Lowest Area Specific Resistance Research Articles

Preparation and Testing of Metal/Ce0.80Gd0.20O1.90 (Metal: Ni, Pd, Pt, Rh, Ru) Co-Impregnated La0.20Sr0.25Ca0.45TiO3 Anode Microstructures for Solid Oxide Fuel Cells

La0.20Sr0.25Ca0.45TiO3 (LSCTA-) is a novel mixed ionic and electronic conductor (MIEC) material which can act as a potential replacement Solid Oxide Fuel Cell (SOFC) anode ‘backbone’ microstructure, for the current state-of-the-art Ni-based cermet. By impregnating this ‘backbone’ with electrocatalytically active coatings of metal oxides and metallic particles, it is possible to create high performance SOFC anodes which offer improved redox stability and tolerance to non-optimal fuel gases. Here, we present short-term test data for SOFC containing LSCTA- anode ‘backbones’ impregnated with a variety of catalyst systems including: Ni/CGO, Pd/CGO, Pt/CGO, Rh/CGO and Ru/CGO. Electrolyte-supported SOFC containing Ni/CGO impregnated anodes showed large reductions in Area Specific Resistance (ASR), in comparison to previous generation research (0.55 Ω cm2 versus 1.2 Ω cm2, respectively). Exchange of the Ni component, for Pd and Rh, led to much lower ASR of 0.39 Ω cm2 and 0.41 Ω cm2 (in 97% H2:3% H2O, at 900°C and 0.8 V), respectively. Equivalent circuit fitting of AC impedance spectra revealed the absence of an anode charge transfer process for the Rh/CGO catalyst system above 875°C, in comparison to all other systems, identifying this system as a potential replacement for the Ni-based cermet.

A Nano-Structured SOFC Composite Cathode Prepared via Infiltration of La0.5Ba0.25Sr0.25Co0.8Fe0.2O3-δ into La0.9Sr0.1Ga0.8Mg0.2O3-δ for Extended Triple-Phase Boundary Area

Mixed ionic and electronic conductors (MIECs) show greatly enhanced electrochemical properties as cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Among promising MIEC candidates, La0.5Ba0.25Sr0.25Co0.8Fe0.2O3-δ (LBSCF) is chosen as a cathode material in this study due to its high oxygen ion diffusivity and oxygen reduction reaction (ORR) activity. It is well known that the composite configuration with superior oxygen ion conductor, e.g., La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM), results in the improvement of cell performance. Here, we successfully fabricate the LBSCF-LSGM composite cathode by infiltration method at a low sintering temperature (< 800°C), and thus nanoparticles are uniformly distributed on the LSGM porous scaffold. A half-cell exhibits an extremely low area-specific resistances (ASRs) of 0.010, 0.020, and 0.049 Ω cm2 at 700, 650, and 600°C, respectively. Further, the peak power density about 0.9 W cm−2 is attained at 700°C, suggesting that infiltrated LBSCF-LSGM composite demonstrates sufficient ORR activities at an intermediate temperature and thus to be a highly promising cathode material for IT-SOFCs.

Evaluation of electroplated Co-Cu metallic coatings for intermediate-temperature solid oxide fuel cells

Co-Cu alloys have been co-deposited onto 430 ferritic stainless steels via electroplating with a citrate solution. At the initial oxidation stage, a three-layer scale composed of a thin CuO outer layer, a thick (Cu,Fe,Cr)-doped Co3O4 middle layer and a (Cu,Fe)-doped (Co,Cr)3O4 inner layer was formed on the coated steel. With extended oxidation, the (Co,Cr)3O4 inner layer has been transformed into a Cr-rich oxide inner layer. An obvious outward diffusion of Fe appeared, leading to the formation of an (Cu,Cr,Mn)-doped (Co,Fe)3O4 interaction zone between the Co3O4-based spinel and the chromia oxides. The Co-Cu coating effectively blocked the outward migration of Cr from the substrate. No Cr element could be found in the coupled La0·8Sr0·2MnO3 (LSM) plate of the coated sample after oxidized at 800 °C in air for 500 h. The highly conductive coating with a structure of CuO/Co-based spinels significantly decreased the growth of the Cr-rich oxide scale, and thus a much lower scale area specific resistance (ASR). The electrical properties and the oxidation mechanism of the coated substrates were discussed.

Structures and Properties of LaFe0.8Cu0.2O3-δ and BaFe0.8Cu0.2O3-δ as Cobalt-Free Perovskite-Type Cathode Materials for the Oxygen Reduction Reaction.

Perovskite oxides with mixed electronic–ionic conduction are important catalysts for the oxygen reduction reaction in solid oxide fuel cells (SOFCs). Here, two cobalt‐free perovskite oxides, LaFe0.8Cu0.2O3−δ (LFCuO) and BaFe0.8Cu0.2O3−δ (BFCuO), were synthesized and comparatively studied with respect to their phase structures, oxygen contents, chemical defects, thermal expansion coefficient (TEC), as well as electrical and electrochemical properties. Different structures and properties have been found for each oxide, which have been interpreted based on their tolerance factors and chemical defects. LFCuO showed much better overall performance than BFCuO, and it proved to be a promising cobalt‐free cathode material of intermediate‐temperature SOFCs with a low TEC (12.0×10−6 °C−1) that matches well with TECs of the electrolytes, high catalytic activity for the oxygen reduction reaction characterized by low area specific resistances (0.090 Ω cm2 at 800 °C and 0.20 Ω cm2 at 750 °C), and high‐temperature chemical stability with electrolytes.

A novel heterogeneous La0.8Sr0.2CoO3−δ/(La0.5Sr0.5)2CoO4+δ dual‐phase membrane for oxygen separation

AbstractDual‐phase membrane is an attractive concept that combines the advantages of two different phases into single membrane matrix. The recently reported significant enhancement of oxygen surface kinetics on the La0.8Sr0.2CoO3−δ (LSC)/(La0.5Sr0.5)2CoO4+δ (LSC214) hetero‐interface due to the formation of fast oxygen transport paths along hetero‐interface is adopted into dual‐phase membrane to achieve enhanced oxygen permeability. The 1300°C sintered LSC/LSC214 (4:1 weight ratio) hollow fiber displayed a maximum oxygen flux of 3.35 ml·min−1·cm−2 at 900°C and 200 ml min−1 helium sweep gas flow rate, which represents up to 80% enhancement relative to that of the 1300°C sintered LSC hollow fiber at the same experimental condition. Such enhancement is enabled by the enlargement of triple phase boundaries to larger areas across the membrane surface for dual‐phase case as confirmed by the significantly lower area specific resistance for LSC/LSC214|Ce0.8Sm0.2O1.9 (SDC)|LSC/LSC214 relative to LSC|SDC|LSC symmetrical cell between 600°C and 800°C. This nominal dual‐phase LSC/LSC214 hollow fiber also showed very stable fluxes of 3.3 and 2.3 ml·min−1·cm−2 during 300‐hr permeation test at 900°C and 850°C, respectively.

Scaling the water cluster size of Nafion membranes for a high performance Zn/Br redox flow battery

Due to their preferential cation transport, dense cation exchange membranes like Nafion membranes are unsuitable for Zn/Br redox flow batteries which require bi-ionic transport of Zn2+ and Br- ions. This work shows that scaling the water cluster size of Nafion membranes by a pre-hydration treatment can achieve not only a high ionic conductivity but also a bi-ionic transport property. Small angle X-Ray scattering, diffusion cell, and electrochemical analysis verify that by increasing the pre-hydration temperature, the water clusters are expanded, resulting in an increase of water uptake, ionic conductivity and the anion transference number. The bi-ionic transport and low area specific resistance induced by the pretreatment enable the successful operation of a Zn/Br redox flow battery with a NRE-212 membrane. Compared with a conventional porous membrane, the properly treated Nafion membrane has an 11.3% higher energy efficiency indicating that the dense structured ion exchange membrane can be used for Zn/Br flow batteries by scaling the water cluster size.

Development and evaluation of a 3-cell stack of metal-based solid oxide fuel cells fabricated via a sinter-joining method for auxiliary power unit applications

Recently, metal-based solid oxide fuel cells (SOFCs) receive much attention for potential application in auxiliary power units (APUs). In this study, a sinter-joining method with a silver bonding layer is proposed. This method enables the fabrication of metal-based SOFCs by joining metal plates and conventional ceramic cells using a silver bonding layer. This sinter-joining method has the advantage of full-sintering of the cathode at 1100 °C, which facilitates a lower area specific resistance (ASR) of the cathode. Furthermore, the entire manufacturing process is conducted under air atmosphere. A 5 × 5 cm2 metal-based cell is successfully fabricated by the sinter-joining method, and a maximum power density of 433 mW cm−2 and a low polarization resistance of 0.12 Ω cm2 is obtained. Using the metal-based cells, a prototype 3-cell SOFC stack is developed considering mechanical robustness and diesel reformate fuel supply for future APU system applications. The stack exhibits a maximum power density of 100 mW cm−2 and is tested for 120 h. After the test, a post-mortem analysis is conducted, and the causes of the low electrochemical performance and degradation issue are investigated. In the conclusion, the sinter-joining method is considered as one of the methods for metal-based SOFCs.

Novel Processing of Cathodes for Solid Oxide Fuel Cells

Solid-oxide fuel cells (SOFCs) are electrochemical devices that efficiently convert chemical energy of fuels into electricity.[1] However, they typically operate at high temperature (800–1000 °C) causing substantial challenges in cost and material compatibility. SOFC that can work at intermediate temperature (IT) (500–750 °C) is thus more attractive.[2] SOFC is generally composed of anode, electrolyte and cathode. A practical cathode for SOFCs should possess sufficiently high thermo-mechanical stability, good thermal and chemical compatibility with the electrolyte, high chemical stability against the surrounding atmosphere, good electro-catalytic activity for oxygen reduction reaction (ORR), as well as high electrical conductivity.[1] However, the current widely used cathode, lanthanum strontium manganite (LSM), rapidly loses activity below 800 °C.[3] According to numerical calculations, the efforts to optimize the oxygen surface exchange reaction are required while very high ionic conductivities are not necessary in order to achieve the goal of a highly active cathode.[4] Nano-sized palladium (Pd) and platinum (Pt) show very high activity towards oxygen activation, which can substantially increase the cathode electrochemical performance by improving the surface properties. However, precious metals are expensive and undergo sintering. Silver is a good alternative for its relatively low price and high electrocatalytic activity for oxygen activation, however more easily sintered than Pt and Pd resulting in the electrode deactivation.[5] As the electrodes and the dense electrolyte are sintered together in SOFC, the deactivated electrodes are normally neither regenerable nor replaceable, what brings the end of the SOFC. On the other hand, the Ag-doped perovskites have promoted catalytic oxidation of CO, CH4, n-hexane, and NO,[6] which was significantly improved by the partial substitution of Ag into the A-site of perovskite together with the additional formation of the oxygen vacancy and the metallic Ag on the surface of the perovskite forming composite materials. [7, 8] Among several ways to process the composites, infiltration has shown promising results bringing the possibility to tailor electronic, ionic and mixed ionic electronic conductivities in a porous backbone of proton conducting oxides. [9, 10] The exsolution of nickel, ruthenium, silver or other metal nanoparticles has been investigated in reducing conditions for the design of the electrodes for SOFC. [11-13] The development of highly electrochemically active cathodes for SOFCs requires the optimization of materials composition together with micro- and nanostructures in order to form stable and catalytically active composite electrodes. Here we report on the novel heterostructured silver nanoparticle-decorated perovskite composites La0.95-xSrxMn1-y-z(Fe,Ni,Zn,Mg)zNbyO3-δ – 0.05Ag (exLSAMN) as highly active and durable cathodes for SOFCs, derived from single phase La0.95-xSrxAg0.05Mn1-y-z(Fe,Ni,Zn,Mg)zNbyO3-δ (LSAMN) perovskite precursors through an exsolution process. We report LSAMN as a novel precursor which can develop into high-performance nanosized silver modified LSM-based electrode under cathodic polarization or reducing atmosphere with improved stability and in situ electrochemical regeneration capability. The LSAMN materials were synthesized by solid state reaction and wet chemical synthesis method in order to compare the activity. The electrochemical intercalation/de-intercalation of metal catalysts is a conceptually attractive approach that is also applicable for the development of other metal-modified oxide electrodes. The composite formation and properties were tailored by changing the synthesis route and thermal treatment. A thorough description of the synthesis methods is presented as well as a careful characterization of the microstructure and phase composition of the resulting composite electrodes. The performance of the new composite cathodes with gadolinia-doped ceria (CGO) electrolyte is demonstrated. The exLSAMN electrode showed fairly high electrochemical activity and low area specific resistance (ASR). These unique features make the new materials highly promising cathodes for SOFCs at intermediate temperatures. References A. B. Stambouli, E. Traversa, Renew. Sust. Ener. Rev., 6 (2002) 433.J. A. Kilner, M. Burriel, Ann. Rev. Materi. Res., 44 (2014) 365.S. P. Jiang, J. Mater. Sci., 43 (2008) 6799.J. Fleig, J. Pow. Sour., 105 (2002) 228.T. Z. Sholklapper et al. J. Pow. Sour., 175 (2008) 206.D. Y. Yoon et al. J. Catal., 319 (2014) 182.K. Wang et al. Catalysis Today, 158 (2010) 423.G. Pecchi et al. App. Catalysis A: General, 371 (2009) 78.C. Duan et al. Science, 349 (2015) 1321.C. Duan et al. Energy Environ. Sci., 10 (2017) 176.Y. Zhu et al. Nano Lett., 16 (2016) 512.J. T. S. Irvine et al. Nature Energy, 1 (2016) 15014.G. Tsekouras, D. Neagu, J. T. S. Irvine, Energy Environ. Sci., 6 (2013) 256.

Influence of particle size and agglomeration in solid oxide fuel cell cathodes using manganite nanoparticles

In this work we studied the influence of particle size and agglomeration in the performance of solid oxide fuel cell cathodes made with nanoparticles of La0.8Sr0.2MnO3. We followed two synthesis routes based on the Liquid Mix method. In both procedures we introduced additional reagents in order to separated the manganite particles. We evaluated cathodic performance by Electrochemical Impedance Spectroscopy in symmetrical (CATHODE/ELECTROLYTE/CATHODE) cells. Particle size was tuned by the temperature used for cathode sintering. Our results show that deagglomeration of the particles, serves to improve the cathodes performance. However, the dependence of the performance with the size of the particles is not clear, as different trends were obtained for each synthesis route. As a common feature, the cathodes with the lowest area specific resistance are the ones sintered at the largest temperature. This result indicates that an additional factor related with the quality of the cathode/electrolyte sintering, is superimposed with the influence of particle size, however further work is needed to clarify this issue. The enhancement obtained by deagglomeration suggest that the use of this kind of methods deserved to be considered to develop high performance electrodes for solid oxide fuel cells.

Protective coating based on manganese–copper oxide for solid oxide fuel cell interconnects: Plasma spray coating and performance evaluation

A solid oxide fuel cell (SOFC) stack requires metallic interconnects to electrically connect unit cells, while preventing fuel from mixing with oxidant. During SOFC operations, chromia scales continue to grow on the interconnect surfaces, resulting in a considerable increase of interfacial resistance, and at the same time, gaseous Cr species released from the chromia scales degrades the cathode performance. To address these problems, in this study, protective Mn2CuO4 coatings are fabricated on metallic interconnects (Crofer 22 APU) via a plasma spray (PS) process. The PS technique involves direct spray deposition of molten Mn2CuO4 onto the interconnect substrate and leads to the formation of high-density Mn2CuO4 coatings without the need for post-heat-treatment. The thickness, morphology, and porosity of the PS-Mn2CuO4 coating are found to depend on the processing parameters, including plasma arc power, gas flow rate, and substrate temperature. The PS-Mn2CuO4 coating fabricated with optimized parameters is completely impermeable to gases and has high adhesion strength on the interconnect substrate. Furthermore, no resistive chromia scales are formed at the coating/substrate interface during the PS process. As a result, the PS-Mn2CuO4-coated interconnects show a very low area-specific resistance below 10 mΩ cm2 at 800 °C in air and excellent stability during both continuous operation and repeated thermal cycling. This work suggests that an appropriate combination of the material and coating process provides a highly effective protective layer for SOFC interconnects.

Exploring a novel ceramic (Ti,W)3SiC2 for interconnect of intermediate temperature solid oxide fuel cell

A solid solution (Ti,W)3SiC2 possessing good oxidation resistance and low area-specific resistance (ASR) after oxidation has been synthesized by an in-situ hot pressing process. The oxidation rate constant at 800 °C in air is 6.29 × 10−14 g2 cm−4 s−1 for (Ti,W)3SiC2. The formed single-layer oxide is composed of W doped rutile TiO2 and amorphous SiO2. SiO2 is evenly inlaid in the communicative body frame of TiO2. W doped in TiO2 mainly exists as W6+. W doping not only hinders the outward diffusion of Ti by decreasing the concentration of native Ti interstitials in TiO2, but also restrains the inward diffusion of oxygen by decreasing the concentration of O vacancies. Furthermore, W dopant in TiO2 enhances the electrical conductivity of TiO2 by increasing the concentration of semi-free electron. Therefore, the low ASR of (Ti,W)3SiC2 after oxidation owes to high electrical conductivity of TiO2 as well as the reduced thickness of oxide scale. All the results render (Ti1-xWx)3SiC2 promising as interconnects for the intermediate temperature solid oxide fuel cell.

Development of lanthanum-doped praseodymium cuprates as cathode materials for intermediate-temperature solid oxide fuel cells

Electrochemical properties of the Pr2-xLaxCuO4 (x = 0.05; 0.1; 0.3) (PLCO) oxides in oxygen reduction reaction (ORR) were examined towards their applicability as cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Pr1.95La0.05CuO4 (PLCO0.05) was defined as a favorable basis for the composite cathode material due to its conducting, thermomechanical and electrocatalytic properties. The optimization of the annealing temperature of the PLCO0.05-xGDC composite electrode deposited on GDC solid electrolyte surface had shown that the lowest area specific resistance (ASR) was achieved at 850 °C. The highest electrochemical activity in ORR was achieved for the composition containing 40 wt% GDC in the temperature range of 600–750 °C. The application of PLCO0.05-40GDC composite cathode instead of pure PLCO0.05 made it possible to reduce ASR up to 10 times at 700 °C in air (from 0.87 Ω·cm2 (x = 0 wt%) to 0.08 Ω·cm2 (x = 40 wt%)). According to the data obtained, PLCO0.05-40GDC can be considered as a promising cathode material for IT-SOFCs.

Performance evaluation of Mn and Fe doped SrCo0.9Nb0.1O3-δ cathode for IT-SOFC application

Cathode materials of Mn and Fe doped SrCo0.9Nb0.1O3-δ, are synthesized by solid state route for intermediate temperature fuel cell applications. Phase pure material is obtained after calcining the precursors at 1100 °C. Phase compatibility is observed between this novel cathode material with gadolinia doped ceria (GDC) electrolyte material as reflected in the diffraction pattern. The state of art YSZ electrolyte is not compatible with this cathode material. Average thermal expansion coefficient of the material varies between 17 to 22 X 10-6 K-1 on doping, from room temperature to 800 °C. Increase in thermal expansion coefficient is observed with Mn and Fe doping associated with the loss of oxygen from the crystal. The electrical conductivity of the cathode material decreases with Fe and Mn doping. Mn doped samples show lowest conductivity. From the symmetric cell measurement lower area specific resistance (0.16 Ω-cm2) is obtained for un-doped samples, at 850 °C. From the initial results it can be inferred that Mn/Fe doping improves neither the thermal expansion co-efficient nor the electrochemical activity.

Electroless deposition of Co(Mn)/Pd-decorator into Y2O3-stabilized ZrO2 scaffold as cathodes for solid oxide fuel cells

In this work, we show that higher Co or Mn dopant content of up to 25 mol% on Pd can be obtained without modifying the original crystal structure of Pd via co-reduction synthesis route using hydrazine (N2H4), which is not achievable via conventional sol-gel route. The synthesized Co/Mn-doped Pd alloys can inhibit Pd agglomeration that hinders Pd use as an oxygen reduction reaction (ORR) promoter on solid oxide fuel cell (SOFC) cathode. The presence of Co or Mn on Pd lattice of Co/Mn-doped Pd alloy-decorated YSZ (Y2O3 stabilized ZrO2) cathode provides dual advantages of improving the ORR performance of the cathode and enhancing the ORR performance stability during long term operation. Between 600 °C and 800 °C, Pd0.90Co0.10O-impregnated YSZ cathode displayed the highest ORR performance among PdO-, Pd0.90Co0.10O-, Pd0.75Co0.25O-, Pd0.90Mn0.10O-, and Pd0.75Mn0.25O-impregnated cathodes as indicated by its relatively low area specific resistance of 0.14 Ω cm2 at 700 °C. Our thermal gravimetric analyses and scanning electron microscopy images revealed that the high electrochemical performance stability of Co/Mn-doped Pd alloys during 30 hour-cathodic current test correlates with their higher metal ↔ metal oxide conversion reversibility and microstructure stability under thermal cycling between room temperature and 900 °C (relative to Pd).

Effects of sintering temperature on the structural and electrochemical properties of SrFe0.5Ti0.5O3‐δ perovskite cathode

AbstractThe effects of sintering temperature on the structural and electrochemical properties of SrFe0.5Ti0.5O3‐δ perovskite cathode film was investigated. For the structural properties of SrFe0.5Ti0.5O3‐δ film sintered at a temperature ranging from 900‐1300°C, changes in surface and cross‐sectional microstructure were studied. Surface porosity and micro hardness were analyzed. The relationship of the structural properties with the electrical and electrochemical performances of the SrFe0.5Ti0.5O3‐δ film was examined. The high densification of the film sintered at 1300°C led to the better electrical conductivity of 16.38 S cm−1 than the 4.86 S cm−1 of the film sintered at 900°C at an operating temperature of 800°C. For the electrochemical performance, the SrFe0.5Ti0.5O3‐δ film sintered at 1300°C gained a low area specific resistance (ASR) value of 38.70 Ω cm2 at 800°C. The ASR further decreased to 0.99 Ω cm2 for the thicker film sintered at the same temperature.

Comparison of iron and copper doped manganese cobalt spinel oxides as protective coatings for solid oxide fuel cell interconnects

MnCo2O4, MnCo1.7Cu0.3O4 and MnCo1.7Fe0.3O4 are investigated as coatings for corrosion protection of metallic interconnects in solid oxide fuel cell stacks. Electrophoretic deposition is used to deposit the coatings on Crofer 22 APU alloy. All three coating materials reduce the parabolic oxidation rate in air at 900 °C and 800 °C. At 700 °C there is no significant difference in oxidation rate between coated samples and uncoated pre-oxidized Crofer 22 APU. The cross-scale area specific resistance (ASR) is measured in air at 800 °C using La0.85Sr0.1Mn1.1O3 (LSM) contact plates to simulate the interaction with the cathode in a SOFC stack. All coated samples have three times lower ASR than uncoated Crofer 22 APU after 4370 h aging. The ASR increase with time is lowest with the MnCo2O4 coating, followed by the MnCo1.7Fe0.3O4 and MnCo1.7Cu0.3O4 coatings. LSM plates contacted to uncoated Crofer 22 APU contain significant amounts of Cr after aging, while all three coatings effectively prevent Cr diffusion into the LSM. A complex Cr-rich reaction layer develops at the coating-alloy interface during oxidation. Cu and Fe doping reduce the extent of this reaction layer at 900 °C, while at 800 °C the effect of doping is insignificant.

Effects of La2O3 content and particle size on the long-term stability and thermal cycling property of La2O3-dispersed SUS430 alloys for SOFC interconnect materials

We developed oxide-dispersed alloys as interconnect materials for a solid oxide fuel cell by adding La2O3 to SUS430 ferritic steels. For this purpose, we prepared two types of La2O3 with different particle sizes and added different amounts of La2O3 to SUS430 powder. Then, we mixed the powders using a high energy ball mill, so that nano-sized as well as micro-sized oxide particles were able to mix uniformly with the SUS430 powders. After preparing hexahedral green samples using uni-axial and cold isostatic presses, we were finally able to obtain oxide-dispersed alloys having high relative densities after firing at 1,400 °C under hydrogen atmosphere. The nano-sized La2O3 dispersed alloys showed properties superior to those of micro-sized dispersed alloys in terms of long-term stability and thermal cycling. Moreover, we determined the optimum amounts of added La2O3. Finally we were able to develop a new oxide-dispersed alloy showing excellent properties of low area specific resistance (16.23 mΩ cm2) after 1000 h at 800 °C, and no degradation after 10 iterations of thermal cycling under oxidizing atmosphere.

Influence of pre-reduction on microstructure homogeneity and electrical properties of APS Mn1.5Co1.5O4 coatings for SOFC interconnects

Atmospheric plasma spray is employed to deposit Mn1.5Co1.5O4 (MCO) coatings onto T441 and porous 430L substrates respectively at room temperature and 400 °C. The coatings are then subjected to redox treatments to achieve a desirable gas tightness. The gas permeability, area specific resistance (ASR) and microstructure homogenization of MCO coatings are evaluated in different stages. The gas permeability of MCO coating deposited at 400 °C and exposed to redox treatments can be as low as ∼8.2 × 10−8 cm4 s−1 gf−1, which is essential for sufficient protection of metallic substrate against oxidation. The MCO-coated T441 without pre-reduction presents a nonuniform microstructure characterized by isolated precipitates rich in Co and dark matrix rich in Mn. In comparison, the MCO coating with 5 h pre-reduction presents a uniform and dense spinel structure. The ASR tests indicates that a homogeneous structure has contributed to an increase in the overall conductivity. While bare T441 shows a substantial increase in interfacial ASR during the 200 h test, MCO-coated T441 exhibites a high stability and a much lower ASR value of 13 mΩ cm2. Besides, the dense MCO coatings effectively inhibit the oxide scale growth and block outward diffusion of Cr during the oxidation tests. Cr-rich oxide scale formed at the MCO/T441 interface is less than 1.2 μm and no further migration of Cr was detected.

(Invited) Role of Ion-Conducting Membranes in Synthesis and Use of Sustainable Fuels

Replacement of conventional catalytic technologies for synthesis of sustainable, carbon-neutral fuels with direct electrochemical synthesis has a potential for big energy savings due to reduction of number of process steps and pressure/temperature. In addition, electrochemical technologies are easily scaled down to allow for low capital, modular plants that match the scale of renewable energy production. The use of these fuels in electrochemical devices opens a path to cost-effective long-term energy storage and distributed energy generation. Development of low cost, ion-selective membranes with low area specific resistance is, along with electrocatalyst development, critical for the success of such technologies. Not less important is development of membrane manufacturing methods at a practical scale. This presentation will review prospective technologies using ion-selective membranes for synthesis of carbon-neutral fuels for chemical energy storage and their use for generation of electricity (using fuel cells) and hydrogen. Advantages of electrochemical synthesis of ammonia from nitrogen and hydrogen or water compared to the conventional Haber-Bosch process will be discussed. Other processes include direct electrochemical synthesis of alcohols from CO2. The requirements to ion-selective membranes for these processes and fuel cells will be presented. 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. The Renewable Electricity to Fuels through Utilization of Energy-dense Liquids (REFUEL) program funds the development of transformational technologies to reduce the barriers to widespread adoption of intermittent renewable energy sources by enabling the conversion of energy from these sources, water and air to energy-dense zero-carbon liquid fuels and their use for electricity or hydrogen generation. REFUEL projects targeting various ion conducting membranes as well as related projects supported by ARPA-E through OPEN program will be highlighted.

The ARPA-E Ionics Program: Advancing Anion Exchange Membranes

In 2016 ARPA-E launched the IONICS (Integration and Optimization of Novel Ion-Conducing Solids) program, motivated by the enabling role of separator technology and the remaining performance and cost gaps across multiple types of electrochemical devices. The 16 teams in the IONICS program are focused on developing breakthrough separators that would be broadly enabling in different areas of electrochemical technology, and also amenable to cost effective manufacturing. The projects include both polymer and inorganic ion conducting separators that enable electrode chemistries that have been previously unsuccessful in practical devices. Project teams are focused on overcoming property tradeoffs to achieve a full set of required attributes, including conductivity, selectivity, stability, mechanical properties, manufacturability, cost, and others. This contrasts with a common approach of optimizing a single variable at the expense of others. The IONICS focus is on solids rather than liquids, due to inherent advantages in selectivity and mechanical properties offered by solids. The IONICS program is focused on three areas: (1) Li+ conductors that enable the cycling of the lithium metal electrode at conditions required for high-energy cells, (2) highly selective polymer separators for flow batteries, and (3) anion-conducting polymer separators for use in alkaline fuel cells, electrolyzers, and other electrochemical devices. This talk will focus on area (3), where the potential benefits of the alkaline environment include the reduction/elimination of platinum-group metal catalysts for both hydrogen and oxygen electrodes, and the ability to use lower cost, uncoated, stainless steel plates. The polymer attributes pursued in the program include extended stability (1,000 h with negligible degradation) in alkaline conditions at a temperature of 80°C or higher, low area-specific ionic resistance (<=0.04 ohm-cm2 in liquid form), limited swelling (<50%), and low cost (<=20 $/m2). Additionally, fuel cell applications require the membrane to retain high conductivity under air exposure and avoid degradation during humidity cycling, while electrolysis applications require it to withstand a differential pressure of tens of bar. A key limitation for the development of improved membranes in this growing field is the lack of specific, consistent test conditions, which makes it difficult to easily identify the most promising membranes. This talk will outline the test conditions developed for the IONICS program teams, which we hope will be used by other research groups to advance progress in this important field.