Preparation method of low overpotential anode and application thereof in electrocatalytic water splitting for oxygen evolution

Abstract

The application relates to the field of electrochemistry and discloses a preparation method of a low-overpotential anode and application of the low-overpotential anode in electrocatalytic water splitting and oxygen evolution. The preparation method comprises the following steps: 1) loading molybdenum metal on foamed nickel after acid pickling pretreatment; 2) immersing the foamed nickel molybdenum in a soaking solution containing uranium and / or thorium metal salt and iron salt to carry out a displacement reaction, and taking out and drying; and 3) oxygen calcining the product obtained in the step 2) at 100-200 DEG C for 0.5-1.5 h to obtain the low-overpotential anode. The anode prepared by the application is foamed nickel as a carrier, after loading molybdenum metal, uranium and / or thorium and iron elements are deposited on the carrier through a displacement reaction between elements, and finally the interaction between the deposited elements and the carrier is strengthened through calcining, and the metal elements in the carrier form corresponding oxides. The anode is applied to electrocatalytic splitting of alkaline water or alkaline seawater and oxygen evolution, and has reduced overpotential and strong stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrochemistry, in particular to a preparation method of a low overpotential anode and its application in electrocatalytic water splitting to generate oxygen. BACKGROUND

[0002] With the increasing demand for renewable energy and the growing severity of environmental problems worldwide, it is particularly urgent to develop efficient and sustainable energy conversion technologies. Electrolysis of water to produce hydrogen as a clean and efficient way of hydrogen production is gradually becoming a research hotspot. However, the oxygen evolution reaction (OER) in the process of electrolysis of water often becomes a key kinetic limiting step due to its complex four-electron transfer process, and its efficiency directly affects the overall water splitting performance. Traditionally, OER electrocatalysts rely on noble metals such as iridium, ruthenium, etc., but these materials are not only high in cost, but also scarce in resources, limiting their large-scale application. Therefore, developing efficient, stable and low-cost non-noble metal electrocatalysts has become an urgent need for current research.

[0003] In recent years, multi-metal oxides have shown great potential in the field of OER catalysis due to their adjustable electronic structure, rich catalytic active sites and good stability. Researchers have continuously improved the catalytic performance of multi-metal oxides by adjusting the metal composition and optimizing the material structure. However, how to further reduce the cost of the catalyst while ensuring the catalytic activity is still an important direction for current research. SUMMARY

[0004] To solve the above technical problems, the present application provides a preparation method of a low overpotential anode and its application in electrocatalytic water splitting to generate oxygen. The anode prepared by the present application uses foam nickel loaded with molybdenum metal as the carrier, and then through the displacement reaction between elements, uranium and / or thorium and iron elements are deposited on the carrier. Finally, through calcination, the interaction between the deposited elements and the carrier is strengthened and the metal elements form corresponding oxides. When used as an anode for electrocatalytic splitting of alkaline water or alkaline seawater to generate oxygen, it has a reduced overpotential and strong stability.

[0005] The specific technical solutions of the present application are as follows:

[0006] Firstly, the present application provides a preparation method of a low overpotential anode, comprising the following steps:

[0007] 1) The foam nickel is pretreated by acid pickling, and then loaded with molybdenum metal to obtain foam nickel molybdenum.

[0008] 2) The foam nickel molybdenum is immersed in a soaking solution containing uranium and / or thorium metal salt and iron salt for displacement reaction, and then taken out and dried.

[0009] 3) oxygen calcining the product obtained in step 2) to obtain a low overpotential anode.

[0010] The anode prepared by the method of the present application uses foamed nickel-molybdenum as the carrier, and through the displacement reaction between elements, uranium and / or thorium and iron elements are deposited on the carrier, and finally through calcination, the interaction between the deposited elements and the carrier is strengthened and the metal elements therein form corresponding oxides.

[0011] The present application finds that the above-mentioned material, when used as an anode for electrocatalytic splitting of alkaline water or alkaline seawater to produce oxygen, has a reduced overpotential and strong stability. The reason is that the interaction between the above-mentioned four specific metal elements can promote the movement of d-band electrons to a low energy level, increase the degree of overlap between the metal 3d orbital and the oxygen 2p orbital, and promote the orbital hybridization between them. The enhancement of this orbital hybridization effect not only strengthens the transfer ability of electrons between the metal and oxygen, but also significantly weakens the original strong metal-oxygen bond, so that the covalent bond between the lattice oxygen and the metal in the anode material is weakened and becomes more active, thereby improving the catalytic efficiency of the anode in the electrocatalytic reaction. In addition, through the small amount of nuclear radiation of uranium and / or thorium, water molecules can be pre-activated and placed in a state of easy dissociation, further reducing the activation energy required for hydrogen evolution.

[0012] In addition, the present application also finds that the ratio of uranium and / or thorium to iron and the calcination conditions are crucial to the performance of the anode. Specifically:

[0013] The present application preferably has a molar ratio of uranium and / or thorium to iron of 1:10-15. Different ratios of uranium and / or thorium to iron have a greater impact on the performance of the electrode material. Taking uranium as an example, the presence of uranium elements pre-activates water molecules and promotes their dissociation. The addition of iron elements enhances the interaction between metals, thereby significantly improving the electrocatalytic performance. Excessive iron elements will cover the active sites of the reaction, affecting the adsorption of water molecules, and thus inhibiting the performance.

[0014] The present application preferably has a calcination temperature of 100-200 o C and a time of 0.5-1.5 h. Different calcination temperatures significantly affect the electrocatalytic performance of the electrode material. When the calcination temperature is low, the metal oxidation on the material is not complete and cannot form a firm metal oxide; the present application finds that when the calcination temperature exceeds 200 o C, the carrier is damaged at too high a temperature and cannot maintain the basic structure, resulting in a decrease in performance.

[0015] Further, in step 1), the method for foamed nickel to load molybdenum elements includes immersion displacement method, electroplating method or high-temperature reduction method, and the immersion displacement method is further preferred. The mass ratio of nickel to molybdenum is 3-8:1.

[0016] Further, in step 1), the thickness of the nickel foam is 1-2 mm, the pore size is 80-150 ppi, and the area range is 0.0001-10 m 2 . More preferably, the area range of the nickel foam is 0.02-0.1 m 2 ;

[0017] Further, in step 1), the pickling specifically comprises: placing the nickel foam into a dilute hydrochloric acid solution with a concentration of 0.5-1.5 mol·L -1 for ultrasonic cleaning for 20-40 min, and then taking it out and immersing it into anhydrous ethanol for ultrasonic cleaning for 20-40 min, and drying.

[0018] Further, in step 2), the uranium and / or thorium metal salt is uranyl nitrate hexahydrate or thorium nitrate hydrate; and the iron salt is one or more of ferric sulfate, ferric nitrate and ferric chloride.

[0019] Further, in step 2), the content of iron in the soaking solution is 0.05-0.2 mol·L -1 ; and the ratio of the area of the nickel foam to the amount of the soaking solution is 0.8-5 cm -2 / ml.

[0020] Further, in step 2), the time of the displacement reaction is 10-60 min, and further preferably 30-50 min.

[0021] Secondly, the application provides the application of the low overpotential anode prepared by the above preparation method in electrocatalytic splitting of alkaline water or alkaline seawater to generate oxygen.

[0022] The anode prepared by the application exhibits excellent performance in the reaction of electrocatalytic water splitting to generate oxygen. The presence of multiple metals greatly promotes the dynamic reconstruction ability of the catalyst itself, significantly accelerating the formation process of high-valence nickel ions (Ni 3+ / Ni 4+ ). In the alkaline water electrolyte, a current density of 100 mA·cm -2 is reached, and the minimum overpotential required is 204 mV, which significantly reduces the energy consumption required. In addition, the anode also has excellent catalytic performance in the complex alkaline seawater electrolyte. A current density of 100 mA·cm -2 is reached, and the minimum overpotential required is 234 mV. The anode has good stability in alkaline water and alkaline seawater, and the current density only decreases by about 10% under continuous electrocatalytic oxygen evolution test for one week.

[0023] Further, the alkaline medium in the alkaline water or alkaline seawater electrolyte system is sodium hydroxide or potassium hydroxide.

[0024] Further, the concentration of the sodium hydroxide or potassium hydroxide is 10-50 wt%.

[0025] In comparison with the prior art, the present application has the following advantages:

[0026] (1) The anode prepared by the present application uses foamed nickel as the carrier, molybdenum is first loaded thereon, and then uranium and / or thorium and iron are deposited on the carrier by displacement reaction between the elements, and finally the interaction between the deposited elements and the carrier is strengthened by calcination, and the metal elements form corresponding oxides. The anode is applied to the electrocatalytic splitting of alkaline water or alkaline seawater to produce oxygen, and has a reduced overpotential and strong stability.

[0027] (2) The present application further improves the electrocatalytic performance of the anode by optimizing the ratio of uranium and / or thorium, iron and the calcination conditions.

[0028] (3) The present application provides an innovative method for utilizing and processing nuclear waste. The nuclear spent fuel after nuclear reaction is recovered to prepare an electrocatalytic anode, which can maximize the potential energy value contained in the waste and realize the recycling of resources. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 SEM image of the FeUNiMo quaternary electrode material prepared in Example 1 of the present application;

[0030] Figure 2 Activity test results of the electrocatalytic oxygen evolution electrode in Test Example 1 and Test Example 2;

[0031] Figure 3 The required overpotential of the electrocatalytic oxygen evolution electrode in Test Example 1 and Test Example 2 at 100 mA·cm -2

[0032] Figure 4 Activity test results of the electrocatalytic oxygen evolution electrode in Test Example 3;

[0033] Figure 5 Activity test results of the electrocatalytic oxygen evolution electrode in Test Example 4;

[0034] Figure 6 Activity test results of the electrocatalytic oxygen evolution electrode in Test Example 5;

[0035] Figure 7 Activity test results of the electrocatalytic oxygen evolution electrode in Test Example 6;

[0036] Figure 8 Stability test results of the electrocatalytic oxygen evolution electrode in Test Example 7;

[0037] Figure 9 ​Stability test results of the electrocatalytic oxygen evolution electrode in Test Example 8. DETAILED DESCRIPTION

[0038] The application will be further described in conjunction with examples. Example 1

[0039] The preparation process of the FeUNiMo (FUNM) quaternary electrode material is as follows:

[0040] Carrier pretreatment: the nickel foam with a pore size of 100 ppi, a thickness of 1.5 mm, and a size of 1*2 cm was placed in a 1 mol·L -1 -1 hydrochloric acid solution, taken out after ultrasonic cleaning for 30 minutes, and then placed in anhydrous ethanol for ultrasonic cleaning for 30 minutes and air-dried.

[0041] Molybdenum metal loading: the pretreated nickel foam was placed in a 50 ml, 0.5 mol·L -1 -1 sodium molybdate solution for electroplating, with an applied current of 0.5 mA·cm -1 -2 and an electroplating time of 5 minutes. After electroplating, the nickel foam loaded with molybdenum metal (i.e., nickel foam molybdenum) was obtained, with a mass ratio of nickel to molybdenum of 9:1.

[0042] Synthesis of the FeUNiMo quaternary electrode material: the nickel foam molybdenum was placed in a 10 ml soaking solution containing 0.0502 g uranyl nitrate hexahydrate (0.01 mol·L -1 ) and 0.404 g ferric nitrate nonahydrate (0.10 mol·L -1 ), taken out after standing for 40 minutes, placed in an oven, dried at 60 o C, then placed in a muffle furnace, heated to 200 o C at a heating rate of 5 o C / min, and kept at this temperature for 1 hour. After cooling to room temperature, the FeUNiMo catalytic electrode was obtained. Figure 1 The SEM image thereof shows that the surface is rough and a layer of displaced metal oxide is deposited, which is beneficial to the electrolysis reaction. Example 2

[0043] The preparation method is the same as that in Example 1, with the only difference being that the muffle furnace calcination was not performed. Example 3

[0044] The preparation method is the same as that in Example 1, with the only difference being that the muffle furnace calcination temperature is 100 o C. Example 4

[0045] The preparation method is the same as that in Example 1, with the only difference being that the muffle furnace calcination temperature is 300o C. Example 5

[0046] The preparation method is the same as Example 1, with the only difference being that the concentration of iron nitrate nonahydrate in the soaking solution is 0.05 mol·L -1 . Example 6

[0047] The preparation method is the same as Example 1, with the only difference being that the concentration of iron nitrate nonahydrate in the soaking solution is 0.15 mol·L -1 . Example 7

[0048] The preparation method is the same as Example 1, with the only difference being that the concentration of iron nitrate nonahydrate in the soaking solution is 0.20 mol·L -1 . Example 8

[0049] The preparation method is the same as Example 1, with the only difference being that the soaking time is 10 minutes. Example 9

[0050] The preparation method is the same as Example 1, with the only difference being that the soaking time is 20 minutes. Example 10

[0051] The preparation method is the same as Example 1, with the only difference being that the soaking time is 30 minutes. Example 11

[0052] The preparation method is the same as Example 1, with the only difference being that the soaking time is 50 minutes. Example 12

[0053] The preparation method is the same as Example 1, with the only difference being that the soaking time is 60 minutes. Example 13

[0054] The preparation method is the same as Example 1, with the only difference being that 0.0502 g of uranyl nitrate hexahydrate in the soaking solution is replaced with 0.0480 g of thorium nitrate hydrate (0.01 mol·L -1 ), and the resulting product is denoted as FTNM. Example 14

[0055] The preparation method is the same as Example 1, with the only difference being that the pretreated foam nickel is soaked in 25 ml of a sodium molybdate solution containing 0.05 mol·L -1 for 30 minutes, and after sufficient replacement, it is taken out and dried. The resulting product is denoted as FUNM-2, with a mass ratio of nickel to molybdenum of 9:1. Example 15

[0056] The preparation method is the same as that of Example 1, except that the immersion solution is ultrapure water containing no metal salt, and the obtained product is denoted as N. Example 16

[0057] The preparation method is the same as that of Example 1, except that the immersion solution contains only 0.0502 g of uranyl nitrate hexahydrate (0.01 mol·L -1 ), and the obtained product is denoted as UNM. Example 17

[0058] The preparation method is the same as that of Example 1, except that the immersion solution contains only 0.404 g of ferric nitrate nonahydrate (0.10 mol·L -1 ), and the obtained product is denoted as FNM. Example 18

[0059] The preparation method is the same as that of Example 1, except that the immersion solution is ultrapure water containing no metal salt, and the obtained product is denoted as NM.

[0060] Performance test

[0061] Test Example 1

[0062] The electrode materials prepared in Examples 1, 16-18 were subjected to linear sweep voltammetry test in 5 wt% KOH solution. The specific test used a saturated Ag / AgCl electrode as the reference electrode, a graphite electrode as the counter electrode, the scanning speed was 10 mV / s, and the electrolyte was 5 wt% KOH electrolyte. The electrode potential was subjected to iR correction to eliminate the influence caused by solution resistance, and was converted into the electrode potential relative to the reversible electrode (RHE), and the calculation formula was: overpotential (V) = electrode potential + pH*0.0591 + 0.1976-1.23. The obtained results are shown by the solid line in Figure 2 .

[0063] Figure 3 The overpotential of the four electrode materials when the current density reached 100 mA·cm -2 . As can be seen from Figure 3 , the quaternary electrode material has the best electrocatalytic water splitting performance. The overpotential is only 204 mV, and the catalytic performance of the ternary material is also better than that of the binary carrier. It shows that the addition of Fe and U promotes the catalytic electrode, and the coexistence of the two can further synergistically improve the catalytic performance. Due to the direct interaction between multiple metals and the interaction with the connecting oxygen, the metal d band center is lowered, the orbital hybridization between metal 3d and O 2p orbitals is enhanced, and the M-O mutual covalent interaction is enhanced. This enhancement effect can enhance the dynamic response of the self-reconstruction of the catalyst in the catalytic process, which is beneficial to the rapid activation of the OER performance following the lattice oxygen mechanism.

[0064] Test Example 2

[0065] The electrode materials prepared in Example 1, Example 16-18 were tested by linear sweep voltammetry in 5 wt% KOH seawater. The specific test method was as follows: the saturated Ag / AgCl electrode was used as the reference electrode, the graphite electrode was used as the counter electrode, the scanning rate was 10 mV / s, and the electrolyte was seawater with a concentration of 5 wt% KOH. The electrode potential was corrected by iR to eliminate the influence caused by solution resistance, and was converted into the electrode potential relative to the reversible electrode (RHE), and the calculation formula was: overpotential (V) = electrode potential + pH * 0.0591 + 0.1976 - 1.23. The results are shown in the dashed line in FIG. 1. Figure 2

[0066] Figure 3 The overpotential of the four materials when reaching a current density of 100 mA·cm -2 . As can be seen from the figure, in the relatively complex seawater, the potential required for the material to reach a current density of 100 mA·cm -2 is increased compared with pure alkali water, but the overpotential of the quaternary material is still the smallest, only 234 mV. The performance of the ternary material is also better than that of the binary carrier material. It shows that the prepared material still has strong adaptability and wide application potential in the relatively complex seawater, and plays an important role in the development and protection of the ocean.

[0067] Test Example 3

[0068] The electrode materials prepared in Example 1, Example 16-18 were tested by linear sweep voltammetry in 5 wt% KOH solution to explore the influence of different methods of loading molybdenum on the performance of the material. The specific test method was the same as that in Test Example 1. The results are shown in FIG. 2. Figure 4

[0069] Different methods of loading molybdenum on the surface of the foamed nickel do not have a significant effect on the performance of the material, and the performance is significantly improved relative to the pure foamed nickel.

[0070] Test Example 4

[0071] The electrode materials prepared in Example 1-4 were tested by linear sweep voltammetry in 5 wt% KOH solution to explore the influence of the calcination temperature on the performance of the material. The specific test method was the same as that in Test Example 1. The results are shown in FIG. 3. Figure 5

[0072] Different calcination temperatures significantly affect the catalytic performance of the electrode material. When the calcination temperature is low, the metal on the material is not completely oxidized, and cannot form a firm metal oxide; when the calcination temperature exceeds 200 o ​​​C, the high temperature causes the support to be destroyed and unable to maintain the basic structure, resulting in reduced performance.

[0073] Test Example 5

[0074] The electrode materials prepared in Example 1, Examples 5-7 and Comparative Example 1 were subjected to linear sweep voltammetry tests in 5 wt% KOH solution to investigate the influence of different metal salt concentration ratios on the performance of the materials. The specific test method was the same as in Test Example 1. The results obtained are shown in Table 2. Figure 6 .

[0075] The different metal salt concentration ratios have a large influence on the performance of the electrode materials. The presence of uranium pre-activates water molecules and promotes their dissociation. The addition of iron enhances the interaction between the metals, thereby significantly improving the electrocatalytic performance. Too much iron will cover the active sites of the reaction and affect the adsorption of water molecules, thereby inhibiting the performance. From Figure 6 it can be seen that the preferred uranium-iron molar ratio is 1:10-15.

[0076] Test Example 6

[0077] The electrode materials prepared in Example 1, Examples 8-12 were subjected to linear sweep voltammetry tests in 5 wt% KOH solution to investigate the influence of different soaking times on the performance of the materials. The specific test method was the same as in Test Example 1. The results obtained are shown in Table 3. Figure 7 .

[0078] Different soaking times have a small influence on the electrode materials. This indicates that the displacement reaction is relatively rapid, and the displaced metals can cover the surface of the support within a short period of time and form a firm interaction with the support. This fully demonstrates the simplicity and convenience of the method, which is conducive to large-scale production and application.

[0079] Test Example 7

[0080] The electrode materials prepared in Example 1, Example 13, Example 15 and Example 18 were subjected to linear sweep voltammetry tests in 5 wt% KOH solution to investigate the influence of thorium and uranium on the performance of the materials. The specific test method was the same as in Test Example 1. The results obtained are shown in Table 4. Figure 8 .

[0081] The electrolytic water splitting and oxygen evolution performance of the materials is significantly improved (the effect is relatively less than that of uranium). This indicates that the adsorbed water molecules are pre-activated. The trace amount of radiation energy carried can penetrate the structure of the water molecules, subtly disturbing the internal electron cloud and hydrogen bond network, thereby activating the dynamic properties of the water molecules in advance and reducing the overall energy barrier of the subsequent chemical reaction.

[0082] Test Example 8

[0083] The electrode material prepared in Example 1 was subjected to stability test in 5 wt% KOH alkaline water and 5 wt% KOH alkaline seawater to explore the tolerance of the material. The specific test was carried out with saturated Ag / AgCl electrode as reference electrode and graphite electrode as counter electrode, and time-current test was carried out. The current density was 150 mA·cm -2 around for one week. The results obtained are shown in Figure 9 .

[0084] After one week of power test, the current density in alkaline water only decreased by 7.9%, and the current density in alkaline seawater only decreased by 11.8%. This shows that whether in alkaline water or in complex seawater, the prepared quaternary electrode has a firm structure and exhibits excellent stability, which has great potential in large-scale application.

Claims

1. A method for preparing a low overpotential anode, characterized in that... Includes the following steps: Carrier pretreatment: Nickel foam with a pore size of 100 ppi, a thickness of 1.5 mm, and a size of 1×2 cm was placed in 1 mol·L⁻¹ solution. -1 After ultrasonic cleaning in a dilute hydrochloric acid solution for 30 minutes, remove the sample and then ultrasonically clean it in anhydrous ethanol for another 30 minutes before air drying. Molybdenum metal loading: Pretreated nickel foam was placed in 50 ml of a solution with a concentration of 0.5 mol·L⁻¹. -1 Electroplating was performed in a sodium molybdate solution with an applied current of 0.5 mA·cm⁻¹. -1 The electroplating time was 5 minutes; after electroplating, foamed nickel loaded with molybdenum metal was obtained, with a nickel to molybdenum mass ratio of 9:

1. Synthesis of FeUNiMo quaternary electrode material: Nickel-molybdenum foam was placed in 10 ml of a soaking solution containing 0.0502 g uranyl nitrate hexahydrate and 0.404 g ferric nitrate nonahydrate. After standing for 40 minutes, it was taken out and placed in an oven. After drying at 60°C, it was placed in a muffle furnace and heated to 200°C at a heating rate of 5°C / min and held at that temperature for 1 hour. After cooling to room temperature, the FeUNiMo catalytic electrode was obtained.

2. The application of the low overpotential anode obtained by the preparation method according to claim 1 in the electrocatalytic cracking of alkaline water or alkaline seawater for oxygen evolution.

3. The application according to claim 2, characterized in that: The alkaline medium in the alkaline water or alkaline seawater is sodium hydroxide or potassium hydroxide.

4. The application according to claim 3, characterized in that: The concentration of sodium hydroxide or potassium hydroxide is 1-50 wt%.

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