One step, In-situ phosphating construction of encapsulated Co2P and Co3(PO4)2 nanoparticles within 3D reticulated carbon for rechargeable Zn-Air batteries

One step, In-situ phosphating construction of encapsulated Co2P and Co3(PO4)2 nanoparticles within 3D reticulated carbon for rechargeable Zn-Air batteries | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article One step, In-situ phosphating construction of encapsulated Co 2 P and Co 3 (PO 4 ) 2 nanoparticles within 3D reticulated carbon for rechargeable Zn-Air batteries Gang Chen, Lina Zhou, Xin Xiong, Xiaonan Xu, Yingying Wang This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7069913/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 27 Oct, 2025 Read the published version in Journal of Nanoparticle Research → Version 1 posted 5 You are reading this latest preprint version Abstract As potential candidates to be employed as air anodes in metal-air batteries, transition metal phosphides (TMPs) have received considerable attention due to its excellent electrocatalytic activity. This work presents a straightforward method for efficiently fabricating CoPO-Co 2 P@NPC, a three-dimensional (3D) reticulated carbon N, P-doped carbon structure generated from polyaniline-phytic acid polymer, with Co 2 P and Co 3 (PO 4 ) 2 nanoparticles implanted on the carbon matrix. The CoPO-Co 2 P@NPC demonstrates impressive bifunctional oxygen reduction reactions (ORR)/oxygen evolution reactions (OER) performances. A diffusion-limiting current density of 6.56 mA cm − 2 , a half-wave potential of 0.80 V, and an overpotential of 1.73 V are detected at 10 mA cm − 2 . The rechargeable ZAB that has been assembled demonstrates a high-power density of 265 mW cm − 2 , with excellent cycling stability over 450 hours. The composite based on Co 2 P-Co 3 (PO 4 ) 2 demonstrates outstanding bifunctional electrocatalytic performance, which makes it a desirable anode material for rechargeable Zn-Air batteries. Co2P nanoparticle Co3(PO4)2 nanoparticle In-situ phosphating Rechargeable Zn-Air batteries Bifunctional electrocatalyst Figures Figure 1 Figure 2 Figure 3 Figure 4 1. Introduction Rechargeable metal-air batteries (ZRBs) have garnered significant interest from scientists worldwide due to their numerous advantageous characteristics, including a high theoretical energy density, a stable discharge voltage, environmental friendliness, cost-effectiveness, and improved safety advantages 1 – 4 . However, the practical applications of ORR and OER have been hindered by their slow kinetics and high overpotentials 5 . At present, precious metals such as RuO 2 , IrO 2 , and Pt/C are widely acknowledged as the most effective catalysts for ORR or OER process 6 . However, the extensive use of these precious metal in industrial applications is limited owing to its raised cost, restricted accessibility, and lack of durability 7 . Hence, the investigation of highly efficient and cost-effective bifunctional electrocatalysts remains an urgent and challenging task 8 . Extensive research has been conducted on transition metal phosphides and phosphates as electrode materials, with the aim of improving their electrochemical performance 9 . These materials possess the capability to enhance electron transport and facilitate redox reactions 10 . The main reason for this effect is that phosphorus (P) has a lower electronegativity than oxygen (O) and sulfur (S) 11 . As a result, transition metal phosphides and phosphates exhibit improved electrical conductivity and redox activity 12 . Li et al. developed a novel electrode material from Co 2 P and Co 3 (PO 4 ) 2 nanoparticles implanted three-dimensional honeycomb-like porous carbon materials. The resulting material has impressive electrochemical performance, including high specific capacitance, capability, and cycle stability 13 . Cobalt phosphides-phosphates possess favorable physicochemical characteristics and a hydrogenase-like catalytic mechanism, which enables them to demonstrate robust electrocatalytic activity 14 . Recent studies have provided evidence suggesting that the combination of TMPs with a carbon matrix exhibits large specific surface areas and outstanding electrical conductivity 15 . This combination has the potential to protect TMPs from irreversible corrosion. Li et al. prepared a series of MOFs-derived Co 2 P/CoP@core-shell composites with sodium hypophosphite as the P source. The resulting composites demonstrated outstanding catalytic activity for both ORR and OER, as well as remarkable stability 16 . It is important to note that the sodium hypophosphite salt has the potential to generate highly flammable and toxic PH 3 gas. Significant corrosion can occur during the phosphidation process, which will decrease the specific surface area of as-fabricated material 17 . Therefore, there are still challenges in the rational development of transition metal phosphides (TMPs) using an efficient and straightforward approach, without the need for additional phosphidation procedures 18 . In this study, we demonstrate the effective synthesis of Co 2 P-Co 3 (PO 4 ) 2 nanoparticles incorporated within a 3D reticulated N, P-doped carbon matrix (CoPO-Co 2 P@NPC). The synthesis process involved the pyrolysis of polyaniline-phytic acid polymer and the in-situ phosphating formation of Co 2 P-Co 3 (PO 4 ) 2 nanoparticles. The as-fabricated composite can serve as ORR/OER bifunctional electrocatalysts in rechargeable ZRBs. The Co 2 P and Co 3 (PO 4 ) 2 nanoparticles were evenly distributed and firmly immobilized on the graphitized carbon framework, which not only improved its bifunctional catalytic performance for ORR and OER, but also provided protection to the main the active centers, preventing irreversible corrosion and ensuring long-term stability. The zinc-air battery, which is based on CoPO-Co 2 P@NPC, demonstrated remarkable performance. It exhibited a specific capacity of 699.86 mA h g − 1 and maintained excellent stability throughout discharge-charge cycles lasting over 450 hours. Several factors contribute to the favorable bifunctional electrocatalysis performances. The high conductivity of the carbon-based matrix plays a significant role. Furthermore, the unique 3D structure of the polyaniline-phytic acid polymer also enhances the efficiency of mass transfer. In addition, the CoPO-Co 2 P@NPC composite has abundant accessible active sites, which further enhance the electrocatalytic performance. Overall, these factors collectively contribute to its exceptional performance. 2. Results and discussion Figure 1 The process of preparing CoPO-Co 2 P@NPC is depicted in Fig. 1 a. The 3D porous polyaniline-phytic acid copolymer was synthesized through chemical oxidation polymerization, utilizing (NH 4 ) 2 S 2 O 8 as initiators. The three-dimensional cross-linked network structure is formed when phytic acid molecules connect to multiple polyaniline chains through intermolecular interactions. The resulting 3D hydrogel can be used as a source of carbon, nitrogen, and phosphorus during the synthesis process. Furthermore, the interaction between phytic acid and Co 2+ ions led to the creation of a coordination complex consisting of polyaniline, phytic acid, and Co 2+ . Afterwards, the coordination complex was subjected to pyrolysis, which led to the formation of a three-dimensional reticulated carbon framework. In this procedure, the in-situ phosphorization reaction is facilitated by the use of phytic acid as a phosphorus source, which can be achieved by infiltrating the phytic acid into the Co atoms. The XRD method was used to investigate the crystal structures of NPC and CoPO-Co 2 P@NPC. The amorphous carbon of NPC can be attributed to the broad diffraction peak located at 26.4° (Fig. 1 b) 19 . The XRD pattern obtained from the CoPO-Co 2 P@NPC sample has distinct peaks at 40.7° and 43.3°, corresponding to the crystallographic planes (121) and (211) of the Co 2 P 20 . In addition, the XRD result of Co 3 (PO 3 ) 2 (JCPDS: PDF#13–0503) exhibits two distinct peaks at 31.9° and 32.4°. These peaks correspond to the crystallographic planes (220) and (211), respectively 21 . The Raman spectra of the NPC and CoPO-Co 2 P@NPC composites are depicted in Fig. 1 c. The D band and the G band, which represent amorphous and graphitized carbons, respectively, exhibit prominent peaks at 1353 and 1595 cm − 1 . The I D /I G ratios for NPC and CoPO-Co 2 P@NPC were determined to be 1.21 and 1.19, respectively. These values are indicative of the presence of disordered and structural carbon defects in polymer-derived materials. Furthermore, Raman spectra are utilized to examine the correlations between various chemicals on uncalcined NPC and CoPO-Co 2 P@NPC complexes. Figure 1 d shows the Raman spectrum of uncalcined NPC, which exhibits four distinct peaks at 1172, 1342, 1450, and 1582 cm − 1 . These peaks should be contributed to the formation of C-H, C-N + , C = N, and C = C bonds, respectively. Moreover, the peak intensities and shifted peak positions of the uncalcined CoPO-Co 2 P@NPC complex may be influenced by the interaction between Co 2+ and PA molecules. As shown in Fig. 1 e, the rapid weight loss of uncalcined NPC between 200 ~ 600°C can be attributed to the carbonization of the pANI-PA composite. In addition, the TG-DSC spectra show that the composite exhibits an exothermic peak at 734.7°C. As shown in Fig. 1 f, BET analysis was used to examine the pore architectures of NPC and CoPO-Co 2 P@NPC. The isotherms of NPC show a mixed type I/IV property with an H3 hysteretic loop, which indicates the presence of stacked macropores and micropores 22 , 23 . Furthermore, an IV adsorption isotherm curve can be seen in the CoPO-Co 2 P@NPC isotherms. Notably, the adsorption capacity of CoPO-Co 2 P@NPC to N 2 decreases significantly when the relative pressure ( P/P 0 ) is less than 0.2. Due to the existence of sufficient micropores, NPC exhibits much larger specific surface area and pore volume than CoPO-Co 2 P@NPC (654.7 m 2 g − 1 and 0.69 cm 3 g − 1 ). Furthermore, the BJH pore size distribution plots depicted in Figure S2 illustrate various pore characteristics of the as-fabricated composites. NPC and the CoPO-Co 2 P@NPC composite have unique porosity features that facilitate fast ionic diffusion and mass transfer, hence increasing the rate of the electrochemical reaction 24 . Furthermore, the microstructure and morphology of CoPO-Co 2 P@NPC have been thoroughly investigated. The SEM pictures shown in Fig. 1 g demonstrate the existence of three-dimensional network architectures and a substantial quantity of nanoparticles that are evenly distributed. The EDS analysis of CoPO-Co 2 P@NPC demonstrates the uniform distributions of N and P elements inside the carbon matrix, with Co based nanoparticle exist on the carbon carrier. The TEM images of CoPO-Co 2 P@NPC (Fig. 1 h) provide evidence that the nanoparticles of Co 2 P and Co 3 (PO 4 ) 2 have been successfully immobilized onto a three-dimensional carbon network, while being covered by protective graphitic layers. Furthermore, the HRTEM picture provides direct evidence that the carbon layers are only a few nanometers thick (Fig. 1 i and j). Figure 2 XPS analysis was employed to examine the physical features and chemical state of NPC and CoPO-Co 2 P@NPC 25 . Similar peaks for N and C elements can be seen in the spectra of NPC and CoPO-Co2P@NPC, as determined by the XPS survey. Figure 2 b depicts the C 1s spectra of NPC and CoPO-Co 2 P@NPC, demonstrating five prominent peaks at 284.3, 284.8, 285.0, 286.6, and 289.9 eV. These peaks correspond to the presence of C–C (C = C), C-N, C-P, C = O, and O = C-O species, respectively 26 . In addition, the N 1s XPS spectra of both the NPC and CoPO-Co 2 P@NPC samples show prominent peaks corresponding to pyridinic-N, graphitic-N, and pyrrolic-N. The presence of various types of N atoms confirms the successful N-doping from the pANI component 27 . Additionally, Furthermore, the appearance of several pyrrolic-N peaks on the surfaces of NPC and CoPO-Co 2 P@NPC materials suggests the presence of topological defects, which may contribute to the improvement of catalyst performance. Moreover, the presence of Co 2 P and Co 3 (PO 4 ) 2 species can be verified by observing the P-Co bonding at 135.1 eV. The energy peaks identified at 132.7 eV and 133.9 eV could be attributable to the P-C and P-O bonds, respectively 28 . The Co 2p 3/2 spectra of CoPO-Co 2 P@NPC were deconvoluted and fitted into two distinct Co sites, located at 781.4 eV, and 783.2 eV, respectively 29 , 30 . The Co 2p 3/2 signals at 797.6 and 783.2 eV, coupled with satellite peaks at 786.3 and 803.4 eV, were identified as belonging to the Co 2+ species, which might exist in the catalysts in the form of Co 3 (PO 4 ) 2 31 . Furthermore, peaks in the Co 2p1/2 region centered at 781.4 and 789.6 eV have been assigned to Co 3+ ions, confirming the existence of Co 2 P 32 . Figure 3 The CoPO-Co 2 P@NPC material, which is derived from polymers of aniline-phytic acid, demonstrates several advantageous properties. These include a high concentration of active sites, a dual-doped carbon matrix with nitrogen and phosphorus, and a rich pore structure. It is anticipated that these properties will lead to exceptional electrocatalytic performance of CoPO-Co 2 P@NPC. Figure 3 a clearly demonstrates the different behavior of the cyclic voltammetry (CV) curves between CoPO-Co 2 P@NPC and NPC. The presence of distinct cathodic peaks in the O 2 -saturated solution indicates that both CoPO-Co 2 P@NPC and NPC have catalytic abilities for ORR. The oxygen reduction peak potential for CoPO-Co 2 P@NPC is 0.77 V, significantly higher compared to NPC (0.74 V). This difference highlights the crucial role of cobalt phosphide and cobalt phosphate sites in enhancing its ORR activity. The polarization curves presented in Fig. 3 b illustrate that the CoPO-Co 2 P@NPC material has E onset and E 1/2 values of 0.99 V and 0.80 V, respectively. The values of these catalysts are comparable to that of the Pt/C catalyst, which has an E onset of 1.15 V and E 1/2 of 0.78 V. The performance of CoPO-Co 2 P@NPC is better than that of recently reported ORR catalysts, as demonstrated in Table S2 . The higher E 1/2 value and j of CoPO-Co 2 P@NPC compared to NPC indicate that transition metal phosphides have a notable impact on improving its ORR performance. Tafel slopes and mass activities of as-fabricated composites provide additional evidence of the remarkable ORR activity. Figure 3 c demonstrates that the CoPO-Co 2 P@NPC exhibits a smaller Tafel slope (81.65 mV dec − 1 ) compared to NPC (107.14 mV dec − 1 ), which is similar to Pt/C (109.27 mV dec − 1 ). Furthermore, the mass activity of CoPO-Co 2 P@NPC at 0.765 V was calculated to be 44.82 mA mg − 1 . This value is approximately 3 times higher than that of Pt/C (14.10 mA mg − 1 ) at the same potential. These findings offer further evidence supporting the active role of implanted cobalt phosphide and cobalt phosphide nanoparticles 33 , 34 . In order to identify the number of electrons transferred (n) during ORR process, a variety of rotating speeds ranging from 400 to 2500 rpm, were utilized to get Koutecky-Levich (K-L) plots 35 – 37 . These plots had been utilized for calculating the 'n' value. As can be seen in Fig. 3 e, the linearity and coincidence of the K-L graphs imply first-order reaction kinetics for the ORR process. The number of electrons transferred for CoPO-Co 2 P@NPC is 3.99, suggesting a four-electron transfer mechanism. Moreover, Fig. 3 f compares the LSV curves of the sample before and after the 5000 CV cycles. The half-wave potential after 5000 cycles of the initial CoPO-Co 2 P@NPC shows a decrease of only 36 mV, indicating its excellent durability. Similarly, the OER catalytic activity of as-fabricated electrocatalysts have been tested by RDE. According to the LSV curves, it can be seen that the CoPO-Co 2 P@NPC catalyst requires an overpotential of 1.73 mV in order to achieve a current density of 10 mA cm − 2 , significantly lower than NPC (1.91 mV). Furthermore, the Tafel slope of CoPO-Co 2 P@NPC is 145.13 mV dec − 1 , higher than that of RuO 2 (127.70 mV dec − 1 ). This indicates that CoPO-Co 2 P@NPC demonstrates rapid kinetics in the OER process, higher than as-reported materials (Table S3 ) 38 , 39 . Furthermore, the catalytic stability of CoPO-Co 2 P@NPC was evaluated through CV cycling, as shown in Fig. 3 i. The resulting plot of LSV showed a minimal deviation of Δ E j =10 mV compared to the original LSV plot. Figure 4 In addition, the important bifunctional activity of a material may be calculated by calculating the potential difference between OER and ORR ( E = E j =10 - E j =−0.3 ), a smaller E suggests better bifunctional activity of material. The potential gap ( E ) of CoPO-Co 2 P@NPC was 0.88 V (Fig. 4 a), which was less than the NPC (1.13 V) and similar to the commercial Pt/C-RuO 2 combination (0.78 V). In order to explore the potential practical applications of the composites, ZABs were assembled using carbon cloth supported CoPO-Co 2 P@NPC as air cathode (Fig. 4 b). In addition, Pt/C ་ RuO 2 mixture are being examined as well for comparison. The ZAB (Zinc-Air Battery) based on CoPO-Co 2 P@NPC showed a noticeably higher open circuit voltage of 1.43 V and the LED light can be easily illuminated. As shown in Fig. 4 c, the power density of CoPO-Co 2 P@NPC-based ZAB (265 mW cm – 2 ) was compared to that of previously reported electrocatalysts, as shown in Table S4, which is significantly higher power density compared to the Pt/C-RuO 2 based ZAB (211 mW cm – 2 ). Additionally, the CoPO-Co 2 P@NPC assembled ZAB exhibits 699.86 mA h g − 1 specific discharge capacity, estimated based on the consumed Zn weight (Fig. 4 d), higher than Pt/C-RuO 2 assembled ZAB (601.34 mA h g – 1 ). Above results demonstrate the excellent efficiency of the CoPO-Co 2 P@NPC-based ZAB. CoPO-Co 2 P@NPC cathodes' cycling stability was also measured with a continuous galvanostatic discharge-charge cycling test at a current density of 5 mA cm − 2 (Fig. 4 e). The assembled ZAB demonstrates stable discharge/charge profiles for over 450 hours, indicating exceptional rechargeability. This lifespan surpasses that of the Pt/C་RuO 2 assembled battery and exceed the majority of reported zinc air batteries (Table S4). Recent years, flexible Zinc-air battery (FZAB) has been identified as a potential energy candidate for wearable devices. However, several challenges still need to be addressed, including high cost, poor cycling performance, and self-discharging. The CoPO-Co 2 P@NPC assembled FZAB can discharge over 9 hours at 1 mA cm − 2 . This is a significant improvement over the Pt/C + RuO 2 assembled FZAB (Fig. 4 g). In addition, the CoPO-Co 2 P@NPC electrode is able to continuously charge and discharge the FZAB over 14 h and maintains a relative low voltage difference of 1.0 V (Fig. 4 h, demonstrating the improved long-term durability compared to the benchmark Pt/C + RuO 2 catalyst. The fabrication process of the CoPO-Co 2 P@NPC material is not only simple, but it is also highly efficient. This technology allows for the development of electrocatalysts that are both cost-effective and high-performance for metal-air batteries. 3. Conclusion In general, we have demonstrated an alternative in-situ phosphating method for synthesizing highly dispersed Co 2 P and Co 3 (PO 4 ) 2 nanoparticles anchored on 3D porous N, P-doped carbon framework as a ORR/OER bifunctional electrocatalyst. The exceptional bifunctional activity of the as-fabricated material can be attributed to the synergistic interactions between graphitized carbon layers coated with Co 2 P or Co 3 (PO 4 ) 2 nanoparticles and an interconnected N, P-doped carbon matrix. The existence of the protective graphitic layers can enhance electron rate of active sites within the carbon network, which can further adjust the charge distribution around the Co 2 P or Co 3 (PO 4 ) 2 sites, resulting in excellent activity and durability in the assembled ZABs battery. The CoPO-Co 2 P@NPC catalyst exhibited a half-wave potential of 0.80 V for ORR and an overpotential of 1.73 V for OER at 10 mA cm - 2 . The CoPO-Co 2 P@NPC assembled ZABs showed excellent discharge-charge cycling stability over 450 hours, with 265 mW cm - 2 of peak power density and 699.86 mA h g - 1 of specific capacity. The current study presents a prospective synthetic methodology for the fabrication of metal-air electrode materials characterized by superior performance and stability. Declarations Acknowledgements This work was supported by the Research Project of Hubei Provincial Department of Education (Q20232503), the College Students Innovation and Entrepreneurship Training Program of China (S202510513072), the Hubei Provincial Natural Science Foundation of China (Grant No. 2025AFB422), and the Doctoral Research Foundation of Hubei University of Science and Technology (BK202432). Contributions Gang Chen involved in investigation, writing-original draft, visualization, methodology. Lina Zhou involved in conceptualization, funding acquisition, writing–review and editing. Xin Xiong involved in investigation, methodology. Xiaonan Xu involved in data curation. Yingying Wang involved in investigation, methodology, validation, funding acquisition, project administration, supervision, writing-original draft and funding. Corresponding authors Correspondence to Li-Na Zhou or Ying-Ying Wang. 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K., Phosphine-free avenue to Co 2 P nanoparticle encapsulated N,P co-doped CNTs: a novel non-enzymatic glucose sensor and an efficient electrocatalyst for oxygen evolution reaction. Green Chemistry 2017, 19 (5), 1327–1335. Qiao, M.; Wang, Y.; Wågberg, T.; Mamat, X.; Hu, X.; Zou, G.; Hu, G., Ni-Co bimetallic coordination effect for long lifetime rechargeable Zn-air battery. Journal of Energy Chemistry 2020, 47 , 146–154. Shao, Q.; Li, Y.; Cui, X.; Li, T.; Wang, H.-g.; Li, Y.; Duan, Q.; Si, Z., Metallophthalocyanine-Based Polymer-Derived Co2P Nanoparticles Anchoring on Doped Graphene as High-Efficient Trifunctional Electrocatalyst for Zn-Air Batteries and Water Splitting. ACS Sustainable Chemistry & Engineering 2020, 8 (16), 6422–6432. Tian, Y.; Xu, L.; Li, M.; Yuan, D.; Liu, X.; Qian, J.; Dou, Y.; Qiu, J.; Zhang, S., Interface Engineering of CoS/CoO@N-Doped Graphene Nanocomposite for High-Performance Rechargeable Zn-Air Batteries. Nanomicro Lett 2020, 13 (1), 3. Shi, Q.; Liu, Q.; Zheng, Y.; Dong, Y.; Wang, L.; Liu, H.; Yang, W., Controllable Construction of Bifunctional Co x P@N,P-Doped Carbon Electrocatalysts for Rechargeable Zinc-Air Batteries. Energy & Environmental Materials 2021. Zhang, Q.; Luo, F.; Long, X.; Yu, X.; Qu, K.; Yang, Z., N, P doped carbon nanotubes confined WN-Ni Mott-Schottky heterogeneous electrocatalyst for water splitting and rechargeable zinc-air batteries. Applied Catalysis B: Environmental 2021, 298 . Chen, X.; Pu, J.; Hu, X.; Yao, Y.; Dou, Y.; Jiang, J.; Zhang, W., Janus Hollow Nanofiber with Bifunctional Oxygen Electrocatalyst for Rechargeable Zn-Air Battery. Small 2022, 18 (16), e2200578. He, Y.; Yang, X.; Li, Y.; Liu, L.; Guo, S.; Shu, C.; Liu, F.; Liu, Y.; Tan, Q.; Wu, G., Atomically Dispersed Fe–Co Dual Metal Sites as Bifunctional Oxygen Electrocatalysts for Rechargeable and Flexible Zn-Air Batteries. ACS Catalysis 2022, 12 (2), 1216–1227. Additional Declarations No competing interests reported. Supplementary Files GraphicalAbstract.docx Highlights.docx SupplementaryInformation.docx Cite Share Download PDF Status: Published Journal Publication published 27 Oct, 2025 Read the published version in Journal of Nanoparticle Research → Version 1 posted Reviewers agreed at journal 29 Jul, 2025 Reviewers invited by journal 29 Jul, 2025 Editor assigned by journal 12 Jul, 2025 Submission checks completed at journal 08 Jul, 2025 First submitted to journal 07 Jul, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7069913","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":492903696,"identity":"3fe63f93-1131-43bb-ae3d-3e2283c04c96","order_by":0,"name":"Gang Chen","email":"","orcid":"","institution":"Wuhan SolidLi New Energy Technology Co., Ltd","correspondingAuthor":false,"prefix":"","firstName":"Gang","middleName":"","lastName":"Chen","suffix":""},{"id":492903697,"identity":"1034e310-ef30-4ed0-82af-a73404d7e49d","order_by":1,"name":"Lina Zhou","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAxElEQVRIiWNgGAWjYDACCeaGAwwMNgkGYB4bUVoYQVrSSNQCJA+ToEV+dmPj4YKa83nm0j0GDB/KDjPwz27Ar4VxzsGGwzOO3S62nHPGgHHGucMMEncO4NfCLJHYcJiH7Xbihhs5Bsy8bYcZDCQS8GthA2v5dw6i5S8xWnhAWnjbDkC0MBKjRQKspS85ceeMtIKDPefSeSRuENAiPyP58Geeb3aJ2yWSNz74UWYtxz+DgBYUcADkUhLUj4JRMApGwSjABQBBAUZXiT7KAQAAAABJRU5ErkJggg==","orcid":"","institution":"Hubei Normal University","correspondingAuthor":true,"prefix":"","firstName":"Lina","middleName":"","lastName":"Zhou","suffix":""},{"id":492903698,"identity":"3a4db219-c691-43a1-b054-55b1afe72e04","order_by":2,"name":"Xin Xiong","email":"","orcid":"","institution":"Hubei Normal University","correspondingAuthor":false,"prefix":"","firstName":"Xin","middleName":"","lastName":"Xiong","suffix":""},{"id":492903699,"identity":"0ce1a49e-4b15-4a5a-ace6-6af07770f917","order_by":3,"name":"Xiaonan Xu","email":"","orcid":"","institution":"Hubei Normal University","correspondingAuthor":false,"prefix":"","firstName":"Xiaonan","middleName":"","lastName":"Xu","suffix":""},{"id":492903700,"identity":"4b0afac2-c4db-4984-8156-480db6a15f84","order_by":4,"name":"Yingying Wang","email":"","orcid":"","institution":"Hubei University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Yingying","middleName":"","lastName":"Wang","suffix":""}],"badges":[],"createdAt":"2025-07-08 03:08:05","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7069913/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7069913/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s11051-025-06484-y","type":"published","date":"2025-10-27T15:58:50+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":88044026,"identity":"e5beff73-ddd1-4e98-8701-f125997a1e4d","added_by":"auto","created_at":"2025-07-31 17:51:36","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":2806135,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Synthesis mechanism diagram of CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC; (b) XRD patterns of NPC and CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC; (c) Raman spectra of NPC and CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC; (d) Raman spectra of as-made NPC and as-made CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC; (e) The TG-DSC result of uncalcined NPC complex at N\u003csub\u003e2\u003c/sub\u003e atmosphere. (f) N\u003csub\u003e2\u003c/sub\u003e adsorption and desorption isotherms of NPC and CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC; (g) The SEM image; (h) The TEM images, (i and j) HRTEM of CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-7069913/v1/ae007005e7e865724f5b2b04.png"},{"id":88044627,"identity":"01ed7cd1-21e1-453a-a17d-6c5440cb0265","added_by":"auto","created_at":"2025-07-31 17:59:36","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1282597,"visible":true,"origin":"","legend":"\u003cp\u003eHigh-resolution XPS spectra of (a) survey (b) C 1s, (c) N 1s, (d) P 2p and (e) Co 3p of NPC and CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-7069913/v1/9f604eeea96798bbc1d01c2d.png"},{"id":88044024,"identity":"d316166f-95a9-476a-b03c-f9949f76317f","added_by":"auto","created_at":"2025-07-31 17:51:36","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":586397,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Cyclic voltammograms, (b) LSV curves, (c) Tafel slopes, (d) mass activities of NPC, CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC, and commercial 20 % Pt/C electrocatalysts in tested in O\u003csub\u003e2\u003c/sub\u003e-purged 0.1 M KOH solution. (e) Koutecky-Levich plots at different potentials of CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC and LSV curves of CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC in O\u003csub\u003e2\u003c/sub\u003e-saturated 0.1 M KOH solution at various rotation rates (inset); (f) ORR polarization curves recorded for CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC before and after 5000 cycles; (g) LSV curves of NPC, CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC, and RuO\u003csub\u003e2\u003c/sub\u003e in O\u003csub\u003e2\u003c/sub\u003e-saturated 0.1 M KOH solution; (h) Tafel slopes of all catalyst at 1600 rpm; (i) OER polarization curves recorded for CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC before and after 5000 cycles.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-7069913/v1/9ba069462b45249717adbc5d.png"},{"id":88044035,"identity":"d26a3311-bc0e-489a-b988-d4fb4f2b094d","added_by":"auto","created_at":"2025-07-31 17:51:36","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1518081,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Overall polarization plots in the ORR and OER potential window for the electrocatalysts (sweep rate: 10 mV s\u003csup\u003e−1\u003c/sup\u003e); (b) The schematic diagram of Zn-air batteries assembled from CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC; (c) Polarization and power density curves of CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC and Pt/C||RuO\u003csub\u003e2\u003c/sub\u003e electrodes; (d) Galvanostatic discharge curves of the ZABs with CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC and Pt/C||RuO\u003csub\u003e2\u003c/sub\u003e cathodes at a current density of 5 mA/cm\u003csup\u003e2\u003c/sup\u003e; (e) Galvanostatic discharge and charge cycling curves with 10 min discharge and 10 min charge at 5 mA/cm\u003csup\u003e2\u003c/sup\u003e; (f) Schematic diagram of the structure components of the flexible ZAB; (g) Galvanostatic discharge curves at 1 mA cm\u003csup\u003e-2\u003c/sup\u003e of the flexible ZAB based on CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC and Pt/C||RuO\u003csub\u003e2\u003c/sub\u003e electrodes; (h) Galvanostatic discharge-charge cycling curves at 1 mA cm\u003csup\u003e-2\u003c/sup\u003e of the flexible ZAB based on CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC and Pt/C||RuO\u003csub\u003e2\u003c/sub\u003e electrodes.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-7069913/v1/1a54fd7a04759d9125fd09b0.png"},{"id":95041091,"identity":"3c3682b0-bc35-4311-8ea2-42daa72ae0c2","added_by":"auto","created_at":"2025-11-03 16:10:48","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6798100,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7069913/v1/5f353808-1c42-4a97-bfea-c127e7546b27.pdf"},{"id":88045718,"identity":"1e983b16-3153-455b-abf4-584663d336ce","added_by":"auto","created_at":"2025-07-31 18:15:36","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":571844,"visible":true,"origin":"","legend":"","description":"","filename":"GraphicalAbstract.docx","url":"https://assets-eu.researchsquare.com/files/rs-7069913/v1/aa677c26fd77c792c6adce2c.docx"},{"id":88044905,"identity":"5dc4f3b0-92fc-4508-acdb-6cb30d644f40","added_by":"auto","created_at":"2025-07-31 18:07:36","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":18649,"visible":true,"origin":"","legend":"","description":"","filename":"Highlights.docx","url":"https://assets-eu.researchsquare.com/files/rs-7069913/v1/8d200521ef5578469cc37a01.docx"},{"id":88044908,"identity":"2b4c0dd5-58e9-4924-a6e0-41ef7d7d1fa9","added_by":"auto","created_at":"2025-07-31 18:07:36","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":218157,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-7069913/v1/0fa6d627d2682569d3bc1166.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eOne step, In-situ phosphating construction of encapsulated Co\u003csub\u003e2\u003c/sub\u003eP and Co\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e nanoparticles within 3D reticulated carbon for rechargeable Zn-Air batteries\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eRechargeable metal-air batteries (ZRBs) have garnered significant interest from scientists worldwide due to their numerous advantageous characteristics, including a high theoretical energy density, a stable discharge voltage, environmental friendliness, cost-effectiveness, and improved safety advantages\u003csup\u003e\u003cspan additionalcitationids=\"CR2 CR3\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. However, the practical applications of ORR and OER have been hindered by their slow kinetics and high overpotentials\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e. At present, precious metals such as RuO\u003csub\u003e2\u003c/sub\u003e, IrO\u003csub\u003e2\u003c/sub\u003e, and Pt/C are widely acknowledged as the most effective catalysts for ORR or OER process\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e. However, the extensive use of these precious metal in industrial applications is limited owing to its raised cost, restricted accessibility, and lack of durability\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e. Hence, the investigation of highly efficient and cost-effective bifunctional electrocatalysts remains an urgent and challenging task\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eExtensive research has been conducted on transition metal phosphides and phosphates as electrode materials, with the aim of improving their electrochemical performance\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e. These materials possess the capability to enhance electron transport and facilitate redox reactions\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e. The main reason for this effect is that phosphorus (P) has a lower electronegativity than oxygen (O) and sulfur (S)\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e. As a result, transition metal phosphides and phosphates exhibit improved electrical conductivity and redox activity\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. Li et al. developed a novel electrode material from Co\u003csub\u003e2\u003c/sub\u003eP and Co\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e nanoparticles implanted three-dimensional honeycomb-like porous carbon materials. The resulting material has impressive electrochemical performance, including high specific capacitance, capability, and cycle stability\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e. Cobalt phosphides-phosphates possess favorable physicochemical characteristics and a hydrogenase-like catalytic mechanism, which enables them to demonstrate robust electrocatalytic activity\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e. Recent studies have provided evidence suggesting that the combination of TMPs with a carbon matrix exhibits large specific surface areas and outstanding electrical conductivity\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e. This combination has the potential to protect TMPs from irreversible corrosion. Li et al. prepared a series of MOFs-derived Co\u003csub\u003e2\u003c/sub\u003eP/CoP@core-shell composites with sodium hypophosphite as the P source. The resulting composites demonstrated outstanding catalytic activity for both ORR and OER, as well as remarkable stability\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e. It is important to note that the sodium hypophosphite salt has the potential to generate highly flammable and toxic PH\u003csub\u003e3\u003c/sub\u003e gas. Significant corrosion can occur during the phosphidation process, which will decrease the specific surface area of as-fabricated material\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e. Therefore, there are still challenges in the rational development of transition metal phosphides (TMPs) using an efficient and straightforward approach, without the need for additional phosphidation procedures\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eIn this study, we demonstrate the effective synthesis of Co\u003csub\u003e2\u003c/sub\u003eP-Co\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e nanoparticles incorporated within a 3D reticulated N, P-doped carbon matrix (CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC). The synthesis process involved the pyrolysis of polyaniline-phytic acid polymer and the \u003cem\u003ein-situ\u003c/em\u003e phosphating formation of Co\u003csub\u003e2\u003c/sub\u003eP-Co\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e nanoparticles. The as-fabricated composite can serve as ORR/OER bifunctional electrocatalysts in rechargeable ZRBs. The Co\u003csub\u003e2\u003c/sub\u003eP and Co\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e nanoparticles were evenly distributed and firmly immobilized on the graphitized carbon framework, which not only improved its bifunctional catalytic performance for ORR and OER, but also provided protection to the main the active centers, preventing irreversible corrosion and ensuring long-term stability. The zinc-air battery, which is based on CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC, demonstrated remarkable performance. It exhibited a specific capacity of 699.86 mA h g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and maintained excellent stability throughout discharge-charge cycles lasting over 450 hours. Several factors contribute to the favorable bifunctional electrocatalysis performances. The high conductivity of the carbon-based matrix plays a significant role. Furthermore, the unique 3D structure of the polyaniline-phytic acid polymer also enhances the efficiency of mass transfer. In addition, the CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC composite has abundant accessible active sites, which further enhance the electrocatalytic performance. Overall, these factors collectively contribute to its exceptional performance.\u003c/p\u003e"},{"header":"2. Results and discussion","content":"\u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e\u003c/p\u003e\u003cp\u003eThe process of preparing CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC is depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea. The 3D porous polyaniline-phytic acid copolymer was synthesized through chemical oxidation polymerization, utilizing (NH\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e as initiators. The three-dimensional cross-linked network structure is formed when phytic acid molecules connect to multiple polyaniline chains through intermolecular interactions. The resulting 3D hydrogel can be used as a source of carbon, nitrogen, and phosphorus during the synthesis process. Furthermore, the interaction between phytic acid and Co\u003csup\u003e2+\u003c/sup\u003e ions led to the creation of a coordination complex consisting of polyaniline, phytic acid, and Co\u003csup\u003e2+\u003c/sup\u003e. Afterwards, the coordination complex was subjected to pyrolysis, which led to the formation of a three-dimensional reticulated carbon framework. In this procedure, the \u003cem\u003ein-situ\u003c/em\u003e phosphorization reaction is facilitated by the use of phytic acid as a phosphorus source, which can be achieved by infiltrating the phytic acid into the Co atoms.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe XRD method was used to investigate the crystal structures of NPC and CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC. The amorphous carbon of NPC can be attributed to the broad diffraction peak located at 26.4\u0026deg; (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb)\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e. The XRD pattern obtained from the CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC sample has distinct peaks at 40.7\u0026deg; and 43.3\u0026deg;, corresponding to the crystallographic planes (121) and (211) of the Co\u003csub\u003e2\u003c/sub\u003eP\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e. In addition, the XRD result of Co\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e (JCPDS: PDF#13\u0026ndash;0503) exhibits two distinct peaks at 31.9\u0026deg; and 32.4\u0026deg;. These peaks correspond to the crystallographic planes (220) and (211), respectively\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e. The Raman spectra of the NPC and CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC composites are depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec. The D band and the G band, which represent amorphous and graphitized carbons, respectively, exhibit prominent peaks at 1353 and 1595 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The \u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003eD\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e/I\u003c/em\u003e\u003csub\u003e\u003cem\u003eG\u003c/em\u003e\u003c/sub\u003e ratios for NPC and CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC were determined to be 1.21 and 1.19, respectively. These values are indicative of the presence of disordered and structural carbon defects in polymer-derived materials.\u003c/p\u003e\u003cp\u003eFurthermore, Raman spectra are utilized to examine the correlations between various chemicals on uncalcined NPC and CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC complexes. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed shows the Raman spectrum of uncalcined NPC, which exhibits four distinct peaks at 1172, 1342, 1450, and 1582 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. These peaks should be contributed to the formation of C-H, C-N\u003csup\u003e+\u003c/sup\u003e, C\u0026thinsp;=\u0026thinsp;N, and C\u0026thinsp;=\u0026thinsp;C bonds, respectively. Moreover, the peak intensities and shifted peak positions of the uncalcined CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC complex may be influenced by the interaction between Co\u003csup\u003e2+\u003c/sup\u003e and PA molecules. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee, the rapid weight loss of uncalcined NPC between 200\u0026thinsp;~\u0026thinsp;600\u0026deg;C can be attributed to the carbonization of the pANI-PA composite. In addition, the TG-DSC spectra show that the composite exhibits an exothermic peak at 734.7\u0026deg;C.\u003c/p\u003e\u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ef, BET analysis was used to examine the pore architectures of NPC and CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC. The isotherms of NPC show a mixed type I/IV property with an H3 hysteretic loop, which indicates the presence of stacked macropores and micropores\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e,\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e. Furthermore, an IV adsorption isotherm curve can be seen in the CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC isotherms. Notably, the adsorption capacity of CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC to N\u003csub\u003e2\u003c/sub\u003e decreases significantly when the relative pressure (\u003cem\u003eP/P\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e) is less than 0.2. Due to the existence of sufficient micropores, NPC exhibits much larger specific surface area and pore volume than CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC (654.7 m\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 0.69 cm\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). Furthermore, the BJH pore size distribution plots depicted in Figure \u003cspan refid=\"MOESM2\" class=\"InternalRef\"\u003eS2\u003c/span\u003e illustrate various pore characteristics of the as-fabricated composites. NPC and the CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC composite have unique porosity features that facilitate fast ionic diffusion and mass transfer, hence increasing the rate of the electrochemical reaction\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eFurthermore, the microstructure and morphology of CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC have been thoroughly investigated. The SEM pictures shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eg demonstrate the existence of three-dimensional network architectures and a substantial quantity of nanoparticles that are evenly distributed. The EDS analysis of CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC demonstrates the uniform distributions of N and P elements inside the carbon matrix, with Co based nanoparticle exist on the carbon carrier. The TEM images of CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eh) provide evidence that the nanoparticles of Co\u003csub\u003e2\u003c/sub\u003eP and Co\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e have been successfully immobilized onto a three-dimensional carbon network, while being covered by protective graphitic layers. Furthermore, the HRTEM picture provides direct evidence that the carbon layers are only a few nanometers thick (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ei and j).\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e\u003c/p\u003e\u003cp\u003eXPS analysis was employed to examine the physical features and chemical state of NPC and CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e. Similar peaks for N and C elements can be seen in the spectra of NPC and CoPO-Co2P@NPC, as determined by the XPS survey. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb depicts the C 1s spectra of NPC and CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC, demonstrating five prominent peaks at 284.3, 284.8, 285.0, 286.6, and 289.9 eV. These peaks correspond to the presence of C\u0026ndash;C (C\u0026thinsp;=\u0026thinsp;C), C-N, C-P, C\u0026thinsp;=\u0026thinsp;O, and O\u0026thinsp;=\u0026thinsp;C-O species, respectively\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e. In addition, the N 1s XPS spectra of both the NPC and CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC samples show prominent peaks corresponding to pyridinic-N, graphitic-N, and pyrrolic-N. The presence of various types of N atoms confirms the successful N-doping from the pANI component\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e. Additionally, Furthermore, the appearance of several pyrrolic-N peaks on the surfaces of NPC and CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC materials suggests the presence of topological defects, which may contribute to the improvement of catalyst performance. Moreover, the presence of Co\u003csub\u003e2\u003c/sub\u003eP and Co\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e species can be verified by observing the P-Co bonding at 135.1 eV. The energy peaks identified at 132.7 eV and 133.9 eV could be attributable to the P-C and P-O bonds, respectively\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e. The Co 2p\u003csub\u003e3/2\u003c/sub\u003e spectra of CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC were deconvoluted and fitted into two distinct Co sites, located at 781.4 eV, and 783.2 eV, respectively\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e,\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e. The Co 2p\u003csub\u003e3/2\u003c/sub\u003e signals at 797.6 and 783.2 eV, coupled with satellite peaks at 786.3 and 803.4 eV, were identified as belonging to the Co\u003csup\u003e2+\u003c/sup\u003e species, which might exist in the catalysts in the form of Co\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e31\u003c/sup\u003e. Furthermore, peaks in the Co 2p1/2 region centered at 781.4 and 789.6 eV have been assigned to Co\u003csup\u003e3+\u003c/sup\u003e ions, confirming the existence of Co\u003csub\u003e2\u003c/sub\u003eP\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e\u003c/p\u003e\u003cp\u003eThe CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC material, which is derived from polymers of aniline-phytic acid, demonstrates several advantageous properties. These include a high concentration of active sites, a dual-doped carbon matrix with nitrogen and phosphorus, and a rich pore structure. It is anticipated that these properties will lead to exceptional electrocatalytic performance of CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea clearly demonstrates the different behavior of the cyclic voltammetry (CV) curves between CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC and NPC. The presence of distinct cathodic peaks in the O\u003csub\u003e2\u003c/sub\u003e-saturated solution indicates that both CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC and NPC have catalytic abilities for ORR. The oxygen reduction peak potential for CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC is 0.77 V, significantly higher compared to NPC (0.74 V). This difference highlights the crucial role of cobalt phosphide and cobalt phosphate sites in enhancing its ORR activity. The polarization curves presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb illustrate that the CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC material has \u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003eonset\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eE\u003c/em\u003e\u003csub\u003e1/2\u003c/sub\u003e values of 0.99 V and 0.80 V, respectively. The values of these catalysts are comparable to that of the Pt/C catalyst, which has an \u003cem\u003eE\u003c/em\u003e\u003csub\u003eonset\u003c/sub\u003e of 1.15 V and \u003cem\u003eE\u003c/em\u003e\u003csub\u003e1/2\u003c/sub\u003e of 0.78 V. The performance of CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC is better than that of recently reported ORR catalysts, as demonstrated in Table \u003cspan refid=\"MOESM2\" class=\"InternalRef\"\u003eS2\u003c/span\u003e. The higher \u003cem\u003eE\u003c/em\u003e\u003csub\u003e1/2\u003c/sub\u003e value and \u003cem\u003ej\u003c/em\u003e of CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC compared to NPC indicate that transition metal phosphides have a notable impact on improving its ORR performance.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eTafel slopes and mass activities of as-fabricated composites provide additional evidence of the remarkable ORR activity. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec demonstrates that the CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC exhibits a smaller Tafel slope (81.65 mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) compared to NPC (107.14 mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), which is similar to Pt/C (109.27 mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). Furthermore, the mass activity of CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC at 0.765 V was calculated to be 44.82 mA mg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. This value is approximately 3 times higher than that of Pt/C (14.10 mA mg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) at the same potential. These findings offer further evidence supporting the active role of implanted cobalt phosphide and cobalt phosphide nanoparticles\u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e,\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eIn order to identify the number of electrons transferred (n) during ORR process, a variety of rotating speeds ranging from 400 to 2500 rpm, were utilized to get Koutecky-Levich (K-L) plots\u003csup\u003e\u003cspan additionalcitationids=\"CR36\" citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e. These plots had been utilized for calculating the 'n' value. As can be seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee, the linearity and coincidence of the K-L graphs imply first-order reaction kinetics for the ORR process. The number of electrons transferred for CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC is 3.99, suggesting a four-electron transfer mechanism. Moreover, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef compares the LSV curves of the sample before and after the 5000 CV cycles. The half-wave potential after 5000 cycles of the initial CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC shows a decrease of only 36 mV, indicating its excellent durability.\u003c/p\u003e\u003cp\u003eSimilarly, the OER catalytic activity of as-fabricated electrocatalysts have been tested by RDE. According to the LSV curves, it can be seen that the CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC catalyst requires an overpotential of 1.73 mV in order to achieve a current density of 10 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, significantly lower than NPC (1.91 mV). Furthermore, the Tafel slope of CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC is 145.13 mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, higher than that of RuO\u003csub\u003e2\u003c/sub\u003e (127.70 mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). This indicates that CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC demonstrates rapid kinetics in the OER process, higher than as-reported materials (Table \u003cspan refid=\"MOESM3\" class=\"InternalRef\"\u003eS3\u003c/span\u003e)\u003csup\u003e\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e,\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e. Furthermore, the catalytic stability of CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC was evaluated through CV cycling, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ei. The resulting plot of LSV showed a minimal deviation of Δ\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003ej\u003c/em\u003e=10\u003c/sub\u003e mV compared to the original LSV plot.\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e\u003c/p\u003e\u003cp\u003eIn addition, the important bifunctional activity of a material may be calculated by calculating the potential difference between OER and ORR (\u003cem\u003eE\u003c/em\u003e\u0026thinsp;=\u0026thinsp;\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003ej\u003c/em\u003e=10\u003c/sub\u003e - \u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003ej\u003c/em\u003e=\u0026minus;0.3\u003c/sub\u003e), a smaller \u003cem\u003eE\u003c/em\u003e suggests better bifunctional activity of material. The potential gap (\u003cem\u003eE\u003c/em\u003e) of CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC was 0.88 V (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea), which was less than the NPC (1.13 V) and similar to the commercial Pt/C-RuO\u003csub\u003e2\u003c/sub\u003e combination (0.78 V).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eIn order to explore the potential practical applications of the composites, ZABs were assembled using carbon cloth supported CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC as air cathode (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb). In addition, Pt/C ་ RuO\u003csub\u003e2\u003c/sub\u003e mixture are being examined as well for comparison. The ZAB (Zinc-Air Battery) based on CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC showed a noticeably higher open circuit voltage of 1.43 V and the LED light can be easily illuminated. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec, the power density of CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC-based ZAB (265 mW cm\u003csup\u003e\u0026ndash;\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e) was compared to that of previously reported electrocatalysts, as shown in Table S4, which is significantly higher power density compared to the Pt/C-RuO\u003csub\u003e2\u003c/sub\u003e based ZAB (211 mW cm\u003csup\u003e\u0026ndash;\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e). Additionally, the CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC assembled ZAB exhibits 699.86 mA h g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e specific discharge capacity, estimated based on the consumed Zn weight (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed), higher than Pt/C-RuO\u003csub\u003e2\u003c/sub\u003e assembled ZAB (601.34 mA h g\u003csup\u003e\u0026ndash;\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e). Above results demonstrate the excellent efficiency of the CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC-based ZAB. CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC cathodes' cycling stability was also measured with a continuous galvanostatic discharge-charge cycling test at a current density of 5 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee). The assembled ZAB demonstrates stable discharge/charge profiles for over 450 hours, indicating exceptional rechargeability. This lifespan surpasses that of the Pt/C་RuO\u003csub\u003e2\u003c/sub\u003e assembled battery and exceed the majority of reported zinc air batteries (Table S4).\u003c/p\u003e\u003cp\u003eRecent years, flexible Zinc-air battery (FZAB) has been identified as a potential energy candidate for wearable devices. However, several challenges still need to be addressed, including high cost, poor cycling performance, and self-discharging. The CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC assembled FZAB can discharge over 9 hours at 1 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. This is a significant improvement over the Pt/C\u0026thinsp;+\u0026thinsp;RuO\u003csub\u003e2\u003c/sub\u003e assembled FZAB (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eg). In addition, the CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC electrode is able to continuously charge and discharge the FZAB over 14 h and maintains a relative low voltage difference of 1.0 V (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eh, demonstrating the improved long-term durability compared to the benchmark Pt/C\u0026thinsp;+\u0026thinsp;RuO\u003csub\u003e2\u003c/sub\u003e catalyst. The fabrication process of the CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC material is not only simple, but it is also highly efficient. This technology allows for the development of electrocatalysts that are both cost-effective and high-performance for metal-air batteries.\u003c/p\u003e"},{"header":"3. Conclusion","content":"\u003cp\u003eIn general, we have demonstrated an alternative \u003cem\u003ein-situ\u003c/em\u003e phosphating method for synthesizing highly dispersed Co\u003csub\u003e2\u003c/sub\u003eP and Co\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e nanoparticles anchored on 3D porous N, P-doped carbon framework as a ORR/OER bifunctional electrocatalyst. The exceptional bifunctional activity of the as-fabricated material can be attributed to the synergistic interactions between graphitized carbon layers coated with Co\u003csub\u003e2\u003c/sub\u003eP or Co\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e nanoparticles and an interconnected N, P-doped carbon matrix. The existence of the protective graphitic layers can enhance electron rate of active sites within the carbon network, which can further adjust the charge distribution around the Co\u003csub\u003e2\u003c/sub\u003eP or Co\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e sites, resulting in excellent activity and durability in the assembled ZABs battery. The CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC catalyst exhibited a half-wave potential of 0.80 V for ORR and an overpotential of 1.73 V for OER at 10 mA cm\u003csup\u003e-\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. The CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC assembled ZABs showed excellent discharge-charge cycling stability over 450 hours, with 265 mW cm\u003csup\u003e-\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e of peak power density and 699.86 mA h g\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e of specific capacity. The current study presents a prospective synthetic methodology for the fabrication of metal-air electrode materials characterized by superior performance and stability.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the Research Project of Hubei Provincial Department of Education (Q20232503), the\u0026nbsp;College Students Innovation and Entrepreneurship Training Program of China (S202510513072), the Hubei Provincial Natural Science Foundation of China (Grant No. 2025AFB422), and the Doctoral Research Foundation of Hubei University of Science and Technology (BK202432).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eContributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eGang Chen involved in investigation, writing-original draft, visualization, methodology. Lina Zhou involved in conceptualization, funding acquisition, writing\u0026ndash;review and editing. Xin Xiong involved in investigation, methodology. Xiaonan Xu involved in data curation. Yingying Wang involved in investigation, methodology, validation, funding acquisition, project administration, supervision, writing-original draft and funding.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCorresponding authors\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCorrespondence to Li-Na Zhou or Ying-Ying Wang.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics declarations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e The authors declare that they have no conflict of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical approval\u003c/strong\u003e Not applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data that support the findings of this study are available upon reasonable request from the authors.\u003cstrong\u003e\u003cbr\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eYu, C.; 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K., Phosphine-free avenue to Co\u003csub\u003e2\u003c/sub\u003eP nanoparticle encapsulated N,P co-doped CNTs: a novel non-enzymatic glucose sensor and an efficient electrocatalyst for oxygen evolution reaction. \u003cem\u003eGreen Chemistry\u003c/em\u003e 2017, \u003cem\u003e19\u003c/em\u003e (5), 1327\u0026ndash;1335.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eQiao, M.; Wang, Y.; W\u0026aring;gberg, T.; Mamat, X.; Hu, X.; Zou, G.; Hu, G., Ni-Co bimetallic coordination effect for long lifetime rechargeable Zn-air battery. \u003cem\u003eJournal of Energy Chemistry\u003c/em\u003e 2020, \u003cem\u003e47\u003c/em\u003e, 146\u0026ndash;154.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eShao, Q.; Li, Y.; Cui, X.; Li, T.; Wang, H.-g.; Li, Y.; Duan, Q.; Si, Z., Metallophthalocyanine-Based Polymer-Derived Co2P Nanoparticles Anchoring on Doped Graphene as High-Efficient Trifunctional Electrocatalyst for Zn-Air Batteries and Water Splitting. \u003cem\u003eACS Sustainable Chemistry \u0026amp; Engineering\u003c/em\u003e 2020, \u003cem\u003e8\u003c/em\u003e (16), 6422\u0026ndash;6432.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eTian, Y.; Xu, L.; Li, M.; Yuan, D.; Liu, X.; Qian, J.; Dou, Y.; Qiu, J.; Zhang, S., Interface Engineering of CoS/CoO@N-Doped Graphene Nanocomposite for High-Performance Rechargeable Zn-Air Batteries. \u003cem\u003eNanomicro Lett\u003c/em\u003e 2020, \u003cem\u003e13\u003c/em\u003e (1), 3.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eShi, Q.; Liu, Q.; Zheng, Y.; Dong, Y.; Wang, L.; Liu, H.; Yang, W., Controllable Construction of Bifunctional Co\u003csub\u003ex\u003c/sub\u003eP@N,P-Doped Carbon Electrocatalysts for Rechargeable Zinc-Air Batteries. \u003cem\u003eEnergy \u0026amp; Environmental Materials\u003c/em\u003e 2021.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eZhang, Q.; Luo, F.; Long, X.; Yu, X.; Qu, K.; Yang, Z., N, P doped carbon nanotubes confined WN-Ni Mott-Schottky heterogeneous electrocatalyst for water splitting and rechargeable zinc-air batteries. \u003cem\u003eApplied Catalysis B: Environmental\u003c/em\u003e 2021, \u003cem\u003e298\u003c/em\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eChen, X.; Pu, J.; Hu, X.; Yao, Y.; Dou, Y.; Jiang, J.; Zhang, W., Janus Hollow Nanofiber with Bifunctional Oxygen Electrocatalyst for Rechargeable Zn-Air Battery. \u003cem\u003eSmall\u003c/em\u003e 2022, \u003cem\u003e18\u003c/em\u003e (16), e2200578.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHe, Y.; Yang, X.; Li, Y.; Liu, L.; Guo, S.; Shu, C.; Liu, F.; Liu, Y.; Tan, Q.; Wu, G., Atomically Dispersed Fe\u0026ndash;Co Dual Metal Sites as Bifunctional Oxygen Electrocatalysts for Rechargeable and Flexible Zn-Air Batteries. \u003cem\u003eACS Catalysis\u003c/em\u003e 2022, \u003cem\u003e12\u003c/em\u003e (2), 1216\u0026ndash;1227.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-nanoparticle-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"nano","sideBox":"Learn more about [Journal of Nanoparticle Research](http://link.springer.com/journal/11051)","snPcode":"11051","submissionUrl":"https://submission.nature.com/new-submission/11051/3","title":"Journal of Nanoparticle Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Co2P nanoparticle, Co3(PO4)2 nanoparticle, In-situ phosphating, Rechargeable Zn-Air batteries, Bifunctional electrocatalyst","lastPublishedDoi":"10.21203/rs.3.rs-7069913/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7069913/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAs potential candidates to be employed as air anodes in metal-air batteries, transition metal phosphides (TMPs) have received considerable attention due to its excellent electrocatalytic activity. This work presents a straightforward method for efficiently fabricating CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC, a three-dimensional (3D) reticulated carbon N, P-doped carbon structure generated from polyaniline-phytic acid polymer, with Co\u003csub\u003e2\u003c/sub\u003eP and Co\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e nanoparticles implanted on the carbon matrix. The CoPO-Co\u003csub\u003e2\u003c/sub\u003eP@NPC demonstrates impressive bifunctional oxygen reduction reactions (ORR)/oxygen evolution reactions (OER) performances. A diffusion-limiting current density of 6.56 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, a half-wave potential of 0.80 V, and an overpotential of 1.73 V are detected at 10 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. The rechargeable ZAB that has been assembled demonstrates a high-power density of 265 mW cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, with excellent cycling stability over 450 hours. The composite based on Co\u003csub\u003e2\u003c/sub\u003eP-Co\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e demonstrates outstanding bifunctional electrocatalytic performance, which makes it a desirable anode material for rechargeable Zn-Air batteries.\u003c/p\u003e","manuscriptTitle":"One step, In-situ phosphating construction of encapsulated Co2P and Co3(PO4)2 nanoparticles within 3D reticulated carbon for rechargeable Zn-Air batteries","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-31 17:51:32","doi":"10.21203/rs.3.rs-7069913/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"219953867579373029367448985088846467468","date":"2025-07-29T23:15:35+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-07-29T19:08:58+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-07-12T19:50:25+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-07-08T21:49:15+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Nanoparticle Research","date":"2025-07-08T02:53:15+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-nanoparticle-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"nano","sideBox":"Learn more about [Journal of Nanoparticle Research](http://link.springer.com/journal/11051)","snPcode":"11051","submissionUrl":"https://submission.nature.com/new-submission/11051/3","title":"Journal of Nanoparticle Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"6b12e9e4-bb28-4f41-b26d-1c19b45e72f5","owner":[],"postedDate":"July 31st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-11-03T16:08:24+00:00","versionOfRecord":{"articleIdentity":"rs-7069913","link":"https://doi.org/10.1007/s11051-025-06484-y","journal":{"identity":"journal-of-nanoparticle-research","isVorOnly":false,"title":"Journal of Nanoparticle Research"},"publishedOn":"2025-10-27 15:58:50","publishedOnDateReadable":"October 27th, 2025"},"versionCreatedAt":"2025-07-31 17:51:32","video":"","vorDoi":"10.1007/s11051-025-06484-y","vorDoiUrl":"https://doi.org/10.1007/s11051-025-06484-y","workflowStages":[]},"version":"v1","identity":"rs-7069913","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7069913","identity":"rs-7069913","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}