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Yuqi Ma, Hyo-Jin Ahn

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TF_Template_Word_Windows_2016Science and Technology of Advanced MaterialsISSN: (Print) (Online) Journal homepage: www.tandfonline.com/journals/tsta20Effect of P doped bimetallic FeCo catalysts on carbonmatrix for oxygen reduction in alkaline mediaYuqi Ma & Hyo-Jin AhnTo cite this article: Yuqi Ma & Hyo-Jin Ahn (03 Feb 2025): Effect of P doped bimetallic FeCocatalysts on carbon matrix for oxygen reduction in alkaline media, Science and Technology ofAdvanced Materials, DOI: 10.1080/14686996.2025.2459051To link to this article:  https://doi.org/10.1080/14686996.2025.2459051© 2025 The Author(s). Published by NationalInstitute for Materials Science in partnershipwith Taylor & Francis Group.View supplementary material Accepted author version posted online: 03Feb 2025.Submit your article to this journal View related articles View Crossmark dataFull Terms & Conditions of access and use can be found athttps://www.tandfonline.com/action/journalInformation?journalCode=tsta20https://www.tandfonline.com/journals/tsta20?src=pdfhttps://www.tandfonline.com/action/showCitFormats?doi=10.1080/14686996.2025.2459051https://doi.org/10.1080/14686996.2025.2459051https://www.tandfonline.com/doi/suppl/10.1080/14686996.2025.2459051https://www.tandfonline.com/doi/suppl/10.1080/14686996.2025.2459051https://www.tandfonline.com/action/authorSubmission?journalCode=tsta20&show=instructions&src=pdfhttps://www.tandfonline.com/action/authorSubmission?journalCode=tsta20&show=instructions&src=pdfhttps://www.tandfonline.com/doi/mlt/10.1080/14686996.2025.2459051?src=pdfhttps://www.tandfonline.com/doi/mlt/10.1080/14686996.2025.2459051?src=pdfhttp://crossmark.crossref.org/dialog/?doi=10.1080/14686996.2025.2459051&domain=pdf&date_stamp=03%20Feb%202025http://crossmark.crossref.org/dialog/?doi=10.1080/14686996.2025.2459051&domain=pdf&date_stamp=03%20Feb%202025https://www.tandfonline.com/action/journalInformation?journalCode=tsta20 Publisher: Taylor & Francis & The Author(s). Published by National Institute for Materials Science in partnership with Taylor & Francis Group. Journal: Science and Technology of Advanced Materials DOI: 10.1080/14686996.2025.2459051  Effect of P doped bimetallic FeCo catalysts on carbon matrix for oxygen reduction in alkaline media Yuqi Ma, and Hyo-Jin Ahn Department of Materials Science and Engineering, Seoul National University of Science and Technology, Seoul 01811, Korea *Corresponding author Tel.: +82-2-970-6622 Email address: hjahn@seoultech.ac.kr (H.-J. Ahn)                          yqma@seoultech.ac.kr (Yuqi Ma)   https://crossmark.crossref.org/dialog/?doi=10.1080/14686996.2025.2459051&domain=pdf Effect of P doped bimetallic FeCo catalysts on carbon matrix for oxygen reduction in alkaline media Abstract Catalysts' redox reactions are crucial for storage and energy conversion. Therefore, the fabrication of cost-effective, structurally rational, and multifunctional advanced catalytic materials continues to be a crucial task. In this study, we obtained P, Fe, and Co co-doped, nitrogen-rich carbon nanofibers by directly forming carbon nanotubes from metal-organic frameworks through electrospinning and pyrolysis. The P0.025-FeCo/C catalyst demonstrated outstanding ORR activity, including an ECSA of 1954.3 cm², a limited current density of -3.98 mA/cm2, an E1/2 of ~ 0.84 V, and an Eonset of ~ 0.94 V. After 5000 cycles, the P0.025-FeCo/C catalyst demonstrated remarkable enduring stability. These function enhancements occurred because of the electronic coupling between the metal and phosphorus, which altered the electron distribution at the metal center and optimized its electronic structure, thereby improving catalytic activity and stability. It exhibits good chemical stability in alkaline media and can maintain its catalytic performance for a long time, demonstrating good durability. Its tubular structure provides many active sites and superior electron transport paths owing to its unique channels and cavities, which help improve its activity and stability. Therefore, P0.025-FeCo/C is expected to become a non-precious metal catalyst for facilitating oxygen reduction reactions. Keywords: Metal-organic framework; oxygen reduction reactions; P doping, transition metal phosphides; carbon nanotubes 1. Introduction Amidst globalization and industrialization, environmental pollution has become a significant challenge for human civilization. The extensive widespread burning of fossil fuels has led to global climate change and a decline in air quality, posing threats to biodiversity and ecological balance and significantly jeopardizing human health and economic developments. To mitigate this trend, new energy technologies are being  sought to replace traditional fossil fuels [1-5]. Fuel cells and metal-air batteries are considered strong candidates for future energy sources due to their renewability, cleanliness, and high energy density [6-7]. Oxygen reduction reactions (ORR) are crucial cathodic reactions in metal-air batteries and fuel cells. Despite this, the sluggish kinetics of the ORR has long been a significant challenge, necessitating high activity and durable electrocatalysts. Although precious metal catalysts like platinum and palladium demonstrate specific catalytic properties, poor stability; their high cost, and scarcity, limit their extensive application. Researchers have developed and applied transition metal catalysts to address these shortcomings. Transition metals, like nickel, cobalt, iron, and copper, have emerged as ideal alternatives to noble metal catalysts owing to their abundant reserves, excellent electrochemical properties, and low cost [8-10]. Through rational structural design, crystal morphology control, and surface modification, the ORR capabilities of transition metal catalysts can be significantly optimized to meet the high efficiency, long life, and cost-effective demands of battery technology [11-14]. Among the various transition metal electrocatalysts explored, transition metal phosphides (TMPs), a class of interstitial compounds, have garnered significant interest due to their high catalytic performance, multifunctionality, and electrochemical stability [15-16]. The unique electronic structure and suitable electron density of TMPs provide excellent electrocatalytic properties [17-18]. Moreover, they have good chemical and electrochemical stability in alkaline environments, and they do not dissolve or structurally collapse easily. Furthermore, their strength does not decrease during long-term use [19]. Therefore, they have broad application prospects in energy conversion and storage. Electrospinning is a processing method that yields ultrafine polymer fibers with multiple functions by forming a jet from a charged polymer solution or melting in an  electrostatic field [20]. Electrospun materials have shown great potential for energy storage and transformation due to their good composition and structural control, exceptional mechanical strength, and flexibility [21]. Metal-organic framework (MOF) has been extensively investigated as promising catalyst supports because of their physical characteristics and distinctive chemical, particularly their highly tunable pore sizes, exceptional chemical functionalities, controllable crystal morphologies, and high surface areas [22-24]. MOFs have regular hexagonal or polyhedral shapes. Among the many structures of MOFs, tubular structures provide many active sites and superior electron transfer paths owing to their unique channels and cavities. Therefore, a tubular structure is an effective catalyst design. This structure enhances catalyst's activity and stability while also promotes the diffusion and adsorption of reactant molecules, further improving the catalytic efficiency [25-28]. However, MOFs may suffer structural damage or oxidation in aqueous solutions and oxygen environments, resulting in an unstable catalytic performance [29-31]. Combining electrospinning with MOF to prepare porous carbon nanofibers (CNFs), which can effectively adjust the porosity and mechanical strength of the composite material, provide abundant active sites, and promote oxygen reduction reactions [32-34]. However, the prepared nanofiber catalysts have limitations that hinder their further application. Zhang et al. successfully prepared a nanofiber membrane loaded with HKUST-1 (one of the extensively researched MOFs) by electrospinning HKUST-1 particles. The membrane exhibited excellent catalytic performance because of its rough single-fiber structure. However, the size of the HKUST-1 particles limited their application [35]. Li et al. synthesized a new NiCo2S4/CNFs composite material using electrospinning and hydrothermal methods, which ensured adequate edge exposure of the material to enhance electron diffusion and transport in the nanoparticles [36]. However, hydrothermal methods increase the cost  and time required for experiments. Polymer nanofiber membranes must be immersed in a precursor solution, and controlling the nucleation and growth stages of crystals is challenging. Therefore, catalytic materials with a simple preparation process, high electrocatalytic activity, and stable products need to be studied and developed as effective ORR electrocatalysts. This study introduces a facile strategy for preparing P, Fe, and Co co-doped carbon matrix (P-FeCo/C) catalysts via electrospinning. During the fabrication, poly (methyl methacrylate) (PMMA) was employed as a template polymer to obtain porous CNFs via high-temperature pyrolysis. Carbon nanotubes grew directionally around CNF from the MOFs, and the porous structure offered additional space for their formation. Subsequently, the synthesized P-FeCo/C was evaluated as an ORR catalyst. The prepared carbon nanotubes had resilient frameworks, and large specific surface areas, thereby exhibiting good mechanical stability, fast mass transfer, and high electrochemical performance. Furthermore, electronic regulation promoted by P, Fe, and Co co-doping significantly enhanced the electrochemical stability and catalytic performance of carbon supports. The prepared P-FeCo/C catalyst demonstrated outstanding ORR catalytic performance in alkaline electrolytes. This study opens a new direction for advancing efficient non-noble metal catalysts for metal-air batteries and fuel cells based on MOFs. 2. Experimental  Iron (III) chloride hexahydrate, cobalt (II) nitrate hexahydrate, polyacrylonitrile (PAN), poly (methyl methacrylate), N, N-dimethylformamide (DMF), 2-methylimidazole (MIM), methanol, potassium hydroxide, phosphoric acid, 2-propanol, and a Nafion® perfluorinated resin solution were acquired from Sigma-Aldrich. Platinum, nominally 20% on carbon black, HiSPEG 3000 (Pt/C) was acquired from Thermo Scientific  Chemicals. Water purified with a Milli-Q purifier (IQ 7003; Millipore Co., USA) was utilized in all experiments. All reagents were used without further purification. P, Fe, and Co co-doped CNFs were successfully synthesized via electrospinning, in situ growth, and pyrolysis. PAN (1 g), PMMA (1 g), MIM (0.3 g), and phosphoric acid (0.01, 0.015, 0.025, or 0.03 wt. %) were dissolved in DMF (11 mL) with constant stirring for 6 h to obtain a uniform electrospinning solution. The applied needle distance, flow rate, and voltage were 15 cm, 0.06 mL h-1, and 16 kV, respectively. A membrane was collected after 12 h, and it was denoted as P/MIM/PAN/PMMA. Subsequently, iron (III) chloride hexahydrate (0.27 g) and cobalt (II) nitrate hexahydrate (0.29 g) were completely mixed into methanol (20 mL). Following this, the composite membrane (0.5 g) was directly submerged in the prepared solution and allowed to react for 12 h. The obtained composite membrane was denoted as P/MOF/PAN/PMMA. Finally, the P/MOF/PAN/PMMA composite membrane was stabilized for 2.5 h at 280 °C in air and then heat-treated in nitrogen for 2 h at 800 °C. The collected samples were designated as PX-FeCo/C (where X denotes the phosphoric acid weight ratio = 0.01, 0.015, 0.025, or 0.03). FeCo/C: The preparation method was the same as P0.025-FeCo/C, but phosphoric acid was not added to prepare the electrospinning solution. P0.025-Co/C: The preparation method was the same as P0.025-FeCo/C; iron chloride hexahydrate was not added during the experiment. P0.025-Fe/C: The preparation method was the same as P0.025-FeCo/C; cobalt nitrate hexahydrate was not added during the experiment. The elemental distribution and morphology of the synthesized samples were examined using energy-dispersive spectroscopy (EDS; JEOL, NEO ARM) mapping and field-emission scanning electron microscopy (FESEM; EVO10, Carl Zeiss). The crystal structure, chemical bonding configurations, and surface functional characteristics of the samples were investigated by Raman spectroscopy (JASCO NRS-5100), X-ray  diffraction (XRD; Rigaku D/Max-2500 diffractometer with Cu Kα radiation in the 2 theta range from 10 to 90° with a step size of 0.02°at a 40 kV and 40 mA), and X-ray photoelectron spectroscopy measurements (XPS, ESCALAB 250 equipped with an Al Kα X-ray source (hν = 1486.6 eV), the vacuum of the analysis chamber was 8 × l0−10 Pa, the operating voltage was 12.5 kV, the filament current was 16 mA. The binding energies of target elements were calculated using a pass energy of 29.3 eV and a precision of roughly 0.3 eV), respectively. Electrochemical evaluations were conducted using a galvanostat/potentiostat (Ecochemie Autolab) and 0.1 M KOH electrolyte. A three-electrode system is composed of a working electrode (glassy carbon), a counter electrode, and a reference electrode (Ag/AgCl) (sat. KCl). This potentiostat/galvanostat had an electrochemical workstation and a rotating disc electrode featuring a speed regulator. The prepared sample was used as a catalyst (0.01 g). It was dissolved in a mixture of 2-propanol (900 μL), deionized water (50 μL), and Nafion® perfluoro resin solution (57.4 μL) and stirred for 12 h to achieve a uniform ink. Cyclic voltammetry (CV) was conducted under O2- and Ar- saturated conditions. Linear sweep voltammetry (LSV) was performed in an O2-saturated environment at a scan rate of 5 mV/s. Finally, an accelerated durability test (ADT) was performed over 5000 cycles at a scanning rate of 100 mV/s to verify the sustained electrocatalytic performance. After completion of the ADT, the LSV analyses were conducted again at 1600 rpm. 3. Results and discussion As shown in Figure 1, P, Fe, and Co co-doped CNFs were successfully synthesized via electrospinning, in situ growth, and pyrolysis. During the fabrication, PMMA was employed as a template polymer to obtain porous CNFs via high-temperature pyrolysis. Carbon nanotubes grew directionally around CNF from the MOFs, and the porous  structure offered additional space for their formation. The prepared P-FeCo/C catalyst demonstrated outstanding ORR catalytic performance in alkaline electrolytes. As depicted in Figures 2 (a–h), the microstructure and morphology of the samples annealed at 800 °C were examined by FESEM. As shown in Figure 2 (a, e), P0.01-FeCo/C exhibited uniform, densely packed hair-like nanotube growth on the carbonized fibers. The diameters of the carbonized fibers and hair-like nanotubes were approximately 650 and 280 nm, respectively. In Figures 2 (b, f and c, g), nanotubes with gradually decreasing densities can be observed on the carbon fibers of P0.015-FeCo/C and P0.025-FeCo/C. Furthermore, no nanotubes were observed on the P0.03-FeCo/C (Figure 2 (d, h)) CNFs, and irregular polygonal granular structures appeared. This was attributed to excess phosphoric acid, which caused phosphates to form new coordination complexes with metal ions [37]. Figure 3 (a) shows carbon nanotubes with a diameter of about 220 nm in the carbon matrix, and particles sized approximately 160 nm in the carbon nanotubes. Magnify the nanotubes using high-resolution transmission electron microscopy (HR-TEM). The bright area of a lattice edge space, representing the plane of graphite (002), was approximately 0.34 nm. In addition, the lattice fringes corresponding to the (210) and (111) planes of iron phosphide and cobalt phosphide were observed at approximately 0.20 nm and 0.25nm, respectively (Figure 3 (b)). During heat treatment, the coordination bonds linking the organic ligands with metal ions are severed, and the metal ions capture P ions to form metal phosphides (MPs) nanoparticles. Organic residues are catalyzed into carbon nanotubes on nanocatalysts. TEM-EDS mapping was performed on P0.025-FeCo/C to verify its elemental distribution. Figure 3 (c) illustrates that N and C were evenly distributed in the carbon matrix, whereas Fe, Co, and P were more localized along the MP nanoparticles. Moreover, large amounts of N, Fe, Co, and  P were similarly distributed throughout the carbon matrix, leading to heavy heteroatom doping of the carbon matrix, which can destroy the integrity of π-conjugated structures and induce defects. The XRD pattern in Figure 4 (a) shows the sample's crystal structure. All samples displayed a broad diffraction peak at approximately 25.7°, attributed to the graphite (002) plane (JCPDS 65-6212) [38], with sharp peaks of diffraction at 44.7, 65.0 and 82.3, which corresponds to the (110), (200), and (211) planes of FeCo (PDF 01-075-7975), and sharp peaks of diffraction at 45.9, which corresponds to the (110) planes of Fe (PDF 04-006-4261). Additionally, the sharp diffraction peaks were observed at approximately 40.2°, 47.3°, 52.9, 54.1°, 54.7°, 74.6°, and 79.4 corresponding to the (111), (210), (002), (300), (211), (400), and (302) planes of Fe2P plane (PDF 00-027-1171). Moreover, Furthermore, a sharp diffraction peak, corresponding to the CoP2 plane (PDF 00-026-0481), was observed for P0.025-FeCo/C and P0.03-FeCo/C at approximately 35.7°. The unique electronic structure and suitable electron density of the Metal-P bond provide excellent electrocatalytic performance. Furthermore, sharp diffraction peaks were observed at about 37.4, 39.9, and 43.7 for P0.01-FeCo/C, P0.015-FeCo/C, and P0.025-FeCo/C, corresponding to the (100), (111), and (110) planes of the FexN plane (PDF 04-009-6567, 04-007-3379). Fe-N, as the catalyst's active site, can improve the catalyst's performance [43-44]. Figure 4(b) shows the assessment of the degree of graphitization and defects in all the samples using Raman spectroscopy. A G band, corresponding to the vibrational frequency of the graphite lattice, served to assess the level of graphitization in the material. A high-intensity G band, typically around 1580 cm-1, indicates a high graphitization level. A D band at approximately 1350 cm-1 resulted from radiation scattering due to the amorphous state or defects within the material [45-46]. The  intensity of the D band reflected the degree of the defects. A stronger D-band signal suggests a higher degree of defects in a material. An ID/IG ratio served to compare the extent of graphitization across the different samples. Specifically, the ID/IG values of P0.01-FeCo/C, P0.015-FeCo/C, P0.025-FeCo/C, and P0.03-FeCo/C were 1.001, 1.008, 1.009, and 1.013, respectively. Heteroatom doping introduces defects in the carbon lattice and exposes edge planes. As the phosphoric acid content increases, the degree of defects increases. ORR activity was generated by activating the π electrons, which was achieved by disrupting the integrity of its π-conjugated structure. Therefore, p doping in sp2 carbons resulted in defects by breaking the integrity of its π-conjugated structure, thus enhancing the activity of the ORR [47-48]. Figure 5 presents the chemical bonding characteristics of P0.01-FeCo/C, P0.015-FeCo/C, P0.025-FeCo/C, and P0.03-FeCo/C, as analyzed by XPS. The binding energies observed in the XPS spectrum were adjusted using the binding energy of C 1s (284.5 eV) used as a reference. Figure 5(a) shows the P 2p XPS spectrum. The characteristic peaks for P 2p3/2 and P 2p1/2 in metal phosphides were observed at 128.76 and 129.76 eV, respectively. The spectra of P0.03-FeCo/C exhibited a slightly negative shift compared to that of P0.01-FeCo/C. The peak around 133.57 eV corresponds to the P–O bond and can be attributed to the phosphate species on the catalyst surface [49-50]. The Fe 2p XPS spectrum (Figure 5(e)) exhibited a spin-orbit doublet. In P0.01-FeCo/C, the Fe 2p peaks observed at 732.50, 727.21, 723.35, 719.52, 714.19, 711.18, and 707.70 eV corresponded to satellite peaks, Fe 2p1/2 of Fe3+, Fe 2p1/2 of Fe2+, satellite peaks, Fe 2p3/2 of Fe3+, Fe 2p3/2 of Fe2+, and Fe-C respectively [50, 51]. The binding energy of Fe 2p3/2 of Fe3+ and Fe2+ in P0.03-FeCo/C was shifted to higher binding energies compared with that in P0.01-FeCo/C, whereas the P 2p1/2 and 2p3/2 spectra shift to lower energies. This indicates more positively charged Fe (Feδ+) and negatively charged P (Pδ−) in P0.03- FeCo/C than in P0.01-FeCo/C. This may benefit the ORR because more positive Feδ+ and negative Pδ− are favorable to work cooperatively as proton-acceptor centers, respectively [52-54]. The electron donation from the surrounding phosphorus can make Feδ+ of P-FeCo/C less positive, thereby reducing the binding strength with OH* and showing better catalytic performance and kinetics. The C 1s XPS spectrum (Figure 5(b)) reveals characteristic peaks corresponding to C–C, C–O/C–P, N-C and O–C=O bonds at 284.5, 285.22, 286.01, and 288.36 eV, respectively. The polarity of the C-P bond is opposite to that of the C-N bond. This means that phosphorus-doped carbon materials can generate more defective sites and new active sites that are different from nitrogen-doped carbon materials.  Figure 5(c) shows the N 1s spectrum. The detection of N–C and C–P bonds revealed the doping of N and P atoms into the carbon support. The peaks around 401.16, 400.40, 398.72, and 398.07 eV corresponded to graphitic, pyrrolic, metallic, and pyridinic N, respectively. Metal-coordinated nitrogen (Fe-N and Co-N) is crucial for improving the ORR performance of carbon-based catalysts. The O 1s XPS spectrum of P0.01-FeCo/C (Figure 5(d)) showed characteristic peaks at 533.82, 532.50, and 531.00 eV, representing O–H/O–C, O–P, and O–M bonds, respectively. Compared to those of P0.01-FeCo/C, the O–H/O–C and O–M peaks of P0.03-FeCo/C were slightly negative shifted, indicating charge redistribution due to the increased P content. Figure 5(f) shows the Co 2p XPS spectrum. The peaks located at 791.28 and 776.45 eV corresponded to the Co-P bond [50, 55]. The peaks located at 804.89 and 785.68 eV corresponded to the satellite peaks [56]. The peaks located at 796.45 and 781.80 eV corresponded to Co 2p1/2 and Co 2p3/2 [57]. The above characterizations prove that we have successfully prepared P, Fe, and Co co-doped carbon matrix catalysts. Heteroatom doping can introduce charge delocalization and asymmetric spin density of carbon atoms, enhancing ORR kinetics.  The electrochemically active surface area (ECSA) of an electrode is regarded as an essential factor for ORR efficiency, and it provides a basis for assessing the catalytic sites available for electrochemical reactions. For ECSA measurements, cyclic voltammograms are typically obtained in an O2-free electrolyte to avoid the influence of ORR currents [58]. Figures 6 (a–d) show the CVs of P0.01-FeCo/C, P0.015-FeCo/C, P0.025-FeCo/C, and P0.03-FeCo/C, respectively, measured in 0.1 M KOH electrolyte an Ar-saturated at different various spin speeds. Four electrodes exhibited quasi-rectangular CV curves, which are characteristic of the charge and discharge process of electrostatic double-layer capacitors. The electric double-layer capacitance (Cdl) and ECSA calculation equations under the non-Faraday potential window (0.1-0.3 V) [59-60] are as follows [61-63]. Cdl = j/r (1) ECSA = Cdl /Cs (2) Here, j corresponds to the current density, Cs represents the specific capacitance, and r corresponds to the scan rate. The Cdl linear fitting and ECSA values of P0.01-FeCo/C, P0.015-FeCo/C, P0.025-FeCo/C, and P0.03-FeCo/C are shown in Figures 6 (e and f). The Cdl values of P0.01-FeCo/C, P0.015-FeCo/C, P0.025-FeCo/C, and P0.03-FeCo/C electrodes were 36.5, 56.6, 68.4, and 49.8 mF cm-2, respectively. The ECSA values were 1422.3, 1616.9, 1954.3, and 1043.1 cm2, respectively. The results showed that P0.025-FeCo/C had the highest ECSA, demonstrating that it had a greater number of electrochemically active sites than the other electrodes [64]. This was attributed to the P-doping, which introduced defects into the carbon lattice, exposed edge planes, and enhanced the available active sites. This tubular offered numerous active sites and superior electron transport pathways through its unique channels and cavities.  As shown in Figure 7 and S1, LSV tests were conducted to investigate the ORR activities of the catalysts. P0.025-FeCo/C exhibited an excellent limited current density of -3.98 mA/cm2, a half-wave potential (E1/2) of ~ 0.84 V, and an onset potential (Eonset) of ~ 0.94 V, compared with the P0.01-FeCo/C, P0.015-FeCo/C, and P0.03-FeCo/C electrodes. (P0.01-FeCo/C: limited current density = -3.27 mA/cm2, E1/2 = 0.79 V, and Eonset = 0.90 V; P0.015-FeCo/C: limited current density of -3.40 mA/cm2, E1/2 = 0.82 V, and Eonset = 0.92 V; P0.03-FeCo/C: limited current density = -2.95 mA/cm2, E1/2 = 0.78 V, and Eonset = 0.89 V). Compared with other published papers, P0.025-FeCo/C sample outperformed the Eonset and E1/2 (Table 1) [65-72]. To evaluate the ORR performance of these catalysts compared with Pt/C. For comparison, the Eonset and E1/2 values of Pt/C were 0.95 and 0.86 V under the same condition, respectively. P0.025-FeCo/C is comparable to that of the benchmark Pt/C catalyst (Table 2). We demonstrated that P0.025-FeCo/C exhibited good catalytic activity. This trend indicates that P doping can enhance the ORR activity by introducing defects to promote the generation of π electrons. Because of its unique channels and cavities, the tubular structure provides superior electron-transfer paths and numerous active sites. The unique electronic structure and suitable electron density of TMPs provide them with excellent electrocatalytic performance. However, compared with the other samples, the ORR performance of P0.03-FeCo/C dropped sharply. This was attributed to the excessive phosphoric acid content, which destroyed the nanotube structure, reduced the electrical conductivity of the carbon support, and affected the transmission efficiency of electrons in the catalyst, ultimately resulting in reduced catalytic performance. To evaluate the electrocatalytic stability of the electrodes, an accelerated durability test was performed. After completion of the ADT, the LSV analyses were conducted again at 1600 rpm. As shown in Figure 8 and S2, P0.025-FeCo/C showed  excellent long-term stability in terms of ORR activity among all samples, with the potential degradation evaluated at E1/2 (∆E1/2) being 3.3 mV (FeCo/C: ∆E1/2 of 24.6 mV; P0.01-FeCo/C: ∆E1/2 of 10.7 mV; P0.015-FeCo/C: ∆E1/2 of 8.6 mV; P0.03-FeCo/C: ∆E1/2 of 11.8 mV). Furthermore, we evaluated the electrocatalytic stability of P0.025-Fe/C and P0.025-Co/C (Figure S2 (b) and (c)). The results showed ∆E1/2 values of approximately 11.0 mV and 5.5 mV, respectively. More importantly, P0.025-Fe/C, P0.025-Co/C, and Px-FeCo/C exhibit better potential degradation evaluated than Pt/C catalyst (∆E1/2 of 16.7 mV. Figure 8 (e). Table 2). These findings suggest that metal phosphides play a crucial role in enhancing the electrochemical stability of carbon-supported catalysts in alkaline environments. Incorporating P helps prevent dissolution or structural degradation, maintaining the structural integrity of the catalyst over prolonged use. Co–P bonds exhibit higher binding energies and more substantial chemical stability than Fe–P bonds. This stronger bond reduces the dissociation or decomposition of the catalyst structure during the reaction, further enhancing the material's long-term stability. However, excessive P-doping destroys the carbon nanotube structure, blocks the active sites on the carbon nanocarriers, and reduces the stability of the catalyst. The durability and methanol poisoning resistance of non-precious metal catalysts in alkaline solutions is key for practical applications. The stability of the catalysts in oxygen-saturated electrolytes was evaluated by chronoamperometric curves (i-t curves) (Figure 9). After running in 0.1 M KOH for 10,000 seconds, the current density of catalyst P0.025-FeCo/C remained at 86% of the initial value, which was higher than 72% of the commercial Pt/C catalyst, indicating that P0.025-FeCo/C has better long-term stability. In addition, Pt/C electrodes are easily deactivated in the presence of methanol. To study the performance of the catalyst against the cross-effect of methanol, 10 mL of methanol was added to the electrolyte at 300 seconds (total electrolyte volume  was 100 mL) in the experiment. The results showed that the oxygen reduction reaction current density of Pt/C decreased significantly compared with catalyst P0.025-FeCo/C, showing poor methanol tolerance. Overall, P0.025-FeCo/C exhibits excellent stability and methanol poisoning resistance in alkaline media. These characteristics make it a promising non-precious metal electrocatalyst, providing a vital research basis for practical applications. 4. Conclusion In this research, we prepared P-doped bimetallic FeCo catalysts on carbon matrix via electrospinning, in situ growth, and pyrolysis. Carbon nanotubes grew directionally around CNF from the MOFs, and the porous structure offered additional space for their formation. The P0.025-FeCo/C catalyst demonstrated outstanding ORR activity, including an ECSA of 1954.3 cm², a limited current density of -3.98 mA/cm2, an E1/2 of ~ 0.84 V, and an Eonset of ~ 0.94 V. After 5000 cycles, the P0.025-FeCo/C catalyst demonstrated remarkable enduring stability. These performance improvements are due to the following: First, P doping introduces defects into the carbon lattice, which disrupt the π-conjugated structure and promote the generation of π electrons to enhance the ORR activity. Secondly, the unique electronic structure and suitable electron density of TMPs provide excellent electrocatalytic performance. Furthermore, they resist dissolution or collapse in alkaline environments and maintain good chemical and electrochemical stability during long-term cycling. Finally, the tubular structure within the carbon carrier provides numerous active sites and superior electron transport pathways owing to its unique channels and cavities, which enhance both the durability and activity of the catalyst.  Acknowledgements This work is supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2021R1A6A1A03039981) and National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (RS-2023-00209244). Disclosure statement The authors report there are no competing interests to declare. Data availability statement Data will be made available on request. References [1] Wuebbles D J, Jain, A K. Concerns about climate change and the role of fossil fuel use. Fuel Process. Technol. 2001;71(1-3):99–119. [2] Dincer I, Renewable energy and sustainable development: a crucial review. Renew. Sust. Energ. Rev. 2000;4(2):157–175. [3] Bilgen S. Structure and environmental impact of global energy consumption.  Renew. Sust. Energ. Rev. 2014;38:892–902. [4] Dudin M N, Frolova E E, Protopopova O V, et al. 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Angew. Chem. Int. Ed. 2019;58:12874–12878.    Tables and captions Table 1.  Compared to other published papers, the value of Eonset and E1/2. Catalysts Eonset (V) E1/2 (V) CCNTs-Co-800 0.90 0.84 Co/FN-C 0.917 0.753 1T-MoS2 0.90 0.81 CoOP@bio-C 0.91 0.81 CoNi/NTUC 0.90 0.84 NPCN-900 0.92 0.78 Co–N–PCN 0.90 0.82 Pt3.5%Ni PF 0.92 0.80 P0.025-FeCo/C (this paper) 0.94 0.84  Table 2. Comparing all samples, the value of Eonset, E1/2, Limited current density, and ∆E1/2. Catalysts Eonset (V) E1/2 (V) Limited current density ∆E1/2(mV) P0.01-FeCo/C 0.90 0.79 -3.27 10.7 P0.015-FeCo/C 0.92 0.82 -3.40 8.6 P0.025-FeCo/C 0.94 0.84 -3.98  3.3 P0.03-FeCo/C 0.89   0.78 -2.95 11.8 Pt/C 0.95 0.86 -3.95 16.7     Figures and captions Figure 1. Illustration of the fabrication process of Px-FeCo/C.  Figure 2. FESEM images of (a, e) P0.01-FeCo/C, (b, f) P0.015-FeCo/C, (c, g) P0.025-FeCo/C, and (d, h) P0.03-FeCo/C.  Figure 3. (a) Low- and (b) high-resolution TEM images and (c) EDS mapping of C, N, Fe, Co, and P of P0.025-FeCo/C.    Figure 4. (a) XRD and (b) Raman spectra I D /I G ratio of P0.01-FeCo/C, P0.015-FeCo/C, P0.025-FeCo/C, and P0.03-FeCo/C.   Figure 5. XPS spectrum of P0.01-FeCo/C, P0.015-FeCo/C, P0.025-FeCo/C, P0.03-FeCo/C: (a) P 2p, (b) C 1s, (c) N 1s and (d) O 1s (e) Fe 2p, and (f) Co 2p.    Figure 6. Cyclic voltammetry curves of (a) P0.01-FeCo/C, (b) P0.015-FeCo/C, (c) P0.025-FeCo/C, and (d) P0.03-FeCo/C at different scan rates of 10–50 mV s−1 in Ar-saturated 0.1 M KOH electrolyte. (e) Cdl linear fitting and (f) ECSA values of P0.01-FeCo/C, P0.015-FeCo/C, P0.025-FeCo/C, and P0.03-FeCo/C.  Figure 7. LSV curves of P0.01-FeCo/C, P0.015-FeCo/C, P0.025-FeCo/C, and P0.03-FeCo/C.   Figure 8. LSV curves of (a) P0.01-FeCo/C, (b) P0.015-FeCo/C, (c) P0.025-FeCo/C, (d) P0.03-FeCo/C and (e) Pt/C before and after ADT.  Figure 9. (a) The methanol crossover chronoamperometric curves and chronoamperometric response for ORR of P0.025-FeCo/C, and Pt/C in 0.1 M KOH solution at a rotation rate of 1600 rpm. Statement of Novelty     Effect of P doped bimetallic FeCo catalysts on carbon matrix for oxygen reduction in alkaline media Yuqi Ma, and Hyo-Jin Ahn  The P0.025-FeCo/C catalyst exhibits excellent ORR activity and significant long-lasting stability. It is expected to become a non-noble metal catalyst that promotes oxygen reduction reaction.          Graphical abstract    Effect of P doped bimetallic FeCo catalysts on carbon matrix for oxygen reduction in alkaline media Yuqi Ma, and Hyo-Jin Ahn Department of Materials Science and Engineering, Seoul National University of Science and Technology, Seoul 01811, Korea *Corresponding author Tel.: +82-2-970-6622 Email address: hjahn@seoultech.ac.kr (H.-J. Ahn)                          yqma@seoultech.ac.kr (Yuqi Ma)      Figure S1. Comparing P0.01-FeCo/C、P0.015-FeCo/C、P0.025-FeCo/C, P0.03-FeCo/C, and Pt/C, the value of Eonset, E1/2, and ΔE1/2   Figure S2. LSV curves of (a) FeCo/C, (b) P0.025-Fe/C, and (c) P0.025-Co/C before and after ADT.