Flat-tube Solid Oxide Research Articles

Reversible operation of solid oxide cells fed with syngas derived from underground coal gasification

Underground coal gasification (UCG) technology can directly convert coal resources to syngas underground, making it important for coal utilization. In this work, the power generation, CO2 electrolysis, and reversible operation of flat-tube solid oxide cells (SOCs) fueled with UCG syngas were studied. The factors affecting the performances of flat-tube solid oxide cells were investigated. Fueled with syngas (Swan Hills, Canada) at 750 °C, the flat-tube cell achieved a maximum power density of 329.4 mW cm−2 and a current density of 650.8 mA cm−2 at 1.4 V. 100-cycle (250 h) reversible operation of flat-tube SOCs running on syngas (Swan Hills) was accomplished. No carbon deposition on the surfaces of the cell fuel channels was detected. The syngas conversion in flat-tube cells was illuminated based on density functional theory calculations.

Flat-tube solid oxide stack with high performance for power generation and hydrogen production

This study presents the design, fabrication, and evaluation of a high-performance flat-tube solid oxide cell (FT-SOC) stack, which demonstrates exceptional power generation and hydrogen production capabilities. Comprising three large-sized FT-SOCs, each with an active area of 60 cm2, the stack was tested at 750 °C. It achieved a peak power density of 1.222 W/cm2 in fuel cell (FC) mode and an electrolysis current density of 1.283 A/cm2 at an average voltage of 1.3 V in electrolysis cell (EC) mode, marking the highest reported values for FT-SOC stacks to date. These results surpass the performance of most large-sized planar SOC stacks. Post-operation analysis revealed excellent interfacial contact between components, contributing to the stack's high performance. This study underscores the potential of FT-SOCs in efficient power generation and electrolytic energy storage applications, providing insights that could facilitate their industrial application.

Efficiency and stability of seawater electrolysis through flat-tube solid oxide cell stack without air

Efficiency and stability are critical for solid oxide electrolysis cell (SOEC) applications. In this study, the effect of airless on the efficiency and stability of electrolysis seawater in a flat-tube SOEC stack is investigated. Considering gas heating loss, the maximum electrolysis efficiency of the stack with airless is 94.7 %, while that of the stack with air is 69.8 %. The 2-cell SOEC stack is operated for 500 h in airless at 300 mA/cm2 with an efficiency of 89.2 %. The degradation rate of Cell 1 and Cell 2 is 2.5 %/kh and 4.8 %/kh, respectively. The overall degradation of the stack is less than that of cell, which could be attributed to the improved interfacial contact between interconnect and cell inside the stack. The results show that the flat-tube SOEC stack has high efficiency and excellent stability for seawater electrolysis with airless, which provides a reference for efficient conversion and storage of offshore power.

Effect of seawater on the performance of flat-tube solid oxide cell for CO2/H2O co-electrolysis

Solid oxide electrolysis cell (SOEC) for CO2/H2O co-electrolysis is an advanced technology that converts excessive power into synthesis gas. The products from CO2/H2O electrolysis can be used to synthesize liquid fuels, which are easy to store and transport. This work compared the electrolytic performances of syngas preparation in CO2/seawater and CO2/deionized water atmospheres using a flat-tube SOEC. The results showed that there was no significant difference in the instantaneous performance and the stability of the cells when electrolyzed in a CO2/seawater atmosphere and a CO2/deionized water atmosphere. The voltage degradation rate of the cell in the CO2/seawater atmosphere was about 5.38%/kh with an operating time of nearly 400 h and a current density of 300 mA/cm2; the degradation rate of the cell in CO2/deionized water atmosphere was about 7.37%/kh with an operating time of nearly 400 h and current density of 300 mA/cm2. The microstructure characterization results showed that the degradation of the electrolytic cells under the two atmospheres might be caused by the agglomeration and loss of Ni particles, and the volatile components from seawater would not diffuse to the fuel electrode near the electrolyte and affect the electrode reaction.

Degradation of flat-tube solid oxide electrolytic stack for co-electrolysis of H2O and CO2 under pulsed current

The coupling of CO2 electrolysis and renewable energy storage is of great significance, especially to CO2 capture and utilization. In this work, the factors influencing the performance and degradation of flat-tube solid oxide electrolytic cell stack (SOEC stack) for CO2/H2O co-electrolysis under an intermittent pulsed current are investigated by inserting a voltage lead inside the SOEC stack to monitor the variations in the cell and stack voltages during the electrolysis process. The results show that after 64 pulsed electrolysis cycles (900 h), the average voltage degradation rate is about 0.018%/cycle at 50–250 mA/cm2, and the useful life is expected to reach more than 1100 cycles (10,000 h). The microstructural analysis shows that a SrCrO4 barrier layer is formed on the contact surface between the metal interconnect and the current collecting layer of the cell, which increases the interface resistance of the metal interconnect and the cell, resulting in the degradation of the electrolytic performance. This study provides useful information for improving the stability of the SOEC stack for CO2/H2O co-electrolysis.

Energy harvesting from algae using large-scale flat-tube solid oxide fuel cells

Energy harvesting from algae using large-scale flat-tube solid oxide fuel cells

Anti-poisoning performance of flat-tube solid oxide fuel cell in high concentration [formula omitted]S environment

In this work, the anti-poisoning performance of flat-tube solid oxide fuel cells (FT-SOFCs) is investigated in high concentrations of H2S. The degradation rate of the cell is 0.52%/ h, 0.27%/ h and 0.305%/ h at 750 °C, when the concentration of H2S is 161 ppm, 182∼222 ppm and 226 ppm, respectively, and the performance can be restored by humidification of H2. The resistance to sulfur poisoning breaks through the limitation, proving the stability advantage of the flat-tube structure. Through energy dispersive spectrometer (EDS) and Raman spectrum analysis, it is found that the cell performance degradation under high concentration of H2S is mainly caused by the loss of metallic nickel caused by the migration and decomposition of nickel-sulfur compounds, which will reduce the active sites of H2 participating in the anode reaction. This study provides a reference for the application of flat-tube structure cells under high concentrations of H2S.

Efficient conversion of ethanol to electricity using large-scale flat-tube solid oxide fuel cells

Conversion of renewable energy sources like bioethanol to electricity using solid oxide fuel cells (SOFCs) is promising to reduce the consumption of fossil fuels and to mitigate global warming. However, direct ethanol-fed SOFCs are susceptible to carbon deposition on Ni-based anode. In this study, the power generation from and degradation mechanism of large-scale flat-tube SOFCs by direct internal reforming of ethanol are investigated. The steam/carbon (S/C) ratio causes minor influence on the cell performance but considerably affects the long-term durability. Elevating temperature improves ethanol conversion rate and cell performance. Ethanol is efficiently reformed by the thick anode support and long anode channels, with low selectivity for CH4 and C2H4. Stable power generation with current density of 200 mA/cm2 is obtained over 300 h under S/C = 2 and 3 at 800 °C. Due to the high operating temperature and complex cell structure, the in-situ measurements of the temperature and gas compositions within the cell, related to carbon deposition, are difficult. The distributions of the gas compositions and temperature within the cell before and after the durability test are clarified by simulation. Simulation results reveal that, in addition to CH4 and C2H4, the cold zone near inlet contributes to carbon formation.

Enhancing durability of solid oxide cells for hydrogen production from seawater by designing nano-structured Sm0.5Sr0.5Co3-δ infiltrated air electrodes

In this work, the nano-structured Sm0.5Sr0.5CoO3-δ (SSC) was infiltrated into La0.6Sr0.4Co0.2Fe0.8O3-δ-Gd0.1Ce0.9O2-δ (LSCF-GDC) electrode of a large-area flat-tube solid oxide cell for hydrogen production. The electrolysis current density under 76% H2O-24% H2 increased only approximately 3% at about the thermal neutral voltage (1.29 V) and 750 °C, but the electrolysis durability with 76% H2O-24% H2 and 500 mA cm−2 improved significantly by more than 90%, with the degradation rate being approximately 1/10th of that of the non-infiltrated cell. This work indicates that SSC infiltration of the air electrode could suppress Sr segregation in LSCF, thus greatly enhancing the cell durability. The study provides a reference for large-scale hydrogen production of high durability SOECs by designing nanostructured electrodes via infiltration.

Understanding thermal and redox cycling behaviors of flat-tube solid oxide fuel cells

The performance stability of solid oxide fuel cells (SOFCs) under thermal and redox cycles is vital for large-scale applications. In this work, we investigated the effects of thermal and redox cycles on cell performances of flat-tube Ni/yttria-stabilized zirconia (Ni/YSZ) anode-supported SOFCs. Cell performance was considerably affected by the duration of oxidation during redox cycles and the heating rate during the thermal cycles. The cell tolerated 20 short-term redox cycles (5 min oxidation) without significant performance degradation. Besides, the cell exhibited superior stability during 8 thermal cycles with a slow heating rate (4 °C min−1) to that with a fast heating rate (8 °C min−1). These results reflected that the thick anode support (2.7 mm) offered strong resistance to the shocks caused by redox and thermal cycling. Moreover, the morphological changes of the Ni phase during the redox and thermal cycling were investigated using Ni-film anode cells. Agglomeration of Ni particles and dissociation between the Ni film and the YSZ substrate were confirmed after 5 redox cycles, whereas no significant changes in Ni film emerged after 8 thermal cycles.

Degradation behavior under alternating constant-current/constant-voltage discharge for flat-tube solid oxide fuel cells inside stack

An alternating constant-current (CC)/constant-voltage (CV) discharge for the optimal operation mode of solid oxide fuel cells (SOFCs) inside stack is carried out, and the degradation of SOFCs is discussed. The SOFCs are operated alternately in CC/CV mode for 985 h at 750 °C. The results show that the degradation rate of SOFCs first decreases and then increases in the CC/CV alternating operation mode. And the lowest degradation rate is 3.64%/100 h in the CV operation mode at ∼0.85 V, which is about one order of magnitude higher than the average degradation rate (0.36%/100 h) in the corresponding CC operation mode. The EIS analysis indicates that the ohmic resistance increases and the polarization resistance decreases after the CV operation mode, while the impedance change after CC discharge shows the opposite trend.

Effect of the steam/hydrogen ratio on the performance of flat-tube solid oxide electrolysis cells for seawater

This work investigated the durability of seawater electrolysis and degradation mechanism for hydrogen production at different seawater steam contents using a flat-tube solid oxide electrolysis cell (SOEC).

Power generation from flat-tube solid oxide fuel cells by direct internal dry reforming of methanol: A route for simultaneous utilization of CO2 and biofuels

Dry reforming of liquid alcohols coupled with solid oxide fuel cells (SOFCs) is a promising approach for clean and efficient energy conversion. Herein, the feasibility of power generation from flat-tube SOFCs with direct internal dry reforming of methanol has been studied. The effects of CO2/MeOH ratio, temperature, and current density on cell performance and long-term durability were investigated. Higher CO2/MeOH ratios reduced the power density, but suppressed carbon deposition and enhanced long-term durability. A cell was operated stably over 500 h with a constant current density of 200 mA/cm2 under CO2/MeOH = 1 and 2 at 750 °C. In addition to stable power generation, simultaneous syngas production and reduction in CO2 emissions were achieved. Density functional theory (DFT) calculations elucidated the possible pathways for methanol dry reforming and mechanism of carbon removal. Our experimental and simulation results provide insights into the direct utilization of methanol in SOFCs using dry reforming.

Effects of physical properties and operating parameters on numerically developed flat-tube solid oxide fuel cell performance

Fuel cells are promising as a clean energy conversion device in the era of global warming threat. Solid oxide fuel cells stand out among other fuel cell types because they are especially feasible for high-temperature applications. Besides the operating parameters, which are frequently encountered problems in SOFCs, physical parameters also directly affect cell performance. For this reason, careful examination of the effects of the parameters while designing the SOFC will contribute to the increase of the maximum power to be provided from the cell in applications. In this study, a solid oxide fuel cell (SOFC) created in flat-tube geometry is numerically modeled. The effect of the electrode and electrolyte layers on the performance is investigated parametrically on the created geometry. In addition, the effect of temperature on cell power is investigated comparatively by making analyzes at different temperatures for each case. In the analyzes, performance values are investigated for electrode layer thicknesses of 0.75 mm, 0.5 mm, and 0.25 mm, and electrolyte layer thicknesses of 1.25 mm, 1 mm, and 0.75 mm, respectively. As a result of the study, the highest cell power is obtained at 0.25 mm of the anode layer thickness. The maximum predicted average cell power of the flat tubular solid oxide fuel cell (FT-SOFC) is approximately 68.2 mW/cm2 for the operating temperature of 1273 K. In the study, the effect of electrolyte conductivity on the performance of the developed cell is also investigated. It is observed that the cell with a conductivity value of 100 S/m at 1073 K operating temperature has the best performance. In addition, in the last part of the study, the performance of SOFC under non-uniform operating temperature conditions is also examined and a comparison is made for this situation, which is frequently experienced in practice. The results show that small changes in fuel cell operating temperature affect the cell performance in positive and negative directions depending on the increasing and decreasing temperature values.

Enhancing coking tolerance of flat-tube solid oxide fuel cells for direct power generation with nearly-dry methanol

The state-of-the-art Ni/yttria-stabilized zirconia (YSZ) anodes in direct methanol solid oxide fuel cells (SOFCs) are vulnerable to carbon deposition. We propose two strategies to enhance coking tolerance of the cell, focusing on promoting the oxygen storage capacity of the Ni/YSZ anode and the methanol conversion in flat-tube SOFCs with an active area of 60 cm2. The Ni/YSZ anodes are decorated with nanosized gadolinia-doped ceria (GDC) by wet impregnation method and the fuel channels are filled with extra GDC-Ni/YSZ catalyst. Through these measures, carbon deposition in the modified cells is mitigated, and therefore the steam/carbon (S/C) ratio for successful long-term cell operation is significantly lowered, and the cell durability is improved. A GDC-Ni/YSZ cell with extra catalyst is operated for over 1200 h directly on methanol under low S/C ratios at 750 °C and carbon deposition is considerably suppressed. In addition, the degradation mechanism of the cell directly fueled with nearly-dry methanol (S/C = 0.1) is investigated. This work provides insight into efficient and durable SOFCs using biofuels, towards renewable energy conversion in large-scale commercial applications.

Multi-physics modeling of a symmetric flat-tube solid oxide fuel cell with internal methane steam reforming

Methane is regarded as one of the ideal fuels for solid oxide fuel cells (SOFCs) due to its huge reserves and transportation properties. In this study, a 3D numerical model coupling with chemical reaction, electrochemical reaction, mass transfer, charge transfer, and heat transfer is developed to understand the heat and mass transfer processes of methane steam direct internal reforming based on double-sided cathodes (DSC) SOFC. After the model verification, the parametric simulations are performed to study the effects of operating voltage, inlet temperature, and steam to carbon (S/C) ratio on the performance of a DSC. It is found that the non-uniform distribution of flow rate among channels results in the non-uniform distribution of each physical field. Increasing the inlet temperature significantly enhances the performance of DSC, however, when the temperature is above 1073 K, the concentration loss and the temperature gradient of DSC increase, which is not conducive to the long-term operation of the DSC. In addition, we revealed the effect of the S/C ratios on the heat and mass transfer process. This study provides an insight into the heat and mass transfer process of SOFC with a mixture of steam and methane and operating conditions for enhancing the performance.

Performance evaluation of ammonia-fueled flat-tube solid oxide fuel cells with different build-in catalysts

The corrosion of ammonia atmosphere to Ni-cermet anode significantly affects the performance and durability of direct ammonia fuel solid oxide fuel cells. In this study, we investigate the impedance behavior of the flat-tube solid oxide fuel cells (SOFCs) fed with pure ammonia in details, assisted with distributions of relaxation time analysis under different fuels, operating temperatures, flow rates, and cell voltages. In addition, we use Ni/Al2O3 particles and nickel foam strips as the built-in catalysts to enhance ammonia decomposition within the anode support of the flat-tube cells. It is confirmed that the increased catalytic activity of ammonia decomposition brought by the built-in catalyst and the change of internal fuel gas resistance would affect the initial performance of the cell. In addition, enhancing the catalytic activity of ammonia decomposition through the built-in catalyst could effectively inhibit the corrosion effect of ammonia on the Ni surface in the anode support, thus enhancing the long-term durability of ammonia-fueled SOFC.

Power Generation by Flat-Tube Solid Oxide Fuel Cells with Enhanced Internal Reforming of Methanol

Power Generation by Flat-Tube Solid Oxide Fuel Cells with Enhanced Internal Reforming of Methanol

In-situ analysis of anode atmosphere in a flat-tube solid oxide fuel cell operated with dry reforming of methane

In-situ characterization of solid oxide fuel cells (SOFCs) under operating conditions is of great significance to mechanism studies on performance or long-term stability. In this study, real-time visualization of the two-dimensional gas distribution inside a large flat-tube SOFC is realized by built-in gas sampling tubes combined with external gas chromatography, validated by simulating calculation. The gas composition inside anode of the cell fueled with CH4/CO2 is in-situ monitored during a 1000-h discharge test. Decrease in catalytic activity for methane dry reforming during the long-term test differs at different region of the cell, and is related with local carbon deposition and sintering of Ni particles. Based on these experimental results, the mechanism of cell performance degradation of the large flat-tube SOFCs under methane dry reforming conditions is discussed.

Reversible cycling performance of a flat-tube solid oxide cell for seawater electrolysis

Hydrogen production by electrolysis of seawater using a reversible solid oxide cell (rSOC) can potentially realize offshore wind power energy storage.In this work, a flat-tube solid oxide cell was used to simulate the “peak shaving and valley filling” aspects usually encountered with wind power, and the reversible cycle of charge and discharge of seawater electrolysis was studied.The results show that the reversible cell runs successfully for more than 1000 h with 31 cycles under the charging voltage of less than 1.22 V and the discharge voltage of higher than 0.71 V. During the reversible operation, the charging degradation rate was 0.73 mV/h and the discharge degradation rate was 0.82 mV/h. The overall calculated efficiency during one reversible cycle was up to 104.9%.Under reversible cycle, the performance degradation of the cell is similar to that under constant current electrolysis, and is mainly due to the coarsening and loss of fuel electrode nickel and the partial cracking of electrolyte/air electrode interface.