Method for activating a fuel cell stack

Abstract

A method for activating a fuel cell stack, comprising: Supplying oxygen and hydrogen to the fuel cell stack after starting an activation process in a fuel cell activation process to allow the stack to enter an open-circuit (OCV) state, and shutting off the supply of oxygen and hydrogen; electrically connecting adjacent cells of a plurality of cells forming the stack through a cell voltage measuring board and short-circuiting the adjacent cells to reduce the cell voltage to approximately 0 V; resupplying oxygen and hydrogen to the stack and performing a preconditioning process by applying a predetermined current density for a predetermined period of time; Repeating the reduction of the voltage to approximately 0 V by short-circuiting by applying a current density exceeding the specified current density for a period exceeding the specified time period until the open-circuit state is reached in order to remove the oxygen remaining in the stack; and After a predetermined rest period and after the removal of the remaining oxygen, oxygen and hydrogen are added again.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a method for activating a fuel cell stack, and more particularly, to a method for activating a fuel cell stack to shorten the process time and reduce hydrogen consumption by rapidly lowering the stack voltage by means of an electrical short-circuit phenomenon between adjacent cells of the fuel cell stack and by removing the oxygen remaining in the stack. BACKGROUND

[0002] Since the activity of a fuel cell stack is generally low after assembly and manufacturing due to an electrochemical reaction during initial operation, a process known as stack activation is performed to ensure the normal initial performance of the fuel cell stack to the greatest extent possible. Fuel cell activation, known as preconditioning or running-in, serves to activate the catalyst not involved in the reaction and to sufficiently hydrogenate an electrolyte membrane and an electrolyte contained in an electrode to ensure the passage of hydrogen ions.In particular, to ensure the performance in the normal state after the assembly of the fuel cell stack, the stack activation process is carried out with the aim of ensuring a three-phase electrode reaction area, removing impurities of the polymer electrolyte membrane or the electrode, and improving the ionic conductivity of the polymer electrolyte membrane.

[0003] In a method for activating a stack according to the related art described above, a pulse discharge is repeated at a high current density in the off-state, wherein the process duration is approximately 1.5 to 2 hours based on a 220-cell submodule. In particular, the method for activating a stack according to the related art is repeatedly carried out by a process in which a high current density (e.g., 1.2 or 1.4 A / cm 2) is discharged repeatedly for 3 minutes, and a process in which the pulse discharge is carried out about 11 times for 5 minutes in the off state.

[0004] However, in the activation process according to the related technology using the aforementioned pulse discharge, the amount of hydrogen used increases and the process time becomes longer. In other words, the existing method for activating a stack using pulse discharge in the off-state has the advantage of increasing the activation speed by changing the internal water flow in the fuel cell. However, since the activation time is approximately 105 minutes and approximately 2.9 kg of hydrogen is consumed based on the 220-cell sub-module, the process time is longer and the hydrogen consumption is higher.

[0005] DE 10 2007 056 119 A1 already discloses devices and methods for accelerating the activation of fuel cells. The devices comprise the following: a fuel cell stack; air supply devices coupled to a cathode catalyst side of the fuel cell stack via a mass flow control device and a humidifier; hydrogen supply devices coupled to an anode catalyst side of the fuel cell stack via a mass flow control device and a humidifier; and a cable coupled to both ends of the fuel cell stack for short-circuiting the cathode and the anode.

[0006] JP 2000-277136 A discloses a method for starting a solid polymer fuel cell in which multiple cell units, each having a fuel chamber on one side and an oxidant chamber on the other side, are laminated onto a cell having electrodes on both surfaces of an electrolyte membrane. Power is generated by supplying an oxidizing gas to the fuel chamber and the oxidant chamber. The method is characterized in that the rolling polarity of each cell unit is prevented and the cell unit is activated by generating power for each cell unit or two adjacent cell units before power supply to the external load is started.

[0007] Furthermore, JP 5 957 209 B2 discloses an apparatus and method for activating a fuel cell stack, which significantly reduces the time required for activation and the amount of hydrogen used for activation by applying a vacuum wetting process during a shutdown. Specifically, an open-circuit voltage operation at high humidity humidifies the fuel cell stack and operates the fuel cell stack at an open-circuit voltage, and a vacuum wetting operation wets the surface of a polymer electrolyte membrane by creating a vacuum atmosphere in the fuel cell stack. OVERVIEW

[0008] It is the object of the present disclosure to provide a method for activating a fuel cell stack and, in particular, a method for activating a fuel cell stack to shorten the process time and to reduce hydrogen consumption by rapidly lowering the stack voltage by means of an electrical short-circuit phenomenon between adjacent fuel cells and removing the oxygen remaining in the stack.

[0009] The object is achieved by a method having the features of claims 1 or 8. Advantageous further developments can be found in the subclaims.

[0010] According to an embodiment of the present disclosure, a method for activating a fuel cell stack may include: supplying oxygen and hydrogen to the fuel cell stack after starting a fuel cell activation process to allow the stack to enter an open-circuit (OCV) state, and shutting off the supply of oxygen and hydrogen; electrically connecting adjacent cells among a plurality of cells constituting the stack through a cell voltage sensing board and short-circuiting the adjacent cells so that the cell voltage is 0 V; after the second step, supplying oxygen and hydrogen to the stack again and performing a preconditioning process by applying a predetermined current density for a predetermined period of time;Reducing the voltage to 0 V by applying a current density exceeding the specified current density for a period of time exceeding the specified time period until the open-circuit state in order to remove the oxygen remaining in the stack; and after a specified rest period (e.g., switched-off state), after the removal of the remaining oxygen, re-supplying oxygen and hydrogen.

[0011] In addition, the specified current density can be adjusted to approximately 0.6 to 1.0 A / cm 2 and the specified time period can be set to approximately 10 to 60 seconds. The current density exceeding the specified current density can be set to approximately 1.0 to 1.4 A / cm 2and the time exceeding the specified time can be set to approximately 30 to 180 seconds. The specified time for resupplying oxygen and hydrogen can be set to approximately 30 to 300 seconds. In addition, the time for short-circuiting the cell voltage to 0 V can be set to less than approximately 5 seconds. By repeating the voltage reduction and resupply of oxygen and hydrogen approximately 11 times, the activation process can be completed in approximately 75 minutes, and the hydrogen consumption can be reduced to 1.7 kg. The cell voltage measuring board may have a connecting part formed from the center to both ends for connecting the adjacent cells.

[0012] According to another embodiment of the present disclosure, a method for activating a fuel cell stack may include: supplying oxygen and hydrogen to the fuel cell stack after starting an activation process in a fuel cell activation process to allow the stack to enter the open circuit (OCV) state, and shutting off the supply of oxygen and hydrogen; electrically connecting adjacent cells among the plurality of cells constituting the stack through a connector in a cell voltage sensing board and short-circuiting the adjacent cells to establish a cell voltage of 0 V; resupplying oxygen and hydrogen to the stack and performing a preconditioning process by applying a current density of approximately 0.6 to 1.0 A / cm 2 for a duration of approximately 10 to 60 seconds; the voltage is then reduced again to 0 V by applying a current density of approximately 1.0 to 1.4 A / cm 2for a period of 30 to 180 seconds until the open-circuit state to remove the oxygen remaining in the stack; and resupplying oxygen and hydrogen after a rest period of approximately 30 to 300 seconds after the removal of the remaining oxygen. In particular, the time for shorting the cell voltage to 0 V can be set to less than approximately 5 seconds. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. Fig. 1 is a flowchart of a method for activating a fuel cell stack according to an embodiment of the present disclosure; and Fig. 2 is a graph of the average voltage and activation duration of the method for activating a fuel cell stack according to an embodiment of the present disclosure and related art. DETAILED DESCRIPTION

[0014] It is understood that the term "vehicle" or "vehicular" or other similar terms used herein generally refer to motor vehicles, such as passenger cars, including sports utility vehicles (SUVs), buses, trucks, various commercial vehicles, personal watercraft including various boats and ships, aircraft, and the like, and also includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles (chargeable from a wall outlet), hydrogen-powered vehicles, and other alternative fuel vehicles (e.g., fuels derived from resources other than petroleum). As used herein, a hybrid vehicle is a vehicle with two or more power sources, e.g., vehicles with both gasoline and electric power.

[0015] Although the embodiment is described as using a plurality of units to execute the example process, it should be understood that the example processes may also be executed by one or more modules. Furthermore, it should be understood that the term controller / controller refers to a hardware device that includes a memory and a processor. The memory is configured to store the modules, and the processor is specifically configured to execute the modules to perform one or more of the processes described later.

[0016] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Furthermore, it is to be understood that the terms “comprise” and / or “comprising,” when used in this specification, indicate the presence of stated features, integer quantities, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integer quantities, steps, operations, elements, components, and / or groups thereof. As used herein, the phrase “and / or” includes all combinations of one or more of the listed items.

[0017] Unless expressly stated or obvious from the context, the term "about, approximately," as used herein, should be understood to refer to values ​​within normal engineering tolerances, such as two standard deviations from the mean. "About" or "approximately," may be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless the context otherwise clearly indicates, all numerical values ​​contained herein are modified by the term "about, approximately."

[0018] Embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings.

[0019] As in Fig. 1, a method for activating a fuel cell stack according to an embodiment of the present disclosure may include: supplying oxygen and hydrogen to the fuel cell stack and stopping the supply of oxygen and hydrogen in a fuel cell activation process (S10), electrically connecting and short-circuiting between adjacent cells of the stack (S20), resupplying oxygen and hydrogen to the stack and applying a current (S30), lowering the voltage by a short circuit to remove the oxygen remaining in the stack (S40), and resupplying oxygen and hydrogen (S50).

[0020] As in the Fig. 1 and Fig.2, in the start-up process (S10) of the method for activating a fuel cell stack according to the present disclosure, oxygen and hydrogen may be supplied to the fuel cell stack after the activation process in the fuel cell activation process has been started, thereby allowing the stack to enter the open-circuit voltage (OCV) state.

[0021] When the stack is in an open-circuit state, the short circuit can be induced by stopping the supply of oxygen and hydrogen. Specifically, the cell voltage can be reduced to nearly 0 V (S20) by electrically connecting adjacent cells of the plurality of cells constituting the stack (e.g., electrically connected adjacent cells) using a cell voltage sensing board and short-circuiting the adjacent cells connected to each other. The cell voltage sensing board connecting the cells can have a terminal part (not shown) configured from the center to both ends for connecting the adjacent cells.

[0022] In the preconditioning process (S30), oxygen and hydrogen can be added to the stack again, and a predetermined current density can be applied for a predetermined period of time after the cell voltage has been reduced to nearly 0 V (S20). In particular, the predetermined current density can be set to approximately 0.6 to 1.0 A / cm 2 can be set to detect defective cells and ensure voltage stability at both low and high current densities. The preset time can be set to approximately 10 to 60 seconds to ensure voltage stability over a period of time. The preset current can be specifically set to approximately 360 A and the preset time to approximately 30 seconds.

[0023] When removing the oxygen remaining in the stack (S40), the voltage can be reduced to approximately 0 V again by the short circuit by applying a current density exceeding the specified current density (e.g., approximately 0.6 to 1.0 A / cm2 ) is applied for a period exceeding the specified period (e.g., approximately 10 to 60 seconds) above the open-circuit state after the preconditioning process in order to remove the oxygen remaining in the stack. In particular, the current density exceeding the specified current density can be limited to approximately 1.0 to 1.4 A / cm 2The time period exceeding the specified time period can be set to approximately 30 to 180 seconds to achieve a reduction in mass transfer resistance by swelling the Nafion around the catalyst with a high-current pulse and inducing a structural change in an electrode from closed to open pores. The time period exceeding the specified time period can be set to approximately 30 to 180 seconds to achieve a sufficient reduction in mass transfer resistance. Specifically, the current exceeding the specified current of approximately 360 A can be set to approximately 432 A, and the time period exceeding the specified time period of approximately 30 seconds can be set to approximately 120 seconds.

[0024] Furthermore, a short holding time, in which the cell voltage is short-circuited to 0 V, can be set to less than approximately 5 seconds (e.g., the voltage drop time can be set so that it does not exceed 5 seconds) with respect to the hydrogen stoichiometry of 1.5 for Pt-Ox reduction and the optimization of the platinum / binder interface by rapidly removing the oxygen remaining in the stack by means of a rapid voltage drop, and can be kept below approximately 5 seconds if the hydrogen stoichiometry value is not changed during activation. If the voltage is forcibly reduced quickly by applying an external short-circuit equivalent load, a current of approximately 20 A can be applied. In particular, the current density can be proportional to the activation area, relative to the activation area of ​​approximately 360 A / cm 2 be increased.

[0025] When oxygen and hydrogen are reintroduced (S50) after a rest period (e.g., shutdown) has elapsed, after a predetermined period of time following the removal of the remaining oxygen, oxygen and hydrogen can be reintroduced to activate the stack. Specifically, the predetermined time period can be set to approximately 30 to 300 seconds to achieve a sufficient effect to enhance catalyst activation by removing mixed impurities or surface oxides formed during electrode preparation and residual organic solvents (IPA, alcohol, propanol, etc.) from the surface during the rest period. Specifically, the predetermined time period can be set to approximately 180 seconds. The rest period is completed.

[0026] According to the present disclosure, the repeated voltage reduction by short-circuiting to remove the oxygen remaining in the stack and the re-supply of oxygen and hydrogen after the rest period can be repeated at least 11 times, so that the fuel cell stack meets the reference performance, thereby accelerating the activation process. Specifically, the activation can be accelerated due to the reduction rate of oxides on a Pt catalyst surface formed during the manufacturing process of the electrode separator plate in the cell, which further increases due to cathode degradation due to overvoltage, and the oxygen remaining in a cathode can be completely removed through Pt-Ox reduction and optimization of the platinum / binder interface.

[0027] In other words, according to the present disclosure, the duration of an activation process can be significantly shortened to about 75 minutes by reducing the consumption time and the number of repetitions of an intermediate process compared to the related art, and marketability can be improved by reducing hydrogen consumption (e.g., hydrogen consumption can be reduced to about 1.7 kg based on the duration of the activation process and the number of repetitions).

[0028] The method for activating a fuel cell stack may include: supplying oxygen and hydrogen to the fuel cell stack after starting the activation process in the fuel cell activation process to allow the stack to enter the open circuit (OCV) state, and stopping the supply of oxygen and hydrogen (S10); electrically connecting adjacent cells of the plurality of cells constituting the stack through a cell voltage sensing board and short-circuiting the adjacent cells to lower the cell voltage to 0 V (S20);Resupplying oxygen and hydrogen to the stack and performing a preconditioning process by applying a predetermined current for a predetermined period of time (S30); repeating the short-circuiting of the voltage to 0 V by applying a current exceeding the predetermined current for a period of time exceeding the predetermined period of time above the idle state to remove the oxygen remaining in the stack (S40); and resupplying oxygen and hydrogen after the expiration of the rest period for a predetermined period of time after the removal of the remaining oxygen (S50).

[0029] After the cell voltage of the open-circuit state has been lowered to approximately 0 V by short-circuiting the adjacent cells of the fuel cell, the activation can be repeated, and oxygen remaining in the stack can be removed by rapidly lowering the voltage by short-circuiting during the activation process to accelerate the activation process, thereby shortening the time required for recovery and reducing the amount of hydrogen used for activation.

Claims

[1] A method for activating a fuel cell stack, comprising: Supplying oxygen and hydrogen to the fuel cell stack after starting an activation process in a fuel cell activation process to allow the stack to enter an open-circuit (OCV) state, and shutting off the supply of oxygen and hydrogen; electrically connecting adjacent cells of a plurality of cells forming the stack through a cell voltage measuring board and short-circuiting the adjacent cells to reduce the cell voltage to approximately 0 V; resupplying oxygen and hydrogen to the stack and performing a preconditioning process by applying a predetermined current density for a predetermined period of time; Repeating the reduction of the voltage to approximately 0 V by short-circuiting by applying a current density exceeding the specified current density for a period exceeding the specified time period until the open-circuit state is reached in order to remove the oxygen remaining in the stack; and After a predetermined rest period and after the removal of the remaining oxygen, oxygen and hydrogen are added again. [2] The method according to claim 1, wherein the predetermined current density is approximately 0.6 to 1.0 A / cm 2 and the specified time period is set to approximately 10 to 60 seconds. [3] The method according to claim 2, wherein the current density exceeding the predetermined current density is approximately 1.0 to 1.4 A / cm 2 and the time period exceeding the specified time period is set to approximately 30 to 180 seconds. [4] The method according to claim 3, wherein the predetermined time period for the renewed supply of oxygen and hydrogen is set to approximately 30 to 300 seconds. [5] The method of claim 1, wherein the time period of lowering the cell voltage to about 0 V is set to less than about 5 seconds. [6] The method according to claim 1, wherein by repeating the lowering of the voltage and the resupply of oxygen and hydrogen 11 times, an activation process takes about 75 minutes and the hydrogen consumption is reduced to about 1.7 kg. [7] The method according to claim 1, wherein the cell voltage measuring board includes a connecting part formed from the center to both ends for connecting the adjacent cells to each other. [8] A method for activating a fuel cell stack, comprising: Supplying oxygen and hydrogen to the fuel cell stack after starting an activation process in a fuel cell activation process to allow the stack to enter an open circuit (OCV) state, and shutting off the supply of oxygen and hydrogen; electrically connecting adjacent cells of a plurality of cells forming the stack through a terminal part of a cell voltage measuring board and short-circuiting the adjacent cells to reduce the cell voltage to approximately 0 V; Resupplying oxygen and hydrogen to the stack and performing a preconditioning process by applying a predetermined current density of approximately 0.6 to 1.0 A / cm 2 for approximately 10 to 60 seconds; Repeat the voltage reduction to approximately 0 V by short-circuiting, applying a current density of 1.0 to 1.4 A / cm 2for approximately 30 to 180 seconds until the idle state is reached in order to remove the oxygen remaining in the stack; and renewed supply of oxygen and hydrogen after a rest period of approximately 30 to 300 seconds after the removal of the remaining oxygen. [9] The method of claim 8, wherein the time period of lowering the cell voltage to about 0 V is set to less than about 5 seconds.

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