Stable solid oxide electrolysis cells with SSF-based symmetrical electrode for direct high-temperature steam electrolysis

Technology readiness levels (TRLs) of electrolysis systems have dramatically increased in recent years as the interest in clean hydrogen production and decarbonization of transportation, industrial and other sectors increases across the globe. This is especially true of high temperature steam electrolysis (HTSE) / solid oxide electrolysis cell (SOEC) systems which show promise of much higher system efficiencies than other more developed electrolysis technologies. This possibility of higher efficiencies of HTSE / SOEC systems has been previously assumed to be theoretically possible but in recent years it has become less theoretical and more realistic as an increasing amount of suppliers complete lab and pilot tests showing very promising results. Research in the areas of manufacturing techniques, material selection, electrode and electrolyte compositions, and balance of plant size and integration continues at a fast pace as an increasing number of suppliers both internationally and domestically become involved. The advantages of HTSE become more pronounced when HTSE is coupled with nuclear power plants (NPPs). This is because thermal energy produced by the nuclear reactor can be used in a series of heat transfer loops and heat exchangers to vaporize HTSE feedwater, which drastically improves the economics of the process. Idaho National Laboratory (INL) has been very involved in the research and modeling of HTSE systems for a number of years, in collaboration with other national laboratories, academia, and industry stakeholders both on the hydrogen production as well as the hydrogen demand side. The modeling completed over the years on a large variety of projects has led to a wealth of knowledge at INL including in the area of the technoeconomic assessment (TEA) of HTSE systems. TEAs include process modeling of the HTSE systems to calculate system energy requirements and equipment sizing, followed by estimation of capital and operating costs to enable calculation of the levelized cost of hydrogen (LCOH). The TEA work performed has produced incremental improvements and tuning of the methods, assumptions, models, and results of the analyses as well as providing some opportunities for validating these results. The purpose of this document is to record the current baseline HTSE analyses led by INL to show the current status of assumptions and costs of these systems. Given the rapid development of this technology, the variety of suppliers entering the space, and the increasing attention government and industry are giving to such systems, this document may be updated on a periodic basis with updated analysis and assumptions. This document compiles various analyses results and approaches completed over a period of years into a single document to be used as a baseline going forward. It represents what the INL HTSE analysis group assumes to be the internal best estimate of the current operation, costs, and landscape of the HTSE industry state of the art capability for current SOEC technology in an Nth-of-a-Kind (NOAK) plant, which in this study is defined as existence of the manufacturing capacity to support previous deployment of N = 100 count of 25 MWe modular HTSE blocks (with modular equipment component cost reductions specified as following a 95% learning curve). That said, Tthis is a public document and as such so no proprietary data was used or included in this report. There may be HTSE suppliers that have performance specifications, and cost estimates, and test data that differ from the analysisose presented in this document. This document is meant to be a best conservative estimate of the technology and not an absolute reference.

Due to the random fluctuations in power experienced by high-temperature green electric hydrogen production systems, further deterioration of spatial distribution characteristics such as temperature, voltage/current, and material concentration inside the solid oxide electrolysis cell (SOEC) stack may occur. This has a negative impact on the system’s flexibility and the corresponding control capabilities. In this paper, based on the SOEC electrolytic cell model, a comprehensive optimization method using an adaptive incremental Kriging surrogate model is proposed. The reliability of this method is verified by accurately analyzing the dynamic performance of the SOEC and the spatial characteristics of various physical quantities. Additionally, a thermal dynamic analysis is performed on the SOEC, and an adaptive time-varying LPV-MPC optimization control method is established to ensure the temperature stability of the electrolysis cell stack, aiming to maintain a stable, efficient, and sustainable SOEC operation. The simulation analysis of SOEC hydrogen production adopting a variable load operation has demonstrated the advantages of this method over conventional PID control in stabilizing the temperature of the stack. It allows for a rapid adjustment in the electrolysis voltage and current and improves electrolysis efficiency. The results highlighted that the increase in the electrolysis load increases the current density, while the water vapor, electrolysis voltage, and H2 flow rate significantly decrease. Finally, the SOEC electrolytic hydrogen production module is introduced for optimization scheduling of energy consumption in Xinjiang, China. The findings not only confirmed that the SOEC can transition to the current load operating point at each scheduling period but also demonstrated higher effectiveness in stabilizing the stack temperature and improving electrolysis efficiency.

High-temperature electrolysis of water steam is a promising approach for hydrogen production. The potential is even more promising when abundant heat source from nuclear power reactors can be efficiently utilized. Hydrogen production through the above approach also allows for low electric consumption. Overall energy conversion efficiencies for high temperature electrolysis are in the 45-50% range compared to ~30% for the conventional electrolysis. Under such motivation, this research is focused on increasing the operation time and high temperature stability of solid oxide electrolyzer cells (SOEC) for splitting water into hydrogen. Specifically, our focus is to improve the SOEC seal thermal stability and performances by alleviating thermal stress and seal cracking issues.

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B-site doped, A-site deficient perovskite oxide titanates with formula La0.4Sr0.4Mn+xTi1−xO3−γ−δ (M = Fe3+ or Ni2+; x = 0.06; γ = (4 − n)x/2) were employed as solid oxide electrolysis cell (SOEC) cathodes for hydrogen production via high temperature steam electrolysis at 900 °C. A-site deficiency provided additional driving force for the exsolution of a proportion of B-site dopants at the surface in the form of metallic nanoparticles under reducing SOEC cathode operating conditions. In the case of La0.4Sr0.4Fe0.06Ti0.94O2.97, this represents the first time that Fe0 has been exsolved from a perovskite in such a way. Exsolution was due in part to the inability of the host lattice to accommodate vacancies (introduced (δ) oxygen vacancies () and fixed A-site () and inherent (γ) oxygen vacancies) beyond a certain limit. The presence of electrocatalytically active Fe0 or Ni0 nanoparticles and higher concentrations dramatically lowered the activation barrier to steam electrolysis compared to the parent material (x = 0). The use of defect chemistry to drive the exsolution of less reducible dopant cations could conceivably be extended to produce new catalytically active perovskites with unique properties.

An ongoing project at Idaho National Laboratory involves generating hydrogen from steam using solid oxide electrolysis cells (SOEC). This report describes background information about SOECs, the Integrated Laboratory Scale (ILS) testing of solid-oxide electrolysis stacks, ILS performance degradation, and post-test examination of SOECs by various researchers. The ILS test was a 720- cell, three-module test comprised of 12 stacks of 60 cells each. A peak H2 production rate of 5.7 Nm3/hr was achieved. Initially, the module area-specific resistance ranged from 1.25 Ocm2 to just over 2 Ocm2. Total H2 production rate decreased from 5.7 Nm3/hr to a steady state value of 0.7 Nm3/hr. The decrease was primarily due to cell degradation. Post test examination by Ceramatec showed that the hydrogen electrode appeared to be in good condition. The oxygen evolution electrode does show delamination in operation and an apparent foreign layer deposited at the electrolyte interface. Post test examination by Argonne National Laboratory showed that the O2-electrode delaminated from the electrolyte near the edge. One possible reason for this delamination is excessive pressure buildup with high O2 flow in the over-sintered region. According to post test examination at the Massachusetts Institute of Technology, the electrochemical reactions have been recognized as one of the prevalent causes of their degradation. Specifically, two important degradation mechanisms were examined: (1) transport of Crcontaining species from steel interconnects into the oxygen electrode and LSC bond layers in SOECs, and (2) cation segregation and phase separation in the bond layer. INL conducted a workshop October 27, 2008 to discuss possible causes of degradation in a SOEC stack. Generally, it was agreed that the following are major degradation issues relating to SOECs: • Delamination of the O2-electrode and bond layer on the steam/O2-electrode side • Contaminants (Ni, Cr, Si, etc.) on reaction sites (triple phase boundary) • Loss of electrical/ionic conductivity of electrolyte.

Electrolyte degradation in anode supported microtubular yttria stabilized zirconia-based solid oxide steam electrolysis cells at high voltages of operation

Through the carbon combustion process, the oxygen produced by solid oxide electrolysis cell (SOEC) in the purging gas can be consumed. And the purging gas with low oxygen partial pressure can be recycled into the anode of SOEC, which achieves ultra-low power consumption for hydrogen production. In this study, the I-V curve of steam electrolysis in SOEC with CO2 anode gas is analyzed and discussed. The results show that the cell voltage for hydrogen production can be reduced to 0.62 V at 400 mA/cm2 under CO2 atmosphere. A combined process coupled with carbon fuel combustion and SOEC hydrogen production is proposed. By comparing three different processes of single SOEC, SOEC with heat supply directly by combustion and SOEC coupled with combustion, the advantages of SOEC hydrogen production coupled with carbon fuel combustion are analyzed. The results show that the ultra-low power consumption of SOEC can be achieved by matching the anode circulating gas flow rate, carbon fuel usage and external oxygen amount. When considering the energy efficiency of electricity to hydrogen, carbon fuel combustion can significantly reduce the electrolysis voltage and improve the energy efficiency of the system, but it will lead to an increase in the amount of anode circulating gas.

A composite cathode based on scandium-doped chromate for direct high-temperature steam electrolysis in a symmetric solid oxide electrolyzer

High temperature electrolysis is a promising option for carbon-free hydrogen production and huge energy storage with high energy conversion efficiencies from renewable and nuclear resources. Over the past few decades, yttria-stabilized zirconia (YSZ) based ion conductor has been widely used as a solid electrolyte in solid oxide electrolysis cells (SOECs). However, its high operation temperature and lower conductivity in the appropriate temperature range for solid electrochemical devices were major drawbacks. Regarding improving ionic-conducting electrolytes, several groups have contributed significantly to developing and applying LaGaO3 based perovskite as a superior ionic conductor. La(Sr)Ga(Mg)O3 (LSGM) electrolyte was successfully validated for intermediate-temperature solid oxide fuel cells (SOFCs) but was rarely conducted on SOECs for its high efficient electrolysis performance. Their lower mechanical strengths or higher reactivity with electrode compared with the YSZ electrolysis cells, which make it difficult to choose compatible materials, remain major challenges. In this field, SOECs have attracted a great attention in the last few years, as they offer significant power and higher efficiencies compared to conventional YSZ based electrolysers. Herein, SOECs using LSGM based electrolyte, their applications, high performance, and their issues will be reviewed.

To support the development of hydrogen production by high temperature electrolysis using solid oxide electrolysis cells (SOECs), the effects of operating conditions on the performance of the SOECs were investigated using a one‐dimensional model of a cathode‐supported planar SOEC stack. Among all the operating parameters, temperature is the most influential factor on the performance of an SOEC, in terms of both cell voltage and operation mode (i.e. endothermic, thermoneutral and exothermic). Current density is another influential factor, in terms of both cell voltage and operation mode. For the conditions used in this study it is recommended that the SOEC be operated at 1,073 K and with an average current density of 10,000 A m–2, as this results in the stack operating at almost constant temperature along the cell length. Both the steam molar fraction at the inlet and the steam utilisation factor have little influence on the cell voltage of the SOEC but their influence on the temperature distribution cannot be neglected. Changes in the operating parameters of the SOEC can result in a transition between endothermic and exothermic operation modes, calling for careful temperature control. The introduction of air into the anode stream appears to be a promising approach to ensure small temperature variations along the cell.

Complementary techniques for solid oxide electrolysis cell characterisation at the micro- and nano-scale

In order to address the issue of the anthropogenic greenhouse effect, the supply with renewable energy will play a major role in the future energy systems. A particularly promising approach to store or even use renewable energy in sectors where electricity cannot be used effectively yet (for example in aviation) are synthetic fuels. Within the synthetic fuel generation process, known as Power-to-X, syngas (H2+CO) can be synthesized into liquid hydrocarbons, such as gasoline or jet fuel, via the Fischer-Tropsch process. In comparison with alternative processes, such as a steam electrolyzer in combination with a reverse water gas shift reactor, solid oxide electrolysis cells (SOEC) offer great potential for producing the required syngas in a single, less complex, and more efficient step within Power-to-X utilizing only steam (H2O), carbon dioxide (CO2), and electricity from renewable sources.This so-called co-electrolysis, which involves the simultaneous reduction of H2O and CO2 in SOECs, is of particular importance. It enables direct and efficient syngas production with a tailored H2/CO ratio, thereby reducing the need for additional downstream processing steps. This integrated approach enhances overall system efficiency, minimizes energy losses, and supports carbon utilization efforts, making it a crucial technology for sustainable fuel and chemical production. However, different syngas applications and associated SOE operating conditions can cause performance deterioration of SOECs. Consequently, a comprehensive understanding of losses incurred by diverse inlet mixtures, in conjunction with other operational conditions, such as temperature or the total flow rate, during electrolysis is essential.To the best of the authors’ knowledge, there is currently a lack of literature on operating cells with CO at the inlet, especially in CO2-electrolysis, where H2 is often added to avoid oxidation of Nickel in the fuel electrode. In order to investigate the influence of different gas components (H2O, H2, CO2, CO) of inlet compositions on performance and losses of SOECs, a series of experiments was performed on a commercial fuel electrode-supported cell with an active area of 81 cm2. To maintain a total flow rate of 2.2 slpm nitrogen was added, and the amount of H2O, H2, CO2, CO was varied, depending on the desired mixture. It is noteworthy that the air flow rate applied to the air electrode remained constant at 2.2 slpm throughout the experimental series. Initially, H2O electrolysis was conducted as a reference, followed by various mixtures for co-electrolysis and CO2 electrolysis, each with distinct H2O/CO2-, H2/CO-, and product/reactant-ratios. In the final experiment, pure CO2 was utilized as the feedstock for CO2-electrolysis, aiming to determine the losses in electrolysis in the absence of product species (CO).During the experiments polarization curves and electrochemical impedance spectroscopy (EIS) in 50 mA/cm2 steps were used for characterizing the performance of the cell at current densities up to 350 mA/cm2. The monitoring of the temperature distribution over the active area was realized through thermocouples integrated in the cell-housing near the gas flow channels on both the anode and cathode side. This approach enables further analysis of the reaction mechanism over the cell area, correlation of impedance data with thermal effects, and detection of hotspots. The outlet gas composition was monitored via a gas analyzer to determine the dry composition.This study investigates the impact of gas components at the inlet in co- and CO2-electrolysis on the performance of fuel electrode-supported SOECs, emphasizing losses in specific operating conditions. Furthermore, it offers a distinctive perspective on CO2 electrolysis with pure CO2 in an industrially sized cell, emphasizing substantial losses with no products at the inlet. The results show that the resistance in co-electrolysis is close to H2O-electolysis and way lower than in CO2-electrolysis which indicates that the main electrochemical reaction is the H2O-electolysis and CO2 is mostly converted to CO via the reverse water gas shift reaction. Figure 1

High‐temperature electrolysis (HTE) using solid oxide electrolysis cells (SOECs) is a promising hydrogen production technology and has attracted substantial research attention over the last decade. While most studies are conducted on hydrogen electrode‐supported type cells, SOEC operation using metal‐supported cells has received minimal attention. The development of metal‐supported SOECs with performance similar to the best conventional SOECs is reported. These cells have stainless steel supports on both sides, 10Sc1CeSZ electrolyte and electrode backbones, and nano‐structured catalysts infiltrated on both hydrogen and oxygen electrode sides. Samarium‐doped ceria (SDC) mixed with Ni is infiltrated as a hydrogen electrode catalyst, and the effect of ceria:Ni ratio is studied. On the oxygen electrode side, catalysts including lanthanum strontium manganite (LSM), lanthanum strontium cobalt ferrite (LSCF), praseodymium oxide (Pr6O11), and their composite catalysts with SDC (i.e., LSM‐SDC, LSCF‐SDC, and Pr6O11‐SDC) are compared. Using the materials with highest catalytic activity (Pr6O11‐SDC and SDC40‐Ni60) and optimizing the catalyst infiltration processes, excellent electrolysis performance of metal‐supported cells is achieved. Current densities of −5.31, −4.09, −2.64, and −1.62 A cm−2 are achieved at 1.3 V and 50 vol% steam content at 800, 750, 700, and 650 °C, respectively.

Enhancing catalytic activity of CO2 electrolysis by building efficient and durable heterostructure for solid oxide electrolysis cell cathode