Gadolinia-doped Ceria Research Articles

Aqueous electrophoretic deposition of gadolinium doped ceria

Homogeneous, bubble-free and smooth gadolinium doped ceria (GDC) films were successfully obtained with the application of alternating current electrophoretic deposition (AC-EPD) in the aqueous suspension. GDC particles were well dispersed in the aqueous suspension at a pH of 9.0. The alternating current was achieved through the application of an asymmetric square wave voltage to the electrodes of the deposition cell. An optimum frequency of 1 kHz showed the best balance between the suppression of bubble evolution and enhancement of the particle migration. The deposit yield increased monotonically with increasing time under the AC-EPD with a frequency of 1 kHz, suggesting its great potential to fabricate tunable thicknesses of deposition layers. The quality of the GDC film improved with an increase in frequency. An optimum combination of forward and reverse voltages and half-widths of the pulses was found.

Alkaline-earth-free quasi-ternary La(Co, Ni, Fe)O3−δ perovskite as potential cathode for solid oxide fuel cells

The purpose is to develop alternative alkaline-earth-free quasi-ternary LaCoO3−LaNiO3−LaFeO3 cathode materials for solid oxide fuel cells (SOFCs), which demonstrate high electrical conductivity, good electrochemical performance and excellent chemical stability against CrO2(OH)2 released from the metallic interconnects at operation temperatures. Three different perovskites of lanthanum in combination with iron, cobalt and nickel oxides, i.e. LaFe0.8Co0.1Ni0.1O3−δ (LFCN), LaNi0.8Co0.1Fe0.1O3−δ (LNCF) and LaCo0.8Fe0.1Ni0.1O3−δ (LCFN), were synthesized by the modified Pechini method, and then systematically investigated in the phase structure, thermal expansion, electrical conductivity and catalytic activity. LFCN have the best combination to the requirements of high-performance cathodes for SOFCs. Button cells with LFCN cathode were prepared on anode-supported YSZ electrolyte with gadolinium-doped cerium (GDC) buffer layer by screen printing. Excellent electrochemical performance with high maximum power density of 643 mW.cm−2 at 750 °C and corresponding low polarization resistance of 0.62 Ω cm2 further demonstrate that LFCN is a very competitive candidate as SOFC cathode.

Evaluation of Strontium Doped Lanthanum Chromium Manganite (LSCM) and Gadolinium Doped Ceria (GDC) Anode with Different Compositions

In the present study, the Ni-free anode fabricated with La0.9Sr0.1Cr0.5Mn0.5O3- δ (LSCM) and Gd0.1Ce0.9O2- δ (GDC) powders is evaluated. The sintering temperature, electrode thickness and composition are optimized. The anodes with GDC share over 70% exhibited the lowest initial polarization resistance. However, anodes with share of GDC over 80% significantly degraded in the accelerated degradation test. The reason of the degradation is attributed to the nano-cracking of the GDC phase. It was found out that LSCM stabilizes the GDC phase, and LSCM-GDC 30:70 wt.% was found to be the optimal composition considering the initial performance and stability.

Fabrication and Performance of La, Co-Substituted SrTiO3 as Cathode Materials of Solid Oxide Fuel Cell

SrTiO3-based materials have been investigated to be a candidate for anode of solid oxide fuel cell (SOFC) due to good chemical stability and high ionic conductivity in reducing atmosphere. However, the electronic conductivity is relatively low, which might be increased by doping. In this work, La, Co-substituted SrTiO3 (LSTC) was fabricated and evaluated as cathode of SOFC. Pechini method was successfully used for material synthesis. By doping of La and Co, the conductivity of materials can be increased to more than 1 S/cm at 800 °C. LSTC|Gadolinium-doped ceria|LSTC symmetric cells were also fabricated for electrode performance testing. The results showed that the interface resistance of LSTC cathode can be optimized to be 0.02 Ω·cm2 at 800 °C and 0.3 Ω·cm2 at 600 °C, which indicates possible application of LSTC cathode materials for SOFC. Maximum power density of LSTC cathode on button-sized anode-supported SOFC reached 0.360 W/cm2 at 800 °C.

Influence of Current Load on the Growth of SrZrO3 at the GDC/YSZ Interface

The influence of current load on the growth of SrZrO3 formed at the interface of a gadolinia-doped ceria (GDC) interlayer and yttria-stabilized zirconia (YSZ) electrolyte was analyzed using high-resolution electron microscopy. A cell with LNF (LaNi0.6Fe0.4O3) cathode was prepared after removing the LSCF cathode using HCl. The LNF cathode was used to eliminate the effect of Sr diffusion during cell operation. These cells were operated under 0.2 A cm−2 at 800°C. For the cell with the LNF cathode, no significant change was observed in the amount of SrZrO3. At the SrZrO3/GDC interface, crystal orientation was the same from the GDC side to the SrZrO3 side. Before cell operation, the GDC grain had some defects and no clear boundary was distinguished between GDC and SrZrO3. After cell operation, the SrZrO3/GDC interface was clearer and crystallization of SrZrO3 proceeded.

Evaluation of Praseodymium and Gadolinium Doped Ceria as a Possible Barrier Layer Material for Solid Oxide Cells

In this work, nanocrystalline layers based on the Pr, Gd co-doped CeO2 were investigated. For the preparation of thin layers, low-temperature spray pyrolysis technique was used. Different stoichiometries of the layers were produced for comparison on polished sapphire substrates. The microstructure of the prepared thin layers was studied by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and x-ray diffractometry (XRD). The total electrical conductivity as a function of Gd or Pr dopant were determined by DC electrical measurements using the Van der Pauw method in air atmosphere. The oxygen electrode interface analysis confirm protective character of the diffusion barrier layer based on doped CeO2.

Fabrication and Characterisation of Nanoscale Ni-CGO Electrode from Nano-Composite Powders

Incorporating nanoparticles into SOC electrode is a viable method to improve the electrochemical performance. In this work, nanoparticles of NiO and gadolinia-doped ceria (CGO) approximately 10 nm in diameter fabricated using a continuous hydrothermal flow synthesis are made into nano-structured SOC fuel electrodes via mixing and co-sintering. Both the Ni and CGO are of 50-100 nm in diameter in the final electrode. FIB-SEM 3-D tomography is carried out on the nanoscale Ni-CGO electrode which has been aged for 70 h, showing a high active triple phase boundary density of 3 µm-2 and a high active double phase boundary density of 2 µm-1. The total polarisation resistance of the electrode is stable at 0.20 Ω cm2 under open circuit conditions at 800 °C annealing in humidified 5% H2-N2.

Development of a Versatile, High-Performance Solid Oxide Fuel Cell Stack Technology

A high-performance solid oxide fuel cell (SOFC) stack technology is being developed, based on a design concept that incorporates prime-surface metallic interconnects with the versatility of stacking different types of single cells (sintered cells or metal-supported cells). A preliminary design of the prime-surface interconnect based on an egg-carton shape configuration has been advanced for this stack concept. Laboratory-scale prime-surface interconnects have successfully been fabricated by stamping and evaluated for mechanical loading, flow distribution and current collection properties. A process based on sputtering has been developed for fabricating supported thin-film (several micrometers thick) cells for this stack technology. Fabricated thin-film cells have shown desirable structural characteristics and exceptional performance on different fuels at reduced temperatures (550º-650ºC). Sputtered cells (with yttria stabilized zirconia (YSZ) for the electrolyte, gadolinia-doped ceria (GDC) for the electrolyte/cathode interlayer, nickel-YSZ for the anode and lanthanum strontium cobalt iron perovskite (LSCF)–YSZ for the cathode) have exhibited peak power densities of ~1.7 W/cm2 and ~2.1 W/cm2 with hydrogen fuel and air at operating temperatures of 600ºC and 650ºC, respectively.

Distribution of Relaxation Time Analysis of the Initial Performance Degradation on Ni-YSZ Anode Support Cells

Lifetime is still one of the constraints of Solid Oxide Fuel Cells (SOFCs) commercialization, which should be evaluated and predicted before market. During the initial period of two types of Ni-YSZ anode supported cells just after reduction, their voltage characteristic were found of nonlinear degradation. Experiment results showed that this stage almost terminated within 24 hours. Secondly, current density seemed to have little effect on the initial degradation, except for the open circuit condition, which saw lower degradation. Thirdly, one of the SOFCs' anode was infiltrated with gadolinium-doped ceria, and the initial degradation could be inhibited, which reduced cell’s voltage loss from 60 mV to 20 mV. By comparing different SOFCs using distribution of relaxation time method, results showed that the initial nonlinear degradation of SOFCs was mainly caused by the increase of polarization impedance, and the prime cause was the increase of activation polarization in both anode and cathode.

In Situ Densification of Gadolinium-Doped Ceria Interlayer by Infiltration Process in SOFC

Gadolinium-doped ceria (GDC) interlayer is commonly inserted between electrolyte yttria-stabilized zirconia (YSZ) and cathode La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) to prevent the Sr migration from cathode to electrolyte and improve the stability of the solid oxide fuel cell (SOFC). However, it is difficult to make a dense GDC interlayer during the traditional process. Co, Gd and Ce nitrates solution is used as the infiltration solution to modify and in situ densify the GDC interlayer in this study. The GDC interlayer shows high density when it is pre-sintered at 1175°C and final sintered at 1300°C, and the cell shows high performance and stability, the voltage has little degradation after running for 100 hours at 800°C and 0.5Acm-2, Sr is not observed at the YSZ/GDC interface.

Fabrication and Characterization of YSZ/GDC Bilayer Electrolyte Thin Films by Spray-Coating and Co-Sintering

Yttria-stabilized zirconia (YSZ) is the most popular electrolyte material for solid oxide fuel cells (SOFCs). However, when cobaltite-based perovskite cathode materials, for example lanthanum strontium cobalt ferrite (LSCF), are used, an insulating layer is easy to be formed at the cathode-electrolyte interface. For preventing the interfacial reaction, a gadolinium-doped ceria (GDC) interlayer is usually employed between YSZ and cathode. In this work, we investigated the fabrication of YSZ/GDC bilayer electrolyte thin films by a simple spray coating process and co-sintering. Dense YSZ/GDC bilayer electrolyte thin films were successfully fabricated. There is no crack and delamination observed for the YSZ/GDC bilayer. A Ni-YSZ/YSZ/GDC/LSCF-GDC anode-supported single cell with 4 µm thick YSZ layer and 2 µm thick GDC layer shows an open-circuit voltage of 1.1 V and a maximum power density of about 0.6 W/cm2 with humidified H2 as fuel and air as oxidant at 700°C.

Effect of Interfacial Properties on the Electrochemical Performance of Solid Oxide Fuel Cells

In this study, we examined the properties of model heterointerfaces created with yttrium-doped SrZrO3 (SZY) thin films, a type of secondary phase that most frequently occurs at interfaces of solid oxide fuel cells utilizing yttria-stabilized zirconia (YSZ) electrolytes. Electrochemical impedance results of symmetrical cells prepared with LSCF cathodes were evaluated using DRT (distribution of relaxation times) analysis, and 18O isotope exchange depth profiling with SIMS (secondary ion mass spectrometry) analysis was performed on post-tested samples to examine the ionic transport across heterointerfaces. Results showed high polarization resistance contributed by interfacial resistance associated with interfaces with SZY, i.e., LSCF/SZY, SZY/YSZ or SZY/GDC (gadolinia-doped ceria). The careful selection of heterostructure configurations lead to the conclusion that the interfacial contact of SZY with LSCF, YSZ and GDC results into high interfacial resistances, possibly due to an ion blocking effect.

High Performing and Durable Anode-Supported Solid Oxide Fuel Cell by Using Tape Casting, Lamination and Co-Firing Method

This work reports development of large-area (12cm×12cm) planar anode-supported SOFC with 100cm2 active area by a tape casting, lamination and co-sintering method. The cell consists of the nickel-8mol.% yttria-stabilized zirconia as support with 0.7 mm thickness and of the nickel-scandia stabilized zirconia (ScSZ) as an anode functional layer. Processing optimization of binder/plasticizer ratio of tape casting slurry allowed to obtain the green tapes with good mechanical strength and homogenous microstructure. Casting process parameter had also a great influence on the microstructure and mechanical properties of green tapes. The anode-support showed high mechanical strength and sufficient porosity for gas transport. A 6µm thick ScSZ electrolyte and 3µm thick gadolinium-doped ceria (GDC) buffer layer were fabricated using tape casting method and co-firing process. A lanthanum strontium cobalt ferrite-GDC composite cathode was screen-printed on the GDC layer. The single cell showed a peak power density of 509mWcm-2 at 750oC.

Ceria/Lanthanum Silicate Bi-Layer Electrolytes for SOFC Operating at Intermediate Temperatures

Lanthanum silicate (LS) was used as a blocking layer for preventing the current leakage of gadolinia-doped ceria (GDC) electrolyte. The anode-supported microtubular SOFCs with the GDC/LS bi-layer electrolytes were developed and characterized. The effect of Bi2O3 addition on the sintering characteristic of LS was also investigated. Thermal shrinkage measurement demonstrated that the addition of 5 wt. % Bi2O3 in LS electrolyte (LSB5) led to the decrease in the sintering temperature of the LS and improved the densification of the GDC/LS bi-layer electrolyte. As a result, the OCV for the cell with GDC/LS and GDC/LSB5 bi-layer electrolyte effectively increased in comparison with that of cell with GDC single-layer electrolyte.

Enhancing the Sinterability of Gadolinium-Doped Ceria by Wet Chemical Processing

Gd0.1Ce0.9O2-δ (GDC) powders with the addition of transition elements (Co, Cu, Fe, Mn, and Zn) were synthesized by a sol-gel based wet processing route. The resulting transition element doped GDC powders were characterized for their sintering properties. Dilatometric results indicated a significant enhancement in the sintering properties of transition element doped GDC powders when compared with commercially available GDC powder (Fuel Cell Material, USA). Average grain sizes calculated for the sintered pellets of the newly synthesized GDC powders also indicated a high degree of sintering. Transition element doped GDC powders were further employed for the fabrication of GDC buffer layers for solid oxide fuel cells using a simple screen printing method. Highly dense microstructures were observed for the sintered buffered layers of the new GDC powders. The transition elements doped GDC system is expected to help in producing stable and high performing solid oxide fuel cells

Effect of Fe on high performing nanostructured Ni/Gd-doped ceria electrocatalysts

Metal supported solid oxide fuel and electrolysis cells (SOFC/SOEC) impregnated with nanosized catalysts are attractive as highly efficient low cost cells operating at relatively low temperature. Recent studies have focused on catalysts based on Ni and gadolinia-doped ceria (CGO) at the fuel side of the cell, and in some cases with the addition of Fe. Here we investigate FeNi/CGO catalyst in relation to SOFC/SOEC fuel electrodes with focus on the Fe diffusion into Ni/CGO during catalyst reduction. The reduction process was followed by in-situ XRD and in situ TEM, and the experiments show that for low metal loadings the CGO nanoparticle size is unaffected by the presence of metals. However, for a high Fe loading the oxide particle size increases and Fe is widely spread in the catalyst, both, in the form of NiFe alloy and by converting most of the CGO to CeFeO3 and GdFeO3.

Interface engineering of yttrium stabilized zirconia/gadolinium doped ceria bi-layer electrolyte solid oxide fuel cell for boosting electrochemical performance

La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) is a promising cathode material for solid oxide fuel cells due to its high oxygen reduction reaction (ORR) activity. A gadolinium-doped ceria (GDC) barrier layer is essential to preventing side reactions between LSCF and an yttrium-stabilized zirconia (YSZ) electrolyte. However, several challenges are associated with the coating of GDC barrier layer on the YSZ electrolyte, including delamination of the GDC layer due to sinterability differences and formation of an insulating layer at a high annealing temperature. In this study, we describe a structure for a newly designed interfacial layer consisting of a GDC barrier layer and a nano-web–structured LSCF thin-film layer (NW-LSCF) through a facile spin-coating method. A dense GDC barrier layer with a thickness of approximately 400 nm was successfully applied to the surface of a YSZ electrolyte without delamination at a low annealing temperature. The high surface area of the NW-LSCF enhanced ORR due to an increased triple-phase boundary length. Cells employing a GDC barrier layer and NW-LSCF interlayer exhibited improved electrochemical performance. Peak power density reached 1.29 W/cm2 at an operating temperature of 550 °C and 2.14 W/cm2 at 650 °C.

Industrial mass production of nanocrystalline Ce0.9Gd0.1O1.95 via a solid–liquid method using gluconic acid

Abstract To achieve industrial mass production, a simple and efficient solid–liquid method (SLM) was applied to synthesize nanocrystalline gadolinium-doped ceria (Ce 0.9 Gd 0.1 O 1.95 , GDC), using gluconic acid (GA) as a complexing agent and polyethylene glycol (PEG) as a surfactant. Unlike traditional wet-chemical methods, this method of forming metal-complex compounds does not involve heating processes, which are known to pose risks of fire and explosion. The substitution of GA for traditional citric acid (CA) reduces the corrosion of stainless-steel equipment. The effects of the varying amounts of GA and polymerization degrees of PEG were discussed. The physical properties of the precursors were characterized using thermogravimetry/differential thermal analysis (TG/DTA). The crystallinity and grain size of the GDC powders were analysed using X-ray diffractometry (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET), and particle-size distribution (PSD) analyses. The results show that the GDC powder with additions of 20 wt% GA and 1 wt% PEG2000 that was sintered at 800 °C has a single phase with a particle size of around 40 nm; it is also homogenous and highly pure. In addition, the ionic conductivity of the GDC pellet that was sintered at 1450 °C for 5 h is 0.046 S/cm at 750 °C. These results indicate that this novel SLM is suitable for the mass synthesis of high-performance nanocrystalline Ce 0.9 Gd 0.1 O 1.95 powders.

Kinetics Analysis of Multichannel Hydrogen Reactions on Plasmonic-Based Au–GdC Thin-Film Nanocomposites

The reaction kinetics of hydrogen on gold nanoparticles (AuNPs) embedded in gadolinium-doped ceria has been studied in an oxygen-free environment through the time-dependent analysis of the localize...

Modified Energy Efficiencies of Proton‐conducting SOFCs with Partial Conductions of Oxide‐ions and Holes

AbstractAn analytical method to determine the electrochemical energy efficiencies of electrolytes with partial electronic conduction has been developed previously and reported in the literature. However, this analytical method does not address the effects of differing ionic species in electrolytes, i.e., the oxide‐ions or protons. Therefore, we aimed to modify this analytical method to account for the effects of differing ionic species, and applied it to compare the energy efficiencies of oxide‐ion conducting solid electrolytes such as yttria‐stabilized zirconia (YSZ) and gadolinia‐doped ceria (GDC) to proton‐conducting solid electrolytes, such as yttria‐doped barium zirconate (BZY). With the modification, difference in the influence of the fuel consumption between the oxide‐ion conducting electrolyte and the proton‐conducting electrolyte has been successfully taken into account. The energy efficiency of the BZY electrolyte relatively increased against those of YSZ or GDC electrolytes by the modification. Additionally, partial oxide‐ion conduction in the proton‐conducting electrolyte was successfully estimated using the modified analytical method.