Ir-doped WO3 (at) TiN as well as preparation method and application thereof

Abstract

The invention discloses Ir-doped WO3 (at) TiN as well as a preparation method and application thereof, designs a WO3 and TiN composite carrier, and effectively improves the catalytic effect of noble metal Ir. WO3 and TiN are compounded as a carrier through a hydrothermal reaction, and free Ti in a solution is doped into the position of a W atom in the process, so that the number of oxygen vacancies in WO3 is increased, the electronic configuration of Ir is optimized, and the OER reaction is facilitated; besides, a large number of pores can be generated when WO3 of a hexagonal rod-shaped structure is combined with TiN of a particle structure, diffusion of water and oxygen in the PEMWE process can be promoted, compared with other carriers made of single materials, more comprehensive advantages and higher structure dimension are achieved, and the reaction activity and stability are improved. A three-electrode test result shows that the Ir / WO3 (at) TiN can reach 10 mA cm <-2 > by only needing 253 mV overpotential, and the Tafel slope is only 47.35 mV dec-1. And the mass activity (MA) can reach 920.93 mA mgIr <-1 > when the RHE is 1.53 V vs.

Description

Technical Field

[0001] The present invention relates to the technical field of catalyst preparation, and particularly relates to Ir-doped WO3@TiN, a preparation method thereof and an application thereof. Background Art

[0002] With the emergence of problems such as global warming and energy shortage, the effective utilization of renewable energy has become a topic of great concern at present, and many scientists have carried out research on this. Hydrogen energy is the most promising energy source due to its high energy density and environmental friendliness. There are many ways to produce hydrogen. Among them, proton exchange membrane water electrolysis (PEMWE) for hydrogen production is a hydrogen production method that has attracted much attention at present due to its high power density, fast response for start-up and shutdown, high purity of hydrogen energy, low operating cost and many other advantages, and can realize the sustainable utilization of intermittent energy. Industrially, the oxygen evolution reaction (OER) catalyst at the anode in PEMWE mainly uses noble metal iridium (Ir). However, the annual global production of Ir is only 8 metric tons, and the commercial Ir loading is 2 - 4 mg cm -2 . Therefore, the Ir loading must be reduced by at least one order of magnitude to enable the large-scale use of PEMWE.

[0003] In recent years, it has been found that the interaction between metal and support can effectively prevent the aggregation of metal nanoparticles, increase the electrochemically active surface area, and improve the effective utilization rate of noble metals. In addition, it can also promote the electron transfer between carriers and metal sites, effectively enhancing the electrochemically activity and stability in the device while reducing the Ir loading. Oxygen-deficient tungsten oxide (WO3) is helpful for the adsorption and activation of water molecules, thus accelerating the water oxidation reaction. In addition, there are also many studies using WO3 as a support, showing a strong metal-support interaction.

[0004] However, the low conductivity of tungsten oxide limits its wide application in PEMWE. In addition, the low porosity in the material will limit the water vapor transport during the PEMWE process, increase the mass transfer impedance, and thus reduce the Faraday efficiency of the catalyst. Summary of the Invention

[0005] The present invention provides an Ir-doped WO3@TiN, its preparation method and application. WO3@TiN as a catalyst support can effectively improve the catalytic effect. By incorporating Ti into the position of W atoms, the number of oxygen vacancies in WO3 is increased, and the electronic configuration of Ir is optimized, which is beneficial to the OER reaction. In addition, when hexagonal rod-shaped WO3 combines with particulate TiN, a large number of pores are generated, which can promote the diffusion of water and oxygen in the PEMWE process. Compared with other single materials as supports, it has more comprehensive advantages and higher structural dimensions, increasing the reactivity and stability of the reaction. The three-electrode test results show that Ir / WO3@TiN only requires an overpotential of 253 mV to reach 10 mA cm -2 , and the Tafel slope is only 47.35 mV dec -1 . The mass activity (MA) can reach 920.93 mA mgIr at 1.53 V vs RHE -1 , which is higher than most reported noble metal catalysts. When used in PEMWE, the Ir loading in the anode catalyst layer is 0.3 mg cm -2 , and the current density reaches 1 Acm -2 , and the voltage is only 1.6 V. Moreover, it can stably operate for more than 200 h at 1 A cm -2 .

[0006] One of the technical solutions of the present invention is to provide an Ir-doped WO3@TiN, wherein the WO3@TiN is composed of rod-shaped WO3 and particulate TiN supported on WO3; the Ir is supported on WO3@TiN; wherein Ir and Ti replace the position of W atoms.

[0007] A large number of pores generated when hexagonal rod-shaped WO3 combines with particulate TiN can promote the diffusion of water and oxygen in the PEMWE process. Compared with other single materials as supports, it has more comprehensive advantages and higher structural dimensions, increasing the reactivity and stability of the reaction.

[0008] Further, the Ir is one or more of metallic Ir and iridium oxide.

[0009] In the catalytic material Ir / WO3@TiN, the doping of dual atoms (Ti, Ir) can promote the generation of oxygen vacancies in WO3, regulate the electronic structure of Ir active sites, and reduce the formation of OOH* active intermediates, thereby enhancing the OER activity and stability. In addition, WO3@TiN has high porosity, which is beneficial to the activity and long-term stability of PEMWE.

[0010] Another technical solution of the present invention is to provide a preparation method of the above-mentioned Ir-doped WO3@TiN, which has the following steps:

[0011] (1) Synthesize WO3@TiN with oxygen vacancies. The free Ti atoms at the interface will be doped into the tungsten lattice of tungsten oxide, thereby reducing the formation energy of oxygen vacancies and promoting the increase of oxygen vacancies. The oxygen vacancies will transfer the excess electrons to the surrounding W atoms.

[0012] (2) Load Ir on WO3@TiN; the Ir is one or more of metallic Ir and iridium oxide. The Ir at the interface is doped into the W lattice on the surface of WO3, which will also produce the same effect as Ti doping. The increased oxygen vacancies will transfer the excess electrons to Ir. In addition, WO3, as an electron transfer intermediate, can also transport electrons from titanium nitride to Ir nanoparticles. The electron-rich Ir active sites can promote the OER reaction and avoid its loss as a high-valent species due to electron loss, thereby reducing stability. In addition, the composite structure of rods and particles produces a large number of pores, reducing the mass transfer impedance of PEMWE and increasing the activity and stability of the reaction.

[0013] Further, the WO3@TiN with oxygen vacancies is prepared by the following steps:

[0014] (1) Prepare a 15 mg / ml aqueous dispersion of TiN nanoparticles and stir for 30 min as Liquid 1;

[0015] (2) Mix ammonium tungstate tetrahydrate (ATT) and sodium dodecyl sulfate (SDS) with a mass ratio of (1.0 - 1.2):(0.4 - 0.6) in water and stir for 3 h as Liquid 2, and the concentration of SDS is 0.01 - 0.02 g / ml;

[0016] (3) Mix Liquid 1 and Liquid 2 and stir for 30 - 60 min, and ultrasonicate until completely dispersed to obtain Liquid 3; the volume ratio of Liquid 1 to Liquid 2 is (10 - 15):(30 - 50);

[0017] (4) Transfer Liquid 3 to a reaction kettle and heat at 200 °C for 4 - 8 hours;

[0018] (5) Cool, wash with deionized water, and dry in air at 60 °C for 8 - 12 hours to finally obtain the composite support WO3@TiN.

[0019] Further, the method for loading Ir on WO3@TiN is as follows:

[0020] 80 - 100 mg of WO3@TiN and 10 - 30 mg of cetyltrimethylammonium bromide (CTAB) were added to 50 - 100 ml of ethylene glycol (EG), and stirred for 1 - 2 h; then hydrated iridium(IV) acid containing no less than 50 mg of Ir was added to the obtained suspension, and continuously stirred for 1 - 3 h, and refluxed at 160 - 170 °C for 3 - 4 h; finally, the suspension was centrifuged, and the solid was washed with deionized water and ethanol, and then dried overnight at 60 - 80 °C to obtain Ir / WO3@TiN.

[0021] The third aspect of the technical solution of the present invention lies in providing the application of the above-mentioned Ir-doped WO3@TiN in proton exchange membrane water electrolysis.

[0022] The beneficial effect of the present invention is that: the composite material WO3@TiN as a carrier improves the OER activity and stability of the Ir catalyst, and at the same time realizes excellent proton exchange membrane water electrolysis activity and stability, and the mass activity (MA) can reach 920.93 mA mgIr at 1.53 V vs RHE. -1 。 Description of the Drawings

[0023] Figure 1 Scanning electron microscope (SEM) images and transmission electron microscope (TEM) images of WO3@TiN.

[0024] Figure 2 is Comparison diagram of nitrogen adsorption - desorption isotherms (BET) of TiN and WO3@TiN.

[0025] Figure 3 Comparison diagram of conductivity of TiN, WO3 and WO3@TiN.

[0026] Figure 4 High-angle annular dark-field scanning transmission electron microscope (HADDF-STEM) images of Example 1 and elemental content analysis corresponding to the selected area.

[0027] Figure 5 Comparison diagram of electron paramagnetic resonance spectra (EPR).

[0028] Figure 6 Comparison diagram of polarization curves (LSV) and Tafel slope (Tafel) of Example 1 and commercial iridium oxide.

[0029] Figure 7 Comparison diagram of half-cell stability of Example 1 and commercial iridium oxide.

[0030] Figure 8 Comparison diagram of PEMWE activity of Example 1 and commercial iridium oxide.

[0031] Figure 9 PEMWE stability comparison chart of Example 1 and commercial iridium oxide. Detailed implementation manners

[0032] The following examples are used to further illustrate the present invention, and their purpose is to explain the present invention rather than to limit the scope of the present invention. Unless otherwise specified, all parts and percentages are by weight.

[0033] The raw materials used in the present invention are all conventional commercially available products unless otherwise specified; the methods used in the present invention are all conventional methods in the art unless otherwise specified.

[0034] The embodiments of the present invention will be further described in multiple examples below.

[0035] It should be clear that the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative work belong to the scope of protection of the present application.

[0036] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0037] Example 1

[0038] (1) Add 180 mg of TiN nanoparticles to 12 ml of H2O and stir for 30 min to obtain Liquid 1.

[0039] (2) Mix ammonium tungstate tetrahydrate (ATT) and sodium dodecyl sulfate (SDS) with a mass ratio of 1.0:0.4 in water and stir for 3 h to obtain Liquid 2, and the concentration of SDS is 0.01 g / ml.

[0040] (3) Mix Liquid 1 and Liquid 2 and stir for 30 min, then ultrasonicate until completely dispersed to obtain Liquid 3; the volume ratio of Liquid 1 to Liquid 2 is 10:30.

[0041] (4) Transfer Liquid 3 to a reaction kettle and heat at 200 °C for 4 hours.

[0042] (5) Cool, wash 3 times with deionized water, and dry in air at 60 °C for 8 hours to finally obtain the composite support WO3@TiN.

[0043] By Figure 2 and Figure 3It can be seen that the nitrogen adsorption and desorption capacity of WO3@TiN is significantly better than that of the uncomposited TiN material, and the conductivity is significantly improved compared to pure WO3.

[0044] (6) Add 80 mg of WO3@TiN and 10 mg of cetyltrimethylammonium bromide CTAB to 50 ml of ethylene glycol (EG), and stir for 1 h; then add hydrated iridium(IV) acid containing 50 mg of Ir to the obtained suspension, continuously stir for 1 h, and reflux at 160 °C for 3 h; finally, centrifuge the suspension, wash the solid with deionized water and ethanol, and then dry overnight at 60 °C to obtain Ir / WO3@TiN.

[0045] The obtained product is as Figure 1 shown in (a) the scanning electron microscope (SEM) image, where granular TiN is loaded on rod-shaped WO3. Through transmission electron microscopy (TEM) ( Figure 1 (b)), we analyzed the crystal planes and their corresponding interplanar spacings of the two materials, WO3 and TiN. In addition, the BET specific surface area test results ( Figure 2) show that the specific surface area of WO3@TiN is higher than that of WO3, and the appearance of the hysteresis loop proves the porous structure of the WO3@TiN composite material, which is consistent with the SEM results. The presence of TiN effectively improves the overall conductivity of the composite material ( Figure 3 ). In addition, scanning transmission electron microscopy (STEM) ( Figure 4 ) and the line scan of its elemental content prove the incorporation of Ti and Ir elements in WO3, which is also the main reason for the increase in oxygen vacancies in the Ir / WO3@TiN material ( Figure 5 ).

[0046] The performance of the catalyst was studied using a CORRTEST instrument (CS2350) in a standard three-electrode system. The electrolyte solution was 0.5 M H2SO4, the counter electrode and reference electrode were a platinum foil and a saturated calomel electrode (SCE), respectively, and all potentials were converted to the potential E relative to the reversible hydrogen electrode (RHE) RHE (Equation 1):

[0047] (1)

[0048] where Esce is the measured voltage value, and 0.260 V is the potential value at zero current after calibrating the SCE electrode with a standard hydrogen electrode before the test.

[0049] The catalyst ink was prepared by ultrasonically dispersing 3.27 mg of the catalyst (IrO2) in a mixture of 10 µL of Nafion solution (5 wt%) and 490 µL of ethanol. During linear sweep voltammetry (LSV) testing, a scan rate of 5 mV s-1 scan rate and 85% iR drop compensation. The Tafel slope is calculated according to η = blog j +α, where b is the Tafel slope.

[0050] The stability is detected by chronopotentiometry at 10 mA cm -2 without iR drop compensation. The working electrode is prepared by loading the catalyst on hydrophilic carbon paper. The effective area of the carbon paper is 1.0 cm 2 , and the Ir loading is 0.01 mg cm -2 . The catalyst ink is dropped on the surface of the carbon paper multiple times and dried overnight in an oven at 60 °C. In the PEMWE, the cathode catalyst uses commercial Pt / C (40 wt%, loading of 0.8 mg cm -2 ), and the anode catalyst uses the catalyst of this example or commercial iridium oxide. First, prepare the catalyst slurry by adding 100 mg of the catalyst to 2 mL of H2O and 10 mL of an isopropyl alcohol (IPA) solution containing 200 mg of Nafion solution (20 wt%) and ultrasonically dispersing for 1 h. Subsequently, the electrode preparation is carried out by pneumatic spraying. The Pt / C mass loading (40%) of the cathode is 0.8 mg cm -2 . The mass loadings of C-IrO2 on the anode are 0.3 and 1 mg cm -2 . The mass loading of 30% Ir / WO3@TiN on the anode is 1 mg cm -2 , that is, the Ir mass loading is 0.3 mg cm -2 . The anode catalyst is coated on the membrane (Nafion 115), the gas diffusion layer is Ti felt, and the cathode catalyst is coated on the gas diffusion layer (Ti felt). Finally, the cathode gas diffusion layer, Nafion 115 membrane, and anode gas diffusion layer are combined and hot-pressed (130 °C, 5 MPa, 5 min) to obtain the membrane electrode assembly (MEA) with an effective area of 5 cm 2 . The PEMWE test is carried out at 80 °C, and circulating deionized water passes through the anode, with the temperature and flow rate being 80 °C and 3 mL min -1 . The voltage range of the LSV test is 1.4 V to 2.5 V, and the collected current is normalized using the effective area of the MEA (5 cm 2 ) to obtain the current density. The chronopotentiometry (CP) measurement is carried out at a current density of 1.0 A cm -2 for up to 200 hours.

[0051] Its half-cell activity is as Figure 6As shown, when the Ir loading is 30 wt%, the catalyst Ir / WO3@TiN has higher activity, and the overpotential at a current density of 10 mA cm -2 is only 253 mV. The Tafel slope is also lower than that of commercial IrO2 (C-IrO2), being 47.35 mV dec -1 . At the same time, this catalyst also has higher stability ( Figure 7 ), being able to operate stably for more than 100 hours compared to C-IrO2, and having a lower voltage decay.

[0052] The full-cell activity test results are as Figure 8 shown. The polarization curve comparison of the 30% Ir / WO3@TiN catalyst with an Ir loading of 0.3 mg cm -2 and C-IrO2 with different Ir loadings (0.3 mg cm -2 and 1.0 mg cm -2 ) shows that the catalytic activity of 30% Ir / WO3@TiN is significantly better than that of C-IrO2. The current density can reach 1.0 A cm -2 at 1.6 V, while the voltage of 0.3 mg cm -2 C-IrO2 is higher than 1.9 V at a current density of 1.0 A cm -2 , and even the commercially used MEA (1.0 mg Ir cm -2 ) requires a voltage of 1.8 V. Considering that the stability of MEA is the most important criterion for practical applications, we evaluated the stability of 30% Ir / WO3@TiN at a constant current density of 1.0 A cm −2 and a temperature of 80 °C. As Figure 9 shown, 30 wt% Ir / WO3@TiN can stably operate for up to more than 200 hours, and the voltage drop (0.1 mV h -1 ) is less than that of C-IrO2. This demonstrates its encouraging application value for PEMWE.

[0053] Example 2

[0054] (1) Prepare an aqueous dispersion of TiN nanoparticles at 15 mg / ml and stir for 30 min to obtain Liquid 1.

[0055] (2) Mix ammonium tungstate tetrahydrate (ATT) and sodium dodecyl sulfate (SDS) with a mass ratio of 1.2:0.6 in water and stir for 3 h to obtain Liquid 2, with the concentration of SDS being 0.02 g / ml.

[0056] (3) Mix and stir Liquid 1 and Liquid 2 for 60 min, and ultrasonically disperse until completely dispersed to obtain Liquid 3; the volume ratio of Liquid 1 to Liquid 2 is 15:50.

[0057] (4) Transfer Liquid 3 to a reaction kettle and heat at 200 °C for 8 hours.

[0058] (5) Cool, wash with deionized water, and dry in air at 60 °C for 12 hours to finally obtain the composite support WO3@TiN.

[0059] (6) Add 100 mg of WO3@TiN and 30 mg of cetyltrimethylammonium bromide CTAB to 100 ml of ethylene glycol EG, and stir for 2 h; then add hydrated iridium(IV) acid containing 200 mg of Ir to the obtained suspension, continuously stir for 3 hours, reflux at 170 °C for 4 h; finally, centrifuge the suspension, wash the solid with deionized water and ethanol, and then dry overnight at 80 °C to obtain Ir / WO3@TiN.

[0060] Use the test method of Example 1 for performance comparison.

[0061] Comparative Example 1

[0062] (1) Mix ATT (1.1 g) and SDS (0.5 g) with 50 ml of H2O and stir for 3 h. Then transfer to a 100 ml reaction kettle, heat to 200 °C for 6 hours. After natural cooling, wash several times with deionized water and dry in air at 60 °C for 12 hours to finally obtain the support WO3.

[0063] (2) Add 80 mg of the support material WO3 and 10 mg of CTAB to 35 ml of EG and act for 1 h; then add hydrated iridium(IV) acid with 30 wt% Ir to the obtained suspension, continuously stir for 2 hours, and reflux at 165 °C for 3.5 h. Finally, centrifuge the suspension, wash with deionized water and ethanol, and then dry Ir / WO3 at 60 °C.

[0064] Use the test method of Example 1 for performance comparison.

[0065] Comparative Example 2

[0066] Add 80 mg of the support material TiN and 10 mg of CTAB to 35 ml of EG and act for 1 h; then add hydrated iridium(IV) acid with 30 wt% Ir to the obtained suspension, continuously stir for 2 hours, and reflux at 165 °C for 3.5 h. Finally, centrifuge the suspension, wash with deionized water and ethanol, and then dry Ir / TiN at 60 °C.

[0067] The performance comparison was carried out using the test method of Example 1.

[0068] Table 1 Performance comparison of Examples 1 and 2 and Comparative Examples 1 and 2

[0069] Half-cell stability PEMWE activity PEMWE stability Example 1 <![CDATA[100 h@20 mA cm -2 > <![CDATA[1.6 V@1 A cm -2 > <![CDATA[200 h@1 A cm -2 > Example 2 <![CDATA[60 h@20 mA cm -2 > <![CDATA[1.81 V@1 A cm -2 > <![CDATA[80 h@1 A cm -2 > Comparative Example 1 <![CDATA[20 h@20 mA cm -2 > <![CDATA[1.88 V@1 A cm -2 > <![CDATA[30 h@1 A cm -2 > Comparative Example 2 <![CDATA[40 h@20 mA cm -2 > <![CDATA[1.94 V@1 A cm -2 > <![CDATA[50 h@1 A cm -2 >

[0070] As shown in Table 1, the oxygen evolution catalytic activity and stability of the Ir / WO3@TiN catalysts obtained in Examples 1 and 2 are significantly higher than those in Comparative Examples 1 and 2. In particular, the Ir / WO3@TiN catalyst prepared in Example 1 only requires a voltage of 1.6 V to reach a current density of 1 A cm -2 in the PEMWE full cell test and can stably operate at this current density for more than 200 h, showing the optimal oxygen evolution catalytic performance.

[0071] The above examples have detailed the structure, features and effects of the present invention. The above are only the preferred embodiments of the present invention. Any changes made in accordance with the concept of the present invention, or equivalent embodiments modified into equivalent changes, should still be within the protection scope of the present invention when they do not exceed the scope covered by the specification.

Claims

1. An Ir-doped WO3@TiN, characterized in that: The WO3@TiN is composed of rod-shaped WO3 and granular TiN loaded on WO3, wherein Ir and Ti replace the position of W atoms.

2. The Ir-doped WO3@TiN according to claim 1, characterized in that: The Ir is one or more of metal Ir and iridium oxide.

3. A method for preparing Ir-doped WO3@TiN as claimed in claim 1, characterized in that: The following steps are involved: (1) Synthesis of WO3@TiN with oxygen vacancies; (2) Loading Ir on WO3@TiN; the Ir is one or more of metallic Ir and iridium oxide.

4. The preparation method according to claim 3, characterized in that: The WO3@TiN with oxygen vacancies is prepared by the following steps: (1) TiN nanoparticles were prepared into a 15 mg / ml aqueous dispersion and stirred for 30 min as liquid 1; (2) ammonium tungstate tetrahydrate (ATT) and sodium dodecyl sulfate (SDS) in a mass ratio of (1.0-1.2): (0.4-0.6) were mixed and stirred in water for 3 h, as liquid 2, and the concentration of SDS was 0.01-0.02 g / ml; (3) Mix liquid 1 and liquid 2 and stir for 30-60 min, and perform ultrasonication until they are completely dispersed to obtain liquid 3; the volume ratio of liquid 1 to liquid 2 is (10-15):(30-50); (4) Transfer liquid 3 to a reactor and heat at 200°C for 4-8 hours; (5) Cooling, washing with deionized water, and drying in air at 60°C for 8-12 hours to finally obtain a composite carrier WO3@TiN.

5. The preparation method according to claim 3, characterized in that: The method for loading Ir on WO3@TiN is as follows: Add 80-100 mg of WO3@TiN and 10-30 mg of hexadecyltrimethylammonium bromide to 50-100 ml of ethylene glycol and stir for 1-2 h; then add hydrated chloroiridic acid (IV) containing not less than 50 mg of Ir to the obtained suspension, stir continuously for 1-3 hours, and reflux at 160-170°C for 3-4 h; finally, centrifuge the suspension, wash the solid with deionized water and ethanol, and then dry at 60-80°C overnight to obtain Ir / WO3@TiN.

6. Use of the Ir-doped WO3@TiN as claimed in claim 1 in proton exchange membrane water electrolysis.

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