KR20220147326A - Polymer electrolyte membrane for fuel cell, method for manufacturing the same, and fuel cell comprising the same - Google Patents

Abstract

The present invention relates to a polymer electrolyte membrane for a fuel cell including micro-holes manufactured by a plasma etching process, a method for manufacturing the same, and a fuel cell including the same. A polymer electrolyte membrane for a fuel cell according to various embodiments of the present invention includes a plurality of micro holes having a depth of 2 μm to 12 μm. A method for manufacturing a polymer electrolyte membrane for a fuel cell according to various embodiments of the present invention comprises the steps of: preparing a polymer stencil including micro holes; and performing plasma etching after contacting the polymer stencil with the polymer electrolyte membrane. A fuel cell according to various embodiments of the present invention includes the polymer electrolyte membrane described above.

Description

Polymer electrolyte membrane for fuel cell, manufacturing method thereof, and fuel cell including same

The present invention relates to a polymer electrolyte membrane for a fuel cell including microholes manufactured by a plasma etching process, a manufacturing method thereof, and a fuel cell including the same.

A polymer electrolyte membrane fuel cell is an energy conversion device that converts chemical energy into electrical energy, and is a clean energy conversion device that does not emit harmful substances at all.

A membrane electrode assembly, one of the components of a polymer electrolyte membrane fuel cell, is composed of an anode, a cathode, and a polymer membrane acting as an electrolyte in which a platinum catalyst supported on carbon is composed of a porous layer.

Recently, studies are underway to improve performance by improving hydrogen ion conductivity and reducing ohmic resistance by making a thin polymer electrolyte membrane.

However, the conventional entirely thin membrane has a disadvantage in that it has weak mechanical stability, including a phenomenon in which the membrane is easily wrinkled or torn compared to a commercially available electrolyte membrane.

Therefore, it is important to locally thin the electrolyte membrane using a multi-scale structure to improve performance and maintain mechanical stability.

To this end, micro/nano structures are patterned at the interface between the electrode layer and the polymer electrolyte membrane through processes such as Nafion ionomer casting and thermal imprinting to increase the electrochemically active surface area, improve catalyst utilization, and improve device performance through improved mass transfer. Studies have been going on. However, the Nafion inomer casting method has difficulties in manufacturing such as thickness non-uniformity due to the coffee ring effect during solvent evaporation, and the most commonly used thermal imprint method can cause damage to the electrolyte membrane in high-temperature/high-pressure processes. have limitations

In the case of the non-contact plasma etching process, it is easy to manufacture a large area and has the advantage of being able to control the etching degree and the etching depth by freely adjusting process variables such as plasma power, time, and gas flow rate. Most of the studies applied to the process have focused on increasing the nano-scale roughness, and an approach to improve the overall performance by introducing micro-scale structures to reduce catalyst utilization, membrane resistance, and mass transfer resistance has not yet been performed.

An object of the present invention is to provide a high-quality polymer electrolyte membrane for a fuel cell that can solve the above-mentioned problems and has excellent mechanical rigidity and performance, a method for manufacturing the same, and a fuel cell including the same.

The polymer electrolyte membrane for a fuel cell according to various embodiments of the present invention includes a plurality of microholes having a depth of 2 μm to 12 μm.

In the polymer electrolyte membrane for a fuel cell according to various embodiments of the present invention, the diameter of the micro-holes is 30 μm to 50 μm.

In the polymer electrolyte membrane for a fuel cell according to various embodiments of the present invention, an interval between the plurality of microholes is 30 μm to 50 μm.

In the polymer electrolyte membrane for a fuel cell according to various embodiments of the present invention, the polymer electrolyte membrane includes a bottom surface; and a micro hole disposed on the bottom surface.

A method for manufacturing a polymer electrolyte membrane for a fuel cell according to various embodiments of the present invention includes: preparing a polymer stencil including microholes; and plasma etching the polymer stencil after contacting the polymer electrolyte membrane.

In the method for manufacturing a polymer electrolyte membrane for a fuel cell according to various embodiments of the present invention, in the step of preparing the polymer stencil, the resin is placed between the first polymer mold including the micro-pillar pattern and the flat second polymer mold, and then UV characterized by investigation.

In the method for manufacturing a polymer electrolyte membrane for a fuel cell according to various embodiments of the present invention, the first polymer mold and the second polymer mold include polydimethylsiloxane (PDMS).

In the method for manufacturing a polymer electrolyte membrane for a fuel cell according to various embodiments of the present invention, the resin is characterized in that it contains PUA (Polyurethane acrylate).

In the method of manufacturing a polymer electrolyte membrane for a fuel cell according to various embodiments of the present invention, in the plasma etching step, air in the chamber is flowed at a flow rate of 10 sccm to 100 sccm, and 1.0 x 10 ^-1 torr to 1.0 x 10 ^-3 Maintaining a pressure of torr, characterized in that the plasma treatment for 10 minutes to 180 minutes at 50 W to 100 W.

In the method for manufacturing a polymer electrolyte membrane for a fuel cell according to various embodiments of the present invention, the diameter of the micro-holes is 30 μm to 50 μm.

A fuel cell according to various embodiments of the present invention includes the polymer electrolyte membrane described above.

The fuel cell according to various embodiments of the present invention further includes a catalyst layer disposed on the polymer electrolyte membrane, wherein the catalyst layer includes platinum supported by carbon.

The fuel cell polymer electrolyte membrane according to various embodiments of the present invention has micro-holes through a plasma etching process, and the membrane electrode assembly manufactured using the manufactured membrane maintains mechanical rigidity without significantly lowering the ohmic effect due to the thinning effect of the electrolyte membrane. A reduction in resistance and improvement in hydrogen ion conductivity can be expected. In addition, it is possible to secure higher performance than the conventional membrane electrode assembly by increasing the interfacial contact area between the polymer electrolyte membrane and the catalyst layer and improving mass transfer through patterning.

The method for manufacturing a fuel cell polymer electrolyte membrane according to various embodiments of the present invention is easy to fabricate a large area through a continuous process, and the degree of etching and the depth of etching can be controlled by freely adjusting process variables such as plasma power, time, and gas flow rate. can In addition, the process utilization and commercialization competitiveness in the renewable energy power industry are high.

A fuel cell composed of a membrane electrode assembly including a polymer electrolyte membrane manufactured through the present invention can have improved performance in various environments of high humidity and low humidity.

1 is a schematic diagram of a membrane electrode assembly including a fuel cell polymer electrolyte membrane according to various embodiments of the present invention.
FIG. 2 is a cross-sectional view taken along line I-I' in FIG. 1 .
3 is a schematic diagram for explaining the step of preparing a polymer stencil.
4 is a schematic diagram for explaining a method of manufacturing a membrane electrode assembly including a fuel cell polymer electrolyte membrane according to various embodiments of the present invention.
5 is an SEM image of the polymer electrolyte membrane according to the exposure time of the plasma etching process.
6 is a tensile test result of polymer electrolyte membranes of Examples and Comparative Examples.
7 is an SEM image of a membrane electrode assembly including a polymer electrolyte membrane according to various embodiments.
8 is a polarization (70° C., RH 100%) curve of a membrane electrode assembly according to various embodiments.
9 is a polarization (50 ℃, RH 35%) curve of the membrane electrode assembly according to various embodiments.
10 is an electrochemical impedance spectroscopy result of a membrane electrode assembly according to various embodiments.
11 is a CV curve and a linear sweep voltammograms (LSV) curve of a membrane electrode assembly according to various embodiments.

This study was supported by the 2019 basic research and development project grant from Korea Electric Power Corporation (Project No.: R19XO01-29)

The present invention relates to a polymer electrolyte membrane for a fuel cell including microholes manufactured by a plasma etching process, a manufacturing method thereof, and a fuel cell including the same.

1 and 2 , the polymer electrolyte membrane 100 for a fuel cell according to various embodiments of the present invention may include a plurality of microholes (H) having a depth (D) of 2 μm to 12 μm. . Preferably, the polymer electrolyte membrane 100 may include a plurality of micro holes (H) having a depth (D) of 2 μm to 10 μm. Through this specific depth, the mass transfer resistance of the membrane electrode assembly 10 can be reduced, and the performance of the fuel cell can be improved through improved mass transfer.

In this case, the diameter of the micro-holes H may be 30 μm to 50 μm. In addition, an interval between the plurality of micro-holes H may be 30 μm to 50 μm.

The height of the surface roughness of the micro-holes H may be 0.3 μm to 1.1 μm. In addition, the surface roughness (Rrms) of the micro-holes (H) may be 100 nm to 500 nm. Through such roughness, the interfacial contact area between the polymer electrolyte membrane 100 and the catalyst layer 120 is widened, so that the performance of the fuel cell can be improved.

The polymer electrolyte membrane 100 may include a bottom surface 110 and micro-holes H disposed on the bottom surface 110 . That is, the polymer electrolyte membrane 100 may be formed to have different thicknesses. A portion of the polymer electrolyte membrane 100 in which the micro-holes H is disposed may have a relatively thin thickness, and a portion in which the micro-holes H are not disposed may have a relatively thick thickness. That is, the mechanical stability of the polymer electrolyte membrane 100 can be maintained through a relatively thick portion, and an ohmic resistance reduction effect and improved hydrogen ion conductivity can be achieved through a portion having a relatively thin thickness in which the microholes H are disposed. can be expected

In the polymer electrolyte membrane 100 of the present invention, the interfacial contact area with the catalyst layer 120 formed thereon through the micro-holes H can be widened, and the electrochemical reaction can be effectively carried out by reducing ohmic resistance and improving mass transfer. can occur

The fuel cell of the present invention may include the polymer electrolyte membrane 100 described above. That is, the fuel cell of the present invention may include the membrane electrode assembly 10 including the polymer electrolyte membrane 100 described above. The fuel cell composed of the membrane electrode assembly 10 including the polymer electrolyte membrane 100 of the present invention is effective in improving performance in various environments with high humidity and low humidity.

A method for manufacturing a polymer electrolyte membrane for a fuel cell according to various embodiments of the present invention includes: preparing a polymer stencil including microholes; and plasma etching the polymer stencil after contacting the polymer electrolyte membrane.

Referring to FIG. 3 , in the step of preparing the polymer stencil including micro-holes, the resin 250 is placed between the first polymer mold 210 including the micro-pillar pattern P and the flat second polymer mold 230 . After positioning, UV irradiation can be performed. In this case, the first polymer mold 210 and the second polymer mold 230 may be polydimethylsiloxane (PDMS). In addition, the resin 250 may be PUA (Polyurethane acrylate). The resin 250 may be composed of a photoinitiator, a prepolymer having an acrylate functional group, and a release agent.

After placing the resin 250 on the first polymer mold 210 including the micro-pillar pattern P, it is covered with the second polymer mold 230 and irradiated with UV light of 20 W cm ^-2 intensity. have. Thereafter, the cured PUA polymer stencil 270 may be separated from the mold and prepared. The polymer stencil 270 may include micro holes H1 by a micro pillar pattern P. The diameter of the micro hole H1 may be 30 μm to 50 μm. In addition, an interval between the plurality of micro-holes H1 may be 30 μm to 50 μm.

Next, referring to FIG. 4 , after the polymer stencil 270 prepared as an etching mask is brought into contact with the polymer electrolyte membrane 310 , plasma etching may be performed. That is, after the polymer stencil 270 is in conformal contact with the polymer electrolyte membrane 310 such as a Nafion membrane, plasma treatment may be performed. Meanwhile, the surface of the polymer stencil 270 may be coated with Teflon so that the polymer electrolyte membrane 100 can be easily separated after plasma etching.

At this time, the air in the chamber is flowed at a flow rate of 10 sccm to 100 sccm, maintaining a pressure of 1.0 x 10 ^-1 torr to 1.0 x 10 ^-3 torr, and plasma treatment at 50 W to 100 W for 10 to 180 minutes can do. At this time, by adjusting the plasma exposure time, it is possible to control the depth of the micro-holes (H) formed in the polymer electrolyte membrane (100). Specifically, the plasma etching time may be adjusted so that the micro-holes H have a depth of 2 μm to 12 μm.

The polymer electrolyte membrane 100 in contact with the micro-holes H1 of the polymer stencil 270 may be etched by exposure to plasma, and the polymer electrolyte membrane in contact with the portion without the micro-holes H1 of the polymer stencil 270 . (100) is not exposed and is not etched.

According to the present invention, it is possible to manufacture a large-area electrolyte membrane through a continuous process. Therefore, the utilization and commercialization competitiveness of the process in the renewable energy power industry are high.

On the other hand, the membrane electrode assembly 10 can be manufactured by spraying the catalyst ink on the polymer electrolyte membrane 100 prepared by the above method. Specifically, a platinum (Pt/C) catalyst solution supported by carbon may be applied by a spray method.

Hereinafter, the present invention will be described in more detail through examples of the present application, but the following examples are merely illustrative to aid the understanding of the present application, and the content of the present application is not limited to the following examples.

Example 1: Preparation of Polymer Stencil

Silicon masters with hole patterns were fabricated by photolithography and deep reactive ion etching. The surface of the silicon master was treated with C ₄ F ₈ gas for easy demolding. After master preparation, a mixture of a curing agent and a base (1:10 w/w) of Sylgard 184 PDMS elastomer (Dupont, United States) was poured into the silicone master and cured at 65° C. for 3 hours. Because the surface energy of the silicon master was reduced by the C ₄ F ₈ plasma polymer coating, the cured PDMS mold with the micro-pillar pattern can be easily demolded from the silicon master.

A flat PDMS mold was prepared in the same way as a flat silicon master. Next, a UV-curable polyurethane acrylate (PUA) resin (MINS PUA 311RM, Changsung Sheet, Korea) composed of a photoinitiator, a prepolymer having an acrylate functional group, and a release agent is dispensed into a PDMS mold with a micro-pillar pattern and then soft Covered with a flat PDMS mold with pressure. The sandwich-type assembly was cured under UV light (SANKYO DENKI, F8T5BL, λ~352 nm) with an intensity of 20 W cm ^-2 for about 2 minutes. After that, the flat PDMS mold was demolded from the polymer assembly, and then the cured PUA polymer stencil was separated from the micro PDMS mold. Finally, the polymer stencil was exposed under additional UV light for 3 h to fully cure the uncured PUA resin at the edge of the hole.

Example 2: Preparation of a polymer electrolyte membrane for fuel cell containing micro holes

A polymer stencil prepared as an etching mask according to Example 1 was attached to the surface of a Nafion membrane 211 (Dupont, United States, ~25 μm thick). The polymer stencil with the micro-hole pattern used as the etching mask should have conformal contact to the Nafion membrane and should be easily separated from the membrane after the etching process. The surface of the polymer stencil was coated with Teflon for conformal contact and easy separation. A Teflon solution (Teflon AF 1600, Dupont, USA) was applied over the entire surface of the polymer stencil. Spin coating was carried out at a rotation speed of 500 to 1500 rpm with an acceleration time of 10 seconds and a total rotation time of 60 seconds. The polymer stencil was dried at 65 °C for 1 h to evaporate the residual solvent. After evaporating the Teflon solvent, a polymer stencil and a polyimide film were sequentially placed on a Nafion membrane attached to a glass substrate. The sandwich layer was maintained in conformal contact by applying gentle pressure using a hand roller. A polymer electrolyte membrane etched with a micro-hole pattern having a diameter of 40 μm was obtained through the following plasma process. A plasma chamber (Femto Science, Korea) maintained a pressure of 3.0 × 10 ⁻¹ torr by maintaining a balance between vacuum pumping and supply of air gas at a flow rate of 15 sccm. An air plasma composed of ions, electrons and free radicals was generated with a capacitive plasma power of 50 W. The Nafion 211 membrane covered with a polymer stencil mask was exposed to air plasma according to the etching time. Due to the complete contact between the membrane and the polymer stencil, the contact surface between the stencil and the membrane was not etched, and the exposed areas of the membrane where the holes of the polymer stencil were placed were selectively etched. The etch depth was controlled by adjusting the plasma exposure time.

Example 3: Preparation of a membrane electrode assembly (MEA)

Anode and cathode electrodes were formed on the polymer electrolyte membrane for fuel cells including the microholes prepared in Example 2 above. Anode and cathode electrodes were prepared by spraying a Pt/C catalyst solution. Specifically, a solution of Pt/C catalyst (Johnson Matthey Co., United Kingdom, Pt: 40 wt %) and 5 wt % Nafion ionomer (Sigma-Aldrich, United States, density: 0.874 g/ml ^-1 ) was uniformly mixed. to prepare a Pt/C catalyst solution. (Nafion + Pt/C) The Nafion ionomer loading ratio, which is the weight percentage of Nafion relative to the total weight of the dry mixture, was set to 23% by weight. The viscosity of the catalyst ink was adjusted by addition of deionized water and isopropyl alcohol (Sigma-Aldrich, United Kingdom) and uniformly mixed by ultrasonic waves. Then, the catalyst ink was directly sprayed onto the Nafion 211 membrane surface to construct anode and cathode electrodes with the same Pt loading of about 0.2 mg cm ⁻² . Pt loading was confirmed because the Nafion membrane readily absorbs moisture from the atmospheric environment and can cause errors in the weighing process. To this end, the difference in weight before and after spraying the Pt/C catalyst solution onto the PET film (W _Pt = W _{(Pt + PET)} -W _PET ) was measured. These MEAs were dried at ambient temperature for over 12 hours.

Experimental Example 1: Confirmation of etching depth according to exposure time of plasma etching process

Using a polymer stencil as a plasma etching mask, Nafion 211 membranes were selectively etched to have hole array patterns with different depths. 5 is the corresponding SEM images. To control the etch depth, only the plasma etch time was adjusted, and other process conditions including plasma power, gas flow rate and chamber pressure were kept the same. In this process, plasma etching changes the surface composition of the electrolyte membrane. Treatment of Nafion membranes with high-power plasma for a long period of time may reduce the ionic conductivity of the surface, especially due to a decrease in elemental sulfur (S) content. However, since elemental sulfur (S) mostly disappears from the skin layer of the electrolyte membrane, it does not significantly affect the bulk membrane properties. The etched area of the patterned membrane was only about 20% of the total membrane surface, which can mitigate the loss of surface proton conductivity. In addition, since the thickness of the patterned region is reduced, the reduced ohmic resistance prevents loss of proton conductivity. Through experiments, it was confirmed that the etching depth of the Nafion membrane and the PUA 311 stencil was linearly proportional to the plasma irradiation time, and the etching rate was approximately 4 and 1 μm h ⁻¹ , respectively. For comparison, three polymer electrolyte membranes with etching depths of 4, 8 and 12 μm (PM4, PM8 and PM12) were prepared. Referring to the third row of FIG. 5 (a) to (d), the surface roughness increased as the etching depth increased, which was observed in the enlarged cross-sectional SEM image. To quantitatively investigate the increased surface roughness with increasing etching time, topographic images and 1D surface profiles were obtained for the pristine Nafion membrane and PM4, PM8 and PM12 via atomic force microscopy (AFM) measurements. The AFM scan area was evaluated as 15 μm × 15 μm in non-contact mode for each membrane. The measured roughness heights were about 0.3, 0.7 and 1.1 μm for PM4, PM8 and PM12, respectively. Also, the root mean square of roughness (Rrms) showed 101, 173 and 466 nm for PM4, PM8, and PM12, respectively. It was confirmed that the longer the plasma exposure time on the electrolyte membrane surface, the greater the etching depth and roughness.

Experimental Example 2: Tensile test results

In order to investigate the mechanical stability of the polymer electrolyte membrane (Palsma etched membrane w/pattern) according to Example 2 of the present invention, a commercial Nafion 211 membrane (Conventional Nafion membrane 211), a membrane etched with plasma without a polymer stencil as an etching mask ( A tensile test was performed using a plasma etched membrane w/o pattern). The plasma-etched membrane without the polymer stencil was etched by the average etching depth of the patterned electrolyte membrane using the polymer stencil. All sample sizes tested were fixed at 1 × 2 cm ² , and a constant strain of 10 mm min ⁻¹ was applied to each sample. As shown in Fig. 6, in the strain stress curve of each sample, the plasma-etched membrane (full area etched) without a polymer stencil decreased to 23 μm in thickness and exhibited a tensile stress of ~ 15.3 MPa, an elongation at break of ~ 1.28, and a Young's modulus of ~ 153.1 MPa. This value is smaller than that of the commercial Nafion 211 membrane (tensile stress 19.8 MPa, elongation at break 2.49, Young's modulus 248.9 MPa). These results show that the surface roughness of plasma etching can cause the initiation and propagation of surface destruction. A partially etched polyelectrolyte membrane with a micro-hole pattern with an etch depth of 8 µm was considered to have an average thickness of 23.4 µm (about 20% based on the area ratio of the hole pattern), and a 25 µm-thick commercial Nafion 211 membrane (tensile stress 19.8 MPa, elongation at break 2.49, Young's modulus 248.9 MPa). This is because the portion in contact with the polymer stencil has an unetched surface, thereby providing sufficient mechanical stability of the film. That is, from these results, it can be seen that in order to maintain mechanical stability in the polymer electrolyte membrane for fuel cells, it is necessary to perform the plasma etching process with an appropriate etching mask instead of etching the entire surface area.

Experimental Example 3: Electrochemical performance evaluation result

To establish the MEA for electrochemical performance evaluation, the catalyst ink was directly sprayed onto the commercialized membrane and the membrane according to Example 2 while maintaining the same amount of catalyst ⁽ 0.2 mgPt cm ⁻² ) on both the anode and the cathode. 7 (a) is a SEM image of the cathode of a commercially available MEA including a prinstine Nafion 211 membrane, (b) is a SEM image of the cathode of an MEA including a plasma-etched membrane having an etch depth of ~4 μm, (PE4-MEA) (c) is an SEM image of the cathode of the MEA including a plasma-etched membrane with an etch depth of ~8 μm, (PE8-MEA) (d) is a plasma with an etch depth of ~12 μm SEM image of the cathode of the MEA including the etched membrane (PE12-MEA).

The catalyst layer was uniformly distributed with the form of micro-patterns on the membrane without cracks at the interface and had a thickness of about 10 μm. Each MEA was assembled as a bipolar plate with a gas diffusion layer (GDL, JNTG-30-A3, Korea) and a serpentine channel with a channel width and a rib width of 1 mm in a single cell, fully humidified. and performance was measured under almost dry operating conditions.

8 (a) and (b) show the polarization curves of MEA, PE4-MEA, PE8-MEA, and PE12-MEA compatibilized at 70° C. in fully humidified H ₂ /O ₂ and H ₂ /air conditions. All MEAs with micro-hole patterns (PE4-MEA, PE8-MEA and PE12-MEA) have a maximum power density of 1.380 W cm ^-2 and ^0.754 W cm ^-2 in H ₂ /O ₂ and H ₂ /air conditions, respectively. showed higher performance compared to the commercially available MEA showing

In particular, PE8 ^- MEA exhibited the highest maximum power density of 1.541 W cm ^-2 and 0.876 W cm ^-2 in H ₂ /O ₂ and H ₂ /air conditions, respectively. This means that there is an optimal pattern shape to obtain high performance. As mentioned in Experimental Example 1 above, the surface roughness and the etching depth increased as the etching time increased. The membrane of PE12-MEA had a higher surface roughness, and the morphology of the catalyst layer of PE12-MEA had a steeper wall than that of PE4-MEA and PE8-MEA. In addition, PE12-MEA had a much deeper void space between the catalyst layer and the GDL, which could have a negative impact on mass transport due to the increased mass transfer resistance as the path of the incoming reactants and the outgoing water was long. As a result of observing these geometrical features, it was confirmed that the appropriate roughness of the membrane of PE8-MEA, the depth of the hole, and the conical surface of the catalyst layer were advantageous to achieve high performance PEMFC.

Meanwhile, to compare the mass transfer degree of commercially available MEA, PE4-MEA, PE8-MEA and PE12-MEA, the oxygen gain (ΔV) was calculated using the following equation.

Δ V = V _(H2/O2) V _(H2/air)

Referring to FIG. 8(c), PE8-MEA showed the lowest oxygen gain value among MEAs, and the difference increased as the current density increased. This means that PE8-MEA had an optimal electrode structure to improve mass transport (water management). On the other hand, compared to the oxygen gain value of the commercialized MEA, PE4-MEA showed a slightly decreased value and PE12-MEA showed a similar value. These results show that PE4-MEA with shallow depth cannot significantly contribute to the improvement of mass transfer ability, whereas PE12-MEA with deep depth improves mass transfer because improved water management by pore space and increased transport route are in a trade-off. may not be effective in doing so.

The enhanced mass transport ability of PE8-MEA can be further confirmed by modifying the original polarization curve with iR-free fitting. The iR-free voltage ( V _iRfree ) is calculated by adding the measured cell voltage ( V _cell ) and the ohmic loss voltage ( iR _ohmic ). The ohmic loss voltage (iR _ohmic ) is calculated by multiplying the given current density (i) by the high frequency resistance value (R _ohmic ).

V _iRfree = V _cell + iR _ohmic

Fig. 8(d) is an iR-free polarization curve for each MEA. The performance of all MEAs was similar at the current density less than 1.2 A cm ^-2 , and the performance difference was noticeable in the region above 1.2 A cm ^-2 , and the difference gradually increased as the current density increased. In particular, PE8-MEA showed the best performance with improved mass transport and reduced ohmic resistance effect.

Meanwhile, referring to FIG. 9 , additional polarization curves for each MEA were confirmed under low temperature/humidity (50° C., RH 35%) conditions. Even at low RH conditions, PE-MEA improved its performance. In particular, PE8-MEA showed a maximum power density of 0.607 W cm ^-2 , which increased by 21.9% compared to the commercialized MEA (0.498 W cm ^-2 ). This is achieved due to the combined effects of promoting reverse diffusion of water generated in the locally thinned portion of the etched film, enhanced mass transfer within the catalyst layer, and reduced ohmic loss.

Electrochemical measurements including EIS, CV and LSV measurements were additionally performed to further investigate the effect of the polymer electrolyte membrane according to the examples on the performance of the MEA. Fig. 10(a) and (b) show the EIS spectrum (marked dot) of the tested MEA with a fitted curve (solid line) based on the corresponding equivalent circuit (Fig. 10(c)), and the operating condition is the polarization measurements were the same. Referring to (a) of FIG. 10 , the ohmic resistances of commercially available MEA, PE4-MEA, PE8-MEA and PE12-MEA were 0.0514, 0.0484, 0.0475 and 0.0465 Ω cm ² , respectively, in the case of complete humidification. All PE-MEAs had reduced ohmic resistance (increased proton conductivity) due to a shortened hydrogen ion conduction length from the anode to the cathode, and decreased charge transfer resistance compared to commercially available MEAs (0.1977 Ω cm ² ). In particular, the charge transfer resistance of PE8-MEA (0.1029 Ω cm ² ) was reduced by 48% compared to the commercialized MEA, which is the most effective electrochemical reaction and the interface between the catalyst layer and the membrane with the largest number of active sites. This is because the area has been enlarged. In addition, PE8-MEA showed the lowest Warburg impedance (mass transport resistance) of about 0.0847 Ω cm ² , which is a 43% decrease compared to the commercialized MEA (0.1485 Ω cm ² ). This indicates that the enhanced charge transfer and mass transfer due to the geometric patterning effect mainly contribute to the performance improvement. On the other hand, the charge transfer resistance of PE12-MEA slightly increased compared to PE8-MEA, although PE12-MEA had the highest interfacial area. This may be because the increased hydrogen crossover of PE12-MEA due to the extremely thin etched region adversely affected the charge transfer kinetics on the cathode side.

Referring to FIG. 10 (b), the ohmic and charge transfer resistance of PE8-MEA under low RH conditions (RH 35%) are 0.1069 and 0.1550 Ω cm ² , respectively, in commercially available MEA (0.1280 and 0.2409 Ω cm ² ). significantly decreased compared to Through these results, the effect of plasma etching to improve both film hydration and material transport under low RH conditions was confirmed.

The EIS fitted values and key parameters of the tested MEA are summarized in Table 1 below.

[Table 1]

₁₁ ( _a ) and (b) show CV and Show the LSV curve.

Referring to Figure 11 (a), the ECSA of commercialized MEA, PE4-MEA, PE8-MEA and PE12-MEA was calculated to be about 69.48, 70.49, 75.30 and 72.53 m ² g ^-1 . Compared with the commercially available MEA using a planar membrane, the three-phase interface of PE-MEAs (interface of gas phase, electron-conducting phase, ion-conducting phase) is the interface contact between the membrane and the catalyst layer due to the micro/nano structure of the membrane. increased as the area was enlarged. It is worth noting that the increased ECSA value is not large because the plasma etching process was performed selectively rather than the entire area.

Figure 11 (b) shows the LSV curve of each MEA for identifying the hydrogen crossover (hydrogen crossover), which is an important indicator for evaluating MEA stability. The hydrogen crossover current densities at 0.4 V were 2.677, 2.591, 2.350 and 3.409 mA cm ⁻² for the commercially available MEA, PE4-MEA, PE8-MEA and PE12-MEA, respectively. Interestingly, PE4-MEA and PE8-MEA consisted of thinner membranes, but had lower leakage current densities than commercial MEAs. These results appear to be due to the effect of plasma treatment such as strengthening the membrane surface and the enhancement of the adhesion energy at the interface between the membrane and the electrode. On the other hand, PE12-MEA showed the highest hydrogen crossover current density among all samples. This suggests that, despite the plasma treatment effect, a deep etch depth corresponding to about half of the membrane thickness may cause an increase in hydrogen crossover as well as a decrease in mechanical stability confirmed in Experimental Example 2.

Features, structures, effects, etc. described in the above embodiments are included in at least one embodiment of the present invention, and are not necessarily limited to one embodiment. Furthermore, features, structures, effects, etc. illustrated in each embodiment can be combined or modified for other embodiments by those of ordinary skill in the art to which the embodiments belong. Accordingly, the contents related to such combinations and modifications should be interpreted as being included in the scope of the present invention.

In addition, although the embodiments have been described above, these are merely examples and do not limit the present invention, and those of ordinary skill in the art to which the present invention pertains are exemplified above in a range that does not depart from the essential characteristics of the present embodiment. It can be seen that various modifications and applications that have not been made are possible. For example, each component specifically shown in the embodiments may be implemented by modification. And differences related to such modifications and applications should be construed as being included in the scope of the present invention defined in the appended claims.

Claims (12)

A polymer electrolyte membrane for a fuel cell comprising a plurality of microholes having a depth of 2 μm to 12 μm. According to claim 1,
Polymer electrolyte membrane for fuel cell, characterized in that the diameter of the micro-hole is 30 μm to 50 μm. According to claim 1,
An interval between the plurality of micro-holes is a polymer electrolyte membrane for a fuel cell, characterized in that 30 μm to 50 μm. According to claim 1,
The polymer electrolyte membrane has a bottom surface; and a micro-hole disposed on the bottom surface of the polymer electrolyte membrane for a fuel cell. Preparing a polymer stencil containing micro-holes; and
A method of manufacturing a polymer electrolyte membrane for a fuel cell, comprising the step of plasma-etching the polymer stencil in contact with the polymer electrolyte membrane. 6. The method of claim 5,
In the step of preparing the polymer stencil,
A method of manufacturing a polymer electrolyte membrane for a fuel cell, characterized in that the resin is placed between the first polymer mold including the micro-pillar pattern and the second flat polymer mold and then irradiated with UV. 6. The method of claim 5,
The method of manufacturing a polymer electrolyte membrane for a fuel cell, wherein the first polymer mold and the second polymer mold include polydimethylsiloxane (PDMS). 6. The method of claim 5,
The resin is a method of manufacturing a polymer electrolyte membrane for a fuel cell, characterized in that it contains PUA (Polyurethane acrylate). 6. The method of claim 5,
In the plasma etching step, air in the chamber is flowed at a flow rate of 10 sccm to 100 sccm, a pressure of 1.0 x 10 ^-1 torr to 1.0 x 10 ^-3 torr is maintained, and 50 W to 100 W for 10 minutes to 180 A method of manufacturing a polymer electrolyte membrane for a fuel cell, characterized in that plasma treatment is performed for a minute. 6. The method of claim 5,
The method of manufacturing a polymer electrolyte membrane for a fuel cell, characterized in that the diameter of the micro-hole is 30 μm to 50 μm. A fuel cell comprising the polymer electrolyte membrane according to any one of claims 1 to 4. 12. The method of claim 11,
Further comprising a catalyst layer disposed on the polymer electrolyte membrane,
The catalyst layer is a fuel cell, characterized in that it comprises platinum supported by carbon.

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