Doped catalysts, methods for their preparation and use

Abstract

The application relates to the technical field of electrochemical catalysts, in particular to a doped catalyst and a preparation method and application thereof. The doped catalyst comprises a phosphide base material, the phosphide base material comprises cobalt phosphide and / or nickel phosphide, and a noble metal element is doped in the phosphide base material, wherein the noble metal element comprises at least one of palladium, platinum, gold and silver. The doped catalyst can adsorb and dissociate NO3 ‑ , has excellent catalytic activity, can more efficiently treat nitrate ions and generate ammonium products. The preparation method comprises calcining a catalyst precursor and a phosphorus source under an inert atmosphere to obtain the doped catalyst. The doped catalyst can be widely applied to nitrate treatment, zinc-nitrate batteries and ammonium production.

Description

Technical Field

[0001] This application relates to the field of electrochemical catalyst technology, and in particular to a doped catalyst, its preparation method, and its application. Background Technology

[0002] Currently, the removal of nitrate ions from industrial wastewater primarily relies on biological degradation. This method is time-consuming and requires a large site, causing significant inconvenience. Therefore, utilizing faster electrocatalytic methods for efficient nitrate treatment has been an important area of ​​research focus. Electrocatalytic nitrate reduction (NO3) 3- RR involves two basic processes: adsorption and conversion. These two processes are also crucial for improving the electrocatalytic NO production. 3- The key to RR activity.

[0003] To date, researchers have devoted considerable effort to promoting the adsorption and conversion of nitrate, but the results have been less than satisfactory. Most current work focuses on copper-based materials, which exhibit good nitrate removal efficiency in the laboratory. However, copper-based materials are too reactive and extremely unstable in both acidic and alkaline solutions. During electrolysis, a high concentration of hydroxide ions is generated around the electrodes, which significantly limits the development and application of copper-based catalysts. If a catalyst capable of effectively adsorbing and efficiently converting nitrate could be invented, it could be widely applied in nitrate treatment, zinc-nitrate batteries, and ammonium production. Summary of the Invention

[0004] The purpose of this application is to provide a doped catalyst, its preparation method and application, which aims to solve the problem of poor adsorption and conversion of nitrate by the catalyst in the existing electrocatalytic nitrate reduction.

[0005] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows:

[0006] In a first aspect, this application provides a doped catalyst comprising a phosphide substrate, the phosphide substrate comprising cobalt phosphide and / or nickel phosphide, and the phosphide substrate being doped with a noble metal element, the noble metal element comprising at least one of palladium, platinum, gold, and silver.

[0007] The doped catalyst of this application introduces Lewis acidic sites into the catalyst, which can act as a handle to attract free NO3 in solution. - (Lewis weak base) is converted into the adsorbed state, and then π feedback is used to promote NO3. -adsorption and dissociation. In addition, doping noble metal elements can regulate the electronic band structure of the phosphide substrate, better meet the needs of eight-electron-nine-proton reactions, and the optimized doped catalysts exhibit excellent catalytic activity in the electrolytic reduction of nitrate ions, which can more efficiently process nitrate ions to generate ammonium products.

[0008] In a second aspect, the application provides a preparation method of the doped catalyst, comprising the following steps:

[0009] Under an inert atmosphere, the catalyst precursor is calcined with the phosphorus source to obtain the doped catalyst;

[0010] The catalyst precursor comprises noble metal hydroxide, and further comprises cobalt hydroxide and / or nickel hydroxide.

[0011] The preparation method of the application is to calcine the catalyst precursor with the phosphorus source, so that the phosphorus source reacts with the catalyst precursor, thereby obtaining a phosphide substrate doped with noble metal elements, i.e. the doped catalyst of the application. Thus, the catalyst prepared by the preparation method of the application introduces Lewis acid sites, which can adsorb and dissociate NO3 - , and further improves the catalytic activity. The preparation method of the application is controllable, and the prepared catalyst has high stability.

[0012] In a third aspect, the application provides the application of the doped catalyst of the application or the doped catalyst prepared by the preparation method of the application in nitrate treatment, zinc-nitrate batteries, and ammonium production.

[0013] The doped catalyst provided by the application or the doped catalyst prepared by the preparation method of the application has adsorption and dissociation effects on NO3 - during the electrolytic reduction of nitrate, and has high catalytic activity, so it can efficiently process nitrate ions, has high nitrate conversion rate, and can treat nitrate pollution; it can also be used in zinc-nitrate batteries to promote the reduction reaction and energy conversion; it can also be used in ammonium production, has high selectivity for ammonium production, and has high yield of ammonium. BRIEF DESCRIPTION OF DRAWINGS

[0014] In order to more clearly illustrate the technical solutions in the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the application, and those skilled in the art can obtain other drawings according to these drawings without creative labor.

[0015] Figure 1 LSV curves of the doped catalysts provided for Examples 1 to 4 and the catalyst provided for Comparative Example 1 in the electrolyte;

[0016] Figure 2 The doped catalyst provided in Example 3 and the catalyst provided in Comparative Example 1 are partially characterized.

[0017] in, Figure 2 Figure a shows the tauc plots of CoP and Pd / CoP obtained from UV-Vis diffuse reflectance spectroscopy (the inset shows the UV-Vis diffuse reflectance spectra of CoP and Pd / CoP).

[0018] Figure b shows the ultraviolet photoelectron spectra of CoP and Pd / CoP (the inset is an enlarged view of the cutoff energy regions of CoP and Pd / CoP).

[0019] Figure 3 The doped catalyst provided in Example 3 and the catalyst provided in Comparative Example 1 are partially characterized.

[0020] Figure a shows the XPS spectra of CoP and Pd / CoP in the Co 2p region.

[0021] Figure b shows the XPS spectra of CoP and Pd / CoP in the Pd 3d region;

[0022] Figure 4 The doped catalyst provided in Example 3 and the catalyst provided in Comparative Example 1 are partially characterized.

[0023] in, Figure 4 Image (a) is a SEM image;

[0024] (b) The figure is a TEM image;

[0025] (c) The figure is an HRTEM image;

[0026] (d) is the XRD image;

[0027] Figure 5 The doped catalyst provided in Example 3 and the catalyst provided in Comparative Example 1, in the presence and absence of NO3. - Test results in RR electrolyte solution;

[0028] in, Figure 5 Figure a shows the concentrations of CoP and Pd / CoP at 50 ppm NO3, with and without the presence of these concentrations. - LSV curve of -N in 0.5M Na2SO4 electrolyte;

[0029] Figure b shows the nitrate conversion rate and Faraday efficiency of Pd / CoP at a given potential;

[0030] Figure c shows the ammonium selectivity and yield of Pd / CoP at a given potential;

[0031] d shows NO3 under -0.8 V vs. RHE. - -N, NO2 - -N, NH4 + -N concentration change curve over time;

[0032] Figure e shows the nitrate conversion, Faraday efficiency, selectivity, and yield of Pd / CoP after continuous cyclic testing.

[0033] Figure f shows the nitrate conversion, Faraday efficiency, selectivity, and yield of samples with different Pd doping contents.

[0034] Figure 6 The doped catalyst provided in Example 3 in Zn-NO3 - Test results in the battery;

[0035] in, Figure 6 Figure a shows Zn-NO3 using a Pd / CoP catalyst as the cathode. - The open-circuit voltage of the battery;

[0036] Figure b shows Pd / CoP-based Zn-NO3. - The battery's discharge curve and the resulting power density curve;

[0037] Figure c shows Pd / CoP-based Zn-NO3. - Discharge curves of the battery at different current densities;

[0038] The d-plot is derived from Pd / CoP-based Zn-NO3. - Ammonium yield and corresponding Faraday efficiency of battery system at different current densities;

[0039] The graph is at 8 mA cm -2 At a current density of [value missing], after six cycles of testing using the same Pd / CoP catalyst as the cathode, Zn-NO3 [value missing] - Faraday efficiency and ammonium yield of the battery;

[0040] The f-graph is a Pd / CoP-based Zn-NO3 - Batteries and other Zn-NO3 - A comparison of the battery's Faraday efficiency and ammonium yield. Detailed Implementation

[0041] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0042] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0043] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0044] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0045] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms "a" and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0046] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass in the embodiments of this application can be a well-known unit of mass in the chemical industry, such as µg, mg, g, or kg.

[0047] The terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the embodiments of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0048] The first aspect of this application provides a doped catalyst, including a phosphide substrate, the phosphide substrate including cobalt phosphide and / or nickel phosphide, the phosphide substrate being doped with a noble metal element, the noble metal element including at least one selected from palladium, platinum, gold, and silver.

[0049] The doped catalyst provided in this application embodiment incorporates noble metal elements into a phosphide substrate, wherein the phosphide substrate is cobalt phosphide and / or nickel phosphide. Doping means that the noble metal elements partially replace the cobalt or nickel elements in the phosphide substrate, and has the following beneficial effects: (1) According to the Lewis acid-base theory, NO3 - Belonging to the category of weak Lewis bases, the doped catalyst in this application incorporates noble metal elements into the phosphide. Phosphides doped with noble metal elements are Lewis acidic substances, and the doping sites are the Lewis acidic sites. This successfully introduces Lewis acidic sites into the catalyst. By introducing these sites into the bulk catalyst phase, the free NO3 in the solution is attracted. - It is converted into an adsorbed state, and then π feedback is used to promote NO3. - (2) By using doped noble metal elements to regulate the electronic band structure of the phosphide substrate, the requirements of the octet-nine proton reaction can be better met. The optimized doped catalyst exhibits excellent catalytic activity in the electrolytic reduction of nitrate ions, and can process nitrate ions more efficiently to generate ammonium products. Specifically, the doped catalyst has 88.94% selectivity for ammonium synthesis and a nitrate conversion rate of nearly 95% and an extremely high ammonium yield (reaching 0.099 mmol h) at a potential of -0.8 V vs. RHE (relative to the standard hydrogen electrode). -1 cm -2 Meanwhile, Zn-NO3 containing the doped catalyst of the embodiments of this application - The battery also exhibited excellent performance. In summary, the doped catalyst in the embodiments of this application can achieve electrocatalytic NO3-… - Reduction treatment and Zn-NO3 - Battery energy conversion. The noble metal element may include at least one of palladium, platinum, gold, and silver. Doping these noble metal elements into the phosphide substrate can further increase the generation of Lewis acidic sites in the doped catalyst and further promote the adsorption and dissociation of nitrate ions; it can also further modulate the electronic band structure of the phosphide substrate, promote the polarity of the catalytic reaction, and improve the catalytic activity of the catalyst in the electrolytic reduction of nitrate ions. In some embodiments, the noble metal element may be palladium, the phosphide substrate may be cobalt phosphide, and the doped catalyst may be cobalt phosphide doped with palladium.

[0050] In some embodiments, the noble metal element accounts for 0.01 wt% to 1.04 wt% of the mass percentage of the doped catalyst. These mass ratios of noble metal element in the doped catalyst of this application embodiment can further promote the adsorption and dissociation of nitrate ions by the Lewis acidic sites in the doped catalyst; they can also further modulate the electronic band structure of the phosphide substrate, promote the polarity of the catalytic reaction, and improve the catalytic activity of the catalyst in the electrolytic reduction of nitrate ions. In exemplary examples, the mass percentage may include, but is not limited to, 0.01 wt%, 0.26 wt%, 0.52 wt%, 0.78 wt%, and 1.04 wt%.

[0051] Upon testing, the doped catalysts of the above embodiments possess at least the following characterization features:

[0052] like Figure 4 As shown in Figures (a) and (b), in some embodiments, the doped catalyst forms a needle-like array of microstructures. Since the catalytic reaction is an interfacial reaction, the doped catalyst with the needle-like array microstructure has a larger reaction area with the reactants, which is more conducive to the adsorption and dissociation of phosphate ions, and more conducive to the octet-nine proton reaction, thus improving the catalytic effect.

[0053] In some embodiments, the doped catalyst includes at least one of the features (1) to (4):

[0054] (1) The Fermi level is -5.5 to -6.0 eV;

[0055] (2) The valence band energy is -7.4 to -8.3 eV;

[0056] (3) The conduction band energy is -5.0 to -5.8 eV;

[0057] (4) The lattice spacing of the (201) plane of the crystal in the phosphide substrate is 0.205 to 0.255 nm.

[0058] Doped catalysts with these characteristics can further modulate the electronic band structure of phosphide substrates, promote the polarity of catalytic reactions, and improve the catalytic activity of catalysts in the electrolytic reduction of nitrate ions. In the example, the Fermi level may include, but is not limited to, -5.5 eV, -5.6 eV, -5.76 eV, -5.9 eV, and -6.0 eV; the valence band energy may include, but is not limited to, -7.4 eV, -7.6 eV, -7.82 eV, -8.0 eV, and -8.3 eV; the conduction band energy may include, but is not limited to, -5.0 eV, -5.2 eV, -5.37 eV, -5.6 eV, and -5.8 eV; and the lattice spacing of the (201) plane of the crystal in the phosphide substrate may include, but is not limited to, 0.205 nm, 0.220 nm, 0.238 nm, 0.245 nm, and 0.255 nm.

[0059] The second aspect of this application provides a method for preparing a doped catalyst, comprising the following steps:

[0060] S10: In an inert gas atmosphere, the catalyst precursor and phosphorus source are calcined to obtain a doped catalyst.

[0061] Catalyst precursors include noble metal hydroxides, as well as cobalt hydroxide and / or nickel hydroxide.

[0062] The preparation method of this application involves calcining a catalyst precursor with a phosphorus source, causing the phosphorus source to react with the catalyst precursor, thereby obtaining a phosphide matrix doped with noble metal elements, which is the doped catalyst of the above-described embodiment. Thus, the catalyst prepared by the method of this application introduces Lewis acid sites, which can adsorb and dissociate NO3. - It also improves catalytic activity. The preparation method in this application is controllable, and the resulting catalyst has high stability.

[0063] In some embodiments, the catalyst precursor may be prepared by steps including:

[0064] S11: Prepare a catalyst precursor by mixing at least one of a cobalt source and a nickel source with a noble metal source and a precipitant, and then reacting the solutions via hydrothermal reaction.

[0065] Step S11 involves a hydrothermal reaction of the mixed solution to obtain a catalyst precursor containing noble metal hydroxides, as well as cobalt hydroxide and / or nickel hydroxide. The catalyst precursor contains uniformly distributed substances, which is beneficial for obtaining a high-performance doped catalyst after subsequent reaction with a phosphorus source.

[0066] The cobalt source in step S11 may include at least one of cobalt nitrate hexahydrate, cobalt sulfate monohydrate, cobalt chloride hexahydrate, and cobalt phosphate octahydrate; the nickel source may include at least one of nickel nitrate hexahydrate, nickel chloride hexahydrate, nickel sulfate heptahydrate, and nickel acetate tetrahydrate; and the noble metal source may include at least one of sodium tetrachloropalladate, palladium nitrate, palladium sulfate, and dichlorodiamminepalladium. These raw materials facilitate uniform dispersion in the mixed solution and promote the hydrothermal reaction to obtain the desired catalyst precursor. Furthermore, a substrate (e.g., a titanium mesh) can be placed in the solution to allow the catalyst precursor to adhere to the substrate.

[0067] In some embodiments, the mass ratio of the total mass of the cobalt and nickel sources to the precious metal source can be 30–500:1. Controlling the mass ratio of the total mass of the cobalt and nickel sources to the precious metal source within these ranges ensures that the total mass of the hydrothermal reaction producing precipitates of cobalt and nickel (cobalt hydroxide and / or nickel hydroxide) to the mass ratio of the precipitates containing precious metals such as precious metal hydroxides will also be within a certain range. This results in the final doped catalyst having a phosphide substrate to precious metal elements within a certain range, thereby further improving the catalytic effect of the doped catalyst prepared by the method of this application. In exemplary examples, the mass ratio of the total mass of the cobalt and nickel sources to the precious metal source can be, but is not limited to, 30:1, 100:1, 200:1, 300:1, 400:1, and 500:1.

[0068] A precipitant can be prepared by hydrothermal reaction with a noble metal source, cobalt source, or nickel source to obtain a hydroxide-containing precipitate, i.e., a catalyst precursor. The mass ratio of the precipitant to the noble metal source can be 20–1500:1 to ensure sufficient hydrothermal reaction of the cobalt, nickel, or noble metal sources to generate the desired catalyst precursor. In exemplary cases, the mass ratio can include, but is not limited to, 20:1, 50:1, 150:1, 300:1, 800:1, and 1500:1. The precipitant can include urea (CO(NH2)2). In addition to the above-mentioned precipitation effect, urea is also beneficial for controlling the morphology of the catalyst precursor, allowing these hydroxides to grow into an array of nanoneedle-like structures, thereby facilitating the formation of a needle-like array microstructure in the doped catalyst. Figure 4 As shown in Figures (a) and (b).

[0069] In some embodiments, the preparation of the mixed solution may further include the addition of a crystal form control agent, which may include ammonium fluoride. Adding a crystal form control agent facilitates the growth of each hydroxide crystal into the desired crystal form during the hydrothermal reaction, thereby optimizing the doping state of the noble metal element in the phosphide matrix in the doped catalyst; it also helps control the morphology of the catalyst precursor, allowing these hydroxides to grow into an array of nanoneedle-like structures, thus facilitating the formation of a needle-like array microstructure in the doped catalyst, such as... Figure 4As shown in Figures (a) and (b) in this paper. Therefore, the addition of a crystal form control agent is beneficial to improving the catalytic effect of the doped catalyst prepared by the method of this application.

[0070] The hydrothermal reaction in step S11 can be carried out at 100-140°C for 4-8 hours to obtain the catalyst precursor. After cooling to room temperature, the precursor can be rinsed with deionized water to remove any remaining solution and then dried for later use.

[0071] In some embodiments, the calcination process in step S10 may include using an inert gas as a carrier gas to transport a gaseous phosphorus source to contact the catalyst precursor for calcination. This preparation method facilitates a thorough phosphating reaction between the catalyst precursor and the phosphorus source, improves the doping effect of noble metal elements in the phosphide substrate of the prepared doped catalyst, and enhances the catalytic effect of the prepared doped catalyst on the electrolytic reduction of nitrate. In an exemplary example, a quartz tube furnace can be used for the calcination process. The phosphorus source is placed upstream of the quartz tube, and the catalyst precursor is placed downstream of the quartz tube. Then, an inert gas is used as a carrier gas flow to transport the gaseous phosphorus source from upstream to downstream of the quartz tube, thereby delivering the gaseous phosphorus source to the downstream catalyst precursor for calcination.

[0072] In some embodiments, the phosphorus source may include at least one of sodium hypophosphite monohydrate, phosphorus powder, sodium hypophosphite monohydrate, and sodium phosphate dodecahydrate. These phosphorus sources can be transported to the catalyst precursor by an inert gas carrier gas stream, and can be calcined with the catalyst precursor to obtain a doped catalyst. In some embodiments, the inert gas may be argon, the heating rate may be 1–5 °C / min, including but not limited to 1 °C / min, 2 °C / min, and 5 °C / min; the calcination temperature may be 200–400 °C, including but not limited to 200 °C, 300 °C, and 400 °C; and the calcination time may be 1–3 h, including but not limited to 1 h, 2 h, and 3 h. These calcination conditions allow the phosphorus source and the catalyst precursor to undergo a sufficient phosphating reaction, improving the catalytic effect of the obtained doped catalyst on the electrolytic reduction of nitrate.

[0073] The third aspect of this application provides the application of the doped catalyst of this application embodiment or the doped catalyst prepared by the preparation method of this application embodiment in nitrate pollution treatment, zinc-nitrate batteries, and ammonium production.

[0074] The doped catalyst provided in this application embodiment or the doped catalyst prepared by the preparation method in this application embodiment exhibits good resistance to NO3- during the electrolytic reduction of nitrate. -It has adsorption and dissociation effects and high catalytic activity, so it can efficiently treat nitrate ions with a high nitrate conversion rate, which can treat its pollution; it can also be used in zinc-nitrate batteries to promote reduction reaction and energy conversion; it can also be used to produce ammonium with high selectivity and high yield.

[0075] The following description is based on specific embodiments.

[0076] Examples of doped catalysts and their preparation methods

[0077] Example 1

[0078] This embodiment provides a method for preparing a doped catalyst, including the following steps:

[0079] S1: A 35 mL mixed solution was prepared from 0.485 g Co(NO3)2·6H2O, 0.155 g NH4F, 0.5 g CO(NH2)2, and 0.003 g Na2PdCl4. A pretreated titanium mesh was then placed tilted within this solution. After hydrothermal reaction at 120 °C for 6 h, a precipitate was obtained. After cooling to room temperature, the precipitate was washed three times with deionized water and dried at 60 °C for later use, yielding the precursor catalyst.

[0080] S2: The precursor catalyst prepared above was placed in a tube furnace, with the phosphorus source placed upstream of the quartz tube and the precursor catalyst placed downstream of the quartz tube. Subsequently, under an argon atmosphere, the sample was calcined at 300 °C for 2 h at a heating rate of 2 °C / min to obtain the doped catalyst.

[0081] The doped catalyst provided in this embodiment is a Pd-doped catalyst in CoP, with Pd accounting for 0.26 wt% of the mass of the doped catalyst.

[0082] Example 2

[0083] The only difference between the preparation method of the doped catalyst in this embodiment and that in Example 1 is that 0.003 g Na2PdCl4 in step S1 is replaced with 0.006 g Na2PdCl4.

[0084] The only difference between the doped catalyst provided in this embodiment and that in Example 1 is that Pd accounts for 0.52 wt% of the mass of the doped catalyst.

[0085] Example 3

[0086] The only difference between the preparation method of the doped catalyst in this embodiment and that in Example 1 is that 0.003 g Na2PdCl4 in step S1 is replaced with 0.009 g Na2PdCl4.

[0087] The only difference between the doped catalyst provided in this embodiment and that in Example 1 is that Pd accounts for 0.78 wt% of the mass of the doped catalyst; denoted as Pd / CoP.

[0088] Example 4

[0089] The only difference between the preparation method of the doped catalyst in this embodiment and that in Example 1 is that 0.003 g Na2PdCl4 in step S1 is replaced with 0.012 g Na2PdCl4.

[0090] The only difference between the doped catalyst provided in this embodiment and that in Example 1 is that Pd accounts for 1.04 wt% of the doped catalyst.

[0091] Example 5

[0092] The only difference between the preparation method of the doped catalyst in this embodiment and that in Example 3 is that NH4F is not added in step S1.

[0093] The only difference between the doped catalyst provided in this embodiment and that in Example 3 is that the doped catalyst does not form a needle-like array of microstructures, but rather is in the form of particles.

[0094] Example 6

[0095] The only difference between the preparation method of the doped catalyst in this embodiment and that in Example 3 is that 0.485 g Co(NO3)2.6H2O in step S1 is replaced with 0.291 g Ni(NO3)2.6H2O.

[0096] The only difference between the doped catalyst provided in this embodiment and that in Example 1 is that the phosphide substrate in the doped catalyst is nickel phosphide (NiP).

[0097] Comparative Example 1

[0098] The only difference between the preparation method of this comparative catalyst and that of Example 3 is that Na2PdCl4 is not added in step S1.

[0099] The only difference between this comparative catalyst and Example 3 is that the catalyst contains only CoP substrate and no doped noble metal elements; it is denoted as CoP.

[0100] Relevant performance tests and results analysis

[0101] 1. The doped catalysts provided in Examples 1 to 4 and the catalyst provided in Comparative Example 1 were subjected to NO3. - The current density and relative potential to the standard hydrogen electrode were measured in a 50 ppm, 0.5 M Na₂SO₄ electrolyte solution, and the LSV curves were obtained. The results are as follows: Figure 1As shown, the doped catalysts provided in Examples 1 to 4, by doping noble metal elements into a phosphide substrate, exhibit better electrocatalytic performance for NO3 compared to a phosphide substrate. - The RR performance was improved, and the doped catalyst with a noble metal mass percentage of 0.78 wt% in Example 3 showed the best catalytic activity.

[0102] 2. The effect of noble metal doping on the band structure of phosphide substrates, and the influence of electronic interactions and chemical states between different elements.

[0103] The doped catalysts provided in Example 3 and Comparative Example 1 were analyzed by ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS), ultraviolet photoelectron spectroscopy (UPS), and X-ray photoelectron spectroscopy (XPS). The UV-vis DRS values ​​of CoP and Pd / CoP are as follows: Figure 2 As shown in Figure a, the band gaps (Eg) of CoP and Pd / CoP calculated according to UV-vis DRS are 2.49 eV and 2.45 eV, respectively (e.g., as shown in Figure a). Figure 2 (See illustration a). Furthermore, UPS testing was employed to determine the work function (Φ), Fermi level (EF), valence band (EV), and conduction band (EC) positions for different samples. The work function of Pd / CoP was calculated to be 5.76 eV based on the Ecutoff value, which is greater than that of CoP (…). Figure 2 (b. The figure shows 5.71 eV). Therefore, the EF position of Pd / CoP relative to vacuum is -5.76 eV, lower than the EF position of CoP relative to vacuum (-5.71 eV). The EV positions of CoP and Pd / CoP relative to vacuum are -7.35 eV and -7.82 eV, respectively (see Figure b). Figure 2 b). Based on the EV and Eg results, the EC positions of CoP and Pd / CoP relative to the vacuum level were further determined to be -4.86 eV and -5.37 eV, respectively. This indicates that Pd doping affects the band structure of CoP and promotes the downward shift of the d-band center of CoP from the Fermi level. Figure 3As shown in a and b, the high-resolution XPS spectra of Co and P in CoP and Pd / CoP show almost identical peak types. For Pd / CoP, the specific diffraction peaks with binding energies of 782.1 eV and 798.4 eV in the Co 2p spectrum correspond to Co 2p 3 / 2 and Co 2p 1 / 2, respectively; the Pd 3d spectrum shows diffraction peaks belonging to Pd-P, satellite peaks, and oxide species due to unavoidable air oxidation. Meanwhile, compared to the specific diffraction peaks in the Co 2p spectrum of CoP, the binding energies of the specific diffraction peaks in the Co 2p spectrum of Pd / CoP show a negative shift, mainly attributed to the electron transfer interaction between Co and Pd atoms. In other words, the strong interaction between Pd and Co alters the electronic structure of the metal center, thereby affecting the electrocatalytic activity of Pd / CoP.

[0104] 3. By observing the morphology of the doped catalyst, it can be found that the catalyst electrode is a nanoarray structure.

[0105] The doped catalyst provided in Example 3 was analyzed by SEM and TEM, such as... Figure 4 As shown in Figures (a) and (b), the microstructure of the catalyst can be clearly observed. Nanoneedles grow uniformly and densely on the surface of the titanium mesh, forming an independent microstructure. Figure 4 The high-resolution transmission electron microscope (HRTEM) image in (c) clearly shows that the lattice spacing of the (201) plane in CoP is 0.238 nm. At the same time, numerous defects formed by broken and missing lattice fringes are also observed in the spectrum, which may be due to Pd doping. Figure 4 (d) shows the X-ray diffraction (XRD) patterns of CoP and Pd / CoP. The patterns reveal that the characteristic diffraction peaks of the Pd-doped CoP XRD pattern are almost identical to those of the undoped CoP pattern, both corresponding to the crystal structure of standard CoP (JCPDS NO. 29-0947). However, a magnified view of the XRD diffraction peaks shows that the Pd / CoP diffraction peaks are significantly shifted to a lower angle by 0.12°, indicating a subtle change in the lattice parameters of Pd / CoP. Figure 4 (d) As shown in the illustration. This subtle change can be attributed to the substitution of Co by Pd, which has a larger atomic radius. Specifically, the above tests confirmed the successful doping of Pd into the CoP phase, forming a uniform doped catalyst.

[0106] 4. Doped catalysts, catalysts for NO3 - ammonium production performance of RR

[0107] The doped catalyst provided in Example 3 and the catalyst provided in the comparative example were tested in the presence and absence of NO3.- LSV curves in -N electrolyte solutions were used to preliminarily investigate the effect of the catalyst on NO3. - The current response of RR. For example... Figure 5 As shown in a, CoP and Pd / CoP in the presence of NO3 - Both catalysts exhibited stronger current responses in the electrolyte solution of NO3-, indicating that both catalysts respond more strongly to NO3-. - It possesses a certain reducing ability. Furthermore, the LSV curve clearly shows that the current density begins to deviate at -0.4 V vs. RHE, and the difference becomes more pronounced with increasing voltage. This change may be due to the catalyst initiating NO3-reduction reactions starting at this voltage. - Electrocatalytic reduction of NO3 was investigated. Therefore, -0.5 V to -0.9 V vs. RHE was selected as the voltage window for subsequent performance testing. Secondly, NO3 was subjected to electrocatalytic reduction at different voltages. - RR electrolysis experiments were conducted to investigate the activity of the Pd / CoP catalyst in the electrochemical reduction of nitrate to ammonium and the optimal operating voltage. Figure 5 As shown in b and c, from -0.5 V vs. RHE to -0.9 V vs. RHE, NO3 - The conversion and ammonium yield gradually increased, while the Faraday efficiency and selectivity exhibited a volcano-like pattern, reaching their maximum at -0.8 V vs. RHE. Subsequently, NO3 was evaluated. - -N, NO2 - -N, NH4 + The curve showing the change in -N concentration over time is presented in... Figure 5 In d. When the voltage is constant at -0.8 V vs. RHE, NO3 - -N and NH4 + The concentration of -N showed an opposite trend, indicating the conversion of nitrate to ammonium. Meanwhile, NO2... - The concentration of the -N intermediate showed a trend of first increasing and then decreasing during the reaction, and the concentration was almost negligible, indicating that the material has excellent ammonium selectivity. To further evaluate the stability of the catalyst, the Pd / CoP catalyst was subjected to a 6-cycle performance test, and the results were recorded. Figure 5 The results above show that after multiple cycles of testing, the nitrate conversion, Faradaic efficiency, selectivity, and ammonium yield did not show significant decline, confirming the excellent stability of the catalyst. Finally, the NO3- content of CoP catalysts with different proportions of Pd doping under the same conditions was compared. - RR performance such as Figure 5As shown in f, the effect of different Pd doping contents is revealed more accurately. All doped catalysts provided in Examples 1 to 4 exhibit the ability to reduce nitrate to ammonium. Specifically, Pd / CoP -0.78 wt% exhibits the best catalytic performance, with nitrate conversion, Faradaic efficiency, selectivity, and ammonium yield of 89.14%, 82.46%, 88.94%, and 0.099 mmol / h, respectively. -1 cm -2 The levels were significantly higher than those of CoP (44.64%, 26.42%, 58.74%, and 0.03275 mmol h). -1 cm -2 ), Pd / CoP-0.26 wt% (70.9%, 57.97%, 69.8%, 0.05658 mmol h -1 cm -2 ), Pd / CoP-0.52 wt% (84.12%, 64.997%, 78.77%, 0.08277 mmol h -1 cm -2 ), Pd / CoP-1.04 wt% (64.9%, 41.12%, 64.12%, 0.05678 mmol h -1 cm -2 ).

[0108] 5. Zn-NO3 - Battery research

[0109] The above characterization and analysis confirmed the role of Pd / CoP in the electrocatalysis of NO3. - The RR exhibits excellent activity. Subsequently, a novel Zn-NO3 was assembled using Pd / CoP grown on a titanium mesh as the cathode and Zn foil as the anode. - Battery. For example... Figure 6 As shown in a, Pd / CoP-based Zn-NO3 - Battery relative to Zn / Zn 2+ It has a constant open-circuit voltage of 1.38 V, which is basically consistent with the open-circuit voltage measured by a multimeter. Figure 6 b is a Pd / CoP-based Zn-NO3 - The battery's discharge curve and power density curve. This Zn-NO3 - The battery's discharge curve shows that as the cathode potential decreases, the output current density exhibits the opposite trend. However, the power density curve displays a volcano-like shape, reaching 1.55 mW / cm². -2 The peak power density of Zn-NO3. To verify the peak power density of Zn-NO3. -The battery's discharge stability was assessed by testing discharge curves at different current densities. At 1 mA cm⁻¹ -2 At current density, Zn-NO3 - The battery's discharge voltage tends to a stable value of 1.39 V, and this stability is maintained for 1 hour. Similar stability is observed at other current densities, indicating that Zn-NO3... - The battery exhibits excellent discharge stability. Subsequently, Pd / CoP-based Zn-NO3 was demonstrated at different current densities. - Ammonium yield and corresponding Faraday efficiency of the battery ( Figure 6 c, d). Specifically, Pd / CoP-based Zn-NO3 - The battery is at 12 mA cm -2 The ammonium yield was 15.873 µmol / h. -1 cm -2 , at 8 mA cm -2 It exhibits a maximum Faradaic efficiency of 86.76%. Based on the balance between ammonium yield and Faradaic efficiency, the optimal efficiency was determined at 8 mA cm⁻¹. -2 The optimal current density was found at 8 mA cm⁻¹. In subsequent experiments, this was achieved. -2 Multiple cycle stability tests were conducted at the specified current density, confirming the Zn-NO3... - The positive role of battery systems in the degradation of nitrate and the production of ammonium. Figure 6 e). To more fully evaluate Zn-NO3 - Battery reusability for Zn-NO3 - The battery underwent charging and discharging process testing, and the charging and discharging curves are displayed. Figure 6 In the curve, it can be seen that after multiple charge-discharge processes, Zn-NO3... - The battery's output voltage remained within a specific range, with no significant deactivation, fully demonstrating the effectiveness of Zn-NO3. - The charge-discharge stability of the battery. Meanwhile, this operation is similar to that of Zn-NO3. - The battery system also has unparalleled advantages. Figure 6 f). This further promotes the role of phosphides in Zn-NO3 - Its application in batteries has broadened the development of Zn-based batteries.

[0110] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A zinc-nitrate battery, characterized by: The cathode comprises a doped catalyst, the doped catalyst comprises a phosphide substrate, the phosphide substrate comprises cobalt phosphide and / or nickel phosphide, a noble metal element is doped in the phosphide substrate, the noble metal element comprises at least one of palladium, platinum, gold and silver; the doped catalyst forms a microstructure in the form of a needle array; The noble metal element accounts for 0.01 wt% to 1.04 wt% of the mass percentage of the doped catalyst; The doped catalyst comprises at least one of the following characteristics (1) to (4): (1) Fermi level is -5.5 to -6.0 eV; (2) Valence band energy is -7.4 to -8.3 eV; (3) Conduction band energy is -5.0 to -5.8 eV; (4) The lattice spacing of the crystal (201) plane in the phosphide substrate is 0.205 to 0.255 nm.

2. The zinc-nitrate battery of claim 1, wherein, The preparation method of the doped catalyst comprises the following steps: In an inert gas, a catalyst precursor is calcined with a phosphorus source to obtain the doped catalyst; The catalyst precursor comprises a noble metal hydroxide, and further comprises cobalt hydroxide and / or nickel hydroxide.

3. The zinc-nitrate battery of claim 2, wherein: The calcination process meets at least one of the following conditions (1) to (4): (1) The calcination temperature is 200 to 400 ℃; (2) The heating rate is 1 to 5 ℃ / min; (3) The calcination time is 1 to 3 h; (4) The inert gas is argon.

4. Zinc-nitrate battery according to claim 2 or 3, characterized in that: The calcination process comprises delivering the gaseous phosphorus source to contact with the catalyst precursor and performing the calcination process with the inert gas as the carrier gas.

5. The zinc-nitrate battery of claim 2 or 3, wherein: The phosphorus source comprises at least one of sodium hypophosphite monohydrate, phosphorus powder, sodium hypophosphite monohydrate, and sodium phosphate dodecahydrate; and / or The catalyst precursor is prepared by the following steps: At least one of a cobalt source and a nickel source is prepared into a mixed solution with a noble metal source and a precipitating agent, and the catalyst precursor is prepared by hydrothermal reaction.

6. The zinc-nitrate battery of claim 5, wherein: The cobalt source comprises at least one of cobalt nitrate hexahydrate, cobalt sulfate monohydrate, cobalt chloride hexahydrate, and cobalt phosphate octahydrate; and / or The nickel source comprises at least one of nickel nitrate hexahydrate, nickel chloride hexahydrate, nickel sulfate heptahydrate, and nickel acetate tetrahydrate; and / or The noble metal source comprises at least one of sodium tetrachloropalladate, palladium nitrate, palladium sulfate, and dichlorodiammine palladium; and / or The mass ratio of the total mass of the cobalt source and the nickel source to the mass of the noble metal source is 30 to 500:1; and / or The precipitating agent comprises urea; and / or The mass ratio of the precipitating agent to the noble metal source is 20 to 1500:

1.

7. The zinc-nitrate battery of claim 6, wherein: When preparing the mixed solution, a crystal form control agent is added, and the crystal form control agent comprises ammonium fluoride.

8. A process for the treatment of nitrate, production of ammonium, characterized by, Comprises the following steps: electrolysis of an NO3 - electrolysis of an NO3 - electrolyte solution, the cathode of the electrolysis comprising a doped catalyst; The doped catalyst comprises the doped catalyst in the zinc-nitrate battery according to any one of claims 1 to 7.

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