Preparation method and application of polyindium phthalocyanine oxygen reduction electrocatalyst covalently suspended on carbon nano pits

Abstract

The invention discloses a preparation method and application of a polyindium phthalocyanine oxygen reduction electrocatalyst covalently suspended on a carbon nano pit, polyindium phthalocyanine is anchored on a defective carbon nano tube etched by CO2, and collaborative optimization of InPc electronic structure regulation and metal-carrier electron interaction is realized. Nano-pit defects are generated on the surface of CNT through CO2-driven oxidation etching, rich edge type carbon atoms with unpaired electrons are exposed in the substrate surface of the CNT, meanwhile, a single-layer InPPc polymer is covalently suspended on the carbon nano-pit defects through axial In-C coordination, axial In-C coordination bonds serve as electron bridges, and therefore, the carbon nano-pit defects can be formed in the surface of the CNT through the axial In-C coordination bonds. And strong interface coupling between the In-N4 center and the v-CNT substrate is realized. According to the electrocatalyst prepared by the method, the ORR catalytic activity and stability of the catalyst are remarkably improved.

Description

Technical Field

[0001] The present invention relates to an electrocatalyst, and in particular to a preparation method and application of a polyindium phthalocyanine oxygen reduction electrocatalyst covalently suspended on a carbon nano-pit. Background Art

[0002] Under the dual pressures of rapidly growing global energy demand and the increasingly severe threat of climate change, the development of sustainable energy solutions has become urgent. Among the many renewable energy technologies, fuel cells and metal-air batteries have attracted much attention due to their revolutionary energy storage and conversion properties. Among them, zinc-air batteries (ZABs) are considered ideal for grid energy storage systems due to their ultra-high theoretical energy density, environmental friendliness, and economic advantages. However, the commercialization of zinc-air batteries is largely limited by the sluggish oxygen reduction reaction (ORR) kinetics of the air cathode, which urgently requires the participation of efficient electrocatalysts. The platinum-based catalysts currently in widespread use are not only expensive but also prone to poisoning and deactivation. Therefore, the development of highly active and stable non-precious metal catalysts has become a key scientific challenge facing this field.

[0003] The rise of carbon-supported single-atom catalysts (SACs) has provided a new research paradigm for ORR electrocatalysis. Among them, carbon nanotubes (CNTs) have become ideal SACs catalyst support materials due to their excellent conductivity, mechanical stability and surface chemical tunability. Natural metalloenzymes (such as cytochrome C oxidase and hemoglobin) catalyze oxygen activation processes with efficiencies close to the thermodynamic limit through precisely arranged metal-N4 active centers, which provides important inspiration for the design of efficient catalysts. Inspired by this, molecular catalysts with planar metal-N4 motifs, especially iron phthalocyanine (FePc), have been widely explored for ORR catalysis. FePc molecules have a planar Fe-N4 structure similar to natural oxygen-binding proteins and can effectively activate O2 through π anti-bonding. However, FePc catalysts have key defects: (1) strong π-π stacking leads to the burial of active sites; (2) Fe 2+ions are prone to undergo Fenton reaction and dissolution; (3) symmetrical electron distribution leads to poor adsorption energy of ORR intermediates. These limitations have promoted the development of non-ferrous metal catalysts. However, compared with iron phthalocyanine (FePc), non-ferrous metal phthalocyanines (MPcs) generally exhibit weak O2 adsorption capacity and OO bond breaking efficiency due to the unsatisfactory 3d electron orbital arrangement, resulting in limited catalytic activity. To address this challenge, Li et al. (Adv. Mater. 2023, 35, 2302467) constructed N and P axially coordinated CoPc and NiPc to functionalized CNTs, and proved that they can induce MPc out-of-plane electronic polarization, thereby improving O2 adsorption and reducing ORR overpotential. However, this axial coordination strategy introduces a heteroatom bridging structure between the MPc molecule and the CNT, which objectively weakens the metal-support electronic interaction and weakens its ability to regulate the adsorption energy barrier of ORR intermediates. In addition, most of the current research focuses on monomeric MPc molecules. In contrast, the MPc polymer structure not only has inherent advantages in anti-stacking and metal leaching, but its extended π-conjugated framework is conducive to enhancing metal-support interactions. However, the research on MPc polymer ORR catalysts still lacks in-depth exploration.

[0004] In summary, there is an urgent need to develop a new catalytic system based on MPc that can integrate precise control of electronic structure with enhanced synergistic integration of metal-support interactions, thereby breaking through the intrinsic limitations of traditional carbon CNT-supported metal phthalocyanine MPc catalysts. Summary of the Invention

[0005] In view of the limitations of existing catalysts, the purpose of the present invention is to provide a preparation method and application of a polyindium phthalocyanine oxygen reduction electrocatalyst covalently suspended on carbon nanopits. By constructing a covalent suspension structure of polyindium phthalocyanine on defective carbon nanotubes, precise control of the electronic coupling effect between metal phthalocyanine molecules and carbon nanotubes is achieved.

[0006] To achieve the above object, the present invention adopts the following technical solutions: A method for preparing a polyindium phthalocyanine oxygen reduction electrocatalyst covalently suspended on carbon nano-pits comprises the following steps: (1) Multi-walled carbon nanotubes were first heated to a certain temperature in an inert atmosphere, and then placed in a 5% H2 / CO2 atmosphere for a certain period of time to obtain carbon nanotubes containing nanopit defects v-CNTs; (2) Indium chloride tetrahydrate and 1,2,4,5-tetranitrile benzene are dissolved in anhydrous ethanol, and the carbon nanotube v-CNT obtained in step (1) is added, and after ultrasonic dispersion, the mixture is transferred to an autoclave for reaction.

[0007] (3) After the reaction is completed, the obtained product is washed to obtain the InPPc / v-CNTs oxygen reduction electrocatalyst.

[0008] Furthermore, the inert atmosphere in step (1) is N2, and the heating is carried out to 900°C at a rate of 5°C / min under the N2 atmosphere.

[0009] Furthermore, the holding time in step (1) is 1 to 2 hours.

[0010] Furthermore, in step (2), the usage ratio of indium chloride tetrahydrate: 1,2,4,5-tetranitrile benzene: v-CNT is 7 mg: 18 mg: 15 mg.

[0011] Furthermore, the reaction temperature in step (2) is 160° C. and the reaction time is 6 hours.

[0012] The present invention also provides the application of the InPPc / v-CNTs oxygen reduction electrocatalyst prepared by the above preparation method in the field of electrocatalysis and zinc-air batteries.

[0013] In summary, the present invention generates nano-pit defects on the CNT surface through CO2-driven oxidative etching, exposing abundant edge-type carbon atoms with unpaired electrons within the CNT basal plane, and a single layer of InPPc polymer is covalently suspended to these carbon nano-pit defects through axial In-C coordination. The axial In-C coordination bond acts as an electron bridge to achieve strong interfacial coupling between the In-N4 center and the v-CNT substrate. This special axial interaction causes the symmetry of the electron density distribution at the In-N4 site to be broken, which is beneficial to enhance the O2 adsorption / dissociation kinetics and weaken the desorption energy barrier of the *OH intermediate. At the same time, the polymer structure of InPPc effectively eliminates the π-π stacking between InPc monomers, ensuring maximum exposure of the active sites, and the strong In-C bond can effectively inhibit the leaching of In metal. This strategy significantly improves the ORR catalytic activity and stability of the catalyst.

[0014] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. Precise control of electronic structure: Nanopit defects generated by CO2 etching of carbon nanotubes (v-CNTs) expose more edge carbon atoms (containing unpaired electrons), forming strong axial In-C coordination bonds with the In-N4 center of InPPc, achieving interfacial electronic coupling, optimizing the electron density distribution at the active sites, and enhancing catalytic activity.

[0015] 2. High active site exposure: The polymer structure of single-layer polyindium phthalocyanine (InPPc) avoids the π-π stacking problem of traditional phthalocyanine materials, ensuring that the active site (In-N4) is fully exposed and improving substrate accessibility.

[0016] 3. Superior stability: The covalently anchored In-C bond significantly enhances the metal-support interaction, inhibits metal leaching, and extends the catalyst life; the high conductivity and mechanical strength of v-CNT further ensure structural stability.

[0017] 4. Synergistic effect: The axially coordinated In-C bond acts as an electron bridge, promoting charge transfer between the In-N4 center and the carbon substrate, synergistically optimizing the reaction kinetics, and is suitable for catalytic processes that require efficient electron transport. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 High-resolution transmission electron microscopy (HRTEM), aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and EDS mapping images of the embodiments and comparative examples; (A) is the pristine CNTs and v-CNTs after CO2 etching, (B) is the HRTEM image of InPPc / v-CNTs; (C) is the HAADF-STEM image of InPPc / v-CNTs; (D) is the EDS mapping image of InPPc / v-CNTs.

[0019] Figure 2 The powder X-ray diffraction (XRD) patterns of the examples and comparative examples are shown.

[0020] Figure 3 The Raman spectra of the embodiments and comparative examples are shown in FIG.

[0021] Figure 4 The X-ray photoelectron spectroscopy (XPS) of the examples and comparative examples is shown in FIG.

[0022] Figure 5 The X-ray near-edge absorption fine structure spectroscopy (XANES) and Fourier transform extended X-ray absorption fine structure spectroscopy (EXAFS) of the examples and comparative examples are shown.

[0023] Figure 6 LSV plots, Tafel plots, LSV polarization curves at different rotation rates and corresponding Koutecký-Levich (KL) plots and J at 0.85 V for the examples, comparative examples, and Pt / C in O2-saturated 0.1 M KOH electrolyte at 1600 rpm. k Comparison chart with MA.

[0024] Figure 7 It diagram of Example and Pt / C.

[0025] Figure 8 The ZAB with the embodiment and Pt / C+RuO2 as cathode at 5 mA / cm 2 Discharge-charge cycle diagram. DETAILED DESCRIPTION

[0026] In order to make the contents of the present invention easier to understand, the technical solutions of the present invention are further described below in conjunction with specific implementation methods, but the present invention is not limited thereto.

[0027] Example 1: 200 mg of multi-walled carbon nanotubes (MWCNTs) were placed in a porcelain boat and heated to 900°C at a rate of 5°C / min under a nitrogen atmosphere. The sample was then exposed to a 5% H2 / CO2 environment at 900°C for 1 hour. This CO2 etching process successfully produced carbon nanotubes (v-CNTs) rich in nanopit defects. 35 mg of indium chloride tetrahydrate and 90 mg of 1,2,4,5-tetranitrobenzene were dissolved in 70 mL of anhydrous ethanol to form a transparent solution. 75 mg of v-CNTs were then added and uniformly dispersed by sonication. The resulting mixture was then transferred to a 100 mL Teflon-lined stainless steel autoclave and maintained at 160°C for 6 hours. The synthesized v-CNT-supported polyindium phthalocyanine sample (InPPc / v-CNTs) was then repeatedly washed with 1 M dilute hydrochloric acid and hot ethanol (50°C) to ensure complete removal of impurities.

[0028] Comparative Example 1: 35 mg of indium chloride tetrahydrate and 90 mg of 1,2,4,5-tetranitrobenzene were dissolved in 70 mL of anhydrous ethanol to form a clear solution. 75 mg of pristine MWCNTs, untreated with CO2, were then added and uniformly dispersed by sonication. The resulting mixture was then transferred to a 100 mL Teflon-lined stainless steel autoclave and maintained at 160°C for 6 hours. The synthesized CNT-supported polyindium phthalocyanine (InPPc / CNTs) sample was then repeatedly washed with 1 M dilute hydrochloric acid and hot ethanol (50°C) to ensure complete removal of impurities.

[0029] Figure 1 The high-resolution transmission electron microscope (HRTEM), aberration-corrected high-angle annular dark field scanning transmission electron microscope (HAADF-STEM) and EDS mapping images of the embodiment and comparative example are shown. Figure 1As shown in the figure, the original CNT has a typical smooth tubular morphology, while the v-CNT surface treated with CO2 thermal oxidation etching successfully constructs a uniformly distributed nanoscale pit structure, which confirms the effectiveness of the CO2-driven controllable etching process of CNTs. It is worth noting that InPPc / v-CNTs completely retain the tubular skeleton structure of v-CNTs, and fragmented amorphous InPPc polymer molecules with a particle size of 5 to 10 nm can be clearly distinguished on the surface of v-CNTs. HAADF-STEM images resolve a large number of atomic-level bright spots on the surface of v-CNTs, corresponding to isolated In atoms, thus confirming the molecular-level dispersion of InPPc on the surface of v-CNTs. EDS mapping further confirms that the three elements C, N, and In are highly uniformly distributed in space in the composite system, indicating that InPPc molecules achieve uniform loading on the surface of v-CNTs.

[0030] Figure 2 The powder X-ray diffraction (XRD) patterns of the examples and comparative examples are shown in FIG. Figure 2 It can be seen that the original CNTs show a sharp graphite (002) peak at 26°, while the v-CNTs show a broader peak at the same position, indicating that the graphite crystallinity is reduced due to the presence of a large number of carbon nanopit defects caused by CO2 etching. The XRD pattern of the original InPPc without CNTs support shows a prominent (00 l ) series of substrate reflections, which are the InPPc layer along c In sharp contrast, the InPPc / v-CNTs lack discernible InPPc diffraction peaks, indicating that the InPPc polymer molecules are uniformly dispersed in the form of monolayer fragments on the surface of v-CNTs.

[0031] Figure 3 For the Raman spectra of the embodiment and the comparative example, Figure 3 It can be seen that both CNTs and v-CNTs show carbon D (~1340 cm -1 ) and G (~1586 cm -1 ) bands, corresponding to defective / disordered carbon and sp 2 Type graphite carbon. Original CNTs at 1620cm -1 The G band of v-CNTs is split (attributed to interlayer coupling), while v-CNTs show broadened D and G bands and greatly suppress the split G band. This reflects that due to the presence of high carbon defect density after etching, the degree of graphitization of v-CNTs is reduced and the interlayer van der Waals interaction is weakened, which makes the intensity ratio of its D and G bands (I D / I G) is significantly enhanced, increasing from 0.88 (CNTs) to 1.88 (v-CNTs). Compared with v-CNTs, InPPc / v-CNTs exhibit a reduced I D / I G The ratio (1.38) and the partial restoration of the split G band indicate that the surface loading of the InPPc monolayer partially repairs the carbon nanopit defect sites. This unique geometric configuration of the InPPc fragments suspended on the carbon nanopits is strongly different from that of traditional carbon-supported MPc molecular catalysts. By decoupling the In-N4 active sites from the basal plane of CNTs, it weakens the typical strong π-π interaction between the carbon support and the MPc catalyst, thereby alleviating the electron delocalization of the metal center.

[0032] Figure 4 The X-ray photoelectrometry (XPS) of the embodiments and comparative examples is Figure 4 It can be seen that the high-resolution C 1s spectra of InPPc / v-CNTs and InPPc / CNTs can be deconvoluted into four components, namely sp 2 C=C(284.8 eV), sp 3 CC (285.2 eV), CN (285.6 eV) and CO (286.5 eV). The high-resolution N 1s spectrum of InPPc / v-CNT can distinguish pyrrolic nitrogen (398.1 eV), In-N x (398.8 eV) and graphitic N (400.2 eV) three nitrogen species, confirming the metallophthalocyanine structure of InPPc. High-resolution In 3d XPS of InPPc shows In 3d 5 / 2 (444.8 eV) and In 3d 3 / 2 (452.3 eV) spin-orbit splitting peak, which is the In 3+ Notably, InPPc / v-CNT and InPPc / CNT exhibit a positive binding energy shift in the In 3d peak relative to pristine InPPc, indicating that InPPc donates electrons to the v-CNTs support via metal-support interactions. This binding energy shift is larger for InPPc / v-CNTs compared to InPPc / CNT, suggesting that the InPPc fragments suspended from the carbon nanopits significantly amplify the metal-support electronic interactions between InPPc and v-CNTs.

[0033] Figure 5 The X-ray near-edge absorption fine structure spectra (XANES) and Fourier transform extended X-ray absorption fine structure spectra (EXAFS) of the embodiments and comparative examples are shown in FIG. Figure 5As can be seen, the In K-edge XANES spectra of InPPc / v-CNTs and InPPc / CNTs show a slight rightward shift in the absorption edge compared to the In2O3 reference, with the edge energies following the order InPPc / v-CNTs > InPPc / CNTs > InPPc. This trend, as indicated by the increasing intensities of the white lines, indicates a gradual increase in valence (>+3) throughout the sequence, suggesting an increased electrothermal donation of InPPc to the carbon support. The highest valence in InPPc / v-CNTs is directly related to their unique structure, with InPPc suspended from carbon nanopits within the v-CNTs, which amplifies electron metal-support interactions by optimizing electron transfer pathways. The corresponding FT-EXAFS spectra exhibit a dominant peak around 1.65 Å (without phase correction) in all samples, attributed to In-N / C first-shell coordination, with no In-In bonds observed, consistent with HAADF-STEM analysis. Notably, the In−N peak intensity increases in the order InPPc / v-CNTs > InPPc / CNTs > InPPc, indicating a higher In coordination number after carbon support integration. Quantitative R-space EXAFS fitting confirms that the In-N / C shell of InPPc / v-CNT has a coordination number of 4.64, exceeding that of InPPc / CNT (4.20). This fitting not only confirms the typical planar In-N4 first-layer coordination structure of InPPc loaded onto v-CNTs and CNTs, but also implies that the nanopits on the v-CNT surface induce additional coordination-unsaturated edge carbon defects for axial In-C bonding. This covalent interaction between InPPc and v-CNTs synergizes the fundamental In-N4 coordination, not only favoring the electronic symmetry of the In center but also promoting electronic metal-support interactions.

[0034] Application Example 1: Electrochemical tests were performed using a CHI 760E workstation equipped with a three-electrode system: a glassy carbon rotating disk electrode (RDE, 0.196 cm 2 ) as the working electrode, carbon rod counter electrode, and Ag / AgCl reference electrode. Catalyst ink was prepared by dispersing 5 mg of catalyst powder in a mixture of 300 μL of ethanol, 150 μL of deionized water, and 50 μL of 5 wt% Nafion solution via ultrasonic treatment. The ink was drop-cast onto the RDE to achieve a uniform density of 0.45 mg / cm 2All tests were performed in an O2-saturated 0.1 M KOH electrolyte, with background current subtraction under Ar saturation. The electrolyte was purged with O2 for 30 minutes before measurement and maintained under continuous O2 flow. Linear sweep voltammetry (LSV) was performed over a potential range of 0–1.2 V at a scan rate of 3 mV / s. Durability assessment was performed using chronoamperometric stability testing (IT) and accelerated durability testing (ADT).

[0035] Figure 6 LSV plots, Tafel plots, LSV polarization curves at different rotation rates and corresponding Koutecký-Levich (KL) plots and J at 0.85 V for the examples, comparative examples, and Pt / C in O2-saturated 0.1 M KOH electrolyte at 1600 rpm. k and MA comparison chart. Figure 6 As shown, InPPc / v-CNT exhibits excellent ORR activity with a high half-wave potential (E 1 / 2 ) and 5.77 mA / cm 2 The maximum diffusion limiting current density (J L ), exceeding InPPc / CNTs (0.73 V, 4.23 mA / cm 2 ) and commercial 20 wt% Pt / C benchmark (0.86 V, 5.29 mA / cm 2 The kinetic superiority of InPPc / v-CNT was further confirmed by Tafel slope analysis, which yielded an ultra-low Tafel slope of 33.07 mV / dec, significantly lower than that of InPPc / CNTs (119.04 mV / dec) and Pt / C (93.51 mV / dec). The ORR electron transfer numbers of InPPc / v-CNT and control samples were determined by Koutecký-Levich (KL) analysis of LSV at various rotation speeds. The calculated average electron transfer number of InPPc / v-CNT reached 4.04, indicating an ideal 4e - The ORR pathway only produces OH - Furthermore, the mass activity (975 mA / mg) and turnover frequency (TOF, 1.16 / s) further highlight its inherent superiority over InPPc / CNT (26 mA / mg, 0.014 / s) and Pt / C (38.92 mA / mg, 0.078 / s). This demonstrates that this invention can match or even surpass Pt / C, demonstrating its potential as a commercial alternative.

[0036] Figure 7 For example, it diagram of Pt / C. Figure 7As shown, further evaluation via IT testing at 0.70 V revealed that InPPc / v-CNTs exhibited minimal current density loss of 9.6% over 30 hours, in stark contrast to the 20.5% degradation observed for Pt / C in just 26 hours. This stark difference highlights the exceptional operational durability of InPPc / v-CNTs, making them viable candidates for practical applications requiring long-term stability.

[0037] Application Example 2 A 0.5 mm thick polished Zn plate was used as the anode, and a catalyst-coated carbon paper (1 mg / cm 2 A liquid ZAB (ZAB) was assembled using an aqueous electrolyte containing 6 M KOH and 0.2 M Zn(CH3COO)2 as the air cathode. The electrocatalyst ink was prepared by dispersing 5 mg of the InPPc / v-CNTs catalyst in a mixture of 300 μL of ethanol, 150 μL of deionized water, and 50 μL of a 5 wt% Nafion solution, followed by ultrasonication for 30 minutes to ensure homogeneity. The resulting catalyst ink was evenly coated on carbon paper to prepare the air cathode.

[0038] Figure 8 The ZAB with the embodiment and Pt / C+RuO2 as cathode at 5 mA / cm 2 Discharge-charge cycle diagram. Figure 8 As shown in the actual ZAB application, InPPc / v-CNT as air cathode is 2 The current maintained 95% voltage stability for 865 hours, demonstrating excellent activity and durability.

[0039] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for preparing a polyindium phthalocyanine oxygen reduction electrocatalyst covalently suspended on carbon nanopits, characterized by: The following steps are involved: (1) Multi-walled carbon nanotubes were first heated to a certain temperature in an inert atmosphere, and then placed in a 5% H2 / CO2 atmosphere for a certain period of time to obtain carbon nanotubes containing nanopit defects v-CNTs; (2) dissolving indium chloride tetrahydrate and 1,2,4,5-tetranitrile benzene in anhydrous ethanol, adding the carbon nanotube v-CNT obtained in step (1), and transferring to an autoclave for reaction after ultrasonic dispersion; (3) After the reaction is completed, the obtained product is washed to obtain the InPPc / v-CNTs oxygen reduction electrocatalyst.

2. The preparation method according to claim 1, wherein: The inert atmosphere in step (1) is N2, and the temperature is heated to 900°C at a rate of 5°C / min under N2 atmosphere.

3. The preparation method according to claim 1, wherein: The holding time in step (1) is 1 to 2 hours.

4. The preparation method according to claim 1, wherein: In step (2), the usage ratio of indium chloride tetrahydrate: 1,2,4,5-tetranitrile benzene: v-CNT is 7 mg: 18 mg: 15 mg.

5. The preparation method according to claim 1, wherein: The reaction temperature in step (2) is 160° C. and the reaction time is 6 hours.

6. An InPPc / v-CNTs oxygen reduction electrocatalyst prepared by the preparation method according to any one of claims 1 to 5.

7. Use of the InPPc / v-CNTs oxygen reduction electrocatalyst according to claim 6 in the field of electrocatalysis.

8. Use of the InPPc / v-CNTs oxygen reduction electrocatalyst as claimed in claim 6 in a zinc-air battery.

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