Electrolysis Cell Control System

Abstract

An electrolytic cell control system is provided that can chemically control the maximum power point of environmental power generation, level out fluctuations in input energy, and autonomously manufacture chemical products. [Solution] An electrolytic cell control system 10 controls the process of a chemical reaction in an electrolytic cell using power obtained by environmental power generation, and includes at least an environmental power generation device 20 that generates power using natural energy, an electrolytic cell 30 that performs an electrolytic reaction using power from the environmental power generation device 20, and a supply mechanism 40 that supplies raw materials for the electrolytic reaction to the electrolytic cell 30, wherein the electrolytic cell 30 has a carrier 33 that mediates mass transfer between an anode 31 and a cathode 32, and the carrier 33 is made of a material with a negative temperature coefficient (NTC).

Description

[Technical Field]

[0001] The present invention relates to an electrolytic cell control system that controls a process in which a chemical reaction is carried out in an electrolytic cell using power obtained by energy harvesting. [Background technology]

[0002] Energy harvesting using natural energy such as solar power generation has two limitations compared to existing commercial power sources. The first is the time instability of the output energy amount, which comes from using the natural environment as an input energy source. The second is the existence of a maximum power point for the output energy.

[0003] Existing commercial energy harvesting devices address these constraints by using a large-capacity energy storage device to address the first constraint and an electromechanical maximum power point tracker to address the second constraint. The advantage of this method is that it is easy to scale up because it is a combination of existing electromechanical technologies, and it is versatile because it is compatible with commercial power. However, the energy density of the energy storage device is lower than that of liquid fuel, so the energy storage device is bulky in terms of both weight and volume.

[0004] This problem of storage batteries is now widely recognized, and various technological solutions are being considered. One of these is to convert the generated energy into chemical products such as liquid fuel and store it as chemical energy. In particular, the method of electrolytically reducing and fixing carbon dioxide (CO2) to carboxylic acids or alcohols is gaining importance because it also allows for the effective use of carbon dioxide.

[0005] However, known methods, such as connecting solar cells to an electromechanical control device (Non-Patent Document 1) or directly connecting solar cells but optimized for a specific maximum power point (Non-Patent Document 2), cannot solve the second constraint on renewable energy use mentioned above without an electromechanical maximum power point tracker.

[0006] A method has been reported to solve the second limitation by perfectly matching the electrical characteristics of the photovoltaic (PV) generators with those of the electrolytic cells during the manufacturing of the solar power generation equipment (Non-Patent Document 3). However, in addition to the cost issue, there are still drawbacks, such as the fact that suitable electrolytic cells are not always found.

[0007] Furthermore, in existing methods, the first constraint is that the concentration of the product fluctuates depending on the raw output of the energy harvester (unless it is connected to an electrotechnical control device as mentioned above), and for quality control of the product, uneven concentration should be avoided. An ideal system that claims to use renewable energy must simultaneously and autonomously address these two constraints. For example, existing methods use electrically driven pumps to control the flow of liquids and gases, but these pumps are generally powered by external commercial electricity, and therefore cannot be considered energy independent. [Prior art documents] [Non-patent literature]

[0008] [Non-Patent Document 1] Journal of CO2 Utilization, 2014, Vol.7, p.1-5 [Non-patent document 2] Joule, 2021, Vol.5, pp.687-705 [Non-patent document 3] ACS Applied Energy Materials, 2022, Vol.5, p.8241-8253 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made in view of the above circumstances, and aims to provide an electrolytic cell control system that can chemically control the maximum power point of environmental power generation, level out fluctuations in input energy, and autonomously produce chemical products. [Means for solving the problem]

[0010] One aspect of the present invention is an electrolytic cell control system that controls a process of a chemical reaction in an electrolytic cell using power obtained by environmental power generation, and includes at least an environmental power generation device that generates power using natural energy, an electrolytic cell that performs an electrolytic reaction using power from the environmental power generation device, and a supply mechanism that supplies raw materials for the electrolytic reaction to the electrolytic cell, wherein the electrolytic cell has a carrier that mediates mass transfer between an anode and a cathode, and the carrier is made of a material that has a negative temperature coefficient (NTC). The supply mechanism includes a supply pump that supplies the raw material to the electrolytic cell, and a control device that acquires information about the amount of current from the energy harvester and adjusts the flow rate of the supply pump based on the information. This allows the coefficient in the equation relating the heat dissipation constant δ of the electrolytic cell to the flow rate v of the fluid flowing inside the electrolytic cell, and the current I flowing through the electrolytic cell to be calculated. cell By optimizing the coefficients in the equation relating to the flow velocity v and the input energy fluctuations, it is possible to chemically control the maximum power point of the energy harvester without using any external power source other than the energy harvester, and to autonomously produce chemical products. It is characterized by:

[0013] In one aspect of the present invention, the energy harvesting may be solar power generation.

[0014] In one aspect of the present invention, the electrolysis cell may produce formic acid using carbon dioxide as a raw material. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide an electrolytic cell control system that can chemically control the maximum power point of environmental power generation while leveling out fluctuations in input energy and autonomously producing chemical products. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic diagram illustrating an example of an electrolysis cell control system according to an embodiment of the present invention. [Figure 2] FIG. 1A is a graph showing the power versus time of photovoltaic (PV) power generation in one embodiment of the present invention, and FIG. 1B is a graph showing the concentration of chemical products versus time of an electrolytic cell in one embodiment of the present invention. [Figure 3] FIG. 1 is a diagram comparing the IV characteristics shown in the equation (Equation 5) derived in the present invention with the (theoretical) IV characteristics of the maximum power point in ideal photovoltaic power generation (PV). [Figure 4] FIG. 1 is a diagram showing the dependence of the concentration of chemical products discharged from an electrolytic cell having IV characteristics as shown in the formula (Formula 5) derived in the present invention on the intensity of sunlight. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. Note that the embodiments described below do not unduly limit the content of the present invention as defined in the claims, and not all of the configurations described in the embodiments are necessarily essential as means for solving the problems of the present invention.

[0018] 1 is a schematic diagram showing an example of an electrolytic cell control system according to one embodiment of the present invention. One aspect of the present invention is an electrolytic cell control system 10 that controls a process of a chemical reaction in an electrolytic cell using power obtained by energy harvesting, and includes at least an energy harvesting device 20 that generates power using natural energy, an electrolytic cell 30 that performs an electrolytic reaction using the power from the energy harvesting device 20, and a supply mechanism 40 that supplies raw materials for the electrolytic reaction to the electrolytic cell 30. The electrolytic cell 30 has a carrier 33 that mediates mass transfer between an anode 31 and a cathode 32, and the carrier 33 is made of a material with a negative temperature coefficient (NTC).

[0019] The energy harvesting device 20 is a device that generates power by utilizing natural energy such as sunlight, wind power, hydropower, geothermal power, etc. As an example, the energy harvesting device 20 can use photovoltaic power generation (PV) as shown in Fig. 1, but it may also be a power generation device that utilizes natural energy other than sunlight.

[0020] The electrolytic cell 30 performs an electrolytic reaction using power from the energy harvesting device 20. The electrolytic cell 30 has at least an anode 31, a cathode 32, and a carrier 33 that mediates mass transfer between the anode 31 and the cathode 32, and applies a voltage to the raw material supplied to the carrier 33 to cause an oxidation-reduction reaction, thereby producing a desired chemical product. In FIG. 1, three electrolytic cells are arranged in series, but the number and arrangement of the electrolytic cells are not particularly limited.

[0021] The chemical products produced by the reaction in the electrolytic cell 30 of the present invention are not particularly limited, but an example is the production reaction of formic acid. In this case, the raw materials are water and carbon dioxide, which are supplied from a raw material tank 45 using a supply pump 41. Alternatively, exhaust gas from the external environment or machinery may be recovered and supplied. As an example, an all-solid-state electrochemical cell may be used, in which a catalyst capable of oxidizing water is supported on the anode 31, and a catalyst capable of reducing carbon dioxide is supported on the cathode 32. In this way, protons (H + ) is generated at the cathode 32, and formate anions (HCO2 - ) is produced, and a proton (H + ) and formate anion (HCO2 - ) reacts to liberate formic acid (HCOOH), which is then discharged to the outside of the electrolysis cell 30. For example, the discharged formic acid is stored in a tank or the like, and when necessary, hydrogen (H2) is generated by decomposing the formic acid using a catalyst or the like, and this hydrogen (H2) can be used as an energy source.

[0022] The supply mechanism 40 is a mechanism that supplies raw materials for the electrolysis reaction to the electrolytic cell 30. As an example, as shown in Fig. 1, the supply mechanism 40 can be configured to include a supply pump 41 that supplies raw materials from a raw material tank 45 to the electrolytic cell 30, and a control device 42 that acquires information about the amount of current from the energy harvester 20 and adjusts the flow rate of the supply pump 41 based on that information. The information about the amount of current is acquired, for example, from the measurement value of an ammeter 43.

[0023] In an electrolytic cell control system 10 according to one embodiment of the present invention, as shown in Fig. 1, the positive electrode 21 and negative electrode 22 of an environmental power harvester 20 are directly connected to the anode 31 and cathode 32 of an electrolytic cell 30, respectively. An ammeter 43 is installed in this electric line, and a control device 42 monitors the value of this ammeter 43 while also taking in power. The control device 42 controls the flow rate of a supply pump 41 based on the value of the ammeter 43.

[0024] In one embodiment of the present invention, the supply mechanism 40 is preferably driven by power obtained by energy harvesting. That is, as shown in FIG. 1 , the supply mechanism 40 can be configured to use power from the energy harvesting device 20 as a power source for the supply pump 41 and the control device 42. As will be described later, if the amount of power generated by the energy harvesting device 20 decreases due to the influence of the natural environment, the reaction rate in the electrolytic cell 30 also decreases, and therefore the supply rate of the supply pump 41 that supplies raw materials can also be reduced, thereby reducing power consumption. In this way, the electrolytic cell control system 10 according to one embodiment of the present invention can operate autonomously (self-sustainingly) without requiring external power.

[0025] FIG. 2(A) is a graph showing the power versus time for photovoltaic (PV) power generation in one embodiment of the present invention, and FIG. 2(B) is a graph showing the concentration of chemical products versus time for an electrolytic cell in one embodiment of the present invention. In energy harvesting, as shown in FIG. 2(A), the power generated by power generation fluctuates depending on external factors such as the time of day and weather. Even in such cases, by applying the electrolytic cell control system 10 according to the present invention, it is possible to control the concentration of chemical products generated in the electrolytic cell so that there is almost no fluctuation, as shown in FIG. 2(B).

[0026] In the present invention, the carrier 33 of the electrolytic cell 30 is characterized by being made of a material having a negative temperature coefficient (NTC). Examples of the carrier 33 include ion exchange resins and proton-conductive solids such as Nafion. In the present invention, the carrier 33 (NTC) must have the following two properties: (1) The NTC is a porous carrier that mediates mass transfer (e.g., protons) between the anode 31 and the cathode 32. It distributes substances contained in the fluid from the supply pump 41 to the anode 31 and the cathode 32, and also recovers products at the anode 31 and the cathode 32 and discharges them outside the electrolysis cell 30. (2) The mass transfer rate between the anode 31 and cathode 32 inside the NTC increases with increasing temperature. This means that the electrical resistance of the NTC has a negative temperature coefficient with respect to temperature.

[0027] Furthermore, the electrolytic cell control system 10 according to one embodiment of the present invention achieves the following two things simultaneously without external power: (1) Maximum power control of the energy harvester is automatically performed, and the power transmission obtained by power generation can be maximized by matching the output resistance of the energy harvester with the input resistance of the electrolytic device as closely as possible. (2) The input power is converted into chemical products by the electrolytic device. At this time, the concentration of the resulting chemical products is kept constant (or the influence of input power fluctuations on concentration changes is significantly reduced).

[0028] Next, the principles of the present invention will be explained. First, a method for chemically controlling the maximum power point of energy harvesting according to the present invention will be considered. The "chemical" maximum power point control of the input power generated by the energy harvesting device 20 in the electrolysis cell control system 10 according to one embodiment of the present invention is based on the principle that (1) the ionic conductivity (corresponding to electrical conductivity) inside the NTC can be adjusted by (2) the flow rate of the fluid (water or substrate gas) flowing inside the NTC.

[0029] Electrical resistance (reciprocal of ionic conductivity) R of NTC at a certain temperature T ntc (T) is generally expressed by the following formula 1. Here, T0 is a reference temperature (for example, room temperature of 25 degrees), and B is a temperature coefficient.

number

[0030] On the other hand, in the thermal equilibrium state, the power consumption P cell The relationship between the temperature T of the NTC and the air temperature T0 outside the electrolytic cell is expressed by the heat dissipation constant δ in the following equation 2. δ is related to the flow rate v of the fluid flowing inside the NTC in the following equation 3. Here, a and b are coefficients whose values ​​are determined by the type of fluid used and the internal structure of the electrolytic cell. The value of the flow rate v is determined by the current I flowing through the electrolytic cell. cell The current I cell Any other formula may be used as long as it includes the above formula (formula 3' below).

number

number

number

[0031] Here, if T and T0 in Equation 1 and Equation 2 are the same, the electrical resistance R of the NTC ntc and the power consumption of the electrolysis cell Pcell The relationship expressed by the following formula 4 holds between them.

number

[0032] The internal resistance of the electrolytic cell is the resistance at the anode, R a , resistance at the cathode R c , resistance R of the NTC ntc The IV characteristics of the electrolytic cell are expressed by the following formula 5: R cell I cell and V.

number

[0033] The sum of the electrical resistances of both reactions, R rxn (=R a +R c ) is approximated by the following equation 5', assuming that the kinetics of the anode and cathode reactions follow the Tafel equation for simplicity: where k0 is the standard reaction rate constant, α is the charge transfer coefficient, F is the Faraday constant, R is the gas constant, and E0 is the sum of the standard electrode potentials of the electrochemical reactions occurring in the cathode and anode compartments.

number

[0034] Figure 3 compares the IV characteristics shown by the equation (Equation 5) derived in this invention with the (theoretical) IV characteristics of the maximum power point in an ideal photovoltaic (PV) system. The curve based on Equation 5 shows the results when the internal parameter b of the heat dissipation constant δ is changed in the range of 0.0-1.0. In addition, in the (theoretical) IV characteristics of the maximum power point in an ideal PV system, the solar radiation intensity at AM1.5G is set to 100%, and the corresponding current and current value are shown with black circles in increments of 10%.

[0035] In creating Figure 3, the photovoltaic power generation (PV) was performed using monocrystalline Si solar cells (12 cells in series), T0 was 298K, B was 6000, and R ntc (T0) was set to 2 Ω, a to 0.5, and r and s to 1. By changing the coefficient b in δ from 1 to 0, the IV curve of the electrolytic cell changes significantly. This shows that by optimizing the coefficients a and b in δ, as well as r and s, the IV curve of the electrolytic cell can be adjusted to follow the maximum power point curve of the PV. In the case of Figure 3, the optimal value of coefficient b is around 0.5, which enables the electrolytic cell to operate at the maximum power point in the illuminance range of 20% or more of AM1.5G.

[0036] Second, we consider a method of autonomously producing chemical products while leveling out fluctuations in input energy according to the present invention. As described above, raw materials are supplied to the electrolytic cell 30 by the supply pump 41. By increasing or decreasing (for example, proportionally) the flow rate of the supply pump 41 according to the amount of current from the energy harvester 20, the following three points can be achieved. (1) The concentration of the product discharged from the electrolytic cell 30 can be leveled. (2) The power consumption of the supply pump 41 must be low relative to the power consumption of the electrolytic cell 30 itself so as not to interfere with maximum power point control by the NTC. However, when the power consumption of the electrolytic cell 30 itself is low, the pump flow rate can be slow, and therefore the power consumption of the supply pump 41 is also low. In other words, the ratio of the power consumption of the supply pump 41 to the power consumption of the electrolytic cell 30 itself is always kept constant, ensuring stable operation of maximum power point control. (3) By achieving the above two items, the electrolytic cell control system 10 according to one embodiment of the present invention can operate energetically independently as a package of chemical product manufacturing devices.

[0037] Regarding the above advantages (1) and (2), it is not clear to what extent they are leveled out or under what conditions they are guaranteed, so the principles are explained below. cell The production rate of chemicals m [mol / s] relative to [W] is the energy efficiency coefficient η EEThe relationship is expressed by the following formula 7 using [%].

number

[0038] Here, u [J / mol] is the molar energy density of the chemical. The concentration c [mol / L] of the chemical is related to the flow rate v [L / s] in the following equation 8, so P cell and c are related by the following formula 9. By substituting the above formula 3' into this formula, c is the voltage V and current I cell (where V is both the electrolytic cell voltage and the PV voltage).

number

number

[0039] The dependence of concentration c on the solar radiation intensity is mainly determined by the s value, and c is the cell power consumption P cell When s=1.0, it is proportional to the cell voltage V, and when s=2.0, it is proportional to the cell resistance R cell From the viewpoint of leveling out the concentration, it is important when the s value is close to 1.0.

[0040] Figure 4 shows the dependence of the concentration of chemicals discharged from an electrolytic cell with IV characteristics as expressed by the equation (Equation 5) derived in this invention on the intensity of sunlight. The graph shows the results when the internal parameter s of the flow rate v is varied in the range of 0.0-2.0. The parameters used to calculate the numerical solution of Equation 5 are the same as those in Figure 3, except that b = 0.5.

[0041] The voltage V is calculated using Equation 5 and Equation 10 (IV characteristics in an ideal PV. Here, η PV is the photoelectric conversion efficiency, G is the solar radiation intensity, I s is the saturation current, q is the elementary charge, n is the ideality of the diode, k Bis the Boltzmann constant and T is the surface temperature of the PV), when s = 1.0, it becomes almost constant in the illuminance range of 10% or more of AM1.5G, as shown in Figure 4. In other words, based on Equation 9, in this illuminance range, the concentration of the produced chemicals can be controlled to be almost constant (fluctuation rate ±10%), and advantage (1) can be achieved.

number

[0042] By the way, the power consumption by the pump P pump is f×v=f×r(I cell ) s =V×I pump (where f is the power consumption coefficient). If a pump is installed in parallel with the electrolysis cell as in the configuration of Figure 1, Equation 5 is transformed into Equation 11 below based on the relationship in Equation 12 below. In other words, even when the pump is installed in parallel with the cell, the PV can be operated at its maximum power point by optimizing the parameters δ and v in Figure 3 according to Equation 11, just as in the case of Equation 5. When the power consumption coefficient of the pump is small, f × r(I cell ) s-1 Since the power consumption by the pump is small, it can be ignored. Also, if the power consumption by the pump is proportional to the flow velocity v, it becomes easy to optimize the coefficients. In this way, advantage (2) can also be achieved.

number

number

[0043] Although the embodiments and examples of the present invention have been described in detail above, it will be readily apparent to those skilled in the art that many modifications are possible without substantially departing from the novel features and effects of the present invention. Therefore, all such modifications are intended to be included within the scope of the present invention.

[0044] For example, a term that is described at least once in the specification or drawings together with a different term having a broader or similar meaning can be replaced with that different term anywhere in the specification or drawings. Furthermore, the configuration of the electrolytic cell control system is not limited to those described in the embodiments and examples of the present invention, and various modifications are possible. [Explanation of symbols]

[0045] 10 electrolysis cell control system, 20 energy harvester, 21 positive electrode, 22 negative electrode, 30 electrolysis cell, 31 anode, 32 cathode, 33 carrier, 40 supply mechanism, 41 supply pump, 42 control device, 43 ammeter, 45 raw material tank

Claims

1. An electrolytic cell control system for controlling a process of a chemical reaction in an electrolytic cell using power obtained by environmental power generation, at least, An environmental power generation device that generates electricity using natural energy; an electrolysis cell that performs an electrolysis reaction using power from the energy harvesting device; a supply mechanism for supplying raw materials for the electrolysis reaction to the electrolysis cell Equipped with The electrolytic cell has a carrier for mass transfer between an anode and a cathode; The carrier is made of a material having a negative temperature coefficient (NTC), The supply mechanism includes: a feed pump for feeding the raw material to the electrolysis cell; By providing a control device that acquires information about the amount of current from the energy harvesting device and adjusts the flow rate of the supply pump based on the information, By optimizing the coefficient in the equation relating the heat dissipation constant δ of the electrolytic cell and the flow velocity v of the fluid flowing inside the electrolytic cell, and the coefficient in the equation relating the current I cell flowing through the electrolytic cell and the flow velocity v, An electrolytic cell control system that is capable of chemically controlling the maximum power point of environmental power generation without using any external power source other than the environmental power generation device, while leveling out fluctuations in input energy and autonomously producing chemical products.

2. 2. The electrolytic cell control system according to claim 1, wherein the energy harvesting is solar power generation.

3. 3. The electrolytic cell control system according to claim 1, wherein the electrolytic cell produces formic acid using carbon dioxide as a raw material.

Images