KR101629297B1 - Method for a polymer electrolyte fuel cell of the control for cold start - Google Patents

Abstract

The present invention relates to a method of controlling a polymer electrolyte fuel cell, and more particularly, to a method of controlling a polymer electrolyte fuel cell that prevents oxygen from being reduced in a catalyst layer and a diffusion layer due to freezing of water generated by an oxygen reduction reaction in a cathode catalyst layer at a subzero temperature And more particularly, to a control method of a polymer electrolyte fuel cell for low-temperature start-up.
According to the present invention, it is possible to prevent the water generated in the polymer electrolyte fuel cell from freezing by controlling the rate of temperature rise of the polymer electrolyte fuel cell to be faster than the rate of formation of water by the oxygen reduction reaction inside the polymer electrolyte fuel cell, The durability and the effect of the electrolyte fuel cell can be prevented from deteriorating.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a method for controlling a polymer electrolyte fuel cell,

The present invention relates to a method of controlling a polymer electrolyte fuel cell, and more particularly, to a method of controlling a polymer electrolyte fuel cell that prevents oxygen from being reduced in a catalyst layer and a diffusion layer due to freezing of water generated by an oxygen reduction reaction in a cathode catalyst layer at a subzero temperature And more particularly, to a control method of a polymer electrolyte fuel cell for low-temperature start-up.

A polymer electrolyte fuel cell (FEP) is a fuel cell that uses a polymer membrane with hydrogen ion exchange properties as an electrolyte. The fuel cell is a solid polymer electrolyte fuel cell (SPEFC), a solid polymer fuel cell (SPFC) fuel cell (PEMFC). A polymer electrolyte fuel cell having a lower operating temperature than other types of fuel cells has a high efficiency, a high current density and a high output density, a short startup time and a fast response characteristic to a load change. Especially, since the polymer membrane is used as the electrolyte, there is no electrolyte loss, and it is possible to apply the hydrogen reformer, which is an established technology, and is less sensitive to the change of the reaction gas pressure. In addition, the design is simple, easy to manufacture, and various materials can be used for the fuel cell body material, and the volume and weight are smaller than those of a phosphoric acid fuel cell having the same principle of operation. In addition to these characteristics, the polymer electrolyte fuel cell can be applied to a wide variety of fields such as power source for non-polluting vehicles, locally installed power generation, space power, mobile power, and military power. However, since the polymer electrolyte fuel cell operates at a low temperature, it can not utilize waste heat and is difficult to be connected with a reformer operated at a high temperature. Since the Pt is used as the electrode catalyst, the CO tolerance in the reaction gas is low, It is difficult to reduce the amount of catalyst impregnated. Also, the polymer membrane used as an electrolyte is very expensive and it is difficult to control the moisture content of the polymer membrane during operation.

Polymer electrolyte fuel cells were originally used for special purposes such as the Gemini spacecraft in the 1960s, but by the end of the 1980s it was expected to be used as a power source for pollution-free vehicles. It is progressing. Especially, the regulation of the total amount of CO ₂ through the Green Round (Climate Change Convention) and the regulation of the automobile exhaust gas through the compulsory sale of the low pollution automobile have become imminent, and automobile companies of each country have become urgent to develop pollution-free vehicles such as fuel cell cars . Fuel cell vehicles are considered to have the greatest practical potential among next-generation automobiles as they have environmental friendliness, fuel efficiency, and convenience of fuel supply. In addition, if the fuel cell system for automobiles is put into practical use, it can alleviate environmental pollution and energy consumption caused by automobiles, and can be utilized immediately for military power generation such as small-scale power generation in a building or a local area, submarine and mobile communication have.

A unit cell of a polymer electrolyte fuel cell (PEFC) is composed of an anode and a cathode mainly composed of a proton conductive polymer electrolyte, which is a perfluorinated sulfonic acid polymer. The detailed structure includes a catalyst coated membrane (CCM) in which a catalyst layer (CL) is coated on a polymer electrolyte membrane, a gas diffusion layer (GDL) for uniformly dispersing hydrogen and oxygen gas in the electrode catalyst, A microporous layer (MPL), a bipolar plate (BP) separating the anode and cathode from the stack of PEFC stacks, and the like. have.

The electrochemical reaction takes place in the anode and the cathode catalyst layers. In the anode, two hydrogen ions and two electrons are generated by the hydrogen oxidation reaction (HOR), and hydrogen ions, which have been transferred through the electrolyte membrane in the air electrode, The generated electrons generate electricity by an electrode reaction that reduces oxygen to water.

Polymer Electrolyte Fuel Cell (PEFC) operates at a temperature of 100 ° C or less and warms up at a high speed. Since it has higher output current density and durability than other types of fuel cells It is recognized as a power generation device suitable for automotive or residential systems.

However, one of the technical barriers to automotive polymer electrolyte fuel cells (PEFCs) is the cold start problem. The cold start problem is a phenomenon in which oxygen transport in the catalyst layer and the diffusion layer is reduced due to freezing of water generated by the oxygen reduction reaction (ORR) at the catalyst layer (CL) at a sub-zero temperature, The reaction area is reduced. Therefore, freezing of water generated in the air electrode of a polymer electrolyte fuel cell (PEFC) reduces the area of the active reaction and eventually stops the operation. Moreover, even with a successful cold start, repetitive water freezing and thawing can destroy the structure of polymer electrolyte fuel cell (PEFC) components (especially the catalyst layer), resulting in performance and durability degradation do.

In order to solve the above problems, Korean Patent Laid-Open No. 10-2010-0051509 discloses a method of controlling the cold start sequence of a fuel cell hybrid vehicle, Depending on the voltage of the supercap, the power supply determines whether to use only the auxiliary battery power or the auxiliary battery power and the supercap power simultaneously. Then, the air blower is operated to raise the stack voltage. Thereafter, When the temperature is raised, the heater is connected to increase the stack temperature through the fuel cell output. Then, the fuel cell main relay is connected to connect the super cap and connect to the super cap main relay and enter the hybrid mode. Super Cap It is possible to start the vehicle smoothly. It proposes a cold-start control method for a hybrid vehicle batteries.

Korean Patent Laid-Open No. 10-2011-0058590 discloses a purge apparatus for improving the cold-live performance of a fuel cell. The purge gas is connected to the purge gas outlet of the fuel cell stack to purge the stack and a main pipe through which the impurities are discharged. A purge valve installed in the main pipe and the auxiliary pipe for performing a purging operation; a shutoff valve installed upstream of the purge valve in the auxiliary piping; This paper proposes a purging system for improving the cold start of a fuel cell, which can shorten the total cold start time while shortening the time required for thawing the freezing simultaneously.

In addition, a direct heating purging apparatus and method for improving the cold rolling of a fuel cell of Korean Patent Laid-Open No. 10-2012-0053306, after stopping the operation of the fuel cell system, put a mixed gas of hydrogen and air into the cathode of the fuel cell stack The present invention relates to a direct heating purging apparatus and method for improving the cold live performance of a fuel cell in which a temperature rise of a stack is achieved through heat generation by reaction of hydrogen and air, As a purge step after the operation is stopped, hydrogen and air mixed gas are injected into the cathode of the stack and purging is performed. Thus, heat is generated by direct reaction between hydrogen and air at the cathode of the stack, The anode can be drained by hydrogen purging and the temperature of the stack during the purge step rises, Removal of water by not only proposes a device and method for directly heating the purging naengsi Same improvement of the fuel cell to be obtained by removing water effect by the stack temperature.

However, in order to increase the cost competitiveness and efficiency of the fuel cell system of the automobile, the size of the external heating device system is minimized and the self-cold start capability (self-cold start capability) (PEFC) with a high efficiency and high efficiency.

The inventors of the present invention invented and propose a control method of a polymer electrolyte fuel cell for low-temperature starting capable of self-cold start capability without adding an apparatus.

Korean Patent Publication No. 10-2010-0051509 Korean Patent Publication No. 10-2011-0058590 Korean Patent Publication No. 10-2012-0053306

SUMMARY OF THE INVENTION The present invention provides a control method of a polymer electrolyte fuel cell for low-temperature start-up capable of self-cold start.

The present invention provides a method of controlling a polymer electrolyte fuel cell, comprising: applying a first current density value to a cathode catalyst layer of a polymer electrolyte fuel cell; determining whether moisture inside the polymer electrolyte fuel cell is undersaturated; And applying a second current density value higher than the first current density value to the cathode catalyst layer of the polymer electrolyte fuel cell.

The first current density value may be a current density value for driving the polyelectrolyte fuel cell.

The second current density value may be a current density value of 1.1 to 2.0 times the first current density value.

The step of applying the second current density value may be performed when the water content in the polymer electrolyte fuel cell is undersaturated.

The step of applying the second current density value may be performed when the internal temperature of the polyelectrolyte fuel cell is in a range of -10 ° C to 0 ° C.

The step of determining whether or not it is undersaturated includes the steps of calculating a variable by applying a boundary condition and an initial condition, calculating a velocity and an input value by calculating a mass governance equation and a momentum governance equation, Calculating the temperature value in each lattice by applying the velocity and input values to the energy governing equations, calculating the concentration values of hydrogen, water, and oxygen in each lattice by calculating the chemical dominant equations, and calculating the charge governing equations Calculating a current density and a voltage value, determining whether or not a predetermined convergence condition is satisfied, and determining whether the predetermined convergence condition is greater than a predetermined time.

According to the present invention, it is possible to prevent the water generated in the polymer electrolyte fuel cell from freezing by controlling the rate of temperature rise of the polymer electrolyte fuel cell to be faster than the rate of formation of water by the oxygen reduction reaction inside the polymer electrolyte fuel cell, The durability and the effect of the electrolyte fuel cell can be prevented from deteriorating.

1 is a perspective view of a polymer electrolyte fuel cell to be controlled according to the present invention.
2 is a flowchart of a control method of a polymer electrolyte fuel cell for low temperature start according to an embodiment of the present invention.
3 is a diagram showing a three-dimensional numerical analysis model of a polymer electrolyte fuel cell to be controlled according to the present invention of the present invention.
4 is a diagram showing a governing equation for defining a three-dimensional numerical simulation model of a polymer electrolyte fuel cell to be controlled according to the present invention of the present invention.
5 is a diagram showing equations calculated by applying a three-dimensional numerical simulation model of a polymer electrolyte fuel cell to be controlled according to the present invention to a governing equation.
Fig. 6 is a view showing definition of freezing and thawing of water for a three-dimensional numerical simulation model of a polymer electrolyte fuel cell to be controlled according to the present invention of the present invention.
FIG. 7 is a flowchart illustrating a method for determining whether water in a polymer electrolyte fuel cell is undersaturated in a method of controlling a polymer electrolyte fuel cell for low-temperature start according to an embodiment of the present invention.
FIG. 8 is a graph showing the ice accumulation amount (mg / cm ² ) and the cell temperature with time under the conditions of Example 1 and Comparative Examples 1 to 3. FIG.
FIG. 9 is a graph showing a voltage (V) of a cell with time and a water content according to time under the conditions of Example 1 and Comparative Examples 1 to 3. FIG.

Hereinafter, a control method of a polymer electrolyte fuel cell for low-temperature start-up according to the present invention will be described in detail with reference to the accompanying drawings. The structure and operation of the present invention shown in the drawings and described by the drawings are described as at least one embodiment, and the technical ideas and the core structure and operation of the present invention are not limited thereby.

Although the terms used in the present invention have been selected in consideration of the functions of the present invention, it is possible to use general terms that are currently widely used, but this may vary depending on the intention or custom of a person skilled in the art or the emergence of new technology. Also, in certain cases, there may be a term selected arbitrarily by the applicant, in which case the meaning thereof will be described in detail in the description of the corresponding invention. Therefore, it is to be understood that the term used in the present invention should be defined based on the meaning of the term rather than the name of the term, and on the contents of the present invention throughout.

1 is a perspective view of a polymer electrolyte fuel cell to be controlled according to the present invention. 1, the polymer electrolyte fuel cell 100 includes a cathode diffusion layer 110, a cathode microporous layer 120, a cathode diffusion layer 130, an anode microporous layer 140, and a catalyst coating membrane 150, .

Before describing the polymer electrolyte fuel cell 100, a gas diffusion layer (GDL) and a microporous layer (MPL) will be briefly described as follows. The cathode and anode diffusion layers 110 and 130 allow the reactants such as liquid fuel and gas to be evenly distributed to the respective catalyst layers 151 and 152 in the catalyst coating membrane 150. Further, the microporous layers 120 and 140 of the negative electrode and the positive electrode, which are in contact with the diffusion layers 110 and 130, further increase transmission and diffusion efficiency with respect to reactants such as the liquid fuel and the gas.

The cathode diffusion layer 110 is a portion through which the hydrogen (H ₂ ) corresponding to the fuel flows from the cathode channel 10 into the polymer electrolyte fuel cell 100. The anode microporous layer 120 is disposed in contact with the cathode diffusion layer 110, and the hydrogen (H ₂ ) passes through the anode micropore layer 120. The anode diffusion layer 130 is positioned opposite to the cathode diffusion layer 110 with reference to the catalyst coating membrane 150 and air flows from the anode channel 20. Of course, oxygen (O ₂ ) is contained in the air. The anode microporous layer 140 is disposed in contact with the anode diffusion layer 130, and the oxygen (O ₂ ) can pass through the anode micropore layer 140.

The diffusion layers 110 and 130 and the microporous layers 120 and 140 may be formed by using materials such as a material, a pore size, a gas permeability, a porosity, a wettability, Adjustable.

The diffusion layers 110 and 130 serve to support the electrodes and diffuse the fuel and the oxidant into the catalyst layers 151 and 152 so that the fuel and the oxidant can easily access the catalyst layers. As the diffusion layers 110 and 130, a conductive substrate may be used. As a representative example thereof, a metal film is formed on the surface of a cloth formed of a porous film or polymer fiber composed of carbon paper, carbon cloth, carbon felt, or metal cloth ) May be used, but the present invention is not limited thereto.

Further, it is preferable that the diffusion layers 110 and 130 are made of a fluorine-based resin that is water-repellent, because it is possible to prevent the reactant diffusion efficiency from being lowered due to water generated when the fuel cell is driven. Examples of the fluorine-based resin include polytetrafluoroethylene, polyvinylidene fluoride, polyhexafluoropropylene, polyperfluoroalkyl vinyl ether, polyperfluorosulfonyl fluoride alkoxyvinyl ether, fluorinated ethylene propylene ( Fluorinated ethylenepropylene), polychlorotrifluoroethylene, or copolymers thereof.

The microporous layers 120 and 140 are generally made of conductive powder having a small particle diameter such as carbon powder, carbon black, acetylene black, activated carbon, carbon fiber, fullerene, carbon nanotube, carbon nanowire, carbon And may include a carbon nano-horn or a carbon nano ring.

The microporous layers 120 and 140 are prepared by coating a composition containing conductive powder, a binder resin, and a solvent on the electrode substrate. Examples of the binder resin include polytetrafluoroethylene, polyvinylidene fluoride, polyhexafluoropropylene, polyperfluoroalkyl vinyl ether, polyperfluorosulfonyl fluoride, alkoxyvinyl ether, polyvinyl alcohol, cellulose acetate Or a copolymer thereof, and the like can be preferably used. Examples of the solvent include alcohols such as ethanol, isopropyl alcohol, n-propyl alcohol and butyl alcohol, water, dimethylacetamide, dimethylsulfoxide, N-methylpyrrolidone and tetrahydrofuran. The coating process may be performed by a screen printing method, a spray coating method or a coating method using a doctor blade, depending on the viscosity of the composition, but is not limited thereto.

The catalyst coating membrane 150 is a catalytic coated membrane (CCM), which is formed between the anode microporous layer 120 and the anode microporous layer 140. The oxidation reaction of hydrogen and the reduction reaction of oxygen occur Section. More specifically, the catalyst coating membrane 150 includes a cathode catalyst layer 151 in contact with the anode microporous layer 120, an anode catalyst layer 152 in contact with the anode microporous layer 140, 151, and 152, respectively.

The membrane layer 153 may be made of a polymer having excellent hydrogen ion conductivity. As a typical example thereof, any polymer resin having a cation-exchange group selected from the group consisting of a sulfonic acid group, a carboxylic acid group, a phosphoric acid group, a phosphonic acid group and a derivative thereof in the side chain can be used.

Preferable examples include fluorine-based polymers, benzimidazole-based polymers, polyimide-based polymers, polyetherimide-based polymers, polyphenylene sulfide-based polymers, polysulfone-based polymers, polyether sulfone-based polymers, polyether ketone- - ether ketone-based polymers, polyphenylquinoxaline-based polymers, and copolymers thereof. More preferred are hydrogen-ion conductive polymers such as poly (perfluorosulfonic acid), poly (perfluorocarbons Copolymers of tetrafluoroethylene and fluorovinyl ethers containing sulfonic acid groups, dehydrofluorinated sulfated polyether ketones, aryl ketones, poly (2,2'-m-phenylene) -5,5'- A proton conductive polymer selected from the group consisting of poly (2,2 '- (mphenylene) -5,5'-bibenzimidazole), poly (2,5-benzimidazole) It can be used.

Further, H may be replaced with Na, K, Li, Cs or tetrabutylammonium in the proton conductive group of the proton conductive polymer. In the case of replacing H with Na in the ion exchange group at the side chain terminal, NaOH is used in the preparation of the catalyst composition and tetrabutylammonium hydroxide is used in the case of using tetrabutylammonium. K, Li or Cs is also appropriately substituted . ≪ / RTI > Since this substitution method is well known in the art, a detailed description thereof will be omitted in this specification.

The catalyst layers 151 and 152 refer to a catalyst layer 151 of the membrane layer 153 and the catalyst layers 151 and 152 serve to catalyze a reaction (oxidation of a fuel and reduction of an oxidant) Catalyst.

As the catalyst, any catalyst which can be used as a catalyst in the reaction of the fuel cell can be used. As a typical example thereof, a platinum catalyst can be used. As the platinum-based catalyst, platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy, platinum-M alloy (M is Ga, Ti, V, Cr, Mn, Fe, A transition metal selected from the group consisting of Cu, Zn, Sn, Mo, W, Rh, and combinations thereof), and combinations thereof, more preferably Pt, Pt / Ru, Pt / Co, Pt / Ru / W, Pt / Ru / Mo, Pt / Ru / V, Pt / W, Pt / Ni, Pt / Sn, Pt / Pt / Fe / Co, Pt / Ru / Rh / Ni, Pt / Ru / Sn / W and combinations thereof.

Such a metal catalyst may be used as a metal catalyst itself (black) or may be supported on a carrier. Examples of the carrier include carbonaceous materials such as graphite, denka black, ketjen black, acetylene black, carbon nanotubes, carbon nanofibers, carbon nanowires, carbon nanoballs, or activated carbon, or alumina, silica, zirconia, Titania, or the like may be used, but carbon-based materials are generally used.

The catalyst layers 151 and 152 may further include a binder resin for improving adhesion of the catalyst layer and transferring hydrogen ions.

As the binder resin, it is preferable to use a polymer resin having hydrogen ion conductivity. More preferably, a cation exchanger selected from the group consisting of a sulfonic acid group, a carboxylic acid group, a phosphoric acid group, a phosphonic acid group, Any polymer resin may be used. Preferable examples include fluorine-based polymers, benzimidazole polymers, polyimide polymers, polyetherimide polymers, polyphenylene sulfide polymers, polysulfone polymers, polyether sulfone polymers, - ether ketone-based polymers, polyphenylquinoxaline-based polymers, and copolymers thereof. More preferred are hydrogen-ion conductive polymers such as poly (perfluorosulfonic acid), poly (perfluorocarbons Copolymers of tetrafluoroethylene and fluorovinyl ethers containing sulfonic acid groups, dehydrofluorinated sulfated polyether ketones, aryl ketones, poly (2,2'-m-phenylene) -5,5'- Wherein the polymer is selected from the group consisting of poly (2,2'- (m-phenylene) -5,5'-bibenzimidazole), poly (2,5-benzimidazole) Polymer It can be used to include.

The binder resin may be used singly or in the form of a mixture, and may optionally be used together with a nonconductive compound for the purpose of further improving the adhesion to the polymer electrolyte membrane. It is preferable to adjust the amount thereof to suit the purpose of use.

Examples of the nonconductive compound include polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene / tetrafluoro (PVdF-HFP), dodecyltrimethoxysilane (DMSO), ethylene tetrafluoroethylene (ETFE), ethylene chlorotrifluoroethylene copolymer (ECTFE), polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer Silbenzenesulfonic acid, sorbitol, and a combination thereof.

In the cathode catalyst layer 151, oxidation reaction of hydrogen occurs as shown in the following Chemical Formula 1, and reduction reaction of oxygen as shown in Chemical Formula 2 below occurs in the cathode catalyst layer 152.

(1)

(2)

In order to improve the performance and durability of the polymer electrolyte fuel cell (PEFC) system, an anti-freeze control mechanism is required to prevent the formation of a product due to an electrochemical reaction in a polymer electrolyte fuel cell (PEFC) Is minimized. Referring to the above Chemical Formulas 1 and 2, water (H ₂ O) is generated on the cathode side by the reaction of hydrogen (H ₂ ) and oxygen (O ₂ ). That is, the electrochemical reaction of a polymer electrolyte fuel cell (PEFC) system is performed by cooling the water (H ₂ O) at a sub-zero temperature by the reaction of generating water (H ₂ O) at the cathode side And thus the transfer of oxygen is reduced and the area of the active electrochemical reaction is reduced. Furthermore, by repeatedly freezing and thawing the water (H ₂ O), the structure of the internal components of the polymer electrolyte fuel cell (PEFC, in particular, the structure of the anode catalyst layer 152) Resulting in deterioration of performance and durability.

The polyelectrolyte fuel cell to be controlled according to the present invention includes a cathode separator 160 formed on an outer surface of the diffusion layers 110 and 130 for supplying gas to the diffusion layers 110 and 130, Plate (170).

Bipolar plates 160 and 170 called bipolar plates or flow field plates are core components of the polymer electrolyte fuel cell stack and include a gas flow path for the anode on one side and a cathode cathode is an electrically conductive plate engraved with a gas flow path. The separator serves as a current collecting plate that conducts electrons generated from the anode to the cathode of the next cell and supports the polymer electrolyte membrane-electrode assemblies 110, 120, 130, 140 and 150 And provides a passage for supplying fuel and oxidant to the anode and cathode, respectively, and serves as a passage for removing water generated during operation of the battery. Thus, the separator material should have high electrical conductivity, low gas permeability, good mechanical strength, chemical stability, lightweight materials, and preferably graphite.

The present invention relates to a polymer electrolyte fuel cell,

The method comprising: applying a voltage to a cathode catalyst layer and an anode catalyst layer of a polymer electrolyte fuel cell so that a first current density flows; determining whether moisture inside the polymer electrolyte fuel cell is undersaturated; And applying a voltage to the cathode catalyst layer and the anode catalyst layer such that a second current density higher than the first current density flows through the anode catalyst layer and the anode catalyst layer.

Hereinafter, a control method of a polymer electrolyte fuel cell for low temperature start according to an embodiment of the present invention will be described in detail with reference to the drawings.

Referring to FIG. 2, first, a voltage is applied to a cathode catalyst layer and an anode catalyst layer of a polymer electrolyte fuel cell so that a first current density flows (S100).

The first current density value may be equal to or greater than a minimum value of a driving current density for driving the polymer electrolyte fuel cell, and the first current density value may be at least twice a minimum value of the driving current density. It is preferable that a voltage is applied. The polymer electrolyte fuel cell may not be driven when a voltage is applied to the cathode catalyst layer and the anode catalyst layer such that the first current density value is lower than the minimum value of the driving current density, If it exceeds twice the minimum value of the driving current density, the self-cooling starting effect of the polymer electrolyte fuel cell may not occur.

Next, it is determined whether water in the polymer electrolyte fuel cell is undersaturated (S110).

In the calculation of the chemical species governing equation, the unsaturated state is judged to be saturated when the chemical species is larger than the saturated state. Whether the current density is increased or not is determined whether the current density is increased or maintained when the temperature calculated through the calculation of the energy governance equation is in the range of -10 ° C to 0 ° C.

Next, when the moisture inside the polymer electrolyte fuel cell is undersaturated, a voltage is applied to the cathode catalyst layer and the anode catalyst layer of the polymer electrolyte fuel cell such that a second current density higher than the first current density flows (S120).

The second current density value is preferably controlled to a current density value within a range of 1.1 to 2.0 times the first current density value, and when the second current density value is less than 1.1 times the first current density value, The second current density value is less than the first current density value and the self-cooling starting effect may not occur. When the second current density value is more than 2.0 times the first current density value, The second current density value is excessive and the driving efficiency of the polymer electrolyte fuel cell may be lowered.

The undersaturated state of the polymer electrolyte fuel cell may have an internal temperature ranging from -10 ° C to 0 ° C.

Through the steps S100 to S120, the temperature rising rate of the polymer electrolyte fuel cell is controlled to be faster than the water production rate by the oxygen reduction reaction inside the polymer electrolyte fuel cell to prevent the water generated in the polymer electrolyte fuel cell from freezing And the durability and the effect of the polymer electrolyte fuel cell can be prevented from deteriorating.

Hereinafter, the minimum value of the driving current density will be described in more detail with reference to the following equations and FIGS. 3 and 4. FIG.

3 is a diagram showing a model for three-dimensional numerical analysis of a polymer electrolyte fuel cell to be controlled according to the present invention.

A three-dimensional numerical analysis of the polymer electrolyte fuel cell is performed through a three-dimensional numerical simulation model of the polymer electrolyte fuel cell of FIG. 3, and a governing equation for three-dimensional numerical analysis is shown in FIG.

Referring to FIG. 4, the governing equation can be expressed in terms of Mass, Momentum, Species, Charge, and Energy as shown in FIG. 4 . In addition, the definition of an electrochemical reaction can be represented by an equation.

The governing equation of FIG. 4 was applied to an actual model of the cold start of the polymer electrolyte fuel cell of the present invention to produce the production terms as shown in FIG.

5, mass equations in an anode catalyst layer, mass equations in a cathode catalyst layer, Momentum equations in a gas diffusion layer and a catalyst layer, momentum equations in a membrane, types of catalyst layers for water The equation of equation for the gas diffusion layer for water, the kind equation of the catalyst layer for different kinds, the charge equation of the catalyst layer, the energy equation in the catalyst layer, the energy equation in the gas diffusion layer and the energy equation in the membrane were calculated.

In addition, water freezing and thawing was defined through the equation of FIG. At this time, the three-dimensional numerical analysis model of the polymer electrolyte fuel cell was modeled through the following assumptions. First, the supersaturated water vapor is immediately sublimated into ice and frost, and when it is in a gaseous state, it follows the ideal gas law. Third, the porosity and permeability of the diffusion layer are isotropic and homogeneous. Fourth, Fifth, the charging and discharging phenomena of the electrochemical double layer in the catalyst layer are not taken into consideration. Sixth, the gas channel and the porous region are assumed to be incompressible laminar flow because of the small pressure gradient and velocity.

Meanwhile, the definitions of the variables described in Figs. 4 to 6 are as follows.

variable

: 다공성 물질의 유체의 속도와 표면 속도 (m/s), V_cell: 셀의 전위(V)A is the area (m ² ), C is the molar concentration (mol / m ³ ), c _{p is the} specific heat (J / Kg * K), D _i is the diffusion of the i species (m ² / s), F is the Faraday constant _{96485 C / mol), h sg} : latent heat (kJ / kg), i ₀ of the water sublimation: exchange current density ^{(a / m 2), i} : the operating current density ^{(a / cm 2), j} : transfer current density ( A / m ³ ), K is the water permeability (A / m ² ), MW is the molecular weight (kg / mol), P is the pressure (Pa), n _{d is the} electroosmotic resistance coefficient, R is the universal gas constant (8.314 J / (K), t: time (s), and temperature (K)

: Velocity and surface velocity (m / s) of fluid of porous material, V _cell : potential of cell (V)

(kg / m ³ ), ρ: density (kg / m ³ ), τ: viscous shear (ρ) stress ^{(N / m 2), σ} : electrical conductivity (S / m), κ: ionic conductivity (S / m), ξ: chemical flow rate, δ: thickness (mm)

Superscript

eff: effective value in the porous region, mem: membrane

Subscript

0: an initial state, a: a positive electrode (anode), c: a negative electrode (cathode), e: electrolyte, i: kind sign, in: channel entrance, m: mass equation, mem: film, H _2: hydrogen, H ₂ O : Water, O ₂ : oxygen, sg: sublimation / desublimation, u: momentum equation

The minimum value of the driving current density to be applied to the cathode catalyst layer of the polymer electrolyte fuel cell can be calculated through the three-dimensional numerical analysis of the polymer electrolyte fuel cell for low-temperature start-up modeled by the above-described FIG. 3 to FIG.

In addition, the step of determining whether or not it is undersaturated (S110) may be performed by the method of FIG.

FIG. 7 is a flowchart illustrating a method for determining whether water in a polymer electrolyte fuel cell is undersaturated in a method of controlling a polymer electrolyte fuel cell for low-temperature start according to an embodiment of the present invention.

운동량 지배방정식(Momentum Governing Equation)은 아래와 같다.

화학종 지배방정식(Species Governing Equation)은 아래와 같다.

에너지 지배방정식(Energy Governing Equation)은 아래와 같다.

전하 지배방정식(Charge Governing Equation)은 아래와 같다.

한편, 상기 지배방정식에 기재된 변수들에 대한 정의는 다음과 같다.
변수,
A: 면적(m²), C: 몰농도 (mol/m³), c_p: 비열 (J/Kg*K), D_i: i종의 확산 (m²/s), F: 페러데이 상수 (96485 C/mol), h_sg: 수분 승화의 잠열 (kJ/kg), i₀: 교환전류밀도 (A/m²), I: 동작전류밀도 (A/cm²), j: 전송전류밀도 (A/m³), K: 수분투과성 (A/m²), MW: 분자량(kg/mol), P: 압력 (Pa), n_d: 전기침투저항계수, R: 보편기체상수 (8.314 J/mol*K), S: 전송방정식의 소스용어, s: 얼음파편, T: 온도(K), t: 시간(s),

: 다공성 물질의 유체의 속도와 표면 속도 (m/s), V_cell: 셀의 전위(V), ε: 공극률, φ: 위상 전위 (V), η: 과전압 (V), λ: 막의 수분함유량, μ: 점도 (kg/m*s), ρ: 밀도 (kg/m³), τ: 점성 전단 응력 (N/m²), σ: 전기전도도 (S/m), κ: 이온전도도 (S/m), ξ: 화학적 유량비, δ: 두께 (mm),
윗첨자,
eff: 다공성 지역에서의 실효값, mem: 막,
아랫첨자,
0: 초기상태, a: 양극(anode), c: 음극(cathode), e: 전해액, i: 종류 기호, in: 채널 입구, m: 질량방정식, mem: 막, H₂: 수소, H₂O: 물, O₂: 산소, sg: 승화/탈승화, u: 운동량 방정식.First, the variables are calculated by applying the predetermined initial conditions, and then the five governing equations (mass * momentum, energy, chemical species, and charge governing equations) are sequentially calculated (S111).
The Mass Governing Equation is as follows.

The Momentum Governing Equation is as follows.

The Species Governing Equation is as follows.

Energy Governing Equation is as follows.

The charge governing equations are:

On the other hand, the definitions of the variables described in the governing equations are as follows.
variable,
A is the area (m ² ), C is the molar concentration (mol / m ³ ), c _{p is the} specific heat (J / Kg * K), D _i is the diffusion of the i species (m ² / s), F is the Faraday constant _{96485 C / mol), h sg} : latent heat (kJ / kg), i ₀ of the water sublimation: exchange current density ^{(a / m 2), I} : the operating current density ^{(a / cm 2), j} : transfer current density ( A / m ³ ), K is the water permeability (A / m ² ), MW is the molecular weight (kg / mol), P is the pressure (Pa), n _{d is the} electroosmotic resistance coefficient, R is the universal gas constant (8.314 J / (K), t: time (s), and temperature (K)

: Speed and surface velocity of the fluid in the porous medium _{(m / s), V cell} : the potential of the cell (V), ε: void ratio, φ: phase voltage (V), η: voltage (V), λ: the membrane water content , μ is the viscosity (kg / m * s), ρ is the density (kg / m ³ ), τ is the viscous shear stress (N / m ² ), σ is the electrical conductivity / m),?: chemical flow ratio,?: thickness (mm)
Superscript,
eff: effective value in the porous region, mem: membrane,
The subscript,
0: an initial state, a: a positive electrode (anode), c: a negative electrode (cathode), e: electrolyte, i: kind sign, in: channel entrance, m: mass equation, mem: film, H _2: hydrogen, H ₂ O : Water, O ₂ : oxygen, sg: sublimation / desublimation, u: momentum equation.

Specifically, the mass-momentum governing equation is calculated using the variables calculated by applying the predetermined initial conditions, and then the newly calculated velocity and pressure values are calculated (S112).

The velocity and pressure values calculated and calculated according to the mass-momentum governing equation are applied to the energy governing equations to calculate temperature values in each grid (S113).

Next, the concentration values of hydrogen, water, and oxygen are calculated in each lattice by calculating chemical species governing equations using the temperature value calculated by the energy governing equation (S114).

Next, a charge control equation is calculated using the hydrogen, water, and oxygen concentration values calculated by the chemical species governance equation to calculate a current density and a voltage value (S115).

Next, the current density and voltage value calculated by the charge governing equation are compared with a predetermined convergence condition, and if the predetermined convergence condition (residual <10 ^-6 ) is not satisfied, calculation from the energy governing equations is again performed (S113). After the convergence condition (residual <10 ^-6 ) is satisfied, the next step is performed (S116).

Next, after the convergence condition (residual <10.sup.- ⁶ ) is satisfied (S116), the calculation is terminated if the calculated time is longer than the predetermined calculation time. If the convergence condition is smaller than the predetermined calculation time, the variables are updated to calculate the mass / momentum governing equation, The calculated velocity and pressure values are calculated (S112).

Hereinafter, the present invention will be described in more detail with reference to specific examples. The following examples are provided to illustrate the present invention, but the present invention is not limited by the following examples.

&Lt; Example 1 >

S100: The anode catalyst layer of the polymer electrolyte fuel cell was coated with 0.1 A / cm ² A first current density value was applied.

S120: A second current density value of 0.15 A / cm ² was applied to the anode catalyst layer of the polymer electrolyte fuel cell after 30 seconds (when the inside temperature of the polymer electrolyte fuel cell was -10 ° C).

At this time, ε _i of the polymer electrolyte fuel cell is 0.2, ε _cCL is 0.4, and δ _cCL is 10 ?.

&Lt; Comparative Example 1 &

In the anode catalyst layer of the polymer electrolyte fuel cell, 0.1 A / cm &lt; ² &gt; A first current density value was applied. At this time, ε _i of the polymer electrolyte fuel cell is 0.2, ε _cCL is 0.4, and δ _cCL is 10 μm.

&Lt; Comparative Example 2 &

A first current density value of 0.15 A / cm &lt; ² &gt; was applied to the anode catalyst layer of the polymer electrolyte fuel cell. At this time, ε _i of the polymer electrolyte fuel cell is 0.2, ε _cCL is 0.4, and δ _cCL is 10 μm.

&Lt; Comparative Example 3 &

S100: The anode catalyst layer of the polymer electrolyte fuel cell was coated with 0.1 A / cm ² A first current density value was applied.

S120: A second current density value of 0.15 A / cm &lt; ² &gt; was applied to the anode catalyst layer of the polymer electrolyte fuel cell after 10 seconds (when the inside temperature of the polymer electrolyte fuel cell was about -18 DEG C.). At this time, ε _i of the polymer electrolyte fuel cell is 0.2, ε _cCL is 0.4, and δ _cCL is 10 μm.

FIGS. 8 and 9 are graphs showing the results obtained under the conditions of Example 1 and Comparative Examples 1 to 3. FIG.

FIG. 8 is a graph showing the ice accumulation amount (mg / cm ² ) and the cell temperature over time under the conditions of Example 1 and Comparative Examples 1 to 3, (V) of a cell with time and a water content with time under the conditions of Comparative Examples 1 to 3 and Comparative Examples 1 to 3.

Referring to FIG. 8, when the first current density value is higher, the amount of water produced by the oxygen reduction reaction is increased and the amount of ice produced in the air electrode catalyst layer is higher than that of Comparative Example 1, The heat lost due to the first current density value is increased and the temperature increasing rate is also high. Therefore, it can be seen that the amount of ice produced in the air electrode catalyst layer is larger than that in Comparative Example 1, although the temperature of the Comparative Example 2 is higher than that of Comparative Example 1 because the rate of temperature rise is higher than 0 ° C. On the other hand, in the case of Comparative Example 3 and Example 1, in the case of Comparative Example 3 in which the second current density is applied in the ice producing step, the ice generation rate and the temperature increasing rate similar to those of Comparative Example 2 are shown, It can be seen that Example 1 in which the second current density is applied is an amount of ice produced similar to Comparative Example 1 and that the rate of temperature rise is the same as that in Comparative Example 2. The method of Example 1 was found to be most effective .

Referring to FIG. 9, the degree of the voltage reduction is determined by the applied current density value, and in particular, in Comparative Example 3 and Example 1, the second current density applied in the step of generating ice, The second voltage reduction is shown by the value, but the voltage rises again by the re-watering of the electrolyte membrane due to the water despreading. On the other hand, the water content of the electrolyte membrane initially tends to decrease due to electroosmosis, while it tends to increase again by the back diffusion of water generated in the air electrode catalyst layer by the oxygen reduction reaction, It can be seen that the water content is suddenly increased due to the melting of ice at the time of increase.

Simulation using a three-dimensional low-temperature start-up model showed that the temperature of the polymer fuel cell quickly reached 0 ° C without generating additional ice, which is a problem in the current rise method at the unsaturation step. The method according to the present invention can solve the low-temperature start-up problem only by controlling the current density value applied to the fuel cell without any additional device for raising the temperature of the polymer electrolyte fuel cell vehicle.

100: Polymer electrolyte fuel cell
110: cathode diffusion layer
120: Cathode fine electrode layer
130: anode diffusion layer
140: positive electrode fine electrode layer
150: catalyst coating membrane
151: cathode catalyst layer
152: anode catalyst layer
153: Membrane layer

Claims (6)

A method for controlling a polymer electrolyte fuel cell,
Applying a voltage to the anode catalyst layer and the anode catalyst layer of the polymer electrolyte fuel cell such that a first current density flows;
Determining whether moisture inside the polymer electrolyte fuel cell is undersaturated; And
And applying a voltage to the anode catalyst layer and the anode catalyst layer of the polymer electrolyte fuel cell so that a second current density higher than the first current density flows,
Wherein the step of applying a voltage such that the second current density flows is performed when moisture inside the polymer electrolyte fuel cell is undersaturated.
The method according to claim 1,
Wherein the first current density is a current density,
Wherein the current density value for driving the polymer electrolyte fuel cell is a current density value for driving the polymer electrolyte fuel cell.
The method according to claim 1,
Wherein the second current density is 1.1 to 2.0 times the current density of the first current density.
delete The method according to claim 1,
Wherein the step of determining whether the polymer is undersaturated comprises:
Wherein the control is performed when the internal temperature of the polymer electrolyte fuel cell is in the range of -10 ° C to 0 ° C.
The method according to claim 1,
Wherein the step of determining whether the polymer is undersaturated comprises:
Calculating a variable by applying a predetermined initial condition;
Calculating a velocity and an input value by calculating a mass governance equation and a momentum governance equation using a variable calculated by applying the predetermined initial condition;
Calculating a temperature value in each grid by applying a velocity and an input value calculated and calculated according to the mass governance equation and the momentum governance equation to an energy governing equation;
Calculating a concentration value of hydrogen, water, and oxygen in each lattice by calculating a chemical species governance equation using the temperature value calculated by the energy governing equation;
Calculating a current density and a voltage value by calculating a charge governance equation using the concentration values of hydrogen, water, and oxygen calculated by the chemical species governance equation;
Comparing the current density and voltage value calculated by the charge governing equation with a predetermined convergence condition to determine whether the predetermined convergence condition is satisfied; And
Determining whether the time is greater than a predetermined time,
The control method of the polymer electrolyte fuel cell for low-temperature start-up characterized by the mass governing equations, momentum governing equations, energy governing equations, chemical species governing equations and charge governing equations are as follows:
The mass governance equation,

The momentum governance equation,

The energy governing equations,

The chemical species governing equations,

The charge governance equation,

And

,
The variables, superscripts and subscripts described in the respective governing equations are
variable,
A is the area (m ² ), C is the molar concentration (mol / m ³ ), c _{p is the} specific heat (J / Kg * K), D _i is the diffusion of the i species (m ² / s), F is the Faraday constant _{96485 C / mol), h sg} : latent heat (kJ / kg), i ₀ of the water sublimation: exchange current density ^{(a / m 2), I} : the operating current density ^{(a / cm 2), j} : transfer current density ( A / m ³ ), K is the water permeability (A / m ² ), MW is the molecular weight (kg / mol), P is the pressure (Pa), n _{d is the} electroosmotic resistance coefficient, R is the universal gas constant (8.314 J / (K), t: time (s), and temperature (K)

: Speed and surface velocity of the fluid in the porous medium _{(m / s), V cell} : the potential of the cell (V), ε: void ratio, φ: phase voltage (V), η: voltage (V), λ: the membrane water content , μ is the viscosity (kg / m * s), ρ is the density (kg / m ³ ), τ is the viscous shear stress (N / m ² ), σ is the electrical conductivity / m),?: chemical flow ratio,?: thickness (mm)
Superscript,
eff: effective value in the porous region, mem: membrane,
The subscript,
0: an initial state, a: a positive electrode (anode), c: a negative electrode (cathode), e: electrolyte, i: kind sign, in: channel entrance, m: mass equation, mem: film, H _2: hydrogen, H ₂ O : Water, O ₂ : oxygen, sg: sublimation / desublimation, u: momentum equation.

Images