CN112647086B

CN112647086B - Titanium fiber felt anode diffusion layer for PEM water electrolysis cell and preparation method and application thereof

Info

Publication number: CN112647086B
Application number: CN201910960166.0A
Authority: CN
Inventors: 俞红梅; 范芷萱; 姜广; 韦世慧; 刘凯; 邵志刚
Original assignee: Dalian Institute of Chemical Physics of CAS
Current assignee: Dalian Institute of Chemical Physics of CAS
Priority date: 2019-10-10
Filing date: 2019-10-10
Publication date: 2022-03-11
Anticipated expiration: 2039-10-10
Also published as: CN112647086A

Abstract

The invention discloses a preparation process of an anti-oxidation conductive catalytic coating of an anode diffusion layer for PEM water electrolysis, which adopts a concentrated hydrochloric acid etching method and a brush coating liquid-roasting reduction method to prepare a noble metal oxide coating on the fiber surface of a titanium fiber felt diffusion layer. The invention has low equipment requirement and simple process, has excellent conductivity, catalysis and oxidation resistance in the PEM water electrolyzer, can meet the long-life operation requirement of PEM water electrolysis, and has good effects of reducing the cost of the PEM water electrolyzer and improving the performance.

Description

Titanium fiber felt anode diffusion layer for PEM water electrolysis cell and preparation method and application thereof

Technical Field

The invention belongs to the technical field of PEM water electrolysis, and particularly relates to a titanium fiber felt anode diffusion layer for a PEM water electrolysis cell, and a preparation method and application thereof.

Background

With the continuous improvement of the understanding of the international society on clean energy, the domestic strength for supporting hydrogen energy policies is increased, the demand of hydrogen is more and more, and the PEM water electrolysis technology can utilize the surplus electric quantity of renewable energy sources such as wind, light and the like to electrolyze hydrogen and relieve the pressure of a power grid. PEM water electrolysis hydrogen production has many advantages, only water is needed as raw material in the hydrogen production process, and the product hydrogen and oxygen have high purity and slight mutual permeation. The electrolysis process is efficient, safe, nontoxic and harmless, the equipment structure is compact, the hydrogen production can be realized on site, and the problem of hydrogen transportation does not need to be considered.

The anode diffusion layer is one of the key technologies in the PEM water electrolysis technology, and plays roles in conducting electricity, separating water flow from bubbles, supporting and the like in a PEM water electrolysis cell. Therefore, the method has high requirements on the mechanical property, the conductivity, the chemical stability, the cost and the like of the anode diffusion layer material, the cost of the anode diffusion layer material accounts for a large part of each component of the PEM (proton exchange membrane) stack, and the method is of great importance for the research on the anode diffusion layer with low cost, high chemical stability and high conductivity.

The anode diffusion layer of the PEM electrolytic cell is made of titanium materials, such as a sintered titanium plate, a titanium fiber felt and a titanium mesh. The sintered titanium plate has low price, the porosity is generally lower than 50%, the thickness is generally larger than 0.5mm, the resistance of the electrolytic cell is increased, and the gas-liquid mass transfer requirement is not met. The titanium fiber felt has the porosity of more than 70 percent and the lowest thickness of 0.2mm, the mechanical property can meet the requirement of an electrolytic cell, and the price is expensive. The titanium mesh has low price, high porosity but overlarge pores, the thickness is more than 1mm, the mass transfer requirement can not be basically met, and the titanium mesh is used for the worst actual performance of an electrolytic cell. For cell performance, titanium fiber felt is most suitable for the diffusion layer.

The environment in the PEM water electrolyzer is acidic, the applied voltage is generally higher than 1.5V, the anode generates a large amount of oxygen, and the working environment has extremely high requirement on the stability of the anode diffusion layer. The titanium material is resistant to chemical corrosion, but the surface is very easy to oxidize to generate titanium dioxide with extremely poor conductivity, so the surface treatment is needed to be carried out on the anode diffusion layer. The conventional treatment method is to electroplate a platinum layer on the surface of the anode diffusion layer, and the electroplated platinum layer has poor binding force with the diffusion layer and is easy to fall off. The development of a coating with high conductivity and good bonding force with a metal substrate is greatly helpful for improving the performance of the PEM water electrolytic cell.

At present, a series of researches aiming at noble metal titanium anodes are carried out, and Chinese patent CN201910181241.3 discloses a titanium anode for pesticide removal, wherein an iridium ruthenium mixed oxide coating is prepared by electroplating after an oxide layer on the surface of a titanium electrode is removed, H + ions in pesticide molecules are reduced into hydrogen to damage the molecular structure in the electrolytic process, and the non-toxic treatment effect is achieved. The electrode has a rough structure and cannot be used for a PEM water electrolysis cell, the problems of uneven coating growth, weak binding force and the like possibly exist in the coating prepared by an electroplating method, and important data such as the strengthened electrolytic life and the like are not disclosed in the patent. Chinese patent CN201711247614.X discloses a seawater electrolysis titanium chloride anode prepared by a similar process, the graphene is added into a coating to improve the binding force between the coating and a substrate, and the roughness of a titanium sheet substrate is greatly improved by acid washing, sand blasting and other treatments. Besides iridium oxide and ruthenium oxide, the coating is also doped with graphene which is rapidly corroded at the anode of the PEM electrolytic cell, and tin oxide which pollutes a proton exchange membrane is easy to fall off. And the acid concentration of the traditional oxalic acid, nitric acid and hydrochloric acid etching methods is low, the etching time is long, the mechanical strength of fiber breakage in the titanium fibrofelt is greatly reduced due to long-time low-concentration acid etching, or the surface roughness is too low, the fine structure of the titanium fibrofelt cannot be etched by using a sand blasting method, and the proton exchange membrane is cut by the rough surface caused by the sand blasting method when an electrolytic cell is assembled, so that the membrane electrode fails. The improper surface etching method, improper selection of titanium substrate, improper coating composition and preparation method are the main reasons that the traditional noble metal titanium anode cannot be applied to the PEM electrolytic cell at present.

Disclosure of Invention

The diffusion layer structure and the coating composition are selected aiming at the problems of poor conductivity, easy oxidation, easy falling of the coating and the like of the existing PEM water electrolysis diffusion layer, the electrolysis performance is improved, the cost is reduced, the process flow is simplified, and the effects of slowing down the oxidation problem of the PEM water electrolysis anode diffusion layer and reducing the total consumption of noble metals in an electrolytic cell are good.

The invention provides a preparation method for pretreating a PEM water electrolysis diffusion layer and preparing a conductive and catalytic coating, which is characterized in that the surface etching treatment is carried out on a titanium fiber felt, a precious metal oxide coating suitable for PEM water electrolysis is prepared in a targeted manner, the coating is strengthened according to the water electrolysis property of the PEM, the catalytic effect of the coating is improved, and the service life of the coating is prolonged.

The technical scheme of the invention is as follows:

the invention provides a PEM water electrolysis cell catalytic diffusion layer, which comprises a diffusion layer and a protective coating; the diffusion layer is a titanium fiber felt; the protective coating is a mixed coating of three metal oxides of iridium oxide, ruthenium oxide and tantalum oxide.

Based on the technical scheme, preferably, the thickness of the titanium fibrofelt is 0.2-1.5 mm, and the loading amount of the noble metal (metal iridium and metal ruthenium) is 0.5-2 mg cm^-2Preferably 1mg cm^-2(ii) a In the protective coating, the proportion of tantalum to the total molar weight of metal tantalum, metal ruthenium and metal ruthenium is 20-40%, and the molar ratio of iridium to ruthenium is 6: 4-9: 1.

Based on the technical scheme, it is further preferable that the protective layer is composed of mixed oxides of iridium, ruthenium and tantalum, and the atomic ratio of iridium: ruthenium: tantalum was 4.9:2.1:3, prepared using a coating-roasting reduction process.

The invention also provides a preparation method of the anode diffusion layer of the PEM water electrolysis cell, which comprises the following steps:

1) surface treatment of the titanium fiber felt: and sequentially placing the titanium fiber felt to be prepared into absolute ethyl alcohol and deionized water for cleaning. And then, placing the titanium fiber felt in HCl with the temperature of 50-70 ℃ and the concentration of 30-38%, etching for 3-10 min, taking out, and washing with a large amount of deionized water and absolute ethyl alcohol. So that uniform and fine corrosion cracks appear on the surface of each fiber; a layer of noble metal mixed oxide is prepared on the surface of the titanium fibrofelt by methods of hydrochloric acid etching, noble metal coating liquid brushing, high-temperature roasting and the like, so that a protective layer with high conductivity and catalytic performance is formed. The invention has low equipment requirement and simple process, has excellent conductivity and catalytic performance in PEM water electrolysis, and can meet the use requirement of PEM water electrolysis.

2) Preparing a metal coating liquid: taking chloro-iridic acid, RuCl₃And TaCl₅Preparing a coating liquid with an iridium ruthenium molar concentration of 0.02-0.035 mol/L by using an isopropanol solution as a solvent, wherein the concentration of metal tantalum in the coating liquid is 0.003-0.015 mol/L; calculating the coating amount of the coating liquid according to the noble metal loading on the diffusion layer；

3) Preparing a conductive and catalytic coating: the coating liquid needs to be coated and sintered for 5-8 times, after each coating, the coating liquid is sintered for 5-30 min at 400-500 ℃ in a muffle furnace, and after the last coating, the coating liquid is sintered for 10-30 min. The bonding force between the coating and the substrate is poor easily caused by too few times of sintering, and the metal oxide is highly crystallized easily caused by too many times of sintering, so that the conductivity is reduced.

The invention also provides an application of the anode diffusion layer of the PEM water electrolysis cell, the titanium fiber felt anode diffusion layer prepared by the invention can be applied to a PEM water electrolysis hydrogen production electrolytic cell, has good conductivity, stable catalytic performance and stable mechanical strength, and can adapt to a high current density running ring of PEM water electrolysis.

Advantageous effects

(1) The invention prepares a protective layer with catalytic performance and conductive performance on the titanium fiber felt by using a coating-roasting reduction method with simple operation and equipment, the titanium fiber felt has high porosity and low thickness, the wire diameter is less than 100 microns, and the titanium fiber felt is a titanium material with a structure which is very favorable for gas-liquid mass transfer of an anode of a PEM electrolytic cell.

(2) After the isopropanol system is effectively doped with tantalum, grain-oriented growth occurs on the surface of the coating, and the dispersity of iridium and ruthenium is improved under the condition that the resistivity of the coating is not greatly increased, so that the catalytic activity is improved. The pretreatment and preparation process has little damage to the mechanical properties of the fibers in the titanium fiber felt, maintains the good mechanical properties of the whole and fiber structure of the titanium fiber felt, and avoids the pollution of a catalyst layer of a PEM electrolytic cell and a proton exchange membrane caused by the shedding of titanium ions due to fiber breakage.

(3) The protective coating of the catalytic diffusion layer is composed of three metal oxides, the aim of reducing cost and improving stability is achieved by doping ruthenium with better catalytic activity and cheaper price and tantalum with stronger stability, a platinum coating of the titanium diffusion layer in the traditional PEM electrolytic cell is saved, the coating with the catalytic action can catalyze electrode reaction, and the dosage of a catalyst in a catalyst layer is reduced.

(4) The catalytic diffusion layer is prepared by using the impregnation-roasting method, the impregnation-roasting method is simple in operation method, and the oxide layer on the surface of the titanium fiber felt substrate is completely removed, so that the substrate and the coating form a solid solution structure in the roasting process, and the stability is greatly improved. In conclusion, the diffusion layer prepared by the method has the advantages of good chemical stability, high conductivity and catalytic activity, and is very suitable for being applied to a PEM electrolytic cell.

Drawings

FIG. 1 is a scanning electron microscope image of a titanium fiber mat before (a) and after (b) etching with concentrated hydrochloric acid.

FIG. 2 is a scanning electron microscope image of the catalytic diffusion layer prepared in comparative example 2 and example 1, wherein (a) is comparative example 2; (b) example 1 was used.

Fig. 3 is a graph showing contact resistance between the catalytic diffusion layer and the metal bipolar plate body prepared in comparative example 1, comparative example 2 and example 1 as a function of pressure.

Fig. 4 is a life test chart of the catalytic diffusion layers prepared in comparative example 1, comparative example 2 and example 1.

FIG. 5 is an assembly of 5cm of catalytic diffusion layers prepared in comparative example 1, comparative example 2 and example 1²Cell steady state polarization profile.

FIG. 6 is an assembly of 5cm of catalytic diffusion layers prepared in comparative example 1, comparative example 2 and example 1²Electrolytic cell AC impedance spectrogram.

Detailed Description

Comparative example 1

Commercial platinized porous titanium plates 2 x 2.5mm thick 0.6mm with a porosity of 30% were cut.

Comparative example 2

Test specimens (27X 22) mm in size were cut from commercial titanium fiber mats and washed in absolute ethanol and deionized water in this order. And then placing the mixture in 35% HCl at 53 ℃ for 5min, taking out the mixture, washing the mixture by using a large amount of deionized water, and ultrasonically cleaning the mixture by using absolute ethyl alcohol and deionized water again. 54.53mg of 37% chloroiridic acid, 12.82mg of 35.5% RuCl were weighed out₃And putting the coating solution into a 5mL volumetric flask, and preparing a coating solution with the volume constant by taking isopropanol as a solvent to obtain the coating solution with the total noble metal amount of 0.03mol/L, wherein the iridium-ruthenium atomic ratio is 7: 3. according to the total loading of the noble metal of 1mg/cm²The calculated coating liquid amount is 0.03603mmol, the total amount is 1.200mL, and the coating liquid is dripped on the surface of the titanium fiber felt by a liquid transfer machine for 6 times, and each dripping is connectedAnd roasting the mixture in a muffle furnace at 455 ℃ for 10min, and roasting for the last time for 30 min. The resulting diffusion layer was designated as comparative example 2.

Example 1

Test specimens (27X 22) mm in size were cut from commercial titanium fiber mats and ultrasonically cleaned in absolute ethanol and deionized water in this order. And then placing the mixture in 35% HCl at 53 ℃ for 5min, taking out the mixture, washing the mixture by using a large amount of deionized water, and ultrasonically cleaning the mixture by using absolute ethyl alcohol and deionized water again. 89.55mg of TaCl was weighed out₅Putting the powder into a 5mL volumetric flask, taking isopropanol as a solvent to fix the volume, and performing ultrasonic treatment until TaCl is obtained₅All dissolved to obtain 0.05mol/L TaCl₅And (3) solution. 54.53mg of 37% chloroiridic acid, 12.82mg of 35.5% RuCl were weighed out₃Put into a 5mL volumetric flask, 0.8571mL of 0.05mol/L TaCl was added₅The solution is prepared into coating liquid with the total noble metal amount of 0.03mol/L by taking isopropanol as a solvent for constant volume, wherein the iridium-ruthenium atomic ratio is 7: iridium ruthenium, tantalum, atomic ratio 4.9:2.1: 3. according to the total loading of the noble metal of 1mg/cm²The coating liquid amount is calculated to be 0.03603mmol, 1.200mL in total, the coating liquid is dripped on the surface of the titanium fiber felt by a pipette for 6 times, after each dripping is finished, the titanium fiber felt is placed in a muffle furnace to be roasted at 455 ℃ for 10min, and the final roasting is carried out for 30 min. The resulting diffusion layer is denoted as example 1.

FIG. 1 is a scanning electron microscope image of the titanium fiber mat before (a) and after (b) etching with concentrated hydrochloric acid, from which it can be seen that uniform and fine cracks appear on the surface of the titanium fiber after etching with concentrated hydrochloric acid, and the mechanical strength of the titanium fiber mat is not affected.

FIG. 2 is a scanning electron microscope image of the catalytic diffusion layer prepared in comparative example 2 and example 1, wherein (a) is comparative example 2; (b) example 1 was used; the addition of metallic tantalum in example 1 resulted in a large amount of grain-oriented growth on the surface of example 1 compared to the surface of the sample without tantalum (comparative example 2), indicating that the addition of tantalum increases the iridium ruthenium dispersion and OER catalytic activity.

Fig. 3 is a graph showing the change of contact resistance with pressure between the platinum-plated porous sintered titanium plate of comparative example 1, the catalytic diffusion layer prepared in comparative example 2 and the metallic bipolar plate body of example 1, and it can be seen that the tantalum-doped coated titanium fiber felt prepared in example 1 has a small increase in resistance.

Fig. 4 is a comparative graph of accelerated life tests conducted on the platinum-plated porous sintered titanium plate of comparative example 1, the catalytic diffusion layers prepared in comparative example 2 and example 1. Cutting the sample to 1cm²Sized and clamped with an electrode clamp at 1mol/L H₂SO₄Is electrolyte, graphite electrode is cathode, electrode distance is 2cm, constant current is 4000mA/cm²And (4) operating, and recording the time from the initial voltage to the great increase of the voltage. The lifetime of example 1 is much higher than that of comparative examples 1 and 2, which shows that the coating lifetime can be greatly improved after tantalum is doped.

FIG. 5 is an assembly of 5cm of the platinum-plated porous sintered titanium plate of comparative example 1, the catalytic diffusion layers prepared of comparative example 2 and example 1²Steady state polarization curve diagram of electrolytic cell, anode catalyst is 1mg/cm²Ir black, cathode catalyst 0.4mgPt/cm ²70% Pt/C, the proton exchange membrane is Nafion 115 membrane, and the test temperature is 80 ℃. The titanium fiber felt diffusion layers prepared in the comparative example 2 and the example 1 have OER catalytic activity, and the thickness is lower, so that gas-liquid mass transfer is facilitated, and the performance in a PEM electrolytic cell is better than that in the comparative example 1. Example 1 performed similarly to comparative example 2, indicating that the incorporation of tantalum did not affect performance in PEM electrolyzers.

FIG. 6 is a 5cm assembly of the Pt-coated porous sintered titanium plate of comparative example 1, the catalytic diffusion layers prepared in comparative example 2 and example 1²The test temperature of an electrolytic cell alternating current impedance spectrogram is 80 ℃, the test voltage is 1.45V, and the test frequency range is 0.1 Hz-100000 Hz. The points in the graph are experimental values and the lines are fitted values. Comparative example 2 has a charge transfer resistance similar to that of example 1 and lower than that of comparative example 1, again indicating that the incorporation of tantalum has no significant effect on the PEM electrolyser.

Claims

1. A PEM water electrolysis cell catalytic diffusion layer is characterized by comprising a diffusion layer and a protective coating; the diffusion layer is a titanium fiber felt; the protective coating is a mixed oxide coating of iridium oxide, ruthenium oxide and tantalum oxide;

the thickness of the titanium fibrofelt is 0.2-1.5 mm, and the total load of metal iridium and ruthenium in the protective coating is 0.5-2 mg cm^-2In the protective coating, the molar ratio of tantalum is 20-40%, and the molar ratio of metal iridium to metal ruthenium is 6: 4-9: 1.

2. A method of making a catalytic diffusion layer for a PEM water electrolyser as claimed in claim 1, comprising the steps of:

(1) corroding the titanium fibrofelt for 3-10 minutes at 50-70 ℃ by using hydrochloric acid with the concentration of 30-38 wt%, and washing;

(2) mixing an iridium precursor, a ruthenium precursor and a tantalum precursor with isopropanol to obtain a coating liquid; in the coating liquid, the total concentration of the iridium metal and the ruthenium metal is 0.02-0.035 mol/L, and the concentration of the tantalum metal is 0.003-0.015 mol/L;

(3) coating the coating liquid on the titanium fiber felt treated in the step (1), drying and roasting;

(4) and (4) repeating the step (3) to obtain the catalytic diffusion layer of the PEM water electrolysis cell.

3. The production method according to claim 2, wherein the iridium precursor is chloroiridic acid; RuCl as ruthenium precursor₃(ii) a The tantalum precursor is TaCl₅。

4. The method according to claim 2, wherein the baking is performed at 400 to 500 ℃ for 5 to 30min in an air atmosphere.

5. The method according to claim 2, wherein the step (4) is repeated 5 to 8 times in the step (3).

6. Use of a catalytic diffusion layer according to claim 1 in PEM water electrolysers.

7. The use according to claim 6, wherein the catalytic diffusion layer is used in a PEM water electrolysis hydrogen production electrolytic cell.