposes a unique way of the axial uranyl oxo atoms as hydrogen-bond acceptors to form a dense hydrogen-bonded network within a stable uranyl-based coordination polymer, UO2(H2PO3)2(C3N2H4)2 (HUP-3). It exhibits stable and efficient anhydrous proton conductivity over a super-wide temperature range (-40-170 °C). It was also assembled into a H2/O2 fuel cell as the electrolyte and shows a high electrical power density of 11.8 mW·cm-2 at 170 °C, which is among one of the highest values reported from crystalline solid electrolytes. The cell was tested for over 12 h without notable power loss.

Barium-doped Pr2Ni0.6Cu0.4O4+ with triple conducting characteristics as cathode for intermediate temperature proton conducting solid oxide fuel cell

Proton conducting solid oxide fuel cell (H-SOFC) is an emerging energy conversion device, with lower activation energy and higher energy utilization efficiency. However, the deficiency of highly active cathode materials still remains a major challenge for the development of H-SOFC. Therefore, in this work, K2NiF4-type cathode materials Pr2−xBaxNi0.6Cu0.4O4+δ (x = 0, 0.1, 0.2, 0.3), single-phase triple-conducting (e−/O2−/H+) oxides, are prepared for intermediate temperature H-SOFCs and exhibit good oxygen reduction reaction activity. The investigation demonstrates that doping Ba into Pr2−xBaxNi0.6Cu0.4O4+δ can increase its electrochemical performance through enhancing electrical conductivity, oxygen vacancy concentration and proton conductivity. EIS tests are carried at 750 °C and the minimum polarization impedances are obtained when x = 0.2, which are 0.068 Ω·cm2 in air and 1.336 Ω·cm2 in wet argon, respectively. The peak power density of the cell with Pr1.8Ba0.2Ni0.6Cu0.4O4+δ cathode is 298 mW·cm−2 at 750 °C in air with humidified hydrogen as fuel. Based on the above results, Ba-doped Pr2−xBaxNi0.6Cu0.4O4+δ can be a good candidate material for SOFC cathode applications.

Intermediate temperature proton electrolytes based on cesium dihydrogen phosphate and poly(vinylidene fluoride-co-hexafluoropropylene)

Intermediate temperature proton electrolytes based on cesium dihydrogen phosphate and poly(vinylidene fluoride-co-hexafluoropropylene)

Integrating molecular design and crystal engineering approaches in non-humidified intermediate-temperature proton conductors based on a Dawson-type polyoxometalate and poly(ethylene glycol) derivatives.

Anionic metal-oxygen clusters known as polyoxometalates (POMs) have been widely researched as components of proton conductors. While proton conduction under non-humidified intermediate-temperature (100-250 °C) conditions is advantageous from the viewpoint of kinetics, few solid-state materials, not to mention POM-based crystals, show truly effective proton conduction without the aid of water vapor. In this context, non-volatile proton-conductive polymers have been confined into POM-based frameworks, while fast proton conduction was infeasible. Herein, we demonstrate a new strategy to synthesize POM-polymer composites exhibiting fast proton conduction under non-humidified intermediate-temperature conditions. Specifically, a molecular design approach utilizing poly(ethylene glycol)s (PEGs) of different terminal groups or chain lengths controls the proton carrier density, and a crystal engineering approach using a large Dawson-type POM ([α-P2W18O62]6-) with an anisotropic molecular shape and alkali metal ions as counter cations fine-tunes the mobility of the confined PEGs as proton carriers. By integrating these approaches, proton conductivity over 10-4 S cm-1 at 150 °C, comparable to the well-known highly proton-conductive solid-state materials, is achieved. The proton conduction mechanism is discussed with alternative current impedance spectroscopy jointly with specific heat capacity measurements and solid-state NMR spectroscopy.

Intermediate temperature proton electrolytes based on cesium dihydrogen phosphate and Butvar polymer

The phase composition, electrotransport properties, and spectral characteristics of the (1 − x)CsH2PO4–xButvar system (х = 0–0.2 wt%) were investigated in details. Butvar was proved to be a chemically suitable matrix for CsH2PO4 with a good adhesion to acid salt permitting the formation of flexible membrane. The chemical interaction of organic matrix with acid salt was not observed. A new method of “polymer-CsH2PO4” composites preparation through alcohol solutions of initial components was proposed. The flexible and thin (~ 200 μm) proton membranes with uniform salt distribution were obtained. Composite polymer electrolytes are characterized by high proton conductivity values (~ 5 × 10−3 S/cm) at 240 °C and are stable under conditions of high humidity (PH2O ~ 0.3 atm.).

The Effect of SrCrO4 Impurity Phase in (La0.75Sr0.25)0.95CrxFe1-XO3-Δ (LSCrF) Nanoceramic Powder Series As Catalyst during the Propane Dehydrogenation

Lanthanum strontium chromite based materials are promising candidate for use as electrode components in Intermediate Temperature Proton Conductive Fuel Cell (IT-PCFC)[1]. In this work, (La0.75Sr0.25)0.95CrxFe1-xO3-δ(LSCrF) with x=0.3, 0.4, 0.5, 0.6 and 0.7 perovskite nano-ceramic powder series considered as anode material for IT-PCFCs [2] were focused on due to its structural, physical & chemical and also electrochemical properties corresponding with Cr amount, such as catalytic activities under the operation conditions. The nano-sized LSCrF perovskite powders were systematically synthesized by using sol-gel method[3], to understand whether the increment of Cr amount have any positive or negative effect in terms of catalytic performance, impurity, particle size and surface area. In this regard, all powders were annealed at the different temperatures changing from 500oC to 700oC in order to determine the minimum formation temperature of the powders having different amounts of Cr and Fe in order to enhance smaller particle size with higher surface area. LSCrF nano-powders were structurally characterized by means of X-ray Powder Diffraction (XRD) with Reitveld refinement by using GSAS software [4]. Cr rich samples shows more SrCrO4 impurity phase and bigger crystallite size than Fe-rich samples which leads to poor catalytic performance in the propane dehydrogenation process. Ex-situ X-ray Absorption Spectroscopy study was also performed for Fe (7112 eV) and Cr (5989 eV) K-edge in the fluorescence mode by using a 4-elements Vortex detector. When we looked at the XANES region of both Fe and Cr K edge XAS data to understand the electronic structure of Fe and Cr in the LSCrF powders, Cr K edge XAS data shows a sharp pre-edge peak resulting from SrCrO4 impurity phase having tetrahedral geometry of Cr+6 with 4-fold Oxygen atoms, whereas Fe K-edge XAS data does not show any pre-edge feature due to the octahedral geometry of Fe+3 in LSCrF perovskite structure, as we expect. the C3H8 conversion of Fe rich LSCrF samples (x<0) having more SrCrO4 pre-edge intensity and higher surface area is found higher than Cr-rich samples (x>0). Especially, Fe rich LSCr0.4Fe0.6O3 sample having wt.frac.~13.14% SrCrO4 impurity phase considered as better catalyst shows much lower carbon balance than other samples unsurprisingly due to its higher surface area with smaller crystallite size and having more catalytically active SrCrO4 pre-edge intensity proved by XANES analysis. Morphological analysis of the LSCrF powders was done by Scanning Electron Microscopy (SEM/EDX). BET measurements were also performed to calculate their surface area.

Methane Production and Electricity Generation in a Proton Conducting Tubular Reversible Solid Oxide Cell

Reversible solid oxide cell (RSOC) can efficiently store intermittent renewable energy in the form of fuel. Proton-conducting RSOC is a promising way to reach the goal of reducing the SOFC operating temperature and improve the CH4 production. In this paper, intermediate temperature proton conducting RSOC has been used for the test of micro-tubular RSOC. The experiments have been performed at 480-560°C on a Ni-BCZI / BCZI (BaCe0.5Zr0.4Y0.1O3) / LSC-BCZI micro-tubular cell. The effects of inlet gas composition and temperature on the cell performance and CH4 production has been discussed in detail. The max CH4 production rate reaches 20% in our experiment at 480°C. To further optimize the micro-tubular RSOC, a two-dimensional (2D) micro-tubular RSOC model is developed. Pressurization is proved to be an effective way for CH4 production enhancement.

The Effect of SrCrO4 Impurity Phase in (La​0.75​Sr0.25​)​0.95​Cr​X​Fe​1-X​O​3-Δ (LSCrF) Nano-Ceramic Powder Series As Catalyst for the Propane Dehydrogenation

Lanthanum strontium chromite based materials are promising candidate for use as electrode components in Intermediate Temperature Proton Conductive Fuel Cell (IT-PCFC)[1]. In this work, (La0.75Sr0.25)0.95CrxFe1-xO3-δ (LSCrF) with x=0.3, 0.4, 0.5, 0.6 and 0.7 perovskite nano-ceramic powder series considered as anode material for IT-PCFCs[2] were focused on due to its structural, physical & chemical and also electrochemical properties corresponding with Cr amount, such as catalytic activities under the operation conditions. The nano-sized LSCrF perovskite powders were systematically synthesized by using sol-gel method[3], to figure out whether the increment of Cr amount have any positive or negative effect in terms of catalytic performance, impurity, particle size and surface area. In this regard, all powders were annealed at the different temperatures changing from 500°C to 700°C in order to determine the minimum formation temperature of the powders having different amounts of Cr and Fe in order to enhance smaller particle size with higher surface area. LSCrF nano-powders were structurally characterized by means of X-ray Powder Diffraction (XRD) with Reitveld refinement by using GSAS software[3]. Cr rich samples shows more SrCrO4 impurity phase and bigger crystallite size than Fe-rich samples which leads to poor catalytic performance in the propane dehydrogenation process. Ex-situ X-ray Absorption Spectroscopy study was also performed for Fe (7112eV) and Cr (5989eV) K-edge in the fluorescence mode by using a 4-elements Vortex detector. When we looked at the XANES region of both Fe and Cr K edge XAS data to understand the electronic structure of Fe and Cr in the LSCrF powders, Cr K edge XAS data shows a sharp pre-edge peak resulting from SrCrO4 impurity phase having tetrahedral geometry of Cr+6 with 4-fold Oxygen atoms, whereas Fe K-edge XAS data does not show any pre-edge feature due to the octahedral geometry of Fe+3 in LSCrF perovskite structure, as we expect. the C3H8 conversion of Fe rich LSCrF samples (x<0) having more SrCrO4 pre-edge intensity and higher surface area is found higher than Cr-rich samples(x>0). Especially, Fe rich LSCr0.4Fe0.6O3 sample having ~13.14wt.frac.%SrCrO4 impurity phase considered as better catalyst shows much lower carbon balance than other samples unsurprisingly due to its higher surface area with smaller crystallite size and having more catalytically active SrCrO4 pre-edge intensity proved by XANES analysis. Morphological analysis of the LSCrF powders was done by Scanning Electron Microscopy (SEM/EDX). BET measurements were also performed to calculate their surface area.

Yttrium dependent space charge effect on modulating the conductivity of barium zirconate electrolyte for solid oxide fuel cell

Development of high proton conducting, chemically stable electrolyte for solid oxide fuel cell application still remains as a major challenge. In this work, yttrium (0, 5, 10, 15 and 20 mol%) doped barium zirconate synthesised by hydrothermal assisted coprecipitation exhibited highly crystalline cubic perovskite. The results demonstrate that the proton conductivity is higher than oxygen ion conductivity measured in the temperature range of 200–600 °C. The 20 mol% Y doped BaZrO3 exhibited higher protonic conductivity (6.1 mScm−1) with an activation energy 0.64 eV under the reducing atmosphere. The Mott–Schottky analysis carried out in hydrogen atmosphere at 200 °C revealed that the barrier height of doped BaZrO3 reduced from 0.6 to 0.2 V. The Schottky depletion layer width also decreased from 4 to 2 nm with the increase in yttrium concentration and the boiling water test showed good phase stability. Our study highlights the critical role of space charge in the grain boundary and its suppression with the increase in dopant concentration. The results demonstrate that Y doped BaZrO3 sintered at low temperature is a promising candidate as the electrolyte material for the intermediate temperature proton conducting solid oxide fuel cells.

Nafion/IL Intermediate Temperature Proton Exchange Membranes Improved by Mesoporous Hollow Silica Spheres

AbstractA novel polyelectrolyte composite membrane was designed and prepared for intermediate temperature proton exchange membrane fuel cells (PEMFCs). It was composed of perfluorosulfonic acid resin (Nafion®), protic ionic liquid (IL, [dema][TfO]) and mesoporous hollow silica spheres (MHSi). The morphologies of MHSi and Nafion‐based composite membranes were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The effect of MHSi on proton conductivity of the composite membranes versus relative humidity (RH) and temperature (100–140 °C) were investigated. The results indicated, that the Nafion/IL/MHSi composite membranes exhibited excellent proton conductivity even under 30% RH or high temperature (above 100 °C). A high proton conductivity (5.41 mS cm−1) of the composite membrane at 30 °C and 30% RH can be observed from the test result, which was five times higher than that of the pristine Nafion. The N‐IL‐12S composite membrane showed an outstanding proton conductivity, as far as 14.7 mS cm−1 under 140 °C and low RH, which was almost two orders higher than that of the pristine Nafion membrane. Moreover, the unique hollow and mesoporous structure of MHSi improved IL retention rate of the membrane evidently. Together with high thermal stability of the composite membrane confirmed by thermogravimetric analysis (TGA), the Nafion/IL composite membrane improved by MHSi is a potential candidate in intermediate temperature PEMFC.

A novel thermomechanically stable LaF3CsH5(PO4)2 composite electrolyte with high proton conductivity at elevated temperatures over 150 °C

Abstract A facile strategy is introduced to upgrade thermomechanical stability of the cesium pentahydrogen diphosphate (CPD), which is the most efficient inorganic electrolyte among all solid proton conductors, by constructing P OH•••F hydrogen bonds with lanthanum fluoride (LaF3). The optimal combination of the LaF3 CPD composite electrolyte is found to be 1:2 in a molar ratio (LaF3 CPD-2). LaF3 CPD-2 composite maintains robust solid state, even at a temperature up to 200 °C, which is 50 °C higher than the melting temperature of CPD. Meanwhile, the considerable proton conductivity of CPD is achieved in the LaF3 CPD-2 composite electrolyte due to the synergistic effect of the P OH•••F hydrogen bonds and the intrinsic proton conductive property of CPD. Last but not least, the LaF3 CPD-2 composite manifests excellent conductivity durability at 150 °C and low humidity condition with sizeable proton conductivity of 0.0262 S cm−1 after 60 h operation, implying that the LaF3 CPD composite could be a promising candidate for intermediate temperature proton conductors.

(Invited) Electrochemical Ammonia Synthesis Using Intermediate Temperature Proton Conducting Membranes

Due to the intermittency of many renewable energy sources, their potential to significantly participate in the overall energy mix is strongly dependent on our ability to identify and develop efficient and cheap energy storage technologies1. Liquid fuels are an appealing option with energy densities typically 10-100x higher than batteries. Ammonia, in particular, has many attributes that make it the ideal energy storage compound including high energy density and an existing infrastructure for transportation. The highly developed, large-scale production of ammonia via Haber-Bosch process is not suitable for energy storage applications due to the high-temperatures and pressures used. Theory2 and experiment3 suggest that a more suitable approach is the production of ammonia from nitrogen and water via electrosynthesis whereby small-scale reactors could enable distributed ammonia production closer to the consumer and be more compatible with energy inputs from intermittent renewable energy resources - improvements that could dramatically reduce the energy and carbon intensity of ammonia production and distribution. Prior research pursuing the electrosynthesis of ammonia has focused primarily on the use of proton conducting electrolytes at high temperatures, >600˚C or low temperatures, <100˚C due to materials limitations in the intermediate temperature range. The intermediate temperature range is particularly advantageous as lower temperatures favor the thermodynamics of the forward reaction to form NH3, while higher temperatures aid in the breaking of the incredibly stable di-nitrogen bond (946 kJ/mol). In order to access this intermediate temperature range of operation, we have developed a composite SnP2O7/Nafion based electrolyte material that exhibits conductivity on the order of 20 mScm-1 at 200˚C. We have demonstrated a maximum ammonia production rate of ~1x10-8molcm-2s-1 at 200˚C using N2 and H2 as reactant gases and Pt-based electrodes. This talk will discuss the factors influencing production rates and current efficiencies of these intermediate temperature devices. References J. B. Goodenough, H. D. Abruna and M. V. Buchanan, 2007.T. H. Rod, A. Logadottir and J. K. Nørskov, The Journal of Chemical Physics 112 (12), 5343 (2000).G. Marnellos and M. Stoukides, Science 282 (1998). Acknowledgements This project is supported by ARPA-E under Award No. DE-AR0000687.

Colloidal Nanocrystal Films Reveal the Mechanism for Intermediate Temperature Proton Conductivity in Porous Ceramics

Over the past few years, the observation of unexpected but significant proton conductivity in porous, nanocrystalline ceramics has generated substantial scientific interest mirroring the excitement...

(Invited) Development of High Temperature Materials and Technologies for Electrochemical Storage and Conversion

The Advanced Research Projects Agency (ARPA-E) funds high risk, high reward transformational research to reduce energy related emissions, reduce imports of energy from foreign sources, improve energy efficiency across all economic sectors, and ensure US technological lead in advanced energy technologies, including electrochemical energy storage and transformation for grid scale and automotive applications. High temperature electrochemical technologies and supporting materials (membranes, current collectors, seals, etc.) play an important role in electrochemical (batteries with molten electrodes and molten salt electrolytes) and chemical (electrosynthesis of fuels) energy storage and energy conversion (intermediate and high temperature solid oxide and proton conducting fuel cells and electrolyzers). In addition, high temperature electrochemical technologies to process and recycle metals such as aluminum, titanium, and magnesium are important for advanced manufacturing. The use of high temperatures allows for utilization of ion conducting materials, electrolytes and electrocatalysts, which cannot be utilized at ambient conditions due to low conductivity or activity respectively. Current challenges in high temperature electrochemistry are increasing ionic conductivity of liquid and solid electrolytes to decrease working temperatures and expand material compatibility, improving activity and selectivity of electrocatalysts to decrease energy consumption and costs, increasing power density of stacks to decrease the capital costs, and optimizing the balance of system, which is extremely important for smaller scale devices. ARPA-E funded and currently funds multiple projects targeting high temperature electrochemical processes and development of materials compatible with these processes through OPEN, IDEAS and focused programs. The Modern Electro/Thermochemical Advances in Light Metals Systems (METALS) targets technologies that may provide inexpensive light metal materials for lightweight vehicles and aircraft. The Reliable Electricity Based on Electrochemical Systems (REBELS) program is focused at intermediate temperature fuel cells that operate between 200-500oC and includes cell capable to produce liquid fuels along with electricity to support the distributed energy generation for more reliable and flexible smart grid. The Renewable Electricity to Fuels through Utilization of Energy-dense Liquids (REFUEL) program seeks to fund the development of intermediate and high temperature electrosynthesis and fuel cells technologies to produce and utilize carbon-neutral fuels. This presentation will also highlight high temperature battery technologies using molten metal anodes funded by ARPA-E.

Heterogeneous hybrid of propyl amino functionalized MCM-41 and 1H-1,2,4-triazole for high efficient intermediate temperature proton conductor

In this study, we introduced 1H-1,2,4-triazole into the ordered nanochannels of propyl amino functioned MCM-41 and then investigated the hybrids' proton conducting performance.

Preparation and characterization of zirconium phytate as a novel solid intermediate temperature proton conductor

Zirconium phytate (ZrPA) was prepared via gelation of zirconyl chloride and phytic acid in certain ratios. Fourier-transform infrared spectroscopy was applied to confirm the structure and interactions between Zr4+ and phytate ions, including hydrogen bonding and chelation. Scanning and transmission electron microscopic study have shown that ZrPA has a fusiform shape and a layered structure. Good thermal stability up to 250°C was obtained. ZrPA(3:4) exhibited an ion exchange capacity of 1.04meqg−1. At 140°C, the proton conductivity of ZrPA(3:4) was 0.099Scm−1 at 100% RH, 0.042Scm−1 at 50% RH and 0.018Scm−1 at 0RH.

Effect of Catalyst Layer Ionomer Content on Performance of Intermediate Temperature Proton Exchange Membrane Fuel Cells (IT-PEMFCs) under Reduced Humidity Conditions

For intermediate-temperature polymer electrolyte membrane fuel cells (IT-PEMFCs), the effects of the cathode gas flow rate and the ionomer content are experimentally examined at 120°C under conditions of low relative humidity (RH). The IT-PEMFC operation at low RH should be beneficial in developing compact systems with smaller humidifiers. First, analysis of the effect of gas flow rate at various current densities confirms that drying of the membrane electrode assembly (MEA) is an important factor in IT-PEMFC operation, whereas cathode flooding becomes significant in regions of high current density with low flow rates. Then, MEAs with various contents of Aquivion™ ionomer are fabricated, and the combined effect of drying and flooding is further investigated by IT-PEMFC tests at various RH conditions and current densities. The optimum ionomer content increases with decreasing current density at 20% RH or below, indicating that MEA drying becomes dominant over cathode flooding.