Application of metal cation doped NiO catalyst in two-electron oxygen reduction reaction

Abstract

The application discloses application of a metal cation doped NiO catalyst in a two-electron oxygen reduction reaction, wherein the metal comprises Fe and / or Zn. A preparation method of the metal cation doped NiO catalyst disclosed by the application comprises the following steps: configuring a precursor solution of a Ni salt and a doped metal salt; transferring the precursor solution to a muffle furnace for heating; and obtaining the metal cation doped NiO catalyst after washing and drying of a product. ‑ The application changes the electrocatalytic activity and selectivity of a transition metal oxide NiO to 2e ‑ ORR from the electronic structure by doping with a specific metal cation, and the Zn-NiO catalyst has high selectivity, activity and long-term stability in producing hydrogen peroxide under alkaline conditions.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of two-electron oxygen reduction reaction catalysts; more particularly, it relates to the application of metal cation-doped NiO (nickel oxide) catalysts in two-electron oxygen reduction reactions. BACKGROUND

[0002] Hydrogen peroxide (H2O2) is considered a green, multi-functional, environmentally friendly oxidant, widely used in pulp and papermaking, food processing, water treatment, textiles, laundry, petroleum and electronics industries. Currently, the industrial production of H2O2 mainly relies on the energy-intensive and complex large-scale anthraquinone process, which raises concerns about environmental impact, cost and safety. Another approach is to directly mix gaseous hydrogen (H2) and oxygen (O2) over noble metal-based catalysts. However, this approach poses safety challenges, requiring additional precautions to mitigate the risk of hydrogen gas explosion.

[0003] In comparison with these methods, electrochemical two-electron oxygen reduction (2e - ORR) is a green, efficient, economical, safe and flexible route for H2O2 synthesis. In order to develop a catalyst with high selectivity, high activity, good stability and high cost-effectiveness for the reduction of O2 to H2O2 instead of H2O, it is necessary to develop a catalyst with weak O-O bond dissociation energy and sufficient oxidation ability to promote the formation of H2O2.

[0004] Currently, some pioneering studies have identified noble metals and alloys as efficient electrocatalysts for 2e - ORR in the electro-synthesis of hydrogen peroxide, and satisfactory results have been achieved. However, their high price and scarcity of metal resources have restricted their feasible production and application. In contrast, non-noble transition metal compounds, such as tungsten (W), vanadium (V), nickel (Ni), molybdenum (Mo) and iron (Fe) based compounds, including oxides, chalcogenides, phosphates and single atoms, have many advantages. These advantages include their abundance in the earth's crust, low cost, good environmental compatibility and the ability to adjust their composition and structure, thus showing great potential as advanced 2e - ORR electrocatalysts.

[0005] In recent years, transition metal oxide materials have been widely studied as 2e - ORR catalysts. Doping foreign elements in appropriate metal oxide-based catalysts has become a feasible strategy to improve the 2e - ORR electrocatalytic performance. Element doping significantly changes the electronic structure of the original metal oxide, leading to a narrower band gap, which is beneficial to improve the electrical conductivity. However, how to prepare 2e -It is still a technical problem to obtain cation-doped oxide catalysts with better ORR electrocatalytic performance, especially the influence mechanism and rules of different metal doping on 2e - The influence mechanism and rules of different metal doping on 2e SUMMARY

[0006] The application discloses application of metal cation-doped NiO catalyst in a two-electron oxygen reduction reaction, so as to realize efficient and stable hydrogen peroxide production.

[0007] Specifically, the application relates to application of metal cation-doped NiO catalyst in a two-electron oxygen reduction reaction; wherein the metal comprises Fe and / or Zn.

[0008] Further, the preparation method of the metal cation-doped NiO catalyst comprises the following steps:

[0009] S1, configuring a precursor solution of Ni salt and doping metal salt;

[0010] S2, transferring the precursor solution to a muffle furnace for heating, and obtaining the metal cation-doped NiO catalyst after washing and drying the product.

[0011] Further, the molar ratio of the Ni salt to the doping metal salt is 9:0.5-1.5.

[0012] Further, step S1 comprises: respectively configuring a Ni salt solution and a doping metal salt solution, and then adding an appropriate amount of ethylene glycol into the Ni salt solution, and then mixing the two solutions in proportion.

[0013] Further, the molar concentration of the Ni salt solution and the doping metal salt solution is 0.1-1M.

[0014] Further, the mass ratio of ethylene glycol to metal Ni is 1:0.8-1.

[0015] Further, the Ni salt is Ni(NO3)2 or NiCl2.

[0016] Further, the doping metal salt is any one of Fe(NO3)3 or FeCl3 and Zn(NO3)2 or ZnCl2 or a combination thereof.

[0017] Further, the temperature rising procedure of the muffle furnace in step S2 is as follows: first heating at 5-15 DEG C / min to 100 DEG C, and then heating at 1-5 DEG C / min to 300-400 DEG C and keeping for 0.5-2 hours.

[0018] Further, the two-electron oxygen reduction reaction is carried out in an alkaline environment.

[0019] The technical scheme of the present application has the following beneficial effects:

[0020] The metal cation doped NiO catalyst applied to the two-electron oxygen reduction reaction is doped with Fe and / or Zn, and this specific selection makes the catalyst have optimal adsorption energy for OOH* intermediate, and in particular, the Zn-NiO nanocatalyst has high selectivity, activity and long-term stability for the production of hydrogen peroxide under alkaline conditions. The metal cation doped NiO catalyst disclosed in the application can be synthesized in large quantities using a solution combustion method, does not require harsh production conditions, has a simple preparation method, and can realize low-cost industrial application. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 In the figure, a is the X-ray diffraction (XRD) spectrum of the catalyst of the examples and the comparative examples, and b is the local enlarged view of the XRD in the diffraction range of 40-45°;

[0022] Figure 2 The figure is a scanning electron microscope (SEM) image of the Zn-NiO catalyst;

[0023] Figure 3 In the figure, a and b are scanning electron microscope (SEM) images of the Fe-NiO catalyst, c and d are SEM images of the NiO catalyst, e and f are SEM images of the Co-NiO catalyst, and g and h are SEM images of the Cu-NiO catalyst;

[0024] Figure 4 In the figure, a is a high-resolution transmission electron microscope (HRTEM) image of the NiO catalyst, and b is an HRTEM image of the Zn-NiO catalyst;

[0025] Figure 5 The figure is an X-ray photoelectron spectroscopy (XPS) spectrum of the catalyst of the examples and the comparative examples;

[0026] Figure 6 The figure is a Ni2p X-ray photoelectron spectroscopy (XPS) spectrum of the catalyst of the examples and the comparative examples;

[0027] Figure 7 The figure is an O1s X-ray photoelectron spectroscopy (XPS) spectrum of the catalyst of the examples and the comparative examples;

[0028] Figure 8 The figure is a (Zn, Fe, Cu, Co)2p X-ray photoelectron spectroscopy (XPS) spectrum of the catalyst of the examples and the comparative examples;

[0029] Figure 9 The figure is a Raman spectrum of the catalyst of the examples and the comparative examples;

[0030] Figure 10X-ray absorption near-edge structure (XANES) spectra of the Ni-K edge of the catalysts of examples and comparative examples;

[0031] Figure 11 Extended X-ray absorption fine structure (EXAFS) spectra of the Ni-K edge of the catalysts of examples and comparative examples;

[0032] Figure 12 Cyclic voltammograms (CV) of the catalysts of examples and comparative examples under nitrogen and oxygen saturation, respectively, in 0.1 M KOH;

[0033] Figure 13 Polarization curves (LSV) of the catalysts of examples and comparative examples under nitrogen and oxygen saturation, respectively, in 0.1 M KOH;

[0034] Figure 14 Selectivity plots of the catalysts of examples and comparative examples for hydrogen peroxide under nitrogen and oxygen saturation, respectively, in 0.1 M KOH;

[0035] Figure 15 Number of electrons transferred plots of the catalysts of examples and comparative examples for hydrogen peroxide under nitrogen and oxygen saturation, respectively, in 0.1 M KOH;

[0036] Figure 16 Electrochemical impedance spectroscopy (EIS) plots of the two-electron oxygen reduction reaction of the catalysts of examples and comparative examples;

[0037] Figure 17 Stability and yield plots of the Zn-NiO catalyst for the production of hydrogen peroxide from the two-electron oxygen reduction reaction under 0.1 M KOH, at 0.4 V vs. RHE, for 120 h;

[0038] Figure 18 Stability and yield plots of the Fe-NiO catalyst for the production of hydrogen peroxide from the two-electron oxygen reduction reaction under 0.1 M KOH, at 0.4 V vs. RHE, for 12 h;

[0039] Figure 19 Stability and yield plots of the Cu-NiO catalyst for the production of hydrogen peroxide from the two-electron oxygen reduction reaction under 0.1 M KOH, at 0.4 V vs. RHE, for 12 h;

[0040] Figure 20 Stability and yield plots of the Co-NiO catalyst for the production of hydrogen peroxide from the two-electron oxygen reduction reaction under 0.1 M KOH, at 0.4 V vs. RHE, for 12 h;

[0041] Figure 21The stability and yield of hydrogen peroxide prepared by the two-electron oxygen reduction reaction of NiO catalyst under 0.1M KOH conditions and 0.4V vs. RHE voltage for 12 h are shown in the figure.

[0042] Figure 22 Cyclic voltammetry (CV) spectra and double-layer capacitance (C) of the catalysts in the examples and comparative examples at different scan rates. dl );

[0043] Figure 23 In the diagram: a is the electrophilicity index of the Zn-NiO catalyst, and b is the variation of the two-electron oxygen reduction selectivity and H2O2 yield of the catalysts in the examples and comparative examples with the center of the d-band.

[0044] Figure 24 In the middle: a represents the 2e- of Zn-NiO and NiO catalysts. - ORR Gibbs free energy comparison plot, b is the 2e-energy of NiO catalyst. - ORR and 4e - ORR Gibbs free energy comparison plot, c represents the 2e2e2 of the Zn-NiO catalyst. - ORR and 4e - ORR Gibbs free energy comparison diagram, d represents 2e on Zn-NiO - ORR and 4e - Schematic diagram of the ORR reaction pathway. Detailed Implementation

[0045] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0046] Example 1

[0047] Example 1 relates to a Zn-NiO catalyst, the preparation method of which includes the following specific steps:

[0048] First, prepare an equimolar solution of Ni(NO3)2 and ZnCl2 at 0.5 M. Then, add a certain amount of ethylene glycol (EG) to the Ni(NO3)2 solution, maintaining the mass ratio of EG to metallic Ni at 1:0.95. Mix 9 mL of Ni(NO3)2-EG solution with 1 mL of ZnCl2 dopant solution to obtain a precursor solution (where the molar ratio of Ni to Zn is 9:1.03). Stir the precursor solution vigorously for 1 hour.

[0049] The stirred solution was placed in a porcelain crucible and transferred to a muffle furnace for heating. The heating program of the muffle furnace was as follows: heating to 100°C at a rate of 10°C / min, then heating to 350°C at a rate of 2°C / min, and holding at 350°C for 1 hour. The product was washed three times with deionized water and ethanol, and then dried in a vacuum drying oven at 60°C for 12 hours to obtain the Zn-NiO catalyst.

[0050] Example 2

[0051] Example 2 relates to Fe-NiO catalyst, the preparation method is that the “0.5M ZnCl2 equimolar solution” described in example 1 is replaced by “0.5M FeCl3 equimolar solution”, and other steps are the same as those in example 1, so as to obtain the Fe-NiO catalyst.

[0052] Comparative Example 1

[0053] Comparative Example 1 relates to NiO catalyst, the preparation method is that the “0.5M ZnCl2 equimolar solution” described in example 1 is replaced by “0.5M Ni(NO3)2”, and other steps are the same as those in example 1, so as to obtain the NiO catalyst.

[0054] Comparative Example 2

[0055] Comparative Example 2 relates to Cu-NiO catalyst, the preparation method is that the “0.5M ZnCl2 equimolar solution” described in example 1 is replaced by “0.5M CuCl2 equimolar solution”, and other steps are the same as those in example 1, so as to obtain the Cu-NiO catalyst.

[0056] Comparative Example 3

[0057] Comparative Example 3 relates to Co-NiO catalyst, the preparation method is that the “0.5M ZnCl2 equimolar solution” described in example 1 is replaced by “0.5M CoCl2 equimolar solution”, and other steps are the same as those in example 1, so as to obtain the Co-NiO catalyst.

[0058] Structural characterization and performance test

[0059] Figure 1 a shows the XRD patterns of Zn-NiO, Fe-NiO, NiO, Cu-NiO and Co-NiO, wherein the characteristic peaks located at 37.28°, 43.27°, 62.87°, 75.41° and 79.40° correspond to the (111), (200), (220), (110) and (222) faces of NiO, respectively, and are completely matched with JCPDS card No. 47-1049. The synthesized NiO has a face-centered cubic (fcc) structure, and no additional impurity peaks related to other oxides are detected in the M-NiO (M = Zn, Fe, Cu or Co) samples. Figure 1 b shows that the diffraction peak of the (200) face is shifted after metal doping, indicating that the metal is successfully doped into the crystal lattice of NiO.

[0060] Figure 2 shows the SEM image of Zn-NiO, Figure 3SEM images of Fe-NiO (a and b), NiO (c and d), Co-NiO (e and f), Cu-NiO (g and h) are shown, all NiO exhibit nanoparticle morphology. Different nanoparticle catalysts have different particle sizes, so C dl Figure 22 a-e) were used to evaluate the electrochemically active surface area ECSA, as Figure 22 f shows that the slightly different values indicate that the ECSA of the several oxides is relatively similar, and the size has a small effect on different catalysts, the main factor affecting their two-electron oxygen reduction ability is the different electronic structure of different transition metal oxides. In Figure 4 a, the lattice plane with a spacing of 0.209 nm is attributed to the (200) plane of NiO; while Figure 4 in b, the lattice plane with a spacing of 0.213 nm is attributed to the (200) plane of Zn-NiO, further proving that Zn metal ions are successfully introduced into the NiO lattice.

[0061] As shown in Figure 5 , the XPS full spectrum clearly shows the presence of oxygen and the corresponding metal elements in various catalysts, without any detectable impurity peaks, indicating that the synthesized oxides have high purity. In addition, Figure 6 , the high-resolution Ni 2p spectra of M-NiO and NiO are given, in which the Ni 2+ peak is located at 853.90 eV and 871.52 eV, while the Ni 3+ peak is located at 855.64 eV and 873.46 eV, and the Ni 3+ is related to the surface hydroxyl group. Figure 7 , the high-resolution O 1s spectra of M-NiO and NiO are given. In the O 1s high-resolution spectrum of NiO, two obvious peaks at 529.53 eV and 531.17 eV correspond to lattice oxygen and surface OH group oxygen, respectively. As shown in Figure 8 , the Zn 2p spectrum in Zn-NiO, the Fe 2p spectrum in Fe-NiO, the Cu 2p spectrum in Cu-NiO and the Co 2p spectrum in Co-NiO are given, the addition of Cu, Co metal in nickel oxide forms localized Ni-O-Cu and Ni-O-Co active site structures, the Ni-O-Cu structure will cause the annihilation of intermediate OOH*, and Ni-O-Co is more inclined to occur four-electron oxygen reduction reaction, which has an adverse effect on the 2e - ORR activity of NiO. The addition of Zn, Fe metal in nickel oxide is beneficial to the transfer of electrons, forming localized Ni-O-Zn and Ni-O-Fe active site structures, which is beneficial to improve the 2e - ORR activity.

[0062] As shown in Figure 9 ​Raman spectra show the Ni-O stretching vibration mode of different transition metal cation doped and undoped NiO catalysts. The Ni-O stretching mode of doped and undoped NiO catalysts is in the range of about 470-600 cm -1 . The stretching frequency of Ni-O in Co (~524 cm -1 ), Cu (~521 cm -1 ), Fe (~562 cm -1 ) and Zn doped samples (~493 cm -1 ) appears a blue shift compared to the stretching frequency in the undoped sample (~481 cm -1 ). This blue shift of the Ni-O stretching frequency is attributed to the metal cation incorporation into nickel oxide, replacing a portion of Ni, thus forming metal-oxygen bonds and changing the electronic structure.

[0063] Figure 10 X-ray absorption near-edge spectra (XANES) of different transition metal cation doped and undoped NiO catalysts are shown. The fitting results show that the Ni valence of M-NiO is reduced, between Ni foil and NiO, due to the increase of the electron density of Ni atoms caused by cation incorporation. Figure 11 The k-edge extended X-ray absorption fine structure (EXAFS) oscillations of Ni in the middle show the typical peak of Ni-O bond at about 1.5 A (unphased). The length of Ni-O bond increases slightly when the doping cation.

[0064] To evaluate the electrocatalytic performance of metal cation doped NiO catalysts for 2e - ORR reaction, different transition metal cation doped and undoped NiO catalysts were made into anode catalytic electrodes, with platinum electrode as the cathode, and 0.1 mol / L KOH solution as the electrolyte for electrochemical test.

[0065] As shown in Figure 12 , the cyclic voltammetry (CV) curves of Zn-NiO, Fe-NiO, Cu-NiO, Co-NiO, NiO catalysts were obtained in 0.1 M KOH electrolyte saturated with N2 and O2 respectively, at a low scan rate of 50 mV s -1 . The results show that there is a strong oxygen reduction peak in the oxygen-saturated electrolyte, but not in nitrogen. The oxidation peak near 0.5 V (Vs. RHE ) is attributed to the oxidation of H2O2, indicating the successful preparation of H2O2 in the 2e - ORR process.

[0066] Figure 13 ​The polarization curves of Zn-NiO, Fe-NiO, Cu-NiO, Co-NiO, and NiO catalysts were calculated, and the ring currents of different catalysts related to the synthesis of H2O2 were quite different. Among them, Zn-NiO showed the highest ring current, followed by Fe-NiO, both of which were higher than the other three catalysts.

[0067] As shown in Figure 15 , the selectivity of NiO catalyst and M-NiO catalyst based on the load on the RRDE disc for H2O2 was calculated. Among them, Zn-NiO maintained about 93% selectivity at 0.1-0.5V vs. RHE, and the selectivity of Fe-NiO was 91%, both of which were much higher than Cu-NiO (82%), Co-NiO (67%) and NiO (84%), indicating that Zn-NiO had the best 2e - ORR activity.

[0068] As shown in Figure 15 , the number of transferred electrons of Zn-NiO, Fe-NiO, Cu-NiO, Co-NiO, and NiO catalysts was calculated at 0.1-0.5V vs. RHE, among which Zn-NiO had the highest number of transferred electrons (about 2.13), indicating that Zn-NiO could maintain good production capacity for hydrogen peroxide in actual production.

[0069] As shown in Figure 16 , the electrochemical impedance (EIS) of Zn-NiO, Fe-NiO, Cu-NiO, Co-NiO, and NiO is shown. Zn-NiO showed higher charge transfer rate and current density. Previous studies have shown that the exposure of active sites and electrical conductivity determine the charge transfer resistance (Rct).

[0070] As shown in Figure 17-21 , the hydrogen peroxide yield of Zn-NiO, Fe-NiO, Cu-NiO, Co-NiO, and NiO was further tested, among which Zn-NiO showed the highest yield of 514.59mmol g -1 h -1 at 0.4V vs. RHE, much higher than the yield of Cu-NiO, Co-NiO, and NiO, indicating that Zn-NiO could accumulate high concentration of hydrogen peroxide faster in actual application. Among them, the yield of Zn-NiO in 25ml electrolytic cell did not decay within 120 hours, indicating its excellent stability, which showed that Zn-NiO could be applied to the actual production of hydrogen peroxide.

[0071] As shown in Figure 23As shown in Fig. a, the electrophilic index of Ni sites in Zn-NiO increases. With the incorporation of Zn, the electron transfers through the Ni-O-Zn bridge, resulting in the increase of charge density of certain Ni sites. As the active sites, Ni weakens the adsorption of the key intermediate *OOH. Meanwhile, Figure 23 As shown in Fig. b, with the d-band center of different doped metals moving away from the Fermi level, the 2e - ORR selectivity and H2O2 yield increase, among which Zn-NiO exhibits the best 2e - ORR selectivity and excellent H2O2 yield.

[0072] As shown in Fig. a, the electrophilic index of Ni sites in Zn-NiO increases. With the incorporation of Zn, the electron transfers through the Ni-O-Zn bridge, resulting in the increase of charge density of certain Ni sites. As the active sites, Ni weakens the adsorption of the key intermediate *OOH. Meanwhile, Figure 24 As shown in Fig. a, the electrophilic index of Ni sites in Zn-NiO increases. With the incorporation of Zn, the electron transfers through the Ni-O-Zn bridge, resulting in the increase of charge density of certain Ni sites. As the active sites, Ni weakens the adsorption of the key intermediate *OOH. Meanwhile, - The occurrence of 2e - ORR is thermodynamically more favorable. In addition, the response trend between 2e - and 4e - ORR of Zn-NiO and NiO was studied. The PDS of 2e - ORR of both catalysts is smaller than that of 4e - ORR, indicating that both catalysts are more inclined to occur 2e - ORR. The theoretical calculation results show that Zn-NiO has the best adsorption energy of the key intermediate *OOH, and is more thermodynamically favorable for the occurrence of 2e - ORR, which is consistent with the experimental results.

[0073] Based on the above analysis, the doping of Zn and Fe is beneficial to improve the electrocatalytic performance of NiO for 2e - ORR, while the doping of Cu and Co presents the opposite effect. Especially, the Zn-NiO catalyst has excellent catalytic activity and selectivity for the preparation of hydrogen peroxide by 2e

[0074] The specific embodiments of the present application are described in detail above, but the present application is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the purpose of the present application.

Claims

1. The application of metal cation-doped NiO catalysts in two-electron oxygen reduction reactions, characterized in that: The metals include Fe and / or Zn.

2. The application according to claim 1, characterized in that... The preparation method of the metal cation-doped NiO catalyst includes the following steps: S1. Prepare precursor solutions of Ni salt and doped metal salt; S2. The precursor solution is transferred to a muffle furnace and heated. The product is washed and dried to obtain the metal cation-doped NiO catalyst.

3. The application according to claim 2, characterized in that: The molar ratio of the Ni salt to the doped metal salt is 9:0.5 to 1.

5.

4. The application according to claim 2, characterized in that... Step S1 includes: preparing a Ni salt solution and a doped metal salt solution respectively, then adding an appropriate amount of ethylene glycol to the Ni salt solution, and then mixing the two solutions in a certain proportion.

5. The application according to claim 4, characterized in that: The molar concentrations of the Ni salt solution and the doped metal salt solution are 0.1–1 M.

6. The application according to claim 4, characterized in that: The mass ratio of ethylene glycol to metallic Ni is 1:0.8 to 1.

7. The application according to claim 3, characterized in that: The Ni salt is Ni(NO3)2 or NiCl2.

8. The application according to claim 3, characterized in that: The doped metal salt is any one of Fe(NO3)3 or FeCl3 and Zn(NO3)2 or ZnCl2 or a combination thereof.

9. The application according to claim 2, characterized in that: The heating program of the muffle furnace in step S2 is as follows: first heat to 100°C at 5-15°C / min, then heat to 300-400°C at 1-5°C / min and hold for 0.5-2 hours.

10. The application according to claim 1, characterized in that: The two-electron oxygen reduction reaction is carried out in an alkaline environment.

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