Gadolinia-doped Ceria Research Articles

Development of High-Entropy Alloy (HEA) Anode for Carbon-Free and Electrochemically-Stable Operation of SOFC on Hydrocarbon Fuels

High-entropy alloy (HEA) anode, consisting of multicomponent alloy and gadolinium-doped ceria (GDC) powders, were synthesized and evaluated for ethanol steam reforming under SOFC operating conditions using a fixed-bed reactor as well as electrochemical performance using a button cell test configuration. Both bench-top and cell tests were conducted at 700 °C with a steam-to-carbon (S/C) ratio of 2. While Ni anode showed filamentary carbon formation, and performance degradation with time, HEA/GDC catalyst showed stable performance without carbon deposition. As an anode, HEA/GDC demonstrated high electrochemical stability and comparable current density compared to the Ni electrode.

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

Although solid oxide fuel cells (SOFC) offer high fuel-to-electric energy conversion efficiencies, their relatively low power-to-weight ratios make it difficult to integrate them with aircraft propulsion systems. This paper explores the feasibility of designing high throughput SOFCs for hybridization with gas turbines in aircraft powerplants. This paper explores and compares two SOFC technologies for achieving high specific power (kW/kg) with different membrane electrode assembly architectures, one with thin-film yttria-stabilized zirconia (YSZ) electrolytes and the second with high-power density gadolinia doped-ceria (GDC) electrolytes. The studies explore the operation of the respective SOFC stacks with synthetic CH4 as a carbon-neutral aviation fuel. Down-the-channel SOFC models are calibrated to experimental measurements of YSZ- and GDC-electrolyte cells at Elcogen and at the University of Maryland respectively. The model results provide a basis for determining the flow inlet conditions that enable each cell type to achieve high specific powers. The results also indicate the requirement of high airflows and upstream fuel preprocessing to sustain the high specific powers with sustainable cell operating conditions.

Characterization of a Nickel / Gadolinia Doped Ceria Fuel Electrode for Co-Electrolysis

Modelling of the co-electrolysis process requires understanding of the underlying reaction pathways. These include the electrochemical steam reduction, the electrochemical CO2 reduction and their coupling via the catalytic (reverse-)water-gas-shift reaction (RWGS). The assumption of a very fast water-gas-shift reaction and therefore neglectable CO2 electro-reduction is commonly used to model the co-electrolysis process. In contrast to that, it was proposed from previous studies, that the electrochemical conversion of CO / CO2 can be present under H2 / H2O / CO / CO2 gas mixtures on Ni/GDC fuel electrodes. We present results from a complex variation of operating parameters for process identification by the use of electrochemical impedance spectroscopy and the subsequent impedance analysis by the distribution of relaxation times (DRT). Four peaks are identified, including one yet undocumented suspected gas diffusion process. A possible influence of the electrochemical conversion of CO/CO2 starting from pCO2 / pH2O > 1 is shown.

Chromium Poisoning Mitigation Strategy in Strontium-Doped Lanthanum Manganite-Based Air Electrodes in Solid Oxide Fuel Cells

Abstract Chromium poisoning of the air electrode remains an obstacle to the long-term performance of solid oxide fuel cells (SOFCs). In Sr-doped LaMnO3 (LSM) air electrodes, the poisoning process results in two types of deposits, chromium oxide (Cr2O3), and Mn, Cr spinel (MnCr2O4). The former forms electrochemically and the latter forms via a chemical reaction. By applying a small anodic reverse bias, Cr2O3 deposits can be removed because their formation is electrochemical in nature. However, MnCr2O4 deposits remain because their formation is chemical, rather than electrochemical, in nature. In situ chemical decomposition of the Mn, Cr spinel was investigated as an alternate removal method as thermodynamics supports its decomposition into constituent oxides below ∼540 °C in pure oxygen. The spinel decomposition process was characterized using thermogravimetric and X-ray diffraction analyses. The experimentally determined rate of spinel decomposition was undetectable (very slow) with isolated MnCr2O4 powders. The addition of 10 mol% gadolinia doped ceria (GDC) and silver powders significantly increased the rate of decomposition. However, the rate is limited by the diffusion of oxygen through the decomposed oxide layer. Although one strategy may be the addition of GDC and silver to the LSM air electrode to enhance spinel decomposition, the more effective mitigation strategy would be to prevent the formation of MnCr2O4 spinel in the first place through the removal of the reactants: Cr2O3 via electrochemical cleaning and mobile Mn ions in the zirconia electrolyte by incorporating a diffusion barrier layer such as GDC between the air electrode and electrolyte.

A highly stable Co3O4-GDC nanocomposite cathode for intermediate temperature solid oxide fuel cells

Here, we report a cobalt spinel oxide (Co3O4) and gadolinium-doped ceria (GDC) nanocomposite cathode to achieve superior performance and durability in solid oxide fuel cells. A simple sol-gel process was used to create the Co3O4-GDC nanocomposite, which allowed for separate precipitation of the Co3O4 and GDC phases during calcination. HR-TEM revealed the nanocrystalline nature of the composite, consisting of nanocrystallites ranging in size from 5 to 10 nm. XRD and HAADF-STEM showed the formation of two distinct phases. The SOFC, consisting of a Co3O4-GDC nanocomposite cathode, showed high durability while operating at 800 °C for 300 h under a galvanostatic load of 1 A cm−2. The SOFC exhibited a continuously increasing performance, achieving a maximum power density of 1382 mW cm−2 after a 300 h operation. The findings demonstrate the efficacy of using Co3O4-GDC nanocomposite cathode for superior electrochemical performance as well as durability for the advancement of SOFC technology.

Electrochemical Impedance Spectroscopy Integrated with Environmental Transmission Electron Microscopy.

The concept of combining electrical impedance spectroscopy (EIS) with environmental transmission electron microscopy (ETEM) is demonstrated by testing a specially designed micro gadolinia-doped ceria (CGO) sample in reactive gasses (O2 and H2 /H2 O), at elevated temperatures (room temperature-800 °C) and with applied electrical potentials. The EIS-TEM method provides structural and compositional information with direct correlation to the electrochemical performance. It is demonstrated that reliable EIS measurements can be achieved in the TEM for a sample with nanoscale dimensions. Specifically, the ionic and electronic conductivity, the surface exchange resistivity, and the volume-specific chemical capacitance are in good agreement with results from more standardized electrochemical tests on macroscopic samples. CGO is chosen as a test material due to its relevance for solid oxide electrochemical reactions where its electrochemical performance depends on temperature and gas environment. As expected, the results show increased conductivity and lower surface exchange resistance in H2 /H2 O gas mixtures where the oxygen partial pressure is low compared to experiments in pure O2 . The developed EIS-TEM platform is an important tool in promoting the understanding of nanoscale processes for green energy technologies, e.g., solid oxide electrolysis/fuel cells, batteries, thermoelectric devices, etc.

Green synthesis of ammonia from steam and air using solid oxide electrolysis cells composed of ruthenium‐modified perovskite catalyst

AbstractThe green electrochemical synthesis of ammonia (NH3) through solid electrolysis has been intensively investigated. This research reported an improvement of NH3 production rate using in situ exsolution of ruthenium (Ru) atoms into lanthanum strontium chromium ferrite perovskite (LaxSr1−xCryFe1−yO3−δ) catalyst. The in situ Ru exsolution was achieved by reducing the optimized stoichiometric La0.33Sr0.67Cr0.33Fe0.52Ru0.15O3−δ (LSCrFRu) powders obtained in 10‐vol% H2/Ar at 800°C for 1.0 h. These Ru nanoparticles (NPs) were embedded on the surface of the LSCrFRu matrix, evenly distributed with a size varying from 4.4 ± 0.5 nm. With the exsolution of Ru atoms, greater oxygen vacancies were formed in ex‐LSCrFRu and gadolinium‐doped ceria (GDC) composite than those in LSCrF‐GDC electrocatalyst, beneficial to N2 gas adsorption and triple bond cleavage. These Ru‐modified LSCrFRu‐GDC catalysts showed a synthesis rate of 4.73 × 10−10 mol s−1 cm−2 at 550°C under 1.6 V, doubling the rate using LSCrF‐GDC catalyst. The improved ammonia synthesis kinetic is mainly attributed to embedded Ru NPs and the increased oxygen vacancies formed during the in situ exsolution process. More active sites and higher activity for H2O and N2 adsorption and activation collectively advanced facile transportation of O2− that further promotes the cleavage of covalent bonds in H2O, providing more H+ for the hydrogenation in the nitrogen reduction reaction. This research will open a new paradigm for the electrochemical synthesis of ammonia with mitigating the drawbacks of traditional NH3 production.

Electrical Behavior of Lanthanum Aluminate (LAO) and Gadolinium Doped Ceria (GDG) Composite Electrolyte for Electrochemical Devices

The LAO-GDC solid composite electrolyte has been proposed for use in Solid Oxide Fuel Cells (SOFC). The material conductivity of Solid Carbonate-Ceria (SCC) composite electrolytes is 0.04Scm-1 between 400 and 700°C. For this purpose, mixtures of LaAlO3 (LAO) and gadolinium doped ceria Ce0.8Gd0.2O2 (GDC) were created in weight ratios of 3:1, 2:2, and 1:3. The composite electrolyte material was studied separately to improve conductivity. The phase structure and microstructure were studied using an X-Ray Diffractometer (XRD) and Scanning Electron Microscopy (SEM), and the electrical behavior was investigated using Impedance Spectroscopy (IS). The SEM and Energy Dispersive X-ray spectroscopy (EDX) demonstrated a compact structure with an acceptable atomic percentage of constituent elements and a uniform grain distribution. Experimental investigation showed that this composite electrolyte had a high density of LaAlO3 (LAO)-Ce0.8Gd0.2O2 (GDC) composites and an approximate 97% density of its theoretical. The electrical behavior of LAO-GDC composites had the highest value of 0.1Scm-1 at 700°C, which is more extreme than the individual conductivities of LAO and GDC, according to Electrochemical Impedance Spectroscopy (EIS) techniques. Among the three composite ratios of the system, only the weight ratio of 3:1 had better conductivity. The LaAlO3 (LAO)-Ce0.8Gd0.2O2 (GDC) composite material has a higher activation energy of 1.5eV.

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.

Performance, electrochemical process analysis and degradation of gadolinium doped ceria as fuel electrode material for solid oxide electrolysis cells

One major challenge that has to be solved to enable a market entry of solid oxide electrolysis cells (SOECs) technology is the poor degradation behaviour caused by nickel agglomeration and migration in the state-of-the-art fuel electrodes. Novel fuel electrode materials that either suppress the nickel migration or even nickel-free electrodes could lead to a decrease in degradation rates. In this work, single cells based on the mixed ionic electronic conducting (MIEC) gadolinium doped ceria (GDC), acting as single-phase fuel electrode, were prepared. The cell performance was investigated by current density-voltage characteristics (jV) for steam and co-electrolysis conditions at various operating temperatures. Furthermore, electrochemical processes occurring in the single cells were analysed using electrochemical impedance spectroscopy (EIS), distribution of relaxation times (DRT) analysis and equivalent circuit model (ECM) fitting. Current densities of –914 and –969 mA‧cm−2, respectively, at 1.5 V and 900 °C operating temperature for steam and co-electrolysis were obtained, which corresponds to about 70% of the current density achieved in similar produced Ni-GDC fuel electrode cells. In addition, a long-term stability test was carried out during steam electrolysis (50% H2O + 50% H2) at 900 °C with a constant current load of –0.5 A‧cm−2 for 1070 h. In comparison to Ni-YSZ and Ni-GDC fuel electrode single cells reported in the literature, a significantly lower degradation rate of 112 mV‧kh−1 was observed. The electrochemical investigations and post-test analyses using SEM-EDX reveal that the GDC fuel electrode does not contribute significantly to the degradation, while the LSCF oxygen electrode is the major contributor to the cells’ degradation.

Suppressing the Surface Amorphization of Ba0.5Sr0.5Co0.8Fe0.2O3-δ Perovskite toward Oxygen Catalytic Reactions by Introducing the Compressive Stress.

Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) perovskite has been recognized as a promising oxygen evolution reaction (OER) catalyst due to its superior intrinsic catalytic activity. However, BSCF suffers from serious degradation during the OER process due to its surface amorphization caused by the segregation of A-site ions (Ba2+ and Sr2+). Herein, we construct a novel BSCF composite catalyst (BSCF-GDC-NR) by anchoring the gadolinium-doped ceria oxide (GDC) nanoparticles on the surface of a BSCF nanorod by a concentration-difference electrospinning method. Our BSCF-GDC-NR has greatly improved bifunctional oxygen catalytic activity and stability toward both oxygen reduction reaction (ORR) and OER compared with the pristine BSCF. The improvement of the stability can be related to that anchoring GDC on BSCF effectively suppresses the segregation and dissolution of A-site elements in BSCF during the preparation and catalytic processes. The suppression effects are ascribed to the introduction of compressive stress between BSCF and GDC, which greatly inhibits the diffusions of Ba and Sr ions. This work can give a guidance for developing the perovskite oxygen catalysts with high activity and stability.

A Self-Crystallized Nanofibrous Ni-GDC Anode by Magnetron Sputtering for Low-Temperature Solid Oxide Fuel Cells.

The optimum composition ratio of the anode cermet (Ni-GDC) for solid oxide fuel cells (SOFCs) varies because the electron-collecting mechanism is different depending on its applications. A Co-sputtering method facilitates ratio control with sputtering power adjustment. However, there is a practical issue with fabricating anode cermet with various ratios attributed to the large sputtering yield gap of the metal target, Ni, and the ceramic target, gadolinia-doped ceria (GDC). Therefore, in this study, a Gd-Ce metal alloy was applied instead of GDC to match the sputtering rate with that of Ni, which enables a wide ratio range achievement. A thin film of Gd-Ce oxidized after deposition and successfully transformed to crystallized GDC under a SOFC operation environment. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) confirmed its crystallinity, and the film deposited with various power ratios was sputtered on the ScSZ electrolyte pellet to clarify the optimum Ni-GDC ratio for thin-film SOFCs. Last, the Ni-GDC was applied to anodized aluminum oxide (AAO)-supported SOFCs to maximize the performance. The performance change according to the thickness of Ni-GDC was identified, and the best performance among them was 638 mW/cm2 at 500 °C.

Reduction of Reactive Oxygen Species Accumulation Using Gadolinium-Doped Ceria for the Alleviation of Atherosclerosis.

Atherosclerosis is a common cardiovascular disease with increasing morbidity and mortality. The pathogenesis of atherosclerosis is strongly related to endothelial dysfunction, which is induced by severe oxidative stress damage derived from reactive oxygen species (ROS). Thus, ROS plays a critical role in the pathogenesis and progression of atherosclerosis. In this work, we demonstrated that the gadolinium doping of CeO2 (Gd/CeO2) nanozymes as effective ROS scavengers delivered high performance for antiatherosclerosis. It was found that the chemical doping of Gd promoted the surface proportion of Ce3+ in the nanozymes and thereby enhanced the overall ROS scavenging ability. In vitro and in vivo experiments unambiguously showed that the Gd/CeO2 nanozymes efficiently scavenged harmful ROS at the cellular and histological levels. Further, Gd/CeO2 nanozymes were demonstrated to significantly reduce vascular lesions by reducing lipid accumulation in macrophage and decreasing inflammatory factor levels, thereby inhibiting the exacerbation of atherosclerosis. Moreover, Gd/CeO2 can serve as T1-weighted magnetic resonance imaging contrast agents, which can generate sufficient contrast to distinguish the location of plaque during living imaging. Through those efforts, Gd/CeO2 may serve as a potential diagnostic and treatment nanomedicine for the ROS-induced atherosclerosis.

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.

Heavily Gd-Doped Non-Toxic Cerium Oxide Nanoparticles for MRI Labelling of Stem Cells.

Recently, human mesenchymal stem cells (hMSc) have attracted a great deal of attention as potential therapeutic agents in the treatment of socially significant diseases. Despite substantial advances in stem-cell therapy, the biological mechanisms of hMSc action after transplantation remain unclear. The use of magnetic resonance imaging (MRI) as a non-invasive method for tracking stem cells in the body is very important for analysing their distribution in tissues and organs, as well as for ensuring control of their lifetime after injection. Herein, detailed experimental data are reported on the biocompatibility towards hMSc of heavily gadolinium-doped cerium oxide nanoparticles (Ce0.8Gd0.2O2-x) synthesised using two synthetic protocols. The relaxivity of the nanoparticles was measured in a magnetic field range from 1 mT to 16.4 T. The relaxivity values (r1 = 11 ± 1.2 mM-1 s-1 and r1 = 7 ± 1.2 mM-1 s-1 in magnetic fields typical of 1.5 and 3 T MRI scanners, respectively) are considerably higher than those of the commercial Omniscan MRI contrast agent. The low toxicity of gadolinium-doped ceria nanoparticles to hMSc enables their use as an effective theranostic tool with improved MRI-contrasting properties.

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.

A single-phase gadolinium-doped ceria cathode for highly efficient CO2 electrolysis

We demonstrate high and stable performance of gadolinium-doped ceria as a cathode during CO2 electrolysis. Mechanistic insights are provided by transmission line modelling of electrochemical impedance data.

Interface segregation of iron sintering aid in gadolinium-doped ceria

Increased sintering activity of Fe-doped CGO is related to the preferential segregation of iron species in CGO grain boundaries.

Atomically dispersed platinum electrocatalysts supported on gadolinia-doped ceria nanoparticles for practical high-temperature solid oxide cells

Atomically dispersed Pt catalysts supported on ceria nanoparticles are synthesized in situ and improve the performance and stability of high-temperature solid oxide cells for electricity and hydrogen production.

Impregnation of gadolinium-doped ceria backbone electrodes modified by addition of pore-formers for SOFC application

Impregnation of gadolinium-doped ceria backbone electrodes modified by addition of pore-formers for SOFC application