Electrode Polarization Resistance Research Articles

Development of Nanostructured Lanthanum Strontium Cobalt Ferrite/Gadolinian-Doped Ceria Composite Electrodes of Solid Oxide Cells Formed by In Situ Polarization.

In the development of nanoscale oxygen electrodes of high-temperature solid oxide cells (SOCs), the interface formed between the nanoelectrode particles and the electrolyte or electrolyte scaffolds is the most critical. In this work, a new synthesis technique for the fabrication of nanostructured electrodes via in situ electrochemical polarization treatment is reported. The lanthanum strontium cobalt ferrite (LSCF) precursor solution is infiltrated into a gadolinia-doped ceria (GDC) scaffold presintered on a yttria-stabilized zirconia (YSZ) electrolyte, followed by in situ polarization current treatment at SOC operation temperatures. Electrode ohmic and polarization resistances decrease with an increase in the polarization current treatment. Detailed microstructure analysis indicates the formation of a convex-shaped interface between the LSCF nanoparticles (NPs) and the GDC scaffold, very different from the flat contact between LSCF and GDC observed after heating at 800 °C with no polarization current treatment. The embedded LSCF NPs on the GDC scaffold contribute to the superior stability under both fuel cell and electrolysis operation conditions at 750 °C and a high peak power density of 1.58 W cm-2 at 750 °C. This work highlights a novel and facile route to in situ construct a stable and high-performing nanostructured electrode for SOCs.

Optimisation of electrochemical performance of Sr(Fe,Sb)O3-δ air electrodes for intermediate-temperature solid oxide cells through spray-pyrolysis processing

The effects of replacing iron with cobalt and employing either Pechini or spray pyrolysis synthesis routes have been studied for the perovskite system SrFe0.9-xCoxSb0.1O3-δ (x = 0; 0.45; 0.9) to optimise sustainable air electrodes for intermediate-temperature solid oxide cells. The electrochemical performance of Pechini-prepared compositions improves with increasing cobalt content, attributable to higher electronic conductivity and oxygen-vacancy concentration, and lower processing temperature from 1300 ᵒC, for SrFe0.9Sb0.1O3-δ, to 1200 and 1100 ᵒC, for SrFe0.45Co0.45Sb0.1O3−δ and SrCo0.9Sb0.1O3−δ, respectively, with SrCo0.9Sb0.1O3-δ exhibiting an area specific resistance (ASR) of 0.084 Ω cm2 at 700 °C. The electrochemical stability of Fe-containing Pechini-based compositions is impaired, most likely due to a higher processing temperature. However, the very low processing temperature of 800 °C for spray-pyrolysed electrodes produces similar electrochemical performances for Co-containing and Co-free compositions (ASR≈ 0.065 Ω cm2 at 700 °C for SrFe0.9Sb0.1O3-δ) and high electrochemical stability with practically unaltered electrode polarisation resistance on thermal cycling.

Study of a novel microstructured air electrode/electrolyte interface for solid oxide cells

Solid Oxide Cells (SOCs) are promising high temperature electrochemical devices to obtain clean energies from renewable sources. Their high operating temperatures (800–1000 °C) contribute to the degradation of the cell components. Intermediate Temperature SOCs (IT-SOCs) appear as an alternative to decrease the operating temperatures (600–800 °C) and avoid cell degradation, nevertheless, the electrochemical performance is affected by energy dissipation, principally by the air electrode overpotentials. This work presents the surface modification of Ce0.80Sm0.20O2-δ (SDC) electrolyte by Femtosecond Laser Micromachining (FLM) to increase the surface/area ratio and therefore improve the electrochemical performance. A pattern with an equally spaced pillar shape microstructure was obtained and characterized. (La0.60Sr0.40)0.95Co0.20Fe0.80O3-δ (LSCF) powder was used as porous air electrode to determine the electrochemical benefits of the pattern. Polarization resistance (Rp) of air electrode in patterned sample was about five times lower than in flat one at 600 °C and after 45 h, which suggested an improvement in the electrical and chemical features over time. These enhancements could be explained by the synergistic effect among surface/area ratio, nano-microcrystalline domains and superficial Ce3+ concentration in the patterned electrolyte. Rp values are higher than those reported for best air electrodes, however, FLM has proven its benefits in electrochemical performance.

High Performance Protonic Ceramic Electrochemical Cells Operating at

Protonic ceramic electrochemical cells (PCECs) can operate in both fuel cell and steam electrolysis modes for efficient power generation and green hydrogen production. Thanks to the low activation energy of proton conduction, PCECs are uniquely capable of operating at temperatures below 600°C. Although some intriguing demonstrations of intermediate-temperature (500-600°C) PCECs (IT-PCECs) have been made in the last decade, the operating temperature of PCECs is still too high to revolutionize ceramic electrochemical cell technology, which is ascribed to the high ohmic resistance and positive electrode polarization resistance. It has been also recognized the electrode polarization resistance dominates the total resistance at <500°C. These challenges suggest both the electrolyte and positive electrode should be redesigned to lower the PCEC operating temperature.In this work, we present two main approaches to reducing electrolyte ohmic resistance, electrolyte-positive electrode contact resistance, and electrode polarization resistance, which enables PCECs operation at <500°C. First, by using the ultrasonic spray coating system to coat the electrolyte layer on a negative electrode substrate with low Ba-deficiency, a bamboo-structured, ultrathin, and chemically homogeneous electrolyte can be fabricated. Second, a newly in-situ formed composite positive electrode was developed, which enhances the interfacial bonding between the positive electrode and electrolyte, further reducing ASRo , while improving both bulk oxygen-ion diffusion coefficient and surface oxygen exchange coefficientat <500°C.The newly developed LT-PCECs attain outstanding power densities in fuel cell mode (as high as 0.77 W cm-2 at 450°C), and exceptional current densities in electrolysis mode (over -1.28 A cm-2 at 1.4 V and 450°C). Furthermore, reducing the temperature does not sacrifice the fuel flexibility of these ceramic fuel cells. We demonstrated that the PCECs can directly utilize ammonia and methane for power generation at <500°C. Exceptional durability has been also demonstrated in both fuel cell and electrolysis modes at <500°C.These results further emphasize that through the PCEC scalable manufacturing processes and novel positive electrode materials presented here, PCECs can be employed for power generation and H2 production at <500°C, thereby transforming the architectures and removing previous operational constraints of ceramic electrochemical cells for scaled operation. PCECs can therefore be considered as one part of the growing hydrogen economy, while leveraging the existing fossil fuel infrastructure and achieving higher energy efficiency and lower CO2 emissions.

Approaches to Reduce the Operating Temperature of Protonic Ceramic Electrochemical Cells to

Protonic ceramic electrochemical cells (PCECs) have been developed as a promising technology for efficient power generation and hydrogen production via steam electrolysis. However, the current operating temperature range of 450-600°C still limits their widespread application and adoption in ceramic electrochemical cell technology. To address this issue, lowering the operating temperature range to 250-450°C has been proposed, which would expand the range of materials for building PCEC systems and reduce their cost. In this presentation, I will discuss our group's series of approaches to redesign PCECs. These approaches include using readily fabricated single-grain thick, chemically homogeneous, and robust electrolytes, as well as newly developed positive electrode materials. Our innovations have simultaneously reduced the electrolyte ohmic resistance, electrolyte-positive electrode contact resistance, and electrode polarization resistance, while also improving durability. As a result, we have set several new records of using PCECs for both power generation and renewable hydrogen production.

Ni and Fe Doped (La,Sr)TiO3 Fuel Electrodes for Solid Oxide Cells – Electrical and Electrochemical Properties

Development of robust and impurity tolerant solid oxide cells (SOCs) has attracted a significant R&D-effort in recent years. The shortcomings of Ni-YSZ fuel electrodes in terms of redox stability, carbon and sulfur tolerance and long-term durability under strong polarization has spurred the search for alternative fuel electrode materials. Among them, doped strontium titanate materials has shown promising performance due to their good electrical transport properties, chemical and redox stability and tolerance towards impurities.In the present study, the electrical properties of the La0.477Sr0.33Ni0.03Fe0.03Ti0.94O3- δ (LSFNT) material, which is designed with the potential for exsoluting Ni and Fe nanoparticles, is investigated in detail. In addition, the performance of LSFNT based fuel electrodes is characterized in a symmetrical cell configuration. The electrical conductivity measurements are performed on both dense and porous LSFNT layers, as a function of temperature and pO2. The pre-reduced (1100oC, 24 hours, dry 5%H2/N2) dense LSFNT sample showed an electrical conductivity of ca. 10 S/cm at 850 oC in dry 5%H2/N2. The “in-situ reduced” (850oC, 700 hours) porous LSFNT layer showed a conductivity 10 times smaller. The conductivity was tracked as a function of pO2 showing an approximate pO2 -1/6 dependence. Also the ionic conductivity of the material was determined using an electron blocking method. At 850oC at a pO2 of 10-20 bar the ionic conductivity is ca. 0.05 S/cm at which is similar to that of Y2O3 doped ZrO2 electrolytes demonstrating that LSFNT is indeed a very good mixed ion- and electron-conducting material.Motivated by the observed conductivities SOC fuel electrodes of LSFNT were prepared by incorporating Gd-doped CeO2 electrocatalyst into LSFNT porous backbones and their electrochemical performance was measured in 50% H2 / 50% H2O at OCV. An electrode polarization resistance of 0.05 Ω cm2 at 850oC and 0.26 Ω cm2 at 650 oC is measured for these electrodes. The polarization resistance at 850 oC is comparable to that of Ni-YSZ fuel electrodes; while at 650oC it is significantly lower in similar atmospheres. This promising electrochemical performance shows the potential of the LSFNT fuel electrodes, as an alternative to Ni-YSZ fuel electrodes, in solid oxide cell applications.

Manufacturability of bolt-microtubular anode supports for solid oxide fuel cells

The effects of anode support tape length on the manufacturability and level of surface patterning in bolt-microtubular anode supports (BMASs) for solid oxide fuel cells (SOFCs) are investigated in this study. Continuous anode support tapes of ∼5–25 cm are wrapped on a threaded rod for this purpose and five-layered bolt-microtubular cells (BMCs) are manufactured on these supports. Similarly, microtubular anode supports (MASs) by using a pin and corresponding microtubular cells (MCs) are also fabricated and examined for comparison. The tape lengths ≤9.9 cm yield mechanically unstable BMASs or BMSs due to fractures that occur during sintering in the anode supports or during testing in the cells. The electrochemical performance tests show that all BMCs exhibit relatively higher performances compared to those of MCs for a certain tape length. The highest maximum power density of 0.479 Wcm−2 at 800 °C operating temperature is obtained from BMC prepared with 12 cm long anode support tape, whereas that of MC fabricated with the same anode support length is measured as 0.313 Wcm2 under the same testing conditions. The impedance measurements reveal that the improvement in the cell performances is due to reduced electrode polarization resistance achieved by the bolt-like microtube design.

INFLUENCE OF THE METHOD OF FORMING A Pr2CuO4-BASED CATHODE ON THE ELECTROCHEMICAL CHARACTERISTICS OF&#x0D; A PLANAR ELECTROLYTE-SUPPORTED SOFC

The influence of the method of organising the cathode microstructure based on Pr2CuO4 (PCO) on the electrochemical characteristics of a model electrolyte-supported solid oxide fuel cell (SOFC) has been investigated. It is shown that an increase in the thickness of the PCO cathode layer and the introduction of a pore-forming agent contribute to an increase in the power density of the SOFC test cell compared to a sample with an initial unmodified cathode structure, whose power density at 850°C was 34 mW/cm2. It was found that the optimum thickness of the cathode layer to achieve maximum electrochemical performance was in the range of 40-50 μm, while the power density achieved was 116 mW/cm2 at 850°C. At the same time, the transition from a single-phase PCO cathode to a composite of PCO-Ce0.9Gd0.1O1.95 (60/40 wt. %) provides an increase in power density up to 130 mW/cm2 at 850°C, while the dynamics of its decrease with reducing temperature is slower compared to the single-phase cathode. The analysis of the changes in the values of the total electrode polarisation resistance of the model SOFC, determined by impedance spectroscopy, as a function of the method of cathode formation, showed that during the transition from the initial sample to the samples with increased thickness of the cathode layer and the composite cathode, a twofold (in the first case) and threefold (in the second case) decrease in the level of polarisation losses is observed, which correlates with an increase in the power density. The proposed methods of modifying the initial cathode microstructure based on PCO show a positive dynamic of increasing the electrochemical activity of the cathode/electrolyte interface and the power density characteristics of the fuel cell as a whole.

Mechanistic Study on the Corrosion of (La,Sr)(Co,Fe)O3-δ Cathodes Induced by CO2.

Solid Oxide Fuel Cell (SOFC) cathodes operating in ambient atmospheric conditions inevitably encounter CO2 contamination, leading to sustained performance deterioration. In this investigation, we examined the impact of CO2 on three variants of (La,Sr)(Co,Fe)O3-δ cathodes and employed the distribution of relaxation times method to distinguish distinct electrochemical processes based on impedance spectra analysis. We meticulously analyzed and discussed the corrosion resistance of these (La,Sr)(Co,Fe)O3-δ cathodes under high CO2 concentrations, relying on the experimental data. Electrochemical impedance spectroscopy results revealed that La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF-6428), La0.4Sr0.6Co0.2Fe0.8O3-δ (LSCF-4628), and La0.4Sr0.6Co0.2Fe0.7Nb0.1O3-δ (LSCFN-46271) cathodes exhibited persistent degradation when exposed to CO2 at temperatures of 650 °C or 800 °C during the durability-testing period. An increase in electrode polarization resistance was observed upon CO2 introduction to the electrode, but electrode performance recovered upon returning to a pure air environment. Furthermore, X-ray diffraction and scanning electron microscopy analyses confirmed that CO2 did not cause permanent damage to the (La,Sr)(Co,Fe)O3-δ cathodes. These findings indicate that the (La,Sr)(Co,Fe)O3-δ cathodes exhibit excellent resistance to CO2-induced corrosion.

Architecture design of TiO2 with Co-doped CdS quantum dots photoelectrode for water splitting.

Photoelectrochemical hydrogen production is a critical key to solving the carbon-zero goal of countries due to renewable sources of solar light and combustion products of hydrogen-only water. Here, an architecture design for an n-type nano rosettes-rod TiO2 (RT) surface using CdS and Co-doped CdS quantum dots (QDs) is carried out utilizing the SILAR (simple ionic layer adsorption and reaction) method. Furthermore, the photocatalytic behaviour of Co-doped CdS QDs SILAR cycles deposition is investigated in various cycles, including 5, 8, 10, and 12. The FESEM, Raman XRD, Uv-Vis spectrometer, and vibration modes are used to evaluate the photoelectrode surface structure, crystal structure, and solar light absorption, respectively. FESEM images and XRD pattern revealed successive CdS QDS and Co-doped CdS QDs deposition on the RT boundary and rising SILAR cycles of Co-doped CdS QDs lead to further coverage of RT surface. UV-vis spectrometer indicated shifting solar light absorption to the visible region by applying more SILAR cycles of Co-doped CdS QDs deposition. The electrochemical parameters obtained from EIS showed total polarization resistance (Rp) of the RT electrode dramatically decreased with 10 SILAR cycle Co-doped CdS QDs deposition (5093 Ω cm2 and 617 Ω cm2). Linear sweep voltammetry (LSV) and chronoamperometric photocatalytic performance measurements indicated Co-doped CdS QDs on RT extremely enhanced photoresponse under solar irradiation and 10 SILAR cycle Co-doped CdS QDs improved photocurrent density about fourfold according to blank RT electrode.

Microstructural and electrochemical properties of Ni-impregnated GDC10 and 8YSZ freeze tape cast scaffolds as fuel electrodes for solid oxide cells

Ni-impregnated Gd0.1Ce0.9O2 and Y0.08Zr0.92O2 fuel electrodes for solid oxide cells are manufactured by the combination of the freeze tape casting and infiltration techniques. Their morphological properties are investigated by scanning electron microscope and X-Ray microtomography while their electrochemical performance is evaluated in symmetrical Y0.08Zr0.92O2-supported button cells by electrochemical impedance spectroscopy. The microstructural analysis of the manufactured scaffolds highlights the characteristic anisotropy of porosity provided by the freeze tape casting method. The average tortuosity factor across the out of plane direction has been calculated equal to 1.38, being considerably lower than the average values of the other components, (τx = 10.2) and (τy = 6.87). The contribution provided by gas diffusion to the overall polarization resistance of the freeze tape cast electrodes has been estimated around 6·10−4 Ω cm2 in the 600–750 °C temperature range, thus lower than the best reported values for the state-of-the-art electrodes featuring sponge-like porosity. The measured impedance data highlighted the higher electrochemical performance of the Ni-impregnated Gd0.1Ce0.9O2 architecture, holding a polarization resistance of 0.823 Ω cm2 at 750 °C, which is regarded as a very promising result for a ∼600 μm thick electrode. The interpretation of the impedance data was supported by the distribution of relaxation times analysis and the complex non-linear least square fit. In particular, the electrochemical investigation highlighted the presence of two major resistive contributions which have been ascribed to the occurrence of a chemical capacitance within the GDC10 lattice (low frequency contribution) and to the multi-layered architecture of the tested symmetrical cells which increases the contact losses (high frequency contribution).

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.

Study of Ca3Co4O9+δ oxygen electrode with La0.6Sr0.4FeO3-δ interlayer in YSZ-based reversible solid oxide cells

The electrochemical performance of Ca3Co4O9+δ (CCO) oxygen electrode with La0.6Sr0.4FeO3-δ (LSF) interlayer in YSZ-based reversible solid oxide cells (RSOCs) was investigated in present work. Results proved that CCO oxygen electrode with LSF interlayer had a superior stability under alternating anodic and cathodic polarization. Both the polarization resistance and overpotential of the CCO electrode with LSF interlayer were significantly reduced compared to that with Ce0.9Gd0.1O1.95 (GDC) interlayer, which confirmed the improvement of the redox reactivity of the oxygen electrode. The maximum power density of Ni-YSZ/YSZ/LSF/CCO fuel cell was 1276 mW cm−2 at 800 °C. An electrolysis current density of 1695 mA cm−2 was achieved at 1.5 V and 50% H2O. The hydrogen production rate of the electrolysis cell improved by 2 times than that with the GDC interlayer. Results made clear reliability of LSF as an interlayer in YSZ-based RSOCs.

Optimizing the Copper Content in GdBa0.5Sr0.5Co2-XCuxO5+δ Double Perovskites as the High Performance Oxygen Electrodes for Reversible Solid Oxide Cells

Sustainable development and better protection of environment are among the top priority issues for human society. Seeking for cleaner and less greenhouse-emissive energy resources or solutions has been a dominating trend around the world, since daily functioning of the current society is still dependent on fossil energy sources, such as oil, coal, and also natural gas. Tremendous efforts have been made to develop alternative energy production technologies, among them, fuel cells have been found as very promising ones. Especially, reversible Solid Oxide Cells (rSOCs) have become famous for their all-solid structure, which consist of the porous fuel electrode, dense solid oxide electrolyte, porous oxygen electrode, and interconnects. Reversible SOCs can effectively work either in the fuel cell (e.g. H2 + 0.5O2 → H2O and heat) or electrolyzer modes, making them useful for grid balancing and utilization of surplus electrical energy. It is worth noting that the oxygen electrode has a decisive role regarding performance and long-term operation of the whole cell. Until now most of the widely-studied and also practically-implemented oxygen electrode materials are cobalt-based perovskite-type oxides or related compounds having the relatively high concentration of Co. This can be regarded as one of drawbacks, due to the toxicity, carcinogenicity, high costs, and poorly available resources of cobalt, despite impressive electrocatalytic activity and excellent electrochemical properties of such materials. Accordingly, numerous attempts have been carried out, which aim at replacing Co with other transition metal elements, such as Ni, Fe, Mn, and Cu, at least to some extent. For example, copper-doping into Co-based perovskites enabled to limit the excessive thermal expansion, as well as positively influenced redox stability.The A-site ordered double perovskites, REBaCo2O5+δ (RE: rare earth elements and Y), feature the layered structure with alternating configuration of REOδ and BaO layers along the c-axis, which generates fast diffusion channels for migration of oxygen anions, as well as the materials exhibit excellent electrical conductivity. In this work, an attempt has been made to further optimize the compounds, with the target compositions proposed as GdBa0.5Sr0.5Co2-xCuxO5+δ (0 ≤ x ≤ 2). Intermediate-size Gd3+ facilitates layered structure formation, while introducing Sr at Ba sites is beneficial to electrical conductivity, due to alleviated lattice distortion. Comprehensive studies have been directed to optimize the copper content in the selected oxides. After synthesis by a self-combustion sol-gel method, the samples were systematically characterized, including identification of the phase composition and crystal structure, thermal stability and chemical reactivity with solid electrolytes, thermal expansion behavior, oxygen content, total electrical conductivity and electrochemical properties. The adopted characterization methods include the X-ray diffraction at room and high temperatures with Rietveld refinements, iodometric titration and thermogravimetric tests, dilatometric measurements, total electrical conductivity studies. Also, laboratory-scale symmetrical and full cells have been manufactured and characterized concerning morphology of the electrodes, electrode-electrolyte interface, electrode polarization resistance with distribution of relaxation times method, as well as power output. High copper content (x > 1.15) was found as hindering factor for synthesis of pure samples. Bearing in mind a need to reduce cobalt content, GdBa0.5Sr0.5Co2-xCuxO5+δ compositions with x = 1, 1.05, 1.1, and 1.15 were selected for further evaluation. The oxides could be synthesized as practically phase-pure, revealing the desired P/4mmm tetragonal symmetry. All of them maintain stable lattice structure up to 1000 °C in air. They are chemically compatible with La0.8Sr0.2Ga0.8Mg0.2O3-δ and Ce0.9Gd0.1O2-δ electrolytes up to at least 900 °C. A moderate thermal expansion coefficients were measured, which decrease with the increasing Cu-doping content, from 15.8·10-6 K-1 (x = 1) to 14.5·10-6 K-1 (x = 1.15) in the temperature range of 300-900 °C. The equilibrated oxygen content in the considered samples ranges from 5.69 (x = 1) to 5.49 (x = 1.15). All oxides exhibit a sufficiently high total conductivity, above 10 S cm-1 in the working temperature range of 600-900 °C. The recorded electrochemical impedance spectra indicate that the lowest polarization resistance (0.017 Ω cm2 at 850 °C) can be obtained for the electrode with GdBa0.5Sr0.5Co0.9Cu1.1O5+δ composition (on La0.8Sr0.2Ga0.8Mg0.2O3-δ electrolyte), which is lower than for the higher cobalt-content GdBa0.5Sr0.5CoCuO5+δ, 0.025 Ω cm2 at the same temperature. The developed GdBa0.5Sr0.5Co0.9Cu1.1O5+δ material used as the oxygen electrode in the La0.8Sr0.2Ga0.8Mg0.2O3-δ electrolyte-supported full cell enabled to achieve power density output exceeding 1.2 W cm-2 at 850 °C, and 0.57 A cm-2 current density at 1.5 V in electrolysis mode at 700 °C. All the evidence prove that Cu-doping is an effective approach, since it allows for limiting the Co content and obtaining the desirable performance at the same time.

Effective Suppression of LSCF Air Electrode Degradation by Air Cleaning

The performance degradation of air electrodes in solid oxide cells is strongly affected by impurities such as sulfur dioxide. Air filters are applied in most fuel cell systems to avoid poisoning and subsequent degradation of fuel cell stacks [1, 2]. Filtering solutions designed for the high air purity demands of proton-exchange membrane fuel cells (PEMFC) are commercially available.This study evaluates the applicability of such a filter for the LSCF air electrode in an electrolyte-supported SOC. Three different air qualities were applied in single-cell tests to distinguish the degradation mechanism caused by the ambient air impurities from the intrinsic aging phenomena of the cell. The utilized gases are (i) compressed air, (ii) filtered compressed air, and (iii) synthetic air. The compressed air (i) consists of ambient air supplied by a conventional compressor with a downstream particle filtering and oil removal system. In (ii), an additional filter layer was applied between the mass flow controller and the cell housing to filter the compressed air. The filter consisted of specially modified activated carbons designed to remove harmful gases and was operated at ambient temperature and pressure. The active area of the filter was 0.95 cm², corresponding to an air velocity of 0.088 m s-1 at an airflow rate of 500 sccm. The synthetic air is a mixture of 21% oxygen (99.95% O2, the main impurities are H2O and Ar) and 79% nitrogen (99.999% N2) provided by the Air Liquide company. Symmetrical cells based on a 3YSZ substrate coated with GDC buffer layers and LSCF electrode applied on both sides with an active surface area of 1 cm2 were applied in this study.Figure 1 shows the polarization resistance of the LSCF electrode operated in different types of air. Similar to previous reports [3-5], a significant degradation rate is recorded within the first 300 hours of operation. Filtering the air reduces the degradation rate significantly. The performance degradation of the cell with filtered air is comparable to that of the cell with synthetic air, demonstrating the capability of the filter to adsorb the gas impurities. Fig. 1 polarization resistance of the LSCF-cathode of 3 symmetrical cells operated at 750 °C with unfiltered and filtered compressed air and synthetic air, respectively.To better understand the degradation mechanism in the LSCF air electrode, we analyzed the impedance spectra measured during aging tests using the distribution of relaxation times (DRT) and then a complex nonlinear least squares (CNLS) fit. This contribution discusses differences in the temporal development of air electrode impedance and degradation mechanisms related to surface poisoning and subsequent changes in LSCF bulk.Keywords: LSCF air electrode, Impedance spectra, Degradation mechanisms, Air filtration.[1] M. Harenbrock, A. Korn, A. Weber, E. Hallbauer, in, SAE Technical Paper, 2020.[2] M. Harenbrock, E. Hallbauer, T. Heilmann, M. Hanselmann, ATZheavy duty, 14 (2021) 34-37.[3] C. Endler, A. Leonide, A. Weber, F. Tietz, E. Ivers-Tiffée, Journal of the Electrochemical Society, 157 (2010) B292-B298.[4] C. Endler-Schuck, A. Leonide, A. Weber, S. Uhlenbruck, F. Tietz, E. Ivers-Tiffée, Journal of Power Sources, 196 (2011) 7257-7262.[5] C. Endler-Schuck, J. Joos, C. Niedrig, A. Weber, E. Ivers-Tiffée, Solid State Ionics, 269 (2015) 67-79. Figure 1

Reliable Lab-Scale Evaluation for Enhanced SOFCs Electrode Performance - Influence of Electronic Transport

Understanding and optimizing electrochemically active zone for oxygen reduction reaction (ORR) in solid oxide fuel cells (SOFCs) cathodes are indispensable to maximize device’s performance. For a mixed ionic and electronic conducting electrode, the range of this zone depends on the oxygen surface exchange and solid-state oxygen/electron transport properties of electrode materials and the oxygen gas transport through porous electrode. This implies that electrode microstructure, including surface area, porosity, and tortuosity, needs to be carefully designed and controlled to maximize electrochemically active electrode volume. This aspect is also critical to realize valid characterization of the electrode’s electrochemical activities. For instance, when a material’s electronic conductivity is low or the electrical contact points are spaced beyond a critical distance, the electrode polarization resistance measured by electrochemical impedance spectroscopy will be controlled by the sheet resistance not the oxygen exchange resistance. In this presentation, we will discuss our synthesis approach of lanthanum strontium cobalt ferrite (LSCF) and spinel powders by using co-precipitation with a continuous stirred-tank reactor, in order to precisely control powder’s chemistry and morphology (ultimately, electrode microstructure). And, we will discuss the influence of electrode microstructure and current collecting method on electronic conduction in porous electrode and, eventually, on electrochemical performance and its reliable evaluation in a lab-scale button cell configuration.This work was supported by the US Department of Energy (DOE), Office of Fossil Energy, (Office of Fossil Energy & Carbon Management), “Solid Oxide Fuel Cell Manufacturing in Support of Office of Fossil Energy” program through Argonne National Laboratory under FWP No. 27327.1.

Tuning Exsolution of Nanoparticles in Defect Engineered Ruddlesden–Popper oxides for efficient CO2 electrolysis

Solid oxide cell (SOC) is the energy conversion device with a series of advantages such as high efficiency, environmental friendliness and durability, making it a promising way to deal with environmental pollution and energy crisis appearing with the development of human society. Perovskite oxides with hetero-phases which were prepared by in-situ exsolution are widely used as fuel electrode in SOC. In this work, Ni-doped perovskites Ruddlesden–Popper oxides, (La, Sr)nTinO3n-2 with n = 5, 8, and 12 (LSTNn), were synthesized to design novel exsolution materials as solid oxide fuel cell anodes and for electrochemical catalysis applications.Compared with pure LSTNn without Ni, a small A-site deficiency (10%) promoted the exsolution of Ni from the perovskite oxides of Ni-doped LSTNn. It is found that the morphology as well as electrochemical activity of LSTNn anodes can be successfully manipulated by the exsolution of Ni. Since more Ni nanoparticles are exsolved from the parent oxides, LSTN8 displays better electrochemical performance by providing more active sides during the hydrogen oxidation reaction and significantly lowering electrode polarization resistance. DRT analysis is conducted to study substeps of the whole electrode reaction, finding that in-situ precipitation improves rate-limiting steps much. The CO2 reduction reaction performance of LSTN materials is also studied, finding that in-situ grown nanoparticles on surface of LSTN significantly increases the density of surface active sites and three phase boundaries (TPBs), which are beneficial for CO2 adsorption and subsequent conversion.It is clear from these results that varying Ni-doping in Ruddlesden–Popper oxides is a key factor in controlling the electrochemical performance and catalytic activity for hydrogen oxidation reaction in solid oxide fuel cells.

Nanostructured LSC Thin Film Electrodes with Improved Electrochemical Performance and Long-Term Stability

Nanostructured La0.6Sr0.4CoO3-δ (LSC) thin film electrodes exhibit exceptionally high oxygen surface exchange properties, surpassing those of conventional microscale electrode structures, which are desirable for application in solid oxide cells (SOC) [1-2]. On the other hand, the LSC nanostructures also tend to undergo significant morphological changes at typically high temperatures required for SOC operation, leading to rapid degradation in performance. Here, towards the goal of improving the long-term stability of electrochemical performance of nanostructured LSC thin films, a systematic investigation of the effect of processing temperatures on long-term stability was carried out [3]. By varying the deposition temperature (500 °C to room temperature), the as-grown characteristic nanostructures of LSC thin films prepared using pulsed laser deposition can be tuned from highly dense nanocolumnar grains to nanofibrous structures with high porosity. Variations in the deposition temperature also resulted to differences in the proportion of surface-bound/lattice-bound Sr and Co2+/Co3+ at the surfaces of the as-grown LSC thin films; however, prolonged annealing at 700 °C in air essentially transforms the surfaces to a final state with mostly lattice-bound Sr and Co3+. Nevertheless, LSC films with initially nanofibrous structures are found to be less prone to the grain sintering effect occurring at high temperatures and exhibit less degradation of the electrode polarization resistance as compared to well-dense films. Using lower deposition temperatures, cation interdiffusion occurring at LSC/GDC interfaces is also significantly suppressed, thus leading to better interfacial stability as compared to those prepared at higher deposition temperatures. These results highlight the relationship between characteristic nanostructures of thin film electrodes and electrochemical performance and provide guidance on designing electrodes with improved long-term stability.[1] J. Januschewsky, M. Ahrens, A. Opitz, F. Kubel and J. Fleig, Adv. Funct. Mater., 2009, 19, 3151–3156.[2] J. Hayd, L. Dieterle, U. Guntow, D. Gerthsen and E. Ivers-Tiffee, J. Power Sources, 2011, 196, 7263–7270.[3] K. Develos-Bagarinao, O. Celikbilek, R. A. Budiman, G. Kerherve, S. Fearn, S. J. Skinner and H. Kishimoto, J. Mater. Chem. A, 10, 2445-2459 (2022).

Solvent-free direct salt precursor mechanochemical synthesis of La0.5Sr0.5Ti0.5Mn0.5O3-δ oxide perovskite and its electrocatalytic behavior as oxygen electrode for solid oxide cells

In this work, a solvent-free mechanochemical route is proposed as a direct salt precursor solid state synthesis for the mixed ionic-electronic conducting (MIEC) Lanthanum Strontium Titanium Manganese oxide perovskite (La0.5Sr0.5Ti0.5Mn0.5O3-δ, LSTM). The resulting mechanochemically synthesized powder is structurally and morphologically characterized and is comprised of fine spherical nanostructures in the sub-micron scale (≤100 nm), with low polydispersity and homogeneous morphology, while the obtained perovskite structure is pure single-phase without any precursor residuals or metal oxide phases. For comparison, conventional synthetic routes (sol-gel and precursor calcination) are presented which result in inferior samples of mixed metal oxides and micron-sized particles. Symmetrical solid oxide cells with single-phase LSTM and LSTM-YSZ composite electrodes reveal a mixed conduction behavior in the temperature range of 700–850 °C under flowing synthetic air atmosphere. With a developed current density of 172 mA cm−2 at 850 °C and +2 V overpotential, and an electrode polarization resistance of 7.5 Ω cm2, perovskite LSTM synthesized by the presented solvent-free direct salt precursor mechanochemical synthesis is therefore proposed as a potential candidate for MIEC electrodes in symmetrical reversible solid oxide cells (r-SOCs).

High activity and stability of cobalt-free SmBa0.5Sr0.5Fe2O5+δ perovskite oxide as cathode material for solid oxide fuel cells

It is very important to develop cathode material with high stability and strong catalytic activity to realize the commercial application of solid oxide fuel cells (SOFCs). Here, we prepared a cobalt-free cathode material which partial substitution of Sr for Ba in SmBa0.5Sr0.5Fe2O5+δ (SBSF) sample and systematically investigated its electrochemical performance. Density functional theory (DFT) results showed that the oxygen vacancy formation energy of SBSF was lower than that of SmBaFe2O5+δ (SBF). The local density of state (LDOS) results showed that bandwidth center energy of SBSF between O-2p and Fe-3d obviously overlapped compared with parent SBF. The XRD spectra show that the SBSF formed a perovskite structure and had good chemical compatibility with La0.9Sr0.1Ga0.83Mg0.17O3-δ (LSGM) and CeO2-based electrolyte, respectively. At 800 °C, the polarization resistance and maximum power density of SBSF cathode on LSGM electrolyte were 0.023 Ω cm2 and 874 mWcm−2, respectively. In addition, the polarization resistance of SBSF electrode was stable during the 100 h test. The preliminary results show that SBSF oxide is a promising cathode material for SOFCs.