Gd-doped Ceria Research Articles

Effect of Gadolinium Doping on the Structure of Ce1-xGdxO2-x/2 Solid Solutions Prepared by Ionic Gelation Approach

The current research aims to present the structural characterization of Gd-doped ceria powders and ceramics, investigating the structural evolution resulting from cerium substitution with Gd across the entire composition range from 0 to 100 mol.% Gd2O3. Ce1-xGdxO2-x/2 powders with varying Gd contents (0 ≤ x ≤ 1) were synthesized using the ionic gelation method followed by thermal annealing. The resulting powders were subjected to high-temperature treatment to obtain ceramics. Characterization methods included X-ray diffraction (XRD) to identify phase composition and confirm the formation of Ce1-xGdxO2-x/2 solid solutions, infrared spectroscopy (IR) and scanning electron microscopy (SEM) for structural and morphological studies, and X-ray photoelectron spectroscopy (XPS) to evaluate the electronic structure. Comparative analysis of Gd-doped calcined powders and sintered pellets revealed the impact of thermal treatment on the structural features of the resulting solid solutions, elucidating the influence of gadolinium substitution. The novelty of this research lies in demonstrating the successful preparation of Ce1-xGdxO2-x/2solid solutions via an alginate-mediated ion-exchange process and providing a detailed structural investigation over the entire range of dopant concentrations. This assessment highlights the feasibility for further research of these materials as suitable candidates for intermediate-temperature solid oxide fuel cells (IT-SOFCs) or catalyst applications. Doi: 10.28991/ESJ-2024-08-05-01 Full Text: PDF

Boosting Electrochemical Performance via Extra-Role of La-Doped CeO2-δ Interlayer for "Oxygen Provider" at High-Current SOFC Operation.

Utilizing rare earth doped ceria in solid oxide cells (SOCs) engineering is indeed a strategy aimed at enhancing the electrochemical devices' durability and activity. Particularly, Gd-doped ceria (GDC) is actively used for barrier layer and catalytic additives in solid oxide fuel cells (SOFCs). In this study, experiments are conducted with La-doped CeO2 (LDC), in which the Ce sites are predominantly occupied by La, to prevent the formation of the Ce-Zr solid solution. This LDC is comparably used as a functional interlayer between the electrolyte and cathode if sintered at lower temperatures to avoid La2Zr2O7 impurity. In addition, the high substitution of La3+ into the ceria lattice improves the oxygen non-stoichiometry of LDC, leading to accelerated electrochemical high performance by the additional role of LDC for oxygen supplier capacitance at high current operation. Thus, it is confirmed that the improved SOFC high performance is achieved at the maximum power density (MPD) of ≈2.15W cm-2 at 800°C when the optimized LDC buffer layer is hired at the anode-supported typed-Samsung's SOFC by lowering the sintering temperature to prevent LDC's impurity reaction.

In situ observation of reversible phase transitions in Gd-doped ceria driven by electron beam irradiation

Ceria-based oxides are widely utilized in diverse energy-related applications, with attractive functionalities arising from a defective structure due to the formation of mobile oxygen vacancies (VO⋅⋅\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${V}_{O}^{\\cdot \\cdot }$$\\end{document}). Notwithstanding its significance, behaviors of the defective structure and VO⋅⋅\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${V}_{O}^{\\cdot \\cdot }$$\\end{document} in response to external stimuli remain incompletely explored. Taking the Gd-doped ceria (Ce0.88Gd0.12O2-δ) as a model system and leveraging state-of-the-art transmission electron microscopy techniques, reversible phase transitions associated with massive VO⋅⋅\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${V}_{O}^{\\cdot \\cdot }$$\\end{document} rearrangement are stimulated and visualized in situ with sub-Å resolution. Electron dose rate is identified as a pivotal factor in modulating the phase transition, and both the VO⋅⋅\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${V}_{O}^{\\cdot \\cdot }$$\\end{document} concentration and the orientation of the newly formed phase can be altered via electron beam. Our results provide indispensable insights for understanding and refining the microscopic pathways of phase transition as well as defect engineering, and could be applied to other similar functional oxides.

Boosting CO oxidation performance via reaction-induced single-atom active site: DFT and microkinetic investigation of a unified CO oxidation mechanism on Gd-doped ceria supported copper catalysts

Single-atom (SA) catalysts have emerged as a pivotal area drawing extensive research interest due to their high catalytic activities. However, SA catalysts are often plagued by the aggregation and deactivation of SA sites under reaction conditions. This study focuses on CO oxidation over Gd-doped ceria supported Cu catalysts and aims to provide a new strategy to stabilize the SA site, in which a Cu SA site is “prestored” in a relatively stable Cu cluster and can be dynamically activated under reaction conditions. Three typical Cu10/CeO2 catalyst models were built with different Gd-doping contents, which are pristine Cu10/CeO2, Cu10/Gd0.125Ce0.875O2, and Cu10/Gd0.25Ce0.75O2, respectively. We performed density functional theory (DFT) calculations on the Cu10/Gd-CeO2 system to investigate the adsorption of CO and O2 molecules, the formation of surface oxygen vacancy (OV) and dynamic Cu SA site, and potential energy surfaces of CO oxidation process. Ab initio thermodynamic analysis suggests that the saturation adsorption of CO on Cu10 and high Gd-doping in CeO2 lead to a spontaneously formed single Cu−CO site and an OV defect on ceria surface. The CO oxidation process is identified as a two-paths-coupled catalytic cycle, in which Path I is activated by the terminal O atom of adsorbed O2 at surface OV site while Path II initiates with the lattice O atom of CeO2 surface. The microkinetic modeling demonstrates that the dominant pathway is Path I for the undoped and low-doping cases, and Path II for the high-doping case which exhibits a novel mechanism for CO oxidation and the highest reaction activity due to the participation of the dynamic SA site.

Gd-doped ceria with extraordinary oxygen-ion conductivity for low temperature solid oxide fuel cells

Doped ceria has been extensively explored as an efficient electrolyte material for intermediate to low temperature solid oxide fuel cell. Among other ceria electrolytes, gadolinia doped ceria (GDC) is one of the most extensively studied electrolyte materials for low temperature SOFC applications. Here, co-precipitation method is employed to synthesize GDC nanoparticles with stoichiometric ratio of GdxCe1−xO2−δ (with 0 ≤\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\le$$\\end{document} x ≤\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\le$$\\end{document} 0.20). In this process, the molecular water of the precursors has been utilized during the co-precipitation to avoid possible agglomeration caused by hydrogen bonding. The cubic phase formation was examined using X-ray diffraction (XRD) and Raman profile ascribing absence of other phases. XRD along with Reitveld refinement confirm the presence of cubic phase of ceria and Raman profile confirms the oxygen vacancies due to the non-stoichiometry created in CeO2 lattice. The granularity of the sample was observed using field emission scanning electron microscopy (FESEM) with elemental mapping by EDS. It is observed from FESEM that the grains are compact in nature and the density observed was around 98% of the theoretical density. The electrochemical behavior was investigated using electrochemical impedance spectroscopy (EIS), which was taken between the temperature ranges of 350–700 °C. It is observed from the EIS study that ceria doped with 15 mol % Gd3+ (Gd0.15Ce0.85O2−δ) is having highest grain boundary ionic conductivity of about 0.104 S cm−1 at 700 °C with an activation energy of 0.81 eV. This work demonstrates the correlation between oxygen vacancy generation and the enhancement of ionic conductivity with Gd3+ doping in ceria.

Performance and Degradation of Electrolyte Supported SOECs with Advanced Thin-Film Gadolinium Doped Ceria Barrier Layers in Long-Term Stack Test

Electrolyte supported Solid Oxide Cells (ESCs) with advanced thin-film Gd-doped ceria diffusion barrier layers between electrolyte and electrodes were assembled and electrochemically investigated in steam electrolysis mode in a so-called “rainbow” stack with 30 repeat units (RUs). The barrier layers were deposited onto the electrolyte supports via electron-beam physical evaporation deposition (EB-PVD) method at 600 °C. In this paper, the investigation mainly focuses on the electrochemical characteristics of RUs containing the EB-PVD thin-film GDC layers. At the initial stage of the SOEC operation, the stack reached a high performance with an electrical efficiency of 99.65% at 75% steam conversion and a total power input of 1.98 kW. A long-term stack test was performed in SOEC mode for over 5000 h and demonstrated a low voltage degradation of approx. +11.3 mV·kh–1 per RU (+0.9% kh–1). The RUs with EB-PVD GDC thin-films revealed similar initial performance and degradation rate to the state-of-the-art cells with screen printed GDC layers.

Study on damage of Gd2O3-CeO2 under electronic energy loss: comparison between bulk-like and nanostructure.

To understand the physical phenomena responsible for radiation damage of the materials used in nuclear reactors, and thus study their operation life and/or efficiency, it is required to simulate the conditions by exposing the materials to energetic ions. Ceria (CeO2) has been proposed as one of the inert matrices for the transmutation of minor actinides in the futuristic inert matrix fuel (IMF) concept. The inert matrix should also contain burnable poison to compensate for the initial reactivity of fuel. In this context, gadolinium (Gd) is an excellent burnable poison with a high neutron absorption cross-section. In view of this, Gd2O3-CeO2 nano-powders were synthesized and sintered at 800 °C and 1300 °C to obtain different grain sizes and morphologies. FESEM and TEM were carried out to study the grain size of pristine pellets. The sintered pellets were irradiated with 80-MeV Ag ions (electronic energy loss (Se) regime) at room temperature to emulate the effect of fission fragments. For analysis of the effect of grain size on the irradiation-induced structural degradation at different fluences, GIXRD and Raman spectroscopy were performed. Significantly large damage has been observed for the smaller grain-sized samples (sintered at 800 °C) as compared to the large grain-sized sample (sintered at 1300 °C). Neither of the samples amorphized under the present experimental conditions as indicated by the presence of the Raman-active T2g mode (centred at 462 cm-1) and all the XRD peaks of fluorite cubic structure up to the highest fluence employed (1 × 1014 ions cm-2). X-ray photoelectron spectroscopy results demonstrate that Ce4+ to Ce3+ and vacancy-related isolated clusters are the main defects produced in the systems. The radiation tolerance behaviour of the samples is understood with the help of thermal spike simulation, which indicates higher transient lattice temperatures with longer duration in the smaller grain-sized sample upon irradiation. Gd-doped ceria thus possesses good radiation stability in the Se regime, indicating its potential for application in IMFs.

The reversible phase transition of Gd-doped ceria by in situ TEM

The reversible phase transition of Gd-doped ceria by in situ TEM

(Invited) Boosting Solid Oxide Fuel Cell Performance through the Effect of of Interstitial Oxide Ion Supplying of Oxygen Storage Capacitance Materials at Cathodic Functional Layer

Chemical compatibility between the hierachical interface components in solid oxide fuel cells (SOFCs) is an emerging critical issues that significantly impact the durability of SOFCs. However, there are several challenging issues to be solved: cost-effective manufacturing configuration, lowering the operating temperature, and durability. The creation of novel materials or long-lasting electrode/electrolyte interfaces that permit high activity (oxygen reduction or fuel oxidation) while maintaining long-term stability is one of the major barriers to the commercialization of the SOFC Rare-earth doped ceria (REDC) is commonly used to enhance durability and activity in solid oxide cells (SOCs) engineering, with Gd-doped ceria (GDC) being a popular choice for interlayer and additives in solid oxide fuel cells (SOFCs). However, the Ce diffusion into the lattice of ZrO2of YSZ-based electrolyte as a solid solution at high-temperature manufacturing still is remained to be solved. In this study, we conducted La-doped CeO2 (LDC), whose Ce-sites are highly occupied with La to avoid a solid solution of Ce-Zr, as a functionalized interlayer between YSZ-based electrolyte and cathode. When LDC (La-doped CeO2, LDC, Ce0.6La0.4O2−δ) or Bi doped Cerium Oxide buffer layer was optimized at lowering sintering temperature to prevent a La2Zr2O7 impurity reaction, the improved electrochemical performance was achieved at the maximum power density (MPD) of ~1.43 W cm-2 at 800 oC. The high substitution of La3+ into the ceria lattice improves the oxygen non-stoichiometry of LDC, leading to improve the oxide ion supplying of the cathode side during the high current operation. Consequently, we firstly propose that the larger oxygen storage or supplying capacitance (OSC) effect of the interdiffusion layer composition (La, Zr, Ce, Y)O2 in La-doped CeO2 (LDC) is responsible for the positive enhancement of the oxygen reduction reaction (ORR) at high current ranges through interstitial oxygen supply at the cathode/electrolyte interface rather than (Gd, Zr, Ce, Y)O2 in GDC. The OSC of the LDC is higher than that of the GDC, and it effectively enhances the electrochemical performance of the cathode interface in the SOFCs because it may be affected by the high oxygen carrier concentration of the LDC, the higher oxygen releasing, and storage capacitance. This revealed that the effect of oxygen releasing, and storage capacity of the buffer layer might be the cause of improved performance. Consequently, the cell containing the high OSC buffer layer fabricated at 1250 oC to avoid interfacial insulating layers, such as La2Zr2O7 impurities, successfully displayed a dramatically high-power density value. Figure 1

Life testing of 10 cm × 10 cm fuel-electrode-supported solid oxide cells in reversible operation

Reversible solid oxide cells (ReSOCs) can provide significant value by playing different roles – electrical generation or electricity storage – depending on the prevailing electrical grid requirements. Relatively few studies have focused on the life testing of solid oxide cells in this mode-switching operation, and much of that work has focused on small “button” cells. The present study describes electrochemical characterization and post-test characterization from an ∼2600 h life test of a 10 cm × 10 cm fuel-electrode-supported cell operated with periodically reversing current. The cell performance gradually decreased for the first ∼1000 h and then stabilized with low degradation rate until an abrupt test-ending gas crossover failure that resulted in open circuit voltage drop. Post-test characterization of the (La,Sr)CoO3-δ air-electrode showed evidence of Cr vapor contamination from stainless-steel manifolds and Ag contamination from current collection contacts. Partial delamination of the air-electrode and Gd-doped ceria interlayer was observed, along with fractures in the electrolyte near the fuel inlet that probably caused a drop in open circuit voltage near the end of the test. NiNi connectivity was reduced in both the functional and support layers accompanied by Ni particle coarsening, especially at the fuel outlet.

Highly dense and ultrathin gadolinia-doped ceria interlayer for enhanced performance of large-area anode-supported solid oxide fuel cell

The fabrication of a highly dense and ultrathin Gd doped ceria (GDC) interlayer on a large-area, porous electrolyte-coated planar anode support using vacuum slurry coating is studied for application in solid oxide fuel cells (SOFCs). The electrolyte-coated planar anode support body is fabricated by tape casting and pre-sintering is performed at 1100, 1150, and 1200 ​°C. The GDC interlayer is coated onto the pre-sintered electrolyte-coated anode support using a vacuum slurry coating process with different immersion times (30–60 ​s). A highly dense and ultrathin GDC interlayer with a thickness of 1.48 ​μm is produced after co-sintering at 1400 ​°C. The 1200 ​°C pre-sintered electrolyte-coated anode support showed a thin and highly dense GDC interlayer which is attributed to a lower shrinkage difference between the coated GDC interlayer and pre-sintered body. The electrochemical performance of a vacuum slurry-coated GDC interlayer cell is 38 ​% higher compared to that of the screen-printed GDC-coated cell at 700 ​°C due to the greatly reduced Ohmic and electrode polarization resistances. The considerable improvement in the performance is attributed to the ultrahigh GDC density which has prevented the secondary phase formation between the cathode and electrolyte. This study presents the economical, scalable, and reproducible process for the fabrication of highly robust GDC interlayer for the large-area planar anode-supported SOFCs.

Distribution of Relaxation Times of Fuel Electrodes for Reversible Solid Oxide Cells Fabricated Under Various Conditions

Reversible solid oxide cells (r-SOCs) are electrochemical energy devices that can reversibly switch between power generation by solid oxide fuel cells (SOFCs), and hydrogen production by solid oxide electrolysis cells (SOECs) the reverse operation of SOFCs. For the development of high-performance and durable r-SOCs, it is essential to understand not only the I-V characteristics but also the electrode reaction processes systematically. Here in this study, Ni-GDC cermet fuel electrodes, a composite of Ni and mixed-conducting Gd-doped ceria (GDC), were prepared at different sintering temperatures and electrode thicknesses. Electrochemical impedance measurements and distribution of relaxation times (DRT) analysis were performed in both SOFC and SOEC modes to investigate the influence of fabrication conditions on the fuel electrode reaction processes.

Performance and Degradation of Electrolyte Supported SOECs with Advanced GDC Thin-film Layers in Long-term Stack Test

Solid oxide electrolyser (SOE) based on electrolyte-supported cell (ESC) architecture is proven to be highly efficient and reliable technology for green hydrogen production via high temperature electrolysis. Operating under industrial conditions, the performance, lifetime and robustness of the cells and stacks belong to the most important factors for an up-scaled penetration of the SOE technology into energy and chemistry sectors. A typical ESC consists of scandia- or yttria-stabilized zirconia electrolyte, Ni-cermet fuel electrode, lanthanum strontium cobalt ferrite (LSCF) oxygen electrode and either one or two Gd-doped ceria (GDC) layers with a thickness of 5-7 µm between electrolyte and electrodes. At the oxygen electrode side, the GDC layer prevents interdiffusion (mainly of Sr), whereas at the fuel electrode side, the GDC layer may improve the electrode adherence to electrolyte and reduce the interfacial resistance. State-of-the-art fabrication route of the GDC layers is screen-printing followed by partially sintering at high temperature between 1200 °C to 1300 °C. This fabrication process usually results in porous structure in the GDC layers and residual stresses which reduce the mechanical strength of the cells.Aiming to improve the mechanical strength of ESCs and the properties (e.g. porosity and electrical conductivity) of GDC layers, the conventional screen-printed GDC layers either only at the oxygen electrode or at both electrodes were replaced by 0.5 µm thick thin-film GDC layers fabricated by electron-beam physical evaporation deposition (EB-PVD) method at 600 °C. These EB-PVD-fabricated thin-film GDC layers were electrochemically characterized in a so-called “rainbow” stack with 30 repeat units (RUs), including 4 RUs with EB-PVD GDC layers at the oxygen electrode and screen-printed GDC at fuel electrode, 3 RUs with EB-PVD GDC layers at both electrodes and 23 RUs with state-of-the-art screen-printed GDC layers at both electrodes. The stack was operated for over 5000 h in SOEC mode under a current density of -410 mA cm−2 and 75 % steam conversion, with a feed gas composition of 80 % steam + 10 % H2 + 10 % N2 on the fuel electrode and air on oxygen electrode.In this paper, the investigation focuses on the electrochemical characteristics of RUs containing the EB-PVD thin-film GDC layers during the SOEC stack testing. The performance and degradation behavior of the stack and representative RUs were investigated and compared by means of current-voltage curves and electrochemical impedance spectroscopy (EIS). The initial performance and the degradation of the voltage and resistances of the stack and the RUs with EB-PVD GDC thin-film layers were determined and discussed in order to evaluate the effectiveness of the modifications in the scenario of long-term SOEC stack testing.The German Federal Ministry for Education and Research (BMBF) is acknowledged for the financial supports within the project H2GiGa-HTEL (grant no. 03HY124E).

Understanding the Physical Properties of Pr-Gd Co-Doped Ceria and Its Role As the Interlayer in Solid Oxide Cells

In solid oxide cells, a doped ceria interlayer is widely applied between the state-of-the-art yttrium-stabilized zirconia electrolyte and the oxygen electrode to mitigate thermal expansion mismatch and chemical interactions for extended durability. The conventional gadolinium doped ceria is usually a pure ionic conductor and blocks electronic currents under oxidative atmosphere. Adding electronic conduction to the interlayer may increase triple phase boundary areas, thus decrease charge transfer resistance and improve electrode stability. The addition of Pr in Gd-doped ceria results in unique physical properties such as an oxygen partial pressure (pO2) dependent ionic conductivity and electronic conduction in a wide range of pO2. In this study, Pr/Gd co-doped ceria (PGCO) is prepared with varying doping levels and its physical properties such as ionic and electronic conductivities are measured under different oxygen partial pressures and temperatures. PGCO with varying Pr/Gd doping is investigated as interlayer for solid oxide cell applications.

Nano-Functionalization of SOFC Electrodes Via Inkjet Printing

Introduction The future of the international accord on mitigating the impact of climate change is linked to the successful commercialisation and implementation of renewable energy technologies. The latter is strongly dependent on finding commercially viable methods for successful dimensional nano-functionalization of the ceramic materials utilized in the fabrication of various energy devices either in energy generation (fuel cells) or storage (batteries, supercapacitors). Inkjet printing digital methods combining scalability and low equipment cost with high-resolution patterning can be a feasible solution for some of the shortcommings of the conventional fabrication technologies. 3D functionalization - Composite solid oxide fuel cells LSCF/CGO cathodes were nano-engineered via “dual” inkjet printing infiltration. The nano-decorated microstructure was found to extend the active three-phase boundary and to promote adsorbtion – dissociation - surface exchange reactions. Composite La0.6Sr0.4Co0.2Fe0.8O3-δ/Ce0.9Gd0.1O1.9 cathodes were subjected to “dual” inkjet printing infiltration of nitrate salt solutions in a single step procedure. After calcination in air at 700 oC the cathodes were decorated with Ce0.9Gd0.1O1.9 and CoxOy nano particles. The effects of as created nano-decoration on the electrochemical activity and the performance stabilty in the intermediate temperature range (500-700 oC) were investigated. The infiltration was found to extend the active three-phase boundary and to promote adsorbtion-dissociation- surface exchange reactions. Electrochemical impedance tests conducted on symmetrical cells showed a reduction in the polarisation resistance of between 1.5 and 7.0 times depending on temperature (500-700 oC). The nano-decoration led to substantially enhanced stability (0.7 Ω•cm2 at 550oC after 100 hours of aging for CGO:CoxOy infiltration). As the composite LSCF/CGO cathodes had already percolating ionic and electronic networks, a low level loading of nanoparticles was sufficient to lead to an efficient short-range extension of the TPB and the density of ORR reaction sites. The sequence of infiltration was shown to influence the efficiency of the ORR promotion. CoxOy:CGO infiltration expanded the available surface area and promoted the catalytical activity towards ORR reaction. The superior effect of CGO:CoxOy infiltration was assigned to the introduction of additional promotion mechanisms (see Fig. 1) resulting in better electrochemical performance at lower temperatures (<650 oC). Both infiltrations suppressed the Sr surface segregation but only CGO:CoxOy infiltrated cathodes showed substantially improved stability after 100 hours of aging. Scaling up - Single step inkjet printing infiltration with doped ceria Ce0.9Ye0.1O1.95 (YDC) and cobalt oxide (CoxOy) precursor inks was performed in order scale-up the modification of the doped ceria interlayer in commercial (50x50x1 mm size) anode supported SOFCs. The penetration of the inks through the mono-phase La0.8Sr0.2Co0.5Fe0.5O3-δ porous cathode to the Gd0.1Ce0.9O2 interlayer was achieved by optimization of inks rheology jetting parameters. The low temperature calcination resulted in densification of the Gd-doped ceria porous interlayer as well as decoration of the cathode scaffold with nano-particles (~ 20-50 nm in size). The I-V testing in pure hydrogen showed maximum power density gain of 20% at 700oC and 97% at 800oC for the infiltrated cells (see Fig. 1). The effect was largely assigned to the improvement in the interfacial Ohmic resistance. The EIS study of the polarization losses of the reference and the infiltrated cells revealed reduction in the activation and concentration polarizations losses at 700oC due to the nano-decoration of the La0.8Sr0.2Co0.5Fe0.5O3-δ scaffold surface. Such effect was not clearly detectable at 800oC where the drop of Ohmic losses was dominant. This work demonstrated that single-step inkjet printing infiltration, a non-disruptive low-cost technique, could produce significant and scalable performance enhancements in commercial SOFCs. Figure 1

Seeing Cation Dopants in Gd-doped Ceria with STEM-EELS.

Seeing Cation Dopants in Gd-doped Ceria with STEM-EELS.

Tunable voltage polarity-dependent resistive switching characteristics by interface energy barrier modulation in ceria-based bilayer memristors for neuromorphic computing

Synaptic characteristics with tunable dependence on the voltage polarity are demonstrated in ceria (CeO2) and Gd-doped ceria (GDC) bilayer memristors with respect to their stacking orders. Both Pt/GDC/CeO2/Pt and Pt/CeO2/GDC/Pt memristors with different oxide stacking orders exhibit analog, linear, and symmetric synaptic weights for potentiation and depression, paired-pulse facilitation, and short- and long-term plasticity (STP and LTP, respectively). Potentiation and depression behaviors are highly linear and symmetric thanks to the stacking of more oxygen-deficient GDC layer with CeO2, which facilitates the redistribution of oxygen vacancies for analog resistance change. These memristors have opposite dependence of synaptic weight updates on the polarity of potentiation and depression voltages for the stacking order of CeO2 and GDC, which are consistently interpreted by voltage-driven energy barrier modulation at the interface between CeO2 and GDC or with Pt electrodes via oxygen vacancy redistribution. Recognition simulation with modified handwritten digits patterns using a two-layer perceptron neural network exhibits accuracy of approximately 88% with achieved dynamic range, linearity, symmetry, and precision states. These synaptic characteristics are also demonstrated in a 32 × 32 crossbar array of GDC-top memristors. This verifies the potential of bilayer memristors for application in artificial synapse networks in neuromorphic computing systems.

Comparison of the Electrochemical Performances of Solid Oxide Fuel Cells with Sputtered Thin Barrier Layers Fueled by Hydrogen or Ammonia

We investigated the influence of a fuel change from pure hydrogen to a hydrogen–ammonia mixture at different percentages on the electrochemical behavior of 50 mm in diameter Solid Oxide Fuel Cells (SOFCs) with sputtered thin buffer layers of Gd-doped ceria, varying the working temperatures from 800 °C to 650 °C. The results show that the performances of the cells are not affected by the fuel change for high working temperatures (800 °C and 750 °C). As an example, a power density value of 802 mW∙cm−2 at 1 A∙cm−2 is found when directly feeding the cell with 8 NmL∙min−1cm−2 of ammonia and with an equivalent flowrate of 12 NmL∙min−1cm−2 of H2. These power density output values are higher than those obtained in industrial state-of-art (SoA) SOFCs with screen-printed buffer layers fed with equivalent hydrogen flowrates, thanks to the improved electrochemical performances obtained in the case of cells with sputtered thin buffer layers of Gd-doped ceria. At lower working temperatures (700 °C and 650 °C), slight changes in the electrochemical behavior of the cells are observed. Nevertheless, in this temperature range, we also obtain an output current density value of 0.54 A∙cm−2 in a pure ammonia flowrate of 12 NmL min−1cm−2 at 800 mV and 700 °C, equal to the value observed in SoA button cells with industrial screen-printed GDC barrier layer fueled with 16 NmL∙min−1cm−2 of H2. These results pave the way towards the use of innovative SOFC structures with sputtered thin buffer layers fueled by ammonia.

Insight into mechanism of boosted oxygen reduction reaction in mixed-conducting composite cathode of solid oxide fuel cell via a novel open-source pore-scale model

Composite engineering is one of the most practical strategies for mitigating thermo-mechanical instability in state-of-the-art cobalt-based mixed ionic-electronic conducting electrodes for solid oxide cells. Nevertheless, the mechanism underlying improved performance and durability of composite electrodes is not substantially examined and understood. Pore-scale modeling can effectively bridge the gap between material property, microstructure discovery, and performance evaluation. However, most of the previous pore-scale models are built on in-house codes or commercial software that is closed-source to the public, limiting customization and community involvement. Here we report for the first time a microstructure-resolved 3D pore-scale model based on an open-source Lattice Boltzmann library, implementing a well-validated electrochemical module that considers gas, ion and electron transport, as well as electrochemical reaction at triple-phase-boundary (TPB) and double-phase-boundary (DPB). The pure La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) and 50/50 vol% composite LSCF/GDC (Gd-doped ceria) cathodes are reconstructed using focused ion beam-scanning electron microscopy and then are investigated under various current densities, temperatures, oxygen concentrations, and thicknesses. Results reveal the advantages of boosted TPB density and ionic conductivity outweigh the disadvantages of lower DPB density and electronic conductivity for the composite cathode. Furthermore, the composite cathode performs better at low temperatures and low oxygen concentrations due to the presence of more macropores, the stable bulk ion conductivity of GDC, and higher TPB density. Local current distribution at active sites indicates a thickness of 20 to 40 μm is favorable for reduced overpotential and moderate reaction homogeneity.

Phase segregation and miscibility of TiOx nanocomposites in Gd-doped ceria solid electrolyte material.

Electro-chemo-mechanical (ECM) coupling refers to mechanical deformation due to electrochemically driven compositional change in a solid. An ECM actuator producing micrometre-size displacements and long-term stability at room temperature was recently reported, comprising a 20 mol% Gd-doped ceria (20GDC), a solid electrolyte membrane, placed between two working bodies made of TiOx/20GDC (Ti-GDC) nanocomposites with Ti concentration of 38 mol%. The volumetric changes originating from oxidation or reduction in the local TiOx units are hypothesized to be the origin of mechanical deformation in the ECM actuator. Studying the Ti concentration-dependent structural changes in the Ti-GDC nanocomposites is therefore required for (i) understanding the mechanism of dimensional changes in the ECM actuator and (ii) maximizing the ECM response. Here, the systematic investigation of the local structure of the Ti and Ce ions in Ti-GDC over a broad range of Ti concentrations using synchrotron X-ray absorption spectroscopy and X-ray diffraction is reported. The main finding is that, depending on the Ti concentration, Ti atoms either form a cerium titanate or segregate into a TiO2 anatase-like phase. The transition region between these two regimes with Ti(IV) concentration between 19% and 57% contained strongly disordered TiOx units dispersed in 20GDC containing Ce(III) and Ce(IV) and hence rich with oxygen vacancies. As a result, this transition region is proposed to be the most advantageous for developing ECM-active materials.