WO2018036183A1

WO2018036183A1 - Catalyst for water decomposition, preparation method therefor and use thereof

Info

Publication number: WO2018036183A1
Application number: PCT/CN2017/081649
Authority: WO
Inventors: 潘锋; 杨金龙; 郑家新; 许明; 肖荫果; 彭浩为; 闫朝一; 梅宗维; 杨卢奕
Original assignee: 北京大学深圳研究生院
Priority date: 2016-08-26
Filing date: 2017-04-24
Publication date: 2018-03-01
Also published as: CN106378139A; CN106378139B

Abstract

A catalyst for water decomposition, a preparation method therefor and use thereof. The catalyst for water decomposition is at least one of Li₂MSiO₄, Li₂MTiO₄, Li₂MGeO₄, Li₂MSnO₄ or Na₂MP₂O₇ which comprise tetrahedral structures in crystals thereof, M being a transition metal. During the catalytic water decomposition, as Li or Na ions are discharged, the crystal structures are structurally rotated or rearranged, such that hydroxyl groups or water molecules absorbed by two adjacent transition metals on the surfaces of the crystals form short hydrogen bonds. Thus, the potential energy for breaking the hydrogen bonds is reduced and O-H bonds can be broken using lower energy; and the transfer of protons is promoted, such that the protons on the surfaces of the crystals can be transferred more quickly. The catalyst reduces the overpotential during water decomposition and increases the catalytic efficiency by forming a unique low energy barrier and double-center catalytic process on the surfaces of crystals.

Description

Water decomposition catalyst and preparation method and application thereof

Technical field

The present application relates to the field of water decomposition, and in particular to a catalyst for water decomposition, and a preparation method and application of the catalyst.

Background technique

The process of water decomposition to produce hydrogen and oxygen is called 2H ₂ O→2H ₂ +O ₂ . This process involves the cathode hydrogen evolution reaction of the two-electron reaction and the anodic oxygen evolution reaction of the four-electron reaction, ie, the cathode: 4H ₂ O+ 4e ^- = 2H ₂ + 4OH ^- , anode: 4OH ^- -4e ^- = 2H ₂ O + O ₂ , or anode: 2H ₂ O-4e ^- = O ₂ + 4H ⁺ , cathode: 4H ⁺ + 4e ^- = 2H ₂ . The main limitations of the water decomposition process include hydrogen bond cleavage, multi-electron and proton transfer, and oxygen evolution kinetics in the anodic reaction of oxygen-oxygen bond formation. At present, the electrolytic cell of water decomposition hydrogen production equipment in domestic service generally uses foamed nickel as an oxygen evolution electrode, and the oxygen evolution overpotential exceeds 550 mV. It is predicted that if the overpotential can be reduced by 250mV, the annual energy saving value will exceed 100 million yuan.

The water-decomposing catalyst can greatly reduce the activation energy of water decomposition, thereby reducing the overpotential of water decomposition. The current catalysts are mainly oxides of noble metals Ru and Ir. However, precious metals are not only costly, resource scarce, but also have unstable catalytic lifetimes; these factors directly lead to the unsuitable use of Ru and Ir oxides for large-scale applications. Recently, 3D transition metal compounds rich in natural resources and inexpensive are widely studied as oxygen evolution catalysts including Fe, Co, Ni, and Mn. Among them, transition metal phosphates M-Pi, perovskites, layered structures LDH, oxide nanocrystals MOX and amorphous structural materials have all proven to be very competitive non-precious metal catalytic materials. According to reports, the oxygen evolution activity of these non-precious transition metal compound catalysts mainly depends on the crystal size, morphology, surface electronic structure and the coordinated environment of the 3d transition metal, which effectively affect the electron transfer and oxygen diffusion. For example, Zhou et al. reported that ultra-thin porous Co ₃ O ₄ (J. Mater. Chem. A, 2015, ₃ , 8107) has a lower overpotential than ordinary Co ₃ O ₄ nanoparticles; Zhu et al. reported SrNb _0.1 Co _0.7 Fe _0.2 O _3-δ perovskite (Angew. Chem. Int. Ed. 2015, 54, 1-6) has excellent OER performance mainly due to its filled e _g orbital, good electron and ion transfer characteristics. Excellent OH ^- adsorption and O ₂ desorption properties; Song et al. (Nat. Commun., 2014, 5) a series of exfoliated single-layer LDH materials, including FeNi-, CoCo-, NiCo-LDH, etc. The oxygen evolution performance of the IrO ₂ catalytic material is mainly due to the fact that the stripping process increases the active site and conductivity of the catalyst material. However, the above catalysts still fail to achieve the desired state in reducing the effect of water decomposition overpotential.

Summary of the invention

The purpose of the present application is to provide a novel water-splitting catalyst and a preparation method and application thereof.

This application uses the following technical solutions:

_{_{_{Li 2 MSiO 4, Li 2 MTiO}}} 4, Li 2 MGeO 4, Li 2 MSnO 4 or Na ₂ MP aspect the present application discloses a hydrolysis catalyst, the hydrolysis catalyst crystal structure containing tetrahedral structure ₂ At least one of O ₇ , wherein M is a transition metal; and, in the process of catalytic water decomposition, the crystal structure is rotated or rearranged as the Li ion or Na ion in the crystal is released, so that the crystal surface Hydroxyl or water molecules adsorbed by two adjacent transition metals form short hydrogen bonds.

It should be noted that, in the water-splitting catalyst of the present application, in the process of catalytic water decomposition, the oxygen-oxygen distance of the hydroxyl or water molecules adsorbed by two adjacent transition metals is less than

The formation of short hydrogen bonds, on the one hand, can reduce the potential energy of hydrogen bond cleavage, and the energy used to break the OH bond is lower; on the other hand, it can promote proton transfer, making proton transfer on the surface faster; forming a unique low energy barrier The double-center catalytic process effectively reduces the overpotential of water decomposition and improves the catalytic efficiency. It will be appreciated, as long as the crystal structure satisfies the present application claims the _{_{_{Li 2 MSiO 4, Li 2 MTiO}}} 4, Li 2 MGeO 4, Li 2 MSnO 4 or Na _₂ MP ₂ O _7, can be used as hydrolysis catalyst, and reaches the present application Low overpotential, high catalytic efficiency; however, it should be noted that after different high temperature treatments, the crystal structure of the catalyst will undergo a phase change, and the catalytic effects of crystals of different phases will be different, as long as the application is satisfied. The limitation can also reduce the water decomposition overpotential and improve the catalytic efficiency, but only the crystals of different phases, which reduce the degree of water decomposition overpotential and increase the catalytic efficiency.

In the present application, the hydrogen bond is defined by the oxygen-oxygen distance, that is, the hydrogen bond oxygen-oxygen distance (d _oo ) formed between the water molecule or the hydroxyl group, wherein

Hydrogen bonds are defined as weak hydrogen bonds,

Hydrogen bonds are defined as short (strong) hydrogen bonds,

The hydrogen bond is defined as a very short (strong) hydrogen bond, which is formed on the surface of the catalyst during the water decomposition process in this application.

Short (strong) hydrogen bonds or very short (strong) hydrogen bonds.

Preferably, the transition metal is at least one of Fe, Co, Ni, and Mn.

Another aspect of the present application discloses the use of the water-splitting catalyst of the present application in electrolyzed water, photolytic water or photoelectrolyzed water.

It can be understood that the key of the catalyst of the present application is that in the process of water decomposition, due to its special structural form, short hydrogen bonds are formed, thereby reducing the overpotential of water decomposition and improving the catalytic efficiency; Limited to the electrolysis water process, in other photolysis water or photoelectrolytic water processes, the adsorption of hydroxyl groups is also involved, and the catalyst of the present application can also be used to reduce the water decomposition overpotential and improve the catalytic efficiency.

Therefore, a further aspect of the present application discloses the use of a transition metal-containing lithium salt or a sodium salt in water catalysis, in which the crystal structure of a transition metal-containing lithium salt or sodium salt contains a tetrahedral structure, and In the process of catalytic water decomposition, as lithium ions or sodium ions in the crystals are released, the crystal structure is structurally rotated or rearranged, so that two adjacent transition metals on the crystal surface adsorb oxygen or water molecules of oxygen - Oxygen distance is less than

It can be understood that as long as the lithium salt or the sodium salt containing the transition metal satisfies the conditions of the present application, a short hydrogen bond can be formed in the hydrolysis process, thereby achieving the effect of reducing the water decomposition overpotential and improving the catalytic efficiency of the present application. .

It should be noted that the present application has found that the oxygen-oxygen distance of the hydroxyl or water molecules adsorbed by two adjacent transition metals is less than

It is possible to form a short hydrogen bond, reduce the overpotential of water decomposition, and increase the catalytic efficiency; however, the preferred two adjacent transition metals adsorb the hydroxyl or water molecules with an oxygen-oxygen distance less than

Especially less than

The effect is better.

Preferably, the transition metal-containing lithium salt is _{_{_{Li 2 MSiO 4, Li 2 MTiO}}} 4, Li 2 MGeO 4 and Li ₂ MSnO ₄ at least one transition metal-containing salt is Na _₂ MP ₂ O _7, wherein M is a transition metal.

More preferably, the transition metal is at least one of Fe, Co, Ni, and Mn.

A further aspect of the present application discloses a method for preparing a water-splitting catalyst of the present application, comprising the following steps,

(1) dissolving the transition metal salt in a solvent, and dissolving the lithium or sodium salt with a silicate or titanate or a decanoate or a stannate or pyrophosphate starting material in another solvent;

(2) mixing two parts of the solution, reacting in the reaction vessel for 1-100 hours, the reaction temperature is 100-300 ° C;

(3) After completion of the reaction in the reaction vessel, the solid precipitate is washed and dried to obtain a water-splitting catalyst.

Preferably, the step (3) further comprises: after washing and drying the solid precipitate, heat-treating to obtain a water-splitting catalyst having a different phase structure; the heat treatment temperature is 200-1100 ° C, and the time is 0.5-20 hours.

It should be noted that the temperature of the heat treatment directly affects the phase structure of the crystal, and the water-decomposing catalyst of the different phase structure has different degrees of lowering the water decomposition overpotential and improving the catalytic efficiency; however, as long as Li or Ni is removed The oxygen-oxygen distance of the hydroxyl or water molecules adsorbed by the two transition metals on the surface of the crystal is less than

It can also reduce the water decomposition overpotential and increase the catalytic efficiency, but the degree is different.

Preferably, the transition metal salt is at least one of an acetate, a chloride, an oxalate, a nitrate, a carbonate, a lactate or a sulfate.

Preferably, the lithium salt is at least one of lithium hydroxide, lithium acetate, lithium carbonate, lithium chloride, lithium sulfate or lithium nitrate; the sodium salt is sodium hydroxide, sodium acetate, sodium carbonate, sodium chloride, sodium sulfate Or at least one of sodium nitrate.

Preferably, the silicate raw material is nano silicon powder, nano silicon dioxide, sodium silicate, methyl orthosilicate Or at least one of tetraethyl orthosilicate; the titanate raw material is at least one of nano titanium powder, nano titanium dioxide, sodium titanate or tetrabutyl titanate; the raw material of the orthosilicate is nanometer powder, nanometer At least one of cerium oxide or sodium citrate; the stannate raw material is at least one of nano tin powder, nano tin dioxide or sodium stannate; the pyrophosphate raw material is sodium phosphate, phosphorus pentoxide or phosphoric acid At least one of them.

Preferably, the solvent is at least one of distilled water, absolute ethanol, n-propanol, isopropanol, ethylene glycol, propylene glycol, glycerin, tetrahydrofuran and acetone.

A further aspect of the present application discloses a water-splitting catalyst which is Li ₂ CoMSiO ₄ , Li ₂ CoMTiO ₄ , Li ₂ CoMGeO ₄ or Li ₂ CoMSnO ₄ having a tetrahedral structure in a crystal, wherein M is a transition The metal, the transition metal is at least one of Fe, Ni and Mn, and the transition metal doping amount is 50%, and the preferred transition metal is Fe.

Still another aspect of the present application discloses an electrolyzed water catalytic electrode which is chemically bonded in situ to a conductive carbon network by a water-splitting catalyst of the present application to form an integrated electrolyzed water catalytic electrode, or a water-splitting catalyst is transferred to a carbon paper or a foamed nickel substrate. An electrolyzed water catalytic electrode is formed thereon; the conductive carbon network is a network structural material prepared by carbon nanotubes, graphite thin or nanoporous carbon.

A further aspect of the present application discloses a photocatalytic film electrode comprising dispersing a water-splitting catalyst of the present application together with a binder in a solvent and then applying it to FTO or NTO transparent conductive glass to prepare the photocatalytic. Thin film electrode.

The beneficial effects of the present application are:

The water-splitting catalyst of the present application adopts a transition metal-containing lithium silicate, lithium titanate, lithium niobate, lithium stannate or sodium pyrophosphate in a specific crystal structure, and utilizes transition metal adsorption on the surface of the crystal during catalytic hydrolysis. Hydroxyl or water molecules form short hydrogen bonds, which on the one hand reduce the potential energy of hydrogen bond cleavage, and lower the OH bond with lower energy; on the other hand, promote proton transfer, which makes proton transfer on the crystal surface faster. The water-splitting catalyst of the present application forms a unique low-energy double-site catalytic process on the surface of the crystal, effectively reducing the overpotential of water decomposition and improving the catalytic efficiency.

DRAWINGS

1 is an XRD picture of a water-splitting catalyst in an embodiment of the present application;

2 is a phase structural diagram of a water-splitting catalyst having three different phase structures of β _I , β _II , and γ ₀ in the examples of the present application;

Figure 3 is a TEM image of a water-splitting catalyst in the examples of the present application;

Figure 4 is a view showing the structure of a wuff surface of a water-splitting catalyst in the embodiment of the present application;

Figure 5 is an LSV curve of a water-splitting catalyst in the examples of the present application;

Figure 6 is a Tafel slope of a water-splitting catalyst in the examples of the present application;

Figure 7 is a timing potential diagram of a water-splitting catalyst in the examples of the present application;

Figure 8 is a diagram showing the structure of a short hydrogen bond on the surface of a crystal of a water-splitting catalyst in the examples of the present application;

Figure 9 is an infrared characterization diagram of a short hydrogen bond structure on the surface of a water-decomposing catalyst crystal in the examples of the present application;

Figure 10 is a kinetic energy barrier diagram of the O-H bond cleavage on the crystal surface of the water-splitting catalyst of the embodiment of the present application during hydrolysis;

Figure 11 is a thermodynamic comparison diagram of the double-center water splitting of the short hydrogen bond and the conventional single-center water splitting in the examples of the present application;

Figure 12 is an SEM image of a peanut-shaped water-splitting catalyst in the examples of the present application;

Figure 13 is a LSV graph of a peanut-shaped water-splitting catalyst in the examples of the present application.

detailed description

Through extensive research, this application has found that most of the energy consumed during the water decomposition process is mainly used to break the OH bond. Short hydrogen bonds or strong hydrogen bonds can promote a wide range of chemical processes, such as in biocatalytic and small molecule synthesis catalysis, strong hydrogen bonds can cause lower energy barriers to break OH bonds. Therefore, the inventors of the present application have creatively proposed that if a short hydrogen bond can be formed in the process of catalyzing water decomposition, it is also possible to produce the same effect, that is, to use a lower energy barrier to interrupt the OH bond. Based on the above knowledge and assumption, the present application proposes a new water decomposition catalyst, and the crystal structure of Li special phase structure _{_{_{_{2 MSiO 4, Li 2 MTiO 4}}}} , Li 2 MGeO 4, Li 2 MSnO 4 or Na _₂ MP ₂ O ₇ crystal. When these crystals are used as a water-decomposing catalyst, the crystal structure causes structural rotation or rearrangement, and the transition metal on the crystal surface adsorbs hydroxyl groups, so that adjacent hydroxyl groups or water molecules form short hydrogen bonds, that is, the distance between OH is smaller than

In this case, not only can the lower energy barrier be used to interrupt the OH bond, but also the proton transfer is accelerated and the catalytic efficiency is improved.

It should be noted that the existing research on water decomposition has not involved short hydrogen bonds, and there is no relevant research report. This application first proposed to reduce the water decomposition overpotential and improve the catalytic efficiency by using short hydrogen bonds in the water decomposition process, and realized the idea by using a new water decomposition catalyst. Existing catalysts, including Ru and Ir oxides, transition metal phosphates M-Pi, perovskites, layered structures LDH, oxide nanocrystals MOX, and amorphous structural materials, are unable to achieve this function.

It can be understood that the water-splitting catalyst of the present application is not limited to the water decomposition process, and other water decomposition processes, such as water-splitting process of photolysis water, photo-hydrolysis, etc., can also realize short hydrogen bonding by using the catalyst of the present application. effect.

The present application is further described in detail below by way of specific embodiments. The following examples are only for this application. Further explanation is not to be construed as limiting the application.

Embodiment 1

In this example, lithium cobalt silicate is used as a water decomposition catalyst, and the preparation method thereof is as follows:

First, 3.075 g of CoAc ₂ ·4H ₂ O was added to a mixed solvent of 20 mL of ethylene glycol and 10 mL of water, and magnetically stirred for 30 minutes; then, 2.6 g of ethyl orthosilicate and 2.1 g of LiOH 2H ₂ O were dispersed in 30 mL of distilled water. In the middle, the magnetic stirring was carried out for 30 minutes; finally, the two solutions were quickly mixed and uniformly mixed into a 100 mL reaction vessel and reacted at 200 ° C for 48 hours. The obtained product was washed 4 times with distilled water, 2 times with alcohol, and then vacuum dried at 80 ° C for 12 hours, ie The lithium cobalt silicate catalyst of this example was obtained.

The lithium cobalt silicate of this example was divided into three parts, two of which were respectively calcined at 700 ° C and 1100 ° C for 2 hours in a high temperature furnace to obtain two other different high temperature phase structure lithium cobalt silicate catalysts.

The phase structure of three kinds of lithium cobalt silicate prepared by this example was analyzed by XRD. The results are shown in Fig. 1. In Fig. 1, the γ ₀ phase is 1100 ° C high temperature treated lithium cobalt silicate, and the β _I phase is 700 ° C high temperature treatment. the lithium cobalt silicate, β _II with lithium cobalt silicate without high temperature treatment; seen, the present embodiment is obtained β _I, β _II, γ ₀ lithium cobalt silicate material of the three phases structure, the refinement after XRD It is found that in the three structures of β _I , β _II and γ ₀ , the tetrahedral structures of LiO ₄ , SiO ₄ and CoO ₄ have different arrangement patterns, as shown in FIG. 2 .

The morphology of the material was analyzed by TEM. The results are shown in Fig. 3. Among them, ab is the structure of β _II structure, cd is the structure of β _I structure, and ef is the structure of γ ₀ structure. According to the lattice spacing and local electron diffraction analysis, the main exposed surface of the three different crystal structures is the (100) plane. The structure of the wuff surface calculated by the first principle is shown in Fig. 4, which is consistent with the experiment.

The three lithium cobalt silicates prepared in this example were tested as water decomposition catalysts respectively. The water decomposition test methods are as follows:

5 mg of lithium cobalt silicate catalyst was added to 2 mL of alcohol for ultrasonic dispersion for 1 h to obtain a catalyst ink, and then 10 μL of the ink was dropped onto a glassy carbon electrode having a diameter of 5 mm, and dried at room temperature to obtain a uniform catalyst film, and the catalyst film was immersed in In the electrolytic cell with 1 mol/L KOH solution, Ag/AgCl was used as the reference electrode, and Pt wire was used as the counter electrode. The LSV curve characterizing the catalytic performance was taken at a rotation rate of 1600 rpm and a sweep speed of 5 mV/s. The test results are shown in Figure 5. The overpotential of the catalyst at a current density of 10 mA/cm ^{2 and} the current density of 0.35 V were tested, and the test results are shown in Table 1.

At the same time, this example also used the conventional noble metal oxide catalyst IrO ₂ and the existing Co ₃ O ₄ catalyst as a comparison, or tested its catalytic performance under the same conditions. The water decomposition test method is the same as the above method, except that an equivalent amount of IrO ₂ or Co ₃ O _{4 is used to} replace the lithium cobalt silicate of this example, and the test results are shown in FIG. 5 . Among them, the internal illustration is a corresponding redox couple of lithium cobalt silicate materials of three structures of β _I , β _II , and γ ₀ , and it is confirmed that a short hydrogen bond is catalyzed after delithiation.

In Fig. 5, β _II -LCS is a test curve of β _II phase lithium cobalt silicate, β _I -LCS is a test curve of β _I phase lithium cobalt silicate, and γ ₀ -LCS is a test of γ ₀ phase lithium cobalt silicate. The curve, IrO ₂ is a test curve of the IrO ₂ catalyst, and Co ₃ O ₄ is a test curve of the Co ₃ O ₄ catalyst. It can be seen that the three structures of lithium cobalt silicate as the catalyst have better overpotential and current density than the Co ₃ O ₄ catalyst, and the β _II structure catalyst has better water decomposition performance than the reference IrO ₂ catalyst.

Further, the catalytic kinetics of the three lithium cobalt silicate catalysts of this example, and the IrO ₂ catalyst and the Co ₃ O ₄ catalyst were analyzed by Tafel slope, and the results are shown in FIG. 6 . In Fig. 6, 91 is an analysis curve of Co ₃ O ₄ , 78 is an analysis curve of γ ₀ -LCS, 56 is an analysis curve of IrO ₂ catalyst, 47 is an analysis curve of β _I -LCS, and 44 is a β _II -LCS It can be seen from the analytical curve that the β _II structure catalyst has the smallest Tafel slope, indicating that it has the fastest catalytic kinetics.

The chronopotentiometry was used to analyze the three lithium cobalt silicates of this example, as well as the catalytic stability of the IrO ₂ catalyst. The results are shown in FIG. In Fig. 7, β _II -LCS is the catalytic stability curve of β _II phase lithium cobalt silicate, β _I -LCS is the catalytic stability curve of β _I phase lithium cobalt silicate, and γ ₀ -LCS is γ ₀ phase silicic acid. The catalytic stability curve of cobalt lithium and IrO ₂ are the catalytic stability curves of the IrO ₂ catalyst. It can be seen that the three lithium cobalt silicate catalysts have relatively stable catalysis at a current density of 10 mA/cm ² compared to the IrO ₂ catalyst. Voltage.

Short hydrogen bond analysis: The surface water adsorption structure of the three lithium cobalt silicate catalysts in this example was analyzed by a first-principles calculation method. The results are shown in Figure 8 and Table 1. It can be seen that the surface of the lithium cobalt silicate catalyst of β _II structure Has a shorter hydrogen bond structure, which mainly exposes the hydrogen bond length of the 100 faces of the crystal face to

The hydrogen bond length of the surface of the lithium cobalt silicate catalyst of β _I structure is

The hydrogen bond length of the surface of the γ ₀ structure lithium cobalt silicate catalyst is

The short hydrogen bonding structure adsorbed on the surface by infrared is characterized. As shown in Fig. 9, the OH vibration peak of the lithium cobalt silicate catalyst having a short hydrogen bond β _II structure shifts to a low wave number, further demonstrating the surface of the β _II structure. A shorter hydrogen bond structure is formed.

Kinetic energy barrier analysis: The kinetic energy barrier of the surface OH bond cleavage of the three lithium cobalt silicate catalysts in this example and the kinetic energy barrier of OH bond cleavage in water were calculated by first-principles principle. The results are shown in Fig. 10. It can be seen that the β _II structure catalyst has a lower OH bond cleavage energy barrier due to the short hydrogen bonding of the surface compared to the β _I and γ ₀ structures.

Hydrodynamic process of water decomposition: The first-principles calculation is used to further compare and analyze the bicenter water decomposition with short hydrogen bonds and the traditional single-center water decomposition thermodynamic process. The results are shown in Figure 11. In Figure 11, A is a traditional single center. In the water decomposition process, B is a single-center and double-center thermodynamic energy barrier, and C is a traditional single-center water decomposition process. It can be seen that the double-center water splitting of short hydrogen bonds involves a continuous short hydrogen bond network, and the calculated thermodynamic overpotential is 0.35 V, which is lower than the traditional single-center hydrolyzed thermodynamic overpotential of 0.624 V.

Embodiment 2

In this example, lithium cobalt titanate is used as a water decomposition catalyst, and the preparation method thereof is as follows:

First, 2.78 g of CoSO ₄ ·7H ₂ O was added to a mixed solvent of 20 mL of absolute ethanol and 10 mL of water, and magnetically stirred for 30 minutes; then, 2.08 g of butyl titanate and 2.56 g of LiSO ₄ ·H ₂ O were dispersed in 30 mL of no In water ethanol, magnetically stirred for 30 minutes; finally, the two solutions were quickly mixed and uniformly mixed into a 100 mL reaction vessel and reacted at 200 ° C for 96 hours. The obtained product was washed twice with distilled water for 4 times, and then vacuum dried at 80 ° C for 12 hours. The lithium cobalt titanate catalyst of this example was obtained.

Electron microscopy was used to observe the lithium cobalt titanate prepared in this example, and its morphology was a peanut-shaped structure composed of nanoparticles, as shown in FIG.

The catalytic performance of the lithium cobalt titanate of this example was tested by the same water decomposition test method as in Example 1. The LSV curve test results are shown in Fig. 13; the overpotential at a current density of 10 mA/cm ² , and the current density at 0.35 V, The test results are shown in Table 1.

The same first principle calculation method of Example 1 was used to calculate the hydrogen bond length of the surface of the surface of the surface of the surface of the lithium cobalt titanate catalyst. The test results are shown in Table 1.

Embodiment 3

In this example, lithium nickel cobaltate is used as a water decomposition catalyst, and the preparation method thereof is as follows:

First, 1.0 g of CoCl ₂ ·4H ₂ O and 1.0 g of NiCl ₂ ·4H ₂ O were added to a mixed solvent of 10 mL of isopropyl alcohol and 10 mL of water, and magnetically stirred for 30 minutes; then 3.70 g of GeLi ₂ O _{3 was} dispersed in 30 mL. 0.5 g of graphite diluted distilled water, magnetically stirred for 30 minutes; finally, the two solutions were quickly mixed and uniformly mixed into a 100 mL reaction kettle at 200 ° C for 72 h, and the obtained product was washed with distilled water for 5 times, washed with alcohol 3 times, and then vacuumed at 80 ° C. After drying for 12 hours, the lithium cobalt ruthenate catalyst of this example was obtained.

The phase structure of lithium cobalt rutheate prepared in this example was analyzed by XRD. The results showed that the phase structure was β _II structure.

The catalytic performance of lithium cobalt ruthenate in this example was tested by the same water decomposition test method of Example ¹ , and the overpotential at a current density of 10 mA/cm ^{2 and} the current density at 0.35 V were tested. The test results are shown in Table 1.

The same first-principles calculation method of Example 1 was used to calculate the hydrogen bond length of the surface of the surface of the surface of the surface of the lithium cobalt citrate catalyst. The test results are shown in Table 1.

Embodiment 4

In this example, cobalt stannate stannate is used as a water decomposition catalyst, and the preparation method is as follows:

First, 1.4 g of CoSO ₄ ·7H ₂ O and 1.4 g of MnSO ₄ ·4H ₂ O were added to a mixed solvent of 10 mL of acetone and 10 mL of water, and magnetically stirred for 30 minutes; then 2.08 g of tin dioxide and 2.56 g of LiSO ₄ ·H were added. ₂ O was dispersed in 30 mL of absolute ethanol and stirred magnetically for 30 minutes. Finally, the two solutions were quickly mixed and uniformly mixed into a 100 mL reaction kettle and reacted at 200 ° C for 60 h. The obtained product was washed with distilled water for 5 times and washed with alcohol 3 times at 80 ° C. The lithium cobalt stannate catalyst of this example was obtained by vacuum drying for 12 hours.

The phase structure of lithium cobalt stannate prepared in this example was analyzed by XRD, and the phase structure was shown to be β _II structure.

The catalytic performance of the lithium cobalt stannate of this example was tested by the same water decomposition test method of Example ¹ , and the overpotential at a current density of 10 mA/cm ^{2 and} the current density at 0.35 V were tested. The test results are shown in Table 1.

The same first principle calculation method of Example 1 was used to calculate the hydrogen bond length of the surface of the surface of the surface of the surface of the surface of the surface of the lithium cobalt stannate. The test results are shown in Table 1.

Embodiment 5

In this example, sodium cobalt pyrophosphate is used as a water decomposition catalyst, and the preparation method is as follows:

First, 1.0 g of CoCl ₂ ·4H ₂ O and 1.0 g of FeCl ₂ ·4H ₂ O were added to a mixed solvent of 10 mL of tetrahydrofuran and 10 mL of water, and magnetically stirred for 30 minutes; then, 2.08 g of phosphoric acid and 1.69 g of sodium hydroxide were dispersed in 30 mL. In distilled water, magnetically stir for 30 minutes; finally, the two solutions were quickly mixed and uniformly mixed into a 100 mL reaction kettle and reacted at 200 ° C for 72 h. The obtained product was washed with distilled water for 5 times, washed with alcohol three times, and then vacuum dried at 80 ° C for 12 hours. The Na ₂ CoP ₂ O ₇ catalyst of this example.

The phase structure of the sodium cobalt pyrophosphate prepared in this example was analyzed by XRD. The results showed that the phase structure was β _II structure.

The catalytic performance of the sodium cobalt pyrophosphate in this example was tested by the same water decomposition test method of Example ¹ , and the overpotential at a current density of 10 mA/cm ^{2 and} the current density at 0.35 V were tested. The test results are shown in Table 1.

The same first-principles calculation method of Example 1 was used to calculate the hydrogen bond length of the surface of the surface of the surface of the surface of the cobalt pyrophosphate catalyst. The test results are shown in Table 1.

Embodiment 6

In this example, lithium iron silicate cobalt is used as a water decomposition catalyst, and the preparation method thereof is as follows:

First, 1.0 g of Fe(NO ₃ ) ₃ ·9H ₂ O and 1.0 g of Co(NO ₃ ) ₂ ·9H ₂ O were added to a mixed solvent of 20 mL of water, and magnetically stirred for 30 minutes; then 2.08 g of ethyl orthosilicate was added. And 2.76 g of LiNO _{3 was} dispersed in 30 mL of distilled water and magnetically stirred for 30 minutes. Finally, the two solutions were quickly mixed and uniformly mixed into a 100 mL reaction vessel and reacted at 220 ° C for 4 days. The obtained product was washed with distilled water for 5 times and washed 3 times with alcohol. The aluminum iron silicate cobalt catalyst of this example was obtained by vacuum drying at 80 ° C for 12 hours.

The phase structure of the iron cobalt cobalt silicate prepared in this example was analyzed by XRD, and the phase structure was shown to be β _II structure.

The iron cobalt cobalt silicate prepared in this example was tested as a photoelectric water-decomposition catalyst, and the test method was as follows:

5 mg of lithium cobalt silicate catalyst was added to 2 mL of alcohol for ultrasonic dispersion for 1 h to obtain a catalyst ink, and then 100 μL of the ink was dropped onto an FTO glassy carbon electrode having an area of 1*1 cm ² , and dried at room temperature to obtain a uniform catalyst film. The catalyst film was immersed in an electrolytic cell with a 1 mol/L KOH solution, using Ag/AgCl as a reference electrode, Pt wire as a counter electrode, and an overpotential at a current density of 10 mA/cm ² and a 0.35 V Current density, the test results are shown in Table 1.

The same first-principles calculation method of Example 1 was used to calculate the hydrogen bond length of the surface of the surface of the surface of the surface of the surface of the surface of the surface of the surface of the surface of the surface.

Table 1 Overpotential, current density and surface hydrogen bond length of different catalysts

The results in Table 1 show that the transition metal lithium/sodium salt catalysts prepared in Examples 1 to 6 have different short hydrogen bonds on the surface, corresponding to different overpotentials and current densities of water decomposition, indicating that the catalyst surface is short. Hydrogen bond networks play a decisive role in water decomposition performance. According to the results of Table 1, the six water-decomposing catalysts prepared in the examples of the present invention form short hydrogen bonds on the surface during catalytic water decomposition, which can effectively reduce the overpotential of water decomposition, thereby improving water. Decomposition efficiency.

The above content is a further detailed description of the present application in combination with a specific implementation manner, and cannot be recognized. The specific implementation of this application is limited to these descriptions. It will be apparent to those skilled in the art that the present invention can be made in the form of the present invention without departing from the scope of the present invention.

Claims

A water decomposition catalyst, wherein: said crystal Li hydrolysis catalyst containing tetrahedral structure 2 MSiO 4, Li 2 MTiO 4 , Li 2 MGeO 4, Li 2 MSnO 4 or Na 2 MP 2 O 7 in At least one of which M is a transition metal; and, in the process of catalytic water decomposition, as the Li ion or Na ion in the crystal is released, the crystal structure is rotated or rearranged to cause two phases on the crystal surface. Hydroxyl or water molecules adsorbed by the adjacent transition metal form short hydrogen bonds.
The water-splitting catalyst according to claim 1, wherein the transition metal is at least one of Fe, Co, Ni, and Mn.
Use of the water-splitting catalyst according to claim 1 or 2 in electrolyzed water, photolytic water or photoelectrolyzed water.
Use of a transition metal-containing lithium or sodium salt in water decomposition catalysis, characterized in that the crystal of the transition metal-containing lithium or sodium salt contains a tetrahedral structure and, in the process of catalyzing water decomposition In the crystal, the lithium or sodium ions in the crystal are desorbed, and the crystal structure is rotated or rearranged, so that the oxygen-oxygen distance of the hydroxyl or water molecules adsorbed by two adjacent transition metals on the crystal surface is smaller than
Use according to claim 4, wherein: said transition metal-containing lithium salt is Li 2 MSiO 4, Li 2 MTiO 4, Li 2 MGeO 4 and Li 2 MSnO 4 at least one transition metal-containing The sodium salt is Na 2 MP 2 O 7 , wherein M is a transition metal.
The use according to claim 5, wherein the transition metal is at least one of Fe, Co, Ni and Mn.
The method for preparing a water-splitting catalyst according to claim 1 or 2, comprising the steps of

(1) Dissolving the transition metal salt in a solvent, dissolving the lithium salt or the sodium salt, and the silicate raw material or the titanate raw material or the orthosilicate raw material or the stannate raw material or the pyrophosphate raw material to the other In a portion of the solvent;

(2) mixing the two solutions, completing the reaction in the reaction vessel, and then washing and drying the solid precipitate to obtain the water-decomposing catalyst material;

Preferably, the method further comprises the step (3) of subjecting the water-decomposing catalyst material obtained in the step (2) to a high-temperature heat treatment to obtain a water-splitting catalyst having a different phase structure.
A water-decomposing catalyst characterized in that the water-decomposing catalyst is Li 2 CoMSiO 4 , Li 2 CoMTiO 4 , Li 2 CoMGeO 4 or Li 2 CoSnO 4 having a tetrahedral structure in a crystal, wherein M is a transition metal, The transition metal is at least one of Fe, Ni, and Mn, and the transition metal doping amount is 50%, and the preferred transition metal is Fe.
An electrolyzed water catalytic electrode, characterized in that: the electrolyzed water catalytic electrode is claimed in claim 1. The water-splitting catalyst according to 2 or 8 is chemically bonded in situ to the conductive carbon network to form an integrated electrolyzed water catalytic electrode, or the water-splitting catalyst is transferred to a carbon paper or a foamed nickel substrate to form an electrolyzed water catalytic electrode; the conductive carbon network A network structural material prepared for carbon nanotubes, graphite thin or nanoporous carbon.
A photocatalytic film electrode comprising: the water-decomposing catalyst according to claim 1, 2 or 8 dispersed together with a binder in a solvent, and then applied to FTO or NTO transparent conductive glass to prepare The photocatalytic film electrode.