Solid Oxide Research Articles

Sputtered quaternary alloy coating of Fe4CoNiCu for solid oxide fuel cell steel interconnects application

A quaternary Fe4CoNiCu alloy coating is applied on SUS 430 steel substrate for solid oxide fuel cell (SOFC) interconnects application via magnetron sputtering technology. The oxidation behavior of the coated steels is investigated in air at 800 °C. During initial oxidation, Fe and Co in the alloy coating is oxidized preferentially, forming Fe-rich oxide. Ni is oxidized to NiO by inward diffusion of oxygen. Slight Cu diffuses to or near the surface of the oxide scale to form CuO. Some Cu reacts with Fe3O4 to form CuFeO2 inside the oxide scale. The alloy coating is thermally converted into a quaternary spinel coating of (Fe,Co,Ni,Cu)3O4 with a small quantity of CuO existing on the surface and a protective Cr2O3 layer is formed at the steel/coating interface. The (Fe,Co,Ni,Cu)3O4 spinel layer effectively inhibits the growth of Cr2O3 layer and the outward diffusion of Cr. The scale ASR is 13.08 mΩ cm2 at 800 °C after 1680 h oxidation.

Techno-economic evaluation and multi-objective optimization of a cogeneration system integrating solid oxide fuel cell with steam Rankine and supercritical carbon dioxide Brayton cycles

Developing highly efficient thermodynamic cycles is of great importance in the area of distributed energy system, there are still many non-negligible problems on feasibility assessment and performance evaluation in the application of some emerging technologies, especially involving the fuel cells and carbon dioxide power cycles. This study proposes a distributed heat and power cogeneration system composed of a solid oxide fuel cell, a gas turbine, a steam Rankine cycle, a supercritical carbon dioxide Brayton cycle, and a heat exchanger. The system mathematical model is constructed, and the investigation on system energy, exergy, economic, environmental, and techno-economic performance is performed to demonstrate the technology’s feasibility and applicability. The simulation results indicate that the system can provide 367.03 kW of power and 58.02 kW of heating at the design point, and the overall electrical, exergetic, and energy efficiencies are 68.38 %, 72.41 %, and 79.19 %. The total cost rate of system is achieved to be 11.62 $/h with the system carbon dioxide emission and payback period being 0.2829 kg/kWh and 10.87 year. It can be concluded from the sensitivity analysis that the increases of the compressor pressure ratio, fuel flow rate, and SOFC inlet temperature contribute to improving the system electrical efficiency, while the carbon dioxide emission and the payback period can be reduced. Finally, multi-objective optimization of the cogeneration system is further performed to provide a strategy of performance improvement for system designers and decision makers. The optimization result indicates that though the system carbon emission is increased by 0.25 %, the system payback period and levelized cost of energy are obtained to be 9.88 year and 0.2836 kg/kWh, which are decreased by 9.11 % and 1.47 % compared to the design point.

Effect of rib width on the thermo-electro-mechanical behavior of solid oxide fuel cells

In this study, a three-dimensional multi-physics coupled model is employed to investigate the effects of the rib width of the cathode-side interconnect on the flow characteristics, electrochemical performance, temperature distribution and stress distribution of solid oxide fuel cells (SOFCs) under cross-flow conditions based on a fixed gas channel-electrode interface area. The results show that as the rib width is reduced, there is a marked improvement in the uniformity of gas distribution and gas flow velocity within the channels, leading to an increase in the output power density of the SOFC stack, a reduction in the temperature gradient of the cell and a reduction in the thermal stress carried by the cell. However, if the ribs are of insufficient width, the pressure drop within the channels will be significantly increased, reducing the static pressure head of the gas and leading to a decrease in the gas flow velocity within the electrodes. This, in turn, will result in an increase in concentration polarization and higher manufacturing costs. The simulation results facilitate a more detailed comprehension of the internal reaction processes of SOFCs, thereby offering valuable guidance for the structural optimization of interconnects.

La0.3Sr0.7Ti0.3Fe0.7O3-δ derived from Malaysian ilmenite and monazite for application of solid oxide fuel cell cathode

This study investigates the effect of using low-purity oxides in synthesizing lanthanum strontium titanate ferrite (LSTF) on its electrochemical performance as a solid oxide fuel cell (SOFC) cathode material. Lanthanum oxide at 30% and 60% purity is extracted from monazite, and iron oxide at 70% and 90% purity is extracted from ilmenite as the LSTF precursor. Symmetrical pellets are fabricated from yttria-stabilized zirconia (YSZ) as the electrolyte, samarium-doped ceria (SDC) as the buffer layer, and silver paste as the current-collecting layer (CCL). Results from electrochemical impedance spectroscopy (EIS) demonstrate that LSTF made from extracted lanthanum with low purity shows comparable electrical performance with a polarity resistance (Rp) of below 0.2 Ω at operational temperature of 800 °C compared to LSTF made from commercial ingredients, while LSTF made from extracted iron shows equal performance only with high-purity ingredients. LSTF made with extracted lanthanum and iron exhibits an Rp of 0.5 Ω and does not show comparable performance with LSTF made with commercial ingredients, likely due to a high variety of impurities. Based on this study, LSTFLa30 and LSTFFe90 show high potential for SOFC cathode applications at operating temperatures in the range of 700–800 °C.

400 °C operable SOFCs based on ceria electrolyte for powering wireless sensor in internet of things

Solid oxide fuel cells (SOFCs) can generate high-efficiency and clean power but face a high-temperature bottleneck that hinders their widespread application. If alternative electrolytes can be developed to reduce the operating temperatures, the application of SOFCs will possibly be expanded to more scenarios, such as power sources for the Internet of Things (IoT). Herein, as a proof of the concept, a 400 °C operable SOFC is developed based on a precipitation-method prepared CeO2 electrolyte for powering wireless sensor in IoT system. Material studies indicate the CeO2 electrolyte sample forms a coating structure with a thin layer of amorphous carbonate covering the surface of CeO2 particles, which could result in fast hybrid proton and oxygen ion transport. The fabricated CeO2 electrolyte-based SOFCs exhibit promising power densities of 0.275–0.650 W cm−2 with open circuit voltages of 1.04–1.11 V at 400–500 °C, indicative of feasible cell operation at 400 °C. It is also found the cell has high repeatability and good stability for 150 h under different current densities. With the aid of a power management unit, the developed SOFC is further applied to charge a supercapacitor, for powering a customized IoT system to monitor environmental parameters. The charge process is fast and stable. Our study thus developed a 400 °C operable SOFC based on CeO2 electrolyte and demonstrates the feasibility of SOFC as power sources for LoT technology for the first time.

The effect of Mo and Sc dopants on the performance of an Sr2Fe2O6 cathode for use in proton-conducting solid oxide fuel cells

Sr2Fe2O6 was doped with Sc and Mo ions to investigate the effect of these dopants on the material properties and cathode performance. Both Sc and Mo were doped into Sr2Fe2O6 as pure phases, and the thermal expansion coefficient (TEC) increased with the Sc content of the material. A first-principles calculation at the atomic level indicated that Mo facilitated hydration, whereas Sc doping facilitated the formation of oxygen vacancies. Simulation results showed that the lowest energy barrier to O2 adsorption and dissociation was obtained by co-doping Sc and Mo into Sr2Fe2O6, facilitating the cathode reaction. The results of fuel cell tests indicated that co-doping with Sc and Mo resulted in higher fuel-cell performance for Sr2Fe2O6 than doping with Sc or Mo alone. An impedance analysis for Sr2Fe2O6 co-doped with Sc and Mo indicated a good balance between hydration and oxygen vacancy formation, as well as a low energy barrier to O2 adsorption and dissociation, which resulted in this material exhibiting the lowest polarization resistance among the tested cathodes. This study demonstrates that each dopant has unique advantages and disadvantages in terms of cathode properties, and it is necessary to strike a balance among the parameters involved to enhance the cathode performance.

Assessment of carbon capture and utilization in steelmaking: A case study using a hybrid fuel cell - gas turbine system

This paper investigates a carbon capture and utilization plant that converts steelmaking exhaust gases into valuable fuels. It examines the behavior of synthesis gas, identifies optimal operational parameters, and explores kinetics for methanol and ethanol production. Additionally, it examines the impact of varying H2/CO, and H2/CO2 ratios and evaluates the efficiency of a hybrid system combining a solid oxide fuel cell (SOFC) and gas turbine (GT) powered by synthesized methanol. Using the Chemical Equilibrium with Applications software, the study analyzes the dynamic behavior of synthesis gas molar fractions within the water-gas shift reactor and Fischer Tropsch reactor. Optimal operational parameters were identified at a temperature range of 200–250 °C, pressure of 4.5 MPa, H2/CO, and H2/CO2 ratios of 2.0, enabling efficient carbon conversion. Further exploration into the kinetics, alongside the commercial Cu/ZnO/Al2O3 catalyst in the Fischer Tropsch synthesis, supports methanol and ethanol production. Increased H2/CO, and H2/CO2 ratios favor methanol production with lower carbon dioxide fractions, while ethanol production and CO2 emissions decrease as these ratios rise. Finally, a case study incorporates exergoeconomic and exergoenvironmental analyses of a SOFC-GT hybrid system fuelled by methanol from Fischer Tropsch synthesis, where the combustor exhibits the lowest exergy efficiency (62.3%), while the fuel cell achieves an exergy efficiency of about 86.5%.

Enhancing solid oxide electrolysis cell cathode performance through defect and bond engineering: A study on K-doped PrBaMn2O5+δ perovskites

Collaborative design of defects and bonds is a novel strategy to enhance the activity of cathode materials for solid oxide electrolysis cells (SOECs). In this study, we report the synthesis and characterization of layered PrBaMn2O5+δ (PBM) and Pr0.9K0.1BaMn2O5+δ (PKBM) materials, aimed at developing cathodes for high-temperature H2O electrolysis. The effects of K doping on the structural, physicochemical, and electrochemical properties of these materials are thoroughly investigated. The results reveal that K doping induces lattice expansion and reduces the total cation valence state in PKBM. These changes significantly increase oxygen vacancy concentration, enhancing the chemical adsorption capacity of H2O on the electrode surface and improving the H2O reduction reaction activity. Theoretical calculations support these findings, showing that K doping lowers the oxygen vacancy formation energy and strengthens H2O adsorption. Impedance analyses further demonstrate that K doping reduces the polarization resistance, thereby enhancing surface adsorption and diffusion processes. Consequently, the PKBM cathode exhibits superior electrolysis performance, achieving a current density of 739 mA/cm2 at 1.3 V and 800 °C. This strategy provides valuable insights for designing advanced cathodes for high-temperature H2O electrolysis and other electrochemical catalysis applications.

Effect of Sr2+ doping on the structure and electrical properties of hexagonal perovskite Ba7-xSrxNb4MoO20-δ electrolyte: Experimental and DFT modeling studies

Ba7Nb4MoO20 exhibits excellent oxygen ion transport properties and is a promising electrolyte material for solid oxide fuel cell (SOFC). To further enhance its oxygen ionic conductivity, element doping is an effective strategy. However, few studies have delved into the impact mechanism of doping strategies on the electrolyte's conductivity properties from the perspective of electronic structure. Here, the enhancement mechanism of oxygen ionic conductivity in Ba7Nb4MoO20 was analyzed using the the methods of density of states (DOS) and Crystal Orbital Hamilton Populations (COHP). Since the electronic conductivities of the electrolytes are negligible, their total conductivies can essentially be regarded as the conductivies of oxygen ions. As the Sr doping amount increases, the oxygen ionic conductivities of the electrolytes also increase. The bulk conductivity shows a negative correlation with the Sr doping amount, which is due to the higher bond energy of Sr-O compared to Ba-O. On the other hand, Sr promotes grain growth and reduces the number of grain boundaries, thereby decreasing the resistance to oxygen diffusion at the grain boundaries and thus enhancing the grain boundary conductivity. In the Ba7-xSrxNb4MoO20-δ (x=0, 0.1, 0.2, 0.3, and 0.4) perovskite oxides, Ba6.6Sr0.4Nb4MoO20-δ has the highest conductivity, reaching 1.12 × 10-4S cm-1 at 500°C. This work not only develops a SOFC electrolyte material with promising application prospects, but also provides theoretical guidance for its doping modification.

Recent advances in high temperature solid oxide electrolysis cell for hydrogen production

ABSTRACT When renewable energy sources are coupled with high-temperature solid oxide electrolysis cells (SOECs) that produce hydrogen, it seems like future energy sustainability is within reach. The ability to electrolyze water to make hydrogen and then reverse the process to generate electricity in a single solid oxide cell (SOC) device is particularly attractive for renewable energy sources such as solar and wind power. The development of efficient, long-lasting, and economically viable SOEC technologies is hindered by the performance of critical materials, the stability and dependability of electrode and electrolyte materials under reversible electrolysis and fuel cell operating modes, and fuel cell operation modes. Due of their immaturity, SOEC pose both opportunities and challenges to the growing community of material scientists and system engineers studying electrochemical energy conversion and storage.

Plasma-Sprayed La0.2Sr0.8MnO3-La0.3Sr0.7TiO3 Bilayer Coatings Along with the Interface Healing Processing Applied as the High Dense Interconnector for Tubular Solid Oxide Fuel Cells

Plasma-Sprayed La0.2Sr0.8MnO3-La0.3Sr0.7TiO3 Bilayer Coatings Along with the Interface Healing Processing Applied as the High Dense Interconnector for Tubular Solid Oxide Fuel Cells

Oxidation kinetics and electrical properties of oxide scales formed under exposure to air and Ar–H2-H2O atmospheres on the Crofer 22 H ferritic steel for high-temperature applications such as interconnects in solid oxide cell stacks

A 100 h isothermal oxidation kinetics study for Crofer 22H was conducted in air and the Ar–H2-H2O gas mixture (p(H2)/p(H2O) = 94/6) in the range of 973–1123 K. The parabolic rate constant was independent of oxygen partial pressure in the range from 6.2 × 10−24 to 0.21 atm at 1023 and 1073 K, while at 973 and 1123 K it was higher in air than in Ar–H2-H2O. The scales consisted of Cr2O3 and manganese chromium spinel with an Mn:Cr ratio dependent on the oxidation conditions. Cross-scale resistance was evaluated with regards to the application of the steel in solid oxide fuel cells using a number of methods, including X-ray diffraction, scanning electron microscopy, confocal Raman imaging and area-specific resistance measurements.

Regulation of Oxide Pathway Mechanism for Sustainable Acidic Water Oxidation.

The advancement of acid-stable oxygen evolution reaction (OER) electrocatalysts is crucial for efficient hydrogen production through proton exchange membrane (PEM) water electrolysis. Unfortunately, the activity of electrocatalysts is constrained by a linear scaling relationship in the adsorbed evolution mechanism, while the lattice-oxygen-mediated mechanism undermines stability. Here, we propose a heterogeneous dual-site oxide pathway mechanism (OPM) that avoids these limitations through direct dioxygen radical coupling. A combination of Lewis acid (Cr) and Ru to form solid solution oxides (CrxRu1-xO2) promotes OH adsorption and shortens the dual-site distance, which facilitates the formation of *O radical and promotes the coupling of dioxygen radical, thereby altering the OER mechanism to a Cr-Ru dual-site OPM. The Cr0.6Ru0.4O2 catalyst demonstrates a lower overpotential than that of RuO2 and maintains stable operation for over 350 h in a PEM water electrolyzer at 300 mA cm-2. This mechanism regulation strategy paves the way for an optimal catalytic pathway, essential for large-scale green hydrogen production.

Opportunities and Challenges of Fuel Cell Electric Vehicle-to-Grid (V2G) Integration

This paper presents an overview of the status and prospects of fuel cell electric vehicles (FC-EVs) for grid integration. In recent years, renewable energy has been explored on every front to extend the use of fossil fuels. Advanced technologies involving wind and solar energy, electric vehicles, and vehicle-to-everything (V2X) are becoming more popular for grid support. With recent developments in solid oxide fuel cell electric vehicles (SOFC-EVs), a more flexible fuel option than traditional proton-exchange membrane fuel cell electric vehicles (PEMFC-EVs), the potential for vehicle-to-grid (V2G)’s implementation is promising. Specifically, SOFC-EVs can utilize renewable biofuels or natural gas and, thus, they are not limited to pure hydrogen fuel only. This opens the opportunity for V2G’s implementation by using biofuels or readily piped natural gas at home or at charging stations. This review paper will discuss current V2G technologies and, importantly, compare battery electric vehicles (BEVs) to SOFC-EVs for V2G’s implementation and their impacts.

Self‐Assembled Composite Cathodes with TEC Gradient for Proton‐Conducting Solid Oxide Fuel Cells

AbstractOne of the key challenges for high‐performance proton‐conducting solid oxide fuel cells (H‐SOFCs) is the mismatch in thermal expansion coefficients (TEC) between the cathode and electrolyte. While incorporating negative thermal expansion (NTE) materials can mitigate this issue, mechanical mixing often weakens cathode strength. To address this, a TEC gradient cathode is proposed and successfully implemented by co‐sintering PrBa(Co0.7Fe0.3)2O5‐δ(PBCF) with Y2W3O12 (YWO) in this work. In this work, Ba atoms at the A‐site of PBCF migrated from the lattice, generating A‐site defects. The resulting BaWO4 and Y10W8O21 phases, which have low TEC, are uniformly distributed between PBCF and YWO, forming a TEC gradient composite cathode. In addition, the transition phase captures the A‐site element Ba in the electrolyte layer, optimizing the electrolyte‐cathode interface. The composite cathode exhibits a reduced TEC, closely matching that of the electrolyte, significantly enhancing interface bonding, thereby providing a lower ohmic resistance of 0.051 Ω cm2 and a higher power density of 1.88 W cm−2 at 700 °C. Remarkably, thermal cycling tests conducted under temperature switching conditions demonstrate the composite cathode's long‐term thermal and chemical stability.

Parameter Identification of Solid Oxide Fuel Cell Using Elman Neural Network and Dynamic Fitness Distance Balance-Manta Ray Foraging Optimization Algorithm

An accurate solid oxide fuel cell model is a prerequisite for optimizing the operation and state estimation of subsequent cell systems. Hence, this work aimed to utilize a vigoroso algorithmic tool, i.e., Elman neural network, for data prediction to enrich cell measurement data and employ the trained network model for noise reduction of voltage–current data. Furthermore, to obtain reliable cell parameters, a novel parameter identification model based on the dynamic fitness distance balance-manta ray foraging optimization (dFDB-MRFO) algorithm is proposed. Two datasets were applied to extract the electrochemical model and simple electrochemical model parameters of the solid oxide fuel cell model. To verify adequately the superiority of this method, which is compared with another seven conventional heuristic algorithms, four performance indicators were selected as evaluation criteria. Comprehensive case studies demonstrated that through data processing, the precision and robustness of identification could be effectively heightened. In general, the model fitting data obtained via parameter identification using dFDB-MRFO have excellent fitting precision contrast with the measured voltage–current data. Notably, the fitting degree obtained by dFDB-MRFO in the simple electrochemical model reached 99.95% and 99.91% under the two datasets, respectively.

One-pot fabrication of high-entropy heterostructure cathode materials with excellent anti-poisoning properties in solid oxide fuel cells

Degradation of cathode performance in solid oxide fuel cells (SOFCs), which is poisoned by atmospheric CO2 and volatilized Cr from steel connecting plates, is a key factor limiting the long-term stable operation. In this work, high entropy heterostructure La0.5Ba0.5Fe0.2Co0.2Ni0.2Cu0.2Mn0.2O3-δ@Ba2CuO3 (HE-LBF@BCO) is designed and prepared by the one-pot method to improve the anti-poisoning ability of the electrode against CO2 and Cr. Meanwhile, the Ba2CuO3 (BCO) heterostructure formed by self-assembly using atomic size effect improves the electrochemical performance. The peak power density with HE-LBF@BCO cathode reaches 789 mW cm−2 at 800 °C with the polarization impedance of 0.34 Ω cm2. To further extend the three-phase interface and enhance oxygen catalytic activity, for HE-LBF@BCO-Gd0.1Ce0.9O2-δ(GDC) composite cathode, the peak power density reaches 789 mW cm−2 and the polarization impedance decreases to 0.16 Ω cm2 at 800 °C, exhibiting a brilliant application potential of the high entropy cathode. More importantly, HE-LBF@BCO-GDC shows an outstanding stability both in CO2 and Cr-containing atmosphere. After testing in Cr-containing atmosphere at 0.8V, the current density of the single cell with HE-LBF@BCO-GDC cathode decreases from 250.86 to 208.64 mA cm−2 at 700 °C. The results confirm the design of high-entropy heterojunction electrode materials provides a new strategy to address the enhancement of SOFC performance.

Integration of a solid oxide electrolysis system with solar thermal and electrical energy: A testing campaign for operation and control strategy definition

AbstractThe EU project PROMETEO has the scope of testing a 25 kW solid oxide electrolysis system integrated with a concentrated solar power plant via thermal energy storage in a relevant environment. Given the plant layout and the hydrogen demand characteristics, this work aims to identify how to operate the system effectively when renewable electricity is unavailable and how to modulate the load during hydrogen generation, thus defining the system's operation modes and control strategy. A 5 kWe stack has been tested at the FBK facility. The hot standby tests show that feeding a reducing gas at the negative electrode and air at the positive electrode, without polarizing the stack, effectively keeps the stack hot at 750°C and prevents degradation. Conversely, the electric protection approach leads to significant stack degradation (15% voltage drop in 200 h for one cluster). Regarding modulation of hydrogen generation, with low steam flowrates, the stack current and the flow rate of produced hydrogen mainly depend on the steam flow rate, while it is not affected by the stack temperature; conversely, with high steam flowrates, the current depends only on the stack temperature (from 25 A at 670°C to 65 A at 760°C). Based on the results, two hot standby modes and two load control strategies to be implemented and tested in the PROMETEO prototype are proposed.

In-situ dual-exsolved nanometal anchoring on heterogeneous composite nanofiber using as SOEC cathode for direct and highly efficient CO2 electrolysis

An effective strategy for CO2 electrolysis by solid oxide electrolysis cells (SOECs) is to design high-performance cathode material by interface engineering. In this work, a Ni-doped Sr0.95Ti0.3Fe0.7O3-δ/Ce0.9Gd0.1O2-δ (denoted as STFN/GDCN) nanofiber composite is directly obtained via electrospinning. Then, Ni nanoparticles are dual-exsolved by 10%H2/Ar reduction to in-situ anchor on the surface of STFN and GDCN (denoted as Ni@STFN/GDCN), which is used as SOECs cathode. This developed composite cathode not only facilitates CO2 reduction reaction (CO2RR) rate but also resists thermal aggregation and carbon deposition. The Ni@STFN/GDCN cathode operating in pure CO2 with an applied voltage of 1.6 V achieves a current density of 1.85 A cm−2, surpassing most of the advanced electrodes reports by other works. Furthermore, the CO2RR testing at a current density of 1.5 A cm−2 shows no significant voltage fluctuations during 180 h, demonstrating excellent long-term stability. Our testing results show that the in-situ dual-exsolved nanometal anchoring on heterogeneous composite nanofiber is a reliable and stable SOEC cathode for direct and highly efficient CO2 electrolysis.

Application of novel Dy0.06Gd0.02Er0.02Bi1.9O3 oxide ion electrolyte for intermediate-temperature reversible solid oxide cells

Bismuth-based oxides are promising electrolyte materials for Reversible Solid Oxide Cells (RSOCs) due to their high ion conductivity and rapid surface oxygen exchange kinetics. In this work we propose a multi-element doping strategy to obtain a novel Dy0.06Gd0.02Er0.02Bi1.9O3 (DGESB) quaternary oxide bismuth material whose ionic conductivities and crystal structure are characterized by AC impedance and X-ray diffraction technique in the temperature range from 600 to 700 °C. Along with promising structure stability and durability, our novel DGESB showed a remarkable ionic conductivity that is 65 times higher than the commercial yttria-stabilized zirconia (YSZ) electrolyte at 700 °C. With composite electrode of DGESB + LCN (LaCo0.6Ni0.4O3) and DGESB/YSZ bilayer electrolyte consisting of RSOC symmetric cell, which achieves a high peak power density (PPD) of 1.62 W/cm2 in fuel cell mode which is 2.7 times higher than that of YSZ single-layer electrolyte, while the electrolysis current density is as high as 1.66 A/cm2 at 1.3 V under H2/H2O:50/50 in electrolysis mode at the same operation temperature of 700 °C. The electrochemical performance measurements revealed a certain stable operation for 200 h in fuel cell mode. The performance degradation can be attributed to the microstructure evolution at the interface between electrolyte and electrodes. The high ionic conductive DGESB proves to be an excellent intermediate electrolyte layer for improving cell performance in RSOCs.