Self-assembled nitrogen-doped carbon nanotube Pt2Mo catalyst as well as preparation and application thereof

Abstract

The invention provides a self-assembled nitrogen-doped carbon nanotube Pt2Mo catalyst as well as preparation and application thereof, and belongs to the technical field of catalysts. According to the invention, the ultrafine Pt2Mo alloy nanoparticles are combined with the ordered N-CNT carrier, the synergistic enhancement of structure and performance is realized on the nanoscale, the highly ordered bamboo-like N-CNT skeleton provides a support frame with stable structure and good electronic conductivity, the uniform dispersion of the Pt2Mo alloy nanoparticles is promoted, and efficient electron and mass transmission is realized. The three-dimensional structure can reduce agglomeration of nanoparticles, ensure continuous exposure of active sites and accelerate ORR kinetics. In addition to carrier optimization, Pt and Mo are accurately alloyed to form a clear Pt2Mo structure, so that the catalytic activity can be further improved. Different from a surface doping system, the Pt2Mo alloy nanoparticles show lattice shrinkage and electron reconstruction, the d band center of Pt is effectively adjusted, and adsorption of an oxygen intermediate is weakened. The modification of the structures and the electron level jointly accelerates the ORR process and improves the durability of the catalyst.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalysts, in particular to a self-assembled Pt2Mo / nitrogen-doped carbon nanotube catalyst and a preparation and application thereof. BACKGROUND

[0002] Proton exchange membrane fuel cell (PEMFC) is a clean and efficient energy conversion technology with great development prospects, which is expected to achieve revolutionary breakthroughs in transportation and power supply fields. Although PEMFC has the advantages of high efficiency and environmental protection, the bottleneck of its wide application is the insufficient durability of the cathode oxygen reduction reaction (ORR) catalyst. Currently, Pt-based catalysts are considered as the most effective materials for promoting ORR, but their performance is easily affected by various failure mechanisms during long-term operation, including nanoparticle dissolution, carbon monoxide poisoning and electrochemical degradation. These problems, combined with the high cost and scarcity of Pt, force researchers to develop advanced catalysts that can not only reduce Pt usage but also improve catalytic activity and long-term stability.

[0003] To address the above challenges, research focuses on designing and synthesizing new catalysts with high performance and cost-effectiveness. The key to optimizing the performance of PEMFC catalysts lies in the rational selection of support materials. Carbon-based supports, especially carbon nanotubes (CNTs), are widely concerned due to their high electrical conductivity, large specific surface area and excellent chemical stability. CNTs can provide a stable dispersion support framework for Pt-based nanoparticles, which is crucial for maximizing the active surface area of the catalyst. However, the inherent high structural integrity and significant chemical inertness of CNTs lead to insufficient interaction with metal catalysts, which easily causes unstable catalyst anchoring and nanoparticle agglomeration, ultimately weakening the long-term performance of the catalyst. To overcome this limitation, researchers propose to dope CNTs with heteroatoms such as nitrogen. This strategy can effectively regulate the surface properties of CNTs, introduce additional active sites and defect structures, and thus promote the progress of catalytic reactions. Nitrogen-doped carbon nanotubes (N-CNTs) not only strengthen the interaction between metal nanoparticles and the support, but also introduce new active sites, significantly improving the ORR catalytic activity.

[0004] In addition to the unique structure and electronic properties of N-CNTs, constructing a three-dimensional ordered bamboo-like structure is expected to further improve the ORR efficiency. The bamboo-like N-CNTs can form a clear interconnected channel and pore network, promoting the efficient transport of reactants and products within the catalyst layer. This enhanced mass transfer capacity effectively alleviates diffusion limitations, ensuring that active sites are fully utilized, thereby accelerating the ORR reaction kinetics. At the same time, the three-dimensionally ordered N-CNTs can promote the uniform dispersion and stable anchoring of nanoparticles, optimizing the spatial distribution of active sites on the electrode surface. This uniform distribution can reduce local overpotential, improve reaction rate consistency, and thus enhance overall catalytic efficiency.

[0005] While optimizing the support structure can enhance mass transfer and active site distribution, achieving high activity and durability at the single active site level still requires fine-tuning of metal nanoparticles. Alloying Pt with transition metals (such as molybdenum) has become an effective way to improve ORR performance. PtMo nanoparticles exhibit an optimized electronic structure due to the synergistic effect between Pt and Mo. Mo's unique electronic properties can regulate the electronic configuration of Pt, thereby altering the adsorption and activation processes of oxygen species, promoting oxygen molecule reduction, and improving the overall ORR kinetics. Furthermore, the introduction of Mo can enhance the catalyst's resistance to sintering and dissolution in harsh electrochemical environments, significantly improving durability.

[0006] Therefore, combining PtMo alloys with N-CNT supports can form a synergistic strategy to overcome the limitations of traditional fuel cell catalysts. However, the synergistic design of alloy catalysts and ordered supports has not been fully explored. Summary of the Invention

[0007] In view of this, to address the technical problems of high catalyst cost, poor durability, and low mass transfer efficiency in existing technologies, this invention provides a Pt2Mo / N-CNT composite catalyst and its preparation method. By combining ultrafine Pt2Mo alloy nanoparticles with an ordered N-CNT support, synergistic enhancement of structure and performance is achieved at the nanoscale. The highly ordered bamboo-like N-CNT framework provides a structurally stable and electronically conductive support framework, promoting the uniform dispersion of PtMo alloy nanoparticles and achieving efficient electron and mass transport. This three-dimensional structure reduces nanoparticle aggregation, ensures continuous exposure of active sites, and accelerates ORR kinetics. In addition to support optimization, the precise alloying of Pt and Mo, forming a well-defined Pt2Mo structure, further enhances catalytic activity. Unlike surface-doped systems, Pt2Mo alloy nanoparticles exhibit lattice contraction and electronic reconstruction, effectively regulating the d-band center of Pt and weakening the adsorption of oxygen intermediates. These structural and electronic modifications collectively accelerate the ORR process and improve catalyst durability.

[0008] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a Pt2Mo / N-CNT composite catalyst, comprising a three-dimensional ordered bamboo-like nitrogen-doped carbon nanotube support and PtMo alloy nanoparticles supported on the surface of the support; the atomic ratio of Pt to Mo is approximately 2:1, the PtMo alloy nanoparticles are uniformly distributed on the surface of the three-dimensional bamboo-like nitrogen-doped carbon nanotubes, the PtMo alloy nanoparticles exhibit lattice compression, and Pt is simultaneously present on the catalyst surface. 0 Pt 2+ with Mo 4+ Mo 6+ Species.

[0009] Secondly, the present invention provides a method for preparing the above-mentioned Pt2Mo / N-CNT composite catalyst, comprising the following steps: Step (1) An ordered Co nanoparticle array was prepared by self-assembly of block copolymers; Step (2): Using the Co nanoparticle array as a seed, three-dimensional ordered bamboo-like nitrogen-doped carbon nanotubes are grown by chemical vapor deposition. Step (3): Combine Pt source, Mo source and N-CNT, and load PtMo alloy nanoparticles by solvothermal method to obtain Pt2Mo / N-CNT composite catalyst.

[0010] Compared with the prior art, the present invention has the following beneficial effects: The Pt2Mo / N-CNT composite catalyst and its preparation method provided by this invention achieve synergistic enhancement of structure and performance at the nanoscale by combining ultrafine Pt2Mo alloy nanoparticles with an ordered N-CNT support. The highly ordered bamboo-like N-CNT framework provides a structurally stable and electronically conductive support framework. This N-CNT support framework not only possesses stable conductivity but also maximizes the dispersion of PtMo nanoparticles, promoting uniform dispersion of the PtMo alloy nanoparticles and achieving efficient electron and mass transport. Simultaneously, it introduces additional active sites, thereby enhancing the catalyst's activity and stability. More importantly, N doping and the three-dimensional bamboo-like structure promote electron transport between the catalyst and the support, improving electrochemical reaction efficiency. This three-dimensional structure reduces nanoparticle aggregation, ensures continuous exposure of active sites, and accelerates ORR kinetics. In addition to support optimization, the precise alloying of Pt and Mo, forming a well-defined Pt2Mo structure, further enhances catalytic activity. Unlike surface-doped systems, Pt2Mo alloy nanoparticles exhibit lattice contraction and electronic reconstruction, effectively regulating the d-band center of Pt and weakening the adsorption of oxygen intermediates. These structural and electronic modifications collectively accelerated the ORR process and improved catalyst durability. Through comprehensive electrochemical testing, small-angle X-ray scattering (SAXS) modeling, and density functional theory (DFT) calculations, this study revealed the synergistic mechanism of the support and alloy structures at the nanoscale, providing new insights for achieving efficient and stable ORR. The synergistic effect between the PtMo catalyst and the three-dimensional bamboo-like N-CNT support significantly enhances the overall performance of PEMFCs.

[0011] Other beneficial effects of the present invention will be specifically demonstrated in the following detailed description of the embodiments. Attached Figure Description

[0012] Figure 1This section describes the synthesis and structural characterization of N-CNTs. Image a shows a schematic diagram of the formation mechanism of bamboo-like N-CNTs, where an ordered array of nodules (green: Co, purple: PS, pink: P4VP) is formed through an EISA process involving PS-PVP and Co atoms. Image b shows an ordered array of Co particles obtained after plasma removal of the block polymer. Image c shows a carbon cap array formed under C2H2 and NH3 co-deposition conditions. Image d shows the initial growth stage of N-CNTs. Image e shows a magnified structural diagram of the bamboo-like region. Image f is a schematic diagram of the N-CNT growth process using the "Cap Trick" strategy.

[0013] Figure 2 This section presents the morphology and composition information of the PtMo / N-CNT catalyst. Specifically, a) is a cross-sectional SEM image of the PtMo / N-CNT catalyst (showing the three-dimensional interconnected bamboo-like N-CNT network structure); b) is a surface SEM image of the PtMo / N-CNT catalyst (showing the uniform distribution of PtMo nanoparticles on the N-CNT surface); c) is a high-resolution TEM image of PtMo / N-CNT (showing the chamber structure and lattice fringes of the bamboo-like N-CNT); d) is a high-resolution TEM image of PtMo / N-CNT (showing the lattice fringes and dispersion state of PtMo nanoparticles); and e) is an EDS elemental mapping of PtMo / N-CNT (C element distribution, corresponding to bamboo). The diagram shows the structure of PtMo / N-CNTs. f is the EDS elemental mapping of PtMo / N-CNTs (N element distribution, showing the distribution of nitrogen doping sites); g is the EDS elemental mapping of PtMo / N-CNTs (Pt element distribution, showing the spatial distribution of PtMo particles); h is the EDS elemental mapping of PtMo / N-CNTs (Mo element distribution, verifying the co-distribution of Pt and Mo); i is the XRD pattern of PtMo / N-CNTs (showing the characteristic diffraction peaks of the Pt2Mo alloy phase, graphitic carbon, and N-CNTs); j is the XPS full spectrum and high-resolution spectrum of PtMo / N-CNTs (showing the Pt...). 0 / Pt 2+ Mo 4+ / Mo 6+ Valence state and N-doping type).

[0014] Figure 3The figures show the electrochemical performance characterization of the oxygen reduction reaction (ORR) of the PtMo / N-CNT catalyst. Specifically: a) Cyclic voltammetry (CV) curves of the PtMo / N-CNT catalyst (comparison of electrochemical specific surface area and hydrogen desorption peak before and after accelerated durability testing); b) Linear sweep voltammetry (LSV) curves of the PtMo / N-CNT catalyst (relationship between current density and potential in the ORR at different rotational speeds); c) Tafel curves of the PtMo / N-CNT catalyst (comparison of the kinetic slope of the ORR before and after accelerated durability testing); d) Koutecky-Levich (KL) plots of the PtMo / N-CNT catalyst (calculation of electron transfer in the ORR at different potentials); e) Chronopotential (CP) curves of the PtMo / N-CNT catalyst (voltage stability under constant current conditions in an oxygen-saturated electrolyte); f) Performance curves of the PtMo / N-CNT catalyst in a proton exchange membrane fuel cell (PEMFC) (relationship between single-cell IV characteristics and power density).

[0015] Figure 4 The figures show the structural characterization and mass transfer simulation of the Pt2Mo alloy (using aberration-corrected TEM, elemental mapping, SAXS, DFT calculations, and CFD fluid simulations). Specifically, a) is the aberration-corrected AC-TEM image of PtMo nanoparticles, showing atomically ordered lattice fringes and the alloy phase structure; b) is the EDS elemental mapping of PtMo nanoparticles, showing the atomically uniform co-distribution of Pt and Mo within a single particle; c) are the small-angle X-ray scattering (SAXS) curves of Pt / N-CNT and PtMo / N-CNT catalysts, showing the lattice contraction peak shift caused by Mo doping; d) is the Guinier fitting diagram of PtMo nanoparticles (calculated based on SAXS data to determine the radius of gyration and core-shell structure parameters); and e) is the density functional theory (DFT) calculation model of the Pt2Mo alloy surface, showing the optimization of interatomic spacing and interlayer arrangement under compressive strain.

[0016] Figure 5Comparative fluid dynamics (CFD) simulations of mass transfer characteristics of catalyst supports are presented as follows: (Flow field analysis of disordered carbon black structure and three-dimensional ordered bamboo-shaped N-CNTs). Specifically, a) is the CFD velocity distribution simulation of the XC-72 carbon black support, showing the flow inhomogeneity and local high-shear zones in the disordered structure; b) is the CFD velocity vector field simulation of the three-dimensional ordered bamboo-shaped N-CNT support, showing the uniform flow field and low-drag characteristics within the ordered channels; c) is a magnified CFD simulation of the local flow field of the XC-72 carbon black support, showing the vortex and stagnant zone distribution around the spherical holes; d) is the CFD streamline and velocity gradient simulation within the three-dimensional ordered bamboo-shaped N-CNT channels, showing stable laminar flow and parabolic velocity distribution; e) is a comparison of CFD velocity decay curves for carbon black and N-CNT supports, showing the velocity loss rate within a 20 µm channel length and a magnified view within the N-CNT channels. Figure 6 PtMo lattice spacing diagram; Figure 7 XPS elemental and bonding analysis is performed, where a is the full spectrum, b is the high-resolution spectrum of C, c is the high-resolution spectrum of N, and d is the high-resolution spectrum of Pt / Mo. Figure 8 Test diagram of PtMo / N-CNT rotating disk electrode; Figure 9 This is a durability test diagram for PtMo / N-CNT fuel cells; Figure 10 The figures show the fitted curves of the core-shell model and the magnified curves of the high-q region; where a is the fitted curve of the SAXS core-shell model and b is the magnified view of the high-q region. Detailed Implementation

[0017] The technical solution of the present invention will be clearly and thoroughly described below with reference to specific embodiments.

[0018] This invention provides a method for preparing a Pt2Mo / N-CNT composite catalyst, characterized by comprising the following steps: Step (1) involves the preparation of an ordered Co nanoparticle array via block copolymer self-assembly. Specifically: 0.02 g of polystyrene-block-poly(4-vinylpyridine) diblock copolymer (PS-b-P4VP) was added to 5 mL of DMF and stirred at room temperature until homogeneous. Solid CoCl2 was added to the solution to achieve a Co to pyridine nitrogen molar ratio of approximately 1:1, and stirring was continued for 24 h. The resulting solution was then dropped onto clean silicon wafers, approximately 3 drops per wafer, and spin-coated to form a thin film. The spin-coating speed was preferably 800–1500 rpm, more preferably 1000 rpm, and the spin-coating time was preferably 30–90 s, more preferably 60 s. The film was then vacuum-dried at room temperature for 24 h. The dried film was then treated in an air plasma cleaner for 10–30 min, more preferably 20 min, to remove organic matter, resulting in a regularly arranged array of Co nanoparticles.

[0019] Step (2): Using the Co nanoparticle array as a seed, three-dimensional ordered bamboo-like nitrogen-doped carbon nanotubes are grown by chemical vapor deposition. Specifically: The sample obtained in step 1 was placed in a CVD furnace and heated at 1 °C·min in a 10% H2 / Ar atmosphere. -1 The temperature is raised to 750–850℃, preferably 800℃, and annealed. Then, a mixture of C2H2 and NH3 / He with a volume fraction of 8% is introduced, with the volume fraction of NH3 preferably being 5–10%. The gas introduction time is selected from 10 s, 30 s, 1 min, 5 min, or 10 min to obtain bamboo-shaped N-CNTs of different lengths. After naturally cooling to room temperature, the silicon substrate is removed and the sample is collected.

[0020] Step (3): The Pt source, Mo source, and N-CNT are combined, and PtMo alloy nanoparticles are loaded using a solvothermal method to obtain the Pt2Mo / N-CNT composite catalyst. Specifically: Platinum propionyl acetone, molybdenum hexacarbonyl, and ascorbic acid were added to 20 mL of oleylamine at a mass ratio of 6.5:2:20 and stirred until completely dissolved, so that the Pt:Mo molar ratio was approximately 1:0.5. 22 mg of the N-CNTs obtained in step 2 were added to achieve a target platinum mass fraction of 5–30 wt.%, preferably 8–15 wt.%, more preferably 10 wt.%. The mixture was sonicated for 1 h and then stirred overnight in an oil bath at 80 °C. After the reaction was complete, residual organic matter was removed by alternating washing with hot cyclohexane and ethanol to obtain the PtMo / N-CNT catalyst.

[0021] The technical solution of the present invention will be clearly and thoroughly described below with reference to specific embodiments.

[0022] PtMo Synthesis Based on Three-Dimensional Ordered Bamboo-like N-CNTs Synthesis of ordered Co nanoparticle arrays: 0.02 g of polystyrene-block-poly(4-vinylpyridine) diblock copolymer (PS-b-P4VP, Mn, PS=41000 g·mol⁻¹) was used. -1 Mn,P4VP = 24000 g·mol -1 Cobalt chloride (CoCl2) powder (≥97%, Aladdin) was dissolved in 5 mL of N,N-dimethylformamide (DMF, ≥99.5%, Guangzhou Chemical Reagent Factory). The solution was stirred at room temperature until a homogeneous solution was obtained. Then, cobalt chloride (CoCl2) powder (≥97%, Aladdin) was added to adjust the molar ratio of Co to pyridine nitrogen in the solution to 1:1. The mixture was stirred continuously for 24 h to ensure optimal coordination between Co atoms and the polymer matrix. Three drops of the prepared solution were added to a clean silicon wafer and spin-coated at 1000 rpm for 1 min to form a thin film. The sample was then placed in a vacuum drying oven and dried at room temperature for 24 h. The polymer underwent sufficient microphase separation and self-assembly through DMF solvent evaporation. The resulting self-assembled film was treated in an air plasma cleaner for 20 min to remove organic components, thereby forming an ordered array of Co nanoparticles.

[0023] Growth and evolution of three-dimensional ordered bamboo-like N-CNTs Using the Co nanoparticle array prepared above as seeds, three-dimensional ordered bamboo-like N-CNTs were grown by chemical vapor deposition (CVD). First, under a 10% H₂ / Ar atmosphere, the growth was carried out at 1 ℃·min⁻¹. -1 The temperature was raised to 800 °C and annealed. The atmosphere was then switched to a mixture of C2H2 and 8% (v / v) NH3 / He, with venting times of 10 s, 30 s, 1 min, 5 min, and 10 min to study the growth evolution and obtain N-CNTs of different lengths. Finally, the mixture was allowed to cool naturally to room temperature. Samples were collected by removing the silicon substrate.

[0024] Loading of PtMo nanoparticles 6.5 mg of platinum propionyl acetone (Pt(acac)2, 98%, Bio-Pharmaceutical), 2 mg of molybdenum hexacarbonyl (Mo(CO)6, 98%, Maclean's / Meyer Reagent), and 20 mg of ascorbic acid (≥99.5%, Shanghai Yuanju) were added to 20 mL of oleylamine (80–90%, Meyer Reagent) and stirred until completely dissolved, ensuring a Pt to Mo molar ratio of 1:0.5. Then, 22 mg of synthesized N-CNTs were added to the solution to achieve a target platinum mass fraction of 10 wt.%. The suspension was sonicated for 1 h and continuously stirred overnight in an oil bath at 80 °C. After the reaction was complete, residual oleylamine was removed by thorough washing with hot cyclohexane (99.7%, Maclean's) and ethanol (99.7%, Tianjin Fuyu) to obtain the final product PtMo / N-CNT.

[0025] Characterization of PtMo / N-CNT catalysts The morphology of the samples was characterized by scanning electron microscopy (SEM, Hitachi S-4800, 3.0 kV, magnification ×20 to ×800,000) and transmission electron microscopy (TEM, JEOL JEM-2100F, 200 kV, point resolution 0.23 nm, line resolution 0.1 nm). The crystal structure was analyzed by X-ray powder diffraction (XRD, PANalytical X'Pert Pro MPD) using Cu-Kα radiation (40 kV, 40 mA, λ=0.15406 nm). X-ray photoelectron spectroscopy (XPS) was performed on an ESCALAB 250Xi (Thermo VG Scientific, UK) equipped with a micro-focusing monochromator and a charge neutralization system. Monochromatic Al Kα radiation (hv = 1486.6 eV) was used, with a pass energy of 20 eV, an energy step of 0.1 eV, an exit angle of 90°, and a residence time of 0.1 s. To ensure quality, the sample surface was automatically scanned 10–20 times at different locations. The internal carbon structure was characterized by Raman spectroscopy (HoribaJobin Yvon LabRAM HR800, λ = 532 nm). Adsorption / desorption isotherms were analyzed using the BET method and the BJH model.

[0026] Small-angle X-ray scattering (SAXS, q = 0.2–30 Å) -1 The low q region (Ganesha, Ga-Metal-jet X-ray source, EIGER 4M single-photon counting detector) uses the Guinier approximation to determine the gyration radius Rg of the scatterer. This method assumes that the particles are isotropic, do not interact with each other, and have a relatively uniform size distribution.

[0027] The fitting was performed using a nonlinear least squares method; the goodness of fit was evaluated using the residuals: Residual = ln I_exp - ln I_fit. Guinier analysis can estimate the overall particle size and is suitable for dense single particles or first-order aggregates. To obtain structural parameters beyond the Guinier zone, the full q-scattering curves were fitted using a core-shell spherical shape factor model: the particles consist of a dense core and a concentric shell, with the core / shell having different scattering length densities (SLDs) with the medium.

[0028] Electrochemical testing Half-cell testing: An IVIUMSTAT electrochemical workstation with a rotating ring-disk electrode was used. The reference electrode was Ag / AgCl, and the counter electrode was a Pt sheet. Catalyst ink: 2 mg PtMo / N-CNT was dispersed in a mixture of 5 μL 5% Nafion solution (Shanghai Hesen Electric) and 180 μL 1:1:1 mixed solvent (deionized water / ethanol / isopropanol, ≥99.5%, Guangdong Guanghua) and sonicated for 30 min. 10 μL of the ink was drop-coated onto a 5 mm diameter polished glassy carbon disk electrode and dried at room temperature for 8 h. The catalyst was then tested in a 0.1 M N2 saturated HClO4 solution (70%–72%, Guangzhou Chemical Reagent Factory) at 50 mV·s. -1 Cyclic voltammetry (CV) was performed at scan rates in the range of 0.05–1.2 V_RHE, with 50 pre-activation cycles. ECSA was calculated by integrating the hydrogen desorption peaks in the 0.05–0.40 V_RHE region, with the theoretical charge of single-electron transfer during hydrogen desorption taken as Q_H = 210 μC·cm. -2 In linear sweep voltammetry (LSV) testing, in O2-saturated 0.1 MHClO4, at a rate of 10 mV·s... -1 The polarization curves of 0.05–1.00 V_RHE were recorded at a scanning speed of 1600 rpm. The disk current and ring current of the ORR were measured under the same conditions using RRDE (E7R9, disk area 0.25 cm²). 2 The area of ​​the Pt ring is 0.19 cm². 2 The mass activity was recorded based on the current at 0.9 V_RHE and ECSA, and the electron transfer number was determined using the Koutecky-Levich (KL) equation. Durability assessment was performed using accelerated durability testing (ADT): under O2 saturation conditions at 0.6–1.1 V_RHE at 100 mV·s. -1 Cycle 5000 times; simultaneously perform constant current chronopotential (CP) test: at 1600 rpm and -3 mA·cm -2 The constant current was maintained for 10 hours. All experiments were conducted at room temperature; IR compensation was performed using the workstation's automatic compensation function.

[0029] Single-cell testing: An ARBIN FC-100W fuel cell bench was used. Cathode: A PtMo / N-CNT catalyst layer was sprayed onto carbon paper (20 mm × 20 mm, HCP120, Hesen), with a Pt loading of 0.2 mg·cm³. -2 Anode: Commercial Pt / C (JM 40), Pt loading 0.15 mg·cm³ -2 Sprayed onto Nafion 212 film (4 cm) 2 The preparation of the two electrode inks was the same as described above. The battery was operated at 75 °C and 100% relative humidity (RH), with hydrogen supplied at the anode at 200 sccm and oxygen supplied at the cathode at 400 sccm. After activation, the IV polarization curve was tested starting at a back voltage of 0.2 bar and a cutoff voltage of 0.20 V. ADT: at 100 mV·s between 0.6–1.1 V. -1 5000 cycles, anode H2 200 sccm, cathode Ar 100 sccm.

[0030] Computation and Modeling Density Functional Theory (DFT): Calculations were performed using VASP; the projected fused wave (PAW) method and the pseudopotential "PAW_PBE" provided by VASP were used to describe ion-electron interactions; the exchange-correlation function adopted the PBE from the generalized gradient approximation (GGA); spin polarization was considered to improve accuracy. The plane wave cutoff energy was 450 eV; based on k-spacing = 0.03 Å. -1 K-point sampling is performed to ensure dense and uniform sampling of the Brillouin zone. The energy convergence criterion is <1×10⁻⁶. -5 eV / atom, residual force <0.01 eV·Å -1 The structural optimization is considered complete once the condition is met. To investigate the effect of Mo doping on bond length and interlayer spacing, analyses were conducted in both parallel and perpendicular directions. Starting with the initial geometric optimization of the intrinsic surface structure, an interlayer spacing baseline was established. After the system stabilized, Pt and Pt2Mo were measured and compared in the parallel direction (interlayer spacing between the surface and the underlying layer) and the perpendicular direction (interlayer spacing across multiple layers, including the surface and deep layers).

[0031] Flow field simulation: COMSOL was used to simulate the influence of two types of porous structures on internal oxygen flow. The oxygen flow at the cathode was approximated as a laminar flow model, and the oxygen flow field distribution within the two porous structures was obtained by solving the Navier-Stokes and mass conservation equations. During the cathode ORR process, oxygen enters the diffusion layer from the flow channel and reaches the catalyst layer; due to the pore differences between the porous spherical and ordered mesoporous channels, the oxygen flow and diffusion modes differ. A two-dimensional geometry (20 μm × 10 μm), porosity of 0.3, inlet pressure of 0.2 bar, and outlet pressure of atmospheric pressure were established, assuming the gas is incompressible. Under these conditions, the momentum and mass conservation equations were solved to evaluate the flow behavior.

[0032] The test results described above are explained in detail below with reference to the accompanying drawings: Carbon atom "cap trick" mechanism based on self-assembled Co nanoparticle arrays The evolution of bamboo-like nitrogen-doped carbon nanotubes (N-CNTs) through the "cap trick" mechanism is characterized by its initiation of selective anchoring of Co atoms to pyridine nitrogen within the polymer (using PVP as an example). Evaporation-induced self-assembly (EISA) of block copolymers plays a crucial role in regulating the spatial arrangement of Co nanoparticles, which subsequently serve as catalytic centers for N-CNT growth. Figure 1 As shown in Figure a, this initial interaction is crucial, laying the foundation for the ordered self-assembly of Co nanoparticles. By precisely defining the distribution of Co nanoparticles, the EISA method can effectively control the inter-tube spacing, thereby ensuring the uniformity of the resulting N-CNT array. This uniformity is decisive for achieving uniform physicochemical properties throughout the nanotube network. Subsequent plasma cleaning, such as... Figure 1 As shown in Figure b, while removing the polymer matrix, Co atoms are reduced to catalytically active sites, providing nucleation seeds for N-CNT growth.

[0033] During the growth stage, the deposition and diffusion of carbon atoms on these Co particles first induce the formation of a "cap" structure. This cap serves as a precursor to the bamboo-like tubular structure, such as... Figure 1 As shown in Figure d, the continuous aggregation of carbon atoms drives the vertical growth of nanotubes. After the introduction of C2H2 and NH3 gases, C and N atoms co-deposit: carbon atoms participate in building the CNT framework, while nitrogen atoms are introduced into the CNT structure, forming nitrogen-doped defect sites. As growth progresses, existing caps gradually bulge outwards to form a "bamboo joint," while new caps begin to nucleate. This repeated cap formation process ultimately leads to the formation of bamboo-like N-CNTs (e.g., ...). Figure 1 (As shown in c). The precision of this growth mechanism is reflected in the clear separation and identifiability of the lattice fringes at the bamboo nodes.Figure 1 The study further revealed details of this process: the carbon nanotube wall thickness increased with growth, and clearly separated lattice stripes were observed at the bamboo-like nodes. This reflects the unique growth pattern of N-CNTs, a direct result of the stepwise sequential addition of carbon atoms in the "Cap Trick". Figure 1 As shown in Figure f, the entire growth process is summarized and presented in an intuitive manner, from the construction of the Co particle array to the formation of mature N-CNTs, which helps to understand the complex synthesis mechanism of N-CNTs.

[0034] The “Cap Trick” mechanism embodies the precision and complexity inherent in nanomaterial synthesis. N-CNT preparation based on block copolymer self-assembly offers significant advantages, including controlled growth and structural uniformity. This methodological approach facilitates the acquisition of N-CNTs with specific structural characteristics, thereby ensuring reproducibility and consistency at both the macroscopic and microscopic levels.

[0035] Three-dimensional ordered bamboo-like N-CNT-loaded PtMo nanoparticles Introducing PtMo nanoparticles into three-dimensional ordered bamboo-like N-CNTs is a key step in improving ORR performance. Figure 2 A comprehensive analysis of the structure and composition characteristics of the PtMo / N-CNT catalyst was conducted, highlighting its potential in high-efficiency catalytic applications, as detailed below: Figure 2 SEM images a and b show the cross-sectional and surface morphology of PtMo / N-CNTs, revealing a dense, interconnected, bamboo-like N-CNT network. This uniform and high-density structure is extremely important, significantly increasing the active specific surface area, enhancing electron conductivity, and improving accessibility to catalytic sites during the ORR process. Furthermore, Figure 2 Figure a also shows an ordered array with different pore designs, which plays a decisive role in optimizing mass transfer performance. The ordered arrangement and uniform diameter distribution of carbon nanotubes indicate that the synthesis process is highly controllable, which is key to achieving stable and high catalytic performance.

[0036] Figure 2 High-resolution TEM images of the middle c further revealed the atomic-level structure of N-CNTs, showing a clear bamboo-like chamber structure. The lattice fringe spacing is 0.188 nm (e.g., Figure 6As shown in the figure, corresponding to the (002) crystal plane of Pt₂Mo or the (111) crystal plane of Pt, the high crystallinity of PtMo nanoparticles is confirmed, which is the basis for efficient electronic conduction. Compared with the standard spacing (Pt₂Mo(002): 0.1969 nm; Pt(111): 0.1961 nm), the synthesized Pt₂Mo exhibits lattice compression. This compression is attributed to the incorporation of Mo atoms into the Pt lattice or adsorption on the Pt surface, resulting in the local aggregation of Pt atoms. This phenomenon will be explained in detail below.

[0037] also, Figure 2 The image shows the distribution of PtMo nanoparticles on the surface of N-CNTs. The bright spots represent PtMo particles that are uniformly distributed along the tube wall, which can avoid the concentration of catalytic activity in local areas and achieve overall uniform catalysis, which is crucial for maximizing ORR efficiency. Figure 2 EDS elemental mapping of e–h was used to analyze the spatial distribution of C, N, Pt, and Mo in PtMo / N-CNT. The results showed that Pt and Mo were uniformly distributed, accompanied by N doping, verifying the successful synthesis of the composite material. Nitrogen doping introduces defect sites into the carbon framework, which can serve as additional active centers and improve conductivity. This synergistic effect is of great significance for achieving excellent catalytic performance.

[0038] Figure 2 The XRD pattern of the sample reveals the crystal structure and phase composition of PtMo / N-CNT. A comparison of its diffraction peaks with the standard reference spectrum shows that the graphitic carbon peak, marked by the blue line, has shifted to the left compared to the standard position, indicating that N doping increases the lattice parameters, leading to an expansion of the interplanar spacing. The red peak corresponds to Pt₂Mo, and the purple peak corresponds to Pt. The metallic peak positions of the synthesized sample are between those of Pt and Pt₂Mo, suggesting the possible formation of an alloy solid solution, but further confirmation is needed.

[0039] like Figure 7 As shown, XPS further verified the complexity of the material surface composition, revealing that Mo and Pt in PtMo / N-CNT have multiple oxidation states. Figure 7 The full spectrum of the a-type matrix confirmed the presence of Pt, Mo, N, O, and C, demonstrating successful doping and metal introduction. Figure 7 The C1s spectrum of b in the image shows C–C and C–O peaks, indicating the presence of oxygen-containing functional groups that facilitate the metal-support interaction. Figure 7 The c in the figure reveals graphitic nitrogen and pyridine nitrogen in the Ns region, which helps to improve catalytic activity and stability. Figure 7 The O1s spectrum of d in the sample confirmed the O=C–O and O–C bonds, further supporting the inference that oxygen functional groups enhance the metal-support interaction.

[0040] Figure 2 The 3d spectrum of Mo in the middle j shows that Mo 4+ with Mo6+ Two valence states: the 232.2 eV peak corresponds to Mo 4+ This is closely related to improving ORR activity; the 235.4 eV peak corresponds to Mo 6+ This may promote the formation of Mo– species and improve catalyst stability. 4+ / Mo 6+ Coexistence implies the simultaneous presence of different Mo species on the catalytic surface, which can provide synergistic effects through multiple reaction pathways. The Pt 4f spectrum shows metallic Pt. 0 With oxidized Pt 2+ The binding energies are 71.2, 74.5, 72.8, and 76.1 eV, respectively. Pt 0 The peak confirmed the presence of platinum, which is the core of ORR's high activity, while Pt... 2+ This provides additional oxygen adsorption / reduction active sites. The Pt:Mo atomic ratio is approximately 2:1, indicating a significant Mo doping proportion that contributes to overall performance. The close proximity of the Pt and Mo peaks suggests a strong interaction or chemical bond between them. This interaction can significantly modulate the electronic structure and surface properties, enhancing catalytic activity and stability. The coexistence of Mo's multivalent state and Pt's dual-valent state makes the catalytic surface highly active and multifunctional, thus PtMo / N-CNT exhibits excellent performance in ORR.

[0041] Mechanism of Mo-doped Pt nanocrystals enhancing ORR capability To evaluate the role of PtMo nanoparticles in improving ORR performance, the electrochemical properties of PtMo / N-CNT were systematically studied. Figure 3 The cyclic voltammetry (CV) curves shown in figure a indicate that the electrochemical specific surface area (ECSA) of PtMo / N-CNT increases only from 98.36 m² before and after the accelerated durability test (ADT). 2 ·g -1 Slightly decreased to 97.31 m 2 ·g -1The structure exhibits excellent structural stability. Using the Frumkin isotherm model to deconvolve the hydrogen adsorption behavior, three adsorption peaks were identified: A1, A2, and A3. Peak A1 is the strongest, located in the low potential region, mainly attributed to the weak adsorption of hydrogen on the stepped (110) crystal plane; peak A2 corresponds to the strong adsorption of hydrogen at the stepped sites on the (100) crystal plane; peak A3 originates from low-coordination defect atoms or step edge sites (usually located on the (110) / (111) crystal planes), which often form after oxygen adsorption. Notably, the broad and low-intensity (111) step response has minimal impact on the differential adsorption characteristics. The preservation of ECSA and adsorption site integrity after ADT further demonstrates the high stability of PtMo / N-CNT. Although XRD cannot distinguish between the Pt and Pt2Mo phases alone, the consistency between the electrochemical adsorption behavior and hydrogen adsorption characteristics supports the existence of the Pt2Mo alloy phase. Therefore, the introduction of Mo alters the Pt lattice, forming a Pt2Mo alloy, thereby enhancing catalytic performance and durability through a combination of electronic and geometric effects.

[0042] Figure 3 Figure b shows the linear sweep voltammetry (LSV) curves at different rotational speeds. The results demonstrate that PtMo / N-CNT exhibits excellent ORR activity, characterized by high current density and stable half-wave potential (E0). 1 / 2 At 1600 rpm, the E before ADT 1 / 2 It was 0.876 V_RHE, and after ADT it only decreased slightly to 0.872 V_RHE. Figure 3 The Tafel slope of c before and after ADT is 48.66 mV·dec. -1 and 49.24 mV·dec -1 The changes were minimal, indicating almost no decline in ORR kinetics. The maintained kinetic parameters further validated the catalyst's stability and kinetic advantages, demonstrating that PtMo / N-CNT is a highly promising, stable, and efficient ORR catalyst. (KL diagram) Figure 3 Figure d) reveals a linear relationship between the reciprocal of the current density and the reciprocal of the square root of the rotational speed, indicating that ORR follows first-order reaction kinetics with respect to oxygen concentration. The electron transfer number n≈3.83 calculated from the linear fitting slope indicates that ORR mainly occurs via a 4-electron pathway with minimal H₂O₂ byproduct. The current curve of the ring-disk electrode (RRDE) ( Figure 8 (As shown) This further demonstrates that the H2O2 yield is extremely low, proving that PtMo / N-CNT can selectively produce H2O rather than peroxides.

[0043] Chronopotential (CP) measurements of PtMo / N-CNT were performed in an oxygen-saturated 0.1 M HClO4 solution at a constant current density of –3 mA·cm⁻¹. -2After 10 hours of continuous operation, the voltage drop was less than 10%, with a retention rate of 90.67%. This indicates that the catalyst maintains excellent structural and electrochemical stability even under prolonged operation. This outstanding stability is attributed to two factors: firstly, the N-CNT support effectively prevents nanoparticle aggregation and slows down deactivation; secondly, the electronic interaction between Pt and Mo enhances the stability of the active sites. The introduction of Mo modulates the electronic structure of Pt, simultaneously balancing activity and stability, thus maintaining catalytic performance during long-term operation.

[0044] In actual PEMFC testing ( Figure 3 As shown in f), the current density of PtMo / N-CNT at 0.6 V is 1.18 A·cm⁻¹. -2 The corresponding power density is 0.71 W·cm³. -2 Peak power density is 0.869 W·cm³. -2 The corresponding current density is 1.96 A·cm. -2 This demonstrates excellent electrochemical performance. The performance remained stable after prolonged operation at 1600 mA for over 30 hours (see...). Figure 9 This excellent durability demonstrates that PtMo / N-CNT can maintain high efficiency and stability during long-term operation of PEMFC.

[0045] Although XRD and XPS analyses alone are insufficient to definitively confirm the formation of the Pt–Mo alloy structure, the significant improvement in electrochemical performance strongly suggests the presence of the alloy phase. To elucidate this crucial issue, this paper employs aberration-corrected transmission electron microscopy (AC-TEM), atomic-resolution elemental mapping, small-angle X-ray scattering (SAXS), and density functional theory (DFT) calculations for detailed characterization. Figure 4 The high-resolution AC-TEM image shown in Figure a clearly reveals ordered atomic lattice fringes, indicating that the nanoparticles possess high crystallinity and structural order at the atomic scale. Unlike simple surface doping, the uniform lattice arrangement within the particles strongly supports the existence of a bulk Pt–Mo alloy structure, rather than just surface-adsorbed Mo species. Figure 4 Elemental mapping of b further confirms this, showing a uniform co-distribution of Pt and Mo within individual particles. This series of microscopic results is consistent with the conclusions obtained from electrochemical testing, namely that alloying significantly improves catalytic performance.

[0046] SAXS analysis ( Figure 4(As shown in c) provides additional structural information at the nanoscale. Pt / N-CNT served as a control sample, with consistent synthesis conditions. Compared to Pt / N-CNT, PtMo / N-CNT exhibits a peak shift in its scattering curve, particularly in the high-q region, corresponding to a decrease in interatomic spacing, verifying the lattice shrinkage induced by Mo. Lattice shrinkage has been widely demonstrated to optimize ORR kinetics by shifting the d-band center of Pt downwards and weakening the adsorption of intermediates (OH, O). Furthermore, in the high-q region, at approximately 0.51 Å... -1 At ~12.25 Å, both Pt and PtMo samples exhibit significant peaks, possibly related to interparticle spacing or ionomer layer thickness. The slight shift and broadening of this peak in the PtMo sample suggests that Mo induces surface reconstruction or changes in local electron density, further supporting the contribution of alloying effects and interfacial structural reorganization to performance improvement. (Guinier fitting) Figure 4 As shown in d), the radius of gyration of PtMo (Rg = 6.44 Å) is increased compared to Pt (Rg = 3.32 Å), suggesting that Mo doping induces structural evolution. To further reveal the internal structure, a core-shell model was adopted. Figure 10 The fitted scattering data (shown in a and b) (see Table S1 for details) describe a low SLD shell encasing the alloy metal core, possibly originating from an ionomer layer or residual solvent. This shell not only reflects the interfacial environment but also suggests that the PtMo particles are better encapsulated by ionomers and water, facilitating proton conduction and mass transport. This indirect evidence is also consistent with the alloyed structure and distinguishes it from pure Pt particles.

[0047] at last, Figure 4 The paper presents an atomic model based on DFT-optimized geometry, further revealing the mechanism of the alloy structure. In the Pt2Mo model, the interlayer spacing of the surface and subsurface layers are 2.81 Å and 2.77 Å, respectively, stabilizing at 2.78 Å for each layer. The corresponding values ​​for pure Pt are 2.82 Å, 2.80 Å, and 2.81 Å, exhibiting a more relaxed configuration. Furthermore, the interatomic spacing on the Pt2Mo surface is 2.75 Å, while that of pure Pt is 2.81 Å, indicating significant surface shrinkage. This shrinkage is consistent with the experimentally observed diffraction peak shift and leads to a downward shift of the d-band center of Pt, thereby weakening the adsorption of intermediates such as OH* and accelerating ORR kinetics. Previous DFT and experimental studies have shown that compressive strain (shortened interlayer spacing) can optimize adsorption energy and desorption rate, thereby improving catalytic activity.

[0048] In summary, the combined analysis of AC-TEM, elemental mapping, SAXS fitting, and DFT calculations indicates that Mo not only remains on the particle surface but also penetrates deep into the Pt lattice to form an alloy structure. This structural transformation not only alters the lattice but also induces electronic effects favorable to ORR. The resulting Pt–Mo alloy exhibits improved oxygen binding energy and higher stability, thus explaining the excellent electrochemical performance observed in the experiments.

[0049] Advantages of three-dimensional ordered N-CNTs as catalyst support layers Figure 5 This paper presents computational fluid dynamics (CFD) simulation results, comparing the mass transfer characteristics of conventional carbon black (Vulcan® XC-72) and three-dimensional ordered bamboo-like N-CNTs as PtMo catalyst supports. To ensure a rigorous comparison, two pore models were constructed: the XC-72 model represents a disordered structure with randomly distributed spherical pores; the N-CNT model represents neatly arranged cylindrical channels. Both models have the same cross-sectional area, consistent boundary conditions, and an inlet velocity of 0.71 m·s. -1 Regarding key parameters, the Fanning friction factor of the XC-72 model is set to 0.2, while that of the N-CNT model is only 0.02, reflecting their morphological differences.

[0050] Velocity distribution map ( Figure 5 As shown in Figures a and b), a significant difference is observed: the XC-72 model exhibits strong flow inhomogeneity, with pronounced local acceleration and high-shear zones, particularly concentrated in the narrow gaps between particles. Despite the high local velocity peaks, the overall average velocity is only 0.6007 m·s. -1 This indicates high drag and significant energy dissipation. Conversely, the N-CNT framework exhibits stable and uniform flow within its orderly channels, especially in the inlet region (marked in pink), where it stabilizes rapidly with almost no shear zone and an average velocity as high as 0.7099 m·s. -1 The velocity is close to the inlet velocity, indicating extremely low transmission resistance.

[0051] Figure 5 The magnified vector field diagram of c reveals obvious vortices and stagnant zones around the spherical aperture in the XC-72 model, severely hindering momentum transfer and reactant transport. Figure 5 The data in the N-CNT model show that the velocity gradient distribution is approximately parabolic, indicating laminar flow stability, minimal wall friction, and good predictability of mass transfer. Figure 5 The study compared the velocity decay of the two models in the downstream direction: XC-72 (red line) experienced a continuous velocity decrease due to frictional losses, while N-CNT (blue line) maintained almost constant velocity within a 20 µm range, with only about 0.02% decay. This result highlights the significant advantages of ordered N-CNTs in mass transfer.

[0052] In summary, the three-dimensional ordered N-CNT structure enables uniform, low-resistance flow and eliminates the harmful backflow effect found in traditional disordered carbon black supports. The improved hydrodynamic properties directly enhance reactant accessibility and distribution uniformity, thus explaining the observed improvements in ORR performance and durability in the experiments.

[0053] The above description is merely a preferred embodiment of the present invention. However, the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention should be covered within the scope of protection of the present invention.

Claims

1. A Pt2Mo / N-CNT composite catalyst, characterized in that, The catalyst comprises a three-dimensional ordered bamboo-like nitrogen-doped carbon nanotube support and PtMo alloy nanoparticles loaded on the surface of the support; the atomic ratio of Pt to Mo is approximately 2:1, and the PtMo alloy nanoparticles are uniformly distributed on the surface of the three-dimensional bamboo-like nitrogen-doped carbon nanotubes. The PtMo alloy nanoparticles exhibit lattice compression, and Pt is also present on the catalyst surface. 0 Pt 2+ with Mo 4+ Mo 6+ Species.

2. The Pt2Mo / N-CNT composite catalyst according to claim 1, characterized in that, The interplanar spacing of the PtMo alloy nanoparticles is 0.185~0.190 nm.

3. The Pt2Mo / N-CNT composite catalyst according to claim 1, characterized in that, The N-CNT contains graphitic nitrogen and pyridine nitrogen, with an N atom content of 1.5~3.0 at.%.

4. The Pt2Mo / N-CNT composite catalyst according to claim 1, characterized in that, The PtMo alloy nanoparticles have an average particle size of 3~5 nm and a dispersion uniformity of >90% on the N-CNT surface.

5. A Pt2Mo / N-CNT composite catalyst according to any one of claims 1-4, characterized in that, The surface of the three-dimensional ordered bamboo-like nitrogen-doped carbon nanotubes contains C–O functional groups and O=C–O functional groups.

6. A method for preparing a Pt2Mo / N-CNT composite catalyst according to any one of claims 1-5, characterized in that, Includes the following steps: Step (1) An ordered Co nanoparticle array was prepared by self-assembly of block copolymers; Step (2): Using the Co nanoparticle array as a seed, three-dimensional ordered bamboo-like nitrogen-doped carbon nanotubes are grown by chemical vapor deposition. Step (3): Combine Pt source, Mo source and N-CNT, and load PtMo alloy nanoparticles by solvothermal method to obtain Pt2Mo / N-CNT composite catalyst.

7. The method for preparing a Pt2Mo / N-CNT composite catalyst according to claim 6, characterized in that, In step (1), the block copolymer is a polystyrene-block-poly(4-vinylpyridine) containing pyridine nitrogen.

8. The method for preparing a Pt2Mo / N-CNT composite catalyst according to claim 6, characterized in that, The molar ratio of Pt to Mo is 1:0.5, and the target loading of Pt is 10 wt.%.

9. The method for preparing a Pt2Mo / N-CNT composite catalyst according to claim 6, characterized in that, In step (2), the grown bamboo-like N-CNTs have a three-dimensional interconnected channel structure.

10. A method for preparing a Pt2Mo / N-CNT composite catalyst according to any one of claims 6-9, characterized in that, In step (1), an ordered Co nanoparticle array is formed by evaporation-induced self-assembly.

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