Fuel cell potential control device

Abstract

To provide a fuel cell potential control device capable of minimizing the degradation of a cathode catalyst without sacrificing power density and power generation efficiency.SOLUTION: A fuel cell potential control device includes: means for obtaining a load demand P for a polymer electrolyte fuel cell and a total voltage V(i) at time i; means for calculating, based on the V(i), the total amount M(i) of oxide and hydroxide of cathode side metal-based catalyst particles at the time i; means for, when the M(i) is less than ε1, decreasing the upper limit potential VH of a fuel cell and / or increasing the lower limit potential VL, and, when the M(i) is equal to or more than ε2 (≥ε1), increasing the VH and / or decreasing the VL; means for, based on the P, setting a control point determined by an output current IP and an output voltage VP; and means for, when VH>VP is not satisfied, outputting the VH, as a voltage V(i+1) at time (i+1), when VL<VP is not satisfied, outputting the VL, as the voltage V(i+1), and when VL<VP<VH is satisfied, outputting the VP, as the voltage V(i+1).SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a fuel cell potential control device, and more specifically, to a fuel cell potential control device capable of controlling a fuel cell so that, when a load is required for the fuel cell, the requested power is output, the power generation efficiency is relatively high, and deterioration of the cathode catalyst is minimized. [Background technology]

[0002] A polymer electrolyte fuel cell is equipped with a membrane electrode assembly (MEA) in which catalyst-containing catalyst layers are bonded to both sides of an electrolyte membrane. The catalyst layer is the reaction field for the electrode reaction, and generally consists of a composite of carbon carrying catalyst particles such as platinum and a solid polymer electrolyte (catalyst layer ionomer). In a polymer electrolyte fuel cell, a gas diffusion layer is usually arranged on the outside of the catalyst layer. A current collector (separator) equipped with a gas flow path is also arranged on the outside of the gas diffusion layer. A polymer electrolyte fuel cell usually has a structure (fuel cell stack) in which a plurality of unit cells each consisting of such an MEA, gas diffusion layer, and current collector are stacked.

[0003] When a polymer electrolyte fuel cell is used as an on-board power source, the voltage of the polymer electrolyte fuel cell varies greatly depending on the driving conditions of the vehicle. When the polymer electrolyte fuel cell is in a low-load state, the power generation efficiency is high, but the cathode catalyst is exposed to a high potential state, so that the catalytic components are easily eluted from the cathode catalyst. On the other hand, when the polymer electrolyte fuel cell is in a high-load state, the power generation efficiency is low, but the cathode catalyst is exposed to a low potential state, so that the eluted catalytic components are easily redeposited on the surface of the cathode catalyst. Therefore, when the cathode catalyst is repeatedly exposed to high and low potential states, there is a problem that the cathode catalyst gradually deteriorates.

[0004] In order to solve this problem, various proposals have been made in the past. For example, Patent Document 1 discloses a fuel cell system that, when it is determined that the output voltage at an operating point of the fuel cell will exceed an upper limit voltage value, causes the fuel cell to generate electricity so that the upper limit potential becomes the output voltage of the fuel cell instead of the output voltage at the operating point. Patent document 2 discloses a fuel cell system that sets the current drawn from the fuel cell stack so that the voltage of the fuel cell stack is below a predetermined voltage when the idle stop state is released and the fuel cell system transitions to a low-load idle state.

[0005] Patent Document 3 discloses a control device for a fuel cell system that limits the output voltage of the fuel cell to a predetermined upper limit or lower if it is determined that oxidant gas is present at the oxidant electrode when the fuel cell is started up. Patent Document 4 discloses a fuel cell system equipped with a control means for controlling the output voltage of the fuel cell to avoid high potential, with an upper limit of a high potential avoidance voltage that is lower than the open end voltage of the fuel cell.

[0006] Patent Document 5 discloses a fuel cell system in which, when the fuel cell system is in an idle-stop state, an oxidant gas supply means is operated so that the maximum cell voltage of the fuel cell unit is equal to or lower than a preset upper limit voltage. Patent document 6 discloses a fuel cell system that prevents the total voltage of the fuel cell from exceeding a predetermined high-potential avoidance voltage threshold by maintaining the converter command voltage at a high-potential avoidance voltage that is lower than the open circuit voltage of the fuel cell.

[0007] Patent Document 7 discloses a power generation amount control device for a fuel cell that uses the smaller of the output of an output upper limit value calculation means or the output of a target power generation amount calculation means as a command value for the output to be taken from the fuel cell. Patent Document 8 discloses a fuel cell system that judges the predicted state of deterioration of an electrode catalyst layer in a fuel cell, and determines an upper limit of the output voltage of the fuel cell according to the judged state of deterioration.

[0008] Patent Document 9 discloses a fuel cell system in which the lower limit voltage and the upper limit voltage of the fuel cell during system operation are set taking into consideration the progress of deterioration of the carbon support due to potential fluctuations. Patent document 10 discloses a fuel cell system equipped with a control means for controlling the operation of the fuel cell with the output voltage of the fuel cell set at an upper limit of a high potential avoidance voltage that is lower than the open end voltage, and a high potential avoidance voltage setting means for variably setting the high potential avoidance voltage according to the charging state of a power storage device.

[0009] Furthermore, Patent Document 11 states: A fuel cell that receives a supply of reactant gas and generates electricity; a power storage device that stores at least a portion of the power generated by the fuel cell; a control unit that controls a lower limit potential of the fuel cell when it is predicted that the charge amount of the power storage device will reach an upper limit charge threshold so that the charge amount of the power storage device does not exceed the upper limit charge threshold; A fuel cell system comprising:

[0010] Deterioration of a fuel cell can be suppressed to some extent by defining the range (upper and lower limit potential) in which the fuel cell is operated. This is also expected to improve durability. However, in Patent Documents 1 to 7, the range in which the fuel cell is operated is fixed, which results in a tradeoff between a decrease in power generation efficiency and a decrease in the output density of the fuel cell. The reason for the decrease in power generation efficiency is that the lower the load on a fuel cell, the higher its power generation efficiency. If an upper limit potential is set, the fuel cell cannot be used at the most efficient power generation point, and power generation efficiency decreases. Moreover, the reason for the decrease in the power density is that when a lower limit potential is set, the power that can be swept from the fuel cell is limited.

[0011] On the other hand, Patent Document 8 discloses a method for varying the upper limit potential depending on the deterioration state of the electrode catalyst layer. However, the method described in this document only extends the life of the fuel cell by changing the upper limit potential depending on the number of fluctuations, and is unable to achieve both high power generation efficiency and high output density. Patent Document 9 discloses a method for varying the upper and lower limit potentials depending on the deterioration state of the carbon support. However, the method described in this document, like Patent Document 8, is unable to achieve both power generation efficiency and output density. Furthermore, the methods described in Patent Documents 10 and 11 are methods for suppressing deterioration (overcharging) of a power storage device, and are not methods for suppressing deterioration of a fuel cell. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] JP 2012-094257 A [Patent Document 2] JP 2006-309971 A [Patent Document 3] JP 2008-165994 A [Patent Document 4] JP 2009-129639 A [Patent Document 5] JP 2007-109569 A

[0013] [Patent Document 6] JP 2009-104977 A [Patent Document 7] JP 2003-036871 A [Patent Document 8] JP 2012-129069 A [Patent Document 9] JP 2010-021072 A [Patent Document 10] JP 2009-129647 A [Patent Document 11] JP 2013-098052 A Summary of the Invention [Problem to be solved by the invention]

[0014] The problem that the present invention aims to solve is to provide a fuel cell potential control device that can control a fuel cell so as to minimize deterioration of the cathode catalyst when a load is required on the fuel cell, without sacrificing output density or power generation efficiency. [Means for solving the problem]

[0015] In order to solve the above problems, the fuel cell potential control device according to the present invention comprises: (A) a first means for acquiring a load requirement P for a polymer electrolyte fuel cell and storing said P in a memory; (B) a second means for acquiring a total voltage V(i) of at least the solid polymer fuel cell at time i and storing the V(i) in the memory; (C) a third means for calculating a total amount M(i) of precious metal oxide and precious metal hydroxide contained in the cathode-side precious metal-based catalyst particles at the time i based on at least the V(i) and storing the M(i) in the memory; (D) When the M(i) is less than the first threshold ε1 (or the M(i) is equal to or less than the ε1), the potential range V r Upper limit potential V H and / or the V r The lower limit potential V L Increase When the M(i) is equal to or greater than the second threshold ε2 (≧ε1) (or when the M(i) is greater than the ε2), the V H and / or increasing the V L Reduce The V after increase or decrease H and / or the V L A fourth means for storing the above in the memory; (E) Based on the P, the output current I P and output potential V P and a fifth means for setting a control point determined by the above formula and storing the control point in the memory; (F)V H >V P When not (or V H ≧V PWhen the voltage V(i+1) at time (i+1) is not H and V L <V P When not (or V L ≦V P otherwise, set V(i+1) to V L and V L <V P <V H When (or, V L ≦V P ≦V H When V(i+1) is set as V P A sixth means for outputting It is equipped with: Effect of the Invention

[0016] When the cathode-side precious metal-based catalyst particles are exposed to a high potential, the precious metal components in the precious metal-based catalyst particles are oxidized, and a coating containing precious metal oxides and precious metal hydroxides is formed on the surfaces of the precious metal-based catalyst particles. The total amount M(i) of precious metal oxides and precious metal hydroxides at time i depends on the operation history of the fuel cell (mainly the voltage V(i) of the fuel cell at time i). Therefore, by sequentially acquiring the operation history of the fuel cell, it is possible to know M(i) at the current time, that is, the total amount of oxides and hydroxides covering the surfaces of the precious metal-based catalyst particles.

[0017] A small M(i) means that the total amount of oxides and hydroxides covering the surface of the precious metal catalyst particles is small. In such a case, when a sudden potential change acts on the precious metal catalyst particles, dissolution and precipitation of the precious metal components progresses, which causes the catalyst to deteriorate. Therefore, when M(i) is small, the potential range of the fuel cell V r (i.e., the upper limit potential V H and / or the lower limit potential V L By increasing the potential difference, excessive potential fluctuations are suppressed, and as a result, deterioration of the precious metal catalyst particles can be suppressed.

[0018] On the other hand, a large M(i) means that the total amount of oxides and hydroxides covering the surface of the precious metal catalyst particles is large. In such a case, even if a sudden potential change acts on the precious metal catalyst particles, dissolution and deposition of the precious metal components are unlikely to proceed. Therefore, when M(i) is large, the potential range of the fuel cell V r (i.e., the upper limit potential V H and / or the lower limit potential V L By reducing the amount of precious metals in the fuel cell, it is possible to output the required amount of power while suppressing the dissolution and deposition of precious metal components, or to select operating conditions that provide high power generation efficiency. [Brief description of the drawings]

[0019] [Figure 1] FIG. 2 is a schematic cross-sectional view of a Pt particle on which an oxide film is formed. [Diagram 2] FIG. 13 is a graph showing the effect of the coverage ratio θad on the dissolution rate of the catalyst component. [Diagram 3] FIG. 1 is a graph showing the relationship between fuel cell potential and redox current. [Figure 4] 13 is a diagram showing an example of the relationship between the coverage θad and the correction amount of the upper limit electric potential VH. FIG. [Diagram 5] 1 is a diagram showing the relationship between an output current I and an output potential V, and the relationship between the output current I and an output power P. FIG. [Figure 6] 4 is a flowchart of a potential control method according to the present invention. [Figure 7] 1 shows a comparison of the deterioration amount, power generation efficiency, and output density of the fuel cell systems of Example 1 and Comparative Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] An embodiment of the present invention will be described in detail below. [1. Fuel cell potential control device] The fuel cell potential control device according to the present invention comprises: (A) a first means for acquiring a load requirement P for a polymer electrolyte fuel cell and storing said P in a memory; (B) a second means for acquiring a total voltage V(i) of at least the solid polymer fuel cell at time i and storing the V(i) in the memory; (C) a third means for calculating a total amount M(i) of precious metal oxide and precious metal hydroxide contained in the cathode-side precious metal-based catalyst particles at the time i based on at least the V(i) and storing the M(i) in the memory; (D) When the M(i) is less than the first threshold ε1 (or the M(i) is equal to or less than the ε1), the potential range V r Upper limit potential V H and / or the V r The lower limit potential V L Increase When the M(i) is equal to or greater than the second threshold ε2 (≧ε1) (or when the M(i) is greater than the ε2), the V H and / or increasing the V L Reduce The V after increase or decrease H and / or the V L A fourth means for storing the above in the memory; (E) Based on the P, the output current I P and output potential V P and a fifth means for setting a control point determined by the above formula and storing the control point in the memory; (F)V H >V P When not (or V H ≧V P When the voltage V(i+1) at time (i+1) is not H and V L <V P When not (or V L ≦V P otherwise, set V(i+1) to V L and V L <V P <V H When (or, VL ≦V P ≦V H When V(i+1) is set as V P A sixth means for outputting It is equipped with:

[0021] [1.1. First means] The first means is a means for acquiring a load requirement P for a polymer electrolyte fuel cell (hereinafter also simply referred to as a "fuel cell") and storing in a memory the load requirement P. In the case of a fuel cell vehicle, P corresponds to a load required of the fuel cell by the system due to accelerator operation, etc. In the present invention, the method of acquiring P is not particularly limited, and the most suitable method can be selected depending on the purpose. The acquired P is calculated based on the output current I P and the output voltage V P This will be discussed later.

[0022] [1.2. Second means] The second means is a means for acquiring at least a total voltage V(i) of the polymer electrolyte fuel cell at time i, and storing V(i) in a memory. The second means may include means for acquiring, in addition to V(i), the current I(i) and DC resistance R(i) of the polymer electrolyte fuel cell at time i, and storing I(i) and R(i) in a memory. Furthermore, the second means calculates the temperature T e The method may further include means for acquiring (i) and storing it in a memory.

[0023] In the present invention, the method of acquiring V(i) is not particularly limited, and an optimal method can be selected depending on the purpose. The acquired V(i) is used to calculate the catalytic potential Vcat(i) of the cathode catalyst at time i. In addition, when I(i) and R(i) are further acquired, these are also used in the calculation of Vcat(i). The method of measuring the DC resistance R(i) is not particularly limited, but it is preferable to superimpose a high frequency on the current I(i) or the total voltage V(i) using an FDC or the like and measure it. Furthermore, T e If (i) is obtained, T e (i) is used to correct the coverage θ1(i) to θ3(i), that is, to correct M(i). This is because θ1(i) to θ2(i) are, strictly speaking, e This is because it also depends on (i). Also, T e (i) also affects the rate of deterioration (dissolution, precipitation), so T e Depending on (i), V L Or V H This will be discussed later.

[0024] Here, "total voltage V(i)" refers to the potential difference across the stack at time i. Strictly speaking, the "catalytic potential Vcat(i) of the cathode catalyst" refers to the value obtained by adding the potential drop caused by the internal resistance to the potential of the cathode of each single cell. Strictly speaking, Vcat(i) is calculated based on V(i), I(i), and R(i), but when R(i) cannot be obtained, it may be calculated by an approximation using only V(i). Details of the calculation method of Vcat(i) will be described later.

[0025] [1.3. Third means] The third means is a means for calculating the total amount M(i) of precious metal oxide and precious metal hydroxide contained in the cathode-side precious metal-based catalyst particles at time i based on at least V(i) and storing M(i) in a memory.

[0026] [1.3.1. Precious metal catalyst particles] In the present invention, the term "precious metal catalyst particles (hereinafter, simply referred to as "catalyst particles")" refers to particles made of a metal or alloy containing a precious metal element, and which have activity in the oxygen reduction reaction (ORR). In the present invention, the material of the catalyst particles is not particularly limited as long as it exhibits ORR activity. (a) Precious metals (Au, Ag, Pt, Pd, Rh, Ir, Ru, Os), (b) An alloy containing two or more precious metal elements; (c) Alloys containing one or more precious metal elements and one or more base metal elements (e.g., Fe, Co, Ni, Cr, V, Ti, etc.) etc.

[0027] [1.3.2. Calculation of Vcat(i)] M(i) depends on the operation history of the catalyst particles, i.e., Vcat(i). Therefore, in order to calculate M(i), it is necessary to first calculate Vcat(i). Since Vcat(i) is a function of V(i), Vcat(i) can be calculated by obtaining at least V(i). Specifically, Vcat(i) is expressed by the following formula (1) or formula (2).

[0028]

number

[0029] Strictly speaking, Vcat(i) is expressed by formula (1). In formula (1), the first term represents the potential difference (cell voltage) across the single cell. The second term represents the potential drop per single cell due to internal resistance. By using formula (1), Vcat(i) can be calculated accurately. In order to accurately calculate M(i), it is preferable to use formula (1) for calculating Vcat(i). Equation (2) is an approximation of Vcat(i) that ignores the potential drop caused by internal resistance. Equation (2) is less accurate than equation (1). However, by using equation (2), calculation can be performed without obtaining R(i), so the calculation of Vcat(i) can be simplified.

[0030] [1.3.3. Types of oxides] When the catalyst particles on the cathode side are exposed to a high potential, the catalyst components are more likely to dissolve from the catalyst particles. On the other hand, when the catalyst particles are exposed to a high potential, an oxide film (including hydroxide) is formed on the surface of the catalyst particles, which inhibits the dissolution of the catalyst components from the catalyst particles. However, because the rate at which the oxide film forms is slow, if the potential of the cathode fluctuates suddenly, the formation of the oxide film is delayed, and the catalyst components are more likely to dissolve from the catalyst particles. In other words, if the fuel cell is used continuously in an environment where sudden potential fluctuations are repeated, the catalyst particles will eventually deteriorate. In other words, the durability of the cathode-side precious metal-based catalyst particles depends on the total amount M(i) of the precious metal oxide and precious metal hydroxide present on the surface of the precious metal-based catalyst particles.

[0031] The precious metal oxide present on the surface of the precious metal catalyst particles is (a) a precious metal oxide adsorbed on the surface of a precious metal-based catalyst particle; (b) precious metal hydroxide adsorbed on the surface of the precious metal-based catalyst particles, and (c) Precious metal oxide formed just below the surface of a precious metal catalyst particle due to oxygen diffusion into the particle. They can be broadly divided into:

[0032] A schematic cross-sectional view of a Pt particle on which an oxide film has been formed is shown in Figure 1. When a Pt particle is exposed to a high potential, an oxide (including a hydroxide) is formed on the surface of the Pt particle. In this case, the oxide on the surface of the Pt particles is (a) Pt oxide (PtO ad ), (b) Pt hydroxide (PtOH ad ), and (c) Oxygen diffuses into the interior of Pt particles, forming Pt oxide (PtO sub ) It consists of:

[0033] Here, PtO adThe coverage of the precious metal oxide adsorbed on the surface of the precious metal-based catalyst particle at time i is defined as θ1(i). θ1(i) is expressed as the ratio (=S1 / S0) of the area (S1) of the precious metal oxide adsorbed on the surface of the precious metal-based catalyst particle to the surface area (S0) of the precious metal-based catalyst particle. Similarly, PtOH ad The coverage of the precious metal hydroxide adsorbed on the surface of the precious metal-based catalyst particle at time i is defined as θ2(i). θ2(i) is expressed as the ratio (=S2 / S0) of the area (S2) of the precious metal hydroxide adsorbed on the surface of the precious metal-based catalyst particle to S0. Similarly, PtO sub The coverage of the precious metal oxide present inside the precious metal-based catalyst particle at time i is defined as θ3(i). θ3(i) is expressed as the ratio (=S3 / S0) of the area (S3) of the precious metal oxide present inside the precious metal-based catalyst particle to S0. In particular, the sum of θ1(i) and θ2(i) is called θ ad (i).

[0034] When a precious metal oxide and / or a precious metal hydroxide is adsorbed on the surface of a precious metal catalyst particle, the elution of the catalyst component from the particle surface is suppressed. ad When (i) is large, it means that the catalyst particles are less likely to deteriorate even when exposed to a high potential. Figure 2 shows the effect of the coverage ratio θ on the dissolution rate of the catalyst component. ad The effect of is shown in Figure 2. (a) When catalyst particles are exposed to a high potential, the dissolution rate increases; and (b)θ ad The larger the value, the slower the dissolution rate. You can see that.

[0035] On the other hand, when a precious metal oxide is formed inside a precious metal-based catalyst particle, the catalyst particle becomes stable and the precious metal oxide becomes difficult to reduce. This means that when θ3 is large, the oxide on the catalyst particle surface is maintained even if the catalyst particle is exposed to a low potential. Figure 3 shows the relationship between the fuel cell potential and the redox current. The vertical axis of Figure 3 is the reduction current of oxides (including hydroxides; the same applies below). The smaller this value (the lower it is on the graph), the more the oxides adsorbed on the surface are reduced, and the lower the θ ad As shown in FIG. 3, the larger θ3(i) is, the greater the potential (θ ad It can be seen that the potential at which θ3(i) starts to decrease has shifted to the lower potential side. This is because the larger θ3(i) becomes, the more stable the catalyst particles become, and the more difficult it becomes for oxides to be reduced.

[0036] In other words, in order to suppress the deterioration (= dissolution) of catalyst particles, when the proportion of the non-oxidized state is large (θ ad It is preferable to prevent the fuel cell from being exposed to a high potential when (i) is small. H It is preferable to set In addition, since the power generation efficiency is better at higher potentials, in order to increase the power generation efficiency without degrading the catalyst particles, it is preferable to prevent the catalyst particles from being exposed to low potentials for a long period of time (i.e., to prevent θ3 from becoming excessively small). L It is preferable to set

[0037] In order to maximize the accuracy and effectiveness, it is desirable to calculate θ1(i), θ2(i), and θ3(i) at time i individually. However, if the total amount M(i) of precious metal oxides and precious metal hydroxides at time i is generalized using θ1(i) to θ3(i), the potential range V of the fuel cell can be calculated using the generalized M(i). r can be easily controlled.

[0038] 1.3.4. Calculation of M(i) Specifically, the total amount M(i) of the precious metal oxide and precious metal hydroxide contained in the cathode-side precious metal catalyst particles at time i is preferably calculated based on the following formula (3).

[0039]

number

[0040] however, θ1(i) is the coverage of the precious metal oxide adhering to the surface of the precious metal-based catalyst particle at time i, θ2(i) is the coverage of the precious metal hydroxide adhering to the surface of the precious metal catalyst particle at time i, θ3(i) is the coverage of the precious metal oxide present inside the precious metal-based catalyst particle at time i, Γ is the maximum amount of oxygen coverage per unit surface area (constant), ΔT is the calculation step size, α 11 ~α 37 are the fitting coefficients, A PM is the total surface area of ​​the precious metal catalyst particles.

[0041] Equation (3) represents the total amount of oxides and hydroxides formed on the surface of the precious metal-based catalyst particles. v1 to v3 are each oxide or hydroxide (MO ad , M.O.H. ad , M.O. sub ) reaction rate. G1 to G3 represent the free energies of the reactions of v1 to v3. θ1(i-1), θ2(i-1), and θ3(i-1) are the coverage rates at time (i-1), and are already stored in memory. θ1(i-1), θ2(i-1), and θ3(i-1) can be calculated by sequential calculations once the initial values ​​are known. The initial values ​​may be retained and used as the values ​​from the previous shutdown. Generally, when a fuel cell is shut down, it is often held at a low potential, and at that time, all oxides are reduced. Therefore, the initial values ​​after shutdown may be θ1=θ2=θ3=0. α 11 ~α 37 can be calculated from cyclic voltammetry. A PMcan be calculated by integrating the amount of reaction of the catalyst from the reaction current by cyclic voltammetry. Therefore, if Vcat(i) is obtained, M(i) can be calculated from equation (3).

[0042] In addition, α 12 , α 13 , α 22 , α 23 , α 32 , and α 33 can be regarded as a constant, but strictly speaking, the temperature T e (i). Therefore, in the second method, the temperature T e If (i) is obtained, T e These compatibility coefficients may be corrected according to (i). The following formula (3.1) shows an example of the correction formula. α ij = α ij 0 / T e (i) …(3.1) however, α ij 0 is the fitting coefficient α ij The reference value of i=1, 2, or 3, j=2 or 3.

[0043] Similarly, α 11 , α 21 , and α 31 can be regarded as a constant, but strictly speaking, the temperature T e (i). Therefore, in the second method, the temperature T e If (i) is obtained, T e These compatibility coefficients may be corrected according to (i). An example of the correction formula is shown in the following formula (3.2). α ij =k i T e (i) exp(α ij 0 / T e (i)) …(3.2) however, α ij0 is the fitting coefficient α ij The reference value of k i is the rate constant, i=1, 2, or 3, j=1. α ij 0 and k i can be calculated by cyclic voltammetry at different temperatures.

[0044] [1.4. Fourth means] The fourth measure is When M(i) is less than the first threshold ε1 (or M(i) is equal to or less than ε1), the potential range V r Upper limit potential V H and / or V r The lower limit potential V L Increase When M(i) is equal to or greater than the second threshold ε2 (≧ε1) (or M(i) is greater than ε2), V H and / or V L Reduce V after increase or decrease H and / or V L in the memory.

[0045] [1.4.1. First Threshold] The "first threshold ε1" is the potential range V r The value of ε1 is not particularly limited, and it is preferable to select an optimal value depending on the composition of the catalyst particles, the required durability, etc. A relatively small M(i) means that there is little oxide protecting the surface of the catalyst particle. In such a case, if a sudden potential change acts on the catalyst particle, the catalyst particle is likely to deteriorate. Therefore, when M(i) is less than ε1 (or equal to or less than ε1), V r It is preferable to reduce V r The reduction of the upper limit potential V H Decrease in potential or lower limit V L Either one of the increases or both may be performed. In the present invention, when "M(i) is less than ε1 (or equal to or less than ε1)", it means that the boundary value (in this case, M(i)=ε1) belongs to either the "true" side or the "false" side of the proposition. The same applies when judging the truth or falsity of other variables.

[0046] [1.4.2. Second Threshold] The second threshold ε2 is the potential range V r The value of ε2 is not particularly limited, and it is preferable to select an optimal value depending on the composition of the catalyst particles, the required durability, etc. ε2 may be the same value as ε1, or may be a value larger than ε1. A relatively large M(i) means that the catalyst particles are protected by a relatively large amount of oxide. In such a case, even if a sudden potential change acts on the catalyst particles, the catalyst particles are not easily deteriorated. Therefore, when M(i) is ε2 or more (or exceeds ε2), V r It is preferable to enlarge V r The expansion of the upper limit potential V H or the lower limit potential V L Either one of the reductions or both may be performed.

[0047] [1.4.3. Upper limit potential V H and the lower limit potential V L Settings As mentioned above, when M(i) is large, V r On the other hand, when M(i) is small, V is preferably enlarged in order to suppress the deterioration of catalyst particles. r It is preferable to reduce V r The expansion and contraction of V H Or V L It may be performed by increasing or decreasing either one of them, or by increasing or decreasing both of them. In this case, V H The correction amount and V LThe amount of correction is not particularly limited, and an optimal amount of correction can be selected depending on the purpose.

[0048] In general, the larger Vcat(i) and / or θ ad The smaller (i), the greater the amount of catalyst components dissolved. H The correction amount is V H It is preferable to set the value so that the amount of elution of the catalyst component does not increase compared to the reference value even if the amount is increased. Figure 4 shows the coverage ratio θ ad and the upper limit potential V H FIG. 4 shows an example of the relationship between the coverage ratio θ ad The upper limit potential V at which the same dissolution rate as when V is zero is obtained. H That is, the correction amount of each coverage θ ad In the above, the dissolution rates at the upper potential limit after correction are the same. Lower limit potential V L The correction amount for V is also the same. L The correction amount is V L It is preferable to set the value so that the amount of oxide reduction does not increase compared to a reference value (for example, the amount of reduction when θ3 is zero) even if θ3 is decreased.

[0049] The fourth measure is, in particular: Based on the following formula (4), H and / or Based on the following formula (5), L Means of determining It is preferred that the compound contains

[0050]

number

[0051] V H0The higher the V, the more efficient the system is, but the lower its durability. HO The lower the V, the lower the efficiency of the system but the higher the durability. Therefore, V can be selected based on the efficiency and durability required by the system. HO It is preferable to determine V L0 The higher V, the lower the maximum power output (i.e., the larger the body size is to obtain the same power output), but the higher the durability. LO The lower the V, the higher the maximum power output, but the lower the durability. Therefore, V should be selected based on the size and durability required by the system. LO It is preferable to determine It is preferable to determine β1 to β4 based on the durability required by the system.

[0052] Equation (4) expresses the condition that the dissolution rate of the catalyst component is the reference value V H0 From equation (4), θ ad The larger (i), the greater V H It can be seen that increases. In addition, equation (5) shows that the amount of oxide reduction is equal to the reference value V L0 From equation (5), θ ad As (i) becomes larger and / or θ3 becomes larger, V H It can be seen that decreases. Therefore, if β1 to β4 are set to appropriate values, V H and / or V L can be increased or decreased appropriately.

[0053] Furthermore, in formula (4) and formula (5), V L0 and V H0 can be regarded as a constant, but strictly speaking, the temperature T e (i). Therefore, in the second method, the temperature T e If (i) is obtained, T e Depending on (i), V H0 and / or V L0In the following equations (6) and (7), V H0 and V L0 An example of the correction formula is shown below. V H0 =V H0 '+β5T e (i) / T H0 …(6) V L0 =V L0 '+β6T e (i) / T L0 …(7) however, V H0 ' is the temperature T H0 The reference value (constant) of the upper limit potential when V L0 ' is the temperature T L0 The reference value (constant) of the lower limit potential when T H0 is the reference temperature for the upper potential limit (constant), T L0 is the reference temperature for the lower limit potential (a constant), β5 and β6 are the fit coefficients, respectively.

[0054] [1.5. Fifth means] The fifth means calculates an output current I based on P. P and output potential V P and stores the control points in memory. The "control point" is the output current I at which the power corresponding to the load demand P is obtained and the power generation efficiency is the highest. P and the output voltage V P This refers to a combination of the above.

[0055] FIG. 5 shows the relationship between the output current I and the output potential V, and the relationship between the output current I and the output power P. As shown in FIG. 5, when the output power (load demand P) is determined, the output current I required to generate the requested power is calculated. P and output potential V P The combination of is uniquely determined.

[0056] [1.6. Sixth means] The sixth measure is V H >V P When not (or V H ≧V P When the voltage V(i+1) at time (i+1) is not H and V L <V P When not (or V L ≦V P otherwise, set V(i+1) to V L and V L <V P <V H When (or, V L ≦V P ≦V H When V(i+1) is set as V P Output It is a means.

[0057] "V H >V P When not (or V H ≧V P "When not" means V P V H Above (or V P V H In this case, the fuel cell is V P If the fuel cell is operated at 1000V, the catalyst particles are likely to deteriorate. In such a case, the efficiency may be slightly reduced, but it is still possible to operate the fuel cell at 1000V. H It is preferable to operate it at . "V L <V P When not (or V L ≦V P "When not" means V P V L Below (or V P V L In this case, the fuel cell is V P If the fuel cell is operated at 1000 mA, there is a high possibility that the oxides present on the catalyst particle surface will be excessively reduced. In such a case, the power density may decrease slightly, but it is possible to operate the fuel cell at 1000 mA. LIt is preferable to operate it at . "V L <V P <V H When (or, V L ≦V P ≦V H "When it is V P The potential range V is allowed r In such a case, the fuel cell is P It is preferable to operate the device at the boundary value (V L and V H ) can belong to either the "true" side or the "false" side of a proposition. For example, "V L ≦V P <V H When it is" and "V L <V P ≦V H Even when fuel cells are P This means that the device may be operated with

[0058] [2. Potential control method] A flow chart of the potential control method according to the present invention is shown in Fig. 6. First, in step 1 (hereinafter simply referred to as "S1"), a load demand P for the polymer electrolyte fuel cell is acquired, and P is stored in a memory (first procedure).

[0059] Next, in S2, at least the total voltage V(i) of the polymer electrolyte fuel cell at time i is acquired, and V(i) is stored in memory (second procedure). As described above, in S2, in addition to V(i), the coverage θ1(i) to θ3(i), the total amount M(i) of oxides and hydroxides, and the upper limit potential V H , and / or the lower limit potential V L The detection values ​​of various sensors (e.g., I(i), R(i), T e (i) etc.) may be further acquired.

[0060] Next, in S3, the total amount M(i) of precious metal oxides and precious metal hydroxides contained in the cathode-side precious metal-based catalyst particles at time i is calculated based on at least V(i), and M(i) is stored in memory (third step). It is preferable that M(i) is calculated based on the above-mentioned formula (3). When M(i) is calculated based on the formula (3), θ1(i) to θ3(i) are also calculated at the same time. θ3 and θ ad (i)(=θ1(i)+θ2(i)) is V H and / or V L The details of the formula (3) are as described above, and therefore will not be described here.

[0061] Next, in S4, When M(i) is less than the first threshold ε1 (or M(i) is equal to or less than ε1), the potential range V r Upper limit potential V H and / or V r The lower limit potential V L Increase When M(i) is equal to or greater than the second threshold ε2 (≧ε1) (or M(i) is greater than ε2), V H and / or V L Reduce V after increase or decrease H and / or V L is stored in memory (fourth step). V H and V L It is preferable to calculate θ using the above-mentioned formula (4) and formula (5), respectively. ad Substituting (i) and θ3(i) into equations (4) and (5), V H and V L The details of the formulas (4) and (5) are as described above, and therefore will not be described here.

[0062] Next, in S5, the output current I P and output potential V PThe control points are set and stored in memory (fifth step). The method of setting the control points is as described above, and therefore will not be described here.

[0063] Next, proceed to S6. In S6, V H >V P It is judged whether or not. H >V P If not (S6: NO), proceed to S7. In S7, V is set as the voltage V(i+1) at time (i+1). H (sixth procedure). Then, the process proceeds to S8. In S8, it is determined whether or not to continue the control. If the control is to be continued (S8: YES), the process returns to S1, and the above-mentioned steps S1 to S8 are repeated.

[0064] On the other hand, in S6, V H >V P If it is (S6: YES), proceed to S9. L <V P It is judged whether or not. L <V P If not (S9: NO), proceed to S10. In S10, V(i+1) is set to V L (sixth procedure). Then, the process proceeds to S8. If the control is to be continued (S8: YES), the process returns to S1 and repeats each of the above-mentioned steps S1 to S10.

[0065] Furthermore, in S9, V L <V P If it is (S9: YES), proceed to S11. In S11, V(i+1) is set to V P (sixth procedure). Then, the above-mentioned steps S1 to S11 are repeated until the control is terminated (S8: NO).

[0066] [3. Effect] When the cathode-side precious metal-based catalyst particles are exposed to a high potential, the precious metal components in the precious metal-based catalyst particles are oxidized, and a coating containing precious metal oxides and precious metal hydroxides is formed on the surfaces of the precious metal-based catalyst particles. The total amount M(i) of precious metal oxides and precious metal hydroxides at time i depends on the operation history of the fuel cell (mainly the voltage V(i) of the fuel cell at time i). Therefore, by sequentially acquiring the operation history of the fuel cell, it is possible to know M(i) at the current time, that is, the total amount of oxides and hydroxides covering the surfaces of the precious metal-based catalyst particles.

[0067] A small M(i) means that the total amount of oxides and hydroxides covering the surface of the precious metal catalyst particles is small. In such a case, when a sudden potential change acts on the precious metal catalyst particles, dissolution and precipitation of the precious metal components progresses, which causes the catalyst to deteriorate. Therefore, when M(i) is small, the potential range of the fuel cell V r (i.e., the upper limit potential V H and / or the lower limit potential V L By increasing the potential difference, excessive potential fluctuations are suppressed, and as a result, deterioration of the precious metal catalyst particles can be suppressed.

[0068] On the other hand, a large M(i) means that the total amount of oxides and hydroxides covering the surface of the precious metal catalyst particles is large. In such a case, even if a sudden potential change acts on the precious metal catalyst particles, dissolution and deposition of the precious metal components are unlikely to proceed. Therefore, when M(i) is large, the potential range of the fuel cell V r (i.e., the upper limit potential V H and / or the lower limit potential V L By reducing the amount of precious metals in the fuel cell, it is possible to output the required amount of power while suppressing the dissolution and deposition of precious metal components, or to select operating conditions that provide high power generation efficiency. EXAMPLES

[0069] (Example 1, Comparative Example 1) [1. Test method] The deterioration amount of the cathode catalyst, the power generation efficiency, and the output density were calculated by simulation when a fuel cell system in which the cathode catalyst was Pt particles was operated under specified conditions. The simulation is (a) According to the flowchart in Figure 6, the upper limit potential V H is variably controlled in the range of 0.8V to 1.0V, and the lower limit potential V L When variably controlled in the range of 0.4V to 0.7V (Example 1), and (b)V H is fixed at 1.0V, and V L When fixed at 0.4V (Comparative Example 1) I followed him.

[0070] The fuel cell was operated under the LA#4 mode, which is a commonly used pattern for measuring exhaust gas emissions. The deterioration of the cathode catalyst is measured by the potential, θ ad The amount of dissolution was calculated successively from the relationship between the amount of dissolution and the dissolution rate, and was then integrated. The power generation efficiency was calculated as the ratio of the ideal energy of hydrogen, estimated from the integrated amount of hydrogen used, which can be derived from the amount of current, to the amount of work actually used during driving. Furthermore, the power density is limited to the lower limit potential V L This was calculated from the output (maximum output) at this time.

[0071] [2. Results] Fig. 7 shows a comparison of the deterioration amount, power generation efficiency, and power density of the fuel cell systems of Example 1 and Comparative Example 1. It can be seen from Fig. 7 that when the method according to the present invention is used, the deterioration amount of the cathode catalyst increases slightly, but the power generation efficiency and power density are improved.

[0072] Although the embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the gist of the present invention. [Industrial Applicability]

[0073] The fuel cell potential control device according to the present invention can be used for controlling power generation in a fuel cell vehicle.

Claims

1. (A) a first means for acquiring a load requirement P for a polymer electrolyte fuel cell and storing said P in a memory; (B) a second means for acquiring a total voltage V(i) of at least the solid polymer electrolyte fuel cell at time i and storing the V(i) in the memory; (C) a third means for calculating a total amount M(i) of precious metal oxide and precious metal hydroxide contained in the cathode-side precious metal-based catalyst particles at the time i based on at least the V(i) and storing the M(i) in the memory; (D) The M(i) is a first threshold ε 1 (or the M(i) is less than the ε 1 When the potential range of the solid polymer electrolyte fuel cell is V r Upper limit potential V H and / or the V r The lower limit potential V L Increase The M(i) is a second threshold ε 2 (≧ε 1 ) or more (or the M(i) is equal to or greater than the ε 2 When the V H and / or increasing the V L Reduce The V after increase or decrease H And / or the V L in the memory; (E) Based on the P, the output current I P and the output potential V P and a fifth means for setting a control point determined by the above formula and storing the control point in the memory; (F) V H >V P When not (or V H ≧V P When the voltage V(i+1) at time (i+1) is not H and V L <V P When not (or V L ≦V P When not, V(i+1) is set to V L and V L <V P <V H (or, V L ≦V P ≦V H When V(i+1) is V P A sixth means for outputting A fuel cell potential control device comprising:

2. the second means includes means for acquiring, in addition to V(i), a current I(i) and a DC resistance R(i) of the polymer electrolyte fuel cell at the time i, and storing the I(i) and the R(i) in the memory; The third means is A catalyst potential Vcat(i) of the polymer electrolyte fuel cell at the time i is calculated based on the following formula (1): The method includes calculating the M(i) based on the following formula (3):

2. A fuel cell potential control device according to claim 1. [0010] however, N cell is the number of stacked cells of the polymer electrolyte fuel cell, A cell is the area of ​​the cell. [0025] however, θ 1 (i) is the coverage of the precious metal oxide adsorbed on the surface of the precious metal-based catalyst particle at the time i; θ 2 (i) is the coverage of the precious metal hydroxide adsorbed on the surface of the precious metal-based catalyst particle at the time i; θ 3 (i) is the coverage of the precious metal oxide present inside the precious metal-based catalyst particle at the time i; Γ is the maximum surface coverage of oxygen per unit surface area (constant), ΔT is the calculation step size, α 11 ~α 37 are the fitting coefficients, A PM is the total surface area of ​​the precious metal catalyst particles.

3. The third means is Calculating a catalytic potential Vcat(i) of the polymer electrolyte fuel cell at the time i based on the following formula (2): The method includes calculating the M(i) based on the following formula (3):

2. A fuel cell potential control device according to claim 1. [0030] However, N cell is the number of cells stacked in the polymer electrolyte fuel cell. [0045] however, θ 1 (i) is the coverage of the precious metal oxide adsorbed on the surface of the precious metal-based catalyst particle at the time i; θ 2 (i) is the coverage of the precious metal hydroxide adsorbed on the surface of the precious metal-based catalyst particle at the time i; θ 3 (i) is the coverage of the precious metal oxide present inside the precious metal-based catalyst particle at the time i; Γ is the maximum surface coverage of oxygen per unit surface area (constant), ΔT is the calculation step size, α 11 ~α 37 are the fitting coefficients, A PM is the total surface area of ​​the precious metal catalyst particles.

4. The second means calculates the temperature T e (i) and storing it in said memory; The third means is the T e (i) includes a means for correcting said M(i) 4. A fuel cell potential control device according to claim 2 or 3.

5. The fourth means is Based on the following formula (4), H and / or Based on the following formula (5), L Means of determining 5. A fuel cell potential control device according to claim 2, further comprising: [0050] however, V H0 is the upper limit potential reference value, V L0 is the reference value for the lower limit potential, β 1 ~β 4 are the fitting coefficients, respectively.

6. The second means calculates the temperature T e (i) and storing it in said memory; The fourth means is the T e (i) using the V H0 And / or the V L0 Including means for correcting A fuel cell potential control device according to claim 5 .

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