JP5364477B2 - Electrochemical cell - Google Patents

Description

  The present invention relates to an electrochemical cell, and more particularly to an electrochemical cell that can be used for a solid oxide fuel cell, a steam electrolysis cell, a sulfuric acid decomposition cell, a synthesis gas (carbon monoxide and hydrogen) production cell, and the like.

  In general, as a method for producing hydrogen using an electrochemical cell, there is a method utilizing a reverse reaction of a fuel cell. Among them, in the hydrogen production method using the reverse reaction of a solid oxide fuel cell (hereinafter referred to as SOFC), a solid oxide electrolysis cell (hereinafter referred to as SOEC) is used as an electrochemical cell. The hydrogen production method using SOEC is generally called high temperature steam electrolysis (hereinafter referred to as HTE).

  Such SOFC and SOEC are composed of an ion conductive solid electrolyte and a porous electrode (air electrode and hydrogen electrode). A porous electrode having a thickness of about several tens of μm has the highest efficiency (see, for example, Patent Document 1), and a solid electrolyte is generally set to a thickness of about several tens of μm in order to reduce ion transmission loss. The For this reason, many are configured to maintain the overall strength by a conductive porous support that also serves as a gas diffusion layer.

  In recent years, in order to grasp the electrochemical characteristics of the above SOFC and SOEC, analysis methods thereof have been proposed (for example, see Non-Patent Documents 1 and 2). These analysis methods are a combination of heat flow analysis and electrochemical analysis, and their validity has been verified.

JP 2004-265746 A

E. Hoashi, T. Ogawa, K. Matsunaga, K. Nakada, S. Fujiwara and S. Kasai, “Simulation Modeling of a Tubular-type Solid Oxide Electrolysis Cell for Hydrogen Production on Nuclear Power Plant”, Proceedings of 2006 International Congress on Advances in Nuclear Power Plants (ICAPP '06), ANS, Reno, Nevada, pp2287-2294, June 6-10, 2006. E. Hoashi, T. Ogawa, K. Matsunaga, K. Nakada, S. Fujiwara, H. Yamauchi, S. Kasai, K. Yamada, Y. Hirata "Development of simulation method for thermo-fluid-electrochemical coupled phenomena related to hydrogen production technology using nuclear energy ", Proceedings of 2007 ANS Annual Meeting, Embedded Topical Meeting: Safety and Technology of Nuclear Hydrogen Production, Control and Management (ST-NH2), ANS, Boston, MA, pp61-68, June 25-28 , 2007.

  The above-described electrochemical cell is required to have higher performance and higher efficiency.

  The present invention has been made in order to solve the above-described problems, and an object of the present invention is to provide an electrochemical cell that can achieve higher performance and higher efficiency than conventional ones.

  One aspect of the electrochemical cell of the present invention includes a solid electrolyte layer that is an ionic conductor, a first porous electrode layer formed on one surface of the solid electrolyte layer, and the other surface of the solid electrolyte layer. A conductive porous support for supporting the formed second porous electrode layer and the solid electrolyte layer, the first porous electrode layer, and the second porous electrode layer; and the conductive porous support. An electrochemical cell provided with a gas flow passage that circulates in a state where the surface is in contact with gas, wherein the conductive porous support has portions with different porosity, and the portions with different porosity However, the porosity is low on the upstream side in the gas flow direction of the gas flow passage, and the porosity is high on the downstream side.

  ADVANTAGE OF THE INVENTION According to this invention, the electrochemical cell which can achieve high performance and high efficiency compared with the past can be provided.

The figure which shows typically the principal part schematic structure of the electrochemical cell which concerns on 1st Embodiment of this invention. The figure which shows typically the principal part schematic structure of the electrochemical cell which concerns on 2nd Embodiment of this invention. The graph which shows the relationship between an electric current density and a flow direction position. The graph which shows an average current density and a standard deviation. The figure which shows schematic structure of a general flat plate type electrochemical cell. The figure which shows schematic structure of a general cylindrical electrochemical cell. The figure which shows typically the principal part schematic structure of the electrochemical cell which concerns on a reference example. The graph which shows the difference in the characteristic by the porosity of a porous electrode layer. The graph which shows the difference in the characteristic by the porosity of a porous support body.

  Hereinafter, embodiments of the electrochemical cell of the present invention will be described. In electrochemical cells, gas diffusion contributes greatly to its performance. In this embodiment, the combination of the porosity and the power generation (electrolysis) characteristics of the electrochemical cell having a different porosity for each porous medium (porous electrode and conductive porous support) is clarified, and It is intended to improve the performance and efficiency of chemical cells.

  5 and 6 are diagrams showing a schematic configuration of a general electrochemical cell. FIG. 5 shows a configuration of a flat plate electrochemical cell, and FIG. 6 shows a configuration of a cylindrical electrochemical cell. 5 and 6, dotted arrows indicate the flow of air, and solid arrows indicate the flow of water vapor + hydrogen. A porous electrode layer on the air electrode side, between an air flow path through which air flows as indicated by a dotted arrow and a water vapor + hydrogen flow path through which water vapor + hydrogen flows as indicated by a solid arrow, A solid electrolyte layer, a porous electrode layer on the hydrogen electrode side, and a conductive porous support for supporting them are provided. The present invention can be applied to both the flat plate electrochemical cell shown in FIG. 5 and the cylindrical electrochemical cell shown in FIG.

  FIG. 7 is an enlarged view showing a schematic cross-sectional configuration of a main part of an electrochemical cell (SOEC) according to a reference example. As shown in the figure, the electrochemical cell 300 includes an ion conductive solid electrolyte layer 1 and porous electrode layers 2 and 3 formed on both sides of the solid electrolyte layer 1. The porous electrode layer 2 constitutes an air electrode, and the porous electrode layer 3 constitutes a hydrogen electrode.

  The porous electrode layers 2 and 3 have a thickness of about several tens of μm, and the solid electrolyte layer 1 has a thickness of about several tens of μm as well. The porous electrode layer 3 is formed on the conductive porous support 4. The conductive porous support 4 maintains the strength of the electrochemical cell 300 and acts as a gas diffusion layer. For example, Ni—YSZ (nickel oxide-containing yttria stable zirconia) or the like can be used for the conductive porous support 4. For the porous electrode layer 3, for example, Ni—YSZ containing more nickel oxide than the conductive porous support 4 can be used. For the solid electrolyte layer 1, for example, a YSZ electrolyte or the like can be used. For the porous electrode layer 2, for example, perovskite ceramics can be used.

  Next, with respect to the electrochemical cell 300 having the above-described structure, a reference example in which the characteristics are analyzed using a technique combining flow analysis and electrochemical analysis described in Non-Patent Document 1, Non-Patent Document 2, and the like described above. Will be described.

  First, the analysis method will be briefly described. Basically, the electrolytic cell uses the reverse reaction of the battery to decompose water vapor and generate hydrogen. In the analysis, the behavior of water vapor, hydrogen, and oxygen is analyzed by solving the continuous equation (1), momentum conservation equation (2), energy conservation equation (3), and chemical species transport equation (4).

∂ρ / ∂t + (∂ / ∂x _j ) (ρu _j ) = s _m (1)

_{(∂ / ∂t) (ρu j} ) + (∂ / ∂x j) (ρu j u i -τ ij)
= − (∂P / ∂x _j ) + S _i (2)

(∂ / ∂t) (ρh) + (∂ / ∂x _j ) (ρu _j h−F _hj )
= ∂P / ∂t + (∂ / ∂x _j ) (u _j P) −P (∂u _j / ∂x _j )
+ Τ _ij (∂u _j / ∂x _j ) + S _h (3)

(∂ / ∂t) (ρm _m ) + (∂ / ∂x _j ) (ρu _{j mm} −F _mj ) = S _c (4)

  In addition, the potential potential difference obtained as a result of solving the conservation equation (5) of the potential potential φ is obtained as the voltage V of the electrolytic cell.

(∂ / ∂x _i ) [σ _e (∂φ / ∂x _i )] + s _e = 0 (5)

  At this time, the electrode overvoltage η and the current i can be obtained from the equation (6) using the voltage of the electrolytic cell calculated as a result of the equation (5).

V = E + iRt + η _ca + η _an (6)

  The electrode reaction rate r is determined by the following anode (7) equation and cathode (8) equation from the obtained current.

Anode: r _an = i / (4F) (7)
Cathode: r _ca = i / (2F) (8)

Source term S _c of the reaction rate obtained was species transport diffusion equation _(4), the current i is obtained in the source term S _e of electric potential conservation equation (5), each of the behaviors, and the distribution re calculate.

  Table 1 shows the porosity of the porous electrode layers 2 and 3 analyzed for Reference Examples 1 to 3 and the porosity of the conductive porous support 4.

  As shown in Table 1, in Reference Examples 1 to 3, with the porosity of the conductive porous support 4 being constant at 40%, the porosity of the porous electrode layers 2 and 3 was 20% and 15%. It was changed to 10%. The analysis results are shown in the graph of FIG. 8 with the vertical axis representing the electrolysis voltage and the horizontal axis representing the current density. As shown in FIG. 8, Reference Example 3 in which the porosity of the porous electrode layers 2 and 3 is as small as 10% is different from Reference Example 2 in which the porosity is high (Porosity 15%), Reference Example 1 (Porosity 20) %), The slope on the graph is small, a high current density is obtained at a low electrolysis voltage, and the electrolysis efficiency is improved.

  As described above, when the porosity of the conductive porous support 4 is constant, the smaller the porosity of the porous electrode layers 2 and 3, the better the electrolysis efficiency (the smaller the slope in electrolysis). Is good). Therefore, the porosity of the porous electrode layers 2 and 3 is preferably about 10 to 20%, and more preferably about 10%. Thereby, a highly efficient electrochemical cell can be realized.

  Table 2 shows the porosity of the porous electrode layers 2 and 3 analyzed for Reference Examples 4 to 6 and the porosity of the conductive porous support 4.

  As shown in Table 2, in Reference Examples 4 to 6, with the porosity of the porous electrode layers 2 and 3 being constant at 10%, the porosity of the conductive porous support 4 was 20%, 30 % And 50%. The analysis results are shown in the graph of FIG. 9 with the vertical axis representing the electrolytic voltage and the horizontal axis representing the current density. In addition, the graph of FIG. 9 also describes the above-described Reference Example 3 in which the porous electrode layers 2 and 3 have a porosity of 10% and the conductive porous support 4 has a porosity of 40%. .

  As shown in FIG. 9, when the porosity of the porous electrode layers 2 and 3 is constant, the higher the porosity of the conductive porous support 4 is, the smaller the slope on the graph is, and the lower the electrolysis voltage is. A high current density is obtained, and the electrolysis efficiency is improved. Therefore, the porosity of the conductive porous support 4 is preferably about 30 to 50%. Thereby, a highly efficient electrochemical cell can be realized.

  Next, an embodiment of the present invention will be described. In the electrochemical cell 100 of 1st Embodiment, as shown in FIG. 1, the electroconductive porous support body 4 follows the flow direction (it shows with the arrow in a figure) of water vapor | steam + hydrogen (in the case of SOFC). The conductive porous supports 4a, 4b, and 4c having different porosity. These conductive porous supports 4a, 4b, and 4c are arranged such that the upstream porosity in the steam flow direction is low and the downstream porosity is high. In the case of this embodiment, the porosity of the conductive porous support 4a at the most upstream side is 30%, the porosity of the conductive porous support 4b at the intermediate portion is 40%, and the conductive porous support at the most downstream side. The porosity of the body 4c is 50%.

  In addition, since it is the same as that of the electrochemical cell 300 shown in FIG. 7 mentioned above about the structure and material of another part, the same code | symbol is attached | subjected to a corresponding part and the overlapping description is abbreviate | omitted. In FIG. 1, the air flow direction is shown to be the same as the water vapor + hydrogen flow direction. However, the air flow direction may be the reverse direction or the orthogonal direction. . These points are the same in the second embodiment described later.

  FIG. 1 (and FIG. 2 described later) schematically shows the structure of the electrochemical cell 100 (200). The ratio of the dimension in the thickness direction to the dimension in the gas flow direction is as follows. It does not indicate the actual ratio. That is, for example, the thickness in the thickness direction of the solid electrolyte layer 1 and the porous electrodes 2 and 3 is actually about 10 to 50 μm, and the conductive porous support 4 is the actual dimension in the thickness direction. Is about several millimeters and the dimension in the gas flow direction is about several tens of millimeters (eg, about 40 mm).

  FIG. 2 shows the configuration of the electrochemical cell 200 of the second embodiment. In the electrochemical cell 200 of the second embodiment, the conductive porous support 4 has different porosity along the flow direction (indicated by an arrow in the figure) of water vapor + hydrogen (hydrogen in the case of SOFC). It is composed of conductive porous supports 4a and 4c. These conductive porous supports 4a and 4c are arranged so that the porosity on the upstream side in the steam flow direction is low and the porosity on the downstream side is high. In the case of this embodiment, the porosity of the conductive porous support 4a in the upstream portion of the entire length of 30% is 30%, and the downstream conductive porous in the length of 3/4 of the entire length. The porosity of the support 4c is 50%.

  FIG. 3 shows the electrochemical cell 100 according to the first embodiment, the electrochemical cell 200 according to the second embodiment, and the reference examples 1 to 6 described above, where the vertical axis represents current density and the horizontal axis represents the flow direction position of water vapor. Is a graph showing the relationship between the current density and the position in the flow direction when the electrolysis voltage is 1.3V. FIG. 4 shows these values of Reference Examples 1 to 6 and the first and second embodiments, where the vertical axis is the standard deviation (%) from the average current density of the flow direction distribution and the vertical axis is the average current density. Plotted.

  The flow direction distribution of the current density shown in FIG. 3 is more efficient when it is flat, the temperature distribution is smaller, and the load is structurally smaller. FIG. 4 shows that the standard deviation is small and the current density is large, that is, the performance is improved toward the lower right. As shown in FIGS. 3 and 4, in the first and second embodiments, the current density distribution in the flow direction is more uniform, the standard deviation thereof is lower, and the average current density is also higher. Yes.

  As described above, in the first and second embodiments, by increasing the porosity of the conductive porous support on the upstream side and increasing the porosity on the downstream side, the electrolysis efficiency is high, and higher performance and higher performance than in the past can be achieved. An electrochemical cell that can achieve high efficiency can be provided.

  In addition, this invention is not limited to the said embodiment, Of course, various deformation | transformation are possible. For example, the number of portions having different porosity of the conductive porous support may be 4 or more. In addition, there is no conductive porous support whose porosity differs stepwise as in the first and second embodiments, and for example, it is expressed by an arbitrary function such as a first-order or higher polynomial, exponential function, logarithmic function, etc. Alternatively, a conductive porous support having a continuously changing porosity may be used.

  DESCRIPTION OF SYMBOLS 1 ... Solid electrolyte layer, 2 ... Porous electrode layer (air electrode), 3 ... Porous electrode layer (hydrogen electrode), 4, 4a, 4b, 4c ... Conductive porous support, 100, 200 …… Electrochemical cell.

Claims (5)

A solid electrolyte layer that is an ionic conductor;
A first porous electrode layer formed on one surface of the solid electrolyte layer;
A second porous electrode layer formed on the other surface of the solid electrolyte layer;
A conductive porous support for supporting the solid electrolyte layer, the first porous electrode layer, and the second porous electrode layer is provided, and the surface of the conductive porous support and gas are in contact with each other. An electrochemical cell provided with a gas flow path,
The conductive porous support has a portion with a different porosity, and the portion with a different porosity has a low porosity on the upstream side in the gas flow direction of the gas flow passage and a high porosity on the downstream side. An electrochemical cell characterized in that The electrochemical cell according to claim 1, wherein
The electrochemical cell, wherein the conductive porous support has a thickness 100 times or more that of the solid electrolyte layer, the first porous electrode layer, and the second porous electrode layer. The electrochemical cell according to claim 1 or 2,
The electrochemical cell, wherein the solid electrolyte layer, the first porous electrode layer, and the second porous electrode layer have a thickness of 10 to 50 μm. The electrochemical cell according to any one of claims 1 to 3,
The electrochemical cell, wherein the porosity of the first porous electrode layer and the second porous electrode layer is 10 to 20%. An electrochemical cell according to any one of claims 1 to 4, wherein
An electrochemical cell having a porosity of 30 to 50% of the conductive porous support.

Images