Preparation and application of a defective pt (111) / niO heterojunction catalyst
Patent Information
- Application Number
- CN202611333032.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-08-31
- Publication Date
- 2026-11-03
AI Technical Summary
Existing direct ammonia fuel cell anode catalysts suffer from slow ammonia oxidation kinetics, high reaction overpotential, susceptibility to nitrogen poisoning at precious metal active sites, and poor long-term stability, making them unsuitable for industrial fuel cell operating conditions.
A one-step hydrothermal crystal plane-guided synthesis strategy was adopted to construct Pt/NiO heterojunctions. By inducing defects through lattice stress and charge transfer at the heterojunction interface, the electronic structure was optimized, forming a tightly bonded metal-oxide heterojunction interface and generating highly active sites.
Achieving a low overpotential, high kinetic rate, and high stability electrocatalytic ammonia oxidation process, adapting to long-term continuous operation of fuel cells, and improving the catalyst's resistance to poisoning and stability.
Smart Images
Figure CN123033990A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of energy electrochemical catalytic materials technology, and more specifically, relates to a lattice stress-induced defect type Pt / NiO heterojunction direct ammonia fuel cell anode ammonia oxidation catalyst, its preparation method and application. Background Technology
[0002] As a highly efficient electrochemical energy conversion device, fuel cells are one of the core technological pathways for building new power systems and achieving zero-carbon energy utilization. Among various fuel cell systems, direct ammonia fuel cells, using ammonia as fuel, possess significant advantages such as abundant raw material production capacity, a well-developed storage and transportation system, zero carbon emissions during combustion, and high volumetric energy density. They are considered to be clean energy equipment with great industrialization prospects in long-term energy storage, stationary power generation, and transportation. The performance of the anode ammonia oxidation reaction (AOR) electrocatalytic electrode material directly determines the output power, energy conversion efficiency, and overall lifespan of the direct ammonia fuel cell. The development of high-performance anode catalytic electrodes is crucial for the large-scale promotion of direct ammonia fuel cells.
[0003] Currently, the electrocatalytic electrode materials for ammonia oxidation at the anode of direct ammonia fuel cells still face numerous technical challenges, severely hindering the commercialization of ammonia fuel cells. Firstly, the high NH bond breaking energy in ammonia molecules leads to slow kinetics of the ammonia oxidation reaction driven by existing electrode catalysts, resulting in excessively large overpotentials at the anode and significant energy loss, thus reducing the overall energy efficiency of the fuel cell. Secondly, while commercially available platinum-based electrode materials exhibit high conductivity and excellent intrinsic catalytic activity, the thermodynamically stable Pt(111) dominant crystal plane strongly adsorbs and complexes with the *N nitrogen-containing intermediates generated during ammonia oxidation, easily causing irreversible poisoning and deactivation of noble metal active sites. This results in poor long-term cycle stability of the electrode and significantly shortens the service life of the fuel cell.
[0004] Current modification methods for anode catalysts in direct ammonia fuel cells mostly involve simple physical mixing and single-element doping. These methods struggle to achieve directional control of noble metal crystal faces and the construction of tight heterogeneous interfaces, failing to structurally isolate and passivate easily poisoned Pt(111) crystal faces. Furthermore, the random generation of defect sites and the lack of targeted electronic structure control prevent effective balancing of the adsorption and desorption behavior of ammonia oxidation intermediates. Therefore, developing an ammonia oxidation electrocatalytic electrode material with a simple preparation process, high catalytic activity, and long-term anti-poisoning stability is a critical technical problem that urgently needs to be solved in this field. Summary of the Invention
[0005] To address the problems of slow ammonia oxidation kinetics, high reaction overpotential, susceptibility to nitrogen poisoning of noble metal active sites, poor long-term stability, and low energy conversion efficiency in existing direct ammonia fuel cell anode catalysts, which are difficult to adapt to industrial fuel cell operating conditions, this invention provides a lattice stress-induced defect type Pt / NiO heterojunction ammonia oxidation electrocatalyst and its preparation method.
[0006] One objective of this invention is to provide a lattice stress-induced defect type Pt / NiO heterojunction ammonia oxidation electrocatalyst prepared by the aforementioned preparation method. This catalyst relies on a one-step hydrothermal crystal facet-guided synthesis strategy to construct a metal-oxide hetero interface, generates lattice stress-induced defects by relying on interface lattice mismatch, and precisely controls the electronic structure by combining heterojunction charge transfer, thus exhibiting both high catalytic activity and strong resistance to poisoning.
[0007] Another objective of this invention is to provide the application of the aforementioned lattice stress-induced defect type Pt / NiO heterojunction ammonia oxidation electrocatalyst in the anode ammonia oxidation reaction of a direct ammonia fuel cell. This enables a low overpotential, high kinetic rate, and high stability electrocatalytic ammonia oxidation process, which is suitable for long-term continuous operation of fuel cells and is suitable for large-scale industrial application. This provides reliable technical support and an economically feasible solution for the industrial application of ammonia energy.
[0008] The present invention adopts the following technical solutions:
[0009] A method for preparing a defective Pt(111) / NiO heterojunction catalyst includes the following steps:
[0010] Step 1, pretreatment of nickel foil: Take a nickel foil of appropriate size and clean it in sequence with 1 M hydrochloric acid (HCl) solution, ethanol and deionized water under ultrasonic action to ensure surface cleanliness.
[0011] Step 2: Dissolve chloroplatinic acid hexahydrate (H2(PtCl6)·6H2O) and hexadecyltrimethylammonium chloride (CTAC) in deionized water.
[0012] Step 3: Place the nickel foil obtained in Step 1 into the solution in Step 2, and then transfer it to a stainless steel reactor lined with polytetrafluoroethylene for hydrothermal treatment.
[0013] Step 4: After Step 3 has cooled to room temperature, remove the modified nickel foil and perform annealing treatment.
[0014] Step 5: Rinse the nickel foil obtained in step 4 with a mixture of ethanol and water, and then dry it in a vacuum drying oven, denoted as Pt-NiO-4.
[0015] Furthermore, in step 1, the water is first washed with hydrochloric acid, and then washed with ethanol and deionized water. Preferably, the concentration of the hydrochloric acid is 1 mol / L.
[0016] Furthermore, in step 2, the concentration ratio of chloroplatinic acid hexahydrate to hexadecyltrimethylammonium chloride is 1:(1~5), where the unit of concentration is mmol / L.
[0017] Furthermore, step 3, the hydrothermal treatment, is carried out in an oven for 2 to 6 hours.
[0018] Furthermore, in step 4, the annealing is carried out in a muffle furnace at a temperature of 250°C for 1 hour.
[0019] Furthermore, in step 5, the drying is carried out in an oven at a temperature of 50-70°C.
[0020] Furthermore, the defective Pt(111) / NiO heterojunction catalyst obtained by the preparation method described above.
[0021] Furthermore, the Pt loading is less than 1 wt%; the relative content of oxygen vacancy defects on the NiO surface is 30~40%.
[0022] Furthermore, the aforementioned lattice stress-induced defect type Pt / NiO heterojunction ammonia oxidation electrocatalyst is used as an anode catalyst in the ammonia oxidation reaction of a direct ammonia fuel cell.
[0023] Furthermore, this catalyst has a low onset overpotential for ammonia oxidation (0.50 V). RHE The Tafel kinetic slope is small, and the power density of the direct ammonia fuel cell is 20.6 mW / cm². 2 The activity decay rate is less than 12% under continuous electrochemical testing, demonstrating excellent resistance to nitrogen intermediate poisoning and long-term electrochemical stability.
[0024] Compared with the prior art, the present invention has the following advantages:
[0025] Compared to single Pt-based catalysts or pure NiO catalysts, this invention employs a one-step hydrothermal crystal facet-guided synthesis strategy. By using CTAC to induce preferential exposure of the (111) crystal facet of Pt and directional growth of the highly active (101) crystal facet of NiO, a tightly bonded metal-oxide heterostructure interface is constructed. The generation of lattice stress-induced defects is achieved by relying on the two-phase lattice mismatch, and the electronic structure of the active sites is precisely controlled by Ni→Pt unidirectional charge transfer, effectively optimizing the adsorption-desorption balance of the ammonia oxidation intermediate.
[0026] The synergistic effect of heterogeneous interfaces can significantly improve the shortcomings of single catalysts, such as insufficient ammonia activation capacity, excessive adsorption of nitrogen intermediates leading to poisoning, and lag in reaction kinetics. It can also significantly reduce the overpotential of ammonia oxidation reaction and improve catalytic kinetic rate and anti-poisoning stability.
[0027] The prepared lattice stress-induced defect type Pt / NiO heterojunction electrocatalyst can realize a stable and continuous electrocatalytic ammonia oxidation process, which is suitable for the long-term continuous operation of direct ammonia fuel cells. The preparation process is controllable and easy to promote on a large scale, providing a feasible technical solution for the industrial application of ammonia energy. Attached Figure Description
[0028] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0029] Figure 1 This is a scanning electron microscope image of the defective Pt / NiO heterojunction catalyst prepared in Example 1 of this application;
[0030] Figure 2 This is a transmission electron microscope image of the defective Pt / NiO heterojunction catalyst prepared in Example 1 of this application, wherein the scale bar of content (a) is 50 nm, and the scale bars of content (b) and content (c) are 5 nm.
[0031] Figure 3 This is an EDS image of the defective Pt / NiO heterojunction catalyst prepared in Example 1 of this application;
[0032] Figure 4 These are fine XPS images of O in the catalysts prepared in Example 1 and Comparative Example 1 of this application;
[0033] Figure 5 These are the XRD patterns of the catalysts prepared in Example 1 and Comparative Example 1 of this application;
[0034] Figure 6 These are XPS images of the catalysts prepared in Example 1 and Comparative Example 1 of this application;
[0035] Figure 7 These are fine XPS images of Ni in the catalysts prepared in Example 1 and Comparative Example 1 of this application;
[0036] Figure 8 This is a fine XPS image of Pt in the catalyst prepared in Example 1 of this application;
[0037] Figure 9 This is a d-band diagram of the catalysts prepared in Example 1 and Comparative Example 1 of this application;
[0038] Figure 10 These are cyclic voltammetry curves of the catalysts prepared in Example 1 and Comparative Examples 1-3 of this application;
[0039] Figure 11 This is a graph showing the change of capacitive current of the catalysts prepared in Example 1 and Comparative Examples 1-3 of this application with different scan rates;
[0040] Figure 12 This is the accelerated life test of Embodiment 1 of this application;
[0041] Figure 13 The peak current changes of the catalysts prepared in Example 1 and Comparative Examples 1-3 of this application before and after accelerated life test;
[0042] Figure 14 These are the polarization curves and power density curves of a direct ammonia fuel cell with the catalyst prepared in Example 1 of this application as the anode;
[0043] Figure 15 These are in-situ Raman spectroscopy results of the catalysts prepared in Example 1 and Comparative Example 1 of this application. Detailed Implementation
[0044] To gain a deeper understanding of this invention, we will provide a comprehensive and detailed description. However, this invention has various implementations and is not limited to the specific examples listed herein. These examples are presented to enhance a full understanding of the disclosure of this invention.
[0045] Example 1
[0046] The one-step hydrothermal method for preparing defective Pt(111) / NiO heterojunction catalysts (Pt-NiO-4) includes the following steps:
[0047] (1) Take a nickel foil of appropriate size and ultrasonically clean it in sequence with 1 mol / L hydrochloric acid solution, ethanol and deionized water to remove surface impurities and obtain a clean nickel foil substrate;
[0048] (2) Dissolve chloroplatinic acid hexahydrate and hexadecyltrimethylammonium chloride in deionized water at a concentration ratio of 1:1 and stir until homogeneous to prepare a precursor solution;
[0049] (3) Place the nickel foil pretreated in step (1) into the precursor solution prepared in step (2), transfer it to a stainless steel reactor lined with polytetrafluoroethylene, and perform hydrothermal treatment in an oven for 4 h.
[0050] (4) After the reaction system has cooled to room temperature, remove the nickel foil and place it in a muffle furnace for annealing at 250°C for 1 h.
[0051] (5) The annealed nickel foil was rinsed with a mixture of ethanol and water and dried in a vacuum drying oven at 50~70℃ to finally obtain the lattice stress-induced defect type Pt(111) / NiO heterojunction ammonia oxidation electrocatalyst (Pt-NiO-4).
[0052] The scanning electron microscope (SEM) image of the defective Pt(111) / NiO heterojunction catalyst prepared in this embodiment is shown below. Figure 1 As shown, by Figure 1 , 2 It can be seen that Pt-NiO-4 is a typical nanosheet structure.
[0053] Figure 2 and Figure 3 The HRTEM and EDS images of the Pt-NiO-4 heterostructure interface show that Pt-NiO-4 is a typical nanosheet composite, in which Pt particles are loaded on NiO nanosheets.
[0054] Figure 4 The XPS fine spectrum of O in Pt-NiO-4 is shown. The high-defect oxygen characteristic peak obtained by fitting corresponds to oxygen vacancy sites. It can be determined that abundant oxygen vacancies are uniformly distributed on the surface of Pt (111) / NiO heterojunction, and the defect-type active site structure has been successfully constructed.
[0055] Example 2
[0056] The working electrode was prepared using the Pt-NiO-4 obtained in Example 1:
[0057] The Pt-NiO-4 nickel foil prepared in Example 1 was directly used as the working electrode for three-electrode electrochemical experiments.
[0058] Electrochemical experiments were conducted in 0.5 mol / L KOH and 0.05 mol / L electrolyte using a CHI760E electrochemical workstation. Platinum (Pt) foil and Ag / AgCl (saturated KCl aqueous solution) were used as the counter electrode and reference electrode, respectively.
[0059] Example 3
[0060] The anode for a direct ammonia fuel cell was assembled using the Pt-NiO-4 prepared in Example 1:
[0061] Nickel foil containing Pt-NiO-4 was ultrasonically treated in ethanol / deionized water to obtain the active material. The mass ratio of the active material to the carbon support was 0.2:1.0. The catalyst slurry was directly sprayed onto the anode side of an anion exchange membrane (15 μm thick), with a spraying area of 1 × 1 cm. 2Commercial Pt / C was then sprayed onto the cathode side to obtain the membrane electrode assembly. The membrane electrode assembly, carbon paper and graphite flow field plate, bipolar plate, and stainless steel end plate were then assembled.
[0062] Battery performance was tested at 50°C using a fuel cell test platform. 3 mol / L KOH and 5 mol / L electrolyte were continuously introduced into the anode, and fully humidified air was introduced into the cathode. Polarization curves and power density curves were collected under the above steady-state conditions.
[0063] The electrochemical properties of other materials were characterized using the same electrochemical tests, and the results are shown in the following comparative examples.
[0064] Comparative Example 1
[0065] The one-step hydrothermal method for preparing NiO catalyst, denoted as NiO, is basically the same as the method in Example 1, except that chloroplatinic acid hexahydrate is not added in step (2).
[0066] The NiO prepared in this comparative example exhibits an onset overpotential of 0.50 V for ammonia oxidation in an alkaline electrolyte system. RHE The activity decay rate under continuous electrochemical testing is close to 70%.
[0067] Comparative Example 2
[0068] The Pt and NiO heterojunction catalyst, denoted as Pt-NiO-2, was prepared by a one-step hydrothermal method. The method was basically the same as that in Example 1, except that the hydrothermal reaction time in step (3) was 2 h.
[0069] The NiO prepared in this comparative example exhibits an onset overpotential of 0.56 V for ammonia oxidation in an alkaline electrolyte system. RHE The activity decay rate under continuous electrochemical testing is close to 28%.
[0070] Comparative Example 3
[0071] The Pt and NiO heterojunction catalyst, denoted as Pt-NiO-6, was prepared by a one-step hydrothermal method. The method was basically the same as that in Example 1, except that the hydrothermal reaction time in step (3) was 6 h.
[0072] The NiO prepared in this comparative example exhibits an onset overpotential of 0.53 V for ammonia oxidation in an alkaline electrolyte system. RHE The activity decay rate under continuous electrochemical testing is close to 31%.
[0073] Figure 5The XRD patterns of Example 1 and Comparative Example 1 show a shift in the diffraction peaks of Pt-NiO-4 compared to NiO, indicating the presence of compressive strain and successful formation of the NiO-Pt heterostructure. Apart from this, no other crystalline characteristic peaks were observed in the samples.
[0074] Figure 6 The XPS spectra clearly show that the Pt-NiO-4 prepared in Example 1 contains Pt, Ni, C, and O elements; the NiO prepared in Comparative Example 1 contains Ni, C, and O elements.
[0075] Figure 7 The fine Ni 2p spectrum shows that pure NiO exhibits only Ni 2+ Characteristic peaks, complete lattice, and few defects; while the Pt / NiO heterostructure can simultaneously fit Ni 2+ With defect-induced local Ni + Composition. This is attributed to the stress generated by the lattice mismatch at the Pt-NiO interface, which induces the formation of a large number of oxygen vacancies on the NiO surface and forms low-valence nickel defect active sites through charge compensation.
[0076] Figure 8 The XPS fine spectrum of Pt shows that Pt exhibits the characteristics of Pt. 0 Pt 2+ Characteristic peaks.
[0077] Figure 9 The d-band center spectra prepared in Example 1 and Comparative Example 1 show that the d-band of Pt-NiO-4 is closer to the Fermi level.
[0078] Figure 10 This indicates that all samples in the 0.55-0.90 V potential range exhibit a clear oxidation peak. In contrast, Pt-NiO-4 shows the highest peak current density and the lowest onset potential, demonstrating better activity.
[0079] Figure 11 This is a graph showing the change in capacitance current with different sample scan rates. This graph can yield the bilayer capacitance value (C) of the catalyst. dl As can be seen from the figure, Pt-NiO-4 has the highest C content. dl The value is 8.1 mF cm −2 The electrochemically active surface area was significantly higher than that of other samples, and the C of the catalyst was related to the C of the catalyst. dl This is directly proportional to the number of active sites, indicating that Pt-NiO-4 can expose more active sites.
[0080] Figure 12 and Figure 13The stability of the catalyst was evaluated by accelerated life testing. NiO retained only 31.4% of its initial activity after 2000 cycles, while Pt-NiO-4 exhibited extremely high stability at its peak current density, retaining 88.8% of its initial value after 2000 consecutive test cycles.
[0081] Figure 14 This indicates that the Pt-NiO-4-based direct ammonia fuel cell exhibits excellent performance, reaching 20.6 mW / cm² at 50°C. −2 Peak power density.
[0082] Figure 15 The results indicate that as the anolyte potential increases, the characteristic peak of NiOOH (nickel hydroxyl oxide) gradually appears, indicating that NiO in the material is oxidized to form NiOOH; NiOOH is the true dynamic active phase participating in ammonia oxidation. Comparison between NiO and Pt-NiO-4 reveals that after the introduction of Pt, the formation potential of NiOOH is lower, and the peak intensity is higher at the same potential, proving that charge transfer at the Pt-NiO interface promotes the oxidative reconstruction of Ni sites, making it easier to generate highly active Ni-OOH species.
[0083] Contents not described in detail in this specification are prior art known to those skilled in the art. Although illustrative specific embodiments of the invention have been described above to facilitate understanding by those skilled in the art, it should be understood that the invention is not limited to the scope of the specific embodiments. Various modifications are readily apparent to those skilled in the art as long as they fall within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of this invention are protected.
Claims
1. A method for preparing a defective Pt(111) / NiO heterojunction catalyst, characterized in that, Includes the following steps: Step 1: Pre-treat the nickel foil to remove surface impurities; Step 2: Dissolve chloroplatinic acid hexahydrate and hexadecyltrimethylammonium chloride in deionized water to obtain a precursor solution; Step 3: Place the pretreated nickel foil from Step 1 into the precursor solution from Step 2 and perform hydrothermal treatment to grow a Pt(111) / NiO heterojunction in situ on the surface of the nickel foil. Step 4: Anneal the nickel foil after hydrothermal treatment in Step 3; Step 5: Clean and dry the nickel foil after annealing in Step 4 to obtain the defective Pt(111) / NiO heterojunction catalyst.
2. The preparation method according to claim 1, characterized in that, In step 1, the pretreatment includes, in sequence, ultrasonic cleaning of the nickel foil with hydrochloric acid solution, followed by ultrasonic cleaning with ethanol and deionized water.
3. The preparation method according to claim 1, characterized in that, In step 2, the concentration ratio of chloroplatinic acid hexahydrate to hexadecyltrimethylammonium chloride is 1:1~5.
4. The preparation method according to claim 1, characterized in that, In step 3, the hydrothermal treatment temperature is 140~180℃ and the time is 2~6 hours.
5. The preparation method according to claim 1, characterized in that, In step 4, the annealing temperature is 200~300℃ and the time is 0.5~2 hours.
6. The preparation method according to claim 1, characterized in that, In step 5, the drying temperature is 50~70℃.
7. The defective Pt(111) / NiO heterojunction catalyst prepared by the preparation method according to any one of claims 1-6.
8. The defective Pt(111) / NiO heterojunction catalyst according to claim 7, characterized in that, The Pt loading is less than 1 wt%; the relative content of oxygen vacancy defects on the NiO surface is 30~40%.
9. The application of the defective Pt(111) / NiO heterojunction catalyst according to claim 7 or 8 as an anode catalyst in the ammonia oxidation reaction of a direct ammonia fuel cell.
10. The application according to claim 9, characterized in that, In an alkaline electrolyte system, the onset overpotential for ammonia oxidation of the catalyst is no higher than 0.50 V. RHE The power density of direct ammonia fuel cells is no less than 20 mW / cm³. -2 The activity decay rate is less than 12% under continuous electrochemical testing.