Solid Oxide Research Articles

Ni coarsening under humid atmosphere in the electrode of solid oxide cells: A combined study of density-functional theory and phase-field modeling

Ni coarsening in solid oxide cell (SOC) electrodes is known to be significantly faster under a humid atmosphere. The underlying mechanisms, though, have not been fully understood. In this work, we examine the surface diffusion of Ni(OH)x by a combination of density-functional theory and phase-field modeling. Density-functional theory is used to evaluate the adsorption and diffusion of the Ni(OH)x species on Ni (111) surface, and the results are used to obtain the effective surface diffusivity of Ni versus steam and hydrogen gas partial pressures. This diffusivity is used as an input for a phase-field model to investigate the Ni coarsening in SOC electrodes. It is found that Ni(OH)x formed through chemical reaction cannot accelerate coarsening unless an extremely high steam to hydrogen ratio is reached. However, if Ni(OH)x is formed through electrochemical reactions near triple phase boundaries (TPBs), surface diffusion of Ni(OH)x may cause faster Ni coarsening in fuel cell mode under a large overpotential. Specifically, surface diffusion of Ni(OH) may be comparable to or faster than that of Ni under an overpotential that is large but still possible under fuel cell operating conditions.

Fabrication framework for metal supported solid oxide cells via tape casting

Among the different solid oxide cells (SOCs) designs, metal supported SOCs (MSOCs) offer important advantages such as enhanced mechanical robustness, improved thermal resilience and lower material costs. The conventional tape casting method, which is used for the commercial multilayer ceramic technology, is also attractive for the fabrication of MSOCs due to its inherent scalability and cost-efficient fabrication methodology while offering a reliable product without compromising critical microstructural aspects and electrochemical performance during operation.This study is aimed at addressing the main challenges in the fabrication of MSOCs using tape casting, to provide a robust framework for the fabrication parameters, allowing the technology to advance to a more mature stage. It was shown that the dispersion of the powder particles and the physical and chemical characteristics of the binder are found to play a crucial role in obtaining defect free MSOCs and are discussed in detail. Different architectural designs of the cells (asymmetric and symmetric) and electrode configurations (ceramic and metal-ceramic composites) are studied, highlighting their strengths and challenges. The framework established within this work allowed to fabricate, reproduce and test MSOC that exhibited electrochemical performance comparable to state-of-the-art solid oxide cells (electrolysis current density of 0.6 A/cm2 at 1.3 V at 700oC, 50 % steam in H2 at fuel side and air at the oxygen side).

Recycling and reuse of ceramic materials from components of waste solid oxide cells (SOCs)

As one of the main waste streams of the manufacturing process of solid oxide cells (SOCs), scrap half-cells - discarded before the deposition of the barrier layer and the air electrode - imply the loss of significant quantities of ceramic composite material containing critical and hazardous elements, namely yttria-stabilized zirconia (YSZ) and NiO. These materials represent more than 90 wt% of an entire anode-supported cell. In this contribution, scrap half-cells were fragmented and subjected to three subsequent milling and sieving (below 25 μm) steps to recover composite NiO-YSZ powders with the appropriate specifications for reuse in SOC manufacturing. The overall characterization in terms of specific surface area, particle size distribution and crystalline phase retention confirmed the suitability of the recovered powders. Half-cells were manufactured including 30 wt% of recovered NiO-YSZ composite powders in their fuel electrode support, produced via tape-casting in combination with 70 wt% of virgin materials. The obtained cells were morphologically, mechanically and electrochemically tested and compared against standard cells constituted by 100 wt% of virgin materials. The electrochemical characterization highlighted 0.68 A cm−2 for the standard and recycled cells, at 600 °C and 0.7 V, while at 650 °C and same voltage both cells measured 1.12 A cm−2. This demonstrates the feasibility of recovering scrap SOCs through the presented method.

A comparative analysis of the economic feasibility of reversible hydrogen systems based on time-resolved operation optimisation

The expansion of fluctuating renewable energy production, such as wind and PV, increases the mismatch to consumption. Power-to-Hydrogen-to-Power (PtHtP) systems are believed to be a key for balancing under and overproductions. PtHtP systems can provide temporal and spatial flexibilities and among them reversible solid oxide cells (rSOC) are a promising technology. They combine production of hydrogen and power in the same electrochemical stack. This generates a financial and environmental benefit since less resources are necessary for enabling both Power-to-Hydrogen and Hydrogen-to-Power. This work investigates the application of rSOC systems in comparison to reversible PEM systems consisting of electrolysis and fuel cell unit. In the present studies time-resolved optimization is employed for simulation of the optimal operation of the PtHtP technologies in different market price conditions for electricity, hydrogen and natural gas and with coupling to industry and district heat. Both systems have a zone of market prices, that allows for a positive economic performance over lifetime. The electricity‑hydrogen price difference in this zone is in the range from −83 €/MWh to 133 €/MWh depending on the scenario. Furthermore, the electricity price fluctuations are found to have the major impact on the profitability. By studying the influence of gas grid fees, one finds that local compressed hydrogen storages can be used only for very short storage timescales up to a few hours. Finally, the derivation of application conditions, that are suitable for the two different spatial kinds of reversible hydrogen systems – spatially concentrated and delocalized and the two technologies – rSOC and PEM, is made.

Reversible solid oxide cell system with thermocline-type thermal energy storage: Numerical and techno-economic analysis

In this study, a novel system − a reversible solid oxide cell system with a thermocline-type thermal energy storage is proposed to address the limits of green hydrogen. This system utilizes a solid oxide cell, operating selectively in both fuel cell and electrolysis modes. In the fuel cell mode, the system produces electricity and an enormous amount of heat that can be stored in thermal energy storage. Conversely, heat stored in the thermal energy storage during electrolysis produces steam and facilitates the electrolysis reaction to produce hydrogen. We conducted a numerical analysis and determined a design of thermocline-type thermal energy storage at representative driving load. Three alternative setups that operated under the same conditions were compared in this study: the reversible solid oxide cell system integrated with thermal energy storage, a stand-alone reversible solid oxide cell system, and a stand-alone solid oxide electrolysis system. The results indicate that the reversible solid oxide cell system with thermal energy storage outperforms the other two setups in terms of system efficiency, water consumption reduction, and greenhouse gas emissions. The proposed system achieves a 27.5 % improvement in efficiency over the solid oxide electrolysis stand-alone system. The study indicated that the proposed system could achieve 0 kg-CO2-eq/kg-H2 of greenhouse gas emission, by replacing the natural gas burner with a thermocline-type thermal energy storage. Furthermore, a techno-economic analysis was conducted for all three systems, confirming that the proposed system can reduce a hydrogen production cost from $5.15/kg-H2 to $3.03/kg-H2.

Development of an ammonia decomposition reactor, afterburner and post-decomposition reactor for 1 kW solid oxide fuel cells using ammonia

Solid oxide fuel cells can overcome the poor flammability of ammonia by directly converting the chemical energy of ammonia into electricity. However, thermal stress by internal decomposition, nitriding at the solid oxide fuel cells stack and nitrogen oxides emissions must be considered when using ammonia in solid oxide fuel cells. In this study, an ammonia fuel processor was developed for stable operation and low emissions of solid oxide fuel cells using ammonia. The ammonia fuel processor consisting of an ammonia decomposition reactor, an afterburner and a post-decomposition reactor was tested using simulated off-gases of solid oxide fuel cells using ammonia. The ammonia conversion of the decomposition reactor varied from 32 % to 84 % with off-gas temperatures from 360 °C to 670 °C. When ammonia conversion after the solid oxide fuel cell stack was 99.70 %, nitrogen oxides emissions of the afterburner was 1.05 g/kWh, which is higher than the regulatory limit of 0.26 g/kWh. High fuel utilization and excess air ratio made nitrogen oxides emission even worse. The regulatory limit was successfully satisfied by using the post-decomposition reactor even when ammonia conversion after the solid oxide fuel cell stack was 99.10 %. The developed ammonia fuel processor could supply fuel at the optimal hydrogen-to-ammonia ratio and prevent nitrogen oxides emissions in solid oxide fuel cells using ammonia.

Numerical study of temperature distribution in tubular segmented-in-series SOFC with co-flow and counter-flow arrangements

Tubular segmented-in-series solid oxide fuel cells (SIS–SOFCs) are great for industry because they work more efficiently. Temperature uniformity directly affects thermal stress and material degradation. In this study, the coupling effect of electrochemical reaction and mass, momentum, and heat transfer within a 10-cell in-series SOFC are characterized using the finite element method. The temperature distribution under co-flow and counter-flow arrangements is analyzed. The results show that the maximum temperature difference under the co-flow arrangement is 12% smaller than that under the counter-flow arrangement. This reduction is primarily attributed to enhanced convective heat transfer on the fuel side at the location of maximum temperature within the SIS–SOFC. As fuel utilization increases, the maximum temperature difference between the co-flow and counter-flow arrangements gradually decreases from 7 °C at the fuel utilization of 50% to 3 °C at the fuel utilization of 80%. Meanwhile, temperature non-uniformity in the 10-cell series region of the SIS–SOFC increases gradually under the co-flow arrangement while remaining relatively unchanged under the counter-flow arrangement.

Applying high efficiency internal reforming catalyst for direct low concentration coal mine methane solid oxide fuel cells

Solid oxide fuel cells (SOFCs) are green and efficient power generation devices, which can efficiently utilize the abundant low concentration coal mine methane (LC-CMM), and play an important role in energy saving and emission reduction. However, there are still challenges need to be addressed, such as low conversion efficiency and deposit carbon. In this work, a Sr2Fe1.4Ni0.1Mo0.5O6-δ-Gd0.1Ce0.9O2-δ (SFNM-GDC) internal reforming catalyst is prepared, generating abundant oxygen vacancies with in situ precipitates Fe–Ni alloys in the reducing atmosphere, leading to improved methane reforming efficiency and carbon deposition resistance. The results show that the cell exhibits excellent electrochemical performance with the internal reforming catalyst, with the maximum power density (Pmax) of 1212 mW cm−2 and 980 mW cm−2 at 800 °C with H2 and LC-CMM, respectively, corresponding to polarization impedances of 0.16 Ω cm2 and 0.47 Ω cm2. More importantly, the single cell combining SFNM-GDC reformed layer can maintain stable performance for 100 h at 700 °C under the atmosphere of LC-CMM. These results highlight that the reformed layer enhances CH4 reforming, optimizes electrochemistry and increases resistance to carbon deposition.

Durability and kinetic effects of CO2-rich oxidizing streams on LSCF-based solid oxide fuel cells

In the SOS–CO2 cycle, a novel hybrid cycle for blue power production, the solid oxide fuel cell's (SOFC) cathode is supplied with a CO2-rich oxidizing stream (e.g., 21 % O2 79 % CO2 vol.). The durability of state-of-the-art anode-supported SOFCs (25 cm2, SolydEra) with LSCF-GDC/LSC (La0.6Sr0.4Co0.2Fe0.8O3-δ-Gd0.1Ce0.9O3+δ/La0.6Sr0.4CoO3+δ) cathodes was tested at atmospheric pressure for 1090 h with 7 % humidified H2 and reformate, at 700 °C and 0.85 V. The SOFC performance was investigated with periodic I/V curves and electrochemical impedance spectroscopy (EIS) measurements. The results highlighted a 24 % power density loss when air was replaced with the O2/CO2 mixture (672 mW/cm2 in air vs. 508 mW/cm2 in O2/CO2 with humidified H2). A stable power output was observed, and complete reversibility was found when the air supply was restored. A distribution of relaxation times (DRT) analysis of the EIS spectra allowed to extract an anodic rate equation for the hydrogen oxidation reaction (HOR) and evaluate the frequency region affected by cathodic CO2. The kinetic effect of CO2 was also studied via EIS on symmetric button cells at varying O2 and CO2 amounts, and a power-law rate equation was derived. The results verify the feasibility of the SOS–CO2 cycle feed conditions at 700 °C and atmospheric pressure.

Optimal energy management based on real-time performance analysis for the solid oxide fuel cell-combined heat and power system

In order to realize the efficient and stable operation of the solid oxide fuel cell (SOFC)-combined heat and power (CHP) system in the typical applied scenario, three different energy management schemes are proposed in this study. First, a coupled calculation model of the solid oxide fuel cell-gas turbine-combined heat and power (SOFC-GT-CHP) system with a rated power of 30 kW for the SOFC stack is constructed. The inlet temperature and inlet pressure of the SOFC stack are optimized. The recommended design for the proposed system is thence obtained. Second, three operation schemes of SOFC-GT-CHP are proposed. They consist of the operation scheme of single-stack, multi-stack and optimal operation scheme coupled with vanadium redox flow battery (VRB). Finally, four types of typical applied scenarios in North China are selected. The real-time performance of the SOFC-GT-CHP system when applying three different operation schemes is obtained and comparatively analyzed. The results are presented as follows. First, the SOFC-GT-CHP system achieves a rated power of 44.50 kW and a rated system efficiency of 47.20 % when the inlet temperature and pressure of the stack are preferably 505 °C and 709.1 kPa. Second, the application of the multi-stack SOFC-GT-CHP system has the advantage of high efficiency in the low-load operation domain. With a net output power at 20 kW, the time average efficiency of SOFC-GT-CHP is increased from 38.37 % to 46.96 %. Finally, the SOFC-GT-CHP system achieves the highest time average generation efficiency of 46.13 % in the hotel applied scenario when applying the optimal operation scheme coupled with VRB. This meets the practical operation requirement of the SOFC stack. The reduction of the net output power range of SOFC-GT-CHP is 67.87 %. It shows that the optimal operation scheme is efficient and stable. The study can provide a reference for the energy management of the SOFC-GT-CHP system in typical applied scenarios.

Reinforced chemical adsorption ability for efficient CO2 electrolysis in solid oxide electrolysis cell via a dual-exsolution strategy

Accelerating sluggish kinetics of CO2 reduction reaction (CO2RR) is of great importance for efficiently converting CO2 into valuable chemical products in solid oxide electrolysis cells (SOECs). Here, a novel dual-exsolution strategy is proposed to enhance CO2 electrolysis properties of La0.4Sr0.6Co0.2Fe0.7Nb0.1O3-δ (LSCFN) cathode. With simultaneously exsolved CoFe alloy and Bi nanoparticles on LSCFN cathodic matrix, the as-prepared SOEC delivers a high current density of 539 mA cm−2 for CO2 electrolysis at 800 °C and 1.5 V, and successfully runs over 170 h without any attenuation. The introduction of Bi exsolution not only promotes CoFe exsolution, provides additional oxygen vacancies, but also greatly boost the kinetics of CO2 adsorption/dissociation/activation. This work offers new insights into tailoring perovskite electrocatalysts for the CO2 electrolysis via dual-exsolution strategy.

Thermodynamic performance analysis of direct methanol solid oxide fuel cell hybrid power system for ship application

Methanol is a fuel that can be directly supplied to solid oxide fuel cell (SOFC) without carbon deposition. This paper introduces the direct methanol SOFC-Internal combustion engine (ICE) hybrid power and SOFC-Gas turbine (GT) hybrid power systems. Thermodynamic performance analysis of the hybrid power systems and an investigation into the impact of various parameters were conducted. The results indicate that the electric efficiency of the SOFC-ICE system is 56.07 %, which is 3 percentage points higher than the SOFC-GT system but 3–4 percentage points lower than the SOFC-ICE system with pre-reforming. Increasing fuel utilization rate, operation temperature, and excess air ratio is beneficial to the performance of the SOFC, and raising current density helps improve the system's power density. Load-sharing strategy research demonstrates that in a scenario where the power ratio between SOFC and the ICE is 35:65, compared to a methanol engine, the efficiency of the SOFC-ICE hybrid power system increases by 4.3 %. Despite a 1.4-fold increase in weight and a 1.66-fold increase in cost, the fuel consumption rate and carbon emissions decrease by 8.8 %. Therefore, the strategy of combining a high-power engine with a low-power SOFC is currently a suitable load-sharing strategy for ship applications.

Investigation of a solid oxide fuel cell integrated into an internal combustion engine with carbon capture for maritime applications

The significance of limiting greenhouse gas emissions has grown in the maritime sector and regulations in this regard have become increasingly stringent. This leads to the need for new and more environmentally friendly power sources, and technologies to be used in ships. Fuel cells and carbon capture systems can enable ships to both meet the International Maritime Organization’s emissions regulations and contribute to a sustainable environment by reducing greenhouse gas emissions. In this study, the solid oxide fuel cell is electrochemically, and thermodynamically modeled and integrated into the internal combustion engine for maritime applications. Reformed natural gas is used as fuel, so the steam reforming and the carbon capture and storage systems are also integrated into the solid oxide fuel cell and internal combustion engine power system. Integrated systems are simulated and energy, exergy, economy, and environmental analyses are carried out. The effects of solid oxide fuel cell operating temperature, current density, operating time due to degradation, and the use of hydrogen instead of natural gas on analyses results are investigated. The findings obtained in this study showed that the proposed integration could reduce carbon dioxide emissions by 76.1 per cent, while the hydrogen-fuelled alternative system could reduce carbon dioxide emissions by 96.9 per cent at an operating lifetime of 35,000 h for the solid oxide fuel cell. Given the fuel cell degradation, the average overall energy efficiencies of the systems were 44.1 per cent and 57.5 per cent, respectively, while the cost of the proposed system was 41.1 per cent lower than the hydrogen-fuelled alternative. Hydrogen-fueled alternative system was closer to the net zero target in emission and had higher efficiencies, the proposed system might be a more effective solution in the transition to the net zero target because of its lower volume and mass requirements and lower costs.

Revealing the catalytic ability of 5%Rh–5%Pt–5%Al2O3–85%CeO2 for CH4-based mixing fuel gases operating at 550 °C

With the work temperature of solid oxide fuel cells (SOFCs) lower to 400–600 °C, the use of CH4-based fuel gas needs to be pre-reformed into synthesis gas (H2 and CO) to mitigate anode carbon deposition. Although lots of catalysts have been widely studied for methane conversion, the development of low temperatures (below 550 °C) catalyst for efficient methane reforming reactions remains a challenge. Here, we proposed a nanosize 5%Rh–5%Pt–5%Al2O3–85%CeO2 composite catalyst (RPAC-550), which demonstrates excellent reforming reactions for CH4-based mixing fuel gases operating at 550 °C. In this work, the reforming process of RPAC-550 catalyst for dry CH4, CH4/H2O and CH4/CO2/H2O atmospheres in different ratios and operating at 550 °C were systematically studied. Then the obtained reforming gases and carbon deposition were studied thoroughly to get the optimum ratio of mixed fuel gases for SOFCs. At last, the designed RPAC-550 catalyst achieves a CH4 conversion rate as high as 60% with water-methane ratio in 0.6. Herein, the ratio of H2 and CO as reforming gases can be controlled precisely by adjusting the intake amount of oxidant CO2 and H2O into CH4, which is beneficial for customizing fuel gases. In addition, the RPAC-550 catalyst exhibits remarkable catalytic stability and anti-coking ability under 600 h continue test. This work provides new insights for the rational design of efficient catalysts to reform methane-based fuel gas at 550 °C.

Dual doped fluorite oxide enabling enhanced performance for low-temperature ceramic fuel cells

Ceria-based electrolyte materials are of great interest for solid oxide fuel cell applications because they exhibit low ohmic resistance and high ionic conductivity, especially at a low temperature of 550oC. Consequently, we have designed a very interesting electrolyte Al and Nd dual-doped SDC (Sm0.1Ce0.9O2) using the sol–gel technique to function as an electrolyte for LT–CFCs (low-temperature ceramic fuel cells). The AN–SDC (Al0.15N0.15-Sm0.1Ce0.6O2) as an electrolyte shows a maximum power output of 1085 mW/cm2 with a high ionic conductivity of 0.22 S/cm at 550oC. This high performance is mainly because of the co-doping into SDC, which facilitates many oxygen vacancies, enabling faster stabilized ion transportation through the AN–SDC lattice. The low resistance of either the ohmic and grain boundary resistance + the microstructure features of AN–SDC contribute to achieving higher fuel cell performance. In addition, dual doping into SDC might build a synergistic effect, which further improves devices’ performance. The ionic conduction mechanism has been explained based on the dual doping of the incorporation of Al and Nd into the SDC. Dual doping is a promising, feasible avenue for designing electrolytes to enhance the performance of LT–CFC devices.

A new bi-directional surface modification cathode based on conventional cathode La0.6Sr0.4Co0.2Fe0.8O3-δ

The commercialization of proton solid oxide fuel cells (H-SOFCs) is hindered by the lack of high active and durable cathode materials exposed to evil operation conditions. Here, this groundbreaking study addresses two critical challenges impeding the practicality of La0.6Sr0·4Co0·2Fe0·8O3-δ (LSCF), one of the most popular proton-conducting cathode materials contemporarily: inadequate temperature activity and durability issues stemming from surface Sr segregation. The research introduces a transformative solution through the creation of a novel nanofiber cathode, denoted as PrBaCo1.4Fe0·6O6-δ@LSCF, comprising a nanoscale LSCF FP host and PBCF NP guest. Advanced electron microscopy and scanning electron microscopy techniques confirm the seamless integration of the two phases, highlighting a distinctive fiber structure adorned with impregnated nanoparticles. Meanwhile, efficiently reducing oxygen vacancies within the LSCF bulk phase significantly suppresses Sr segregation. Systematic simulations based on density functional theory reveal that the incorporation of PSCF reduces the polarization energy barrier. In practical terms, electrochemical testing of a single cell supported by PBCF@LSCF shows a polarization resistance of only 0.053 Ω cm2 at 700 °C, translating to a remarkable fifty percent reduction. Furthermore, a sustained 100-h test reveals no notable decline in performance. Consequently, a novel dual modification approach is proposed for crafting cathodes tailored for SOFCs.

Enriching Nano-Heterointerfaces in Proton Conducting TiO2-SrTiO3@TiO2 Yolk-Shell Electrolyte for Low-Temperature Solid Oxide Fuel Cells.

A challenging task in solid oxide fuel cells (SOFCs) is seeking for an alternative electrolyte, enabling high ionic conduction at relatively low operating temperatures, i.e., 300-600°C. Proton-conducting candidates, in particular, hold a significant promise due to their low transport activation energy to deliver protons. Here, a unique hierarchical TiO2-SrTiO3@TiO2 structure is developed inside an intercalated TiO2-SrTiO3 core as "yolk" decorating densely packed flake TiO2 as shell, creating plentiful nano-heterointerfaces with a continuous TiO2 and SrTiO3 "in-house" interfaces, as well the interfaces between TiO2-SrTiO3 yolk and TiO2 shell. It exhibits a reduced activation energy, down to 0.225eV, and an unexpectedly high proton conductivity at low temperature, e.g., 0.084 S cm-1 at 550°C, confirmed by experimentally H/D isotope method and proton-filtrating membrane measurement. Raman mapping technique identifies the presence of hydrogenated HO─Sr bonds, providing further evidence for proton conduction. And its interfacial conduction is comparatively analyzed with a directly-mixing TiO2-SrTiO3 composite electrolyte. Consequently, a single fuel cell based on the TiO2-SrTiO3@TiO2 heterogeneous electrolyte delivers a good peak power density of 799.7mW cm-2 at 550°C. These findings highlight a dexterous nano-heterointerface design strategy of highly proton-conductive electrolytes at reduced operating temperatures for SOFC technology.

Unravelling the oxidation behaviors of porous stainless steel 430L substrate for metal-supported solid oxide fuel cells

Metal-supported solid oxide fuel cell (MS-SOFC) has been attracting increasing attention due to relatively low materials cost and robust mechanic strength particularly for mobile applications. However, long term stability has been an issue for its application. It is challenging to isolate the degradation behavior and predict maximum lifetime of the metal substrate when assembled as full cell since many parameters may affect cell performance and life expectancy. We systematically investigated and reported the long-term oxidation behavior of porous stainless steel 430 L for up to 1500 h at 800°C under dry and 3 vol% H2O humidified H2/Ar mixture (10 vol% H2) atmosphere to simulate its applications in MS-SOFC. Our results show that the surface oxide scale of the porous 430Lsubstrate in both atmospheres are dominated by Cr2O3 and small amounts of MnCr2O4 or FeCr2O4 spinel oxides depending on the gas conditions, where the oxidation process could be divided into three stages with distinct characteristics. Stepwise surface color change, morphology and thickness of the formed oxide scale, elemental migration and distribution along the bulk alloy/oxide scale interface, and oxidation kinetics as a function of exposure time are systematically and thoroughly studied at high resolution. Based on the measured weight gains and thicknesses, oxidation kinetic parameters are extracted. These kinetic parameters are not only valuable for understanding the oxidation rate of porous 430 L in high temperature applications such as in MS-SOFC, but also can be used to predict the life expectancy of 430 L supported SOFC device which is critical for real and long-term applications.

Optical and electrical conductivity of secondary phase of Sr2+/Ca2+ doped La1-xSrx/CaxNbO4 (0≤x≤0.4)

In the present study, Sr2+ and Ca2+ ions doped lanthanum niobate (LaNbO4) samples are synthesized using the solid-state reaction method. The effect of sintering temperature on physical, optical and electrical properties are investigated of the pristine and Sr2+/Ca2+ doped LaNbO4 samples using by characterization facilities such as X-ray diffraction, Fourier transform-infrared spectroscopy, thermal gravimetric analysis, scanning electron microscopy & energy-dispersive spectroscopy, UV–Vis spectrophotometer. The observed monoclinic phase is confirmed by XRD. The optical bandgap of LNS samples (3.11 eV–2.08 eV) and LNC samples (2.95 eV–2.86 eV) are calculated. The electrical conductivity of the Sr2+/Ca2+ doped LaNbO4 samples are evaluated by using and Impedance analyzer from ambient temperature to 900 °C, where, the highest conductivity (1.01 × 10−1 Scm−1 at 900 °C) is observed for LNS-4 with 80 % relative density due to presence of higher oxygen vacancies. It is observed that the Sr2+ doping is more effective than Ca2+ doping for enhancing the protonic conductivity of the LaNbO4 system. The doping of Sr2+ and Ca2+ ions is indicated that Sr2+ based polymorphic composites could be more effective electrolytes for solid oxide fuel cell (SOFCs) applications.

Three-Dimensional-Printed Composite Structures: The Effect of LSCF Slurry Solid Loading, Binder, and Direct-Write Process Parameters.

In this research, a direct-write 3D-printing method was utilized for the fabrication of inter-digitized solid oxide fuel cells (SOFCs) using ceramic materials. The cathode electrode was fabricated using the LSCF (La0.6Sr0.2Fe0.8Co0.2O3-δ) slurry loading and the Polyvinyl butyral (PVB) binder. The rheological parameters of slurries with varying LSCF slurry loading and PVB binder concentration were evaluated to determine their effect on the cathode trace performance in terms of microstructure, size, and resistance. Additionally, the dimensional shrinkage of LSCF lines after sintering was investigated to realize their influence on cathode line width and height. Moreover, the effect of the direct-write process parameters such as pressure, distance between the nozzle and substrate, and speed on the cathode line dimensions and resistance was evaluated. LSCF slurry with 50% solid loading, 12% binder, and 0.2% dispersant concentration was determined to be the optimal value for the fabrication of SOFCs using the direct-write method. The direct-write process parameters, in addition to the binder and LSCF slurry concentration ratios, had a considerable impact on the microstructure of cathode lines. Based on ANOVA findings, pressure and distance had significant effects on the cathode electrode resistance. An increase in the distance between the nozzle and substrate, speed, or extrusion pressure of the direct writing process increased the resistance of the cathode lines. These findings add to the ongoing effort to refine SOFC fabrication techniques, opening the avenues for advanced performance and efficiency of SOFCs in energy applications.