Tubular Solid Oxide Electrolysis Cell Research Articles

Realizing high-temperature steam electrolysis on tubular solid oxide electrolysis cells sufficing multiple and rapid start-up

Realizing high-temperature steam electrolysis on tubular solid oxide electrolysis cells sufficing multiple and rapid start-up

Thermal and electrochemical performance analysis of an integrated solar SOEC reactor for hydrogen production

Hydrogen can be produced efficiently by combining solar energy and solid oxide electrolysis cell (SOEC). This paper proposes an integrated solar SOEC reactor, which integrates a volumetric air receiver with a tubular SOEC. The hot air from the air receiver can directly heat the tubular SOEC and thus avoid transport heat loss. Under the reference condition, the reactor's water conversion ratio and energy conversion efficiency are 74.13% and 25.58%, respectively. The simulation results indicate that solar irradiation significantly affects the reactor's thermal and electrochemical performance. When the peak incident flux density of solar irradiation decreases from 0.49 MW/m2 to 0.21 MW/m2, the water conversion ratio and energy conversion efficiency drop by 96.41% and 84.49%, respectively. Adjusting the air flow rate may help maintain the reactor temperature to avoid a reduction in the water conversion ratio and energy conversion efficiency.

Thermal performance analysis of an integrated solar reactor using solid oxide electrolysis cells (SOEC) for hydrogen production

Concentrated solar power and solid oxide electrolysis cells (SOEC) can be combined to produce green hydrogen efficiently. However, heat loss due to fluid transport can be significant. In this paper, a volumetric receiver is first integrated with a tubular SOEC as a whole reactor to reduce the transport heat loss. Numerical investigation shows that the SOEC temperature, in a reference condition, ranges from 760 to 920 °C, which is qualified for regular operation. The efficiency analysis is conducted under different conditions and shows that the reactor efficiency is highly affected by the operating temperature. Therefore, increasing the incident power, decreasing the inlet velocity, or increasing the steam mass fraction would lead to a higher outlet temperature and thus a higher reactor efficiency. Based on the validated model, the integrated design presented in this paper can increase energy conversion efficiency by 2.63–30.21% compared with the separate structure, depending on the operation condition. The last section of this paper discusses the control strategy for the integrated reactor briefly, which aims to stabilize the reactor efficiency in outdoor situations. Compared with the steam mass fraction, the inlet velocity is preferred as a control variable to keep the cathode stable.

High-performance composite cathode for electrolysis of CO2 in tubular solid oxide electrolysis cells: A pathway for efficient CO2 utilization

High temperature solid oxide electrolysis cells (SOECs) have a tremendous potential to provide a practical pathway for onsite on demand production of high purity CO by recycling waste CO2 at industry relevant production scale. CO is an important feedstock for production of numerous chemicals required for the pharmaceutical, food and plastics industry. Recently, SOECs are also being developed to produce renewable fuels and energy carriers to allow transport and storage of renewable energy. Despite promising pre-commercial demonstrations, some key technical challenges need to be addressed to make this technology economically feasible. These include lowering capital costs with low cost materials and cell designs, and improvements in the electrode performance and lifetime, the cathode. The conventional Nickel-YSZ cathode is found to be promising in terms of performance during initial operation; however, a continuous supply of valuable reducing gas is needed to prevent oxidation of Ni to NiO, and accelerated degradation has been observed due to Ni migration and deactivation. In the present study we have evaluated the performance of A-site deficient doped lanthanum ferrites ((La0.60Sr0.40)0.95Co0.20Fe0.80O3-x) - Gd0.20Ce0.80O1.95) dual phase mixed ionic and electronic conducting cathode for CO2 electrolysis in a symmetrical tubular cell without the addition of reductant or protective gas during the cell operation. A polarization resistance as low as 0.36 ohm-cm2 was observed at 1.2 V after 350 h of CO2 electrolysis at 800 °C. The electrochemical performance of the electrode is also compared with state-of-the-art Ni-YSZ cathode using similar cells and experimental conditions.

Geometric synergy of Steam/Carbon dioxide Co-electrolysis and methanation in a tubular solid oxide Electrolysis cell for direct Power-to-Methane

Power-to-methane (PtM) is a strategy for seasonal energy storage to enable wider energy share through the existing natural gas networks H2O/CO2 co-electrolysis and methanation reaction can synchronously occur in a single tubular solid oxide electrolysis cell (SOEC) reactor to facilitate direct PtM. In this study, we aim to intensify the synergy between geometrical structure and complex physical–chemical processes in a tubular SOEC reactor for higher Electricity-to-CH4 efficiency. First, we divided the reactor into two parts: Electrolysis region and Methanation reaction (MR) region, and investigated their respective contribution and interaction. According to a self-developed multi-physics tubular SOEC model, we optimized the geometry of the reactor to synergistically regulate the field temperature of the Electrolysis and MR region. The results indicate that CH4 production ratio and Electricity-to-CH4 efficiency can be enhanced through the lengthening of either the Electrolysis region or the MR region. When fed with a cathode gas of 75%H2O + 20%CO2 + 5%H2 (20 mL min−1), an tubular SOEC reactor optimized with an Electrolysis region of 0.10 m and a MR region of 0.045 m can convert 91% of CO2 to CH4 at 1.5 V with an Electricity-to-CH4 efficiency of 49%. An improved synergy between pressure, operating voltage and gas flow can significantly improve CH4 production with less electricity. A tubular SOEC reactor with the optimized geometry can convert 95% of CO2 to CH4 at 1.2 V and 16 bar with an Electricity-to-CH4 efficiency of 81%, producing 52 vol% of dry CH4 at the cathode outlet. After optimization, tubular SOEC reactor can realize a more efficient PtM, thus, promote the combination of renewable power and natural gas networks.

Pressurized tubular solid oxide H2O/CO2 coelectrolysis cell for direct power‐to‐methane

AbstractTo improve the energy‐to‐CH4 efficiency and enhance renewable power utilization, we investigate direct Power‐to‐Methane at low inlet H2 content (25 vol%) in solid oxide electrolysis cell (SOEC). The synergy of the pressurized operation and the electricity input effectively enhances CH4 yield by one‐order of magnitude from 2.8% to 28.7% and the CO2‐to‐CH4 ratio from 4.4% to 39.5% in the H2‐reduced case, where the ratio of H2 consumption to total energy consumption decreases to 41% and the energy‐to‐CH4 efficiency increases to 53%. We develop a multiphysics tubular SOEC model to understand the intrinsic coupling between electrochemistry and heterogeneous catalytic chemistry. From the perspective of performance enhancement, geometry optimization, and thermal design, inhibiting CH4 production in the inlet gas‐controlled zone and promoting CH4 production synergistically in both the electrochemistry‐controlled zone and the temperature‐controlled zone is the key to improve the energy‐to‐CH4 efficiency.

An integrated concentrated solar fuel generator utilizing a tubular solid oxide electrolysis cell as solar absorber

We numerically assessed the potential of a solar reactor concept for efficient fuel processing under concentrated solar irradiation. This design integrates a cavity receiver, a tubular solid oxide electrolyzer, and the concentrated photovoltaic cells into a single reactor. The tubular electrolyzer simultaneously acts as the solar absorber (for reactant heating) and as the electrochemical device (for water and carbon dioxide splitting). A multi-physics axisymmetric model was developed, considering charge transfer in the membrane-electrolyte assembly, electrochemical and thermochemical reactions at the electrodes' reaction sites, species and fluid flow in the fluid channels and electrodes, and heat transfer for the whole reactor. A high solar-to-fuel efficiency was predicted (18.6% and 12.3% for indirectly and directly connected approaches, respectively, both at CPV = 385 and Cap = 1273). For synthesis gas production, the upper current density threshold to avoid carbon deposition was found to be 8725 A/m2 at reference conditions. A continuous range of H2/CO molar ratios of the synthesis gas was achieved by varying the inlet H2O/CO2 ratio, the irradiation concentration, and the operation current density. Efficiency-optimized operating conditions and design guidelines are presented. Our novel and integrated solar reactor concept for the solar-driven high-temperature electrolysis of H2O and CO2 has the potential to provide a simple, high solar-to-fuel efficiency reactor at reduced cost, all given by the reduced transmission losses of the integrated reactor design.

Synchronous enhancement of H2O/CO2 co-electrolysis and methanation for efficient one-step power-to-methane

Solid oxide electrolysis cells (SOECs) enable the integration of H2O/CO2 co-electrolysis and methanation reactions in a single reactor. The product gas may therefore potentially be sent directly to the existing natural gas pipelines. However, current power-to-methane (P2M) routes are not able to achieve acceptable CO2-to-CH4 conversion in a single SOEC reactor for direct integration into natural gas networks. In order to obtain higher CO2-to-CH4 conversions, a two-dimensional multiscale electro-thermo tubular SOEC model was developed to describe in detail the P2M processes along the whole cell and optimize the materials, flow modes, and operating conditions for CH4 production. The numerical simulations revealed that the stabilized Zr-based SOEC is unable to offer a sufficiently high electrochemical performance at methanation-favoring temperatures (250–650 °C). Such a temperature mismatch limits the peak CH4 production ratio in the tubular-stabilized Zr-based SOEC (with an inlet CO2 content of 20%) to only 13% at 1.5 V. In contrast, a tubular strontium and magnesium doped lanthanum gallate (LSGM)-based SOEC showed remarkable performance at or below 650 °C, improving the CH4 production ratio to over 50% at 550 °C and 1.3 V for the same inlet gas composition. However, the operating temperature was still too high to obtain an acceptable CO2-to-CH4 conversion for direct supply to natural gas pipelines. The model revealed that the H2O/CO2 co-electrolysis and methanation reactions can be synchronously enhanced by feeding a cold gas in counter-flow mode under pressurized conditions. At 29 bar, the tubular LSGM-based SOEC could achieve a CO2-to-CH4 conversion ratio of 98.7%, with an electricity-to-gas efficiency of 94.5% in the thermal neutral mode. The produced gas can be directly sent to the existing natural gas pipelines so that the curtailed renewable power can be stored more efficiently and utilized over a wider area.

Syngas production in high performing tubular solid oxide cells by using high-temperature H2O/CO2 co-electrolysis

By using electricity from renewable sources, high-temperature solid oxide co-electrolysis cells (SOCs) can perform advantageous conversion of H2O/CO2 to high-value syngas. In this work, we investigated the performance of tubular solid oxide co-electrolysis cells for the production of syngas by electrochemical conversion of H2O/CO2. The tubular solid-oxide electrolysis cells comprise Ni-yttria stabilized zirconia (Ni-YSZ) based fuel-electrode supported cells, a yttria or scandia-stabilized zirconia (YSZ and ScSZ) electrolyte, and a composite air-electrode of (La0.85Sr0.15)0.9MnO3 (LSM) and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF). The electrochemical performance of the tubular SOCs for various operating conditions was analyzed using I-V curves, EIS analysis, and gas chromatography. From the results, we confirm the correlation between the operating conditions and the electrochemical performance of the co-electrolysis process in the tubular SOCs. Furthermore, we found that the syngas yield of the ScSZ electrolyte-based SOC cell was better than that of the YSZ electrolyte-based SOC. The results show that using a tubular SOC offered highly efficient conversion of H2O/CO2, with high yield and good-quality syngas.

Millimeter tubular solid oxide electrolysis cells with modified asymmetric hydrogen electrode

Asymmetric structure with pore gradient is fabricated as the hydrogen electrode for millimeter tubular solid oxide electrolysis cells (SOECs). The gradient electrode is achieved with a graphite-assistant phase inversion process using an additional graphite layer to remove the relative dense skin layer. The electrode has demonstrated higher gas permeability than that with normal composite structure. Consequently, the steam starvation (concentration polarization) is successfully eliminated when SOEC is operated at relatively high voltage and low steam concentration. In addition, reduced interfacial polarization resistance and elevated current density are achieved for the tubular SOEC with the unique electrode.

Methane Synthesis Characteristics of H2O/CO2 Co-Electrolysis in Tubular Solid Oxide Electrolysis Cells

Producing methane by H2O/CO2 co-electrolysis through solid oxide electrolysis cell (SOEC) is a promising method to store unstable renewable power and reduce CO2 emission simultaneously. Theoretically, methanation reaction is possible to happen in standard condition when temperature is lower than 600oC. Tubular solid oxide electrolysis cell (TSOEC) has great potential for large-scale application due to easily sealing and high strength. Moreover, gradient distribution of temperature in flow direction is beneficial to CH4 production. In this paper, CH4 synthesis characteristics in TSOEC is studied in the temperature range of 500-650oC by combining experiment and simulation. Experiment demonstrates the addition of H2 increases the outlet molar fraction of CH4 from 0 to 2.85% at 600oC, and from 0.01% to 8.77% at 550oC. In addition, it’s found that electricity significantly promotes CH4 production, especially when H2 is added. The applied voltage of 1.5V just increases CH4 production ratio by <0.04% in the absence of H2. But when 20% H2 is fed in cathode, CH4 production ratio is improved by 3-4%. Finally, the optimal operating condition, thermal distribution and reaction active zones are simulated by a well validated thermal model. The thermal distribution can be changed by outer boundary condition. CH4production can be further improved by increasing the temperature of upstream zone and reducing that of downstream zone. Fig.1 Methane synthesis schematic in TSOEC Figure 1

Possibility of Methane Production from Steam and Carbon Dioxide by Using Solid Oxide Electrolysis Cells

To overcome global warming issue and energy shortage problem, economical hydrogen production technologies from renewable energy or unused fossil fuel with carbon capture technology are being developed all over the world. However it becomes the large problem that it is necessary to reconstruct energy infrastructures for production, transportation and usage of hydrogen and to entail a vast cost. Against this problem, for effectively utilizing existing energy infrastructures, we are developing a methane producing technique from water and carbon dioxide by using renewable electricity instead of hydrogen production. Specifically, solid oxide electrolysis cell (SOEC) technology for producing syn-gas with high efficiency has been developed and we have succeeded in trial manufacture tubular SOECs whose sin-gas production rate is more than 3.5 sccm/cm2 at the operating temperature of 750 oC and electrolytic voltage of 1.35V. Therefore, in this paper, the numerical models of an SOEC methane production system and a conventional methane production system were made in reference to performance of the tubular SOECs and dependence of performance of the each system on operating conditions, such as operating temperature, feed gas composition, is analyzed and compared with each other. The methane producing system which combined a water electrolysis system with a high temperature water-gas shift reactor was considered as a conventional system. From the result of the analysis, advantage of SOEC methane production system is clarified.

Dynamic electro-thermal modeling of co-electrolysis of steam and carbon dioxide in a tubular solid oxide electrolysis cell

SOEC (Solid oxide electrolysis cell) has great potential to store unstable renewable energy in form of steady chemical energy. For this application, transient behavior in variable working condition is crucial. A 2D (two-dimensional) dynamic model was developed to predict the dynamic response of H2O/CO2 co-electrolysis in TSOEC (tubular solid oxide electrolysis cell). The dynamic model comprehensively considered the macroscopic fluid flow, microscopic diffusion, heat transfer and electrochemical/chemical reactions in the TSOEC. In this paper, the TNV (thermal neutral voltage) of TSOEC was specifically defined and calculated. The time constants of charge/mass/heat transport processes were evaluated. Further, the responses of current, gas concentrations, temperature, efficiency, conversions to electricity/gas flow/temperature step inputs were respectively studied. Through the study, appropriate transient operations were designed to improve efficiency and conversions.

Methane Synthesis Characteristics of H2O/CO2 Co-Electrolysis in Tubular Solid Oxide Electrolysis Cells

Producing methane by H2O/CO2 co-electrolysis through solid oxide electrolysis cell (SOEC) is a promising method to store unstable renewable power and reduce CO2 emission simultaneously. In this paper, CH4 synthesis characteristics in tubular SOEC (TSOEC) is studied in the temperature range of 550-650oC by combining experiment and simulation. Experiments demonstrates adding H2 increases the CH4 production ratio from 0 to 4.01% at 600oC. Besides, electricity significantly promotes CH4 production, especially when H2 is added. The voltage of 1.5 V just increases CH4 production ratio by <0.04% in the absence of H2. But when 20% H2 is fed in cathode, a voltage of 1.5 V can increase CH4 production ratio by 3-4%. Finally, chemical reactions, thermal distribution and optimal operating condition are simulated by a well validated thermal model. A reasonable thermal distribution created by operating TSOEC in counter-flow mode and lower inlet steam partial pressure can dramatically improve CH4 production.

Electrolysis of carbon dioxide for carbon monoxide production in a tubular solid oxide electrolysis cell

An active carbon recycling energy system (ACRES) based on carbon recycling has been proposed as a new energy transformation system. This energy transformation system reduces the carbon dioxide (CO2) emissions in the atmosphere during the iron-making process. An experimental study for electrochemical CO production by CO2 electrolysis based on the ACRES concept was carried out using a tubular solid oxide electrolysis cell. Experimental results show that the CO and oxygen (O2) production rates at 800, 850, and 900°C were almost proportional to the current passing through the cell. Both ionic conductivity and the chemical kinetics of CO2 decomposition increased with increasing temperature. The highest current density and CO production rate at 900°C were 2.97mA/cm2 and 0.78μmol/(mincm2), respectively. On the basis of the electrolytic characteristics of the cell, the scale of the combined ACRES CO2 electrolysis/iron-making system was estimated.

Experimental Characterization and Theoretical Modeling of Methane Production by H2O/CO2 Co-Electrolysis in a Tubular Solid Oxide Electrolysis Cell

Methane production by H2O/CO2 co-electrolysis in solid oxide electrolysis cells (SOECs) is a promising method to store unstable renewable power and to reduce CO2 emission. In this paper, the CH4 synthesis characteristics in tubular SOECs (TSOECs) is studied by experiments and numerical simulation in the temperature range of 550–650°C. The experimental results show that the addition of H2 into the cathode inlet gas flow and the increase of electrolysis current could significantly promote CH4 production rate. In the case of the experiments without H2, the CH4 production ratio increased by less than 0.04% when the operating voltage varied from OCV to 1.5 V. After feeding the H2 into the cathode atmosphere, the CH4 production ratio increases by 3–4%. A CH4 yield of 9.94% and a CH4 production ratio of 12.34% were achieved at 550°C with 20% H2 fed into cathode and an applied voltage of 1.5 V. Finally, a theoretical model is developed by considering the chemical/electrochemical reaction and transport processes, and the thermal distribution and optimal operating condition of the TSOEC are studied. An designed thermal distribution in counter-flow mode with lower inlet steam partial pressure could dramatically improve the CH4 production.

Electrolysis of Carbon Dioxide in a Solid Oxide Electrolyzer with Silver-Gadolinium-Doped Ceria Cathode

Splitting CO2 into CO and pure O2 at high temperature through solid oxide electrolyzers (SOEs) could provide an efficient way for energy storage and CO2 utilization. Tubular solid oxide electrolysis cells, with yttrium-stabilized-zirconia (YSZ) as electrolyte, strontium-doped lanthanate (LSM) as anode, cermet of Ag-GDC (gadolinium-doped-ceria) as cathode, is fabricated and operated as SOEs for electrolysis of pure CO2. Such an SOE shows a minimum electrolyzing voltage of 0.70 V and a current density of 1359 mA cm−2 at 2 V. Its CO production rates are 3.1, 6.6 and 10.0 mL min−1 at electrical currents of 0.5, 1.0 and 1.5 A, respectively, at 800°C. The corresponding Faraday efficiencies are 88.6%, 94.3%, and 95.2%, and the electrical energy conversion efficiencies are 75.4%, 65.2%, and 56.5%, respectively. An SOE with Ag-GDC electrode is steadily operated at 1.59 V for pure CO2 electrolysis at 800°C for 18 h, suggesting that Ag-GDC is a promising cathode material for SOEs of CO2 electrolysis.

Comprehensive modeling of tubular solid oxide electrolysis cell for co-electrolysis of steam and carbon dioxide

A two-dimensional (2D) model is developed to analyze the performance and efficiency of H2O/CO2 co-electrolysis in tubular SOEC (solid oxide electrolysis cell). The model fully considers the fluid flow, heat/mass transfer and electrochemical/chemical reactions in the SOEC. The results show that RWGSR (reversed water-gas shift reaction) significantly promotes CO2 conversion ratio. The effect of important operating parameters was comprehensively studied and optimal operating condition was determined. When the inlet gas flows in parallel flow mode with the velocity of 1 m s−1, TSOEC with the H2O/CO2 molar ratio of 1 at 700 °C at 1.4 V achieves the highest efficiency of 59.4% and the syngas conversion ratio of 43.8%. Lowering gas flow velocity decreases the syngas yield but promotes H2O/CO2 convert ratio and efficiency. Finally, calculation found that counter flow is superior to parallel flow.

Direct synthesis of methane from CO2–H2O co-electrolysis in tubular solid oxide electrolysis cells

Methane is directly generated from CO2–H2O with a yield ratio of 41.0% using tubular units integrating electrolysis and methanation processes.

Carbon dioxide reduction in a tubular solid oxide electrolysis cell for a carbon recycling energy system

A new energy transformation system based on carbon recycling is proposed called the active carbon recycling energy system (ACRES). A high-temperature gas reactor was used as the main energy source for ACRES. An experimental study based on the ACRES concept of carbon monoxide (CO) regeneration via high-temperature reduction of carbon dioxide (CO2) was carried out using a tubular solid oxide electrolysis cell employing Ni-LSM cermet|YSZ|YSZ-LSM as the cathode|electrolyte|anode. The current density increased with increasing CO2 concentration at the cathode, which was attributed to a decrease in cathode activation and concentration overpotential. Current density, as well as the CO and oxygen (O2) production rates, increased with increasing operating temperature. The highest CO and O2 production rates of 1.24 and 0.64μmol/mincm2, respectively, were measured at 900°C. Based on the electrolytic characteristics of the cell, the scale of a combined ACRES CO2 electrolysis/iron production facility was estimated.