Rare earth monatomic doped Pd / WO3 material as well as preparation method and application thereof

Abstract

The invention belongs to the field of inorganic materials, and relates to a rare earth monatomic doped Pd / WO3 material as well as a preparation method and application thereof. A series of rare earth monatomic doped Pd nanoparticle loaded WO3 nanorods (RE-Pd / WO3, RE = Ce, Nd, Eu, Tb, Ho and Tm) are successfully synthesized by virtue of a dipping reduction method, and the precise regulation and control of the work function difference between Pd and WO3 are realized by changing the variety of rare earth monatomic, so that the energy barrier of hydrogen (H) migration is reduced, and the overflow of H from Pd to WO3 is accelerated. A device made of the material can monitor low-concentration H2 leakage (0.1 V / V%) in an aluminum-air battery in real time, and rapid detection of low-concentration H2 at room temperature is achieved. Theoretical and experimental guidance is provided for developing efficient room temperature H2 sensors, and actual deployment of the H2 sensors in the fields of energy storage facilities and fuel cell automobiles is expected to be accelerated.

Description

Technical Field

[0001] The present invention belongs to the field of inorganic materials and relates to the preparation of room-temperature hydrogen sensing. Background Art

[0002] Developing highly sensitive gas sensors for rapid and accurate monitoring of trace H2 is of great significance for its safe applications. Compared with catalytic, thermal conductivity, and electrochemical sensors, resistive gas sensors have received extensive attention due to their simpler structure and lower power consumption. Among them, palladium (Pd)-based materials are widely used in the fabrication of advanced H2 sensors. However, the practical application of single palladium materials in H2 sensors is hindered for the following reasons: i) the formation of palladium hydride (PdH x ) always changes the volume of palladium, resulting in unstable sensing performance; ii) the strong affinity of H2 for palladium limits the desorption of hydrogen, leading to unsatisfactory responses.

[0003] Loading palladium on metal oxide semiconductors (Pd / MOS) is an effective method to alleviate the above problems. However, the strong adsorption of hydrogen hinders the spillover of hydrogen from palladium to MOS, which may severely limit the sensing process. So far, many strategies, including morphology regulation, alloying, and heterostructure construction, have been developed to regulate hydrogen spillover and thus enhance H2 sensing performance. The literature (Small 2023, 19, 2208026.) reported the construction of a core-shell structured Pd-NiO / SnO2 buffered nanocavity for H2 detection. The hollow nanocavity layer provides sufficient active sites to enhance H2 adsorption and kinetically promotes the spillover of hydrogen from palladium to the support, thus improving H2 sensing performance at 230 °C. The literature (SensorsActuators B: Chem. 2023, 375, 132967.) reported that in PdCu alloy loaded on WO 18 O 49 nanowires, the presence of Cu affects the electronic structure of palladium, resulting in rapid desorption of hydrogen and the formation of oxygen species, thus enabling rapid H2 detection at 125 °C. The patent (CN118954582A) reported that a porous shell structure Co3O4-SnO2 in-plane heterostructure can achieve a sensitivity of 8.63 to 50 ppm H2 at 170 °C.

[0004] Despite significant efforts, developing efficient room-temperature (RT) H2 sensors remains a great challenge due to the unresolved issue of difficult hydrogen migration at low temperatures. Recent research reports have shown that regulating the work function difference (ΔФ) between palladium and the support can promote hydrogen spillover, accelerate hydrogen migration from palladium to the support, and improve energy storage and conversion performance. Therefore, modulating ΔФ is expected to enhance H2 sensing performance, but there are still two key problems: 1) Continuously and precisely regulating ΔФ between palladium and the support is extremely challenging; 2) The mechanism of hydrogen spillover in H2 sensors is not yet clear. Summary of the Invention

[0005] To solve the above technical problems, the present invention proposes a rare-earth single-atom doped Pd / WO3 material, its preparation method, and application.

[0006] The technical solution of the present invention is realized as follows: A preparation method of a rare-earth single-atom doped Pd / WO3 material, the steps are as follows: (1) Add sulfuric acid solution to sodium tungstate solution, then add sodium sulfate and oxalic acid in sequence, stir and mix, and perform hydrothermal reaction at 180 °C for 16 h. The obtained product is washed, dried, and calcined at 350 °C for 1.5 h in an argon atmosphere to obtain rod-shaped WO3; the molar ratio of sodium tungstate, sulfuric acid, sodium sulfate, and oxalic acid is 5:6:30:12.

[0007] (2) Add palladium nitrate solution to a mixed solution of deionized water and absolute ethanol, then add rod-shaped WO3, ultrasonically dissolve and stir for 24 h, wash the product, vacuum dry, and calcine at 350 °C for 2 h in an argon atmosphere to obtain Pd / WO3; the molar ratio of palladium nitrate to rod-shaped WO3 is 4:3; the volume ratio of deionized water to absolute ethanol is 2:1.

[0008] (3) Add rod-shaped Pd / WO3 to the rare-earth salt solution, ultrasonically stir and react, and the obtained product is washed, vacuum dried, and calcined at 300 - 450 °C for 3 - 9 h in an argon-hydrogen atmosphere to obtain a rare-earth single-atom doped Pd / WO3 material, namely RE-Pd / WO3; add 0.01 - 0.06 mol of rare-earth salt to every 40 g of rod-shaped Pd / WO3, and the concentration of the rare-earth salt is 0.05 - 4 mol / L.

[0009] The above rare-earth salt is any one of cerium acetate hydrate, cerium chloride, cerium sulfate, neodymium acetate hydrate, neodymium chloride, neodymium nitrate, europium acetate hydrate, europium chloride, europium sulfate hydrate, terbium acetate hydrate, terbium chloride, terbium acetylacetonate, holmium acetate hydrate, holmium chloride, holmium chloride hexahydrate, thulium acetate hydrate, thulium chloride, and thulium acetylacetonate.

[0010] The rare earth single-atom doped Pd / WO3 material prepared by the above method; the rare earth single-atom doping of the present application can reduce the work function difference and the oxygen vacancy formation energy, among which Ce-Pd / WO3 has a small work function difference (0.44 eV) and oxygen vacancy formation energy (2.37 eV).

[0011] Application of the above rare earth single-atom doped Pd / WO3 material in the preparation of a room-temperature hydrogen sensor; among which the sensitivity of Ce-Pd / WO3 to 50 ppm H2 can reach 31.3, and the response and recovery times are only 3 s and 15 s, far superior to the H2 sensors reported currently.

[0012] The present invention also discloses an H2 sensor made of Ce-Pd / WO3, which can realize the real-time detection of low-concentration H2 (0.1 V / V%) leakage in an aluminum-air battery.

[0013] The present invention has the following beneficial effects: (1) Under the guidance of theoretical calculations, the present invention precisely designs a rare earth single-atom doped Pd / WO3 material with continuously adjustable work function difference. And a series of rare earth single-atom doped Pd nanoparticles supported on WO3 nanorods (RE-Pd / WO3, RE = Ce, Nd, Eu, Tb, Ho, Tm) are successfully synthesized by the impregnation reduction method. By changing the types of rare earth single atoms, the precise regulation of the work function difference between Pd / WO3 is realized, thereby reducing the energy barrier for hydrogen (H) migration and accelerating the spillover of H from Pd to WO3. At the same time, the doping of rare earth atoms also reduces the oxygen vacancy formation energy, resulting in the formation of more oxygen vacancies on WO3, which is beneficial to the adsorption of oxygen species (O2 - ) and thus accelerates the desorption of H.

[0014] (2) The present invention synthesizes the RE-Pd / WO3 material, realizing the precise adjustment of the oxygen vacancy concentration of Pd / WO3 from 7.9% to 21.8%. The Ce-Pd / WO3 material prepared by the present invention has the highest oxygen vacancy concentration and exhibits the most excellent room-temperature H2 sensing performance: the sensitivity to 50 ppm H2 is 31.3, and the response and recovery times are 3 s and 15 s, far superior to the H2 sensors reported currently. The device made of this material can monitor the low-concentration H2 leakage (0.1 V / V%) in an aluminum-air battery in real time, realizing the rapid detection of low-concentration H2 at room temperature. The present invention provides theoretical and experimental guidance for the development of efficient room-temperature H2 sensors, and is expected to accelerate the practical deployment of H2 sensors in the fields of energy storage facilities and fuel cell vehicles.

[0015] (3) Theoretical calculations and in-situ characterization prove that rare earth doping can reduce the hydrogen migration energy barrier and promote the spillover of H from palladium to tungsten trioxide. The reduction of the oxygen vacancy formation energy can effectively improve O2 on the tungsten trioxide support -The concentration is increased to accelerate the desorption of H. This invention provides theoretical and experimental guidance for the development of efficient room-temperature H2 sensors. Description of the Drawings

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0017] Figure 1 Work function and work function difference of the rod-shaped RE-Pd / WO3 prepared in Examples 1-6.

[0018] Figure 2 XRD of RE-Pd / WO3 prepared in Examples 1-6.

[0019] Figure 3 AC-TEM image of the rod-shaped Ce-Pd / WO3 prepared in Example 1.

[0020] Figure 4 SEM image of the rod-shaped Ce-Pd / WO3 prepared in Example 1; among them, (a) is the low-magnification morphology image, and (b) is the high-magnification morphology image.

[0021] Figure 5 TEM image of Ce-Pd / WO3 prepared in Example 1; among them, (a) is the low-magnification morphology image, (b) is the high-magnification morphology image, and (c) is the SAED image.

[0022] Figure 6 EDS of the rod-shaped RE-Pd / WO3 (RE-Pd / WO3, RE = Ce, Nd, Eu, Tb, Ho, Tm) prepared in Examples 1-6.

[0023] Figure 7 XPS of oxygen in the RE-Pd / WO3 materials prepared in Examples 1-6.

[0024] Figure 8 Proportion of different oxygen species in RE-Pd / WO3 prepared in Examples 1-6.

[0025] Figure 9 Response values of WO3, Pd / WO3, and RE-Pd / WO3 prepared in Example 1 at different temperatures.

[0026] Figure 10 Response and recovery times of RE-Pd / WO3 prepared in Examples 1-6.

[0027] Figure 11 Comparison chart of H2 detection values of Ce-Pd / WO3 prepared in Example 1 and those disclosed in different literatures at different temperatures (100 ppm).

[0028] Figure 12 Application of the H2 sensor prepared from Ce-Pd / WO3 prepared in Example 1 in an aluminum-air battery.

[0029] Figure 13 In-situ Raman spectra of Pd / WO3 and Ce-Pd / WO3 prepared in Example 1.

[0030] Figure 14 Hydrogen spillover experiments of Pd / WO3 and Ce-Pd / WO3 prepared in Example 1.

[0031] Figure 15 Performances of the Pd / WO3 and RE-Pd / WO3 (RE = Ce, Eu, Tm) sensors prepared in Examples 1-6; wherein, (a) is the hydrogen migration energy barrier and (b) is the oxygen vacancy formation energy. Detailed implementation manners

[0032] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the protection scope of the present invention.

[0033] Unless otherwise specified, the test methods used in the following experimental examples are all conventional methods; the materials, reagents, etc. used, unless otherwise specified, are reagents and materials that can be obtained from commercial channels.

[0034] Example 1 The preparation method of the rare earth single-atom doped Pd / WO3 material in this example is as follows: (1) Add 0.005 mol of sodium tungstate to 40 mL of deionized water, ultrasonically dissolve it, then add 2 mL of sulfuric acid solution with a concentration of 3 mol / L, and then sequentially add 0.03 mol of sodium sulfate and 0.012 mol of oxalic acid and stir for 0.25 h. Hydrothermally react the mixed solution at 180 °C for 16 h, wash and dry the product, and calcine it at 350 °C for 1.5 h in an argon atmosphere to obtain rod-shaped WO3; (2) Add 0.8 mL of a palladium nitrate solution with a concentration of 5 mol / L to 20 mL of deionized water and 10 mL of absolute ethanol. Subsequently, add 0.003 mol of rod-shaped WO3, ultrasonically dissolve it, and stir for 24 h. Wash the product, dry it under vacuum, and calcine it in an argon atmosphere at 350 °C for 2 h to obtain Pd / WO3; (3) Using 20 mL of deionized water as the solvent, add 40 mg of rod-shaped Pd / WO3 and 0.01 mol of cerium acetate solution, ultrasonically dissolve it, and stir for 30 h at a stirring rate of 180 r / min. Filter, wash, dry under vacuum, and calcine in an argon-hydrogen atmosphere at 350 °C for 4 h to obtain Ce-Pd / WO3.

[0035] Characterize the obtained Ce-Pd / WO3, Figure 3 which is the AC-TEM image of the rod-shaped Ce-Pd / WO3 prepared in Example 1. It can be seen from Figure 3 that isolated Ce single atoms can be observed on the lattice of Pd, indicating the successful doping of Ce single atoms in Pd nanoparticles. At the same time, obvious lattice spacings of 0.391 and 0.224 nm are observed, corresponding to the (001) plane of WO3 and the (111) plane of Pd, respectively.

[0036] Figure 4 which is the SEM image of the rod-shaped Ce-Pd / WO3 prepared in Example 1; among them, (a) is the low-magnification morphology image, and (b) is the high-magnification morphology image. It can be seen from Figure 4 that the prepared sample has a nanorod structure, and Pd nanoparticles are evenly distributed on the nanorods.

[0037] Figure 5 which is the TEM image of Ce-Pd / WO3 prepared in Example 1; among them, (a) is the low-magnification morphology image, (b) is the high-magnification morphology image, and (c) is the SAED image. It can be seen from Figure 5 that Pd nanoparticles are evenly dispersed on WO3 nanorods, with an average size of about 12.3 nm. In (b), lattice spacings of 0.391 and 0.224 nm can be observed, corresponding to the (001) plane of WO3 and the (111) plane of Pd, respectively. The selected area electron diffraction (SAED) image shows the (001) crystal plane of WO3 and the (111) crystal plane of Pd, confirming the successful modification of Pd nanoparticles on WO3 nanorods.

[0038] Example 2 The preparation method of the rare earth single atom doped Pd / WO3 material in this example is as follows: (1) Add 0.005 mol of sodium tungstate to 40 mL of deionized water. After ultrasonic dissolution, add 2 mL of sulfuric acid solution with a concentration of 3 mol / L. Subsequently, add 0.03 mol of sodium sulfate and 0.012 mol of oxalic acid in sequence and stir for 0.25 h. Carry out hydrothermal reaction on the mixed solution at 180 °C for 16 h. Wash, dry the product, and calcine it at 350 °C for 1.5 h in an argon atmosphere to obtain rod-shaped WO3; (2) Add 0.8 mL of palladium nitrate solution with a concentration of 5 mol / L to 20 mL of deionized water and 10 mL of absolute ethanol. Subsequently, add 0.003 mol of rod-shaped WO3, ultrasonically dissolve and stir for 24 h. Wash, vacuum dry the product, and calcine it at 350 °C for 2 h in an argon atmosphere to obtain Pd / WO3; (3) Use 20 mL of deionized water as the solvent, add 40 mg of rod-shaped Pd / WO3 and 0.04 mol of neodymium acetate solution, ultrasonically dissolve and stir for 24 h, with a stirring rate of 180 r / min. Filter, wash, vacuum dry the product, and calcine it at 400 °C in an argon-hydrogen atmosphere for 3 h to obtain Nd-Pd / WO3.

[0039] Example 3 The preparation method of the rare-earth single-atom doped Pd / WO3 material in this example is as follows: (1) Add 0.005 mol of sodium tungstate to 40 mL of deionized water. After ultrasonic dissolution, add 2 mL of sulfuric acid solution with a concentration of 3 mol / L. Subsequently, add 0.03 mol of sodium sulfate and 0.012 mol of oxalic acid in sequence and stir for 0.25 h. Carry out hydrothermal reaction on the mixed solution at 180 °C for 16 h. Wash, dry the product, and calcine it at 350 °C for 1.5 h in an argon atmosphere to obtain rod-shaped WO3; (2) Add 0.8 mL of palladium nitrate solution with a concentration of 5 mol / L to 20 mL of deionized water and 10 mL of absolute ethanol. Subsequently, add 0.003 mol of rod-shaped WO3, ultrasonically dissolve and stir for 24 h. Wash, vacuum dry the product, and calcine it at 350 °C for 2 h in an argon atmosphere to obtain Pd / WO3; (3) Use 20 mL of deionized water as the solvent, add 40 mg of rod-shaped Pd / WO3 and 0.06 mol of terbium acetate solution, ultrasonically dissolve and stir for 24 h, with a stirring rate of 150 r / min. Filter, wash, vacuum dry the product, and calcine it at 310 °C in an argon-hydrogen atmosphere for 6 h to obtain Te-Pd / WO3.

[0040] Example 4 The preparation method of the rare-earth single-atom doped Pd / WO3 material in this example is as follows: (1) Add 0.005 mol of sodium tungstate to 40 mL of deionized water. After ultrasonic dissolution, add 2 mL of sulfuric acid solution with a concentration of 3 mol / L. Subsequently, add 0.03 mol of sodium sulfate and 0.012 mol of oxalic acid in sequence and stir for 0.25 h. Carry out hydrothermal reaction on the mixed solution at 180 °C for 16 h. Wash, dry the product, and calcine it at 350 °C for 1.5 h in an argon atmosphere to obtain rod-shaped WO3; (2) Add 0.8 mL of palladium nitrate solution with a concentration of 5 mol / L to 20 mL of deionized water and 10 mL of absolute ethanol. Subsequently, add 0.003 mol of rod-shaped WO3, ultrasonic dissolve and stir for 24 h. Wash, vacuum dry the product, and calcine it at 350 °C for 2 h in an argon atmosphere to obtain Pd / WO3; (3) Use 20 mL of deionized water as the solvent, add 40 mg of rod-shaped Pd / WO3 and 0.06 mol of holmium acetate solution, ultrasonic dissolve and stir for 30 h, with a stirring rate of 180 r / min. Filter, wash, vacuum dry the product, and calcine it at 350 °C in an argon-hydrogen atmosphere for 4 h to obtain Ho-Pd / WO3.

[0041] Example 5 The preparation method of the rare earth single-atom doped Pd / WO3 material in this example is as follows: (1) Add 0.005 mol of sodium tungstate to 40 mL of deionized water. After ultrasonic dissolution, add 2 mL of sulfuric acid solution with a concentration of 3 mol / L. Subsequently, add 0.03 mol of sodium sulfate and 0.012 mol of oxalic acid in sequence and stir for 0.25 h. Carry out hydrothermal reaction on the mixed solution at 180 °C for 16 h. Wash, dry the product, and calcine it at 350 °C for 1.5 h in an argon atmosphere to obtain rod-shaped WO3; (2) Add 0.8 mL of palladium nitrate solution with a concentration of 5 mol / L to 20 mL of deionized water and 10 mL of absolute ethanol. Subsequently, add 0.003 mol of rod-shaped WO3, ultrasonic dissolve and stir for 24 h. Wash, vacuum dry the product, and calcine it at 350 °C for 2 h in an argon atmosphere to obtain Pd / WO3; (3) Use 20 mL of deionized water as the solvent, add 40 mg of rod-shaped Pd / WO3 and 0.03 mol of thulium acetate solution, ultrasonic dissolve and stir for 36 h, with a stirring rate of 150 r / min. Filter, wash, vacuum dry the product, and calcine it at 420 °C in an argon-hydrogen atmosphere for 5 h to obtain Tm-Pd / WO3.

[0042] Example 6 The preparation method of the rare earth single-atom doped Pd / WO3 material in this example is as follows: (1) Add 0.005 mol of sodium tungstate to 40 mL of deionized water. After ultrasonic dissolution, add 2 mL of sulfuric acid solution with a concentration of 3 mol / L. Subsequently, add 0.03 mol of sodium sulfate and 0.012 mol of oxalic acid and stir for 0.25 h. Hydrothermally react the mixed solution at 180 °C for 16 h. Wash, dry the product, and calcine it at 350 °C for 1.5 h in an argon atmosphere to obtain rod-shaped WO3; (2) Add 0.8 mL of palladium nitrate solution with a concentration of 5 mol / L to 20 mL of deionized water and 10 mL of absolute ethanol. Subsequently, add 0.003 mol of rod-shaped WO3, ultrasonically dissolve and stir for 24 h. Wash, vacuum dry the product, and calcine it at 350 °C for 2 h in an argon atmosphere to obtain Pd / WO3; (3) Use 20 mL of deionized water as the solvent, add 40 mg of rod-shaped Pd / WO3 and 0.05 mol of europium acetate solution, ultrasonically dissolve and stir for 24 h, with a stirring rate of 150 r / min. Filter, wash, vacuum dry the product, and calcine it at 400 °C in an argon-hydrogen atmosphere for 4 h to obtain Eu-Pd / WO3.

[0043] Example of implementation effect First, use the VASP software to establish models of WO3, Pd / WO3, and RE-Pd / WO3, and calculate the work function of the materials through density functional theory. From Figure 1 It can be seen that the work function of Pd decreases from 5.24 eV (Ce-Pd) to 3.46 eV (Ce-Pd), 3.56 eV (Nd-Pd), 3.59 eV (Eu-Pd), 3.73 eV (Tb-Pd), 3.78 eV (Ho-Pd), and 3.82 eV (Tm-Pd). Correspondingly, further calculate ΔФ (ΔФ = Ф RE-Pd - Ф WO3 ) between RE-Pd and WO3. ΔФ decreases from 2.23 eV (Pd / WO3) to 0.44 eV (Ce-Pd / WO3), 0.55 eV (Nd-Pd / WO3), 0.58 eV (Eu-Pd / WO3), 0.71 eV (Tb-Pd / WO3), 0.76 eV (Ho-Pd / WO3), and 0.80 eV (Tm-Pd / WO3). These results indicate that doping rare earth in Pd is an effective way to adjust ΔФ.

[0044] Second, Figure 2 The XRD of RE-Pd / WO3 prepared in Examples 1-6. The crystal structure was analyzed by powder X-ray diffraction (XRD). From Figure 2It can be seen that the XRD diffraction peaks correspond to the WO3 (JCPDS NO33-1387) card. After loading RE and Pd on WO3, the diffraction peaks corresponding to WO3 are retained, and a new diffraction peak appears at 40.1°, which corresponds to the (111) crystal plane of Pd (JCPDSNO46-1043). No diffraction peaks related to rare earths are observed, indicating that rare earths may exist in the form of single atoms.

[0045] The energy-dispersive X-ray spectroscopy was used to analyze the distribution of W, O, RE, and Pd elements in the rod-shaped RE-Pd / WO3 (RE-Pd / WO3, RE = Ce, Nd, Eu, Tb, Ho, Tm) prepared in Examples 1-6 on the RE-Pd / WO3 nanorods. The results are as Figure 6 shown. It can be Figure 6 seen that W, O, RE, and Pd elements are all distributed on the RE-Pd / WO3 nanorods, proving the successful preparation of RE-Pd / WO3.

[0046] The X-ray photoelectron spectroscopy (XPS) was used to study the chemical state of oxygen on the surface of WO3, Pd / WO3, and RE-Pd / WO3 for the RE-Pd / WO3 materials prepared in Examples 1-6, and the Avantage software was used to perform peak fitting. The results are as Figure 7 shown. It can be Figure 7 seen that the O1s spectrum can be divided into three peaks at 530.6, 532.2, and 532.8 eV, which are attributed to lattice oxygen (O L ), oxygen vacancies (O V ), and adsorbed oxygen (O C ), respectively.

[0047] The X-ray photoelectron spectroscopy (XPS) was used to quantitatively analyze the oxygen content on the surface of WO3, Pd / WO3, and RE-Pd / WO3, and the results were plotted as Figure 8 . It can be Figure 8 seen that after RE doping, the oxygen vacancy concentration increases, which can enhance the adsorption of O2, capture more electrons to form oxygen species (O2 - ), and thus improve the desorption of H. The oxygen vacancy concentration from high to low is Ce-Pd / WO3 > Nd-Pd / WO3 > Eu-Pd / WO3 > Tb-Pd / WO3 > Ho-Pd / WO3 > Tm-Pd / WO3 > Pd / WO3.

[0048] III. The sample prepared in Example 1 was placed in an agate mortar containing an appropriate amount of terpineol and ground into a paste. It was evenly coated on the surface of the alumina tube with a small brush, and then dried at 60 °C for 2 h and sintered in a tube furnace at 300 °C for 2 h to fully vaporize the terpineol. The obtained ceramic tube was directly welded to the element to obtain the sensor. The performance of the sensor was studied using the WS-30B system (Weisheng Instruments Co., Ltd., Zhengzhou, China). The static volumetric method was used for gas-sensing testing. At the beginning, the gas sensor was placed in a sealed 18 L airtight glass test chamber. The operating temperature of the gas sensor was controlled by adjusting the heating voltage of the Ni-Cr alloy resistor. After injecting the target gas, when the sensor resistance reached the equilibrium value, the test chamber was opened, and the analysis system automatically obtained the resistance value and response value of the sensor. The results are as Figure 9 shown.

[0049] During the testing process, a reference resistor (Rload) was added to the sensor circuit, and the operating voltage was 5 V. The sensing response was defined as the ratio of the resistance in air (Ra) to the resistance in gas (Rg). The sensing response of reducing gases was calculated using S = Ra / Rg. The results are as Figure 9 shown. It can be seen from Figure 9 that as the operating temperature increased from 40 °C to 80 °C, the responses of both Pd / WO3 and RE-Pd / WO3 sensors showed an upward trend, and the response of RE-Pd / WO3 was higher than that of Pd / WO3. It is worth noting that the RE-Pd / WO3 sensor showed excellent sensing performance even at room temperature. The response of Ce-Pd / WO3 to 50 ppm H2 was the highest, reaching 31.3, which was 6 times higher than that of Pd / WO3, superior to most reported sensors, and achieved trace detection of H2 at room temperature.

[0050] IV. The RE-Pd / WO3 material samples prepared in Examples 1-6 were placed in an agate mortar containing an appropriate amount of terpineol and ground into a paste. It was evenly coated on the surface of the alumina tube with a small brush, and then dried at 60 °C for 2 h and sintered in a tube furnace at 300 °C for 2 h to fully vaporize the terpineol. The obtained ceramic tube was directly welded to the element to obtain the sensor, and then placed in the WS-30B system (Weisheng Instruments Co., Ltd., Zhengzhou, China) to study the sensor response / recovery time. The response time (Tres) and recovery time (Trec) were the times taken for the change in sensor resistance to reach 90% of its maximum value after the gas was applied and removed on the test bench, respectively. The results are as Figure 10 shown, which are the response / recovery times of RE-Pd / WO3 prepared in Examples 1-6. It can be seen from Figure 10It can be seen that after doping with rare earths, the response and recovery times of the sensor are significantly shortened. Among them, the response and recovery times of the Ce-Pd / WO3 and Pd / WO3 sensors are 3 / 15 s and 45 / 115 s respectively, which are reduced by 15 times and 8 times respectively. The inset shows the resistance curve of Ce-Pd / WO3.

[0051] V. Figure 11 Comparison diagram of the Ce-Pd / WO3 prepared in Example 1 with the H2 detection values at different temperatures (100 ppm) disclosed in different literatures. The operating temperatures and response values of different metal-semiconductor oxides for sensors at a H2 concentration of 100 ppm were summarized from the literature. From Figure 11 it can be seen that compared with the previously reported H2 sensors with a concentration of 100 ppm, the Ce-Pd / WO3 sensor has obvious advantages.

[0052] VI. An 80 mm×100 mm×3 mm commercial aluminum plate was used as the anode, and the cathode was a commercial C / MnO2 cathode. The two were placed in a 100 mm × 130 mm aluminum-air battery mold. A 4 mol / L KOH electrolyte solution was poured into the battery mold to ensure that the cathode and the aluminum plate were in full contact with the electrolyte. Finally, the hydrogen sensor made by combining the Ce-Pd / WO3 element and the control element prepared in Example 1 and the assembled aluminum-air battery were placed in a high and low temperature test bench for testing. The H2 concentration threshold was set to 0.1 V / V%, and when the H2 concentration reached the preset concentration value, the buzzer alarmed to achieve the detection of hydrogen. The results are as Figure 12 shown. From Figure 12 it can be seen that when the H2 concentration reached 0.1 V / V%, the buzzer alarmed, and this concentration is much lower than the explosion limit of H2, indicating that the H2 sensor prepared with Ce-Pd / WO3 has potential applications in the detection of low-concentration H2 at room temperature.

[0053] Under the condition of 40 °C, the Pd / WO3 and Ce-Pd / WO3 samples prepared in Example 1 were exposed to 50 ppm of H2 and then in-situ Raman experiments were carried out to prove the hydrogen spillover effect. The samples were placed on a microscope slide in a quartz reaction cell, and the Raman spectra of the samples were collected. Then a mixture of H2 and air was injected, and another Raman spectrum was collected (the H2 content in the gas mixture was 50 ppm). Finally, data was collected every 30 s, and the last collection time was 270 s. The results are as Figure 13 shown. From Figure 13 it can be seen that after exposure to 50 ppm of H2 at room temperature, the blue shift of this peak in Ce-Pd / WO3 occurred only after 30 s and increased with time, and the blue shift was about 9.1 cm after 270 s of H2 exposure. -1However, the peaks in Pd / WO3 hardly changed, indicating that hydrogen spillover in Ce-Pd / WO3 promoted the reduction of WO3.

[0054] 30 mg of Pd / WO3 and Ce-Pd / WO3 prepared in Example 1 were respectively placed into reagent tubes, and H2 / Ar was injected at a flow rate of 50 mL / min at 40 °C. The colors of the samples before and after 15 minutes were compared to confirm the existence of the hydrogen spillover effect. The results are as Figure 14 shown. As Figure 14 can be seen, Ce-Pd / WO3 showed faster color development than Pd / WO3, indicating that H spillover is beneficial to the reduction of WO3, suggesting that the doping of rare earth promoted hydrogen spillover in Ce-Pd / WO3.

[0055] VII. First, Pd / WO3 and RE-Pd / WO3 (RE = Ce, Eu, Tm) models were established using VASP software, and the hydrogen migration energy barrier and oxygen vacancy formation energy of the materials were calculated by density functional theory. The data results are statistically presented as Figure 15 shown, where (a) is the hydrogen migration energy barrier and (b) is the oxygen vacancy formation energy. As Figure 15 can be seen, the hydrogen migration energy barrier in RE-Pd / WO3 is lower than that in Pd / WO3 (4.04 eV). Among them, the hydrogen spillover energy barrier is positively correlated with ΔФ, and Ce-Pd / WO3 is the lowest, showing the lowest hydrogen spillover energy barrier (2.28 eV). As shown in Figure (b), the oxygen vacancy formation energies in Pd / WO3, Ce-Pd / WO3, Eu-Pd / WO3, and Tm-Pd / WO3 are 3.64, 2.37, 2.66, and 2.84 eV respectively, indicating that RE doping is beneficial to the generation of vacancies. It should be noted that Ce-Pd / WO3 shows the lowest oxygen vacancy formation energy, indicating that it has the highest O2 - concentration, promoting hydrogen spillover on RE-Pd / WO3, thereby improving the H2 sensing performance.

[0056] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a rare earth single-atom doped Pd / WO3 material, characterized in that, The steps are as follows: (1) Add sulfuric acid solution to sodium tungstate solution, then add sodium sulfate and oxalic acid in sequence. After stirring and mixing, carry out hydrothermal reaction. The obtained product is washed, dried and calcined in argon I to obtain rod-shaped WO3; (2) Add palladium nitrate solution to the mixed solution of deionized water and absolute ethanol, then add rod-shaped WO3 and dissolve it. After stirring reaction, the obtained product is washed, dried and calcined in argon II to obtain rod-shaped Pd / WO3; (3) Add rod-shaped Pd / WO3 to the rare earth salt solution. After ultrasonic stirring reaction, the obtained product is washed, vacuum dried and calcined III to obtain rare earth single-atom doped Pd / WO3 material, namely RE-Pd / WO3.

2. The preparation method of the rare earth single-atom doped Pd / WO3 material according to claim 1, characterized in that: In the step (1), the molar ratio of sodium tungstate, sulfuric acid, sodium sulfate and oxalic acid is 5:6:30:

12.

3. The preparation method of the rare earth single-atom doped Pd / WO3 material according to claim 2, characterized in that: The temperature of the hydrothermal reaction is 180 °C and the time is 16 h; the temperature of the argon calcination I is 350 °C and the time is 1.5 h.

4. The preparation method of the rare earth single-atom doped Pd / WO3 material according to claim 3, characterized in that: In the step (2), the molar ratio of palladium nitrate and rod-shaped WO3 is 4:3; the volume ratio of deionized water and absolute ethanol is 2:

1.

5. The preparation method of the rare earth single-atom doped Pd / WO3 material according to claim 4, wherein: The time of the stirring reaction is 24 h; the temperature of the argon calcination II is 350 °C and the time is 2 h.

6. The preparation method of the rare earth single-atom doped Pd / WO3 material according to claim 5, characterized in that: In the step (3), 0.01 - 0.06 mol of rare earth salt is added to every 40 g of rod-shaped Pd / WO3, and the concentration of the rare earth salt is 0.05 - 4 mol / L.

7. The preparation method of the rare earth single-atom doped Pd / WO3 material according to claim 6, wherein: The rare earth salt is any one of cerium acetate hydrate, cerium chloride, cerium sulfate, neodymium acetate hydrate, neodymium chloride, neodymium nitrate, europium acetate hydrate, europium chloride, europium sulfate hydrate, terbium acetate hydrate, terbium chloride, terbium acetylacetonate, holmium acetate hydrate, holmium chloride, holmium chloride hexahydrate, thulium acetate hydrate, thulium chloride and thulium acetylacetonate.

8. The preparation method of the rare earth single-atom doped Pd / WO3 material according to claim 7, wherein: The atmosphere of the calcination III is argon-hydrogen atmosphere, the temperature is 300 - 450 °C, and the time is 3 - 9 h.

9. Rare earth single-atom doped Pd / WO3 material prepared by the method according to any one of claims 1 - 8.

10. Application of the rare earth single-atom doped Pd / WO3 material according to claim 9 in the preparation of a room temperature hydrogen sensor.

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