Electrochemical device comprising bipolar metal selective proton conductor

Abstract

The present invention relates to an electrolyte membrane comprising a bipolar metal selective proton conductor. A hydrogen storage alloy is introduced therein to conduct, without hydration, protons, thereby enabling crossover to be completely blocked, and has excellent mechanical strength, and thus can replace a conventional Nafion electrolyte membrane. In addition, if the electrolyte membrane is applied to a proton-exchange membrane for a fuel cell, electrochemical performance of the fuel cell can be improved.

Description

Electrochemical device including a bipolar metal-selective proton conductor

[0001] The present invention relates to an electrolyte membrane comprising a bipolar metal-selective proton conductor and an electrochemical device manufactured including the same.

[0002]

[0003] Electrochemical devices include fuel cells, water electrolyzers, vanadium redox flow batteries, lithium-mediated nitrogen fixation, supercapacitors, and electrochemical sensors, and these devices are widely used for energy conversion and storage or the synthesis of chemicals.

[0004] First, a fuel cell is a device that produces electrical energy by electrochemically reacting fuel and oxygen. A typical fuel cell system includes a fuel cell stack that generates electrical energy from the electrochemical reaction of reaction gases (hydrogen as fuel and oxygen as an oxidant), a hydrogen supply unit that supplies hydrogen fuel to the fuel cell stack, an air supply unit that supplies oxygen-containing air to the fuel cell stack, a thermal and water management system that controls the operating temperature of the fuel cell stack and performs water management functions, and a fuel cell controller that controls the overall operation of the fuel cell system. Within the stack of such a fuel cell system, water is produced as a byproduct of the reaction between hydrogen and oxygen; if this produced water accumulates within the stack, the residual water can cause performance degradation of the fuel cell system. In addition, there is a crossover problem within the stack where non-desirable ions, such as reactants, products, or solvents, cross over—for instance, nitrogen from the air electrode crosses through the electrolyte membrane to the fuel electrode. Such crossover causes a decrease in stability in electrochemical devices like fuel cells and can increase the risk of explosion in water electrolysis devices, making it a critical issue that must be resolved.

[0005] Meanwhile, water electrolysis is a method of obtaining hydrogen by using electricity to separate water molecules into hydrogen molecules and oxygen molecules. Water electrolysis is an environmentally friendly method of hydrogen production and is the most reliable technology among hydrogen manufacturing methods. It is known as the most cost-effective hydrogen production technology with a simple system configuration and stable operation. Conventional water electrolysis devices are constructed to produce hydrogen and oxygen in a single electrolytic cell and include an electrolyte membrane as an essential component to separate hydrogen and oxygen. This requires an expensive electrolyte membrane, which increases the cost of the water electrolysis device, and there are problems such as the crossover phenomenon where hydrogen and oxygen pass through the electrolyte membrane when operating at low loads or under pressurization.

[0006] To address these issues, ion exchange membranes that selectively conduct specific ions have been developed. These are utilized in electrodes or electrolyte membranes to block physical contact between the anode and cathode and facilitate the transfer of hydrogen ions (protons) from the anode to the cathode. Nafion is the most representative ion exchange membrane developed to date. As a sulfonate polyfluoride polymer, Nafion is widely used due to its excellent mechanical strength, chemical stability, and high ion conductivity. Conventional ion exchange membranes utilize a conduction mechanism that hydrates ions to conduct them; consequently, water movement is unavoidable, making complete suppression of crossover impossible.

[0007] [Prior Art Literature]

[0008] Patent Document 1. Republic of Korea Registered Patent Publication No. 10-1549525

[0009]

[0010] The technical problem that the present invention aims to solve is to provide a proton conductor having significantly improved performance compared to existing commercial proton conductors by minimizing crossover occurring between the cathode and the anode in the electrolyte membrane, and an electrochemical device including the same.

[0011]

[0012] To achieve the above objective, the present invention provides an electrolyte membrane for an electrochemical device comprising a proton conductor made of a hydrogen storage alloy.

[0013] The above hydrogen storage alloy may be any one selected from the group consisting of palladium (Pd)-based, magnesium (Mg)-based, lanthanum (La)-based, titanium (Ti)-based, calcium (Ca)-based, and vanadium (V)-based storage alloys.

[0014] The above hydrogen storage alloy may be composed of a palladium (Pd) system.

[0015] The above proton conductor is pre-charged with hydrogen internally through electrochemical pretreatment, and hydrides (Pd x H y )(x, y are positive real numbers greater than 0) may include an image.

[0016] The above electrochemical pretreatment may be performed for 5 minutes to 120 minutes under constant current conditions of -10 mA to -500 mA.

[0017] The above electrochemical device may be one or more selected from the group consisting of a fuel cell, a water electrolyzer, a redox flow battery, a CO2 electrolyzer, and a lithium-mediated chemical synthesis device.

[0018] To achieve the above other objectives, the present invention provides an electrochemical device manufactured using the electrolyte membrane.

[0019] The above electrochemical device may be a water electrolysis device or a fuel cell comprising a cathode section, an anode section, and an electrolyte membrane located between the cathode section and the anode section.

[0020] The thickness of the above electrolyte membrane may be 0.01 to 1 mm.

[0021]

[0022] The electrolyte membrane comprising the proton conductor of the present invention has a proton conduction mechanism completely different from that of conventional ion exchange membranes. By introducing a hydrogen storage alloy, it conducts protons without hydration, thereby completely blocking crossover. Furthermore, due to its excellent mechanical strength, it can replace conventional Nafion electrolyte membranes. Additionally, applying such an electrolyte membrane to a proton exchange membrane for fuel cells can consequently improve the electrochemical stability of the electrochemical device.

[0023]

[0024] FIG. 1 schematically illustrates the structure of an electrochemical device made of an electrolyte membrane containing a proton conductor according to the present invention.

[0025] Figure 2 schematically illustrates the structure of a water electrolysis device including a palladium metal film as an electrolyte film according to Experimental Example 1.

[0026] Figure 3 shows the results of an analysis using chronopotentiometry in a water electrolysis device containing an electrolyte membrane of different materials.

[0027] Figures 4 and 5 show the electrolyte collected after reacting at 10 mA for 30 minutes in a hybrid electrolyte system.

[0028] FIG. 6 is a schematic diagram showing the structure of an H-type cell configured for electrochemical characteristic analysis and hydrazine oxidation reaction experiments according to an experimental example of the present invention.

[0029] Figure 7 is a graph of potential change analyzed by chronopotentiometry in an H-type cell in which various metal membranes (Pd, H-charged Pd, Pt, Ni, Nafion 211) and a control (Wo membrane) were applied as electrolyte membranes.

[0030] Figure 8 is a graph of potential change analyzed by chronopotentiometry in an H-type cell in which a zirconium metal film (Zr foil) is applied as an electrolyte film as a comparative example to the present invention.

[0031] FIG. 9 is a schematic diagram showing the electrode arrangement and structure of an H-type cell configured to pre-adsorb hydrogen into a palladium (Pd) metal film during a hydrazine oxidation reaction experiment according to Experimental Example 4 of the present invention.

[0032] FIG. 10 is a schematic diagram showing the structure of a three-electrode system reconfigured to desorb residual hydrogen within a palladium (Pd) metal film after the reaction during a hydrazine oxidation experiment according to Experimental Example 4 of the present invention.

[0033] FIG. 11 shows that in Experimental Example 4 of the present invention, the penetration of large molecular size hydrazine (N2H4) is physically blocked and protons (H + This is a conceptual diagram schematically illustrating the principle of selectively transmitting only )

[0034] Figure 12 shows the results of analyzing the oxidation selectivity of hydrazine when a platinum (Pt) metal film is used as an electrolyte film.

[0035] Figure 13 shows the results of analyzing the oxidation selectivity of hydrazine when a nickel (Ni) metal film is used as an electrolyte film.

[0036] Figure 14 shows the results of analyzing the hydrazine oxidation selectivity when a hydrogen-charged palladium (H-charged Pd) metal film according to the present invention is used as an electrolyte film.

[0037] Figure 15 shows the results of oxidation selectivity measurements when a hydrazine oxidation experiment was performed on a palladium (Pd) metal film without charging hydrogen (Charging X).

[0038] Figure 16 shows the results of oxidation selectivity measurements when a hydrazine oxidation experiment was performed after charging hydrogen into a palladium (Pd) metal film for 1 minute.

[0039] Figure 17 shows the results of oxidation selectivity measurements when a hydrazine oxidation experiment was performed after charging a palladium (Pd) metal film with hydrogen for 5 minutes.

[0040] Figure 18 shows the results of oxidation selectivity measurements when a hydrazine oxidation experiment was performed after charging a palladium (Pd) metal film with hydrogen for 10 minutes.

[0041] Figure 19 shows the results of oxidation selectivity measurements when a hydrazine oxidation experiment was performed after charging a palladium (Pd) metal film with hydrogen for 60 minutes.

[0042]

[0043] Below, various aspects and embodiments of the present invention will be examined in more detail.

[0044]

[0045] The objects, other objects, features, and advantages of the present invention will be easily understood through the following preferred embodiments associated with the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided to ensure that the disclosed content is thorough and complete and that the spirit of the invention is sufficiently conveyed to a person skilled in the art.

[0046] In this specification, terms such as “comprising” or “having” are intended to specify the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should not be understood as precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0047] In this specification, where a range is described for a variable, it will be understood that the variable includes all values ​​within the described range, including the described endpoints of the range. For example, the range “5 to 10” will be understood to include not only the values ​​5, 6, 7, 8, 9, and 10, but also any sub-ranges such as 6 to 10, 7 to 10, 6 to 9, 7 to 9, etc., and any values ​​between integers valid for the category of the described range, such as 5.5, 6.5, 7.5, 5.5 to 8.5, and 6.5 to 9. Also, for example, the range “10% to 30%” will be understood to include all integers including values ​​such as 10%, 11%, 12%, 13%, etc. and up to 30%, as well as any sub-range such as 10% to 15%, 12% to 18%, 20% to 30%, etc., and any value between valid integers within the stated range category such as 10.5%, 15.5%, 25.5%, etc.

[0048]

[0049] The present invention will be described in detail below.

[0050] One aspect of the present invention relates to an electrolyte membrane for an electrochemical device comprising a proton conductor made of a hydrogen storage alloy.

[0051] In the present invention, the hydrogen storage alloy is an alloy having the property that allows hydrogen atoms to exist and move within the membrane crystal. Specifically, under an electric field, the hydrogen storage alloy conducts protons by splitting hydrogen near the cathode into electrons and protons, whereby the protons are conducted toward the electrolyte and the electrons travel along the electron cloud inside the membrane toward the anode, reducing the protons in the anode to form hydrogen atoms that are drawn into the membrane, thereby offsetting the consumption of hydrogen generated at the cathode.

[0052] In the present invention, the hydrogen storage alloy may be any one selected from the group consisting of, for example, palladium (Pd)-based, magnesium (Mg)-based, lanthanum (La)-based, titanium (Ti)-based, calcium (Ca)-based, and vanadium (V)-based storage alloys, and the hydrogen storage alloy is preferably an alloy composed of palladium (Pd)-based alloys.

[0053] Palladium was first discovered in 1803 by the British chemist William H. Wollaston. It is calcinable and does not tarnish in air because it does not react with atmospheric oxygen. Palladium can absorb up to 900 times its own volume of hydrogen with a volume change of only 10%, so it has been used as a metal for hydrogen storage. When hydrogen approaches the surface of palladium, it is adsorbed onto the surface and then diffuses into the interior of the palladium to move freely; in the case of a thin film, hydrogen can pass through. Utilizing these properties, palladium has been used as a catalyst for producing high-purity hydrogen or purifying exhaust gases. In order to utilize palladium metal as an ion exchange membrane, the present invention involves placing it inside an electrolyte and inducing it to act as a bipolar electrode; consequently, reduction occurs on the surface of the palladium metal facing the oxidation electrode, while oxidation occurs on the surface of the palladium metal facing the reduction electrode.

[0054] In other words, reduction occurs on the palladium metal surface facing the oxidation electrode, leading to the adsorption of hydrogen by protons (H + + e - -> Pd x H y ) occurs, and oxidation takes place on the palladium metal surface facing the reduction electrode, causing proton emission (Pd x H y -> H + + e -Since ) occurs (Fig. 1), crossover can be fundamentally blocked by transferring protons without hydration through a palladium alloy or palladium metal. In this process, the potential difference across the palladium metal film is theoretically close to 0 V (when hydrogen is charged), which allows proton conduction rather than electron conduction to occur without hydration.

[0055] In addition, the electrolyte membrane for an electrochemical device comprising a proton conductor made of a hydrogen storage alloy according to the present invention can control the proton conduction efficiency by controlling the hydrogen content (H / Pd ratio) inside the membrane. In particular, in a state where hydrogen is sufficiently charged (H-charged), the oxidation reaction of impurities such as hydrazine can be suppressed and only the proton desorption reaction can be selectively activated, thereby enabling the membrane to operate as a high-efficiency and high-selectivity electrolyte membrane.

[0056] The proton conductor according to the present invention undergoes electrochemical pretreatment before use, thereby pre-charging hydrogen within the metal lattice into a hydride (Pd x H y It may include a phase (where x and y are positive real numbers greater than 0). The above hydride (Pd x H y x and y of ) can be defined as positive real numbers greater than zero, which implies that palladium (Pd) and hydrogen (H) do not combine in a fixed integer ratio, but rather, depending on the charging time and the intensity of the applied current, hydrogen atoms are incorporated at various concentrations into interstitial sites within the face-centered cubic (FCC) lattice of palladium or hydrides (Pd x H y It means forming an image.

[0057] These hydrides (Pd x H yThe formation of the phase can determine the proton conduction efficiency of the electrolyte membrane for the electrochemical device of the present invention. For example, in the metal state of a proton conductor, a high activation energy is required for protons introduced from the outside to diffuse into the lattice; therefore, if hydrogen atoms are pre-charged into the lattice through pretreatment (H-charged), the lattice constant expands slightly and an internal hydrogen network is formed. Consequently, a diffusion or hopping mechanism that moves rapidly between hydrogen atoms within the lattice is activated, enabling proton conduction with very low resistance without hydration. Furthermore, as confirmed in Experimental Example 4 described below, as the hydrogen content (y value) within the palladium metal film increases, competing reactions (side reactions) such as hydrazine oxidation are suppressed and proton desorption reactions occur predominantly; thus, hydride (Pd) x H y When the phase is sufficiently formed, the electrochemical reaction pathway at the electrolyte membrane interface switches from 'impurity oxidation' to 'proton transfer,' thereby enabling high proton conduction selectivity of over 99%.

[0058] Therefore, the 'electrochemical pretreatment' in the present invention is not a simple cleaning process, but a process that performs a phase transition of the proton conductor from a reactive metal state to a high-efficiency electrolyte state, which may be performed for 5 minutes to 120 minutes under constant current conditions of -10 mA to -500 mA. Specifically, it was confirmed that when the electrochemical pretreatment time was 1 minute, the effect of reducing hydrazine oxidation selectivity was negligible, but from the point of charging for 5 minutes or more, the oxidation selectivity dropped sharply to 10% or less, and excellent proton conductivity characteristics were exhibited. This indicates that an electrochemical charging time of 5 minutes or more is desirable to reach the threshold concentration required for the interior of the proton conductor lattice, which is made of a hydrogen storage alloy, to function as a proton conduction channel. On the other hand, while conductivity is maintained as the charging time increases, there is a risk of reduced mechanical durability due to lattice expansion if the charging is excessively prolonged beyond 120 minutes. Therefore, in order to simultaneously ensure process efficiency and mechanical stability of the electrolyte membrane, the pretreatment is preferably performed within a range of 5 to 120 minutes, and more preferably may be performed for 10 to 60 minutes.

[0059] The above electrolyte membrane may be any one selected from the group consisting of various energy conversion and storage devices or chemical synthesis devices, including fuel cells, water electrolytic devices, redox flow batteries, CO2 electrolytic cells, and lithium-mediated ammonia synthesis, although the electrochemical device is not particularly limited thereto, and preferably may be a water electrolytic device or a fuel cell.

[0060] In addition, a redox flow battery is a device that converts chemical energy stored in an electrolyte into electrical energy, and an ion exchange membrane separates the positive and negative electrolytes and selectively transmits specific ions. In the case of conventional ion exchange membranes (e.g., Nafion), a crossover problem occurs where active species present in the electrolyte pass through the membrane to the opposite electrolyte, causing a loss of battery capacity and a decrease in charge / discharge efficiency. When using the hydrogen storage alloy proton conductor according to the present invention, the physical movement of large molecular active species is fundamentally blocked through a dense lattice structure, and only protons can be selectively conducted through the diffusion mechanism of hydrogen atoms. This minimizes the crossover of active species present in redox flow batteries, thereby significantly improving the battery's lifespan and energy efficiency.

[0061] A carbon dioxide (CO2) electrolyzer is a device that uses electrical energy to convert CO2 into useful chemical fuels such as CO₂ or formic acid; it also uses an electrolyte membrane to separate the anode and cathode spaces and ions (e.g., H₂) + or OH - ...transmits .... In CO2 electrolytic cells, the crossover phenomenon in which liquid reactants or products cross the membrane is a major problem that impairs electrode activity and reduces overall efficiency. Therefore, when the proton conductor of the present invention is applied as an electrolyte membrane, it conducts protons without hydration and simultaneously has the characteristic of physically blocking the crossover of reactants or products, so it can be applied to a CO2 electrolytic cell to achieve the effect of producing high-purity products and maintaining high current density.

[0062] Lithium-mediated nitrogen fixation (or ammonia synthesis) is an eco-friendly process that electrochemically converts nitrogen (N2) into ammonia (NH3) at room temperature and pressure. In this process, hydrogen ions (protons) must be accurately delivered to the reaction zone to ensure high current efficiency and selectivity. The hydrogen-charged palladium-based electrolyte membrane according to the present invention can achieve high proton conduction selectivity of over 99%. This is because, as demonstrated in hydrazine oxidation experiments, it suppresses the oxidation reaction of impurities (competing reactants) and predominantly activates only the proton transfer reaction. This high selectivity has the effect of suppressing side reactions (e.g., hydrogen generation) in the lithium-mediated ammonia synthesis device and maximizing the efficiency of ammonia production.

[0063] In conclusion, the electrolyte membrane containing the proton conductor according to the present invention, based on the features of a hydration-free proton conduction mechanism and physical crossover blocking due to a dense structure, overcomes the limitations of existing polymer electrolyte membranes and can dramatically improve the performance and stability of various electrochemical devices, such as fuel cells, water electrolytic devices, as well as redox flow batteries, CO2 electrolyzers, and lithium-mediated ammonia synthesis.

[0064]

[0065] Another aspect of the present invention relates to an electrochemical device manufactured using the electrolyte membrane.

[0066] FIG. 1 schematically illustrates the structure of an electrochemical device made of an electrolyte membrane containing a proton conductor according to the present invention.

[0067] The above electrochemical device may be any one selected from the group consisting of a fuel cell, a water electrolytic device, a redox flow battery, a CO2 electrolyzer, and various energy conversion and storage devices or chemical synthesis devices including lithium-mediated ammonia synthesis, and preferably may be a water electrolytic device or a fuel cell.

[0068] The electrolytic cell of an electrochemical device includes a cathode, an anode, and an electrolyte membrane located between the cathode and the anode. In the water splitting electrolysis reaction, an oxygen evolution reaction (OER) occurs at one interface, and a hydrogen evolution reaction (HER) occurs at the other interface.

[0069] The electrolytic cell may include additional components / layers disposed between the electrodes of the cell. For example, the cell may include a porous transport layer (PTL) or a gas diffusion layer (GDL) located between the electrodes (e.g., cathode or anode) and the electrolyte membrane.

[0070] For example, if the electrochemical device described above is a fuel cell, an anode portion is positioned on one side of an electrolyte membrane containing a proton conductor, and a cathode portion is positioned on the opposite side. The anode portion is formed by sequentially arranging an anode catalyst layer and an anode gas diffusion layer on one surface of the electrolyte membrane, and hydrogen is supplied to the anode gas diffusion layer positioned at the outermost edge. Here, a first anode electrode plate may be positioned on top of the anode gas diffusion layer. The hydrogen supplied to the anode gas diffusion layer is decomposed into ions; at this time, hydrogen ions move to the cathode portion through the electrolyte membrane, while electrons move along the anode gas diffusion layer and then move to the cathode portion through a first cathode electrode plate electrically connected to the first anode electrode plate. At this time, the component electrically connecting the first anode electrode plate and the first cathode electrode plate may be a conductive component such as a wire, and a load may be connected to the conductive component.

[0071] At this time, hydrogen ions moving to the cathode react with oxygen supplied to the cathode gas diffusion layer, and the resulting water (H2O) and unreacted oxygen are discharged to the outside. Meanwhile, hydrogen that is not ionized in the anode is also discharged to the outside.

[0072] The above cathode portion is formed by sequentially arranging a cathode catalyst layer and a cathode gas diffusion layer on the other side of the proton exchange membrane, and oxygen or air is supplied to the cathode gas diffusion layer arranged at the outermost edge. Here, a first cathode electrode plate may be arranged on top of the cathode gas diffusion layer.

[0073] The thickness of the electrolyte membrane is preferably within the range of 0.01 to 1 mm. If it is thicker than this, the mobility of protons decreases and the overall electrochemical reaction rate slows down, which may reduce efficiency. In addition, if it is thinner than this, a problem may arise where the mechanical strength is reduced.

[0074] The description of the above electrolyte membrane has been specifically detailed and will be omitted. Due to the excellent properties resulting from the proton conduction mechanism of the above electrolyte membrane, water electrolysis devices and fuel cells comprising the above electrolyte membrane also retain excellent performance, such as improved water electrolysis efficiency, proton conductivity, and mechanical stability.

[0075]

[0076] The present invention is to be explained in more detail below through examples, etc.; however, the scope and content of the present invention shall not be interpreted as being narrowed or limited by the examples, etc. below. Furthermore, based on the disclosure of the present invention including the examples below, it is evident that a person skilled in the art can easily practice the present invention even without specific experimental results presented, and it is natural that such variations and modifications fall within the scope of the appended claims.

[0077]

[0078] Experimental Example 1: Water electrolysis device including a palladium metal film as an electrolyte film.

[0079] A water electrolysis device was fabricated using a palladium metal film (thickness: 0.025 mm) as the electrolyte membrane, a Ni wire as the cathode electrode, and a DSA (dimensionally stable anode) as the anode electrode. Phosphate buffer solutions of various concentrations (0.1, 0.5, 1 M) were supplied as the electrolyte, and the operating temperature was room temperature. To verify the performance of the single-cell water electrolysis device, it was analyzed using chronopotentiometry. Specifically, 0.5 mA / cm² 2 It was performed by the chronopotential measurement method and maintained a cell voltage of 2.06 V for 10 minutes (Fig. 2).

[0080] For comparison, systems were fabricated and measured using Nafion 117, platinum metal film (0.025 mm), gold film (Au 0.025 mm), nickel metal film (Ni 0.025 mm), copper metal film (Cu 0.025 mm), or zirconium metal film (Zr 0.025 mm) as the electrolyte membrane instead of palladium metal film. As a control group (none), a water electrolysis device without an electrolyte membrane was used. The potential change in each unit cell water electrolysis device was analyzed and is shown in Figure 3.

[0081]

[0082] Figure 3 shows the results of an analysis using chronopotentiometry on a water electrolysis device containing an electrolyte membrane of different materials. According to this, it can be seen that a single-cell water electrolysis device containing an electrolyte membrane with a palladium metal membrane as a proton conductor maintains a potential similar to that of the control group (none).

[0083] That is, the water electrolysis device according to the present invention uses a palladium metal film as an electrolyte film, thereby allowing the reaction to proceed through proton adsorption and desorption, maintaining the potential applied to the palladium surface at nearly 0 V and suppressing unnecessary potential loss. In other words, hydrogen within the palladium moves in atomic form and is transferred to the reduction electrode through the adsorption-desorption process while minimizing reactions such as H2O oxidation or hydrogen generation, thus effectively transferring protons without hydration.

[0084] On the other hand, when an electrolyte membrane composed of other metals is used, it cannot support the same proton transfer mechanism as the palladium metal membrane, so hydrogen evolution occurs on the surface facing the anode and H2O oxidation occurs on the surface facing the cathode, so it can be seen that an additional potential of more than 1.23 V is lost.

[0085] In the case of the platinum metal film, although it exhibits a low potential, it was confirmed that, like other metal films, it generates a hydrogen evolution reaction on the surface facing the oxidation electrode and an H2O oxidation reaction on the surface facing the reduction electrode. It was confirmed that the low potential is due solely to the superior oxidation / reduction capabilities of the platinum metal film.

[0086]

[0087] Experimental Example 2: Hybrid electrolyte device including a palladium metal film as an electrolyte film.

[0088] A hybrid electrolyte device was constructed using an organic solvent electrolyte prepared by dissolving 2 M LiTFSI (Lithium bis(trifluoromethanesulfonyl)imide) in THF (Tetrahydrofuran) at a concentration of 2 M as the catholyte and 0.1 M phosphate buffer as the anolyte. Ni wire and DSA were used as the cathode and anode electrodes, respectively. A palladium metal film was used as the electrolyte membrane, and after reacting at 10 mA for 30 minutes at room temperature, the electrolyte was collected and is shown in Fig. 4. When a platinum metal film or a nickel metal film was used as the electrolyte membrane instead of the palladium metal film, the electrolyte was collected and is shown in Fig. 5.

[0089] Figures 4 and 5 show the electrolyte collected after reacting at 10 mA for 30 minutes in a hybrid electrolyte system. According to these figures, it was confirmed that the hybrid system using a palladium metal film as the electrolyte film remained transparent because proton conduction occurred normally, preventing the problem of electrolyte oxidation on the non-aqueous electrolyte side.

[0090] On the other hand, when platinum or nickel metal films are used as electrolyte membranes, it can be observed that an oxidation reaction occurs on the surface facing the reduction electrode, causing the electrolyte color to change to brown. Therefore, only hydrogen storage alloys such as palladium metal films are capable of excellent proton conductivity.

[0091]

[0092] Experimental Example 3: Analysis of Electrochemical Characteristics of a Water Electrolyzer Containing Various Metal Films as Electrolyte Membranes

[0093] 1) Experimental Preparation and Pretreatment

[0094] To evaluate electrochemical characteristics, an H-type cell with fixed electrode positions was fabricated as shown in Fig. 6. Specifically, both the working electrode (WE) and the counter electrode (CE) used platinum (Pt) electrodes.

[0095] A palladium metal foil (Pd foil) with a thickness of 0.1 mm was used as the electrolyte membrane. For comparison, Nafion 211, platinum metal foil (Pt, 0.1 mm), nickel metal foil (Ni, 0.1 mm), and zirconium metal foil (Zr, 0.1 mm) were each installed as electrolyte membranes, and experiments were conducted under the same conditions. In addition, an H-type cell without an electrolyte membrane was used as a control group.

[0096] In order to verify the difference in conductivity depending on whether hydrogen is adsorbed, palladium (Pd) was prepared in two states: one without hydrogen charge (Pd) and the other electrochemically charged with hydrogen (H-Charged Pd). The hydrogen-charged palladium metal film was prepared by using a 0.1 M aqueous perchloric acid solution (HClO4) as the electrolyte, a DSA electrode as the counter electrode, and a Pd foil as the working electrode, and performing chronopotentiometry (CP) for 1 hour under a constant current of -100 mA.

[0097] All metal films were reinforced in thickness by attaching beryllium (Be) tape to an outer section of about 3 mm to prevent electrolyte leakage, and a gasket was used to ensure adhesion.

[0098]

[0099] 2) Measurement and analysis of electrochemical properties

[0100] 1 M phosphate buffer was supplied as the electrolyte, and chronopotentiometry (CP) was performed for 10 minutes at room temperature under a constant current of 0.5 mA to measure the potential change of each electrolyte membrane. The measurement results are shown in Figures 7 and 8.

[0101]

[0102] Figure 7 is a graph of potential change analyzed by chronopotentiometry in an H-type cell in which various metal membranes (Pd, H-charged Pd, Pt, Ni, Nafion 211) and a control (Wo membrane) were applied as electrolyte membranes.

[0103] As shown in Figure 7, the magnitude of the cell voltage according to the type of electrolyte membrane was confirmed to be in the order of control group (Wo membrane) = Nafion < H-charged Pd < Pd < Pt < Ni. Specifically, the lowest cell voltage of approximately 2.2 V was observed when using the control group without a membrane (Wo membrane) and the commercial ion exchange membrane Nafion (Nafion 211).

[0104] Among the metal films, hydrogen-charged palladium (H-charged Pd) exhibited the lowest potential, followed by ordinary palladium (Pd). In contrast, other metal films, such as platinum (Pt), nickel (Ni), and zirconium (Zr), were found to have very high potentials (overpotential).

[0105] Conventional metal films (Pt, Ni, Zr) generate high potentials because ion transport is physically blocked due to their dense lattice structure; however, the palladium (Pd)-based electrolyte membrane according to the present invention was confirmed to exhibit low resistance despite being a metal film, as it possesses a unique proton conduction mechanism in which hydrogen atoms diffuse into the metal lattice. In particular, the result showing that H-charged Pd, which is pre-charged with hydrogen, exhibited a lower potential than ordinary Pd indicates that conductivity improves as the hydrogen concentration within the palladium increases, thereby activating the proton conduction channels. Therefore, it can be seen that the palladium metal film according to the present invention can selectively conduct protons with high efficiency even without hydration.

[0106]

[0107] Figure 8 is a graph of potential change analyzed by chronopotentiometry in an H-type cell in which a zirconium metal film (Zr foil) is applied as an electrolyte film as a comparative example to the present invention.

[0108] As shown in Figure 8, when a zirconium (Zr) metal film was used as an electrolyte membrane, the results were confirmed. Unlike palladium, zirconium is a material that not only cannot adsorb or diffuse hydrogen atoms but also has almost no catalytic activity on the electrode surface. Consequently, the Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER), which are essential for bipolar electrode behavior, do not occur at the membrane interface. This causes the resistance within the system to increase rapidly, resulting in a very high overpotential and effectively blocking current flow. This clearly confirms that ordinary metal films, other than hydrogen storage alloys (Pd), cannot function as proton conductors.

[0109]

[0110] Experimental Example 4: Verification of Selective Permeability through Hydrazine Oxidation Experiment

[0111] (1) Experiment preparation and cell manufacturing

[0112] To evaluate the hydrogen transfer selectivity of the palladium (Pd) metal film according to the present invention, a hydrazine (N2H4) oxidation experiment was performed. Due to its molecular size, hydrazine has difficulty physically passing through the dense lattice structure of the metal. Therefore, this allows for clear verification of whether the electrolyte film selectively transmits only hydrogen ions (protons) or whether the reactant hydrazine is also transmitted (crossover) (Fig. 11).

[0113] The experiment was conducted using an H-type cell in which the anolyte and catholyte were separated. A metal foil with a thickness of 0.1 mm was used as the electrolyte membrane. For the palladium (Pd) metal foil, the behavior of hydrogen was precisely analyzed by performing all three stages of the process: ① absorption, ② reaction, and ③ desorption, while for the control group, only the reaction stage was performed to compare the differences.

[0114] ① Hydrogen Absorption

[0115] The hydrogen adsorption step is a pretreatment process applied only to cells using a Pd metal membrane. To this end, an H-type cell with fixed electrode positions was fabricated as shown in Fig. 9. Specifically, a Pd metal membrane (pd foil + Cu tape) electrically connected via copper tape was used as the working electrode (WE), and a DSA (Dimensionally Stable Anode) electrode was used as the counter electrode (CE). The counter electrode was immersed in 6 mL of 0.1 M phosphate buffer solution as the anolyte, and the working electrode was immersed in 6 mL of a solution prepared by dissolving 50 mM hydrazine (N2H4) in 0.015 M KOH solution as the catholyte. Subsequently, hydrogen was induced to be adsorbed into the Pd metal membrane through the reduction of hydrogen ions by applying a current of -100 mA using chronopotentiometry (CP). At this time, in order to determine the effect of hydrogen charge on proton conduction characteristics, Pd metal films with various hydrogen charge states were prepared by varying the current application time to 0 minutes (uncharged), 1 minute, 5 minutes, 10 minutes, and 60 minutes, respectively.

[0116] ② Reaction

[0117] After the adsorption step is completed, the next step is to evaluate the hydrogen transfer characteristics through the membrane. As shown in Fig. 6, an H-type cell was constructed, but the working electrode (WE) was replaced from a Pd metal film to a platinum wire (Pt wire) and positioned within the cathode electrolyte. For comparative experiments, hydrogen-charged (H-charged Pd foil, 0.1 mm), platinum metal film (Pt foil, 0.1 mm), and nickel metal film (Ni foil, 0.1 mm) were each attached as electrolyte membranes, and experiments were conducted under identical conditions. At this time, argon (Ar) gas was injected to continuously bubble the hydrogen bubbles generated on the electrode surface, and the solution was stirred at 500 rpm to maintain a uniform reaction environment. The reaction was carried out by applying a constant current (CP) of -10 mA for 1 hour.

[0118] ③ Hydrogen Desorption

[0119] This is a step to verify the amount of hydrogen remaining inside the Pd metal film after the reaction is completed. After recovering the entire amount of the reaction-completed cathode electrolyte, the cell was reconfigured into a three-electrode system as shown in Fig. 10. Specifically, both the anode and cathode electrolytes were replaced with a new 0.1 M phosphate buffer solution (5.5 mL), and the working electrode (WE) was replaced from a platinum wire (Pt wire) back to the Pd metal film (Cu tape connected) from Step 2 and positioned within the cathode electrolyte. Additionally, a Pt wire was used as the counter electrode (CE), an Ag / AgCl electrode as the reference electrode (RE), and 1.5 mL of the same electrolyte was injected into the small cell section between the Pd metal film and the separator (Nafion 211). While maintaining argon (Ar) bubbling on the counter electrode (CE), a chronoamperometry (CA) voltage of 1 V (vs. Ag / AgCl) was applied to electrochemically force the desorption of hydrogen remaining inside the Pd metal film. To ensure the reproducibility of the experiment, after completing all experiments, residual moisture on the surface of the metal films used was removed by drying them in an 80°C oven for 1 hour, and then reused.

[0120]

[0121] 2) Analysis Method

[0122] Immediately after each step, the change in hydrazine concentration in the cathode electrolyte was measured. Quantitative analysis of hydrazine was performed using ion chromatography (IC). 0.1 M sulfuric acid (H2SO4) was used as the mobile phase (eluent), and the concentration in the sample was precisely calculated using calibration curves prepared with hydrazine standard solutions at concentrations of 0.5 mM, 2 mM, 4 mM, and 8 mM.

[0123]

[0124] 3) Result

[0125] Figure 12 shows the results of analyzing hydrazine oxidation selectivity when a platinum (Pt) metal film is used as an electrolyte film. Figure 13 shows the results of analyzing hydrazine oxidation selectivity when a nickel (Ni) metal film is used as an electrolyte film. Figure 14 shows the results of analyzing hydrazine oxidation selectivity when a hydrogen-charged palladium (H-charged Pd) metal film according to the present invention is used as an electrolyte film. '1, 2, 3' on the X-axis of Figures 12–14 represent the number of repetitions (Trial 1, 2, 3) to verify the reproducibility of the experiment (n=3).

[0126] As shown in FIGS. 12 to 14, when the hydrazine crossover was quantitatively verified according to the type of metal film, it was confirmed that when the control group platinum (Pt) metal film (Fig. 12) and nickel (Ni) metal film (Fig. 13) were used as electrolyte films, the hydrazine oxidation selectivity (N2H4 oxidation selectivity (%)) approached nearly 100% in all three repeated experiments. This indicates that nearly 100% of the total charge (36 C) applied during the experiment was consumed in oxidizing (decomposing) hydrazine. In other words, in the platinum and nickel films, hydrazine was consumed through active oxidation reactions on the film surface, and as a result, the hydrazine concentration in the cathode electrolyte decreased rapidly.

[0127] On the other hand, when a hydrogen-charged palladium (H-charged Pd) metal film (Fig. 14) was used according to the present invention, the hydrazine oxidation selectivity was found to be very low, ranging from 1.3% to 18%. This indicates that the applied current was hardly used to oxidize hydrazine. In other words, most of the current was used for the desorption reaction in which protons pass through the palladium lattice and are ejected, rather than for the hydrazine decomposition reaction.

[0128] Therefore, the hydrogen-charged palladium electrolyte membrane effectively suppresses the oxidation or crossover of reactants such as hydrazine, while protons (H + It was confirmed that it has excellent performance in selectively conducting only ).

[0129]

[0130] Figure 15 shows the results of oxidation selectivity measurements when a hydrazine oxidation experiment was performed on a palladium (Pd) metal film without charging hydrogen (Charging X). Figure 16 shows the results of oxidation selectivity measurements when a hydrazine oxidation experiment was performed after charging hydrogen on a palladium (Pd) metal film for 1 minute. Figure 17 shows the results of oxidation selectivity measurements when a hydrazine oxidation experiment was performed after charging hydrogen on a palladium (Pd) metal film for 5 minutes. Figure 18 shows the results of oxidation selectivity measurements when a hydrazine oxidation experiment was performed after charging hydrogen on a palladium (Pd) metal film for 10 minutes. Figure 19 shows the results of oxidation selectivity measurements when a hydrazine oxidation experiment was performed after charging hydrogen on a palladium (Pd) metal film for 60 minutes.

[0131] As shown in Fig. 15, in the case of a Pd metal film (0 min) that was not pre-charged with hydrogen, the hydrazine oxidation selectivity was relatively high at 39% to 51%, and it was confirmed that the proton conduction efficiency was low (still lower than that of Pt and Ni).

[0132] On the other hand, as shown in FIGS. 16 to 19, it was clearly observed that the hydrazine oxidation selectivity gradually decreased as the hydrogen charging time increased to 1 minute, 5 minutes, 10 minutes, and 60 minutes. When hydrogen was charged for 5 minutes or more (Figs. 17–19), the hydrazine oxidation selectivity decreased significantly to an average of 19–20%, and when hydrogen was charged for 10 minutes or more, the hydrazine oxidation selectivity was less than an average of 10%, resulting in the suppression of the hydrazine oxidation reaction and the use of most of the applied current for the proton desorption reaction. This indicates that the proton desorption reaction occurs smoothly only when hydrogen pre-charged inside the palladium is present, and consequently, the proton conductivity is improved.

[0133] It was confirmed that when the palladium metal film according to the present invention contains hydrogen through its hydrogen storage capability, the proton desorption reaction is converted into the dominant reaction, thereby enabling efficient conduction.

[0134] Synthesizing the experimental results above, when a proton conductor made of the hydrogen storage alloy according to the present invention is used as an electrolyte membrane, protons can be effectively conducted through intra-lattice diffusion without a hydration process due to the hydrogen storage capacity. Furthermore, since the physical movement of reactants such as hydrazine is fundamentally blocked by the dense structure, not only is the crossover problem eliminated, but high-efficiency proton conduction is also possible while fundamentally blocking crossover by maintaining a hydrogen-charged state even at room temperature.

[0135] Therefore, the present invention can dramatically improve the performance and stability of fuel cells and water electrolysis devices by providing a new electrolyte membrane for electrochemical devices that can solve the crossover and durability problems, which are limitations of existing polymer electrolyte membranes.

Claims

1. Electrolyte membrane for an electrochemical device comprising a proton conductor made of a hydrogen storage alloy.

2. In Paragraph 1, Electrolyte membrane for an electrochemical device, characterized in that the above hydrogen storage alloy is selected from the group consisting of palladium (Pd)-based, magnesium (Mg)-based, lanthanum (La)-based, titanium (Ti)-based, calcium (Ca)-based, and vanadium (V)-based storage alloys.

3. In Paragraph 1, The above-mentioned hydrogen storage alloy is an electrolyte membrane for an electrochemical device characterized by being composed of a palladium (Pd) system.

4. In Paragraph 1, The above proton conductor is pre-charged with hydrogen internally through electrochemical pretreatment, and hydrides (Pd x H y Electrolyte membrane for an electrochemical device characterized by including a phase (x, y are positive real numbers greater than 0).

5. In Paragraph 4, Electrolyte membrane for an electrochemical device, characterized in that the above electrochemical pretreatment is performed for 5 minutes to 120 minutes under constant current conditions of -10 mA to -500 mA.

6. In Paragraph 1, The above electrochemical device is characterized by being one or more selected from the group consisting of a fuel cell, a water electrolytic device, a redox flow battery, a CO2 electrolyzer, and a lithium-mediated chemical synthesis device, and is an electrolyte membrane for an electrochemical device.

7. An electrochemical device manufactured using an electrolyte membrane according to paragraph 1.

8. In Paragraph 7, The electrochemical device is characterized in that the above electrochemical device is an electrolytic cell of a water electrolysis device comprising a cathode section, an anode section, and an electrolyte membrane located between the cathode section and the anode section.

9. In Paragraph 7, An electrochemical device characterized by the thickness of the electrolyte membrane being 0.01 to 1 mm.

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