Preparation method and application of self-supporting armor catalyst

Abstract

A method for preparing a self-supporting armor catalyst and its application, belonging to the field of electrocatalyst technology, is disclosed. The method uses the natural soft biomass Pleurotus eryngii as a precursor, immersing it in a Co salt solution to allow cobalt to adsorb onto the biomass in ionic form. The biomass is then carbonized into graphite carbon with a stable structure. The biomass itself serves as a partial phosphating source, acting as a phosphating agent during the carbonization process to partially phosphate the Co metal. Finally, further phosphating treatment is performed to completely phosphate the Co metal in the form of Co2P, directly yielding the self-supporting armor catalyst. This method is simple to operate, utilizes readily available and low-cost raw materials, and can be used directly as a bifunctional electrode for electrocatalytic water splitting, avoiding the use of conductive agents and binders, facilitating large-scale production and application.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalysts, and in particular relates to a preparation method of a self-supporting armor catalyst and its application. Background Art

[0002] Electrocatalytic water splitting is one of the most promising green hydrogen production methods. This process involves the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode. In 2012, Academician Bao Xinhe first proposed the concept of armor catalysts, which consist of an armor layer and encapsulated metal nanoparticles. The catalytic activity stems from the perturbation of the local electronic state of the armor layer and the transfer of electrons from the metal nanoparticles to the outer surface, resulting in improved electrocatalytic activity and stability. Consequently, armor catalysts have become a hot topic of research.

[0003] However, existing technologies for synthesizing armor catalysts require multiple equipment and a wide variety of chemicals, complex synthesis steps, and the raw materials must be prepared separately. For example, carbon nanotubes and graphene are used as carbon supports. These carbon supports are expensive to prepare and require complex processes. Furthermore, the resulting catalysts are often in powder form and require conductive and binder agents for stabilization. These shortcomings hinder the large-scale production and application of armor catalysts. Therefore, finding a simple and efficient method to synthesize relatively inexpensive and mechanically stable armor catalysts is crucial for advancing the large-scale electrocatalytic water splitting process. Summary of the Invention

[0004] In view of this, the object of the present invention is to provide a method for preparing a self-supporting armor catalyst, which is simple to operate and low in cost. The prepared self-supporting armor catalyst has good mechanical stability and is conducive to large-scale production and application.

[0005] The present invention also provides an application of the self-supporting armor catalyst.

[0006] The technical solutions adopted by the present invention to solve the technical problems are as follows:

[0007] A preparation method of a self-supporting armor catalyst comprises the following steps:

[0008] The natural King Oyster Mushroom was cut into slices of predetermined size along the growth direction, immersed in Co salt solution at room temperature, and freeze-dried overnight to obtain PE-Co 2+ slice;

[0009] PE-Co 2+ The slices were placed in a muffle furnace for low-temperature carbonization, and then high-temperature carbonization was performed in a tube furnace in a nitrogen atmosphere. The carbonized product was polished and ultrasonically cleaned to obtain the Co / Co2P@CPE intermediate.

[0010] The Co / Co2P@CPE intermediate was embedded with sodium hypophosphite powder and then placed in a tube furnace for calcination in a nitrogen atmosphere to phosphate the Co / Co2P@CPE intermediate, thereby obtaining a Co2P@CPE sample, namely, the self-supporting armor catalyst.

[0011] Preferably, in step (1), the concentration of the Co salt solution is 0.2-0.3M Co(NO3)2 solution.

[0012] Preferably, in step (2), the low-temperature carbonization temperature is 250-300°C, the time is 4-7h, the high-temperature carbonization temperature is 800-1000°C, the time is 2-6h, the carbonization heating rate for both times is 2-10°C / min, and the gas flow rate is 40mL / min.

[0013] Preferably, in the step (2), the post-processing operation is as follows: in the step (2), the carbonized product is polished using 2000-grit sandpaper to achieve a thickness of 600 μm.

[0014] Preferably, in step (2), ethanol and water are used for ultrasonic cleaning three times to remove residual carbon.

[0015] Preferably, in step (3), the calcination temperature is 250-350°C, the calcination time is 1.5-2.5h, the heating rate is 2-10°C / min, and the gas flow rate is 40mL / min.

[0016] The invention discloses an application of the self-supporting armor catalyst prepared by the preparation method as a bifunctional electrode for electrocatalytic water decomposition.

[0017] From the above technical solution, it can be seen that the present invention provides a preparation method and application of a self-supporting armor catalyst, and its beneficial effects are: the preparation method uses natural soft biomass King Oyster Mushroom as a precursor, immerses it in a Co salt solution, and makes Co adsorbed on the fiber pores of King Oyster Mushroom in the form of ions to obtain PE-Co 2+ , then PE-Co 2+Carbonization is performed to carbonize the biomass into graphitic carbon (CPE) with a stable structure. Since the biomass itself can serve as a partial phosphating source, it can act as a phosphating agent to phosphate part of the Co metal during the carbonization process to obtain a Co / Co2P@CPE intermediate. Finally, the Co / Co2P@CPE intermediate is further phosphated to completely phosphate the Co metal in the form of Co2P nanoparticles. The obtained Co2P@CPE sample is a self-supporting armor catalyst. The self-supporting armor catalyst encapsulates the internal Co2P nanoparticles through an external stable graphitic carbon shell to effectively protect the internal Co2P nanoparticles from the influence of the corrosive reaction environment. The Co2P nanoparticles acting as an "active source" can transfer more electrons to the external carbon shell, thereby effectively exciting the carbon shell surface, so that the self-supporting armor catalyst has excellent catalytic activity and better stability. This preparation method is simple to operate, the raw materials are easily available and low-cost, and the prepared self-supporting armor catalyst can be directly used as a bifunctional electrode for electrocatalytic water decomposition, avoiding the use of conductive agents and adhesives, which is conducive to large-scale production and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a scanning electron microscope (SEM) image of Co2P@CPE.

[0019] Figure 2 This is a transmission electron microscope (TEM) image of Co2P@CPE.

[0020] Figure 3 are the X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results of CPE and Co2P@CPE.

[0021] Figure 4 These are the HER and OER activity test results of Co2P@CPE.

[0022] Figure 5 This is the result of testing Co2P@CPE as a dual-functional electrode to assemble a water splitting device. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be emphasized that the specific embodiments described herein are only used to better illustrate the present invention and are part of the embodiments of the present invention, not all embodiments, and are therefore not intended to limit the present invention.

[0024] The present invention provides a method for preparing a self-supporting armor catalyst, comprising the following steps:

[0025] (1) Cut the natural King Oyster Mushroom into slices of predetermined size along the growth direction, immerse them in Co salt solution at room temperature, adsorb Co in the form of ions on the fiber channels of King Oyster Mushroom, freeze-dry overnight to obtain PE-Co 2+ slice;

[0026] Specifically, the natural King Oyster Mushroom was cut into 2.5cm×2.5cm×1mm slices along the growth direction, and adsorbed in 0.2M Co(NO3)2 solution at room temperature for 1h, and then freeze-dried overnight to make Co 2+ In this step, the natural King Oyster Mushroom is cut along its growth direction, so that the carbon material obtained by subsequent calcination still retains the microstructure of the original biomass, with a developed pore structure that is conducive to electron transmission.

[0027] (2) PE-Co 2+ The slices were placed in a muffle furnace for low-temperature carbonization, and then high-temperature carbonization was performed in a tube furnace in a nitrogen atmosphere. The carbonized product was polished and ultrasonically cleaned to obtain the Co / Co2P@CPE intermediate.

[0028] In one embodiment, the freeze-dried PE-Co 2+ The slices were placed in a muffle furnace and calcined at 260°C for 6 hours for low-temperature carbonization to remove excess tar from the biomass. The biomass was then transferred to an atmosphere tube furnace and heated to 1000°C at a heating rate of 5°C / min under a nitrogen flow rate of 40 mL / min for 6 hours for high-temperature carbonization. This transformed the non-conductive or poorly conductive biomass material into a conductive carbon material with an ultra-high degree of graphitization. The carbonized product was cooled to room temperature under an argon atmosphere and carefully polished with 2000-grit sandpaper to a thickness of 600 μm. The product was then ultrasonically cleaned three times with ethanol and water to remove residual carbon, yielding the intermediate Co / Co2P@CPE. In this step, the biomass was carbonized into graphite carbon (CPE) with a stable structure through high-temperature pyrolysis. The biomass itself served as a phosphating source, acting as a phosphating agent to partially phosphate the Co metal during the carbonization process.

[0029] (3) The Co / Co2P@CPE intermediate was embedded with sodium hypophosphite powder and then placed in a tubular furnace for calcination in a nitrogen atmosphere to phosphate the Co / Co2P@CPE intermediate and obtain a Co2P@CPE sample, i.e., a self-supporting armor catalyst.

[0030] In one specific embodiment, 1g of sodium hypophosphite powder was placed in a corundum boat to encapsulate the Co / Co2P@CPE intermediate. The sample, a self-supporting armored catalyst, was obtained by heating the sample in a tube furnace at 300°C with a nitrogen flow rate of 40mL / min at a ramp rate of 2°C / min for 2 hours. The Co2P@CPE was then washed and dried in a vacuum oven at 60°C for 12 hours. In this step, the Co / Co2P@CPE intermediate was further phosphated using sodium phosphite as a phosphating agent, completely converting the Co metal to Co2P. The Co2P nanoparticles within the CPE were encapsulated by a robust outer graphitic carbon (CPE) shell, effectively protecting them from the corrosive reaction environment. Furthermore, the Co2P nanoparticles, acting as "active sources," could transfer more electrons to the outer carbon shell, effectively stimulating the carbon shell surface, resulting in excellent catalytic activity and enhanced stability for the Co2P@CPE.

[0031] Please see Figure 1 , the morphology and microstructure of Co2P@CPE electrode were investigated by using scanning electron microscopy (SEM). Figure 1 In the figure, (a) is the SEM image of the overall view of Co2P@CPE, where it can be found that Co2P@CPE is a honeycomb structure with a large number of macropores generated by interconnected fibers. (b) is the top view of Co2P@CPE, which clearly shows that the original PE-Co 2+ The slice shows a fluffy structure containing a large number of cellulose fibers. (c) is a side view of the Co2P@CPE. After high-temperature pyrolysis and phosphating at 1000°C, the electrode remains intact, and the prepared Co2P@CPE electrode can be observed to have a well-developed porous structure, almost replicating the microstructure of the original PE slice. (d) is a SEM image of the Co2P@CPE, showing the uniform distribution of Co2P nanoparticles on the surface. (f) is an SEM image of the Co2P@CPE electrode and the corresponding elemental map, showing that the elements C, O, Co, and P are evenly distributed throughout the carbon skeleton.

[0032] Please see Figure 2 , the microstructure of Co2P@CPE was characterized by transmission electron microscopy (TEM). Figure 2 (a) is a low-resolution TEM image of Co2P@CPE, (b) is a low-resolution image of Co2P@CPE, (c) is a HRTEM image, and (d) is a HAADF-STEM image of Co2P@CPE and the corresponding elemental maps of C, N, Co, and P. Figure 2 (a)-(b) show that the surface of the prepared Co2P@CPE electrode is loaded with a large amount of metal nanoparticles, which is consistent with the SEM results. Figure 2The high-resolution image in (c) further reveals that the lattice spacing of the coated Co2P nanoparticles is 0.20nm, corresponding to the (111) plane of hexagonal metallic Co2P. The nano-Co2P is wrapped by a thin layer of graphitic carbon of about 1.5nm with an interlayer spacing of about 0.34nm ((002) plane of graphitic carbon). Figure 2 (d) Elemental mapping and transmission electron microscopy (TEM) further confirmed the uniform distribution of Co and P elements in the nanoparticles prepared within CPE, and the four elements C, N, Co, and P were evenly distributed, with Co and P elements almost overlapping.

[0033] See Figure 3 The chemical structures of CPF and Co2P@CPF were revealed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Figure 3 (a) is the XRD spectrum, (b) is the XPS measurement spectrum, (c) is the element content diagram, (d) is the XPS spectrum of Co 2p, (e) is the XPS spectrum of P 2p, and (f) is the XPS spectrum of N 1s. Figure 3 As shown in (a), the XRD spectrum of the CPE electrode without the introduction of Co element shows two main diffraction peaks at 2θ of 23.5° and 44°, which belong to the (002) and (100) of carbon, respectively. The Co / Co2P@CPE sample with the introduction of Co element shows the (111), (200) and (220) planes corresponding to the metal Co at 2θ of 44.2°, 51.57° and 75.98°, respectively. The appearance of the diffraction peak at 2θ of 40.81° corresponding to the (212) crystal plane of Co2P metal is due to the phosphorus element contained in the biomass acting as a phosphorus source, acting as a phosphating agent to phosphate part of the Co metal. After further phosphating, the peak at 2θ of 75.98° of the Co2P@CPE sample completely disappears, which means that the Co metal in the sample is completely phosphated, which is consistent with the TEM analysis results. X-ray photoelectron spectroscopy (XPS) was used to characterize the composition and chemical state of CPE and Co2P@CPE. Figure 3 (b) shows that C, N, O, Co, and P elements can be found in the prepared sample. Figure 3 As shown in (c), the element content shows that CPE is mainly composed of C (81.76 at.%), N (1.94 at.%), O (14.92 at.%) and P (1.37 at.%). The presence of P proves that biomass can be used as a source of phosphating. Therefore, a part of the metal Co in the sample Co / Co2P@CPE with the introduction of Co element is phosphated. 2+The subsequent Co / Co2P@CPE sample had Co (3.01 at.%) added to the XPS full spectrum, but the P element (1.87 at.%) was not enough to completely phosphate it. After further phosphating, the P content in the sample increased to 14.74 at.%. Figure 3 (d) shows the Co 2p XPS spectrum of Co2P@CPF, with the Co 2p appearing at 777.9 eV and 793.1 eV. 3 / 2 and Co 2p 1 / 2 The peaks confirm that Co in Co2P@CPE exists in the form of Co-P combination. Figure 3 (e) shows the high-resolution P 2p XPS spectrum of Co2P@CPE, with P2p appearing at 130.6 eV and 129.4 eV. 3 / 2 and P2p 1 / 2 The peaks confirmed that P in Co2P@CPE existed in the form of Co-P combination, indicating that the Co element was completely phosphated to form Co2P, while the peaks at 133eV and 132eV represented the combination of PC and PO, respectively, which also corresponded to the results of EDX element mapping. Figure 3 (f) shows the N1S XPS spectrum of Co2P@CPE, indicating the presence of nitrogen in the sample.

[0034] Please see Figure 4 Based on the unique CPE structure and uniformly distributed Co2P nanoparticles, the HER and OER activities of the prepared Co2P@CPE catalyst were studied using a standard three-electrode configuration in 1.0 M KOH electrolyte, as well as the activities of the original samples CPE, Co / Co2P@CPE, and Pt / C.

[0035] Figure 4 (a) HER polarization curves of different samples at a current density of 10 mA cm -2 When the HER activity of the CPE electrode is the worst, the overpotential is 366 mV. Under the same reaction conditions, the HER activity of Co / Co2P@CPE with the introduction of Co element is slightly enhanced. -2 The overpotential is reduced to 220 mV. The HER activity of the Co2P@CPE sample after further phosphating is further enhanced at a current density of 10 mA cm -2 The overpotential is only 106mV at 100mA·cm -2 The overpotential is 173 mV, indicating that the Co2P nanoparticles embedded in the CPE are highly active HER components. Figure 4 (b) is the Tafel diagram of HER of different electrodes. It can be seen that the Tafel slope of Pt / C is 59mV·dec-1 The Tafel slope of Co2P@CPE is 72mV·dec -1 , close to the Heyrovsky reaction (≈40mV·dec -1 ), indicating that the HER process occurs via the Volmer-Heyrovsky mechanism, with the rate-determining step (RDS) being a Heyrovsky reaction. Figure 4 (c) Evaluation of the long-term HER stability of the Co2P@CPE electrode at high current density in 1.0 M KOH solution. During the 100 h electrocatalytic HER process, the current density at -0.27 V relative to the reversible hydrogen potential increased from 100 mA cm -2 Down to 80mA·cm -2 The excellent stability of Co2P@CPE is the result of the synergistic effect of the highly reactive Co2P nanoparticles and the carbon shell structure. The internal transition metal nanoparticles are encapsulated by the external stable graphite carbon shell layer, effectively protecting the internal metal nanoparticles from the corrosive reaction environment. The metal nanoparticles acting as "active sources" can transfer more electrons to the external carbon shell, thereby effectively stimulating the carbon shell surface, resulting in a certain degree of catalytic activity and better stability.

[0036] Figure 4 (d) shows the OER polarization curves of different electrodes in 1.0 M KOH solution. The CPE electrode without Co2P nanoparticles has almost no OER performance. However, the OER performance of the Co / Co2P@CPE electrode with the introduction of Co element has been improved to a certain extent. -2 At a current density of 100 mV, the overpotential is reduced to 420 mV. After further phosphating, the Co2P@CPE electrode loaded with Co2P nanoparticles has excellent OER activity. The Co2P@CPE electrode only requires an overpotential of 230 and 380 mV to reach 10 mA·cm -2 and 100 mA·cm -2 The current density is much lower than that of commercial catalyst RuO2 (300mV and 350mV). Figure 4 (e) Tafel diagram of OER of different electrodes. The Tafel slope of Co2P@CPE electrode is 133mV·dec -1 , and the Tafel slope of RuO2 (123mV·dec -1), indicating that the first electron transfer process is the rate-determining step (RDS). This exceptionally high OER activity is attributed to the unique structure of the Co2P@CPE electrode. The Co2P nanoparticles directly embedded in the CPE substrate serve as efficient active sites and charge separation sites for OER, while the internal metallic Co2P nanoparticles can quickly transfer electrons to the CPE matrix, resulting in the Co2P@CPE electrode's excellent electrocatalytic OER performance. Figure 4 (f) Evaluation of the long-term OER stability of the Co2P@CPE electrode at high current density in 1.0 M KOH solution. The initial current density of the Co2P@CPE electrode was 100 mA·cm at a potential of 1.67 V relative to the reversible hydrogen electrode. -2 The current density of OER on the Co2P@CPE electrode gradually decreases with the extension of reaction time and still maintains 80% of its original activity after 5 h of electrolysis. The current decay is due to the oxidation of Co2P nanoparticles.

[0037] See Figure 5 Based on the excellent HER and OER activity of Co2P@CPE electrode under alkaline conditions, it was assembled as a bifunctional electrode to test water splitting device in 1.0M KOH solution. Figure 5 (a) The Faradaic efficiency of the overall water splitting of Co2P@CPE measured by Hofmann electrolysis. -2 The Faradaic efficiency of oxygen and hydrogen production was measured at a current density of , indicating that the Faradaic efficiency was around 100%. Figure 5 (b) The LSV curve of Co2P@CPE as a bifunctional electrode in an electrolytic cell shows that it can reach 10 mA cm at 1.66 V and 1.92 V, respectively. -2 and 100mA·cm -2 The current density is close to that of the commercial catalyst Pt / C+RuO2, and as the current density increases, the catalytic performance of the overall catalyst is stronger than that of the combination of commercial powder-based catalysts using a conductive binder. Figure 5 As shown in (c), when the battery voltage is 2.0 V and the initial current density is 100 mA cm -2 Under the conditions of 12 hours, the long-term stability of the combined electrolytic cell was tested. During the electrolysis of water, the current density increased from the initial 100 mA cm -2 Slowly decays to 76 mA·cm -2 , indicating that the Co2P@CPE electrode can not only be used as a bifunctional catalyst, but also has good stability.

[0038] Figure 5 (d) Schematic diagram of the light-driven water splitting system. Figure 5 (e) simulates AM 1.5G, 81mW·cm −2 JV curve of the silicon cell integrating the entire water splitting system under illumination. Figure 5 (f) is a digital photograph of a water electrolyzer driven by a 2.34 V solar cell. Co2P@CPE has a low overpotential and good stability, making it one of the best bifunctional electrocatalysts. Therefore, even a 2.0 V solar cell voltage can drive the Co2P@CPE pair to produce significant bubbles, indicating the potential of the Co2P@CPE electrode for solar energy storage and practical hydrogen production. The JV curve of the tandem solar cell intersects with the JV curve of the electrolyzer, and the expected operating current density of the photoelectrolysis system is 11.43 mA cm at 1.45 V. -2 Furthermore, the combined system was characterized under AM1.5 spectral conditions and 81mW·cm −2 The performance of the system under the light intensity of 200 nm was shown, and the solar-to-hydrogen (STH) conversion efficiency of the system was 18%, demonstrating the application potential of Co2P@CPE in practical light-driven water splitting systems.

[0039] The above disclosure is only a preferred embodiment of the present invention, and it is certainly not intended to limit the scope of the present invention. A person skilled in the art can understand that all or part of the processes of the above embodiment and equivalent changes made in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A method for preparing a self-supporting armor catalyst, characterized in that: The following steps are involved: Step (1) cut the natural King Oyster Mushroom into slices of predetermined size along the growth direction, immerse them in a Co salt solution at room temperature, adsorb Co in the form of ions on the fiber channels of the King Oyster Mushroom, and freeze-dry overnight to obtain PE-Co 2+ slice; Step (2) PE-Co 2+ The slices were placed in a muffle furnace for low-temperature carbonization, and then high-temperature carbonization was performed in a tube furnace in a nitrogen atmosphere. The carbonized product was polished and ultrasonically cleaned to obtain a Co / Co2P@CPE intermediate. The low-temperature carbonization temperature was 250-300°C for 4-7 hours, and the high-temperature carbonization temperature was 800-1000°C for 2-6 hours. The heating rate for both carbonizations was 2-10°C / min, and the gas flow rate was 40 mL / min. Step (3) The Co / Co2P@CPE intermediate is embedded with sodium hypophosphite powder and then placed in a tube furnace for calcination in a nitrogen atmosphere to phosphate the Co / Co2P@CPE intermediate to obtain a Co2P@CPE sample, i.e., the self-supporting armor catalyst.

2. The method for preparing the self-supporting armor catalyst according to claim 1, wherein: In the step (1), the concentration of the Co salt solution is 0.2-0.3M Co(NO3)2 solution.

3. The method for preparing the self-supporting armor catalyst according to claim 1, wherein: In the step (2), the carbonized product is polished using 2000-grit sandpaper to a thickness of 600 μm.

4. The method for preparing the self-supporting armor catalyst according to claim 1, wherein: In step (2), ethanol and water are used for ultrasonic cleaning three times to remove residual carbon.

5. The method for preparing the self-supporting armor catalyst according to claim 1, wherein: In the step (3), the calcination temperature is 250-350°C, the calcination time is 1.5-2.5h, the heating rate is 2-10°C / min, and the gas flow rate is 40mL / min.

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