KR20190028595A - high-pressure solid-oxide coelectrolysis cell and production method of syngas using the same - Google Patents

Abstract

The present invention relates to a high-pressure cylindrical solid-oxide co-electrolysis cell and a module thereof which change syngas from carbon dioxide and steam in pressurized environments and, more specifically, to a high-pressure cylindrical solid-oxide co-electrolysis cell comprising: an electrolytic layer including ScSZ; a GDC buffer layer formed on a surface of the electrolytic layer; and a composite air electrode consisting of La_0.6Sr_0.4Co_0.2Fe_0.8O_3 (LSCF)-GDC, and a high-pressure cylindrical solid-oxide co-electrolysis module comprising: a pressure chamber to pressurize the co-electrolysis cell; a pressure controller to control the differential pressure between the co-electrolysis cell and the pressure chamber; and a vaporizer to supply steam to the co-electrolysis cell in addition to the co-electrolysis cell.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a high-pressure cylindrical solid oxide reforming cell,

The present invention relates to a high-pressure cylindrical solid oxide oxide solid electrolytic cell (SOC) for converting a synthesis gas from carbon dioxide and steam in a pressurized environment, a pressurized operation system using the high-pressure cylindrical solid oxide annular cell, And a method for producing syngas from carbon dioxide and steam using the system.

Hydrocarbon fuels can be produced from water, CO ₂ and renewable electricity by electrochemical conversion in the electrolysis cell. Recent advances in renewable energy technologies have allowed researchers to find very efficient and large-scale energy storage methods to control the inherent variability of wind and solar energy supply (G. Cinti, et al., Int. J. Energy Res. 40 (2016) 207-215). Thus, conversion of CO ₂ to high value-added hydrocarbon fuels using electrolysis cells is considered a viable energy storage method. The high temperature conversion of carbon dioxide and steam from the electrolysis cell to syngas (H ₂ + CO) is easy to control, modular, efficient, and excellent in scalability (Y. Zheng, et al., Chem. Soc. Rev. 46 (2017) 1427-1463).

Producing syngas using nuclear or renewable electricity and waste heat through CO ₂ and steam and hydrotreating is a promising way to reuse CO ₂ . High temperature battery SOC anode (fuel electrode), the cathode (air electrode) and the electrolyte comprises a high-density (O ^2- ion conductor), CO ₂ and steam (Steam) the oxide ion (O ^2-), being supplied to the fuel electrode And is conducted through the high-density electrolyte from the fuel electrode to the anode. Finally, O ² evolves at the anode and syngas is produced at the fuel electrode (JB Hansen, et al., Faraday Discuss. 182 (2015) 9-48). The resulting syngas is an effective energy carrier other than electricity that can be used for large scale energy storage (L. Lei, et al., J. Mater. Chem. A. 5 (2017) 2904-2910). Fischer-Tropsch (FT) processes can also be used to produce chemicals or liquid fuels.

Many studies have shown that increasing the pressure of the SOC can improve the performance of the electrolysis cell. Ni studies have developed an electrochemical model for hydrogen production in fuel electrode-supported SOCs and have shown that as pressure increases, diffusion overvoltage decreases and predicts higher performance of pressurized SOC. LSM (La _0.8 Sr _0.2 ) _{0 . 98 In} a high-pressure experimental study on a SOC cell oxygen electrode based on MnO ₃ , the polarization resistance of the electrode decreased with increasing air pressure at the anode (EC Thomsen, et al., J. Power Sources. -224). Also, the total area specific cell resistance (ASR) at the open circuit voltage (OCV) decreased by about 20% when the cell was operated at 750 ° C, when the pressure SOC test increased the pressure from 1 bar to 10 bar SH Jensen, et al., Int. J. Hydrogen Energy. 35 (2010) 9544-9549). Nickel Nickel is at high pressure because it is known in the methane synthesis catalyst-yttria-stabilized zirconia-based cell may be produced directly from synthesis gas CH ₄ in a single cell. In a study by Jensen, a planar 11-cell solid oxide stack in a fuel cell and electrolysis mode was operated at a high pressure of 1.2 bar to 25 bar under a pressure of 50% H ₂ + 50% H ₂ O (SH Jensen, et al., Fuel Cells 16 (2016) 205-218; SH Jensen, et al., J. Electrochem. Soc. 163 (2016) F1596-F1604). The stack was tested for a long period of time from 10 bar to 200 h. The syngas produced in the SOC is converted to hydrocarbon by FT conversion (WL Becker, et al., Energy 47 (2012) 99-115; JP Stempien, et al., Energy 81 (2015) 682-690) (G. Cinti, et al., Int. J. Energy Res. 40 (2016) 207-215). Chen's recent paper predicted that it would be appropriate to model the effect of pressure on the methanation process in the SOC-FT reactor and to operate the pressurized SOEC at lower temperatures for CH ₄ production with improved catalytic activity (G. Cinti, et al., Appl. Energy 162 (2016) 308-320). Thus, high pressure generation of syngas provides high overall efficiency and direct integration and reduces process costs. According to Bernadet's work, modeling and experimental studies have shown that the high ASR values of the air electrode at high steam rates and high steam conversion rates of the input gas are balanced and the high performance of the electrolysis is expected (L. Bernadet , et al., Int. J. Hydrogen Energy. 40 (2015) 12918-12928). They also pointed out that cell performance at high pressure is less sensitive to changes in the microstructure properties of the cermet support. Gas diffusion plays a crucial role in the electrolysis mode. In addition, the optimized microstructure of the anode support under high pressure increases the current density during co-electrolysis (AR Hanifi, et al., Sci. Rep. 6 (2016) 27359).

The cylindrical shape of the SOC provides inherent advantages of easier sealing, better thermal properties and higher strength at pressurized conditions than flat cells. In recent years, microcylindrical solid oxide electrolytic cells (MT-SOEC) have been extensively studied for H ₂ O electrolysis, CO ₂ electrolysis and H ₂ O-CO ₂ co-electrolysis (Z. Wang, et al., Int J. Hydrogen Energy 35 (2010) 4451-4458; L. Kleiminger, et al., Electrochim. Acta 179 (2015) 565-577). Simultaneous electrolysis of CO ₂ -H ₂ O and methane using microcylindrical SOC cells has been reported in Lei's study (L. Lei, et al., J. Mater. Chem. A. 5 (2017) 2904-2910 ). Most studies have reported the conversion of syngas using cylindrical SOC cells to methane and hydrocarbons. The advantage of the increased diffusion rate of the reactants, which can reduce the area resistance of the cells at high pressure, can be advantageous in a cylindrical cell.

Accordingly, the inventors have made efforts to develop a high-pressure cylindrical SOC (solid-oxide coelectrolysis cell, SOC) for producing synthesis gas from H ₂ O-CO ₂ under pressure. As a result, The analysis of the detailed performance characteristics of the high pressure cylindrical SOC equipment, the analysis of related factors affecting the synthesis of syngas, and the microstructure of the fuel and air electrode The present invention has been completed through the analysis of the influence on the characteristics.

It is an object of the present invention to provide a high pressure cylindrical SOC system for pressurized operation with excellent syngas conversion and a high pressure cylindrical SOC system including said high pressure cylindrical SOC.

It is still another object of the present invention to provide a method for efficiently converting synthesis gas from CO ₂ and steam by pressurized operation using the high-pressure cylindrical SOC system of the present invention.

In order to achieve the above object,

A cylindrical support;

A cathode layer formed on the surface of the cylindrical support;

An electrolyte layer comprising Scandia-Stabilized Zirconia (ScSZ) formed on the surface of the cathode layer;

A GDC buffer layer (Gadolinium-Doped Ceria buffer layer) formed on the surface of the electrolyte layer; And

A high pressure cylinder to a solid oxide cell comprising a revolution; LSCF formed on a surface of the buffer layer GDC _{(.... La 0 6} Sr 0 4 Co 0 2 Fe 0 8 O 3) anode layer (anode layer) consisting of a composite -GDC .

In addition,

A high-pressure cylindrical solid oxide annular austenitic cell according to the present invention;

A pressure chamber for pressurizing said revolving cell;

A pressure controller for adjusting a pressure difference between the revolving cell and the pressure chamber;

A vaporizer for providing steam to the idol cell;

A fuel injector for injecting fuel gas and steam of hydrogen, nitrogen, and carbon dioxide into the revolving cell;

A mass flow controller for regulating the flow rate of the fuel gas; And

And a gas discharge part for discharging the gas after the reaction from the revolvable cell. The present invention also provides a high-pressure cylindrical solid oxide perturbation system.

In addition,

In the high pressure cylindrical solid oxide perturbation system according to the present invention,

The pressure in the pressure chamber is 8 to 10 bar and the temperature is 800 to 850 占 폚,

And a pressure difference between the pressurizing chamber and the revolute cell is controlled to be 0.3 bar or less.

In the high-pressure cylindrical solid oxide annular reforming cell according to the present invention, the maximum output density was increased by 44.2% by increasing the pressure from 1 bar to 8 bar, and the open circuit voltage (OCV) and the reaction rate (electrode performance) And by increasing the operating pressure in the impedance spectroscopy analysis, the polarization resistance associated with diffusion of the gas at the fuel electrode at a high pressure of 8 bar was reduced by 50%, indicating a significant improvement in the performance of the cylindrical SOC, Gas conversion rate, exhibits excellent durability even under pressure operation, and exhibits excellent performance.

In addition, the high-pressure cylindrical solid oxide annular aolyte cell according to the present invention can improve the stability of the entire system in a high-temperature pressurization reaction by forming an electrolyte layer including ScSZ and a GDC buffer layer between the electrolyte layer and the cathode layer, .

1 (a) and 1 (b) are schematic views of a cylindrical solid oxide a rechargeable battery used in a pressurizing operation, and Fig. 1 (c) is a photograph showing the overall configuration of a cylindrical solid oxide rechargeable battery connected to a sensor for gas supply and a stainless steel connection device 1 is a photograph showing fuel electrode current collection, and FIG. 1 e is a SEM micrograph showing a cross section of a sal showing various layers of a cylindrical cell, wherein f in FIG. 1 is a photograph showing fuel electrode current collection to be.
Fig. 2 (a) is a schematic view of the setting used in the test of the pressurized cylindrical solid oxide aeration cell, and Fig. 2 (b) is an actual photograph of the experimental apparatus for the pressure test.
3 is a graph showing the performance of a cylindrical solid oxide aeration cell at atmospheric pressure. 3 (b) is a graph showing the effect of temperature on the iV characteristic of the cylindrical solid oxide aeration cell, and FIG. 3 (c) is a graph showing the effect of temperature on the inflow gas 3 is a graph showing the effect of steam content, and FIG. 3 (d) is a graph showing the composition of H ₂ and CO fished at various polarizing conditions at 750 and 800 ° C.
4 is a graph showing the effect of the pressurization on the OCV of the pressurized cylindrical solid oxide aeration cell measured at 800 ° C in H ₂ . At this time, the theoretical value of OCV was calculated from the Nernst equation.
5 is a graph showing electrochemical performance characteristics of a pressurized cylindrical solid oxide annular dissolution cell in an SOFC mode. Figure 5a shows polarization (iV) at different pressure conditions, and Figures 5b and 5c show electrochemical impedance spectroscopy (EIS) at different pressure conditions.
6 is a graph showing electrochemical performance characteristics of a pressurized cylindrical solid oxide annular dissolution cell in the SOC mode. Figure 6a shows polarization (iV) at different pressure conditions, and Figures 6b and c show electrochemical impedance spectroscopy (EIS) at different pressure conditions.
7 is a graph showing the influence of the pressure on the polarization resistance of the pressurized cylindrical solid oxide aeration cell. FIG. 7A shows the Ohmic polarization (Rs) as a function of pressure, and FIG. 7B is a graph showing the influence of the pressure on the active polarization during SOFC and SOC modes.
8 is a graph showing the effect of pressure on the outlet syngas composition at the tubular SOC at 800 < 0 > C. At this time, the inlet gas composition was selected as 10% H ₂ + 30% CO ₂ + 60% H ₂ O and the gas composition was determined when the cell was operated at -800 mA / cm ² current density for all pressure conditions.
9 is a cross-sectional SEM photograph of a cylindrical solid oxide annular austenitic cell before and after operation under a pressurizing condition. FIG. 9C is a SEM photograph of a section of the cylindrical solid oxide aeration electrolysis cell before and after the operation under the pre-test pressure condition, and FIG. 9D is a high-resolution SEM photograph of the fuel electrode function layer of the cylindrical solid oxide aeration cell before the press operation And FIG. 9E is a high-resolution SEM photograph of the fuel electrode functional layer of the cylindrical solid oxide annular dissolution cell after the pressurization operation of 8 bar.

Hereinafter, the present invention will be described in detail.

The present invention

A cylindrical support;

A cathode layer formed on the surface of the cylindrical support;

An electrolyte layer comprising Scandia-Stabilized Zirconia (ScSZ) formed on the surface of the cathode layer;

A GDC buffer layer (Gadolinium-Doped Ceria buffer layer) formed on the surface of the electrolyte layer; And

A high pressure cylinder to a solid oxide cell comprising a revolution; LSCF formed on a surface of the buffer layer GDC _{(.... La 0 6} Sr 0 4 Co 0 2 Fe 0 8 O 3) anode layer (anode layer) consisting of a composite -GDC .

The above-mentioned idle cell is a device for producing syngas by injecting carbon dioxide and steam into the cathode, air into the anode, and applying electricity while maintaining a high temperature. The device is a device for producing syngas from steam and carbon dioxide, And the like.

As shown in Fig. 1, the above-mentioned revolving cell is preferably a cylindrical annularly-aided cell which maintains excellent durability even in a pressurized operation.

The support of the revolute cell is cylindrical, and is an optimal structure capable of maintaining excellent durability even in a pressurized operation.

The cylindrical support may be NIO and YSZ may be a cermet of nickel (NIO) / yttria stabilized zirconia (YSZ), but is not limited thereto.

The cathode is a metal-ceramic composite of Ni-YSZ, a perovskite-based ceramic cathode in _{LSCM ((La 0 .75, Sr} 0 25) 0.95 Mn 0 5 Cr 0 5 O 3...), LST -based ceramic cathode a (Sr _{1 -x} La _x) may be used a _{(Ti 1-y M y)} O 3 (M = V, Nb, Co, Mn), but is not limited to such.

The electrolyte has a problem in that the conventional YSZ operates stably at a high temperature, but ion conductivity is low. To improve the YSZ problem, a Scandia-Stabilized Zirconia (ScSZ) having a high ionic conductivity is used.

By forming a GDC buffer layer between the electrolyte layer and the anode layer, the reaction at a high temperature can be suppressed and the overall stability can be enhanced.

The thickness of the cathode layer is 8 to 13 μm, the thickness of the electrolyte layer is 4 to 8 μm, the thickness of the GDC buffer layer is 1 to 4 μm, and the thickness of the anode layer is 13 to 18 μm, but not limited thereto .

The lower limit of the above-mentioned respective thickness ranges is a compact SOC and a movable thickness with a minimum thickness. However, if the lower limit is smaller than this lower limit, there is a problem that the operation efficiency is lowered. The upper limit of the above-mentioned thickness range is a thickness value that allows the cylindrical SOC to exhibit the maximum output and can be moved to the maximum thickness. However, if the upper limit is larger than the upper limit, the reaction efficiency is lowered and waste of unnecessary raw materials occurs Will be. The above thicknesses are such that the cells fabricated under a pressure environment of up to 10 bar can sufficiently retain their shape and function.

Preferably, the cell has a diameter of 0.5 to 2.0 cm, a length of 3.0 to 7.0 cm, and an effective electrode area of 3.0 to 4.0 cm ² , but is not limited thereto.

In addition,

A high-pressure cylindrical solid oxide annular austenitic cell according to the present invention;

A pressure chamber for pressurizing said revolving cell;

A pressure controller for adjusting a pressure difference between the revolving cell and the pressure chamber;

A vaporizer for providing steam to the idol cell;

A fuel injector for injecting fuel gas and steam of hydrogen, nitrogen, and carbon dioxide into the revolving cell;

A mass flow controller for regulating the flow rate of the fuel gas; And

And a gas discharge part for discharging the gas after the reaction from the revolvable cell. The present invention also provides a high-pressure cylindrical solid oxide perturbation system.

The pressurizing chamber includes a fuel gas supply feed-through for supplying the fuel gas and steam to the tubular electrodialysis cell, a fuel gas discharge feed for discharging the substance generated after the reaction and the unreacted substance from the tubular rechargeable cell, Through. ≪ / RTI > It may also include an air feedthrough for feeding air into the cell and an air exhaust feedthrough for discharging unreacted air. It also includes a pair of feedthroughs for collecting the inside of the idler cell, and a pair of feedthroughs for collecting the outside of the idler cell. It may also include a pair of heating line feedthroughs that supply energy to the heating device.

The pressurizing chamber may include a heating device for heating the aeration cell.

It is preferable that the pressurizing chamber is assembled using metal fittings at all the connection portions so that the inside of the pressure chamber is completely sealed, and it is preferable to check whether gas is leaked from the connection portions at the time of assembly. Finally, after covering the cover of the pressurizing chamber, the pressure chamber can be formed by high-pressure sealing and insulating processing.

The fuel gas in the revolving cell includes hydrogen, nitrogen, carbon dioxide, and steam, and includes a mass flow controller capable of regulating a flow rate supplied for each fluid.

In addition to the carbon dioxide used as the fuel, hydrogen and nitrogen are introduced as a stabilizing gas, and a stabilizing gas is injected, thereby achieving a revolving reaction while maintaining the durability of the idling cell.

A hydrogen supply pipe, a nitrogen supply pipe, and a carbon dioxide supply pipe among the supply pipes for supplying the fuel gas to the cathode of the tubular static-dissipative cell meet at the rear end of each supply pipe to form a mixed gas of hydrogen, nitrogen and carbon dioxide.

A pump for supplying steam may be connected to the vaporizer.

The steam vaporized and discharged from the vaporizer in the gas mixture is mixed to form a fuel gas, and the fuel gas can be supplied to the fuel electrode of the cell.

The mixed gas containing hydrogen, nitrogen, carbon dioxide and steam is supplied to the fuel electrode and the pressure for supplying air to the pressure chamber is higher than 1, Respectively.

As described above, it is possible to increase the production amount of the synthesis gas produced by the reaction of the revolving reaction by simultaneously forming the inside and outside of the revolving cell.

In order to maintain the durability of the cell itself while increasing the production amount of syngas, the pressure applied to the inside and outside of the cell must be adjusted so that the pressure felt by the cell itself becomes zero, so that the pressure difference between the cell and the pressure chamber And a pressure controller (differential pressure regulator)

And a differential pressure transmitter for monitoring the pressure inside the pressure chamber.

In the pressure controller (differential pressure regulator), the differential pressure regulating system includes a first valve installed in the air injecting unit; A pressure gauge installed in the air outlet; A pressure regulator installed between the air injection unit and the air discharge unit; A second valve installed in the idler fuel injection unit; A differential pressure gauge for measuring a differential pressure between the idler cell discharge portion and the air discharge portion; And a differential pressure regulator connected to the second valve.

The pressure control (differential pressure control) is performed by measuring the pressure of a pressure gauge installed in the air discharge unit through the pressure chamber, and then adjusting the pressure regulator provided between the air injection unit and the air discharge unit to 4 to 10 bar The pressure in the pressure chamber is adjusted to a predetermined pressure by using a first valve provided in the air injection unit and then the differential pressure of the differential pressure gauge for measuring the differential pressure between the air discharge cell discharge portion and the air discharge portion is adjusted to 0.3 bar or less The differential pressure regulator connecting the differential pressure gauge and the second valve installed in the idle fuel cell injecting unit may be adjusted so that the pressure of the fuel gas supplied to the inside of the idler cell and the pressure of the air supplied to the pressure chamber become equal.

Comparing the volume of the revolving cell with the volume of the pressure chamber, the volume of the pressure chamber is much larger than that of the idler cell. Therefore, it is difficult to control the pressure difference due to such a volume difference and a problem may arise in controlling the pressure difference. The buffer chamber may further be provided.

Since the pressure chamber is formed to be completely closed, a safety device for preventing the danger due to the pressure can be additionally provided.

The safety device may include, for example, a rupture disk to prevent rupture by a sudden pressure rise inside the pressure chamber, and when the concentration of hydrogen, carbon monoxide or carbon dioxide in the pressure chamber is detected to exceed a certain amount, A device for locking the supply line may be used.

A pressure gauge for measuring a pressure of steam supplied to the idler cell, a pressure of the revolving cell, and a pressure of the pressurizing chamber, and a pressure gauge for measuring the pressure of the pressurizing chamber. And may further include a monitoring system for checking pressure, flow rate, voltage, etc. at each point.

In addition,

In the high pressure cylindrical solid oxide perturbation system according to the present invention,

The pressure in the pressure chamber is 8 to 10 bar and the temperature is 800 to 850 占 폚,

And a pressure difference between the pressurizing chamber and the revolute cell is controlled to be 0.3 bar or less.

The present invention tests the performance of a high pressure cylindrical solid oxide aeration system for producing syngas from carbon dioxide and steam. Specifically, the effect of pressure on the electrochemical performance of the cylindrical SOC in the fuel cell mode and the electrolysis mode using the IV Curve and EIS analysis increases the pressure of the system, resulting in higher performance with respect to the maximum power density of the fuel cell And shows that the electrolysis mode can achieve high performance at a specific voltage and current density.

In a high pressure cylindrical solid oxide airconditioning system according to the present invention, the OCV increased from 8 bar to 1.23 V at 1.14 V at 1 bar and the maximum power density increased from 586 mW / cm ² to 845 mW / cm ² , and the voltages obtained for the pressure tubular cells at -800 mA / cm ² in the electrolysis mode were 1.46 and 1.28 V at 1 and 8 bar, respectively. As a result of the impedance spectroscopic analysis, The amount of methane in the composition of the exhaust gas at high pressure was higher than that at atmospheric pressure, and it was confirmed that CO ₂ To ensure the suitability to produce sustainable fuels.

Hereinafter, the present invention will be described in detail with reference to Examples and Experimental Examples.

However, the following Examples and Experimental Examples are merely illustrative of the present invention, and the present invention is not limited to the following Examples and Experimental Examples.

Example 1 Production of cylindrical SOC cell

The new Ni-YSZ cermet-support based cylindrical SOC cell was fabricated along the existing ceramic processing path. A detailed manufacturing process of the cermet-support and the thin electrode and electrolyte layer was used as reported in another study (S.-H. Lee, et al., Int. J. Hydrogen Energy. 41 (2016) 7530-7537) . Schematic and actual drawings of the cylindrical cell used for high pressure operation are shown in Figures 1 (a) and 1 (b). Fig. 1 (c) shows a cylindrical cell assembled with all connectors and sensors. Stainless steel pipes were used to supply gas at high pressure and incorporate current collection from the fuel electrode side as shown in Figures 1 (d) and 1 (e). Figure 1 e shows a material having different thicknesses of SOC after sintering. ScSZ (Scandia-stabilized zirconia) electrolyte and _{GDC (Ce 0. 8 Gd 0} . 2 O 1 .9-δ) thickness was 6.15 and 3.67 μm and the composite air electrode, each of the double layer La _{0. 6} Sr _{0 . 4} Co _{0 . 2} Fe _{0 . 8} O ₃ (LSCF) with an average thickness of ~ 16 μm (GDC). The diameter of the cell is 1.0 cm, the length is 5.0 cm, and the effective electrode area is 3.14 cm ² (electrode length: 1 cm). Then, the fabricated SOC cell was sealed with a sealing sealant (Mico, South Korea). A ceramic pipe was inserted for insulation between the cylindrical SOC cell and the metal cap of the cell.

< Example  2> Manufacture of pressurized SOC cell test equipment

2 (a) is a schematic view of a high-pressure SOC battery testing facility developed in the laboratory. Pressure vessels or pressurized chambers are designed to provide a cylindrical SOC cell with a heating capacity of up to 850 ° C and to provide a convenient sealing system for the cell. The differential pressure transmitter (DPT) is configured to monitor and control the pressure inside the pressure chamber. In addition, a rupture disk was installed inside the pressure chamber to prevent the risk of accidents due to the sudden upward pressure. The pressure chambers have facilities for air and fuel supply, current collection and temperature, and pressure data monitoring. The inlet on the fuel electrode side was connected to continuously supply the vapor to the vaporizer pump, and a mass flow controller (HFC) for H ₂ , CO ₂ , and N ₂ was installed to control the gas flow rate. In addition, an electronic pressure controller (EPC) was installed as shown in FIG. 2B to monitor the pressure value through the DPT to control the pressure difference. In addition, on-line gas chromatography equipment was installed in the experimental equipment for pressurized operation of the cylindrical cell, and the gas composition discharged from the SOC cell was confirmed. These experimental instruments are designed to be controlled by a remote computer program that can adjust the gas flow rate, pressure and other operating conditions according to the experimental requirements.

< Example  3> Evaluation of electrochemical performance of pressurized SOC cell

The test of the pressurized SOC cell was performed in an electrolysis mode and a fuel cell mode. Before testing the cell at high pressure, a dummy cell was installed and the test facility was inspected under high pressure conditions for testing at high pressure. The fuel electrode was supplied with various CO / H ₂ O compositions using a peristaltic pump (model EMS-200S, EMS Tech, error <± 2%) using a digital flow meter and distilled water to control the flow rate of CO ₂ . The water is evaporated into steam using a heating tape and mixed with H ₂ / CO ₂ gas flowing in the heating coil and finally supplied to the fuel electrode side of the cylindrical SOC as shown in FIG. 2 a. The current-voltage electrochemical performance of the SOC cell under each operating condition was measured using an Agilent DAQ system (34970 A, USA) and a load device (DP30-03TP, Toyotech, South Korea). All data (temperature, voltage, flow, etc.) was continuously monitored, collected, stored and controlled by the computer via the Agilent DAQ system. Impedance spectroscopy (EIS) was measured with an impedance measuring instrument (SP 240, Bio-Logic Science Instruments SAS, France) at an AC amplitude of 10 mV and 10 data points per 10 dB of frequency in the frequency range of 1 MHz to 10 mHz. Finally, for syngas production analysis and quantification, we used on-line gas chromatography (PerkinElmer Clarus 580 GC) equipped with one capillary column. GC Columns Velocity-Wax 30 M x 0.32 mm x 0.25 μm Polyethylene Glycol. The detection columns for CO, CO2, H2 and CH4 were calibrated to standard gas components and different readings were used for each measurement. The measured value was the average value of the gas composition. The microstructure of the SOC cell before and after the pressurization operation was measured using SEM (SEM, Hitachi X-4800).

< Experimental Example  1> Atmospheric pressure  Performance Analysis of Cylindrical SOC Cell

The performance of cylindrical SOC was investigated under atmospheric pressure conditions and reference data for pressurized operation were obtained. Cylindrical SOC cell electrolysis and IV curve of CO ₂ / H ₂ O electrolysis are shown in FIG. 3 a at 850 ° C. 10% H ₂ was supplied to the fuel electrode side as a safety gas. The SOC cell was operated in an idle mode with H ₂ O / CO ₂ ratio 2.

As a result, it was shown that the current density increases with increasing voltage. Cylindrical SOC performance showed higher performance when steam and CO ₂ were revolving than water. It was also found that increasing the amount of vapor from 40 to 60% reduced the cell voltage from 1.61V to 1.42V at a current density of -800 mA / cm ² .

Figure 3b shows the effect of temperature on SOC performance when the fuel electrode gas was supplied with 60% H ₂ O, 30% CO ₂ and 10% H ₂ . As expected, a performance increase was observed at 800 ° C. SOC cell was at 800 ℃ maximum current density at 1.8V when operating in the bay 750 ℃ represent a 1.75V at -800 mA / cm ² was 760 mA / cm ^2. A clear improvement at high temperature is due to the improved conductivity of ScSZ-based electrolytes and the high conversion efficiency from CO ₂ to CO by reverse water gasification reaction (RWGS).

FIG. 3C shows the effect of increasing the steam content of the fuel electrode injection gas. At 20% H ₂ O the cell showed very low performance and the voltage rapidly increased. This shows an increased loss tendency associated with concentration polarization. By increasing the steam flow rate from the inlet gas to 20% to 60%, the cell voltages were achieved at 1.8 V at -500 and -900 mA / cm ² , respectively. To obtain a current density of -500 mA / cm ² , cell voltages of 1.6, 1.49 and 1.38 V were required at 20, 40 and 60% H ₂ O cell voltages, respectively. Providing a sufficient supply of reactants for electrolysis as the steam flow rate of the feed gas increases.

Figure 3 (d) shows the composition of the synthesis gas produced during the electrolysis. The exhaust of the cylindrical SOC was analyzed by on-line GC during testing under different operating conditions. When the cylindrical SOC is operated at a higher current density, the amounts of CO and H ₂ are present at higher mole fractions. The maximum mole fraction of 45% H ₂ and 14% CO was observed at 800 ° C. When a voltage higher than OCV was applied, H ₂ O and CO ₂ were electrochemically separated into CO and H ₂ . Syngas produced electrochemically in the cylindrical SOC in the atmospheric state has shown that it is possible to convert H ₂ O / CO ₂ to high quality syngas.

< Experimental Example  2> Pressurized cylindrical type Of the SOC cell  Performance analysis

<2-1> Cylindrical Of the SOC cell OCV  Influence of Pressurization

The influence of the pressure on the OCV (open circuit voltage) of the cylindrical SOC cell at 800 ° C is shown in FIG. The theoretical OCV was calculated from the Nernst equation.

As a result, the OCV increased with increasing pressure from 1 bar to 8 bar. However, in the experiment, the OCV value was slightly lower than the OCV calculated from the theory. The maximum difference between theoretical and experimental values is about 3% at 8 bar pressure. This is because the gas leakage of the cell may have increased at higher pressures. The electrolyte of the SOC is sintered at a high temperature of 1400 ° C and is completely dense. However, during the manufacturing process, small pinholes may occur in the electrolyte microstructure. As the high-pressure (8 bar) gas passes through the cylindrical SOC cell fuel electrode, some leakage of gas occurs in these pinholes and the experimental OCV can be lower than the theoretical value (L. Bernadet, et al., J. Hydrogen Energy 40 (2015) 12918-12928 '; SY Gomez, et al., Renew Sustain Energy Rev. 61 (2016) 155-174). It can be seen that the OCV difference at low pressure (1 bar) may be due to electrical leakage and is due to high pressure (eg 8 bar) due to electrical leakage and gas diffusion leakage through pin holes and cracks in the sealant (JFB Rasmussen, et al. , Fuel Cells 8 (2008) 385-393). However, in a cylindrical SOC cell, the cylindrical cell is easily sealed, so leakage through the cell is minimized. Therefore, we can see that the difference between the theoretical and experimental OCV is significantly less than the value reported by Hashimoto's study.

Cylindrical SOC cells therefore provide better sealing properties and higher experimental OCV values. It is also important to increase the OCV of tubular SOC to 7.3% by increasing the pressure of 1 to 8 bar. Since pressurization can improve vapor diffusion at the porous electrode, this effect can increase the fuel supply at the reaction point and increase the OCV value. The high OCV of a cylindrical SOC cell can contribute to improving electrochemical performance for electrochemical reactions and fuel cell reactions.

<2-2> Fuel cell In mode  Pressurized cylindrical type Of the SOC cell  characteristic

The electrochemical performance of a pressurized cylindrical SOC cell was studied in both fuel cell and electrolysis mode. Figure 5a shows the electrochemical performance of SOC under various pressure conditions in fuel cell mode. Cylindrical SOC cells used humidified H ₂ as fuel and ambient air as oxidant at 800 ° C. The fuel flow rate was 200 cc / min and the air was maintained at 300 cc / min.

As a result, the OCV of the cell increased from 1.14V to 1.23V as the pressure of the H ₂ gas increased from 1 bar to 8 bar. The maximum power density of the cell at 1 bar was 586 mW / cm ² . A 44.2% increase in the maximum power density of the SOFC cell was observed by increasing the pressure to 8 bar. The increase in performance due to the pressure observed from the maximum power output is caused by an increase in OCV and a decrease in the polarization resistance of the cell.

The influence of the pressurization can be explained in more detail in the electrochemical impedance spectroscopy (EIS) as shown in Fig. 5 (b). The series resistance Rs of the cell remained the same when the pressure was applied, but the polarization resistance Rp remarkably decreased.

The shape of the EIS Nyquist plot is a typical anode supported SOFC cell. The low frequency and high frequency arcs of the EIS plot are affected by the increase in operating pressure. The characteristic frequencies were found to be about 0.1-1 and 100-150 Hz for the low and high frequency arcs, respectively (Fig. 5c). Low frequency arcing is generally attributed to the diffusion process in the anode and anode supports of the SOFC cell and high frequencies are regarded as the result of activation polarization of the fuel electrode and anode (YD Hsieh, et al., J. Power Sources. 299 (2015) 1-10; J. Nielsen, et al., Solid State Ionics. 189 (2011) 74-81). From the high frequency and low frequency intersections of the EIS plot, the ohmic resistance Rs and the polarization resistance Rp of the cylindrical SOFC cell were determined under the pressurized condition. In the SOFC mode operation of the pressurized cell, the value of Rs remained almost constant while the value of Rp decreased from 1.294 to 0.597 Ω.cm ² . The gas conversion resistance at the SOFC cell electrode depends on the flow rate of the reactive molecules in TPB (X. Sun, et al., Fuel Cells 15 (2015) 697-702). Due to the pressurization, the flux is increased, the polarization resistance is significantly reduced, and the performance of the cylindrical SOFC cell can be improved. The EIS trend observed in a cylindrical SOFC cell was similar to that of an anode supported flat plate SOFC cell (YD Hsieh, et al., J. Power Sources. 299 (2015) 1-10; R. Barfod, J. Electrochem. Soc. 154 (2007) B371-B378).

<2-3> Electrolysis In mode  Pressurized cylindrical type Of the SOC cell  characteristic

The electrochemical performance of the cylindrical SOC cell in the electrolysis mode was examined to determine the effect of various pressure parameters. 6 (a) shows the IV Curve of the pressurized cylindrical SOC cell during the electrolysis process. The inlet gas composition at the fuel electrode was H ₂ O - 60%, CO ₂ - 30% and H ₂ - 10% at 800 ° C and air was supplied to the anode (air electrode). The SOC was operated at 1 to 8 bar.

As a result, it can be seen that the slope of IV decreases as the pressure increases due to high OCV and low ASR value in FIG. 6A. A current density of 970 mA / cm ² was achieved at an applied voltage of 1.38 V at 8 bar pressure and the same current density was achieved at an applied voltage of 1.58 V under atmospheric pressure. Increasing the pressure for the electrochemical performance of SOC in the electrolysis mode is less advantageous in fuel cells. This is because the OCV is increased by increasing the pressure and the maximum voltage required at a specific current density for electrolysis is reduced at high pressure. Thus, the benefits of increasing the pressure due to high OCV values are reduced, but the performance of the SOC under pressurized conditions is significantly higher than the ambient pressure conditions.

6B and 6C show the EIS data for the SOC in the electrolysis mode. The impedance spectrum shows that increasing the pressure significantly reduces the low frequency arc but the ohmic resistance is not affected by the pressure.

As a result, the normal frequencies of low frequency and high frequency arcs were about 0.5-1 Hz and 100-150 Hz, respectively. The normal frequency of the gas conversion arc (low frequency arc) decreases with increasing pressure. EIS results showed that the ohmic resistance is significantly reduced to ² from 0.04Ωcm 0.09Ωcm ^2, 8bar at a constant 0.14Ωcm ² and the polarization resistance 1bar. FIG. 6C shows that the high-frequency arc has changed due to the high pressure. The normal frequency of the high frequency arc was affected by the pressure increase, but the effect of the pressure increase was less than that of the low frequency arc when compared with the low frequency arc. This is because low-frequency arcs are described in connection with diffusion-related polarization, whereas high-frequency arcs are described in connection with active polarization. The effect of the high pressure condition on the EIS spectrum is remarkable because it greatly affects the gas diffusion in the TPB. A comparison of 1 arc and 8 bar arcs shows that the arc size is significantly reduced. At high pressure, the mass transfer limit at the electrode is reduced, resulting in improved electrochemical performance.

Figures 7a and 7b show a comparison of ohmic and electrode polarization of a pressurized cylindrical SOC cell, respectively.

As a result, the ohmic resistance of the cell did not increase significantly by increasing the pressure in both the fuel cell and the electrolysis mode. However, as shown in Fig. 7 (b), the polarization of the electrode was considerably reduced by increasing the pressure.

FIG. 7C shows a decrease in electrode polarization resistance due to an increase in pressure.

As a result, it can be seen that the electrode polarization can be reduced by about 60% by increasing the pressure to a maximum of 8 bar. The polarization resistance values at the electrodes in both modes are reduced in the same manner, indicating that the electrochemical performance in the operating mode of the cell against pressure in the fuel cell does not significantly change. This means that the increase in pressure has a large effect on the variables related to the diffusion and availability of fuel at the reaction site.

< Experimental Example  3> Analysis of exhaust gas composition of compressed SOC cell

Figure 8 shows the effect of pressure on syngas outlet configuration at 800 占 폚 in tubular SOC. Inlet gas composition has been selected as _{10% H 2 + 30% CO} 2 + 60% H 2 O. The gas composition was determined when the cell was operated at a current density of -800 mA / cm ² for all pressure conditions. As the current density progressively increases, the H ₂ mole fraction increases significantly more than the CO mole fraction. Because the voltage required for electrolysis of H ₂ O in the current value of all densities is lower than the voltage of the electrolytic CO _2, H ₂ O electrolysis is easier than CO ₂ electrolysis (due to the faster reaction kinetics). The following reactions occur during a pressurized electrolysis operation in a cylindrical SOC cell.

2H ₂ O = 2H ₂ + O ₂ (steam electrolysis) (1)

₂ CO ₂ = ₂ CO + O ₂ (CO ₂ electrolysis) (2)

CO ₂ + H ₂ = CO + H ₂ O (reverse water gasification reaction, RWGS) (3)

CO ₂ + 4H ₂ = CH ₄ + 2H ₂ O (methanation reaction) (4)

_{CO + 3H 2 = CH 4 +} H 2 O ( methane forming reaction) 5

According to FIG. 7, it appears that the concentration of H ₂ in the outlet syngas is significantly higher than the concentration of CO. The higher the concentration of H ₂ , the faster the reaction of steam electrolysis (Equation 1) than the electrochemical conversion of carbon dioxide. It has been observed that the concentrations of reactions (1), (2) and (3) are reduced at high pressure, leading to the formation of methane resulting from the methanation reaction.

< Experimental Example  4> Cylindrical Of the SOC cell  minuteness Pressurization electricity for structure  Influence of decomposition

The microstructure of the SOC before and after the pressurization operation was observed by SEM and is shown in Fig. 9 (a) is a cross-sectional SEM micrograph of the cylindrical cell before operation. 9b and 9c show the microstructure after the pressurization operation at 1 bar and 8 bar, respectively.

As a result, FIG. 9B shows that the positive electrode side of the cell is peeled off after measurement. When operated at 8 bar, the electrolyte was observed to have not only small cracks but also peeling of both the fuel electrode and the anode.

Cracks in the electrolyte can occur for the following reasons. The cylindrical SOC cell manufacturing process consists of deposition of an electrolyte layer by vacuum slurry coating. Occasionally, during fabrication, as seen in Figure 9a, the impurities will form pinholes of micron size in the electrolyte. So the small pinhole would have undergone high pressure and would have caused crack propagation up to 8 bar at high pressure.

At high pressure, some researchers point out that carbon formation can occur due to the Boudouard reaction (2CO (g) = C (s) + CO (g)) during the electrochemical reaction. Thus, as in FIGS. 9D and 9E, the high-resolution SEM microstructure of the fuel electrode functional layer of the cell before and after operation at high pressure was analyzed.

As a result, no trace of carbon adhesion was detected from the after-test sample. In their modeling studies, the possibility of carbon formation on the Ni surface at pressures of 25 bar and above was calculated according to Sun's study (X. Sun et al., Fuel Cells. 15 (2015) 697-702) No carbon deposits were found.

SOC cell degradation during long-term operation is one of the biggest problems in high temperature electrolysis research and high-voltage operation increases cell and system stresses and results in performance loss. However, systematic and detailed studies are needed to investigate what kind of decomposition takes place when tubular cells are operated at high pressure. Ebbesen's work (Faraday Discussions 2015, 182, 393-422) explained that the operation of Ni-YSZ-based solid oxide batteries in fuel cell and electrolysis mode is different and that a further degradation in performance is observed in electrolysis mode. The diffusion limit at the fuel and air electrodes during the electrolysis operation can be easily solved by high voltage operation of the cylindrical cell as shown in the EIS analysis of the cylindrical SOC cell of FIG. In addition, studies in Hauch show that degradation contribution of the fuel electrode during electrochemical analysis seems to be related to reducing active electrode sites.

However, post-analysis of the SOC cell showed no significant degradation in microstructure due to high pressure. Thus, operation at high pressures can help mitigate the degradation effects associated with the diffusion limitations of both fuel and air electrodes. Operation of the SOC at high pressure can ensure that a value-added syngas is obtained. In addition, the cylindrical SOC cell can easily be extended to the stack with minimal leakage and the FT-reactor can be easily integrated.

Claims (9)

A cylindrical support;
A cathode layer formed on the surface of the cylindrical support;
An electrolyte layer comprising Scandia-Stabilized Zirconia (ScSZ) formed on the surface of the cathode layer;
A GDC buffer layer (Gadolinium-Doped Ceria buffer layer) formed on the surface of the electrolyte layer; And
A high pressure cylinder to a solid oxide cell comprising a revolution; LSCF formed on a surface of the buffer layer GDC _{(.... La 0 6} Sr 0 4 Co 0 2 Fe 0 8 O 3) anode layer (anode layer) consisting of a composite -GDC (solid-oxide coelectrolysis cell, SOC).
The method according to claim 1,
Wherein the electrolyte layer, the GDC buffer layer, and the anode layer have thicknesses of 4 to 8 μm, 1 to 4 μm, and 13 to 18 μm, respectively.
The method according to claim 1,
Wherein the cell has a diameter of 0.5 to 2.0 cm, a length of 3.0 to 7.0 cm and an effective electrode area of 3.0 to 4.0 cm ² .
A high-pressure cylindrical solid oxide annulus cell according to claim 1;
A pressure chamber for pressurizing said revolving cell;
A pressure controller for adjusting a pressure difference between the revolving cell and the pressure chamber;
A vaporizer for providing steam to the idol cell;
A fuel injector for injecting fuel gas and steam of hydrogen, nitrogen, and carbon dioxide into the revolving cell;
A mass flow controller for regulating the flow rate of the fuel gas; And
And a gas discharging portion for discharging the gas after the reaction from the revolving cell.
5. The method of claim 4,
Wherein the pressurizing chamber includes a heating device for heating the orbital cell. &Lt; RTI ID = 0.0 &gt; 11. &lt; / RTI &gt;
5. The method of claim 4,
And a pressure differential pressure transmitter for monitoring the pressure inside the pressure chamber.
5. The method of claim 4,
And a rupture disk for preventing rupture due to an abrupt pressure rise inside the pressure chamber.
5. The method of claim 4,
And a pump for supplying steam is connected to the vaporizer.
In the pressurized cylindrical solid oxide perturbation system of claim 4,
The pressure in the pressure chamber is 8 to 10 bar and the temperature is 800 to 850 占 폚,
Wherein the pressure difference between the pressure chamber and the idol cell is controlled to be 0.3 bar or less.

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