Engineering the performance of bifunctional oxygen electrocatalysts by modulating the atomically dispersed Co,Ni on N-doped cotton biomass aerogel of carbon fiber catalysts for rechargeable zinc-air battery

Engineering the performance of bifunctional oxygen electrocatalysts by modulating the atomically dispersed Co,Ni on N-doped cotton biomass aerogel of carbon fiber catalysts for rechargeable zinc-air battery | 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 Engineering the performance of bifunctional oxygen electrocatalysts by modulating the atomically dispersed Co,Ni on N-doped cotton biomass aerogel of carbon fiber catalysts for rechargeable zinc-air battery Zhengyu Yang, Wan Jin, Zhengyu Yang This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4010883/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Rational construction of advanced bifunctional catalysts with dual-active-sites is still challenging for both oxygen reduction (ORR) and oxygen evolution reactions (OER).The design of metal single atom catalysts prepared through high-temperature gas transport is an emerging method. The CoNi-N-C catalyst was prepared by using Co powder and Nickel foam to volatilize atomic dispersed Co,Ni element embedded in nitrogen doped cotton biomass biomass aerogel of carbon fibers in a high temperature tubular furnace in ammonia atmosphere. In this work, CoNi-N-C-1000 monoatomic catalyst was successfully synthesized by using the above method The resulting CoNi-N-C-1000 exhibited excellent bifunctional catalytic performance for ORR (E 1/2 =0.85V) and OER (E j=10 =1.54V) in alkaline electrolytes, which can compete with previously reported bifunctional electrocatalysts. In addition, compared to the Pt/C+RuO 2 mixed catalyst, this bifunctional catalyst can endow the self-made zinc-air battery with better power density (128.5 mW/cm 2 ) and cycle stability (142.3 hours), demonstrating its potential feasibility in practical applications of rechargeable zinc-air batteries. Single-atom catalyst Oxygen reduction reaction Oxygen evolution reaction Biomass aerogel Zinc-air battery Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. Introduction The problem of global energy shortage is becoming increasingly prominent in the future, and researchers are investing their research direction in renewable green energy fields such as fuel cells( 1 ) and metal air batteries( 2 ). Zn-air battery have attracted the attention of researchers in metal air batteries due to their theoretically high energy density( 3 , 4 ). However, developing practical and feasible rechargeable zinc-air battery still is a challenge( 5 , 6 ). Firstly, the catalytic activity of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) currently exhibited by air electrodes is relatively low( 7 ), resulting in poor power density performance of the battery. Secondly, due to the uneven deposition and dissolution of the zinc negative electrode, corrosion of the zinc electrode material, and solid-state carbonate deposition, evaporation, or dilution of the electrolyte, the cycle life of zinc-air battery is reduced( 8 ). For rechargeable zinc-air battery, the air electrode should exhibit excellent ORR and OER catalytic activity during discharge and charging processes, respectively. Platinum (Pt) based materials are considered the best ORR catalysts, but often exhibit unsatisfactory OER activity( 9 , 10 ). However, Ru and Ir exhibit excellent OER activity but lack ORR activity( 11 , 12 ). In addition, precious metals are often constrained by their scarcity and high prices, so efficient and cost-effective bifunctional catalysts are highly needed( 13 , 14 ). In addition to precious metal catalysts, transition metal based catalysts are one of the most promising non precious metal electrocatalysts in OER and ORR( 15 – 17 ). Due to its low price and ability to cross multiple valence states, transition metals can play a dominant role in the formation of active sites( 18 ). By adjusting the composition of elements and creating atomic structure, the electrocatalytic activity can be maximized, allowing transition metal based catalysts to withstand constant oxidation and reduction conditions in rechargeable zinc-air battery( 19 ). In recent years, carbon based catalysts have attracted attention due to their high porosity, large specific surface area, excellent conductivity, and relative chemical stability( 20 ). They can regulate the electronic structure and promote electron and material transport by doping with hetero-atom and introducing defects reasonably, thereby solving the slow kinetics of ORR and OER( 21 ). In fact, researchers also have shifted their focus to studying catalytic materials enriched on Earth, such as metal oxides, transition metal carbon based catalysts (M-N-C), and single atom catalysts (SAC)( 22 , 23 ). This has opened up a new path for efficient and economical dual functional catalyst design engineering. Firstly, doping with heteroatoms (S, N, O, P, B, and metal atoms) and defect control (edges and vacancies) will redistribute charges and alter electronic structures, which can reduce the adsorption energy of oxygen-containing substances on them and improve their intrinsic catalytic performance. Secondly, regulating the porous structure can increase the density of active sites( 24 – 26 ). Macropores can increase more mass transfer channels, while mesopores and micropores provide a larger specific surface area to improve the accessibility of reactants to active centers. Finally, excellent conductivity is the foundation of electron transfer in the electrochemical reaction of zinc-air battery( 27 ). Moreover, single atom catalysts (SACs) break through the limitations of nanoscale catalysts, achieving high atomic utilization, consistent catalytic activity at active sites, easy separation of products after catalytic reactions, and easy recovery and immobilization( 28 ). Combined with the advantages of the above materials, CoNi-N-C-1000 bifunctional catalyst was successfully prepared in this study with cotton as raw material and biomass aerogel as precursor by the high-temperature gas transport method, demonstrating excellent half wave potential (0.85V) and overpotential (1.54V) performance. It also demonstrated excellent performance in zinc-air battery with an open circuit voltage of 1.49V, a power density of 128.5mW/cm 2 , and a charge discharge cycle of 142.3 hours. 2. Experimental 2.1 Materials Cotton, high purity 50nm Co powder and the thickness is 0.2mm of Nickel foam (Taobao), hydrochloric acid (HCl, 37.5 wt%), sodium hydroxide (NaOH), potassium hydroxide (KOH), commercial Pt/C (20 wt% Pt), RuO 2 , and Nafion solution (5 wt%) were used as received without further purification (Shanghai Aladdin Biochemical Technology Co., Ltd.). 2.2 Synthesis of biomass aerogel Five grams of cotton was gradually added to 50 mL of 3 M KOH aqueous solution, autoclaved at 150°C for 6 h, then washed until neutral pH. The cotton solution was blended for 3 min to obtain a white biomass aerogel solution, frozen at -5°C in the refrigerator, then freeze-dried at -48°C to obtain the final biomass aerogel. 2.3 Synthesis of CoNi-N-C catalyst As shown in Fig. 1 , Co powder, Nickel foam and the biomass aerogel obtained from freeze-drying are separately located in the porcelain boat. They are then treated with ammonia gas as a reducing agent at high temperatures. The temperature was ramped to 350°C (5°C/min) at first, then increased to 700, 800, 900, or 1000°C (5°C/min) for 1 h carbonization to obtain CoNi-N-C-800, CoNi-N-C-900, CoNi-N-C-1000, and CoNi-N-C-1100, respectively. 2.4 Materials characterization X-ray diffraction (XRD) patterns were obtained using Cu Kα radiation (λ = 1.54 Å) at 40 kV and 30 mA, with 2θ scans from 10° to 90° at 10° min − 1 . Scanning electron microscopy (SEM) images were taken on a FEI Nova 400. Transmission electron microscopy (TEM) imaging and energy dispersive X-ray spectroscopy (EDS) elemental mapping were conducted on a JEOL JEM-2100F. X-ray photoelectron spectroscopy (XPS) for elemental analysis was performed on a Thermo Scientific Escalab 250Xi with monochromated Al Kα radiation (1486.6 eV), calibrating spectra to the C 1s peak at 284.8 eV. The pore size and specific surface area were measured using a BET specific surface area and pore size analyzer (Micrometrics ASAP 2460). 2.5 Electrochemical measurements Electrochemical measurements were performed in 0.1 M KOH (for ORR) or 1 M KOH (for OER) with a CHI 760E instrument using a standard three-electrode rotating ring-disk electrode system at room temperature. The working electrode was a 4 mm diameter rotating ring-disk electrode (RRDE). An Ag/AgCl electrode and Pt wire served as the reference and counter electrodes, respectively. Catalyst ink was prepared by dispersing 5 mg catalyst powder in 500 µL water, 450 µL ethanol and 50 µL Nafion solution with 30 min sonication. 10 µL ink was loaded onto a polished 4 mm glassy carbon electrode cleaned with ethanol and water. For ORR, O 2 and N 2 were bubbled into the cell for ≥ 30 min before CV and LSV. CVs were acquired in 0.1 M KOH from 0.1 to 1.2 V vs RHE at 50 mV/s. RDE and RRDE measurements were performed from 400 to 2500 rpm at 10 mV/s. Stability was assessed by comparing CVs after 3000 cycles to the 1st cycle at 1600 rpm. EIS was conducted at 0.5 V vs RHE and 1600 rpm. For OER, CVs were obtained in 1 M KOH from 1.0 to 1.9 V vs RHE at 50 mV/s. OER LSVs were measured from 1.0 to 1.9 V vs RHE with iR-correction at 1600 rpm. The Koutecký-Levich equation was used to determine the electron transfer number (n) ( 29 ): where J is the measured disk current density (mA/cm 2 ), j k is the kinetic-limiting current, and ω is the electrode rotating rate (rpm). The theoretical Levich slope (B) was calculated as ( 30 ): where B is the K-L plot slope, ω is the electrode rotation rate, F is the Faraday constant, D 0 is the O 2 diffusion coefficient (1.9×10 − 6 cm 2 /s in 0.1 M KOH), and C 0 is the O 2 concentration (1.2×10 − 6 mol/cm 3 ). 2.6 Zn-air battery testing The anode was a 1 mm thick polished Zn plate. The 6 M KOH and 0.2 M Zn(CH 3 COO) 2 electrolyte was used. For the cathode, 5 mg catalyst was dispersed in 500 µL water, 450 µL ethanol and 50 µL Nafion solution by sonication for 2 h. 200 µL catalyst ink was dropped on the matrix at 0.5 mg/cm 2 loading and air dried. A 20% Pt/C + RuO 2 cathode was fabricated identically for comparison. Polarization curves were obtained on a CHI760E. Charge-discharge cycling was performed on a Neware-CT-4008-5V10mA at 10 mA/cm 2 cycling between 10 min charge and 10 min discharge. 3. Results and discussion 3.1 Characterizations of CoNi-N-C electrocatalyst XRD patterns of the CoNi-N-C-X and N-C-1000 samples (X = 800, 900, 1000, 1100) are shown in Fig. 2 (a). The XRD patterns are similar for all samples, with only one diffraction peak appearing at 24–25°, corresponding to the (002) plane of graphitic carbon( 31 ). In the XRD results of Fig. 2 (a), there is no metal peak for Co, Ni, metal peak and oxidized Co, oxidized Ni. This can preliminarily confirm that Co and Ni elements do not agglomerate into Co, Ni particles or exist in the form of other low catalytic activity compounds during high-temperature gas transport( 32 ). XPS was used to study the elemental compositions and valence states of CoNi-N-C-1000 and N-C-1000. The CoNi-N-C-1000 survey spectrum (Fig. 2 b) shows distinct Co, Ni, N, and C peaks, confirming Co, Ni and N co-existence in the carbon fibers. Through comparison, it was found that N-C-1000 lacked Co and Ni peak. CoNi-N-C-1000 showed three main peaks at approximately 284.6 eV (C 1s), 401 eV (N 1s), and 532 eV (O 1s) along with small Co 2p peak at around 780.3 eV and Ni 2p peak at around 852.7 eV. The high-resolution spectra of C1s (Fig. 2 c) show the peaks of C = C (284.8 eV), C = N (285.7 eV), and C-C (286.3 eV). Four N species were identified in the N1s spectrum (Fig. 2 d): pyridine N (398.6 ± 0.3eV), M-N x (M = Co,Ni 400.5 ± 0.3eV), pyrrole N (401.5 ± 0.3eV), and graphite N, indicating successful doping of N into the carbon substrate to promote ORR and OER( 33 ). Compared with N-C-1000, additional M-N x peaks were detected in CoNi-N-C-1000, which significantly contributed to the catalytic activity of the CoNi-N-C system( 34 ). The high-resolution spectrum of Co 2p (Fig. 2 e) shows two peaks at ~ 781.3 eV and ~ 796.7 eV, belonging to Co 2p3/2 and 2p1/2, respectively.The high-resolution spectrum of Ni 2p (Fig. 2 f) shows two peaks at ~ 855.7 eV and ~ 873.5 eV, belonging to Ni 2p3/2 and 2p1/2, respectively. These pieces of evidence collectively indicate that Co and Ni elements were successfully incorporated into carbon fibers. The porosity of five catalysts was studied by nitrogen adsorption/ desorption isotherms. The BET surface area of CoNi-N-C-1000 (819 m 2 g − 1 ) was revealed to be much larger than those for N-C-1000 (226 m 2 g − 1 ), CoNi-N-C-800 (373 m 2 g − 1 ), CoNi-N-C-900 (542 m 2 g − 1 ), CoNi-N-C-1100 (610 m 2 g − 1 ) in Fig. S1 (a). The reason why CoNi-N-C-1000 achieves a larger specific surface area under the same temperature conditions compared to N-C-1000 is due to the introduction of Co and Ni single atoms during the pyrolysis process( 35 ). In CoNi-N-C-X (X = 800, 900, 1000, 1100) catalyst, the specific surface area increases with increasing temperature. However, at a high temperature of 1100 ℃, the N-C matrix structure was destroyed and resulting in a decrease in the specific surface area( 36 ). The pore size of N-C-1000, CoNi-N-C-800, CoNi-N-C-900, CoNi-N-C-1000 and CoNi-N-C-1100 in Fig. S1 (b) were 30.73 nm, 30.27 nm, 27.05 nm, 17.26 nm, 22.48 nm, respectively. A large number of microporous structures are beneficial for material transport during reactions( 37 ). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to measure the morphology of samples. As displayed in Fig. 3 .(a)(b) and (c)(d), both N-C-1000 and CoNi-N-C-1000 exhibit interconnected porous network, which are made up of highly dense carbon fibers( 16 ).High-resolution transmission electron microscopy (HRTEM) further investigated the microstructure and Co, Ni dispersion in CoNi-N-C-1000. Figures 3 e and 3 f show carbon sheets without observable nanoparticles, indicating the coexistence of amorphous carbon and graphite layers, as shown by the twisted lattice stripes in Fig. 3 f and the calculated lattice spacing is 0.56nm, and a smaller lattice spacing is beneficial for ion transport( 38 ). The energy dispersive X-ray (EDS) spectrum shows that C, N, Co and Ni are uniformly distributed on the carbon fibers (Fig. 3 g), which may indicate that the separated Co, Ni atoms are uniformly dispersed on the carbon fiber without any nanoparticle or agglomeration phenomenon. 3.2 Electrochemical performance measurement Evaluate the ORR performance of all catalysts in a 0.1M KOH solution using the Rotating Disc Electrode (RDE) technique. All potentials are measured relative to the standard hydrogen electrode (RHE). The CV of CoNi-N-C-800, CoNi-N-C-900, CoNi-N-C-1000, and CoNi-N-C-1100 under O 2 and N 2 atmospheres (Figure S2) show different oxygen reduction peaks. As shown in Figure S3, both the half wave potential and current density increase with the heating temperature reaching 1000°C, indicating that 1000°C is the optimal temperature. The ORR activity of the prepared catalyst was measured using LSV. Figure S3 shows that as the pyrolysis temperature increases from 800°C to 1000°C, the oxygen reduction performance becomes better, but when the temperature further increases to 1100°C, the oxygen reduction characteristics slightly decrease. This is because higher temperatures have disrupted the structure of N-C precursors. The CoNi-N-C-1000 catalyst exhibits the best electrochemical oxygen reduction catalytic performance in alkaline solutions. CoNi-N-C-1000 has a starting potential of 0.91V (E onset ) and a half wave potential of 0.85V (E 1/2 ) relative to RHE, significantly higher than N-C-1000 and comparable to 20%Pt/C at 0.838V, the current density (J) of CoNi-N-C-1000 reaches 5.5mA/cm 2 , which is equivalent to Pt/C (Fig. 4 a and 4 b). Figure S4 shows that ORR polarization curves of CoNi-N-C-1000 at different rotating rates. CoNi-N-C-1000 also has a lower Tafel slope than Pt/C (Fig. 4 c), indicating excellent kinetics and lower overpotential at the same current density. Koutecký-Levich analysis (Fig. 4 d) shows that the electron transfer number (n) of CoNi-N-C-1000 is close to 4, consistent with an ideal 4-electron ORR pathway. The rotating ring disk electrode test (Fig. 4 e-f) further confirms that CoNi-N-C-1000 follows the 4e − pathway and has a lower H 2 O 2 yield, similar to Pt/C. In addition, the electrochemical impedance spectrum (Fig. 4 g) during the ORR process indicates that CoNi-N-C-1000 (Rct = 28.8) has a lower charge transfer resistance than N-C-1000 (37.4) and Pt/C (32.7), reflecting faster electron transfer kinetics( 39 ). After 6000 acceleration cycles, CoNi-N-C-1000 E 1/2 maintained its original value, while Pt/C E 1/2 decreased by 10mV (Fig. 4 h), CoNi-N-C-1000 demonstrating excellent ORR cycling stability. In addition to demonstrating excellent ORR performance, CoNi-N-C-1000 also exhibits excellent OER activity. As shown in Fig. 5 a, CoNi-N-C-1000 reaches a current density of 10 mA/cm 2 at 1.54 V, lower than commercial RuO 2 (1.58 V) and N-C-1000 (1.61 V). Tafel slopes in Fig. 5 b are 294.7, 313.2, and 341.3 mV/dec − 1 for CoNi-N-C-1000, RuO 2 , and N-C-1000, respectively, confirming the superior OER kinetics of CoNi-N-C-1000. After 6000 acceleration cycles, CoNi-N-C-1000 E 10 almost maintained its original value, while RuO 2 E 10 increased by 70mV (Fig. 5 c), CoNi-N-C-1000 also demonstrating excellent OER cycling stability. Overlaying the ORR and OER LSVs (Fig. 5 d) reveals CoNi-N-C-1000 has a smaller potential gap E (0.69 V) than Pt/C and RuO 2 (0.742 V), demonstrating that the CoNi-N-C-1000 is an excellent bifunctional catalyst. Considering the excellent dual functional electrocatalytic performance of CoNi-N-C-1000, we have constructed a self-made zinc-air battery to demonstrate its feasibility in practical energy equipment. To compare the performance of single cells, traditional Pt/C + RuO 2 catalysts (with a mass ratio of Pt/C and RuO 2 of 1/1) were used as air cathodes to manufacture control cells. Figure.6(a) shows the charging and discharging reaction principle of Zn-air batteries. Figure.6(b) shows that the open circuit voltage of CoNi-N-C-1000 is 1.49V higher than commercial Pt + RuO 2 (1.43V). Figure.6(c) displays the galvanodynamic behaviors of the CoNi-N-C-1000 and the mixed Pt + RuO 2 catalysts in the charge and discharge processes of Zn-air batteries. The zinc-air battery driven by CoNi-N-C-1000 provides a high power density of 128.5 mW/cm 2 (Figure.6d), which far exceeds the power density of Pt/C + RuO 2 (86.7 mW/cm 2 ) catalysts. Figure.6(e) compared the long-term charge discharge cycle stability of CoNi-N-C-1000 and Pt/C + RuO 2 assembled zinc-air battery. CoNi-N-C-1000 exhibits a long-term cycle of 142.3h, indicating the stability of the CoNi-N-C-1000 catalyst. The above discussion indicates that strongly coupled CoNi-N-C-1000 catalyst can provide high efficiency and long cycle life for zinc-air battery. 4. Conclusion In summary, we have successfully prepared CoNi-N-C-1000 atomic level catalysts and studied in detail the morphology, structure, and catalytic performance of CoNi-N-C-1000 catalyst materials. The synergistic combination of highly active Co, Ni monoatoms and N-C carbon aerogels enables CoNi-N-C-1000 catalyst to exhibit excellent bifunctional electrocatalytic performance for ORR and OER, which is comparable to the most advanced Pt/C or RuO 2 catalysts. The uniform dispersion of Co and Ni atoms in the porous carbon fiber aerogel provides additional synergistic effect to further enhance the catalytic activity and stability. In addition, the zinc-air battery driven by CoNi-N-C-1000 has a high power density of 128.5mW/cm 2 and can stably charge and discharge for up to 142.3 hours, which is superior to the more expensive Pt/C + RuO 2 catalyst. Declarations Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐ The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Data Availability Statement Data available on request from the authors. The data that support the findings of this study are available from the corresponding author, [author initials], upon reasonable request. Funding Statement None. Author Contribution Author 1 (First Author: Zhengyu Yang): Conceptualization, Methodology, Formal Analysis, Writing - Original Draft；Author 2(Second Author: Wan Jin): Data Curation;Author 3 (Corresponding Author: Zhengyu Yang): Conceptualization, Funding Acquisition, Resources, Supervision, Writing - Review & Editing. Ethical Approval Statement All studies in this article do not involve ethical issues, and the researchers strictly adhere to the journal's regulations. References Wang Y, Wang H, Wang G, Li H, Zhao Y, He W. Enhancement of water droplet drainage performance in a cathode flow channel with baffles for a polymer electrolyte membrane fuel cell. Renewable Energy. 2023;219:119395. Xu X, Wang S, Guo S, San Hui K, Ma J, Dinh DA, et al. Cobalt phosphosulfide nanoparticles encapsulated into heteroatom-doped carbon as bifunctional electrocatalyst for Zn−air battery. Advanced Powder Materials. 2022;1(3):100027. Zhang Y, Cai D, Sha J, Xiang L, Wang L, Liu Q, et al. 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FeCo nanoparticles wrapped in N-doped carbon derived from Prussian blue analogue and dicyandiamide as efficient oxygen reduction electrocatalysts for Al-air batteries. Chemical Engineering Journal. 2020;395:125158. Wang X-T, Ouyang T, Wang L, Zhong J-H, Liu Z-Q. Surface Reorganization on Electrochemically-Induced Zn–Ni–Co Spinel Oxides for Enhanced Oxygen Electrocatalysis. Angewandte Chemie International Edition. 2020;59(16):6492-9. Xiao Z, Wu Y, Cao S, Yan W, Chen B, Xing T, et al. An active site pre-anchoring and post-exposure strategy in Fe(CN) 6 4- @PPy derived Fe/S/N-doped carbon electrocatalyst for high performance oxygen reduction reaction and zinc-air battery. Chemical Engineering Journal. 2021;413:127395. Wang H-Y, Ren J-T, Weng C-C, Lv X-W, Yuan Z-Y. Hierarchical porous N,S-codoped carbon with trapped Mn species for efficient pH-universal electrochemical oxygen reduction in Zn-air battery. Journal of Industrial and Engineering Chemistry. 2021;100:92-8. Additional Declarations No competing interests reported. Supplementary Files Supportinginformation.doc Graphicalabstract.png Graphical abstract Cite Share Download PDF Status: Posted Version 1 posted 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. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-4010883","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":277284567,"identity":"aca8f945-106d-42fe-a6da-d51736a57e44","order_by":0,"name":"Zhengyu Yang","email":"","orcid":"","institution":"Wuhan University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Zhengyu","middleName":"","lastName":"Yang","suffix":""},{"id":277284569,"identity":"31cdaf20-3ea3-4e0a-8c67-f6d0f5177701","order_by":1,"name":"Wan Jin","email":"","orcid":"","institution":"Wuhan University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Wan","middleName":"","lastName":"Jin","suffix":""},{"id":277284570,"identity":"767f7a40-945f-4e0d-92af-dabeba00c5e4","order_by":2,"name":"Zhengyu Yang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABAElEQVRIiWNgGAWjYLACxgYI9QDKNyBaCzNIqQRJWtgkiNJicPzs4Zc/d9jkyUfkmFXzttXVMbA3b5NgqLmDW8uZvDQLyTNpxYY3csxu87YdlmDgOVYmwXDsGW4tB3LMDAzbDidunAHUktt2QIJBIsdMgrHhMG4t59+YGSS2/QdrKc5tq5NgkH9DQMuNHOMHB9sOJM4HGs6c28YMtIUHvxbJG2/MGBvbkhM38Dwrlv5z7rBkG09asUXCMdxa+M7nGH/82WaXOL89eePHGWV1/Pzshzfe+FCDW4vCAUh0MBhcSICIsIGIBJwaGBjkGxiYP4AZ/QfwKBsFo2AUjIIRDQDGRlgwwICNqQAAAABJRU5ErkJggg==","orcid":"","institution":"Wuhan University of Science and Technology","correspondingAuthor":true,"prefix":"","firstName":"Zhengyu","middleName":"","lastName":"Yang","suffix":""}],"badges":[],"createdAt":"2024-03-04 06:59:49","currentVersionCode":1,"declarations":{"humanSubjects":false,"vertebrateSubjects":false,"conflictsOfInterestStatement":false,"humanSubjectEthicalGuidelines":false,"humanSubjectConsent":false,"humanSubjectClinicalTrial":false,"humanSubjectCaseReport":false,"vertebrateSubjectEthicalGuidelines":false},"doi":"10.21203/rs.3.rs-4010883/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4010883/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":52478963,"identity":"cef8864e-c1e9-481d-a3c4-16b9df0fdf49","added_by":"auto","created_at":"2024-03-12 05:23:29","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1483648,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic illustration of the synthesis of the CoNi-N-C single atom catalyst\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4010883/v1/fd34403bad99fe057dfd386c.png"},{"id":52478962,"identity":"05ecd03f-6bd1-4cde-b730-44e4fece5a74","added_by":"auto","created_at":"2024-03-12 05:23:29","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":137697,"visible":true,"origin":"","legend":"\u003cp\u003e(a) XRD patterns of the N-C1000, CoNi-N-C catalysts. (b) XPS survey spectra, high-resolution XPS spectra of (c) C 1s, (d) N 1s (e) Co 2p, and (f) Ni 2p for the N-C-1000 and CoNi-N-C-1000\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4010883/v1/ae195409c7a51d1f66318496.png"},{"id":52479357,"identity":"7289d513-54dc-4816-bf6b-22c75da4d8e4","added_by":"auto","created_at":"2024-03-12 05:31:29","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":2843854,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images showing fiber morphology and wrinkled fiber surfaces of (a, b) N-C-1000 and (c, d) CoNi-N-C-1000; (e, f) TEM and HRTEM images of CoNi-N-C-1000; (g) EDS elemental mapping of C, N, Co and Ni distributed uniformly in CoNi-N-C-1000.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4010883/v1/4dbf3e338071234e03b07649.png"},{"id":52478965,"identity":"ff6c2acb-3acc-4b6e-bd66-9c9eda2a3a8f","added_by":"auto","created_at":"2024-03-12 05:23:29","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":168219,"visible":true,"origin":"","legend":"\u003cp\u003e(a) The CV curves of CoNi-N-C-1000, N-C-1000 and Pt/C in 0.1 M KOH at 50 mv s\u003csup\u003e-1\u003c/sup\u003e; (b) LSV curves and (c) corresponding Tafel plots of the as-prepared catalysts and Pt/C in the O\u003csub\u003e2 \u003c/sub\u003esaturated 0.1 M KOH at 1600 rpm; (d) K-L plots and electron transfer numbers; (e) Ring currents and (f) H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e yields and electron transfer numbers of CoNi-N-C-1000 and Pt/C; (g) EIS Nyquist plots (at 0.5 V vs RHE); (h) LSVs before and after 6,000 cycles.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4010883/v1/4f1f88ce88708490f9490b87.png"},{"id":52478969,"identity":"5c1d3227-d3e3-454b-9ddf-8d6a327998d0","added_by":"auto","created_at":"2024-03-12 05:23:30","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":107145,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Polarization curves and (b) corresponding Tafel plots of CoNi-N-C-1000, N-C-1000 and RuO\u003csub\u003e2\u003c/sub\u003e for OER; (c) LSVs before and after 6,000 cycles. (c) Overlay of ORR and OER polarization curves showing bifunctional activity of CoNi-N-C-1000.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-4010883/v1/27fefad9a30aa3a78715cd70.png"},{"id":52479358,"identity":"2d14711b-9941-4c83-b132-fe899d7c6f0c","added_by":"auto","created_at":"2024-03-12 05:31:29","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":510910,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Schematic of the aqueous rechargeable Zn-air battery; (b) The ZAB with CoNi-N-C-1000 and Pt/C+RuO\u003csub\u003e2\u003c/sub\u003e cathode open-circuit voltages; (c) Charge-discharge polarization curves ; (d) Power density plots; (e) Galvanostatic cycling at 10 mA cm\u003csup\u003e−2\u003c/sup\u003e for 142.3 h.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-4010883/v1/6b85c18aea98ddd069a6a69e.png"},{"id":53055125,"identity":"df1d593c-e32c-487b-a854-9ee937e68216","added_by":"auto","created_at":"2024-03-20 05:59:47","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3225740,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4010883/v1/11aebf00-b9a0-49a2-9d60-f9644411d586.pdf"},{"id":52478967,"identity":"f1e28cfe-fb0b-45c5-9707-fb42e51483a2","added_by":"auto","created_at":"2024-03-12 05:23:29","extension":"doc","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":1125376,"visible":true,"origin":"","legend":"","description":"","filename":"Supportinginformation.doc","url":"https://assets-eu.researchsquare.com/files/rs-4010883/v1/e6e074cac7a9a17e58a11d0a.doc"},{"id":52478968,"identity":"8209555e-abf2-457b-b6ad-401b1e95e79c","added_by":"auto","created_at":"2024-03-12 05:23:29","extension":"png","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":926390,"visible":true,"origin":"","legend":"\u003cp\u003eGraphical abstract\u003c/p\u003e","description":"","filename":"Graphicalabstract.png","url":"https://assets-eu.researchsquare.com/files/rs-4010883/v1/b77cfd25ba40c14ccab0b6a4.png"}],"financialInterests":"No competing interests reported.","formattedTitle":"Engineering the performance of bifunctional oxygen electrocatalysts by modulating the atomically dispersed Co,Ni on N-doped cotton biomass aerogel of carbon fiber catalysts for rechargeable zinc-air battery","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe problem of global energy shortage is becoming increasingly prominent in the future, and researchers are investing their research direction in renewable green energy fields such as fuel cells(\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e) and metal air batteries(\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e). Zn-air battery have attracted the attention of researchers in metal air batteries due to their theoretically high energy density(\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e). However, developing practical and feasible rechargeable zinc-air battery still is a challenge(\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e). Firstly, the catalytic activity of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) currently exhibited by air electrodes is relatively low(\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e), resulting in poor power density performance of the battery. Secondly, due to the uneven deposition and dissolution of the zinc negative electrode, corrosion of the zinc electrode material, and solid-state carbonate deposition, evaporation, or dilution of the electrolyte, the cycle life of zinc-air battery is reduced(\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e). For rechargeable zinc-air battery, the air electrode should exhibit excellent ORR and OER catalytic activity during discharge and charging processes, respectively. Platinum (Pt) based materials are considered the best ORR catalysts, but often exhibit unsatisfactory OER activity(\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e). However, Ru and Ir exhibit excellent OER activity but lack ORR activity(\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e). In addition, precious metals are often constrained by their scarcity and high prices, so efficient and cost-effective bifunctional catalysts are highly needed(\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn addition to precious metal catalysts, transition metal based catalysts are one of the most promising non precious metal electrocatalysts in OER and ORR(\u003cspan additionalcitationids=\"CR16\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e). Due to its low price and ability to cross multiple valence states, transition metals can play a dominant role in the formation of active sites(\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e). By adjusting the composition of elements and creating atomic structure, the electrocatalytic activity can be maximized, allowing transition metal based catalysts to withstand constant oxidation and reduction conditions in rechargeable zinc-air battery(\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn recent years, carbon based catalysts have attracted attention due to their high porosity, large specific surface area, excellent conductivity, and relative chemical stability(\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e). They can regulate the electronic structure and promote electron and material transport by doping with hetero-atom and introducing defects reasonably, thereby solving the slow kinetics of ORR and OER(\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e). In fact, researchers also have shifted their focus to studying catalytic materials enriched on Earth, such as metal oxides, transition metal carbon based catalysts (M-N-C), and single atom catalysts (SAC)(\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e). This has opened up a new path for efficient and economical dual functional catalyst design engineering. Firstly, doping with heteroatoms (S, N, O, P, B, and metal atoms) and defect control (edges and vacancies) will redistribute charges and alter electronic structures, which can reduce the adsorption energy of oxygen-containing substances on them and improve their intrinsic catalytic performance. Secondly, regulating the porous structure can increase the density of active sites(\u003cspan additionalcitationids=\"CR25\" citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e). Macropores can increase more mass transfer channels, while mesopores and micropores provide a larger specific surface area to improve the accessibility of reactants to active centers. Finally, excellent conductivity is the foundation of electron transfer in the electrochemical reaction of zinc-air battery(\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e). Moreover, single atom catalysts (SACs) break through the limitations of nanoscale catalysts, achieving high atomic utilization, consistent catalytic activity at active sites, easy separation of products after catalytic reactions, and easy recovery and immobilization(\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eCombined with the advantages of the above materials, CoNi-N-C-1000 bifunctional catalyst was successfully prepared in this study with cotton as raw material and biomass aerogel as precursor by the high-temperature gas transport method, demonstrating excellent half wave potential (0.85V) and overpotential (1.54V) performance. It also demonstrated excellent performance in zinc-air battery with an open circuit voltage of 1.49V, a power density of 128.5mW/cm\u003csup\u003e2\u003c/sup\u003e, and a charge discharge cycle of 142.3 hours.\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials\u003c/h2\u003e \u003cp\u003eCotton, high purity 50nm Co powder and the thickness is 0.2mm of Nickel foam (Taobao), hydrochloric acid (HCl, 37.5 wt%), sodium hydroxide (NaOH), potassium hydroxide (KOH), commercial Pt/C (20 wt% Pt), RuO\u003csub\u003e2\u003c/sub\u003e, and Nafion solution (5 wt%) were used as received without further purification (Shanghai Aladdin Biochemical Technology Co., Ltd.).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Synthesis of biomass aerogel\u003c/h2\u003e \u003cp\u003eFive grams of cotton was gradually added to 50 mL of 3 M KOH aqueous solution, autoclaved at 150\u0026deg;C for 6 h, then washed until neutral pH. The cotton solution was blended for 3 min to obtain a white biomass aerogel solution, frozen at -5\u0026deg;C in the refrigerator, then freeze-dried at -48\u0026deg;C to obtain the final biomass aerogel.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Synthesis of CoNi-N-C catalyst\u003c/h2\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, Co powder, Nickel foam and the biomass aerogel obtained from freeze-drying are separately located in the porcelain boat. They are then treated with ammonia gas as a reducing agent at high temperatures. The temperature was ramped to 350\u0026deg;C (5\u0026deg;C/min) at first, then increased to 700, 800, 900, or 1000\u0026deg;C (5\u0026deg;C/min) for 1 h carbonization to obtain CoNi-N-C-800, CoNi-N-C-900, CoNi-N-C-1000, and CoNi-N-C-1100, respectively.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Materials characterization\u003c/h2\u003e \u003cp\u003eX-ray diffraction (XRD) patterns were obtained using Cu Kα radiation (λ\u0026thinsp;=\u0026thinsp;1.54 \u0026Aring;) at 40 kV and 30 mA, with 2θ scans from 10\u0026deg; to 90\u0026deg; at 10\u0026deg; min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Scanning electron microscopy (SEM) images were taken on a FEI Nova 400. Transmission electron microscopy (TEM) imaging and energy dispersive X-ray spectroscopy (EDS) elemental mapping were conducted on a JEOL JEM-2100F. X-ray photoelectron spectroscopy (XPS) for elemental analysis was performed on a Thermo Scientific Escalab 250Xi with monochromated Al Kα radiation (1486.6 eV), calibrating spectra to the C 1s peak at 284.8 eV. The pore size and specific surface area were measured using a BET specific surface area and pore size analyzer (Micrometrics ASAP 2460).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Electrochemical measurements\u003c/h2\u003e \u003cp\u003eElectrochemical measurements were performed in 0.1 M KOH (for ORR) or 1 M KOH (for OER) with a CHI 760E instrument using a standard three-electrode rotating ring-disk electrode system at room temperature. The working electrode was a 4 mm diameter rotating ring-disk electrode (RRDE). An Ag/AgCl electrode and Pt wire served as the reference and counter electrodes, respectively. Catalyst ink was prepared by dispersing 5 mg catalyst powder in 500 \u0026micro;L water, 450 \u0026micro;L ethanol and 50 \u0026micro;L Nafion solution with 30 min sonication. 10 \u0026micro;L ink was loaded onto a polished 4 mm glassy carbon electrode cleaned with ethanol and water. For ORR, O\u003csub\u003e2\u003c/sub\u003e and N\u003csub\u003e2\u003c/sub\u003e were bubbled into the cell for \u0026ge;\u0026thinsp;30 min before CV and LSV. CVs were acquired in 0.1 M KOH from 0.1 to 1.2 V vs RHE at 50 mV/s. RDE and RRDE measurements were performed from 400 to 2500 rpm at 10 mV/s. Stability was assessed by comparing CVs after 3000 cycles to the 1st cycle at 1600 rpm. EIS was conducted at 0.5 V vs RHE and 1600 rpm. For OER, CVs were obtained in 1 M KOH from 1.0 to 1.9 V vs RHE at 50 mV/s. OER LSVs were measured from 1.0 to 1.9 V vs RHE with iR-correction at 1600 rpm. The Kouteck\u0026yacute;-Levich equation was used to determine the electron transfer number (n) (\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e):\u003c/p\u003e \u003cp\u003e\u003cimg src=\"data:image/png;base64,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\" width=\"360\" height=\"67\"\u003e\u003c/p\u003e\u003cp\u003ewhere J is the measured disk current density (mA/cm\u003csup\u003e2\u003c/sup\u003e), j\u003csub\u003ek\u003c/sub\u003e is the kinetic-limiting current, and ω is the electrode rotating rate (rpm).\u003c/p\u003e \u003cp\u003eThe theoretical Levich slope (B) was calculated as (\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e):\u003c/p\u003e\u003cp\u003e\u003cimg src=\"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAUgAAAAsCAYAAAAHBiHLAAAILUlEQVR4Ae2aMU4cSxCGuQOxEyw5duKE1EgQEzh0RkCKOIBFhmRxAZwjYuQDYEdOfABLpHAADjBP3z79q6LcPbvN9FvQm7+kUc9UV1dV/zP9b/XMbg0WI2AEjIARKCKwVdRaaQSMgBEwAoMJ0g+BETACRqCCgAmyAozVRsAIGAETpJ8BI2AEjEAFARNkBRirjYARMAImSD8DRsAIGIEKAibICjBWGwEjYARMkH4GjIARMAIVBEyQFWCsNgJGwAiYIP0MGAEjYAQqCJggK8BYbQSMgBEwQc7gGfj8+fOwtbU1bG9vD79//34y4x8/fgyPj4/D169fqzZPBjReyC9tFMWVjhw+fvxYzFE2bo3AphEwQW4a8Q3Hu7m5GTgQSAoSgowQ2m/fvi1I8/LycqHDFkLtKfiMBKm4igFpQ97RRn1ujcBLImCCfEn0Nxz7/v5+2NvbG2gRiOn29nZ4eHhYkibkKELtlV4mSMXFvypHk2MvtO2nJwImyJ5ovnJfEOOXL1+WWV5fXy/JEhJjG76zs7PULQ0nnmSCjHEhyw8fPiyIm/i9q9eJqXv4zBHoSpB618WDHo93794NV1dX3aD+8+fPYlERg8XF9TqC3dHR0WI7F4mAKga9cm7xGePW5i+/tDGuxkISBwcHT+J///59UcmVqrlaHHBmHjU8IjHlba5yidvwHCfmjp3m9ebNm+X9kI5W2/lIkDkufVS1YACBE6M0Z+Xn1ghsEoGuBEniPNzxYwALQgutx4OvRSTCpY0LtwYeduQFgbAYJeR3enq6JBXIBX/r+JSP2PIuL84/9kEqYCEhtgib/LhGyGHVBwt85TiqxtBnrLlmjARbttdZlJO24bqfcazGMJeTk5Nl3tLnNsbOcWMf44iDzmIEXgMC3QmSB1yVgybIomDRRnJQX2tb8o/fMd+MyWSiuJAE+UVRvoxrlVJ+8hHJAQKiUoWISxUftp8+faqSD/PNOBMHgkMfCR7CET7KIVaTyo+WfkhPwnWNcKOd7EttJMEcFxz0XpTcmTMxLUaghMD+/v7w8+fPRdf5+flyF/P27dulOf3Y9ZDuBFkiKxYIW66plYGqx0xcXEdCiMDUFni0yee1ONkuX4ucREb0ozs7O/uL6LCpkTbjyCG+L4yxSnFiv/AGF4647RUh8/VaEm0y6eIr5wmmvBIgx1USfUN+Ma7GKt8ez4h8uv3/IcDzEXeOEKSEvkiS2KGbKtM9hAxELCJCFrK2tutWG8HdX6c1sistYg2GiFj0FxcXi4UOaGxrya0mzIPqjniaE+NY7IjmJLKRH9lq/ugZo3GyEyFEIlXfOm0NB41V/3P9yw8tuccfH3BzlRcR8vkmEKAiFDkSL57rmjV6d3e3TAebqZVkV4LUwidRHWMfPFjAsqu1kVy08CMBgQbXucpBL8KCILWNBTRijZEH/mK/Kjb0vGPEB7nwUYRWQn9pHuij4LuUb7QZO8ff2HjhFOcw5m+sDx+xquSHLs9nbLz7jMBUBFhvsTos+WNbzdqLBIldJtbS2DFdV4KEzOJi0gcPSBKymipa+HmB1gijZj9GUJAhFWbMF/9UUVSh3CxEumiXyaRUbYlsY1XWikuOk8eTGw9L/HHJNutcK1fiIfjtsRNYJ7ZtjIAQgOTidlr62EKQJRJl3JQqshtB5sWk5HstVvzVCI8YpYqq1Z4YvPdjXBSIhmoxkgOkIeLAtjZ/3rnRJ4lVbdSrf1Wr8TF2HkNfCY9st+pac2L+xOVr/3NyXhXH/UZgDAF+7FWY1OyOj4+XH2+ijSrLqGs570aQWriQVRQRZGlBoyttSaMuVkGKEXXE4rpUkbUSJNvnnL9IIvqXLuZRixWx4Fxjo79sw7X8ZaKTPucpH+oHW51nH7Jd1Ua8+XHAn8UIbBIBtszwAURXE/ogyJKIIPPWu2Rb0nUjSBZsadGLBGsLupTUmA5/cRuPLTqOLCKj3Ecu2YfeLcoHY9lS84dt5pXJsPT+cV0iwhc3PfpUXNpfv34N79+/X1RtkJT+BkMfY2px9EqDuXGucdlHjDV2LoLli3Wv+zcWz31GICOwDkGObaFfBUGKiCLpsEB5lwcRZILKILRcq6pRyU0biZmFDIFoQWuRi4xEIuontggrVq6cM5/sX/b08Z8+/JMT13H+Y3MSXsRgS881Qku8w8PDJ5iBH/kq9xiHMeSgP5xT6aHDPuIuH2N55T58kKOwy/2+NgKbQIBnUOs9xyu9d4w2IsioazmfXEHWyIVJ7e7uVifWkmS2hRD48EOM/JWcRR0JkrHRnsqPqlAylj99HJGQGAfZEIM/mefxtepO8dRCYlSo5MM8ODjnQVBc2XJNRSm73DIOgoRAJSUfYNMi+MhzbxlvWyPQA4HaRxrIMW+dczX5aj7S9ADCPv5FoBe54UfCeStBaqxbI/CSCFA05EoxFwm6pmKMAmHWqs9oVzufXEHWHFv/fAQgsrg9fs4Hkh4+nj8DjzQCfRF4DtFBlplYW7MyQbYitgH7+FGFc7bPbMlbpIePlni2NQL/NQKQ3ar/QyoHqkaqyqky3cPUDDy+iAAVIDd43XeaJSc9fJT8WmcEXgqB2v8dYz5UjvldZOxvOTdBtqBlWyNgBGaFgAlyVrfbkzUCRqAFARNkC1q2NQJGYFYImCBndbs9WSNgBFoQMEG2oGVbI2AEZoWACXJWt9uTNQJGoAUBE2QLWrY1AkZgVgiYIGd1uz1ZI2AEWhAwQbagZVsjYARmhYAJcla325M1AkagBQETZAtatjUCRmBWCJggZ3W7PVkjYARaEPgH5FL0QDXo9fgAAAAASUVORK5CYII=\"\u003e\u003cbr\u003e\u003c/p\u003e \u003cp\u003ewhere B is the K-L plot slope, ω is the electrode rotation rate, F is the Faraday constant, D\u003csub\u003e0\u003c/sub\u003e is the O\u003csub\u003e2\u003c/sub\u003e diffusion coefficient (1.9\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e cm\u003csup\u003e2\u003c/sup\u003e/s in 0.1 M KOH), and C\u003csub\u003e0\u003c/sub\u003e is the O\u003csub\u003e2\u003c/sub\u003e concentration (1.2\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e mol/cm\u003csup\u003e3\u003c/sup\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.6 Zn-air battery testing\u003c/h2\u003e \u003cp\u003eThe anode was a 1 mm thick polished Zn plate. The 6 M KOH and 0.2 M Zn(CH\u003csub\u003e3\u003c/sub\u003eCOO)\u003csub\u003e2\u003c/sub\u003e electrolyte was used. For the cathode, 5 mg catalyst was dispersed in 500 \u0026micro;L water, 450 \u0026micro;L ethanol and 50 \u0026micro;L Nafion solution by sonication for 2 h. 200 \u0026micro;L catalyst ink was dropped on the matrix at 0.5 mg/cm\u003csup\u003e2\u003c/sup\u003e loading and air dried. A 20% Pt/C\u0026thinsp;+\u0026thinsp;RuO\u003csub\u003e2\u003c/sub\u003e cathode was fabricated identically for comparison. Polarization curves were obtained on a CHI760E. Charge-discharge cycling was performed on a Neware-CT-4008-5V10mA at 10 mA/cm\u003csup\u003e2\u003c/sup\u003e cycling between 10 min charge and 10 min discharge.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Characterizations of CoNi-N-C electrocatalyst\u003c/h2\u003e \u003cp\u003eXRD patterns of the CoNi-N-C-X and N-C-1000 samples (X\u0026thinsp;=\u0026thinsp;800, 900, 1000, 1100) are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(a). The XRD patterns are similar for all samples, with only one diffraction peak appearing at 24\u0026ndash;25\u0026deg;, corresponding to the (002) plane of graphitic carbon(\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e). In the XRD results of Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(a), there is no metal peak for Co, Ni, metal peak and oxidized Co, oxidized Ni. This can preliminarily confirm that Co and Ni elements do not agglomerate into Co, Ni particles or exist in the form of other low catalytic activity compounds during high-temperature gas transport(\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e). XPS was used to study the elemental compositions and valence states of CoNi-N-C-1000 and N-C-1000. The CoNi-N-C-1000 survey spectrum (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb) shows distinct Co, Ni, N, and C peaks, confirming Co, Ni and N co-existence in the carbon fibers. Through comparison, it was found that N-C-1000 lacked Co and Ni peak. CoNi-N-C-1000 showed three main peaks at approximately 284.6 eV (C 1s), 401 eV (N 1s), and 532 eV (O 1s) along with small Co 2p peak at around 780.3 eV and Ni 2p peak at around 852.7 eV. The high-resolution spectra of C1s (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec) show the peaks of C\u0026thinsp;=\u0026thinsp;C (284.8 eV), C\u0026thinsp;=\u0026thinsp;N (285.7 eV), and C-C (286.3 eV). Four N species were identified in the N1s spectrum (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed): pyridine N (398.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3eV), M-N\u003csub\u003ex\u003c/sub\u003e (M\u0026thinsp;=\u0026thinsp;Co,Ni 400.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3eV), pyrrole N (401.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3eV), and graphite N, indicating successful doping of N into the carbon substrate to promote ORR and OER(\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e). Compared with N-C-1000, additional M-N\u003csub\u003ex\u003c/sub\u003e peaks were detected in CoNi-N-C-1000, which significantly contributed to the catalytic activity of the CoNi-N-C system(\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e). The high-resolution spectrum of Co 2p (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee) shows two peaks at ~\u0026thinsp;781.3 eV and ~\u0026thinsp;796.7 eV, belonging to Co 2p3/2 and 2p1/2, respectively.The high-resolution spectrum of Ni 2p (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef) shows two peaks at ~\u0026thinsp;855.7 eV and ~\u0026thinsp;873.5 eV, belonging to Ni 2p3/2 and 2p1/2, respectively. These pieces of evidence collectively indicate that Co and Ni elements were successfully incorporated into carbon fibers. The porosity of five catalysts was studied by nitrogen adsorption/ desorption isotherms. The BET surface area of CoNi-N-C-1000 (819 m\u003csup\u003e2\u003c/sup\u003e g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) was revealed to be much larger than those for N-C-1000 (226 m\u003csup\u003e2\u003c/sup\u003e g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), CoNi-N-C-800 (373 m\u003csup\u003e2\u003c/sup\u003e g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), CoNi-N-C-900 (542 m\u003csup\u003e2\u003c/sup\u003e g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), CoNi-N-C-1100 (610 m\u003csup\u003e2\u003c/sup\u003e g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) in Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e(a). The reason why CoNi-N-C-1000 achieves a larger specific surface area under the same temperature conditions compared to N-C-1000 is due to the introduction of Co and Ni single atoms during the pyrolysis process(\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e). In CoNi-N-C-X (X\u0026thinsp;=\u0026thinsp;800, 900, 1000, 1100) catalyst, the specific surface area increases with increasing temperature. However, at a high temperature of 1100 ℃, the N-C matrix structure was destroyed and resulting in a decrease in the specific surface area(\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e). The pore size of N-C-1000, CoNi-N-C-800, CoNi-N-C-900, CoNi-N-C-1000 and CoNi-N-C-1100 in Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e(b) were 30.73 nm, 30.27 nm, 27.05 nm, 17.26 nm, 22.48 nm, respectively. A large number of microporous structures are beneficial for material transport during reactions(\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eScanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to measure the morphology of samples. As displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.(a)(b) and (c)(d), both N-C-1000 and CoNi-N-C-1000 exhibit interconnected porous network, which are made up of highly dense carbon fibers(\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e).High-resolution transmission electron microscopy (HRTEM) further investigated the microstructure and Co, Ni dispersion in CoNi-N-C-1000. Figures\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef show carbon sheets without observable nanoparticles, indicating the coexistence of amorphous carbon and graphite layers, as shown by the twisted lattice stripes in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef and the calculated lattice spacing is 0.56nm, and a smaller lattice spacing is beneficial for ion transport(\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e). The energy dispersive X-ray (EDS) spectrum shows that C, N, Co and Ni are uniformly distributed on the carbon fibers (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eg), which may indicate that the separated Co, Ni atoms are uniformly dispersed on the carbon fiber without any nanoparticle or agglomeration phenomenon.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Electrochemical performance measurement\u003c/h2\u003e \u003cp\u003eEvaluate the ORR performance of all catalysts in a 0.1M KOH solution using the Rotating Disc Electrode (RDE) technique. All potentials are measured relative to the standard hydrogen electrode (RHE). The CV of CoNi-N-C-800, CoNi-N-C-900, CoNi-N-C-1000, and CoNi-N-C-1100 under O\u003csub\u003e2\u003c/sub\u003e and N\u003csub\u003e2\u003c/sub\u003e atmospheres (Figure S2) show different oxygen reduction peaks. As shown in Figure S3, both the half wave potential and current density increase with the heating temperature reaching 1000\u0026deg;C, indicating that 1000\u0026deg;C is the optimal temperature. The ORR activity of the prepared catalyst was measured using LSV. Figure S3 shows that as the pyrolysis temperature increases from 800\u0026deg;C to 1000\u0026deg;C, the oxygen reduction performance becomes better, but when the temperature further increases to 1100\u0026deg;C, the oxygen reduction characteristics slightly decrease. This is because higher temperatures have disrupted the structure of N-C precursors. The CoNi-N-C-1000 catalyst exhibits the best electrochemical oxygen reduction catalytic performance in alkaline solutions. CoNi-N-C-1000 has a starting potential of 0.91V (E\u003csub\u003eonset\u003c/sub\u003e) and a half wave potential of 0.85V (E\u003csub\u003e1/2\u003c/sub\u003e) relative to RHE, significantly higher than N-C-1000 and comparable to 20%Pt/C at 0.838V, the current density (J) of CoNi-N-C-1000 reaches 5.5mA/cm\u003csup\u003e2\u003c/sup\u003e, which is equivalent to Pt/C (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea and \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb). Figure S4 shows that ORR polarization curves of CoNi-N-C-1000 at different rotating rates. CoNi-N-C-1000 also has a lower Tafel slope than Pt/C (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec), indicating excellent kinetics and lower overpotential at the same current density. Kouteck\u0026yacute;-Levich analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed) shows that the electron transfer number (n) of CoNi-N-C-1000 is close to 4, consistent with an ideal 4-electron ORR pathway. The rotating ring disk electrode test (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee-f) further confirms that CoNi-N-C-1000 follows the 4e\u003csup\u003e\u0026minus;\u003c/sup\u003e pathway and has a lower H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e yield, similar to Pt/C. In addition, the electrochemical impedance spectrum (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eg) during the ORR process indicates that CoNi-N-C-1000 (Rct\u0026thinsp;=\u0026thinsp;28.8) has a lower charge transfer resistance than N-C-1000 (37.4) and Pt/C (32.7), reflecting faster electron transfer kinetics(\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e). After 6000 acceleration cycles, CoNi-N-C-1000 E\u003csub\u003e1/2\u003c/sub\u003e maintained its original value, while Pt/C E\u003csub\u003e1/2\u003c/sub\u003e decreased by 10mV (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eh), CoNi-N-C-1000 demonstrating excellent ORR cycling stability.\u003c/p\u003e \u003cp\u003eIn addition to demonstrating excellent ORR performance, CoNi-N-C-1000 also exhibits excellent OER activity. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea, CoNi-N-C-1000 reaches a current density of 10 mA/cm\u003csup\u003e2\u003c/sup\u003e at 1.54 V, lower than commercial RuO\u003csub\u003e2\u003c/sub\u003e (1.58 V) and N-C-1000 (1.61 V). Tafel slopes in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb are 294.7, 313.2, and 341.3 mV/dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for CoNi-N-C-1000, RuO\u003csub\u003e2\u003c/sub\u003e, and N-C-1000, respectively, confirming the superior OER kinetics of CoNi-N-C-1000. After 6000 acceleration cycles, CoNi-N-C-1000 E\u003csub\u003e10\u003c/sub\u003e almost maintained its original value, while RuO\u003csub\u003e2\u003c/sub\u003e E\u003csub\u003e10\u003c/sub\u003e increased by 70mV (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec), CoNi-N-C-1000 also demonstrating excellent OER cycling stability. Overlaying the ORR and OER LSVs (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed) reveals CoNi-N-C-1000 has a smaller potential gap E (0.69 V) than Pt/C and RuO\u003csub\u003e2\u003c/sub\u003e (0.742 V), demonstrating that the CoNi-N-C-1000 is an excellent bifunctional catalyst.\u003c/p\u003e\u003cp\u003eConsidering the excellent dual functional electrocatalytic performance of CoNi-N-C-1000, we have constructed a self-made zinc-air battery to demonstrate its feasibility in practical energy equipment. To compare the performance of single cells, traditional Pt/C\u0026thinsp;+\u0026thinsp;RuO\u003csub\u003e2\u003c/sub\u003e catalysts (with a mass ratio of Pt/C and RuO\u003csub\u003e2\u003c/sub\u003e of 1/1) were used as air cathodes to manufacture control cells. Figure.6(a) shows the charging and discharging reaction principle of Zn-air batteries. Figure.6(b) shows that the open circuit voltage of CoNi-N-C-1000 is 1.49V higher than commercial Pt\u0026thinsp;+\u0026thinsp;RuO\u003csub\u003e2\u003c/sub\u003e (1.43V). Figure.6(c) displays the galvanodynamic behaviors of the CoNi-N-C-1000 and the mixed Pt\u0026thinsp;+\u0026thinsp;RuO\u003csub\u003e2\u003c/sub\u003e catalysts in the charge and discharge processes of Zn-air batteries. The zinc-air battery driven by CoNi-N-C-1000 provides a high power density of 128.5 mW/cm\u003csup\u003e2\u003c/sup\u003e (Figure.6d), which far exceeds the power density of Pt/C\u0026thinsp;+\u0026thinsp;RuO\u003csub\u003e2\u003c/sub\u003e (86.7 mW/cm\u003csup\u003e2\u003c/sup\u003e) catalysts. Figure.6(e) compared the long-term charge discharge cycle stability of CoNi-N-C-1000 and Pt/C\u0026thinsp;+\u0026thinsp;RuO\u003csub\u003e2\u003c/sub\u003e assembled zinc-air battery. CoNi-N-C-1000 exhibits a long-term cycle of 142.3h, indicating the stability of the CoNi-N-C-1000 catalyst. The above discussion indicates that strongly coupled CoNi-N-C-1000 catalyst can provide high efficiency and long cycle life for zinc-air battery.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eIn summary, we have successfully prepared CoNi-N-C-1000 atomic level catalysts and studied in detail the morphology, structure, and catalytic performance of CoNi-N-C-1000 catalyst materials. The synergistic combination of highly active Co, Ni monoatoms and N-C carbon aerogels enables CoNi-N-C-1000 catalyst to exhibit excellent bifunctional electrocatalytic performance for ORR and OER, which is comparable to the most advanced Pt/C or RuO\u003csub\u003e2\u003c/sub\u003e catalysts. The uniform dispersion of Co and Ni atoms in the porous carbon fiber aerogel provides additional synergistic effect to further enhance the catalytic activity and stability. In addition, the zinc-air battery driven by CoNi-N-C-1000 has a high power density of 128.5mW/cm\u003csup\u003e2\u003c/sup\u003e and can stably charge and discharge for up to 142.3 hours, which is superior to the more expensive Pt/C\u0026thinsp;+\u0026thinsp;RuO\u003csub\u003e2\u003c/sub\u003e catalyst.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eDeclaration of interests\u003c/strong\u003e\u003cbr\u003e\u0026nbsp;☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u0026nbsp;\u0026nbsp;\u003cbr\u003e\u0026nbsp;☐ The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eData Availability Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData available on request from the authors.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe data that support the findings of this study are available from the corresponding author, [author initials], upon reasonable request.\u003c/p\u003e\u003ch2\u003eFunding Statement\u003c/h2\u003e \u003cp\u003eNone.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eAuthor 1 (First Author: Zhengyu Yang): Conceptualization, Methodology, Formal Analysis, Writing - Original Draft；Author 2(Second Author: Wan Jin): Data Curation;Author 3 (Corresponding Author: Zhengyu Yang): Conceptualization, Funding Acquisition, Resources, Supervision, Writing - Review \u0026amp; Editing.\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eEthical Approval Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll studies in this article do not involve ethical issues, and the researchers strictly adhere to the journal's regulations.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eWang Y, Wang H, Wang G, Li H, Zhao Y, He W. 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Journal of Industrial and Engineering Chemistry. 2021;100:92-8.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Single-atom catalyst, Oxygen reduction reaction, Oxygen evolution reaction, Biomass aerogel, Zinc-air battery","lastPublishedDoi":"10.21203/rs.3.rs-4010883/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4010883/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eRational construction of advanced bifunctional catalysts with dual-active-sites is still challenging for both oxygen reduction (ORR) and oxygen evolution reactions (OER).The design of metal single atom catalysts prepared through high-temperature gas transport is an emerging method. The CoNi-N-C catalyst was prepared by using Co powder and Nickel foam to volatilize atomic dispersed Co,Ni element embedded in nitrogen doped cotton biomass biomass aerogel of carbon fibers in a high temperature tubular furnace in ammonia atmosphere. In this work, CoNi-N-C-1000 monoatomic catalyst was successfully synthesized by using the above method The resulting CoNi-N-C-1000 exhibited excellent bifunctional catalytic performance for ORR (E\u003csub\u003e1/2\u003c/sub\u003e=0.85V) and OER (E\u003csub\u003ej=10\u003c/sub\u003e=1.54V) in alkaline electrolytes, which can compete with previously reported bifunctional electrocatalysts. In addition, compared to the Pt/C+RuO\u003csub\u003e2\u003c/sub\u003e mixed catalyst, this bifunctional catalyst can endow the self-made zinc-air battery with better power density (128.5 mW/cm\u003csup\u003e2\u003c/sup\u003e) and cycle stability (142.3 hours), demonstrating its potential feasibility in practical applications of rechargeable zinc-air batteries.\u003c/p\u003e","manuscriptTitle":"Engineering the performance of bifunctional oxygen electrocatalysts by modulating the atomically dispersed Co,Ni on N-doped cotton biomass aerogel of carbon fiber catalysts for rechargeable zinc-air battery","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-03-12 05:23:25","doi":"10.21203/rs.3.rs-4010883/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"ff229f21-b6cb-46bf-bc90-7b2992d85e76","owner":[],"postedDate":"March 12th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-03-20T05:59:18+00:00","versionOfRecord":[],"versionCreatedAt":"2024-03-12 05:23:25","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4010883","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4010883","identity":"rs-4010883","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}