An electrolyzed water catalyst and its preparation method

Abstract

The present invention belongs to the field of electrochemistry technology, and particularly relates to an electrolytic water catalyst and a preparation method thereof. The electrolytic water catalyst of the present invention comprises a substrate and a bimetal supported thereon. The substrate is IrO2, and the bimetal supported on the substrate is Fe and Cu. The molar ratio of IrO2 to the bimetal is 1:20 to 1:5, and the atomic ratio of Fe / Cu is 1 / 10 to 10 / 1. The electrolytic water catalyst of the present invention uses IrO2 as a noble metal supported substrate, which has good electrochemical activity, and its excellent acid and alkali resistance improves the durability of the catalyst. The colloid method is adopted. By adjusting the pH and in a certain reaction temperature environment, Fe and Cu are introduced to replace part of the positions of Ir, changing the electronic structure of IrO2, introducing defects as active sites to promote the electrocatalytic reaction. The transition bimetals Fe and Cu are uniformly crystallized and grown on IrO2, reducing the consumption of noble metals. While reducing the cost of the catalyst, it can also improve the activity of the catalyst.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemistry, and particularly relates to an electrolyzed water catalyst and a preparation method thereof. Background Art

[0002] Hydrogen is known as the most promising energy carrier in the 21st century. Using renewable energy sources such as solar energy and wind energy, electrolyzed water to produce hydrogen is a relatively effective hydrogen production technology.

[0003] In principle, the structure of a PEM water electrolysis device is similar to that of a PEM fuel cell, but they operate in different ways. During the operation of a PEM fuel cell, oxygen reduction occurs at the cathode of the fuel cell, and hydrogen oxidation occurs at the anode. In short, water is generated and current is produced.

[0004] In PEM water electrolysis, the current and electrodes are reversed, and water decomposition occurs. Oxygen is released at the anode (abbreviated as "OBR" - oxygen evolution reaction), and proton reduction occurs at the cathode (abbreviated as "HER" - hydrogen evolution reaction), where protons migrate through the polymer electrolyte membrane. Therefore, water is decomposed into hydrogen and oxygen by means of an electric current.

[0005] A PEM water electrolysis device usually includes a polymer electrolyte membrane (such as Nafion@ of Dupont Company), which is sandwiched between a pair of electrode layers and is respectively installed between a pair of porous current collectors (or gas diffusion layers) on both sides of the electrode layers.

[0006] In a PEM water electrolysis device, a platinum / carbon catalyst is used as the anode electrocatalyst (for hydrogen oxidation) and the cathode electrocatalyst (for oxygen reduction). In a PEM water electrolysis device, a gas diffusion layer made of a carbon-based material (such as a platinum / carbon catalyst and a carbon fiber-based material) cannot be used on the anode side because carbon is corroded by the oxygen released during the process of water electrolysis.

[0007] Among all noble metals, platinum is the most active catalyst for the hydrogen evolution reaction (HER) at the cathode and can be applied at a medium loading. Regarding the oxygen evolution process, the unique electrocatalytic properties of iridium and iridium oxide are well-known. Therefore, for the oxygen evolution reaction (OER) at the anode, a higher proportion of iridium metal is beneficial. However, for some occasions, other noble metal oxides (preferably ruthenium or platinum oxides) can be added.

[0008] Currently, the IrO2 catalysts prepared by methods such as the colloid method, precipitation method, and melting method generally have the problem of a relatively high starting potential. Summary of the Invention

[0009] The object of the present invention is to overcome the deficiencies existing in the prior art and provide an electrolyzed water catalyst and a preparation method thereof. The electrolyzed water catalyst of the present invention uses precious metal oxide IrO₂ as the matrix, and the matrix is loaded with bimetals Fe and Cu. It can not only reduce the consumption of precious metals, but also introduce defects by using transition metal ions to form more active sites. The prepared catalyst can reduce the starting potential, making the PEM electrolysis device have higher stability and durability.

[0010] To achieve the above technical objectives, the technical solutions adopted in the embodiments of the present invention are as follows:

[0011] In the first aspect, the embodiments of the present invention provide an electrolyzed water catalyst, including a matrix and the bimetals loaded thereon. The matrix is IrO₂, and the bimetals loaded on the matrix are Fe and Cu, wherein the molar ratio of IrO₂ to the bimetals is 1:20 to 1:5, and the atomic ratio of Fe / Cu is 1 / 10 to 10 / 1.

[0012] In the second aspect, the embodiments of the present invention provide a preparation method of an electrolyzed water catalyst, including the following steps:

[0013] (1) Material weighing: Weigh polyvinylpyrrolidone, ferric nitrate, and copper nitrate according to the molar ratio of 5 to 1:1 to 10:1 to 10 respectively;

[0014] (2) Introduction of surfactant: Dissolve the polyvinylpyrrolidone weighed in step (1) in deionized water and stir for 0.5 to 1 h;

[0015] (3) Bimetal feeding: Add the ferric nitrate and copper nitrate weighed in step (1) to deionized water respectively, and stir at room temperature for 1 to 12 h to form a mixed solution;

[0016] (4) Weighing of IrO₂ material: Weigh IrO₂ according to the mass ratio of (ferric nitrate + copper nitrate) / (IrO₂ + ferric nitrate + copper nitrate) of 0.05 to 0.5;

[0017] (5) Adjusting pH: Adjust the pH of the mixed solution described in step (3) to pH = 11 to 13;

[0018] (6) Loading of Fe-Cu / IrO₂: Add the IrO₂ weighed in step (4) to the solution in step (5), and place it in an ultrasonic cleaner and ultrasonicate for 0.5 to 3 h;

[0019] (7) Providing an element doping environment: Transfer the solution in step (6) to a water bath and stir;

[0020] (8) Precipitation after element substitution: Adjust the pH of the solution in step (7) to pH = 6 to 8 to form a precipitate;

[0021] (9) Removal of surfactant and impurity ions: The substances and impurity ions that did not participate in the reaction in the precipitate described in step (8) were removed by centrifugally washing the solid sample.

[0022] (10) Drying of the catalyst: The solid sample after washing in step (9) was dried and cooled in the furnace to obtain an electrolytic water catalyst.

[0023] Further, the specific surface area of IrO2 described in step (4) is 50 - 200 m 2 / g.

[0024] Further, a 0.1 - 1 M NaOH solution was added in step (5) to adjust the pH value of the mixed solution.

[0025] Further, the temperature of the water bath in step (7) is 60 - 95 °C, and the reaction time is 2 - 24 h.

[0026] Further, a 0.1 - 1 M dilute nitric acid solution was added in step (8) to adjust the pH value of the solution.

[0027] Further, the solvent used for washing the solid sample in step (9) is one or more of deionized water, n-butanol, and absolute ethanol, and the number of washing times is 5 - 12 times.

[0028] Further, the drying temperature in step (10) is 50 - 120 °C, and the vacuum drying time is 8 - 24 h.

[0029] The beneficial effects brought by the technical solution provided by the embodiment of the present invention are as follows:

[0030] (1) The electrolytic water catalyst of the present invention improves the existing iridium oxide preparation process, introduces two low-cost transition metals Fe and Cu for modification doping in the catalyst, and can improve the electrochemical activity of the catalyst while reducing the amount of precious metals used.

[0031] (2) The electrolytic water catalyst of the present invention conducts element doping by the colloid method to form impurity energy levels, forms oxygen vacancies by introducing defects, and optimizes the electron path and proton path to improve the electrochemical activity.

[0032] (3) The electrolytic water catalyst of the present invention uses IrO2 as the precious metal loading matrix, has good electrochemical activity, and its excellent acid and alkali resistance improves the durability of the catalyst; by using the colloid method, by adjusting the pH, in a certain reaction temperature environment, Fe and Cu are introduced to replace part of the Ir positions, changing the electronic structure of IrO2, introducing defects as active sites to promote the electrocatalytic reaction, and the transition bimetals Fe and Cu are uniformly crystallized and grown on IrO2, reducing the amount of precious metals used, and can improve the activity of the catalyst while reducing the cost of the catalyst.

[0033] (4) The electrolyzed water catalyst of the present invention uses iridium oxide as the matrix material. Iridium oxide is used as the anode catalyst in the PEM electrolysis device and has a very low oxygen overpressure (i.e., a low starting potential for oxygen release) during the electrolysis of water, resulting in a lower specific energy consumption for producing hydrogen per unit volume. Therefore, at a given electrolytic cell voltage, there is a higher hydrogen production rate. Doping a little conductive metals Fe and Cu on the catalyst surface can enable water electrolysis at a lower voltage than traditional iridium oxide-based catalysts. Detailed implementation mode

[0034] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0035] Embodiment 1

[0036] A preparation method of an electrolyzed water catalyst includes the following steps:

[0037] (1) Weighing of materials: Weigh polyvinylpyrrolidone, ferric nitrate and cupric nitrate respectively according to the molar ratio of 1:0.5:0.5;

[0038] (2) Introduction of surfactant: Dissolve the surfactant polyvinylpyrrolidone in step (1) in deionized water and stir for 0.5 h;

[0039] (3) Feeding of double transition metal elements Fe and Cu: Add the ferric nitrate and cupric nitrate weighed in step (1) into deionized water respectively, and stir for 1 h at room temperature to form a mixed solution;

[0040] (4) Weighing of IrO2 material: Take IrO2 with a specific surface area of 49.8 m 2 / g, and weigh IrO2 according to the mass ratio of (ferric nitrate + cupric nitrate) / (IrO2 + ferric nitrate + cupric nitrate) being 0.1;

[0041] (5) Adjusting pH: Add 1 M NaOH solution to the mixed solution in step (3) to adjust the pH of the mixed solution to 13;

[0042] (6) Loading of Fe-Cu / IrO2: Add the IrO2 weighed in step (4) to the solution in step (5), and place it in an ultrasonic cleaner and ultrasonicate for 1 h;

[0043] (7) Providing an element doping environment: Transfer the solution in step (6) to a water bath at 80 °C and stir for 12 h;

[0044] (8)Precipitation after element substitution: Add 1 M dilute nitric acid solution to the solution after stirring in step (7), adjust the pH of the solution to 6 to form a precipitate;

[0045] (9)Removal of surfactant and impurity ions: Use the method of centrifugally washing the solid sample to remove the unreacted substances and impurity ions in the precipitate obtained in step (8), and alternately wash 3 times with absolute ethanol and deionized water, and retain the solid part;

[0046] (10)Catalyst drying: After vacuum drying the washed solid sample in step (9) at 120 °C for 12 h, cool it with the furnace to obtain the electrolytic water catalyst.

[0047] Example 2

[0048] A preparation method of an electrolytic water catalyst, comprising the following steps:

[0049] (1)Weighing of materials: Weigh polyvinylpyrrolidone, iron nitrate and copper nitrate at a molar ratio of 1:0.2:0.2 respectively;

[0050] (2)Introduction of surfactant: Dissolve the surfactant polyvinylpyrrolidone in step (1) in deionized water and stir for 1 h;

[0051] (3)Feeding of double transition metal elements Fe and Cu: Add iron nitrate and copper nitrate in step (1) to deionized water respectively, and stir for 4 h at room temperature to form a mixed solution;

[0052] Loading of Fe-Cu / IrO2

[0053] (4)Weighing of IrO2 material: Weigh IrO2 at a mass ratio of (iron nitrate + copper nitrate) / (IrO2 + iron nitrate + copper nitrate) of 0.5;

[0054] (5)Adjusting pH: Add 0.2 M NaOH solution to the mixed solution in step (3), and adjust the pH of the mixed solution to 11;

[0055] (6)Loading of Fe-Cu / IrO2: Add IrO2 with a specific surface area of 77.2 m 2 / g to the solution in step (5), and place it in an ultrasonic cleaner and sonicate for 3 h;

[0056] (7)Providing an element doping environment: Transfer the solution in step (6) to a water bath at 95 °C and stir for 6 h;

[0057] (8)Precipitation after element substitution: Add 0.1 M dilute nitric acid solution to the solution after stirring in step (7), adjust the pH of the solution to 8 to form a precipitate;

[0058] (9) Removal of surfactant and impurity ions: The substances and impurity ions that did not participate in the reaction in the precipitate obtained in step (8) were removed by centrifugally washing the solid sample, and it was alternately washed 3 times with n-butanol and deionized water, and the solid part was retained;

[0059] (10) Drying of the catalyst: The solid part in step (9) was vacuum dried at 80 °C for 8 h and then cooled in the furnace to obtain the electrolyzed water catalyst.

[0060] Example 3

[0061] A preparation method of an electrolyzed water catalyst includes the following steps:

[0062] (1) Weighing of materials: Polyvinylpyrrolidone, ferric nitrate and copper nitrate were weighed respectively according to a molar ratio of 1:0.3:0.1;

[0063] (2) Introduction of surfactant: The surfactant polyvinylpyrrolidone in step (1) was dissolved in deionized water and stirred for 1 h;

[0064] (3) Feeding of double transition metal elements Fe and Cu: Ferric nitrate and copper nitrate in step (1) were respectively added to deionized water, and after stirring at room temperature for 1 h, a mixed solution was formed;

[0065] Loading of Fe-Cu / IrO2

[0066] (4) Weighing of IrO2 materials: IrO2 was weighed according to a mass ratio of (ferric nitrate + copper nitrate) / (IrO2 + ferric nitrate + copper nitrate) of 0.15;

[0067] (5) Adjusting pH: 0.5 M NaOH solution was added to the mixed solution in step (3) to adjust the pH of the mixed solution to 13;

[0068] (6) Loading of Fe-Cu / IrO2: IrO2 with a specific surface area of 138.1 m 2 / g was added to the solution in step (5), and it was placed in an ultrasonic cleaner and ultrasonicated for 2 h;

[0069] (7) Providing the element doping environment: The solution in step (6) was transferred to a water bath at 60 °C and stirred for 24 h;

[0070] (8) Precipitation after element substitution: 0.2 M dilute nitric acid solution was added to the solution stirred in step (7) to adjust the pH of the solution to 7 to form a precipitate;

[0071] (9) Removal of surfactant and impurity ions: The substances and impurity ions that did not participate in the reaction in the precipitate in step (8) were removed by centrifugally washing the solid sample, and it was washed 3 times with deionized water, and the solid part was retained;

[0072] (10) Catalyst drying: After vacuum drying the solid part in step (9) at 60 °C for 12 h, it is cooled with the furnace to obtain the electrolytic water catalyst.

[0073] Comparative Example 1

[0074] A preparation method of an electrolytic water catalyst includes the following steps:

[0075] (1) Weighing of materials: Weigh polyvinylpyrrolidone and iron nitrate respectively according to a molar ratio of 1:0.5;

[0076] (2) Introduction of surfactant: Dissolve the surfactant polyvinylpyrrolidone in step (1) in deionized water and stir for 1 h;

[0077] (3) Feeding of transition metal element Fe: Add the iron nitrate weighed in step (1) to deionized water, and stir for 1 h at room temperature to form a mixed solution;

[0078] Loading of Fe / IrO2

[0079] (4) Weighing of IrO2 material: Weigh IrO2 according to a mass ratio of iron nitrate / (IrO2 + iron nitrate) of 0.1;

[0080] (5) Adjusting pH: Add 1 M NaOH solution to the mixed solution in step (3) to adjust the pH of the mixed solution to 13;

[0081] (6) Loading of Fe / IrO2: Add IrO2 with a specific surface area of 49.8 m 2 / g to the solution in step (5), and place it in an ultrasonic cleaner and ultrasonicate for 1 h;

[0082] (7) Providing the element doping environment: Transfer the solution in step (6) to a water bath at 60 °C and stir for 6 h;

[0083] (8) Precipitation after element substitution: Add 0.2 M dilute nitric acid solution to the solution after stirring in step (7) to adjust the pH of the solution to 7 and form a precipitate;

[0084] (9) Removal of surfactant and impurity ions: Use the method of centrifuging and washing the solid sample to remove the substances and impurity ions that did not participate in the reaction in the precipitate in step (8), wash 3 times with deionized water, and retain the solid part;

[0085] (10) Catalyst drying: After vacuum drying the solid part in step (9) at 60 °C for 12 h, it is cooled with the furnace to obtain the electrolytic water catalyst.

[0086] Comparative Example 2

[0087] A preparation method of an electrolyzed water catalyst, comprising the following steps:

[0088] (1) Weighing of materials: Weigh polyvinylpyrrolidone and copper nitrate respectively at a molar ratio of 1:0.5;

[0089] (2) Introduction of surfactant: Dissolve the surfactant polyvinylpyrrolidone in step (1) in deionized water and stir for 1 h;

[0090] (3) Feeding of transition metal element Cu: Add the copper nitrate weighed in step (1) to deionized water, and stir for 1 h at room temperature to form a mixed solution;

[0091] Loading of Cu / IrO2

[0092] (4) Weighing of IrO2 materials: Weigh IrO2 at a mass ratio of copper nitrate / (IrO2 + copper nitrate) of 0.1;

[0093] (5) Adjusting pH: Add 1 M NaOH solution to the mixed solution in step (3) to adjust the pH of the mixed solution to 13;

[0094] (6) Loading of Cu / IrO2: Add IrO2 with a specific surface area of 49.8 m 2 / g to the solution in step (5), and place it in an ultrasonic cleaner and ultrasonicate for 1 h;

[0095] (7) Providing an element doping environment: Transfer the solution in step (6) to a water bath at 60 °C and stir for 6 h;

[0096] (8) Precipitation after element substitution: Add 0.2 M dilute nitric acid solution to the solution after stirring in step (7) to adjust the pH of the solution to 7 to form a precipitate;

[0097] (9) Removal of surfactant and impurity ions: Use the method of centrifuging and washing the solid sample to remove the substances and impurity ions that did not participate in the reaction in the precipitate in step (8), wash 3 times with deionized water, and retain the solid part;

[0098] (10) Drying of the catalyst: Vacuum-dry the solid part in step (9) at 60 °C for 12 h, and then cool it in the furnace to obtain the electrolyzed water catalyst.

[0099] Evaluate the catalytic activities of the catalysts prepared in Examples 1 to 3 and Comparative Examples 1 to 2

[0100] By measuring the initial potential of oxygen evolution (in volts) and the current density (in mA / cm 2 at 1.5 V with respect to NHE (in mA / mg)The electrochemical properties of the catalyst materials were measured by cyclic voltammetry. In these experiments, the catalyst samples were dispersed in an aqueous isopropanol solution of 5 wt% Nafion@ (Aldrich), and then fixed on a glassy carbon electrode to form a working electrode. Cyclic voltammograms were obtained in a sulfuric acid electrolyte with a concentration of 0.5 mol / L at room temperature (25 °C). The counter electrode was a platinum wire, the reference electrode was Ag / AgCl, the scanning rate was 50 mV / s, and the 5th scan of the voltammogram was taken.

[0101] Two parameters were used to determine the electrochemically active area: (1) the onset potential of oxygen evolution; (2) the current density against the standard hydrogen electrode at a constant voltage. The test results are shown in Table 1.

[0102] Table 1 Activity evaluation results of the catalysts prepared in Examples 1-3 and Comparative Examples 1-2

[0103]

[0104] As can be seen from Table 1, in Comparative Example 1 and Comparative Example 2, a single impurity ion (Fe or Cu) was introduced to change the electronic structure of the IrO2 matrix, achieving similar electrochemical properties. In Examples 1-3, different ratios of bimetallic Fe and Cu were co-doped into the IrO2 matrix. There was a synergistic effect between the bimetallic Fe and Cu. At the same doping amount, the simultaneous introduction of Fe and Cu significantly reduced the onset potential of the catalyst and had a higher current density at the same voltage, indicating that the electrochemical performance of the catalyst was improved.

[0105] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the examples, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing an electrolyzed water catalyst, characterized in that, The electrolyzed water catalyst includes a substrate and a bimetal supported thereon. The substrate is IrO2, and the bimetal supported on the substrate is Fe and Cu. The molar ratio of IrO2 to the bimetal is 1:20 to 1:5, and the atomic ratio of Fe / Cu is 1 / 10 to 10 / 1; The preparation method of the electrolyzed water catalyst includes the following steps: (1) Material weighing: Weigh polyvinylpyrrolidone, iron nitrate, and copper nitrate according to a molar ratio of 5 to 1:1 to 10:1 to 10 respectively; (2) Introduction of surfactant: Dissolve the polyvinylpyrrolidone weighed in step (1) in deionized water and stir for 0.5 to 1 h; (3) Bimetal feeding: Add the iron nitrate and copper nitrate weighed in step (1) to deionized water respectively, and stir at room temperature for 1 to 12 h to form a mixed solution; (4) Weighing of IrO2 material: Weigh IrO2 according to a mass ratio of (iron nitrate + copper nitrate) / (IrO2 + iron nitrate + copper nitrate) of 0.05 to 0.5; (5) Adjusting pH: Adjust the pH of the mixed solution described in step (3) to 11 to 13; (6) Loading of Fe-Cu / IrO2: Add the IrO2 weighed in step (4) to the solution in step (5), and place it in an ultrasonic cleaner for ultrasonic treatment for 0.5 to 3 h; (7) Providing an element doping environment: Transfer the solution in step (6) to a water bath and stir; (8) Precipitation after element substitution: Adjust the pH of the solution in step (7) to 6 to 8 to form a precipitate; (9) Removal of surfactant and impurity ions: Remove the substances and impurity ions that did not participate in the reaction in the precipitate described in step (8) by centrifugally washing the solid sample; (10) Drying of the catalyst: Dry the solid sample washed in step (9) and cool it in the furnace to obtain the electrolyzed water catalyst.

2. The method for preparing an electrolyzed water catalyst according to claim 1, characterized in that, The specific surface area of IrO2 described in step (4) is 50 to 200 m 2 / g.

3. The method for preparing an electrolyzed water catalyst according to claim 1, characterized in that, In step (5), a 0.1 to 1 M NaOH solution is added to adjust the pH value of the mixed solution.

4. The method for preparing an electrolyzed water catalyst according to claim 1, characterized in that, In step (7), the temperature of the water bath is 60 to 95 °C, and the reaction time is 2 to 24 h.

5. The method for preparing an electrolyzed water catalyst according to claim 1, characterized in that, In step (8), a 0.1 to 1 M dilute nitric acid solution is added to adjust the pH value of the solution.

6. The method for preparing an electrolyzed water catalyst according to claim 1, characterized in that, In step (9), the solvent used for washing the solid sample is one or more of deionized water, n-butanol, and absolute ethanol, and the number of washing times is 5 to 12 times.

7. The method for preparing an electrolyzed water catalyst according to claim 1, characterized in that, In step (10), the drying temperature is 50 to 120 °C, and the vacuum drying time is 8 to 24 h.

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