Gadolinia-doped Ceria Electrolyte Research Articles

Study on the performance of GDC electrolytes fabricated by atmospheric plasma spraying and vacuum plasma spraying

For metal-supported solid oxide fuel cells (MS-SOFCs), gadolinium-doped ceria (GDC) is one of the most promising electrolyte materials due to its high ionic conductivity. The plasma spraying technique has unique advantages in the preparation of MS-SOFCs, such as high efficiency, low cost, and low thermal impact on the metal support. However, few studies have been conducted on the preparation of dense GDC electrolytes using plasma spraying technology. In addition, it is not clear whether the composition and Ce valence state of GDC change during the plasma spraying process. In order to investigate this issue, GDC electrolytes were fabricated by atmospheric plasma spraying (APS) and vacuum plasma spraying (VPS) techniques. It is found that the GDC electrolyte fabricated by VPS is denser and has better electrochemical performance. The open circuit voltage and maximum power density of the VPS-cell at 600 °C are 0.90 V and 175.7 mW/cm2, respectively, while those of the APS-cell are 0.86 V and 124.8 mW/cm2, respectively. Moreover, the valence state of Ce4+ in the GDC electrolyte remains unchanged after plasma spraying, while the composition of Ce/Gd changes. This work successfully fabricates GDC electrolytes with qualified performance and provides a reference for further optimizing spraying parameters to prepare high-performance MS-SOFC.

Electrical and microstructural characteristics of GDC electrolyte synthesised by benzoate coprecipitation for solid oxide fuel cells

Gadolinium-doped ceria (GDC) is a promising electrolyte material for developing solid oxide fuel cells (SOFCs) because it offers a higher ionic conductivity at the intermediate operating temperature. In this work, nanocrystalline GDC (Ce1-xGdxO2-x/2, where x = 0.1 and 0.2) powders were synthesised through a novel co-precipitation synthesis method (benzoate route) using ammonium benzoate as a low-cost precipitant. The effect of the synthesis route and processing variables (calcination temperatures and time) on the microstructural and electrical properties of the resulting GDC powder was studied systematically. Multiple GDC electrolyte pellets were fabricated by pressing the GDC powders, followed by sintering the samples at 1100 °C for 6 h. The ionic and electronic conductivity of the GDC pellets were measured in air using EIS at different temperatures (450–750 °C). Huggins' model was used to determine the ionic and electronic conductivity of the GDC pellets. The fabricated electrolyte pellets showed a high relative density of 98.31and 99.02 % for the pre-calcined non-washed and pre-calcined washed powders, respectively, with a crystal size lower than 12 nm. Among all samples, the GDC electrolyte pellet fabricated using the pre-calcined washed powder exhibited the highest ionic conductivity of 3.63E-01 S cm−1 at 750 °C and activation energy of 0.52 eV with an average crystal size of 7–8 nm. The results of this study help to understand and design more efficient ceramic fuel cells with controlled microstructure and compositions at a lower cost.

Synergistic effects and electrocatalytic insight of single-phase hexagonal structure as low-temperature solid oxide fuel cell cathode

Enhancing the electrocatalytic activity of the electrode materials, specifically oxygen reduction reaction (ORR), at lower operating temperatures (<600 °C) is the prime rank to realize the commercialization of solid oxide fuel cells (SOFCs) research. Herein, a new hexagonal structure-based cathode material was developed with the co-doping of Gd2O3 and Cr2O3 of parent SrFe12O19 oxide, respectively. At 550‒475 °C, Sr0.90Gd0.10Fe11.90Cr0.10O19 (SFO-10) cathode sample leading to the large peak power density (PPD) of 395 mW/cm2, has appropriate surface oxygen defects (Oβ) up to 17%, as verified by X-ray photoelectron microscopy (XPS). Theoretical calculations reveal that the co-doping of Gd and Cr oxides creates lattice disorder at the hexagonal lattice, which decreases the energy barrier for ion transport and enhances the electrocatalytic characteristics of ORR. Consequently, the SFO-10 cathode shows a favorable ORR activity with the least lower polarization resistance (ASR) at 550 °C with gadolinium-doped ceria (GDC) electrolyte. This work provides a self-assembled single-phase hexagonal cathode to accelerate the low-temperature hindrance of SOFC technology.

Boosting the catalytic activity of high-order Ruddlesden–Popper perovskite SrEu2Fe2O7-δ air electrode by A-site La doping for CO2 electrolysis in solid oxide electrolysis cells

Ruddlesden–Popper (R-P) oxides (An+1BnO3n+1) are potential air electrodes for solid oxide electrolysis cells (SOECs) because of their good electrochemical performance. Among them, SrEu2Fe2O7-δ (SEF) with n = 2 has received extensive attention because of its special structure and promising ionic–electronic conductivity. However, the SEF material is prone to degradation at high temperatures (600 °C–800 °C), and its long-term stability is easily affected. In this study, R-P oxide Sr1-xLaxEu2Fe2O7-δ (SLEFx; x = 0, 0.05, 0.1) was successfully synthesized using the sol–gel method. XRD results showed that La-doped SEF displayed good chemical and thermal compatibility with the gadolinia-doped ceria electrolyte. The SLEF0.05 electrode exhibited a polarization resistance of 0.075 Ω cm2 at 800 °C, which was 88.2 % lower than that of SEF. The half-cell based on the SLEF0.05 air electrode exhibited improved performance under the long-term stability test at a current density of − 0.5 A cm−2 for over 110 h at 800 °C, indicating excellent stability. Moreover, an electrolysis current density as high as 0.712 A cm−2 at 1.5 V was obtained for the full cell with the SLEF0.05 air electrode, which was 45.8 % higher than the SEF electrode when the temperature and feed gas were 800 °C and 50 % CO2–50 % CO, respectively. The XPS and cell testing results confirmed that La with high valance and small radius promoted the formation of oxygen vacancies and effectively enhanced the electrochemical performance and structural stability of the SEF material. Therefore, the R-P oxide SLEF0.05 is a promising air electrode material for SOECs.

Multi-scale numerical simulation of fracture behavior for the gadolinia-doped ceria (GDC) under mechano-electrochemical coupling fields at high temperature

The fracture toughness of gadolinia-doped ceria (GDC) solid oxide fuel cells (SOFCs) electrolyte with a central crack is significantly reduced under the mechano-electrochemical coupling fields at high temperature. In this work, an atom-to-continuum (AtC) multi-scale method combining the finite element method (FEM) and the molecular dynamics (MD) simulation is developed. Firstly, the AtC multi-scale method is validated by investigating the uniaxial tensile stress–strain curves of GDC with a central crack at different temperatures. Then, based on the theory of fracture mechanics, the macrostructure of GDC is transformed into a microscopic intermediate transition model, and a detailed computational procedure for analyzing the fracture toughness of the macrostructure of the GDC is given by the AtC multi-scale method. Finally, the fracture toughness of GDC macrostructure under the mechano-electrochemical coupling fields is studied by the proposed approach. The simulation results show that the fracture toughness of 10GDC and 20GDC under the mechano-electrochemical coupling fields is clearly reduced compared to the uniaxial tensile loading. Among them, the fracture toughness of 10GDC under the mechano-electrochemical coupling fields is decreased by 12.28% and 30.67% at 800℃ and 900℃, and the fracture toughness of 20GDC under the mechano-electrochemical coupling fields is decreased by 17.25% and 29.52% at 800℃ and 900℃. These findings are critical in predicting the fracture behavior of GDC electrolyte under real working conditions.

Benchmarking Electrolytes for the Solid Oxide Electrolyzer Using a Finite Element Model

The demand for green hydrogen is increasing, as it is estimated to reduce ten percent of total global green-house-gas emissions from fossil fuel. The solid oxide electrolysis cell (SOEC) is an electrochemical energy-conversion device (EECD) that produces green hydrogen via steam electrolysis. It is preferred to other EECDs for clean hydrogen production owing to its high efficiency, robust kinetics, and lack of precious-metal requirements for cell construction. Herein, we report a Multiphysics model describing the transport phenomena in the SOEC. The governing equations used in the model include a thorough description of the electrode kinetics and of the behavior of the three electrode–electrolyte interfaces in the cell. For the first time, the effect of the scandium-doped zirconia (SCGZ), yttrium-stabilized zirconia (YSZ), and gadolinium-doped ceria (GDC) electrolytes was modeled at different temperatures and pressures. By linking the convection and diffusion equations with the Butler–Volmer at shorter scales, a true representation of the cell operation was simulated. Our models show a R2 value of over 0.996 in predicting the cell-polarization curves and electrochemical properties at the given operating conditions. The impedance of the SCGZ was 0.0240 Ohm.cm2. This value was two- and four-fold lower than the values of the YSZ and GDC, respectively. Furthermore, our theoretical findings of both the polarization data and the impedance were in good agreement with the experimental data.

Modeling High-Power Density Ceria-Based Direct Ammonia Fueled SOFC Stacks for Mobile Applications

The transport sector currently accounts for 23% of the global energy-related CO2 emissions, with an average annual growth of +1.8% since 2010, which is faster than for any other end-use sector [1]. Decarbonization of the mobility sector is particularly challenging due to the highly strenuous space, weight and efficiency demands for a power generation system applied for vehicle propulsion. Batteries have established themselves as a solution for the electric propulsion of passenger cars. However, their low energy densities and high recharging durations hinders their deployment in vehicles with large gross weight including trucks, ships, trains and airplanes [2, 3]. High-temperature solid oxide fuel cells (SOFCs) possess many advantageous characteristics compared to polymer electrolyte membrane (PEM) fuel cells that can be effectively exploited in a vehicle, such as high efficiency, fuel flexibility and impurity tolerance. SOFCs can be directly run with a great variety of fuels, such as NH3, which is currently regarded to be a very promising energy and hydrogen carrier, mostly due to its carbon neutrality, favorable volumetric energy density (12.7 MJ/L) and transportability [4].In this contribution, we assess the performance of intermediate temperature direct NH3-fueled SOFC stacks as a highly efficient power generation source for mobile applications by means of a detailed multi-physics modeling approach, comprising investigations on electrode, button cell, and stack scales. The modeled SOFC stack is intended to be integrated in a hybrid system concept by coupling with a gas turbine.Firstly, a 1D model of cell containing a gadolinium-doped ceria (GDC) electrolyte is developed based on an established multi-scale computational framework [2]. The electrochemical sub-model is subsequently parametrized and validated through reproducing measurements collected on a high-power density Ni-GDC/GDC/SSC-GDC cell. In order to physically account for the electronic leakage current due to mixed ionic-electronic conduction (MIEC) properties of the ceria-based electrolyte, the model contains the implementation of a distributed charge-transfer model that solves individual electronic and ionic conduction pathways across all constituents of the membrane-electrode assembly (MEA) [5]. The decomposition of NH3 on the surface of the Ni particles in the fuel electrode is modeled based on a thermodynamically consistent 12-step elementary kinetic mechanism [6]. The thermo-catalytic and electrochemical sub-frameworks are then integrated into a 3D stack model, which is built upon a lightweight design.The numerical simulations indicate that the performance of the SOFC stack based on the anode-supported GDC-electrolyte cell design is not only highly sensitive to the temperature, but also to the selection of the absolute pressure level. Results suggest the stack to reach a very promising performance in the intermediate temperature range with a predicted ASR of ~0.7 Ω cm2 at 550 °C, pure NH3 feed and 50% anode off-gas recirculation. By predicting species, temperature and current density distributions across the stack, the developed model proves itself to be highly instrumental for the identification of design points that provide a feasible trade-off between performance and safety metrics.

Model Based Comparative Analysis of GDC and YSZ Based Solid Oxide Fuel Cells

Designing solid oxide fuel cell (SOFCs) stacks for transportation applications places new challenges on SOFC architecture and operation with respect to power density, dynamic response, and thermal management. Recent developments in SOFCs with either thin-film yttria stabilized zirconia (YSZ) electrolytes (thickness ≤ 5 μm) or highly conductive, gadolinia-doped ceria (GDC) electrolytes (thicknesses ≥10 μm) enable thigh-power-density stack operation at inlet temperatures well below 700ºC with the potential for using compliant seals and lower cost ferrous interconnect materials. Applications, such as hybridized aircraft engines, can use such SOFC stacks if they meet strict requirements with respect to specific power and thermal management. Highly conductive GDC-based electrolytes offer pathways to high power-density SOFCs at operating temperatures below 650ºC, but the rise in mixed ionic electronic conductivity (MIEC) above 650ºC reduces open circuit voltages and thus fuel cell efficiency [1,2]. This necessitates thermal management to maintain operating temperatures and mitigate thermo-mechanical stresses within an SOFC. Thin-film YSZ electrolytes offer lower power densities below 650ºC, but avoid the penalties associated with MIEC behavior at higher temperatures and therefore reduce the challenges associated with thermal management at high power densities. In this work, a model-based approach is used to compare SOFC stack operation with thin-film YSZ electrolytes and with GDC-based electrolytes for operation on hydrogen and reformate fuels at high-power densities relevant for transportation applications.To calibrate models to experimental cell performance, polarization curves of a commercially available YSZ-based cell operating between 600-750ºC and of a high-power-density GDC cell operating between 500-650ºC are used to fit electrochemical model parameters for both electrolytes. Modeling of the YSZ based cell can neglect electronic charge transfer through the membrane electrolyte, but GDC-cell modeling must account for the multiple charge carriers (ceria polarons and oxygen vacancies) in the electrolyte [3]. Electrochemical parameters for ionic conductivities and electrochemical reaction rate parameters for oxide cathodes and nickel-electrolyte-composite anodes are fit to the experimental polarization data over the broad range of operating temperatures. Global rate expressions to account for internal reforming on the active nickel surfaces of anode are adopted from literature [4,5]. The calibrated cell model for each cell type is adopted to a down-the-channel discretized cell simulation to predict heat loss and temperature gradients at high current densities.This presentation compares GDC- and YSZ-based SOFCs in high power-density applications from fundamental and practical perspectives. The open-circuit voltages for GDC-based cells drops with increasing temperature to about 0.85 V/cell at 650°C which is lower than the Nernst open-circuit voltage of YSZ-based cells (≥ 1.05 V/cell) at similar conditions. Both types of cells can sustain power densities around 1.0 W/cm2 with high excess cathode air ratios ≥ 5 to keep temperature gradients near 10°C/cm. These results show that GDC-based cells support higher power densities at lower cell flow inlet temperatures < 600°C, whereas thin-film YSZ cells provide superior performance at flow inlets that drive cell temperatures > 600°C. Higher stack power densities > 1.0 W/cm2 must be supported by stack designs that alleviate high thermal stresses and allow steeper gradients of temperature. A summary of stack design and operational strategies that meet the stringent requirements of high power-density operation will be presented in the light of the modeling resuls..

Direct-methane anode-supported solid oxide fuel cells fabricated by aqueous gel-casting

Direct methane Solid Oxide Fuel Cells (SOFCs) operated under catalytic partial oxidation (CPOX) conditions are investigated, focusing on the processing of the anode support and the anode deactivation caused by carbon deposition. Anode-supported SOFCs based on gadolinium-doped ceria (GDC) electrolyte, and NiO-GDC anode support were fabricated by the gel-casting method. Suitable aqueous slurries formulations of NiO–GDC were prepared, starting NiO-GDC nanocomposite powders, agarose as gelling agent and rice starch as pore former. Electrochemical and mechanical tests evidenced that the support of 550 ± 50 µm thickness and 10 wt% pore former is a good candidate for direct-methane SOFCs. The cells operating under stoichiometric conditions of CPOX reached a performance of 0.64 W·cm−2 at 650 ºC, a very close value to that measured under humidified hydrogen (0.71 W·cm−2). The best electrochemical stability of the cell is achieved at a CH4/O2 ratio of 2.5, showing no evidence of carbon deposition and reducing nickel re-oxidation significantly.

Multi-scale simulation of the fracture behavior of non-stoichiometric gadolinia-doped ceria solid electrolytes under the coupled mechanical and electrochemical field

Solid oxide fuel cell (SOFC) works in a complex working environment, which is affected by many factors such as temperature, load and electrochemical reaction. When there are cracks in the material, the multi-field coupling effect will cause the electrolyte performance degradation, even failure and damage. In this paper, the coupling effects of mechanical and electrochemical field on mechanical behavior of gadolinia-doped ceria (GDC) electrolyte are investigated by using the Atom-to-Continuum (AtC) multi-scale method combining molecular dynamics (MD) and finite element method (FEM). Based on the electrochemomechanical coupling theory, we derive the defect diffusion equation of the finite element form. The non-stoichiometry of the cracked GDC electrolyte is calculated, and it is found that the stress concentration at the crack tip will induce non-stoichiometric effects, causing further concentration of oxygen vacancy defects at the crack tip. Subsequently, the effect of electrochemomechanical coupling effect on the fracture toughness of GDC electrolyte is studied by using the AtC multi-scale method. At 800°C under oxygen partial pressure logPO2=−22, this multi-field coupling effect reduces the fracture toughness of 10GDC and 20GDC by 16.13% and 23.33%, and this effect is more apparent with the increase of oxygen partial pressure gradient and external load.

Superior Electrochemical Performance of a Ce0.8Gd0.2O2-δ/Zr0.8Sc0.2O2-δ Thin Bilayer-Protected Gadolinium-Doped Ceria Electrolyte in Intermediate-Temperature Solid Oxide Fuel Cells.

To improve the performance of the Ce0.8Gd0.2O2-δ (GDC) electrolyte in a solid oxide fuel cell, it is necessary to block the electronic conduction due to Ce3+/Ce4+ transitions occurring at elevated temperatures. In this work, a GDC/ScSZ double layer consisting of 50 nm GDC and 100 nm Zr0.8Sc0.2O2-δ (ScSZ) thin films were deposited on a dense GDC substrate by the pulsed laser deposition (PLD) technology. The effectiveness of the double barrier layer in blocking the electronic conduction of the GDC electrolyte was investigated. The results showed that the ionic conductivity of GDC/ScSZ-GDC was slightly lower than that of GDC in the temperature range of 550-750 °C, but the difference gradually decreased with the increase in temperature. At 750 °C, the conductivity of GDC/ScSZ-GDC was 1.54 × 10-2 S·cm-1, which was almost the same as that of GDC. The electronic conductivity of GDC/ScSZ-GDC was 1.28 × 10-4 S·cm-1, which was lower than that of GDC. The conductivity results showed that the ScSZ barrier layer can reduce electron transfer effectively. More obviously, the open-circuit voltage and the peak power density of the (NiO-GDC)|GDC/ScSZ-GDC|(LSCF-GDC) cell were higher than those of the (NiO-GDC)|GDC|(LSCF-GDC) cell in the temperature range of 550-750 °C. The superior performance of the GDC/ScSZ-GDC electrolyte is attributed to the ScSZ thin layer, which is effective in blocking the electronic conduction of the GDC electrolyte.

Designing Gadolinium-doped ceria electrolyte for low temperature electrochemical energy conversion

Reducing the operational temperature of solid oxide fuel cells (SOFC) is vital to improving their durability and lifetime. However, a traditional SOFC suffers from high ohmic and polarization losses at low temperatures, leading to poor performance. Gadolinium-doped ceria is the best ionic conductor for SOFC at lower temperatures. The present work envisages the GDC as an electrolyte for applying low-temperature solid oxide fuel cells (LT-SOFCs). So, in this regard, herein, GDC is synthesized through a wet chemical co-precipitation technique as a functional electrolyte layer fixed between two symmetrical porous electrodes NCAL (Ni0.8Co0.15Al0.05LiO2). Due to the improved surface properties of the synthesized GDC, particles perform better than commercially available GDC. The synthesized GDC electrolyte shows an impressive fuel cell performance of 569 mW/cm2 and a high ionic conductivity of 0.1 S/cm at a shallow temperature of 450 °C. Moreover, the fuel cell device utilizing the synthesized GDC remained stable for 150 h of operation at a high current density of 110 mA/cm2 at 450 °C. The high conduction mechanism has been proposed in detail. The results show that excellent fuel cell performance, high ionic conductivity, and better stability can be achieved at exceptionally low enough temperatures. Also, the proposed work suggests that new electrolytes can be designed for developing advanced low-temperature fuel cell technology.

Surface and interfacial conduction using gadolinium-doped ceria electrolyte for advanced low temperature 400–500 °C fuel cell

Lowering the operating temperature with enhanced performance and better efficiency is considered a universal R&D bottleneck for the progress of low-temperature (<520 °C) solid oxide fuel cells (SOFCs) or ceramic fuel cells (CFCs) to avail the opportunities of commercialization. Bulk doping is the primary ionic conduction mechanism in traditional electrolyte materials for CFC, mainly influenced by the operating temperature and bulk density, thus resulting in high operational temperature. Herein, we proposed a new mechanism for tunning Ce0.9Gd0.1O2-δ (GDC) electrolyte based on a nanocrystalline structure from surface or grain boundary conduction to interfacial conduction by introducing the carbonates to form the heterostructure, exhibiting an extremely high ionic conductivity of (0.2 S·cm−1) at 520 °C. At first, we noticed that the grain boundary conduction of GDC is causing to enhance the charge carrier leading to establishing surface conduction. We further modify the GDC with carbonates to form the core–shell heterostructure to boost ionic conduction. The constructed cell with core–shell heterostructure has exhibited a remarkable performance of 968 mW/cm2.In contrast, 578 mW/cm2 was achieved from the surface conduction of GDC, and at the same time, we observed immensely low grain-boundary resistance from the impedance analysis. The mechanism of core–shell structure formation has been discussed in detail, and the ionic conduction at the surface and interfaces can be considered the dominant conduction mechanism for GDC electrolytes. This work has explored a new approach by tuning the ionic property from surface to interface to develop advanced CFCs, significantly improving the state-of-art GDC electrolyte via enhancing surface/interface conductions. This may be developed as a more functional approach for advanced energy materials, e.g., battery and electrolysis devices.

Ink formulation and printing of electrolyte for a doped ceria solid oxide fuel cell

• Synthesis of highly printable ceria-based electrolyte for a solid oxide fuel cell. • Polymeric 20 mol% gadolinium-doped ceria nanoparticle ink formulated. • Printed gadolinium-doped ceria films of thickness 130 nm obtained. • Proper adjustment of ink rheology and particle size ensures successful printing. We propose a simple ink formulation and a rapid preparation technique to deposit a 20 mol% gadolinium-doped ceria electrolyte utilizing nanopowders and a polymeric dispersant. The ink was assessed for printability and was successfully printed using a piezoelectric inkjet materials printer. The ejected drops were investigated using built-in stroboscopic imaging during ejection, and the deposited thin films were characterised using optical microscopy and surface profilometry. Inkjet material deposition provides a highly repeatable process for the fabrication of solid oxide fuel cells (SOFCs) that can be up-scaled to industrial levels.

The Properties of Intermediate-Temperature Solid Oxide Fuel Cells with Thin Film Gadolinium-Doped Ceria Electrolyte.

Mixed ionic-electronic conducting materials are not used as a single-layer electrolyte of solid oxide fuel cells (SOFCs) at relatively high operating temperatures of ~800 °C. This is because of a significant decrease in the open-circuit voltage (OCV) and, consequently, the SOFC power density. The paper presents a comparative analysis of the anode-supported SOFC properties obtained within the temperature range of 600 to 800 °C with yttria-stabilized zirconia (YSZ) electrolyte and gadolinium-doped ceria (GDC) electrolyte thin films. Electrolyte layers that are 3 µm thick are obtained by magnetron sputtering. It is shown that at 800 °C, the SOFC with the GDC electrolyte thin film provides an OCV over 0.9 V and power density of 2 W/cm2. The latter is comparable to the power density of SOFCs with the YSZ electrolyte, which is a purely ionic conductor. The GDC electrolyte manifests the high performance, despite the SOFC power density loss induced by electronic conductivity of the former, which, in turn, is compensated by its other positive properties.

Effects of electrolyte variation on ammonia sensing temperature for BiVO4 sensing electrode in mixed potential gas sensor

The aim of the present study is to investigate BiVO4 sensing electrode (SE) based electrochemical gas sensor for ammonia (NH3) sensing. Additionally, this study is also focused to reduce the operating temperature of sensor by applying different electrolytes i.e., yttria stabilized zirconia (YSZ) and gadolinia doped ceria (GDC). The maximum sensor response obtained for YSZ and GDC based cells towards 80 ppm NH3 were − 103.03 and − 78.81 mV at 600 ℃ and 550 ℃, respectively. Corresponding sensitivity of YSZ and GDC based cells for NH3 sensing were − 99.24 and − 42.66 mV/decade, respectively. Both the sensors demonstrate excellent selectivity as well as stability against 80 ppm NH3 (10 cycles) and humidity variation (pH2O = 0–0.12 atm.). Electrochemical impedance spectra (EIS) and dc polarization (I-V) curves confirms the mixed-potential sensing mechanism of the sensors. The systematic dependency of electrode’s resistance at a given frequency on the gas concentration reveals a novel pathway for prediction of sensors’ behavior. Additionally, the presence of GDC electrolyte decreases the response/recovery time (16/125 s) compared to YSZ-based cells (21/159 s) against 320 ppm NH3 at 550 ℃ which demonstrate its low temperature sensing capability. This 50 ℃ reduction in the operating temperature can be useful for extension of lifetime of sensor.

Radio-frequency magnetron sputtered thin-film La0.5Sr0.5Co0.95Nb0.05O3-δ perovskite electrodes for intermediate temperature symmetric solid oxide fuel cell (IT-SSOFC)

The present work explores the application of La0.5Sr0.5Co0.95Nb0.05O3-δ (LSCNO) perovskite as electrode material for the symmetric solid oxide fuel cell. Symmetric solid oxide fuel cells of thin-film LSCNO electrodes were prepared to study the oxygen reduction reaction at intermediate temperature. The Rietveld refinement of synthesized material shows a hexagonal structure with the R-3c space group of the prepared perovskite material. Lattice parameter and fractional coordinates were utilized to calculate the oxygen ion diffusion coefficient for molecular dynamic simulation. At 973 K, the oxygen ion diffusion of LSCNO was 1.407 × 10−8 cm2 s−1 higher by order of one magnitude than that of the La0.5Sr0.5CoO3-δ (7.751 × 10−9 cm2 s−1). The results suggest that the Nb doping provide the structural stability which improves oxygen anion diffusion. The enhanced structural stability was analysed by the thermal expansion coefficient calculated experimentally and from molecular dynamics simulations. Furthermore, the density functional theory calculation revealed the role of Nb dopant for oxygen vacancy formation energy at Sr–O and La–O planes is lower than the undoped structure. To understand the rate-limiting process for sluggish oxygen diffusion kinetics, 80 nm and 40 nm thin films were fabricated using radio frequency magnetron sputtering on gadolinium doped ceria electrolyte substrate. The impedance was observed to increase with an increasing thickness, suggesting the bulk diffusion as a rate-limiting step for oxygen ion diffusion. The electrochemical performance was analysed for the thin-film symmetric solid oxide fuel cell, which achieved a peak power density of 390 mW cm−2 at 1.02 V in the presence of H2 fuel on the anode side and air on the cathode side.

Analysis of the effect of ionic conductivity of electrolyte materials on the solid oxide fuel cell performance

SOFC solid electrolytes are known for their ionic conductivity characteristics, which increase with increasing SOFC operating temperature. Using COMSOL Multiphysics numerical simulation, analysis of SOFC power performance with yttria-stabilized zirconia (YSZ) and lithium sodium carbonate – gadolinium-doped ceria ({LiNa}2CO3-GDC) electrolytes was conducted to determine the potential of these electrolytes in their application in SOFC. The ionic conductivity of YSZ was differentiated based on the mole value of the yttria content, namely 8, 8.95, 10 and 11.54 mol. Meanwhile, GDC varied based on the (LiNa)2CO3 content such as 7.8, 10, 16.8 and 30 %. With the numerical model, the calculation error is an average of 7.32 % and 6.89 % for the experimental power and voltage values. In SOFC with the YSZ electrolyte, it was found that the power output can increase 26.4–35 times with an increase in operating temperature from 500 °C to 750 °C. SOFC with 8YSZ can produce the highest power compared to other YSZ, which is 123 A/m2 at a current of 198 A/m2 with an operating temperature of 500 °C and 3,440 A/m2 at a current of 5,549 A/m2 with an operating temperature of 750 °C. Whereas in SOFC with the GDC electrolyte, it was found that the power output can increase 18.6–22.6 times with an increase in operating temperature from 500 °C to 750 °C. SOFC with 30 % (LiNa)2CO3-GDC produced the highest power compared to other GDC, which is 231 A/m2 at a current of 444 A/m2 with an operating temperature of 500 °C and 5,240 A/m2 at a current of 10,077 A/m2 with an operating temperature of 750 °C. YSZ also showed the potential for an increase in power output as the SOFC temperature increases above 750 °C, while the 30 % variation (LiNa)2CO3-GDC shows a limited increase in ionic conductivity at 750 °C

Effects of monovalent alkali metals on grain boundary conductivity and electrochemical properties of gadolinia-doped ceria electrolyte

In the present work, 1 mol% alkali metals (Li, Na, K) doped Ce0.9Gd0.1O2-δ (GDC) electrolytes are prepared by citrate-nitrate sol-gel autoignition process. The effects of monovalent alkali metals on the phase structure, micromorphology and grain boundary conductivity of GDC electrolyte are investigated. All Ce0.89Gd0.1A0.01O2-δ (AGDC, A = Li, Na, K) ceramics exhibit a complete fluorite-type structure. SEM results show that all samples sintered at 1400 °C for 5 h have been achieved high densification, and the addition of alkali metals is conducive to the growth of grains. The space charge potential calculated by impedance data has decreased obviously after alkali metals are incorporated into GDC and the value of Ce0.89Gd0.1K0.01O2-δ ceramic is apparently reduced from 0.063 V (GDC) to 0.033 V at 400 °C. These results indicate monovalent alkali metals are beneficial to improve grain boundary conductivity and even total electrical conductivity. Additionally, among all the samples, the Ce0.89Gd0.1K0.01O2-δ electrolyte shows the highest total ionic conductivity of 2.64 × 10−2 S/cm at 700 °C in dry air. The single cell with Ce0.89Gd0.1K0.01O2-δ electrolyte promises the best power density of 624.5 mW cm−2 at working temperature of 700 °C. Therefore, the monovalent alkali metals dopants have promoting effects on improving the grain boundary conductivity, enhancing the sintering activity and output performance of GDC as an electrolyte for IT-SOFCs.

The fracture behavior of non-stoichiometric gadolinia-doped ceria solid electrolytes using molecular dynamics simulations

Gadolinia-doped ceria (GDC) electrolytes create non-stoichiometric oxygen vacancies and reduce mechanical properties under reducing conditions. Especially when there are crack defects in the material, an excess of oxygen vacancies create and propagate cracks to the point of ultimate failure of the electrolyte membrane. In this paper, we investigate the effect of crack defects on anisotropic mechanical behavior of non-stoichiometric GDC by using the molecular dynamics (MD) method. It is found that in the [100] and [110] crystal orientations, crack defects cause a change from ductile to brittle fracture. For non-stoichiometric GDC with low doping concentration, oxygen vacancies increase fracture stress by increasing critical nucleation stress of phase transformation. However, for non-stoichiometric GDC with high doping concentration, excess oxygen vacancies reduce the strength of fluorite phase. The fracture stress exhibits anomalous characteristics that first increases and then decreases with increasing oxygen vacancies. Due to the electrostatic repulsion between the adjacent oxygen ion layers in the [111] crystal orientation, the material strength decreases with increasing oxygen vacancies and crack defects.