bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of Mn Co-doping on the Electrochemical Properties of Gd0.2Ce0.8O1.9-
d/Pt Model-composite Electrodes
Authors: Velicsanyi Peter , Gerstl Matthias , Nenning Andreas , Hutter Herbert , Fleig Jürgen , Opitz Alexander Karl
Published: February 2020

For solid oxide fuel cells (SOFCs) to reach widespread commercial distribution several obstacles still have to be overcome. Material-wise one of the main problems remains the optimization of the anode for use in harsh environments or operation conditions.

The still prevalent anodes based on Ni/YSZ cermets offer excellent catalytic properties for hydrogen oxidation and reformation of hydrocarbon fuels. Nevertheless, when feeding a fuel containing hydrogen sulphide impurities to an SOFC, a dramatic drop in the anode performance is the consequence. Therefore, work is in progress to identify the causes of this sulphur triggered polarization resistance increase, which is partially explained by sulphur adsorption. The hope is that a more complete understanding in this degradation will help to formulate mitigation strategies as a way to prolong the life of an SOFC.

In this contribution alternative SOFC anode materials are being surveyed and compared to the classic Ni/YSZ cermet. By exchanging the ionically conductive YSZ phase with e.g. gadolinium doped ceria (GDC) and/or the electronically conducting nickel with e.g. donor doped strontium titanate, formulations may be found, which increase the sulphur tolerance of an SOFC anode. Moreover, a fully oxidic anode may offer a significantly higher redox cycling stability than the conventional Ni/YSZ cermet.

By using impedance spectroscopy on geometrically well-defined model-composite electrodes of alternative SOFC anode materials, we are able to separate elementary processes such as ionic and electronic conductivity as well as the chemical capacitance and the surface reaction resistance. By introducing H2S in the feed gas system the effects of sulphur poisoning on these parameters can be studied. This way a fair comparison of alternative SOFC anode materials to Ni/YSZ is possible.
Simulation of Interfacial Cracking of the Joint between Glass-Ceramic Sealant and Metallic Interconnect in a Planar Solid Oxide Fuel Cell Stack
Authors: Lin Chih-Kuang , Shiu Wei-Hong , Wu Si-Han , Lee Ruey-Yi
Published: February 2020

Interfacial cracking in the joint between a glass-ceramic sealant and a metallic interconnect under thermal stresses is characterized for a prototypical planar solid oxide fuel cell (pSOFC) stack, using finite element analysis (FEA).  A three dimensional FEA model is constructed for a multiple-cell stack to perform thermal stress analysis at both steady operation and shutdown stages and to locate the highly stressed region in each component.  Stress intensity factor and energy release rate for fracture are calculated at the crack front of a crack placed at the highly stressed interfacial region between a glass-ceramic sealant and a metallic interconnect in the given pSOFC stack for each stage.  The critical crack or defect size at the interface of the joint of glass-ceramic sealant and metallic interconnect in the given pSOFC stack is determined by comparing the calculated energy release rates with the experimental measurements of interfacial fracture energy of the glass-ceramic/metallic interconnect joint.
Estimation of 3D Effective Properties from 2D Cross Sections in Porous Electrodes
Authors: Ferrari Tommaso , Bertei Antonio , Nicolella Cristiano
Published: February 2020

Nowadays tomographic techniques are used to reconstruct the 3D microstructure of Solid Oxide Fuel Cell (SOFC) electrodes from a sequence of 2D cross sections and to evaluate the effective properties of real samples. However, this approach involves expensive instrumentation and time-consuming procedures. Thus, there is the need of short-cut methods to infer 3D properties from a single 2D cross section for a rapid characterization of the electrode properties.

In this study, the correlation between 2D and 3D properties is studied through the numerical reconstruction of the electrode microstructure by using packing algorithms. 3D effective geometrical properties, such as the mean particle diameter, the pore size, the specific surface area and the three-phase boundary length per unit volume are calculated and correlated to 2D properties evaluated in a cross section, such as the mean diameter of the sectioned particles, the mean chord length, the particle perimeter exposed to the porous phase and the number of three-phase boundary points per unit area, respectively. A strong correlation is found between 2D and 3D properties in a wide range of porosity, particle size and electrode composition. A statistical analysis on the accuracy of the estimated properties as a function of the size of the cross section is also reported.

The results of this study provide practical indications that can be easily applied to Scanning Electron Microscope (SEM) images of real samples for a rapid estimation of the effective properties of the electrodes.
High Fuel Utilization Operation of Solid Oxide Fuel Cells - a Modeling Study
Authors: Monder Dayadeep S. , Pawar Vishal , Kumar Sanjay , Shekhar Rustam Singh
Published: February 2020

High fuel utilization (Uf
) is desirable in fuel cells as it has a direct impact on efficiency – the higher the Uf

 the higher the fuel cell efficiency. However, the Ni phase in Ni based SOFC anodes is susceptible to oxidation to NiO when the fuel cell is operated at high fuel utilizations. This phase transition is problematic because a) NiO is inactive to the fuel oxidation reactions, and b) the larger specific volume of NiO results in damage to the anode microstructure if this Ni to NiO transition is reversed and repeated a few times.  The second problem listed above is known as Ni redox cycling. Thus, there are conflicting objectives where the designer/operator of a SOFC system desires a high fuel utilization Uf

 while avoiding Ni oxidation.

Ideally, one would like to identify a safe operating zone where the fuel utilization Uf

 can be maintained in a high enough range without risking Ni oxidation. In this presentation we will use simulation results from a detailed multiphysics model to outline some of the challenges of operating a SOFC at high fuel utilization and attempt to identify the above mentioned “safe operating zone”.

The multiphysics model used in this work is for a planar anode supported geometry and includes a fully coupled description of the flow and mass transfer in the air/fuel channels and the electrodes, and the current/potential distribution in the electrodes. One of the mechanisms for Ni oxidation is through reaction (1).

Ni + H2O ↔ NiO + H2                                                 (1)

The favourability of reaction (1) at a particular location in the anode is dictated by the thermodynamics of the reaction and the local fuel composition. As the model is able to predict the fuel side composition as a function of position, the output of the model can be used to predict whether there is a risk of Ni oxidation in the anode at any given set of operating conditions.

We will present results from a parametric study over a wide range of different temperatures, cell voltage, as well as inlet fuel flow-rates and composition. An example set of results is given in Fig 1 where the inlet flow-rate is varied for a given cell voltage and temperature. The Ni oxidation reaction is thermodynamically favourable in the latter section of the anode where the partial pressure ratio PH2O/PH2 exceeds the threshold value given by the thermodynamics of the reaction and shown as a dot-dash line in the bottom plot. According to Fig 1, the threshold Uf

  for these conditions is ~99%. This is a much higher value than the typical 80-85% used in most SOFC designs. Another noteworthy point is that at this high fuel utlization, the last 1/3 of the cell is producing a very small fraction of the total current.

Figure 1
SOFC Stack Operation: Effects of Electrode-Interconnect Contacts
Authors: Minh Nguyen , Budur Abhijith , Dogan Fatih
Published: February 2020

Planar SOFC multicell stacks incorporating metallic interconnects generally exhibit average cell performance lower than that observed for out-of-stack cells under similar conditions. It has been suggested that electrode/interconnect, especially cathode/interconnect, contacts (and their ohmic resistances) are the main cause for this observed difference. In addition, cathode/interconnect contacts can evolve in long-term operation, resulting in stack performance reduction/degradation with time. Experiments using current interruption, AC electrochemical impedance and other characterization techniques have been conducted on one-cell stacks and button cells in contact with various types of interconnect materials. The data obtained to date confirmed the hypothesis that contact ohmic resistance significantly contributes to stack performance losses. Thsi paper summarizes and discusses experimental results on the effects of cathode/interconnect contacts on stack performance.
Three Dimensional Temperature Distribution Analysis in Directly Internal Reforming SOFC Fuelled by Methane
Authors: Ogura Teppei , Wakamatsu Katsuhiro
Published: February 2020

High SOFC operating temperature allows direct internal reforming (DIR) of methane within the SOFC anode, which is expected to be load-following simple dispersed power system. However, temperature decrease by endothermic reforming reaction leads to carbon formation and increase of thermal stress which cause decrease in the performance and durability of SOFC cells. We have developed a reactor model coupled with computer fluid dynamics and reactions to predict three dimensional temperature distributions. Calculated temperature distributions along flow direction agree with experimentally measured ones in both cases of homogeneous and functionally-graded paper structure catalysts. Detailed three dimensional analyses of temperature distributions tell us the importance of cell structures, gas inlet position, and catalyst thickness. Then, we have extended the analysis tool to more practical model where three SOFC cells are stacked. Temperature distribution in an upstream cell has steeper gradient than that in a downstream cell. Better temperature distribution was obtained by designing functionally-graded paper structure catalysts in two dimensions, along the stacking direction and the gas flow in a cell.
A Thermo Fluid and Thermo Mechanical Modelling of a Microtubular Solid Oxide Fuel Cell Stack for Unmanned Aerial Vehicles
Authors: Hari Bostjan , Dhir Aman , Steinberger-Wilckens Robert
Published: February 2020

This work presents a three-dimensional thermo fluid and thermo mechanical computational analysis of a microtubular solid oxide fuel cell (SOFC) stack as part of a microtubular SOFC generator. The latter powers a lithium-ion battery as a microtubular SOFC hybrid power system to extend the flight endurance of a mini unmanned aerial vehicle.

The microtubular SOFC stack and balance of plant components, comprising microtubular SOFC generator, were designed based on computational fluid dynamics (CFD) assumptions. The stack design process has been further upgraded with thermo mechanical finite element analysis (FEA) simulation to capture deformations and stresses in the stack due to thermal expansion of microtubular SOFCs and manifolds.

The developed microtubular SOFC stack will be built based on CFD and FEA predictions and tested to determine the suitability of the microtubular SOFC hybrid power system for this application.
In-Situ Exsolution of Nano Transition Metal Particles on Lanthanum Chromite Perovskite Anode for Solid Oxide Fuel Cells
Authors: Sun Yi-Fei , Wang Meng-Ni , Luo Jing-Li
Published: February 2020

The physical and electrochemical properties of lanthanum chromite perovskites in which a portion of Cr cations have been substituted with transition metals (La0.6Sr0.3Cr0.85M0.15, M= Ni, Fe, Co) were investigated and the suitability of the materials for use as anode in solid oxide fuel cell (SOFC) was assessed. The SEM results show that the well dispersed nano transition metal particles were successfully prepared by growing them in-situ directly from its perovskite parent backbone under anode reaction condition. And these particles can re-resolve into the lattice when exposed to oxidizing condition. The SOFCs exhibited desirable electrochemical performance in both sweet and sour fuels. It is demonstrated that the promoting effect should be attributed to the decoration of nano transition metals which enhanced the electronic conductivity and catalytic activity.

Figure 1
Reversible Fuel Cells with Tri-Layer Electrolytes
Authors: Virkar Anil V.
Published: February 2020

Reversible solid oxide fuel cells (SOFC) are operated as solid oxide fuel cells and as solid oxide electrolyzer cells (SOEC). In SOFC mode, hydrogen is consumed at the fuel electrode to convert chemical energy of fuel oxidation into water vapor. In SOEC mode, water vapor is decomposed at the fuel electrode to generate hydrogen under an applied DC voltage. Much of the reported work on reversible solid oxide cells is based on yttria-stabilized zirconia (YSZ) electrolyte, Ni + YSZ fuel electrode, and a perovskite-based oxygen electrode. At high operating voltages in the SOEC mode, cell degradation can occur which involves oxygen electrode delamination, formation of cracks within the electrolyte, and also reduction of the electrode near the fuel electrode. The higher the applied voltage, the greater is the propensity to degradation. These observations are consistent with the chemical potential of oxygen in the electrolyte exceeding both electrode bounds under an applied voltage. It has been shown that a small amount of electronic conductivity can minimize degradation. The principal role of electronic conductivity is to smoothen out the variation in oxygen chemical  potential through the electrolyte such that it does not exceed electrode bounds. YSZ-based electrolyte if doped with sufficient amount of CeO2 can create significant electronic conductivity such that the electrolyte becomes a mixed ionic electronic conductor. Doping with ceria also lowers the ionic transference number of the electrolyte. A possible bi-layer electrolyte consists of a thin layer of YSZ (or another purely oxygen ion conductor) deposited on a mixed ionic electronic conducting material. As long as electronic conduction through the blocking layer is negligible, the overall ionic transference number of the bi-layer electrolyte can approach unity. In this paper, theoretical analysis of the bi-layer electrolyte for reversible cells is presented. Two configurations of the bi-layer electrolyte are investigated. (1) The electron blocking layer adjacent to the oxygen electrode. (2) The electron blocking layer adjacent to the fuel electrode. For both configurations, the spatial distribution of oxygen chemical potential through the bi-layer electrolyte in both the SOFC and the SOEC modes are evaluated. The ionic transference number of the MIEC part of the bi-layer electrolyte is varied over a wide range. Theoretical analysis shows that such bi-layer electrolyte cells should exhibit good performance characterstics and excellent stability. The net variation of the oxygen chemical potential through the bi-layer electrolyte is determined as a function of transport properties of both layers, electrode polarizations and interfacial resistances to electron transfer.
Effect of Bismuth Oxide as Sintering Aid for Gadolinia-doped Ceria at 1050°C
Authors: De Marco Vincenzo , Sglavo Vincenzo Maria
Published: February 2020

Dense GDC electrolytes can work as high ion-conducting material for innovative IT-SOFCs. These electrolytes will be used as a base to develop sulfur resistant anodes using copper oxide and GDC, in order to avoid the use of nickel oxide. An aqueous tape casting process to produce dense gadolinia-doped ceria (GDC) electrolyte was developed. The study developed in three main steps. First, the dispersant concentration was idealized for slurries consisting of only distilled water, an ammonium polyacrylate (PAA) dispersant and ceramic powder (commercial Ce0.9Gd0.1O1.95). By examining the rheological behavior of the slurry,  the ideal ratio between the active part of dispersant and powder surface was found to be between  0.15 and 0.30 mg/m2 . Second, starting with the dispersed slurry, fixed amounts of acrylic binder and plasticizer were added and the pH was varied in order to identify the optimum pH interval in which the suspension is stable and no agglomerates form. The ideal pH was found to be between 8 and 9. Finally, the amounts of binder and plasticizer were varied and the suspensions were tape casted (thickness 200 µm) to produce a defect free, smooth and high relative green density (about 50%) tape. SEM observations of samples sintered at 1500 °C showed satisfactory dense section profile (about 95%).

Figure 1
Oxygen Ion Adsorption Studies on La10Si6O27 (001) Surface with DFT Calculation for SOFC Electrolyte
Authors: Ma Yangzhou , Fenineche Nouredine , El-Kedim Omar
Published: February 2020

The apatite-type material La10-xSi6O27-1.5x (LSO) has promising future as electrolyte in SOFC for its high ionic conductivity [1-3]. In this work, ab-initio calculation based on density functional theory (DFT) [4] has been used to investigate the oxygen ion adsorption mechanisms and energy at different sites on the LSO (001) surface. The oxygen ion migration channel can be predicted using the results of adsorption energies on various sites. The most stable adsorption is shown at the hollow between La and O (located away from O-Si Tetrahedron), thus it should be a candidate channel of oxygen ion migration. Furthermore, the electronic properties, including the Fermi energy level, bond strength and length, have been changed with the ion adsorption, and the electrons transition features were obtained by density of states analysis. The calculated results also imply that LSO could be employed as possible electrolyte material due to its low formation and migration energies for the oxygen ion.

Keywords: Apatite electrolyte, Ab initio calculations, DFT, SOFC, ion adsorption. 

Reference:

1. H. Yoshioka, Y. Nojiri, S. Tanase, Solid State Ionics 179 (2008) 2165-2169

2. Guangchao Yin, et al, Journal of Alloys and Compounds 586 (2014) 279–284

3. Susumu Nakayama, et al, Ceramics International 40 (2014) 1221–1224

4. T.Q. Nguyen et al. Applied Surface Science, 288 (2014) 244–250

Figure 1
EIS Study on SOFC Short Stack
Authors: Cinti Giovanni , Boigues Muñoz Carlos
Published: February 2020

SOFCs are a strong potential technology for increasing energy efficiency and reducing CO2 emissions. One of the most significant bottleneck for the development of this technology is stack duration. Demonstration activity all around Europe is showing that efficiency decreases due to cells degradation caused by delamination, reduction of active site, increase of component resistance, etc. With the aim of detecting degradation causes the impedance technology technique (EIS) was applied to SOFC with interesting results. This study presents the application of EIS directly to stack performance. Experimental results and analysis is reported using equivalent circuit study and distribution of relation time (DRT) with the aim of individuate degradation causes.
Performance Enhancement of LSM Cathode of SOFCs through Sequential Infiltration of Ag and Ceria
Authors: Babaei Alireza
Published: February 2020

In this study, the effect of sequential infiltration and catalyst loading of metallic and ceramic catalysts on the performance and stability of La0.8Sr0.2MnO3 (LSM) cathode of solid oxide fuel cell was investigated. Small loading of catalytic silver nanoparticles along with ceria catalytic nanoparticles were sequentially infiltrated into the porous structure of LSM cathode and the electrochemical performance of the cells was evaluated at intermediate temperature range of 600-800°C. Cathode performance was investigated by electrochemical impedance spectroscopy (EIS) and Chrono potentiometery technique at dc bias of 200 mA/cm2 on cathode half cells. The results indicate that electrochemical performance of dually infiltrated cathode is significantly improved compared with those of LSM cathodes separately infiltrated with Ag and ceria. The results show that while individual infiltration of Ag and Ceria decreased the electrode polarization resistance of the cell by %56 and %79, respectively, dual infiltration of Ag and Ceria with equal total loading of catalyst decreased the polarization resistance of the electrode by %98 at open circuit potential and 700°C. Scanning electron microscopy (SEM) studies showed the random distribution of discrete nano catalysts in the vicinity of cathode/electrolyte interface which proves effectiveness of the infiltration technique for performance enhancement of cathode electrodes. Long term stability of cathode was also investigated and a stable performance was observed for dually infiltrated cathode which can be attributed to well distribution of catalyst nanoparticles.
High Temperature Metal / Metal Oxide Battery
Authors: Yildiz Saffet , Loll Isabelle , Vinke Izaak C. , de Haart L.G.J. , Eichel Rüdiger-Albrecht
Published: February 2020

In future there will be a strong demand for large capacity rechargeable batteries to store electrical energy (e.g. from renewable power sources) in long-term stationary applications  [1]. A high temperature metal / metal oxide battery can be built up by combining solid oxide fuel cell (SOFC) technology and a metal/metal oxide storage system [2]. Such a type of battery promises charging and discharging capacities of more than 250 W/cm2 [3]. Requirements for a reversible working solid oxide cell (SOC) are a high performance, minimum internal resistance of the cell, and long-term stability at operating conditions. In the present work the performance of solid oxide cells (SOC) operating in fuel cell and steam electrolysis mode over a temperature range of 650-900 °C and as a function of humidity were studied. Results presented were obtained from single SOCs, with an active area of 16 cm2 and button cells with an active area of 0.5 cm2. The SOCs investigated were anode substrate cells (ASC), with nickel-YSZ-cermet steam/hydrogen electrodes, yttria-stabilized zirconia (YSZ) electrolytes, and lanthanum strontium iron cobalt perovskite (LSCF) air electrodes. Current-voltage measurements were coupled with electrochemical impedance spectroscopy (EIS), in order to identify the different loss terms in cell behaviour during the fuel cell and electrolysis mode. EIS measurements are conducted under practical load conditions in SOCs in both modes. The cells show stable current-voltage curves during cycling between fuel cell and electrolysis mode at short cycling times between 2.5 h and 5 h. Measurements at different humidity show that high electrical-to-hydrogen energy conversion efficiencies are achieved and the amount of steam content is the limiting factor for the electrolysis mode. During electrolysis mode remarkable high current densities around -1.3 A/cm2 were achieved at a cell voltage of 1.3 V and a temperature of 800 °C. Below 50 % steam content, however, a strong efficiency loss was observed. It is also well known that the degradation of the SOC during steam electrolysis is still a limiting factor for the long term application [4]. Hence the focus of interest was also the degradation of the air electrode. Increasing the current density and elongating the duration of electrolysis experiments resulted frequently in a very fast delamination of the LSCF electrode.
Solid Oxide Cell and Stack Testing, Safety and Quality Assurance (SOCTESQA)
Authors: Auer Corinna , Lang Michael , Couturier Karine , Nielsen Eva Ravn , McPhail Stephen J. , Tsotridis Georgios , Fu Qingxi , Chan Siew Hwa
Published: February 2020

The market penetration of fuel and electrolysis cell energy systems in Europe requires the development of reliable assessment, testing and prediction of performance and durability of solid oxide cells and stacks (SOC). To advance in this field the EU-project “SOCTESQA” was launched in May 2014. Partners from different countries in Europe and one external party from Singapore are working together to develop uniform and industry wide test procedures and protocols for SOC cell/stack assembly. In this project new application fields which are based on the operation of the SOC cell/stack assembly in the fuel cell (SOFC), in the electrolysis (SOEC) and in the reversible SOFC/SOEC mode are addressed. This covers the wide field of power generation systems, e.g. stationary SOFC µ-CHP, mobile SOFC APU and SOFC/SOEC power-to-gas systems. The paper presents the results which have been achieved so far in the SOCTESQA project. Besides a summary of existing test procedures a so called “test matrix” was created. This document includes generic test modules, e.g. current-voltage curves, electrochemical impedance spectroscopy, thermal cycling, electrical current cycling and long term tests both under steady state and dynamic operating conditions. The application specific test programs are created by combining several of these test modules. In a next step defined test modules will be applied for the initial test bench validation, which will be improved by several validation loops. The final test protocols will be confirmed by round robin tests.
Improved Performance and Durability of Anode Supported SOFC Operating on Biogas
Authors: Troskialina Lina , Dhir Aman , Steinberger-Wilckens Robert
Published: February 2020

Performance curves for both Sn-doped Ni-YSZ and un-doped Ni-YSZ single cells are presented in Fig.1.  The cell tests were carried out at 750oC under dry hydrogen flowing at 7mL/min Helium and 21mL/min H2 followed by biogas flowing at 7mL/min CO2: 14mL/min CH4: 7 mL/min He with the cathode side open to ambient air.   The cells were allowed to reduce under H2 for a minimum of 3hrs in OCV mode before any initial   data was obtained. Operation on hydrogen was run for 26 hours to stabilize cell performance before the fuel was switched to biogas. After stabilization on hydrogen the Sn-doped Ni-YSZ gave 390mA/cm2 at 0.7V compared to the un-doped Ni-YSZ cell which gave 100mA/cm2 at 0.7V.
Electrolyte Stability in Direct-Carbon Fuel Cells with Molten Sb Anodes
Authors: Oh Tae-Sik , Zhou Xiaoliang , Vohs John M. , Gorte Raymond J.
Published: February 2020

Direct carbon fuel cells (DCFC) using oxide ion conducting electrolytes and molten Sb anodes have much promise for the efficient conversion of carbonaceous solid fuels into electricity. However, etching of the electrolyte, and ultimately cell failure, has been observed during operation. In this study, we have investigated this etching phenomenon as a function of the electrolyte composition and cell operating conditions and demonstrated that it is not electrochemical in nature, but rather results from reaction between the electrolyte and Sb2O3 that is produced during cell operation. Sintered solid electrolyte coupons of uniform thickness were immersed in molten Sb2O3 to check thickness change after high temperature annealing.
Mechanism and Activity of Ni-Based (Ni-M: M = Fe, Mo, W, Ta) Cermet Anodes for Ammonia Oxidation in SOFCs
Authors: Hashinokuchi Michihiro , Yokochi Ryuji , Akimoto Wataru , Doi Takayuki , Inaba Minoru , Kugai Junichiro
Published: February 2020

Ammonia (NH3) is attractive as a hydrogen (H2) carrier and a suitable fuel for solid oxide fuel cells (SOFCs) because it has high hydrogen density (17.6 %) and can be easily liquefied at an ambient temperature. However, the activity of conventional Ni cermet anodes of SOFCs for NH3 oxidation is much lower than that when H2 is used as a fuel [1]. It is necessarily to improve the anode activity for NH3 oxidation for realizing NH3-fueled SOFCs.

 We have investigated the activity of anodes prepared with transition metals nickel(Ni), iron (Fe) and their alloy for NH3-SOFCs[2,3]. The Fe/Sm-doped ceria (SDC) cermet anode was more active for NH3 oxidation than Ni/SDC. We also found that the activity of the Ni40-Fe60//SDC for NH3 oxidation was highest by optimizing the metal composition. These results suggested that the rate limiting steps in a direct NH3 oxidation (or reforming NH3) at the anode were (i) NH3 adsorption and (ii) N2 desorption. We concluded that Fe and Ni atoms had the roles of accelerating reactions (i) and (ii), respectively, and the synergetic effect of Fe and Ni resulted in the enhancement of the anode activity for NH3oxidation.

 On the basis of the mechanism of NH3 oxidation at the anode, we prepared the anode of Ni and Molybdenum (Mo) since Mo has the high ability of NH3 adsorption, and evaluated their performance for NH3-SOFCs. The Ni-Mo/SDC anodes were fabricated by impregnating a MoCl5 aqueous solution into a Ni/SDC pre-sintered cermet on an electrolyte. It was revealed that the optimum addiction of Mo enhanced the anode activity for NH3 oxidation. Our experimental results suggested that the anode activity for NH3 oxidation was determined by a balance between abilities of NH3 adsorption and N2desorption.

Acknowledge

This work was supported by “Kyoto Environmental Nanotechnology Cluster” and “Kyoto Regional Scientific Innovation Hub” from MEXT in Japan.

Reference

[1] Q. Ma et al., J. Power Sources 161 (2006) 95.

[2] W. Akimoto et al., Solid State Ionics 256 (2013) 1.

[3] W. Akimoto et al., ECS Transactions 57 (2013) 1639.
Understanding the Aging Degradation of Doped Barium Cerate Proton Conductor in Ambient Air at Room Temperature
Authors: Yan Ning , Gao Tong , Wang Wei , Luo Jing-Li
Published: February 2020

As a promising alternative power generation technology, solid oxide fuel cells (SOFC) have been intensively studied during the past several decades [1]. Among all the solid electrolyte candidates, proton conducting materials, e.g., BaCeO3, exhibit relatively high ionic conductivity at intermediate temperature (< 750 oC). Particularly, Zr and Y doped cerate, e.g., BaZr0.1Ce0.7Y0.2O3 (BZCY) was widely reported to have excellent conductivity as well as adequate stability in resisting concentrated CO2 up to 30 % with moisture at elevated temperatures typical for SOFC operation [2,3].

Herein, via using a combinations of various electrochemical measurements together with materials characterization techniques including XRD, TEM, SEM, XPS, TG-MS and FTIR, we firstly report that BZCY was prone to a gradual degradation in ambient air at room temperature with considerably minor CO2 (~0.04%) and humidity (<45% relative humidity). The adsorbed H2O acted as an effective catalyst that promoted the decomposition of BZCY via reaction with CO2, subsequently leading to the formation of BaCO3 nanorods as the major impurity phase, presumably following a microcrucible mechanism. Yttrium (oxy)carbonate and amorphous CeO2 and ZrO2 were also produced. It is also confirmed that the doping elements of Ce and Y caused the degradation of BZCY. During the fuel cells tests, the formed impurities on BZCY significantly hindered the electrocatalytic reactions at the electrolyte/electrode interfaces. We also proposed the regeneration and appropriate storage method of the electrolyte materials.

Figure 1. TEM microscopic analysis of: (left) HAADF-STEM image of degraded BZCY with amorphous mixed oxides microcrucible and BaCO3 nanorods: (right) elemental mapping of Ba, Ce, Zr and Y.

[1]       X. W. Zhou, N. Yan, K. T. Chuang, J. L. Luo, RSC Adv., 4(2014), 118.

[2]       N. Yan, X. Z. Fu, K. T. Chuang, J. L. Luo, J. Power Sources, 254(2014),48.

[3]       L Yang, et. al., Science 326 (2009), 126.

Figure 1
Challenges of Solid Oxide Electrolysis for Production of Fuel and Oxygen from Mars Atmospheric CO2
Authors: Hartvigsen Joseph J , Elangovan S , Larsen Dennis , Elwell Jessica , Bokil Mukul , Frost Lyman J , Clark Laurie M.
Published: February 2020

Due to the potential for unmatched efficiency, solid oxide electrolysis has long been considered a leading technology for enabling the hydrogen economy. More recently, the potential of co-electrolysis to “fix” intermittent renewable energy by recycling CO2 to storable, transportable liquid transportation fuels has demonstrated substantial progress. A new field of application for solid oxide electrolysis producing fuels from CO2 is emerging in the area of human exploration of Mars. The Martian atmosphere is 96% CO2, making it a prime resource for extraction of oxygen that will be needed by human explorers and for production of the fuel that will be needed for the ascent vehicle to return them to earth.

There are innumerable logistical and programmatic challenges to designing, qualifying, delivering and operating any process for insitu resource utilization (ISRU) on the surface of such a remote and inhospitable place such as Mars. This paper makes no attempt to address any beyond the design of the solid oxide electrolysis device itself.

Ceramatec has been active in solid oxide fuel cell R&D for nearly three decades, and solid oxide electrolysis for the later half of that period. The fundamental operating principles and materials of the Mars ISRU application are no different than the hydrogen and synfuel applications of past decades. However there are circumstances of the ISRU application that place challenging constraints on the design and performance that have not been previously encountered in our SOEC development efforts. These issues are outlined and the design, analysis, materials and operational approaches to address them are presented. Ceramatec is designing and building the SOEC (aka SOXE) stack for the MOXIE instrument on the Mars 2020 mission.
Metal-supported Solid Oxide Fuel Cell with La0.4Sr0.6Co0.2Fe0.7Nb0.1O3-δ Cathode
Authors: Zhu Tenglong , Han Minfang , Yang Zhibin
Published: February 2020

Metal-supported solid oxide fuel cells (SOFCs) exhibited significant advantages, for example the superior mechanical strength, easy-processing and lower cost. In this paper, we report a new fabrication method for metal-supported SOFC single cell. The single cell with NiO and Fe2O3 (Ni:Fe=1:1) anode support, Gd0.1Ce0.9O1.95 (GDC) electrolyte and La0.4Sr0.6Co0.2Fe0.7Nb0.1O3-δ (LSCFN) cathode was fabricated by traditional tape-casting, drop-coating, co-sintering and screen-printing techniques. Then the as-prepared single cell was reduced at 500, 600, 700 oC under 5%H2-95%N2. Results show that after treated the whole cell at 700 oC in the reducing atmosphere, the oxide support was mostly reduced into metal, while the LSCFN cathode maintained its perovskite structure. Then the cell performance was tested using humidified hydrogen, by comparison, the as-prepared cell without reduction was also tested. Electrical impedance spectroscopy tests were carried out with symmetrical LSCFN electrodes reduced at 500-700 oC. Results show that the polarization resistance lowered down with the reduction temperature increased, which may possibly due to the more oxygen vacancies created at higher reduction temperature. The fabrication method to reduce the whole cell is a promising way to fabricate the easy-processing metal-supported SOFC single cell.
Development of La0.6Sr0.4TiXFe1-XO3-Based Composite Cathode Materials for Solid Oxide Fuel Cells
Authors: Iwai Hiroyuki , Suzuki Shinsuke , Inaoka Koji , Murakami Ayumi , Takahashi Yosuke
Published: February 2020

Solid oxide fuel cells (SOFCs) have received a lot of attention as promising electrochemical power generation devices due to their high electrical efficiency and adaptability to a variety of fuels such as hydrocarbons, ammonia, and hydrogen. The utilization of LaSrTiFeO3-δperovskite oxide was proposed as an oxygen permeable membrane and electrode materials of SOFCs. Durability in thermal cycling test is an important factor for applying SOFCs to power sources. The reduction of operating temperature and enhancement of thermal-cycling capability are indispensable requirement for industrial-scale commercialization of SOFCs.

   A new cathode material for SOFCs has been developed in R&D Center of Noritake Co., Ltd. In which, it contain La0.6Sr0.4TixFe1-xO3-δ (0<x<0.4) and La0.6Sr0.4CoyFe1-yO3-δ (0<y<1). Here, we report the performance evaluation of our developed cathode material. It was found that the developed cathode material had a high power density and extremely high stability to hydrogen and ammonia fuel.
Oxide-Ion Dynamics in the SOFC Cathode Material La2NiO4+d by Experimental and Computational Solid-State 17 O NMR Spectroscopy
Authors: Halat David M. , Dervisoglu Riza , Kim Gunwoo , Grey Clare P
Published: February 2020

Mixed ionic-electronic conductors (MIECs) show promise as next-generation solid oxide fuel cell (SOFC) cathode materials with improved performance at intermediate temperatures (500-800°C) as compared to materials lacking oxide-ion conductivity. The complex interplay of electronic and ionic conductivity in these strongly correlated systems often derives from the mutual influence of transition metal cation mixed valency and oxygen nonstoichiometry. Among MIECs tested as SOFC cathodes, the Ruddlesden-Popper phase La2NiO4+
δ exhibits rapid oxygen transport at low temperatures, attributed to loosely bound interstitial oxides (0 < δ < 0.3). Key to understanding the high oxide-ion conductivity in La2NiO4+
δ is experimental confirmation of hypothesized interstitial- and vacancy-mediated mechanisms at the atomic level.

In this study, solid-state 17O MAS-NMR spectroscopy of La2NiO4+
δ at temperatures up to 800°C is supported by a theoretical methodology equipped with results from periodic hybrid DFT calculations. Three distinct 17O resonances are observed and assigned to equatorial, axial, and interstitial oxygen environments in La2NiO4+
δ. Moreover, with high-resolution MAT-PASS experiments, the axial feature splits into several resonances, consistent with local structural distortions due to nearby interstitials. Loss of the interstitial oxygen feature in the NMR spectra upon heating to ~150°C is attributed to onset of exchange of interstitial and axial oxygen sites. Structural rearrangements due to interstitial motion also manifest as linewidth changes in the axial and equatorial resonances. At operational SOFC temperatures (600-800°C), interstitialcy and vacancy mechanisms of oxide-ion conduction are tentatively confirmed for the first time, showing that interstitial-axial exchange continues to dominate transport at the highest temperatures. Slow vacancy diffusion (equatorial-axial exchange) is surmised to limit the overall three-dimensional ionic conduction. This work is among the first examples of dynamics in a paramagnetic oxide-ion conductor studied by 17O solid-state NMR.
Effect of Chromium Vapor Pressure on Accelerated Poisoning Tests for (La0.6Sr0.4)(Co0.2Fe0.8)O3 Cathode
Authors: Cho Do-Hyung , Bagarinao Katherine Develos- , Kishimoto Haruo , Yamaji Katsuhiko , Horita Teruhisa , Yokokawa Harumi
Published: February 2020

One of the most critical issues causing degradation of SOFCs is poisoning of cathodes by a trace amount of impurities transferred with air such as sulfur (S) and chromium (Cr), and therefore, we are continuously investigating the test method on accelerated degradation by these impurities.  In our previous studies on Cr poisoning, chromium metal covered with Cr2O3 was directly placed on the current collector of the cathode as a source of Cr vapor.  However, the setting accelerated the performance degradation in surplus.  In order to perform accerelated poisoning test at an appropriate rate, we improved the cell operating equipment to control the Cr vapor pressure during the cell tests.  The Cr vapor pressure was controlled by adjusting the place and temperature of the Cr source. The cell tests were operated at 1073 K under controlled feeding rate of Cr vapor after the cell performance became stable. The degradation behavior was analyzed with AC impedance analysis, field emission scanning electron microscopy (FE-SEM) with energy dispersive X-ray analysis (EDX) / wavelength-dispersive X-ray spectrometer (WDS).  The vapor pressure of Cr species was estimated from the amount of Cr trapped by (Sm,Sr)CoO3cathode in the same equipment of cell tests.  The degradation rate decreased with decreasing the Cr vapor pressure, and the amount of Cr species deposited in LSCF cathode decreased with decreasing the Cr vapor pressure.
Fabrication of Mn1.5Co1.5O4 by Electrostatic Spray Deposition for Application as Protective Coating on Alloy Interconnects for Solid Oxide Fuel Cells
Authors: Conceição Leandro Da , Djurado Elisabeth , Dessemond Laurent , Muccillo Eliana Navarro Santos
Published: February 2020

Mn1.5Co1.5O4 (MCO) protective coating was deposited by Electrostatic Spray Deposition on SS446 alloy for application as interconnects in Solid Oxide Fuel Cells. The main purpose of this work is to verify the feasibility of a thin coating layer prepared by this technique to inhibit the Cr volatilization and the subsequent cathode poisoning. Phase crystallization was obtained after deposition by thermal annealing at 800 °C in air. The corrosion resistance behavior of uncoated and coated steels was investigated by electric and thermogravimetric measurements. The coating films, 400 nm thick, are found efficient for reducing the oxidation rate by limiting the outward Cr3+ diffusion. The area specific resistance of the coated steel is found to be considerably low (6.7 mW.cm2) and stable compared to uncoated SS446 alloy (80 mW.cm2) after oxidation for 200 h at 800 °C in ambient air. These results evidence the excellent performance of the deposition technique for fabricating thin, crack free and dense conductive Mn1.5Co1.5O4-coated ferritic alloys.
Synthesis of Bi-Sr-Co-O Compound As Novel Cathode for Intermediate Temperature-Solid Oxide Fuel Cells
Authors: Zou Jing , Yoon Heechul , Park Sungtae , Chung Jong Shik
Published: February 2020

The monoclinic Bi-Sr-Co-O compound was successfully synthesized by ethylene glycol-citrate acid polymerization method. The prepared sample was evaluated by various experimental tests. Powder X-ray diffraction (XRD) data shows the Bi-Sr-Co-O powder with good crystallinity. Its good thermal stability and chemical compatibility with Ce0.9Gd0.1O2−
γ electrolyte was also proved by XRD data. The chemical composition of Bi-Sr-Co-O powder was confirmed by ICP-AES and XPS analysis. The compatibility with the electrolyte, along with the encouraging electrical conductivity (around 10 S·cm−1 in the temperature range of 600-700 °C), allows us to conduct further study on Bi-Sr-Co-O as a potential novel cathode material for intermediate temperature-solid oxide fuel cells.
Influence of the Solid Oxide Electrolysis Component Characteristics on the Electrochemical Performance of SOE Cells
Authors: Tamm Kadi , Kukk Freddy , Salvan Laur Kristjan , Kanarbik Rait , Möller Priit , Nurk Gunnar , Lust Enn
Published: February 2020

Four solid oxide electrolysis cells (SOEC) with different cathode microstructure and chemical composition (Ni-YSZ and Ni-GDC) and electrolyte thickness (ScSZ) have been prepared using tape casting and screen printing methods. Electrochemical performance of the single cells at various working temperatures and gas mixtures in the cathode compartment has been analyzed using cyclic voltammetry, impedance spectroscopy and other electrochemical methods. It was established that the ratio of the rate-determining steps (mass transfer, charge transfer and adsorption of intermediates and fuel products) changes from mixed kinetics process at 1 V (solid oxide fuel cell regime) towards mainly the diffusion (δ = -45°) limited process at 1.4 V (electrolysis regime).  It was shown that the total polarization resistance decreases with the replacement of Ni-YSZ to Ni-GDC. The lowest total polarization resistance (and highest current density values) has been measured for single cell consisting on the supportive ScSZ electrolyte and thin Ni-GDC cathode layer.
Electrochemical Properties of DLC/Lzo Double Coated LiNi0.8Co0.15Al0.05O2 cathode Material of All-Solid-State Lithium Ion Battery
Authors: Visbal Heidy , Aihara Yuichi , Ito Seitaro , Watanabe Taku , Tsujimura Tomoyuki , Park Youngsin , Doo Seokgwang
Published: February 2020

The surface of LiNi0.8Co0.15Al0.05O2  (NCA) cathode material was coated with diamond like carbon (DLC) and LZO (Li2O-ZrO2)  by chemical vapor deposition and sol-gel method respectively, in order to prevent the side reaction at the interface and stabilize the surface Ni-O bonds during charge and discharge process for sulfide based all-solid state lithium-ion batteries.  The double coated (DLC/LZO) material showed a higher capacity with significantly improve in surface resistance and high rate performance than the single coating of DLC or LZO and without coating.  The interface resistance between the cathode active material and the solid electrolyte significantly decreases by double coating onto the NCA powder.  The discharge capacity of DLC coated sample at 0.05C was 123 mAhg−1 while that of bared one was about 102 mAhg−1.  The charge and discharge cut off potentials were 4.0 and 2.8 V, respectively.  The thickness of the DLC/LZO coated layer was verified by transmission electron microscope (TEM), and was about 10-20 nm.  The sp2 bonding ratio of the DLC coated LiNi0.8Co0.15Al0.05O2  powder was estimated from the C-KELNES spectra to be 50-55%.  In this work, the diamond like carbon (DLC) and combination with LZO coating were proposed for the first time as buffer coating layers for all-solid state battery.  We demonstrated that the combination of lithium ion conductivity (LZO) and DLC will reduce the interface resistance between cathode material and sulfide based electrolyte.