Self-assembled conductive phase of anode catalyst layer and preparation method and application of self-assembled conductive phase

Abstract

The invention relates to a self-assembled conductive phase of an anode catalyst layer and a preparation method thereof, the self-assembled conductive phase is conductive oxide particles and a thiol wrapping layer wrapping the outer surface, when the loading capacity of a catalyst is reduced, discontinuous catalysts in the catalyst layer can be bridged, and the self-assembled conductive phase has good self-assembled performance. And the utilization rate of the catalyst and the conductivity of the catalyst layer in-plane direction are improved. When the self-assembled conductive polymer prepared by the invention is applied to an anode catalyst layer of a proton exchange membrane electrolysis water membrane electrode, compared with a control group, the performance of the membrane electrode is improved by 26.8% at 2V, and the electrochemical active area is increased by 33%.

Description

Technical Field

[0001] The present invention belongs to the technical field of proton exchange membrane electrolyzed water, and particularly relates to a self-assembled conductive phase of an anode catalyst layer, a preparation method thereof, and an application thereof. Background Art

[0002] At present, the high cost is the reason hindering the large-scale application of PEMWE (proton exchange membrane electrolyzed water). The commonly used anode and cathode catalysts of PEMWE are IrO2 and Pt / C respectively. The use of noble metal catalysts greatly increases the cost of the electrolytic cell. Among them, the annual production of iridium is about 7-8 tons, and only 20% of the annual production is expected to be used for PEMWE without causing unsustainable pressure on the iridium supply. Therefore, it is necessary to reduce the loading of the anode catalyst while improving the performance of the electrolytic cell as much as possible. The current method for preparing the catalyst layer is to uniformly mix the catalyst and the ionomer in a dispersant and then coat it on the surface of the polymer electrolyte membrane. However, in the current technology, when the anode catalyst loading is reduced, the three-phase active sites of the reaction decrease, and the kinetic loss of the electrochemical reaction increases; when the catalyst loading is too low, the catalyst distribution is uneven, the catalyst aggregates are separated, and the electron channels in the in-plane direction of the catalyst layer are broken, resulting in electrons being unable to reach the surface of some catalysts, presenting the phenomenon of catalyst isolation, reducing the catalyst utilization rate, and sharply decreasing the performance of PEMWE. Summary of the Invention

[0003] Aiming at the deficiencies of the existing technology, the present invention provides a self-assembled conductive phase of an anode catalyst layer, a preparation method thereof, and an application thereof.

[0004] The technical solution of the present invention is as follows:

[0005] A self-assembled conductive phase of an anode catalyst layer, the self-assembled conductive phase comprising conductive oxide particles and a thiol-based coating layer wrapped on the outer surface of the conductive oxide particles.

[0006] Further, the thickness of the thiol-based coating layer is 2-4 nm.

[0007] Further, the conductive oxide particles are submicron-sized.

[0008] Further, the conductive oxide particles are Ti4O7 particles.

[0009] Further, the thiol-based coating layer is a long-chain thiol coating layer.

[0010] Even further, the long-chain thiol is n-octadecanethiol.

[0011] The preparation method of the above-mentioned self-assembled conductive phase of the anode catalyst layer includes the following steps:

[0012] 1) Add conductive oxide particles and a thiol-based coating liquid to absolute ethanol and stir evenly to obtain a mixed solution A;

[0013] 2) Let the mixed solution A stand and then perform centrifugal separation until the pH of the supernatant is 7 to obtain a mixed solution B;

[0014] 3) Dry the mixed solution B to obtain the self-assembled conductive phase of the anode catalyst layer.

[0015] Furthermore, the molar ratio of the conductive oxide particles to the coating liquid is 1:(1 - 2).

[0016] Furthermore, the conductive oxide particles are Ti4O7 particles.

[0017] Furthermore, the preparation method of the Ti4O7 particles is as follows:

[0018] S1. Prepare TiO2 powder;

[0019] S101. Mix isobutyl titanate and hydrofluoric acid and perform hydrothermal treatment to obtain intermediate A;

[0020] S102. Centrifuge intermediate A until the pH of the supernatant is 7, separate to obtain intermediate B, and dry and grind to obtain TiO2 powder;

[0021] S2. Prepare Ti4O7 particles;

[0022] S201. Add TiO2 powder and nano carbon black to absolute ethanol and mix evenly to obtain intermediate C;

[0023] S202. Dry, grind, calcine, ball mill, and centrifuge intermediate C to obtain submicron Ti4O7.

[0024] Furthermore, in step S101, the volume ratio of isobutyl titanate to hydrofluoric acid is (4 - 6):1, and in step S201, the molar ratio of nano carbon black to TiO2 powder is 1:(3 - 5).

[0025] Furthermore, the process parameters of the calcination in step S202 are as follows: in a nitrogen or argon atmosphere, at 1000 - 1200 °C, heat up at a rate of 10 °C / min for 1 - 3 h, keep warm for 1 - 3 h, and cool down for 3 - 5 h.

[0026] Application of the self-assembled conductive phase of the anode catalyst layer prepared according to the above preparation method in the preparation of a proton exchange membrane electrolyzed water membrane electrode.

[0027] Compared with the prior art, the present invention has at least the following advantages:

[0028] 1. The present invention relates to a self-assembled conductive phase of an anode catalyst layer. The self-assembled conductive phase is ODT@Ti4O7 formed by coating the outer surface of sub-micron Ti4O7 particles with a n-octadecanethiol coating layer. After ODT coats Ti4O7, an S-O bond is formed between the two. When the catalyst loading is reduced (especially < 0.5 mg cm -2 ), ODT@Ti4O7 can bridge the discontinuous catalysts in the catalyst layer, without affecting the conductivity of Ti4O7 and without affecting the coating of the catalyst IrO2 by PFSA ionomer, improving the utilization rate of the catalyst and the conductivity of the catalyst layer in the in-plane direction, thus improving the performance of PEMWE.

[0029] 2. The self-assembled conductive phase of an anode catalyst layer of the present invention, wherein the sub-micron Ti4O7 is prepared by carbon reduction method and ball milling of TiO2 powder, effectively reducing the particle size of Ti4O7 from 2 - 4 μm to the sub-micron level.

[0030] 3. When the self-assembled conductive phase of the anode catalyst layer prepared by the method of the present invention is used in a proton exchange membrane electrolyzed water membrane electrode, compared with the prior art, the performance of the membrane electrode is improved by 26.8% @ 2V, and the electrochemically active area is increased by 33%. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the specific embodiments of the present invention, the following will briefly introduce the drawings required for use in the specific embodiments or the description of the prior art.

[0032] Figure 1 It is the SEM image of Ti4O7 before and after ball milling in Example 2 of the present invention;

[0033] Figure 2 It is the TEM detection image of the self-assembled conductive phase (ODT@Ti4O7) of the anode catalyst layer prepared in Example 2 of the present invention;

[0034] Figure 3 It is the comparison chart of the current-voltage curves of the membrane electrodes prepared from four kinds of anode catalyst slurries in the application example of the present invention;

[0035] Figure 4 It is the comparison chart of the electrochemically active area (ECSA) of the membrane electrodes prepared from three kinds of anode catalyst slurries in the application example of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] The following will describe the present invention in further detail. It is necessary to point out here that the following specific embodiments are only used to further illustrate the present invention and should not be construed as limiting the protection scope of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above application content.

[0037] The present invention generally and / or specifically describes the materials and test methods used in the experiments. The test methods or measurement methods involved are all conventional methods unless otherwise specified; the reagents or instruments used are all commercially available conventional products prepared or used by conventional methods if the manufacturer is not indicated.

[0038] Material source:

[0039] Isobutyl titanate: AR, purchased from Macklin;

[0040] Hydrofluoric acid: purchased from Macklin;

[0041] n-Octadecanethiol: purchased from Aladdin;

[0042] Commercial IrO2: product number 043396, purchased from Alfa Aesar;

[0043] Commercial Pt / C: product number HISPEC4000, purchased from Johnson Matthey;

[0044] Nafion solution: product number D520, purchased from DuPont;

[0045] n-Propanol: purchased from Chengdu Kelong Reagent;

[0046] Nafion 115 membrane: product number N115, purchased from DuPont.

[0047] Example 1 Preparation of the conductive agent Ti4O7 and the self-assembled conductive phase (ODT@Ti4O7) of proton exchange membrane electrolyzed water

[0048] 1.1 Preparation of nano-TiO2 powder: Isobutyl titanate and hydrofluoric acid were slowly added to a polytetrafluoroethylene inner liner in a volume ratio of 4:1, mixed and stirred for 10 minutes, then placed in a stainless steel autoclave and hydrothermally treated at 200 °C for 24 hours; the obtained product was placed in a centrifuge tube and centrifuged several times at a rotation speed of 8000 rpm until the pH of the supernatant was 7; the obtained powder was dried overnight at 80 °C and ground to obtain nano-TiO2.

[0049] 1.2 Preparation of Ti4O7 using the carbothermal reduction reaction (CRR): Subsequently, nano carbon black and nano TiO2 were added to 20 ml of absolute ethanol at a molar ratio of 1:3 and mixed evenly. The slurry was dried overnight at room temperature, ground, and then fired at 1150 °C in a nitrogen atmosphere. The temperature was raised at a rate of 10 °C / min for 2 hours, held for 3 hours, and cooled for 5 hours. Finally, the product Ti4O7 powder was obtained, which basically corresponded to the Ti4O7 standard card (PDF#50-0787, A-1). Subsequently, the mixture of Ti4O7 and 20 ml of absolute ethanol was added to a ZrO2 container containing 40 ZrO2 balls (average diameter 3 mm). Using a planetary ball mill, it was rotated at a speed of 300 rpm, running alternately forward and backward for a total of 12 h (running for 30 minutes and pausing for 2 minutes). The ball-milled slurry was placed in a centrifuge tube and centrifuged several times at a speed of 8000 rpm until the pH of the supernatant was 7. The obtained powder was dried overnight at 80 °C and ground to obtain submicron Ti4O7 powder.

[0050] 1.3 Preparation of ODT@Ti4O7: Submicron Ti4O7 powder and n-octadecanethiol at a molar ratio of 1:2 were added to a beaker containing an appropriate amount of absolute ethanol, stirred and heated for 20 minutes, and then left standing at 25 °C for one day. The mixed solution was placed in a centrifuge tube and centrifuged at a speed of 8000 rpm until the pH of the supernatant was 7. The obtained powder was naturally dried at 25 °C to finally obtain n-octadecanethiol-coated Ti4O7, denoted as ODT@Ti4O7.

[0051] Example 2 Preparation of the conductive agent Ti4O7 and the self-assembled conductive phase (ODT@Ti4O7) of proton exchange membrane electrolyzed water

[0052] 2.1 Preparation of nano TiO2 powder: Isobutyl titanate and hydrofluoric acid were slowly added to a polytetrafluoroethylene liner at a volume ratio of 5:1 and mixed and stirred for 10 minutes. Subsequently, it was placed in a stainless steel autoclave and hydrothermally treated at 200 °C for 24 hours. The obtained product was placed in a centrifuge tube and centrifuged several times at a speed of 8000 rpm until the pH of the supernatant was 7. The obtained powder was dried overnight at 80 °C and ground to obtain nano TiO2.

[0053] 2.2 Preparation of Ti4O7 using the carbothermal reduction reaction (CRR): Subsequently, nano carbon black and nano TiO2 were added to 20 ml of absolute ethanol at a molar ratio of 1:4 and mixed evenly. The slurry was dried overnight at room temperature, ground, and then fired at 1150 °C in an argon atmosphere. The temperature was increased at a rate of 10 °C / min for 2 hours, held for 2 hours, and decreased for 4 hours. Finally, the product Ti4O7 powder was obtained, which basically corresponded to the Ti4O7 standard card (PDF#50 - 0787, A - 1). Subsequently, the mixture of Ti4O7 and 20 ml of absolute ethanol was added to a ZrO2 container containing 40 ZrO2 balls (average diameter 3 mm). Using a planetary ball mill, it was rotated at a speed of 300 rpm, running alternately forward and backward for a total of 12 h (running for 30 minutes and pausing for 2 minutes). The ball - milled slurry was placed in a centrifuge tube and centrifuged several times at a speed of 8000 rpm until the pH of the supernatant was 7. The obtained powder was dried overnight at 80 °C, ground, and then sub - micron Ti4O7 powder was obtained.

[0054] 2.3 Preparation of ODT@Ti4O7: Sub - micron Ti4O7 powder and n - octadecyl mercaptan at a molar ratio of 1:1 were added to a beaker containing an appropriate amount of absolute ethanol, stirred and heated for 20 minutes, and then left to stand at 25 °C for one day. The mixed solution was placed in a centrifuge tube and centrifuged at a speed of 8000 rpm until the pH of the supernatant was 7. The obtained powder was naturally dried at 25 °C, and finally, n - octadecyl mercaptan - coated Ti4O7, denoted as ODT@Ti4O7, was obtained.

[0055] Example 3 Preparation of the conductive agent Ti4O7 and the self - assembled conductive phase (ODT@Ti4O7) of proton - exchange membrane electrolyzed water

[0056] 3.1 Preparation of nano TiO2 powder: Isobutyl titanate and hydrofluoric acid were slowly added to a polytetrafluoroethylene inner liner at a volume ratio of 6:1 and mixed and stirred for 10 minutes. Subsequently, it was placed in a stainless - steel autoclave and hydrothermally treated at 200 °C for 24 hours. The obtained product was placed in a centrifuge tube and centrifuged several times at a speed of 8000 rpm until the pH of the supernatant was 7. The obtained powder was dried overnight at 80 °C, ground, and then nano TiO2 was obtained.

[0057] 3.2 Preparation of Ti4O7 by carbothermal reduction reaction (CRR): Subsequently, nano carbon black and nano TiO2 were added to 20 ml of absolute ethanol at a molar ratio of 1:5 and mixed evenly. The slurry was dried overnight at room temperature, ground, and then fired at 1200 °C in an argon atmosphere. The temperature was increased at a rate of 10 °C / min for 1.5 hours, held for 2 hours, and cooled for 3 hours. Finally, the product Ti4O7 powder was obtained, which basically corresponded to the Ti4O7 standard card (PDF#50-0787, A-1). Subsequently, the mixture of Ti4O7 and 20 ml of absolute ethanol was added to a ZrO2 container containing 40 ZrO2 balls (average diameter 3 mm), and a planetary ball mill was used to rotate forward and backward alternately at a speed of 300 rpm for a total of 12 h (running for 30 minutes and intermittent for 2 minutes). The ball-milled slurry was placed in a centrifuge tube and centrifuged several times at a speed of 8000 rpm until the pH of the supernatant was 7. The obtained powder was dried overnight at 80 °C and ground to obtain submicron Ti4O7 powder.

[0058] 3.3 Preparation of ODT@Ti4O7: Submicron Ti4O7 powder and n-octadecanethiol with a molar ratio of 1:1 were added to a beaker containing an appropriate amount of absolute ethanol, stirred and heated for 20 minutes, and then left standing at 25 °C for one day. The mixed solution was placed in a centrifuge tube and centrifuged at a speed of 8000 rpm until the pH of the supernatant was 7. The obtained powder was naturally dried at 25 °C, and finally, Ti4O7 coated with n-octadecanethiol, denoted as ODT@Ti4O7, was obtained.

[0059] Test Example

[0060] Taking Example 2 of this application as an example, the performance of the prepared Ti4O7 and the self-assembled conductive phase (ODT@Ti4O7) of proton exchange membrane electrolyzed water was detected. Specifically:

[0061] The morphology test of Ti4O7 before and after ball milling is as Figure 1 shown, where Figure 1 a is the SEM image of Ti4O7 before ball milling, Figure 1 b is the SEM image of Ti4O7 after ball milling; it can be seen from the figure that the particle size range of Ti4O7 before ball milling is 2-4 μm, and the particle size after ball milling becomes significantly smaller and becomes submicron.

[0062] The TEM detection image of the self-assembled conductive phase (ODT@Ti4O7) of proton exchange membrane electrolyzed water is as Figure 2 shown. It can be observed from the figure that the particle size of Ti4O7 is about 300 nm, and Ti4O7 is completely and evenly coated with ODT (n-octadecanethiol), and the coating thickness is 2-4 nm.

[0063] Application Example: Application of Self-Assembled Conductive Phase in Proton Exchange Membrane Water Electrolysis

[0064] In this application example, Example 2 is selected as an example to test the electrical performance of its application to the membrane electrode:

[0065] Application Example 1: Preparation of IrO2+PFSA Anode Catalyst Slurry (Control)

[0066] A mixture of 8.6 mg of commercial IrO2, 0.9 ml of deionized water, 29 mg of Nafion solution and 1.8 ml of n-propanol was ultrasonically treated in an ice bath for 20 minutes using a cell disruptor at a power of 35% to obtain the anode catalyst slurry, denoted as IrO2+PFSA.

[0067] Application Example 2: Preparation of IrO2+PFSA+Ti4O7 Anode Catalyst Slurry

[0068] A mixture of 8.6 mg of commercial IrO2, 1.5 mg of Ti4O7 prepared in Example 2, 0.9 ml of deionized water, 29 mg of Nafion solution and 1.8 ml of n-propanol was ultrasonically treated in an ice bath for 20 minutes using a cell disruptor at a power of 35% to obtain the anode catalyst slurry, denoted as IrO2+PFSA+Ti4O7.

[0069] Application Example 3: Preparation of IrO2+PFSA+ODT@Ti4O7 Anode Catalyst Slurry

[0070] A mixture of 8.6 mg of commercial IrO2, 1.5 mg of Ti4O7 prepared in Example 2, 0.9 ml of deionized water, 29 mg of Nafion solution, 1.9 mg of octadecanethiol ODT and 1.8 ml of n-propanol was ultrasonically treated in an ice bath for 20 minutes using a cell disruptor at a power of 35% to obtain the anode catalyst slurry, denoted as IrO2+PFSA+ODT+Ti4O7.

[0071] Application Example 4: Preparation of IrO2+PFSA+ODT@Ti4O7 Anode Catalyst Slurry

[0072] A mixture of 8.6 mg of commercial IrO2, 1.5 mg of ODT@Ti4O7 prepared in Example 2, 0.9 ml of deionized water, 29 mg of Nafion solution and 1.8 ml of n-propanol was ultrasonically treated in an ice bath for 20 minutes using a cell disruptor at a power of 35% to obtain the anode catalyst slurry, denoted as IrO2+PFSA+ODT@Ti4O7.

[0073] Test Example: Performance Detection of Membrane Electrodes Prepared from Anode Catalyst Slurries Prepared in the Above Application Examples

[0074] The same cathode catalyst was used in Application Examples 1-4.

[0075] Preparation of cathode catalyst slurry: A mixture of 9 mg of commercial Pt / C, 2.4 ml of deionized water, 36 mg of Nafion solution and 1.8 ml of n-propanol was ultrasonically treated in an ice bath for 20 minutes using a cell disruptor at a power of 35% to obtain the cathode catalyst slurry.

[0076] Four membrane electrodes were prepared by spraying fresh catalyst slurry onto a Nafion 115 membrane using an ultrasonic atomization sprayer. The catalyst loading on the anode side was 0.2 mg cm -2 , and the catalyst loading on the cathode side was 0.2 mg cm -2 .

[0077] The comparison chart of the current-voltage curves (Current density / Cell Voltage) of the membrane electrodes prepared from the four anode catalyst slurries prepared in this test example is shown in Figure 3 ; In the figure, IrO2+PFSA is the membrane electrode with an anode catalyst loading of 0.2 mg cm -2 , which is a membrane electrode of the prior art; in the figure, IrO2+PFSA+Ti4O7 is the membrane electrode with an anode catalyst loading of 0.2 mg cm -2 and with Ti4O7 added to the anode catalyst layer; in the figure, IrO2+PFSA+ODT@Ti4O7 is the membrane electrode with an anode catalyst loading of 0.2 mg cm -2 and with the self-assembled conductive phase ODT@Ti4O7 added to the anode catalyst layer. In the figure, IrO2+PFSA+ODT+Ti4O7 is the membrane electrode with an anode catalyst loading of 0.2 mg cm -2 and with ODT and Ti4O7 added to the anode catalyst layer. It can be observed from the figure that at the same IrO2 loading, the current density of the IrO2+PFSA+Ti4O7 membrane electrode shows a performance decline compared to the control sample IrO2+PFSA membrane electrode (~12.3% @ 2V). Although the IrO2+PFSA+ODT+Ti4O7 membrane electrode shows a performance improvement compared to the IrO2+PFSA+Ti4O7 membrane electrode (~7.8% @ 2V), it still shows a performance decline compared to the control sample IrO2+PFSA membrane electrode (~5.7% @ 2V). However, the current density of the IrO2+PFSA+ODT@Ti4O7 membrane electrode shows a performance improvement compared to the control sample IrO2+PFSA membrane electrode (~26.8% @ 2V).

[0078] When Ti4O7 is added to the anode catalyst layer alone, due to the competitive adsorption of Ti4O7 and IrO2 on PFSA ionomer, PFSA ionomer will coat on the surfaces of both Ti4O7 and IrO2 simultaneously. On the one hand, this will form an electron-insulating ionomer film on the surface of Ti4O7, causing Ti4O7 to lose its conductivity; on the other hand, Ti4O7 adsorbs part of the PFSA ionomer, resulting in a reduction of the ionomer on the surface of IrO2 and restricted proton transport, ultimately leading to a performance decline.

[0079] When ODT and Ti4O7 are directly added to the anode catalyst layer without treatment, competitive adsorption of Ti4O7 and IrO2 on PFSA ionomer, as well as competitive adsorption of Ti4O7 and IrO2 on ODT, will occur, resulting in great randomness in the coating of ODT on Ti4O7. Most of the Ti4O7 will still adsorb part of the PFSA ionomer, causing Ti4O7 to lose its conductivity, and ODT fails to perform its function of hindering the coating of PFSA on Ti4O7. Therefore, although there is a certain performance improvement compared to adding Ti4O7 alone, the problem existing at low Ir loadings is not essentially solved.

[0080] When self-assembled conductive phase ODT@Ti4O7 is first prepared by treating Ti4O7 with ODT and then added to the anode catalyst layer, ODT blocks the adsorption of PFSA on Ti4O7, forms S-O bonds, enabling Ti4O7 to exhibit its high conductivity, bridging the discontinuous catalysts in the catalyst layer, improving the utilization rate of the catalyst and the in-plane conductivity of the catalyst layer, and ultimately enhancing the performance of PEMWE.

[0081] The comparison chart of the electrochemically active surface area (ECSA) of the membrane electrodes prepared from the three anode catalyst slurries in this test example is shown in Figure 4 ; It can be observed from the figure that at the same IrO2 loading, the electrochemically active surface area of the membrane electrode IrO2+PFSA+Ti4O7 with Ti4O7 particles added to the anode catalyst layer shows a decrease in the active surface area (~20%) compared to the control sample IrO2+PFSA membrane electrode, while the electrochemically active surface area of the membrane electrode IrO2+PFSA+ODT@Ti4O7 with ODT@Ti4O7 in the anode catalyst layer shows an increase in the active surface area (~33%) compared to the control sample IrO2+PFSA membrane electrode.

[0082] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the various embodiments of the present invention, and they should all be covered within the scope of the claims and the description of the present invention.

Claims

1. A self-assembled conductive phase of an anode catalyst layer, characterized in that, The self-assembled conductive phase includes conductive oxide particles and a thiol-based coating layer wrapped around the outer surface of the conductive oxide particles.

2. A method for preparing a self-assembled conductive phase of the anode catalytic layer according to claim 1, characterized in that, It includes the following steps: 1) Add the conductive oxide particles and the thiol-based coating layer liquid to absolute ethanol and stir evenly to obtain a mixed solution A; 2) Let the mixed solution A stand and then perform centrifugal separation until the pH of the supernatant is 7 to obtain a mixed solution B; 3) Dry the mixed solution B to obtain the self-assembled conductive phase of the anode catalyst layer.

3. The preparation method according to claim 2, wherein The molar ratio of the conductive oxide particles to the coating layer liquid is 1:(1-2).

4. Application of the self-assembled conductive phase of the anode catalyst layer prepared by the preparation method according to claim 2 in the preparation of a proton exchange membrane electrolyzed water membrane electrode.

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