Noble-metal-free Cu-Co/f-MWCNT electrocatalyst for methanol and ethanol oxidation reactions

Noble-metal-free Cu-Co/f-MWCNT electrocatalyst for methanol and ethanol oxidation reactions | 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 Article Noble-metal-free Cu-Co/f-MWCNT electrocatalyst for methanol and ethanol oxidation reactions Biuck Habibi, Sepideh Khalili, Sara Pashazadeh, Younes Bahadori, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8058781/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 35 You are reading this latest preprint version Abstract In this study, the design and preparation of a nanohybrid electrocatalyst; Cu-Co/f-MWCNT was presented. The fabrication of present nanohybrid based electrocatalyst was carried out in two steps: firstly, the copper and cobalt nanoparticles were immobilized on/in functional multi-walled carbon nanotubes (f-MWCNT) by chemical deposition, then the Cu-Co/f-MWCNT nanohybrid was used to modified the carbon paste electrode (CPE). The Cu-Co/f-MWCNT/CPE was comprehensively investigated and confirmed using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, elemental mapping, transmission electron microscopy and electrochemical techniques. The obtained results indicate a uniform distribution of Cu-Co nanoparticles on/in the f-MWCNT structure and the formation of a nanohybrid structure with a high specific surface area and favorable electrical conductivity. The fabricated electrocatalyst; Cu-Co/f-MWCNT/CPE showed excellent electrocatalytic activity for the oxidation of methanol and ethanol in alkaline medium. Linear sweep voltammetry experiments have revealed wide linear ranges for the oxidation of methanol (0.5 to 3.0 M) and ethanol (1.0 to 3.5 M) in this condition. The outstanding performance of this system is due to the synergistic effect between Cu-Co nanoparticles in the nanohybrid structure and the high conductivity of f-MWCNT, which leads to fast electron transfer and an increase in the number of activated sites on the modified electrode surface. These results make Cu-Co/f-MWCNT/CPE a promising candidate for application in direct alcohol fuel cells. Physical sciences/Chemistry Physical sciences/Energy science and technology Physical sciences/Materials science Physical sciences/Nanoscience and technology Alcohol electrooxidation Methanol Ethanol Cu-Co nanoparticles f-MWCNT nanohybrid electrocatalyst Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 1. Introduction Humanity’s continuous reliance on fuel and energy resources has long posed a significant challenge to sustainability and environmental stability [ 1 ]. Due to the widespread consumption of fossil fuels and the increase in greenhouse gases, replacing these fuels with other energies is necessary [ 2 ]. Nanoscience researchers have studied various materials using synthetic techniques and have presented materials that have attracted attention for the production and storage of energy in fuel cells, solar cells, batteries, and supercapacitors [ 3 – 5 ]. Fuel cells such as methanol and ethanol fuel cells have gained great popularity among researchers due to the renewable nature of these fuels [ 6 – 8 ]. Direct alcohol fuel cells (DAFCs) are promising energy sources for portable electronic devices and fuel-cell electric vehicles [ 9 – 11 ]. The DAFCs is divided into two types: direct methanol fuel cells (DMFCs) and direct ethanol fuel cells (DEFCs) [ 12 – 14 ]. DAFCs has features such as simplicity in the design system, high energy density, low cost, low noise, low thermal impact, lack of toxicity, lack of risks in displacement, easy storage, and lack of pressure and high temperatures [ 15 – 17 ]. Methanol is the simplest and most electroactive organic fuel that can be produced on a large scale, with lower production cost compared to fossil fuels such as coal and natural gas [ 18 – 20 ]. The electrochemical activity of methanol is at least three times lower than that of hydrogen, while its reforming temperature (~ 200 ˚C) is significantly lower than those of other organic fuels such as natural gas and ethanol (~ 700 ˚C) [ 21 – 23 ]. Despite their advantages over other fuel cell technologies, DMFCs remain underdeveloped. A major contributing factor is the limited progress in synthesizing efficient catalyst materials for both anode and cathode electrodes, which ultimately leads to reduced overall system performance and efficiency [ 24 – 26 ]. Ethanol has been introduced as an alternative and renewable fuel higher energy content compared to some fossil fuels. Using agricultural raw materials to produce ethanol also contributes to reducing greenhouse gas emissions and supports economic growth through sustainable practices and the future of sustainable energy [ 27 – 29 ]. The interaction of ethanol with fuel cell components with fuel cell components leads to minimal interference with electrocatalytic activity and thus reduces the risk of catalyst poisoning at the anode [ 30 – 32 ]. The chemical stability and reduced catalyst poisoning during methanol and ethanol oxidation reactions contribute significantly to maintaining high electrochemical efficiency over extended operational periods [ 33 – 35 ]. Designing and manufacturing clean energy production, conversion, and storage equipment such as solar photovoltaic systems, geothermal power plants, and wind energy converters is a critical step toward achieving global sustainability goals [ 36 – 38 ]. Advancements in electrochemistry and the application of diverse electrode materials have significantly enhanced the performance of energy storage and conversion systems such as fuel cells, batteries, and supercapacitors, leading to increased research focus on this field [ 39 – 41 ]. Various materials, including carbon-based structures, conductive polymers, metal oxides, metal-organic frameworks (MOFs), layered double hydroxides (LDHs) and MXenes, are widely utilized for electrode surface engineering to improve electrochemical activity, stability, and energy storage capacity [ 42 – 44 ]. Carbon-based nanomaterials such as carbon nanotubes (CNTs), graphene, carbon black, carbon quantum dots, and fullerenes exhibit excellent electrical, thermal, and mechanical properties, making them promising candidates for application as electrode modifiers. These nanomaterials are widely utilized in fields such as electronics, energy storage, biomedical devices, environmental monitoring, and advanced composites [ 45 – 47 ]. CNTs are cylindrical nanostructures made of carbon atoms include single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). MWCNTs are formed from several nanotubes consist of multiple concentric graphene layers rolled into coaxial cylinders [ 48 – 50 ]. Core-shell structured multi-walled carbon nanotubes (MWCNTs), often combined with metal nanoparticles, demonstrate enhanced electrocatalytic performance. These Core-Shell architectures consist of an inner core material encapsulated by an outer shell layer that provides protection and enhances catalytic activity [ 51 – 53 ]. Modifying the structural and electronic properties as well as the surface morphology of these nanomaterials can significantly enhance their catalytic activity, stability, and selectivity, surpassing the performance of conventional single-component catalysts [ 54 – 56 ]. The rational design and synthesis of composite materials such as metal/metal oxides, bimetallic core-shell architectures, and multifunctional nanocomposites offer enhanced electrocatalytic performance by addressing the limitations of conventional single-component catalysts in electrochemical reaction systems [ 57 – 59 ]. In this work, Cu-Co nanoparticles with f-MWCNTs as nanohybrid was used as modifier for the first time. Carbon paste electrode (CPE) modified with Cu-Co/f-MWCNTs (Cu-Co@f-MWCNT/CPE) is investigated as an electrocatalyst for the electrooxidation of methanol and ethanol in an alkaline medium. The physiochemical characterization of the synthesized material and modified electrode were studied step by step using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), elemental mapping, transmission electron microscopy (TEM) and electrochemical techniques. The electrocatalytic activity, stability, and reproducibility in the electrooxidation reactions of methanol and ethanol were investigated by electrochemical techniques including cyclic voltammetry (CV), linear sweep voltammetry (LSV) and chronoamperometry (CA). The experimental results showed that Cu-Co/f-MWCNT/CPE) exhibits excellent performance in the electrocatalytic oxidation of methanol and ethanol in alkaline media. 2. Experimental 2.1. Materials This study used the chemicals: sodium hydroxide (NaOH), ethanol (C 2 H 6 OH), methanol (CH 3 OH), cobalt (II) chloride hexahydrate (CoCl 2 .6H 2 O), copper (II) chloride dihydrate (CuCl 2 .6H 2 O), citric acid (C 6 H 8 O 7 ), sodium borohydride (NaBH 4 ), nitric acid (HNO 3 ), potassium chloride (KCl), potassium ferricyanide (K 3 [Fe(CN) 6 ]) and graphite powder were all purchased from Sigma Aldrich company with a purity of more than 99% and used without further purification. Multi-walled carbon nanotubes (MWCNT) with a 95% purity (10–20 nm) and 1µm length were purchased from Nanolab (Brighton, MA, USA). Double-distilled water served as the solvent in all stages of the experiment. 2.2. Instruments and apparatus Electrochemical investigations were conducted using a conventional three-electrode cell system, incorporating a carbon paste or modified carbon paste electrode (2 mm diameter) as the working electrode, a platinum wire as the auxiliary electrode, and an Ag/AgCl (3 M KCl) electrode as the reference electrode. The electrochemical measurements were carried out at room temperature (≈ 25˚C) using a computer-controlled electrochemical workstation (Atom lab potentiostat/galvanostat, Atom lab. Co., Esfahan, I.R. Iran) and data processing software. The physicochemical characterization of the synthesized materials and modified electrodes was carried out using various analytical techniques. Surface morphology and elemental composition were determined by scanning electron microscopy and energy-dispersive X-ray spectroscopy on a TESCAN MIRA3 instrument. Crystallographic information was collected by X-ray diffraction using a Bruker D8 Advance diffractometer with Cu K α radiation having a wavelength of 0.15406 nm. Transmission electron microscopy analysis was carried out on PHILIPS-CM 200 electron microscope with operating voltages of 20 – 200 kV and resolution of 2.4 Å. Microsoft Excel (Version 2021) was employed for data analysis and plotting. Experimental procedures were maintained under regular ambient laboratory conditions. 2.3. Synthesis of Cu-Co/f-MWCNT nanohybrid and preparation of modified electrode 2.3.1. Synthesis of Cu-Co/f-MWCNT For the preparation of functional multi-walled carbon nanotubes (f-MWCNT), the MWCNT were dissolved in the mixture of concentrated H 2 SO 4 and HNO 3 (3:1, v/v), and refluxed for about 5 h to obtain carboxylated MWCNT (f-MWCNT). The resulted f-MWCNT was separated by centrifugation (6000 rpm) and washed with double distilled water until the pH of the resulted f-MWCNT solution became neutral. Then, the Cu-Co/f-MWCNT nanohybrid was prepared by the following process: the f-MWCNTs (1.0 mg mL − 1 ) in a flask were dispersed in an ultrasonic bath (40 kHz) for about 3 min and then the 10 mL of 30 mM CuCl 2 .6H 2 O and 30 mM CoCl 2 .6H 2 O solution was added and stirred for 30 min at room temperature using a stirrer. Then, the solution of 30 mM sodium borohydride (NaBH 4 ) was added dropwise to the solution for 1 h. Finally, the solution of 4.5 M citric acid solution was added to the solution and stirred for 2 h. The final solution was centrifuged and washed with ethanol and double-distilled water (50/50). The obtained precipitate, Cu-Co/f-MWCNT was placed in an oven at 60 ˚C for 1 h. For the synthesis of Cu/f-MWCNT and Co/f-MWCNT, the above process was repeated only with one ion metal solution: 10 mL of 30 mM CuCl 2 .6H 2 O for Cu/f-MWCNT and 10 mL of 30 mM CoCl 2 .6H 2 O solution, while other solutions and concentrations as the same as above. 2.3.2. Preparation of CPE and modified CPE To prepare the electrode, carbon graphite paste (CPE) was mixed with paraffin oil in a ratio of 75:25 (w/w). The prepared paste was molded into a polyethylene syringe with a diameter of 2 mm. For the preparation modified electrode, first, 0.1 g of graphite powder was mixed with 0.01 g of modifier (Cu-Co/f-MWCNT) to obtain uniform particles. Then, paraffin oil was added to a uniform mixture, and a paste state was created. After that, the mixture was molded into a polyethylene tube. The surface of Cu-Co/f-MWCNT/CPE was polished and then used as a working electrode. A copper wire was connected to prepared electrodes for an electrical connection between the electrode and the source of the potential application. The surface of the prepared electrodes was polished on a piece of paper before being used as a working electrode. To clean the electrode surface, it was thoroughly washed with double-distilled water. For the preparation of Cu/f-MWCNT/CPE and Co/f-MWCNT/CPE, the Cu/f-MWCNT and Co/f-MWCNT were as modifiers. 3. Results and discussion 3.1. Physicochemical characterization of Cu-Co/f-MWCNT nanohybrid SEM was used to characterize the surface morphology of the nanohybrid martials. The surface morphology of the f-MWCNT and Cu-Co/f-MWCNT are shown in Fig. 1A-B. The SEM images presented here clearly show the structural changes of the samples from raw carbon nanotubes to metallic and bimetallic nanoparticles on/in the f-MWCNT structure. Image (A) shows the surface structure of f-MWCNTs, which have a tubular morphology, uniform diameter, and relatively smooth surface. In image (B), after adding Cu-Co nanoparticles, larger particles with higher contrast are seen, indicating the formation of Cu-Co nanoparticles on/in the f-MWCNT substrate. The increase in the thickness of the bimetallic shell and the change in the surface morphology compared to the Cu/f-MWCNT and Co/f-MWCNT confirm the successful coating of Cu-Co nanoparticles. On the other hand, image B shows the Cu-Co/f-MWCNT nanohybrid in which Cu and Co nanoparticles are uniformly immobilized on the surface of the f-MWCNT substrate, indicating the successful synthesis and formation of the final structure with high potential for electrocatalytic applications. Elemental mapping of the Cu-Co/f-MWCNT nanohybrid reveals a coherent and engineered distribution of elements in the final structure. The observed pattern indicates that the elements are located in a targeted and spatially ordered manner on the surface and inside the nanohybrid (Fig. 2). This uniform distribution indicates proper control over the synthesis process and stability of the resulting nanohybrid. The simultaneous presence of metals along with the carbon substrate indicates the creation of a multicomponent composite with a precise structural arrangement. Such a structure can provide a suitable basis for advanced functions in the field of electrocatalysis. The EDX spectrum of the Cu-Co/f-MWCNT nanohybrid (Fig. 3A) clearly confirms the presence of Cu and Co elements. The distinct peaks of Cu and Co have appeared in their specific energy regions, indicating the successful loading of these metals on the surface of the nanotubes. Also, the presence of a peak of carbon element at about 0.27 keV is related to the f-MWCNT substrate. The absence of peaks of interfering elements or impurities indicates the proper purity of the final composition. The relative intensity of the peaks indicates the proper ratio between the two metals in the final structure. The XRD pattern of the Cu-Co/f-MWCNT nanohybrid clearly shows the presence of carbon and metal components (Fig. 3B). The sharp peak observed at 2θ ≈ 26.76° is related to the (002) bond of graphite and indicates the crystalline structure of multi-walled carbon nanotubes (f-MWCNT) in the nanohybrid matrix. The set of peaks appearing at Bragg angles of 16.65°, 28.24°, 35.43°, 41.65°, 45.97° and 49.79° can be attributed to the electrodeposition of copper, indicating the successful formation of Cu crystalline phases in the final structure. Also, the peaks observed at 21.95°, 34.34°, 38.94°, 42.53°, 49.76° and 57.87° are respectively attributable to Co-related phases, which are probably related to the mixed HCP and FCC phases of Co [ 60 ]. This peak distribution indicates the simultaneous and structured presence of the two metals in the form of nanoparticles with a well-defined crystal order. The absence of additional peaks due to impurities confirms the phase purity and the success in controlling the synthesis of the nanohybrid structure. Also, as can be seen in Fig. 4, the TEM images (A low magnification and B high magnification) of Cu-Co/f-MWCNT nanohybrid show the distinct structure of f-MWCNT decorated and covered by the Cu-Co metallic nanoparticles. These nanoparticles are visible with bright contrast around the nanotubes, confirming the formation of a uniform metallic nanoparticles structure on/in the MWCNT surface. This uniform and separable distribution of bimetallic nanoparticles indicates good control in the synthesis and successful formation of the metallic nanohybrid structure. Also, the lack of aggregation of metals and their good dispersion indicates the stability and uniformity of the final nanohybrid. These results are in complete agreement with the EDX spectrum and elemental mapping analysis of nanohybrid. 3.2. Investigation of the electrochemical performance of the Cu-Co/f-MWCNT/CPE To investigate the electrochemical behavior of the Cu-Co/f-MWCNT/CPE, the freshly prepared modified electrode was scanned for 10th cycles in the selected potential range from − 240 to 1600 mV. The obtained currents from the cyclic voltammetry for the modified electrode gradually increased from the first cycle to the 10th cycles. So that after 10 cycles (as the optimal number of potential cycles), the repeated potential cycle shows almost constant situation in the cyclic voltammogram. Surface coverage (Γ*) which is the number of redox moles per unit area of ​​the modified electrodes, can be calculated using Eq. (1). Γ * = Q/nFA (1) Where, F: Faradaic constant (96845C mol − 1 ), Γ * : coverage of redox species (mol cm − 2 ), n: number of electrons involved in the redox reaction (n = 1), and A: electrode area (cm 2 ). Where Q is obtained from the integration of the area under the anode peak from the 10th cycle. The surface coverage of the modified electrode was calculated to be about 2.08×10 − 6 mol cm − 2 at a scan rate of 100 mV s − 1 . However, for the investigating the electrochemical behavior of other electrodes; for the bare CPE (curve a), f-MWCNT/CPE (curve b), Co/f-MWCNT/CPE (curve c), Cu-Co/CPE (curve d), Cu/f-MWCNT/CPE (curve e) and Cu-Co/f-MWCNT/CPE (curve f), cyclic voltammograms were recorded in 0.1 M NaOH and shown in Fig. 5. Cyclic voltammetry shows that the bare CPE (curve a) has the lowest anodic current, which is due to its low active surface area. The addition of f-MWCNT (curve b) causes a significant increase in the current due to their high specific surface area and effective conductivity. In the Co/f-MWCNT/CPE (curve c), the presence of Co nanoparticles leads to the appearance of quasi-capacitance peaks related to the Co 2+ /Co 3+ transitions [ 61 ]. In the Cu-Co/CPE (curve d), the synergy between Cu and Co nanoparticles species improves the redox behavior, increases the active sites and increase the current. The electrochemical response of Cu/f-MWCNT/CPE (curve e) also increases significantly due to the redox activity of Cu + /Cu 2+ and Cu 2+ /Cu 3+ in alkaline medium [ 62 ]. The highest current is observed for the Cu-Co/f-MWCNT/CPE (curve f), which is due to the synergistic combination between active metals, conductive nanotube substrate, and facilitation of electron and OH⁻ ion transport. Comparison between curve d (Cu-Co/CPE) and curve f (Cu-Co/f-MWCNT/CPE) shows an increase in the current in the presence of f-MWCNT, whose presence, in addition to increasing electrical conductivity, increases the electrochemically active surface area of metal nanoparticles in the nanohybrid. These results confirm the role of the proton-electron transfer mechanism and the high potential of this nanohybrid modified electrode in electrochemical applications. 3.3. Evaluation of the electrocatalytic activity of the Cu-Co/f-MWCNT/CPE toward the oxidation of methanol and ethanol The electrocatalytic activity of the prepared modified electrode was studied using the cyclic voltammetric technique from − 0.5 to 1.6 V. Cyclic voltammograms of the unmodified CPE, f-MWCNT/CPE, Co/f-MWCNT/CPE, Cu-Co/CPE, Cu/f-MWCNT/CPE, and Cu-Co/f-MWCNT/CPE in 0.1 M sodium hydroxide solution containing 0.3 M methanol are shown in Fig. 6A. As can be seen, there is no signal for methanol electrooxidation at the bare CPE, indicating that bare CPE is inactive and clearly shows that this electrode does not show any electrocatalytic activity towards methanol oxidation without modification. As can be seen for the f-MWCNT/CPE a minor electrocatalytic property is observed, indicating low electrocatalytic activity of f-MWCNT toward methanol oxidation. However, other metal nanoparticles modified electrode show electrocatalytic activity towards methanol oxidation (Co/f-MWCNT/CPE, Cu-Co/CPE, Cu/f-MWCNT/CPE). For the Cu-Co/f-MWCNT/CPE, the electrooxidation peak current increased from 5808.86 µA for Cu-Co/CPE to 8998.42 µA for the Cu-Co/f-MWCNT/CPE with the presence of nanohybrid as electrocatalyst. On the other hand, for Cu-Co/f-MWCNT/CPE, the methanol oxidation reaction is strongly influenced by the presence of Cu, Co nanoparticles, and f-MWCNT doped in the nanohybrid structure, and as a result, the methanol electrooxidation current increases significantly. In the electrode modified with Cu-Co nanoparticles, the methanol oxidation reaction starts simultaneously with the formation of Cu/Cu(OH) 2 and Co/Co(OH) 2 on the electrode surface [ 63 ]. The anodic peak potential of methanol oxidation at the modified electrode is much more positive than the potential for the conversion of Cu + to Cu + 2 and Co 2+ to Co 3+ in the absence of methanol, and it also has a higher anodic current, which may be due to the increase in electron conductivity due to the presence of f-MWCNT and the electrocatalytic properties of Cu-Co nanoparticles. From the point of peak potential and also the onset potential of methanol oxidation at the surface of Cu-Co/f-MWCNT/CPE are lower than that of the other modified electrodes. The electrochemical parameters for methanol oxidation at the modified electrodes surface are listed in Table 1. Figure 6B shows the cyclic voltammograms of bare CPE (curve a), f-MWCNT/CPE (curve b), Co/f-MWCNT/CPE (curve c), Cu-Co/CPE (curve d), Cu/f-MWCNT/CPE (curve e) and Cu-Co/f-MWCNT/CPE (curve f) in the presence of 0.3 M ethanol. As expected, the bare CPE lacks any electrochemical response for ethanol oxidation and therefore has no electrocatalytic activity. In contrast, the electrodes containing Cu, Co and Cu-Co metal nanoparticles, especially in the presence of f-MWCNT, show favorable electrocatalytic activity, indicating the effective role of these components in the facilitating the of ethanol oxidation process. For the Cu-Co/f-MWCNT/CPE, the electrooxidation peak current increased from 3982.63 µA for the Co/f-MWCNTC/CPE to 8251.13 µA with the presence of Cu atoms as electrocatalyst; Cu/f-MWCNTC/CPE. With the presence of f-MWCNT as the electrocatalyst support, it increased from 4679.09 µA for Cu-Co/CPE to 13.8251 µA in Cu-Co/f-MWCNT/CPE. In the Cu-Co/f-MWCNT/CPE, a significant increase in the anodic current due to ethanol oxidation is observed, indicating high electrocatalytic activity and synergistic behavior of its components. This performance improvement can be attributed to the simultaneous presence of Co and Cu metal nanoparticles in the nanohybrid structure and conductive substrate of f-MWCNT. In this system, the proposed mechanism is based on the formation of stable hydroxymetal species such as Cu(OH) 2 and Co(OH) 2 on the electrode surface, which, by facilitating electron transfer and effective absorption of ethanol species, cause the oxidation process to start at lower potentials and higher anodic currents [ 64 ]. Also, the shift of the oxidation peak potential to more positive regions compared to the equilibrium oxidation potentials of metal ions confirms the active interaction of metals with ethanol molecules. f-MWCNT also plays a key role in improving the electrochemical performance of nanohybrid by increasing the effective surface area, electrical conductivity, and uniform distribution of metal nanoparticles [ 65 ]. The results show that the peak current of ethanol oxidation in Cu/f-MWCNT/CPE and Cu-Co/f-MWCNT/CPE are significantly higher than that of Cu-Co/CPE without f-MWCNT, which indicates the effective role of f-MWCNT in improving charge transfer and expanding the active surface area. Also, the decrease in the onset potential and peak potential of ethanol oxidation at the Co/f-MWCNT/CPE and Cu-Co/f-MWCNT/CPE compared to Cu-Co/CPE indicates the facilitation of the electrocatalytic process due to the presence of optimized nanostructures. Among them, Co/f-MWCNT/CPE has the lowest values ​​of onset potential and peak potential, which can be due to the high intrinsic activity of cobalt in the ethanol oxidation reaction. The performance of different electrodes in the electrochemical oxidation of ethanol was investigated based on three key parameters including onset potential, anodic peak potential and anodic peak current. The results show that the Cu-Co/f-MWCNT/CPE initiates the oxidation reaction at a lower potential (about 569 mV) than Cu-Co/CPE and also provides the maximum current at a lower potential. Also, the anodic peak current is higher in the presence of f-MWCNT, indicating more efficient charge transfer and increased electrochemical active surface area. This improvement can be attributed to the synergistic role between metal nanoparticles and the conductive and diffusive role of f-MWCNT. 3.4. Evaluation and optimal setting of operating conditions to improve the electrocatalytic activity of the Cu-Co/f-MWCNT/CPE 3.4.1. Supporting electrolyte concertation To achieve optimal performance in electrocatalytic oxidation reactions of methanol and ethanol, the presence of a suitable concentration of supporting electrolyte in the test solution is essential. The supporting electrolyte facilitates the passage of electric current and improves the transport of ions by increasing the conductivity of the solution and reducing the ohmic resistance [ 66 ]. Also, increasing the ionic strength of the solution helps to better dissolve the reactant species and provides more favorable conditions for the reaction. In this study, the effect of sodium hydroxide (NaOH) concentration as a supporting electrolyte, in the range of 0.01 to 0.25 M, on the anodic peak current of methanol (Fig. 7A) and ethanol (Fig. 7B) oxidation reactions at the Cu-Co/f-MWCNT/CPE was investigated. The results showed that by increasing the NaOH concentration to 0.1 M, the anodic current for methanol (inset of Fig. 7A) and ethanol (inset of Fig. 7B) increase due to the reduction of ohmic resistance and improvement of ion separation, but an excessive increase in the concentration causes a decrease in ion separation and a decrease in the conductivity of the solution, which leads to a decrease in the anodic current. Also, for further investigating the effect of the concentration of the supporting electrolyte at different concentrations, in addition to investigating the effect of its concentration on the anodic peak current of methanol and ethanol oxidation reactions in the cyclic voltammetry method, Tafel analysis was performed at different concentrations of the supporting electrolyte at a scan rate of 5 mV/s in the same method. The results for five concentrations are shown in Fig. 7 for methanol (7A) and ethanol (7B). As can be seen, the lowest Tafel slope for both fuels were observed at the concentration of 0.1 M NaOH. In Tafel analysis, a low Tafel slope signifies efficient electrocatalysis, indicating that a small increase in overpotential is required to achieve a large increase in observed anodic currents, thus reflecting faster interfacial kinetics and a highly active catalyst. On the other hand, the obtained results indicate the high kinetics and high anodic currents at the 0.1 M concentration of NaOH. Therefore, 0.1 M NaOH concentration was identified as the optimum point in both methanol and ethanol oxidation reactions. 3.4.2. Amount of modifier material The electrocatalytic performance of the Cu-Co/f-MWCNT/CPE directly depends on the loading the amount of modifier material in the modified electrode structure. In order to determine the optimal composition and achieve the highest electrocatalytic efficiency in the oxidation reaction of alcohols, the effect of different amounts of nanohybrid in the weight range of 5 to 40% relative to graphite (W/W) was investigated. For this purpose, modified electrodes were prepared with a combination of 0.150 g of graphite powder and different amounts of Cu-Co/f-MWCNT nanohybrid and tested in solutions containing 0.3 M methanol and ethanol. The results of the cyclic voltammograms showed that with an increase in the percentage of nanocomposite to about 21% by weight, the anodic peak current increases. This increase indicates an improvement in the number of active sites and an increase in the effective catalytic surface area. However, after this amount, further increase of the modifier (up to 40%) caused a significant decrease in the electrocatalytic performance. This performance loss can be attributed to reasons such as the decrease in the conductivity of graphite powder in the electrode structure and excessive coverage of the active centers, which prevents the access of reactive species to the active surface. Finally, 21 wt% of the Cu-Co/f-MWCNT nanohybrid was selected as the optimal composition to achieve the highest electrocatalytic performance in the oxidation reaction of methanol and ethanol and was used in the following experiments. 3.4.3. Effect of methanol and ethanol concentration One of the important characteristics of an ideal electrocatalyst for fuel oxidation is a linear response and the ability to absorb the maximum amount of fuel to produce the maximum anodic peak current. To investigate the effect of methanol and ethanol concentrations on the anodic peak current generated in the Cu-Co/f-MWCNT/CPE nanocomposite, linear sweep voltammetry (LSV) experiments were performed under optimal conditions. The results of LSV showed that the anodic current density increases significantly with increasing methanol (Fig. 9A) concentration in the range of 0.25 to 1.0 M (inset of Fig. 9A) and the response of the electrocatalyst in this range is completely linear. This linear response indicates the sensitive and reliable performance of the nanocomposite in sensing methanol concentration. Also, for ethanol (Fig. 9B) in the range of 0.25 to 1.0 M (inset Fig. 9B), it was observed that the anodic current density also increases linearly with increasing ethanol concentration. This feature indicates the stability and reliability of Cu-Co/f-MWCNT/CPE over a wide range of alcohol fuel concentrations. The plots of anode peak current density versus different methanol and ethanol concentrations also confirm the linearity of the electrocatalyst response in these ranges. These features indicate that our nanocomposite is capable of analyzing a wide range of alcohol fuel concentrations accurately and with high sensitivity. In addition, the linearity of the electrode response in these ranges makes this electrode easily applicable in electrochemical sensors and high-performance fuel cells. Therefore, the Cu-Co/f-MWCNT/CPE nanocomposite is a suitable choice for applications related to the oxidation of alcohol fuels in alkaline environments and also offers remarkable performance under practical conditions. 3.4.4. Effect of potential scan rate To more accurately analyze of the kinetic behavior of the oxidation of methanol and ethanol at the surface of Cu-Co/f-MWCNT/CPE, cyclic voltammetry experiments were performed over a range of scan rates (5 to 150 mV/s) in a solution containing 0.1 M NaOH and 0.3 M of methanol (Fig. 10A and its inset) and ethanol (Fig. 10B and its inset). With increasing scan rate, it was observed that the anodic peak current increased continuously and, at the same time, the anodic peak potential shifted towards more positive values. This potential shift indicates the existence of kinetic limitations in the oxidation process of methanol and ethanol at higher rates, such that the electron transfer rate from the electrode surface does not keep pace with the increase in scan rate, leading to a delay in the reaction. Furthermore, plotting the anodic peak current intensity against the square root of the sweep rate showed an acceptable linear relationship, indicating that the methanol and ethanol oxidation reactions on the surface of the modified Cu-Co/f-MWCNT/CPE are controlled by a diffusion-type mass transfer process. In other words, the rate of transfer of reactant species from the bulk solution to the electrode surface is the dominant factor in determining the overall reaction rate, and not simply surface electron exchange. These results confirm the appropriate efficiency of this nanocomposite in facilitating electrocatalytic processes under different kinetic conditions. 3.5. Investigating the charge transfer mechanism and determining the number of effective electrons through Tafel analysis To better understand the kinetic behavior of the electrooxidation process of methanol and ethanol and to determine the number of electrons participating in the rate-determining step, Tafel analysis was used. The Tafel diagram, which examines the relationship between current density and applied overpotential, can be obtained by plotting the potential graph in terms of log I (in the ascending part of the voltammogram with a low sweep rate (here 5 mV/s)) and using the slope of this graph, the number of electrons involved in the rate-determining step can be obtained according to the following equation [ 66 ]: $$\:\left(\frac{I}{{I}_{0}}\right)log\frac{2.303RT}{\alpha\:nF}=\eta\:$$ In this relation, R is the gas constant, F is the Faraday number, T is the temperature in Kelvin, α is the reaction charge transfer coefficient, I 0 is the exchange current, n is the number of electrons transferred in the rate-determining step, and η is the overpotential. By analyzing the Tofel diagrams for alkaline solutions containing 0.3 M methanol and ethanol, slopes of about 112 and 92.1 mV/decade were obtained for methanol (Fig. 11A) and ethanol oxidation (Fig. 11B), respectively. Using the Tafel equation and assuming a charge transfer coefficient of α = 0.5, the value of nα for both fuels was calculated to be approximately equal to 1.04 and 1.28 for methanol and ethanol, respectively. This value indicates that the rate-determining step in these processes is probably accompanied by the transfer of one electron. Also, the exchange current density (I 0 ) for methanol and ethanol was calculated to be about 2.28×10 − 8 and 5.87×10 − 8 Acm − 2 , respectively, indicating the suitable electrocatalytic activity of the modified electrode in alkaline medium. The electrooxidation process of methanol and ethanol in alkaline medium is carried out through metal oxyhydroxide (MOOH) intermediates. These species are first generated from the reaction of OH⁻ ions with active metal species (Cu and Co) on the electrode surface and then participate in the reaction with the fuel (methanol or ethanol). In other words, in an alkaline environment, hydroxide ions ( OH − ) react with metal hydroxides (such as Cu(OH) and Co(OH)) and convert them into higher valence metal oxyhydroxy species such as CuOOH and CoOOH: Step I = Formation of the active metal intermediate: $$\:Cu,\:Co={e}^{-}\:\left(M+{H}_{2}O+MOOH\rightleftharpoons\:\:{OH}^{-}+2M(OH\right)2)$$ These oxyhydroxy species (MOOH) act as strong oxidants and react with alcohols. During this reaction, the alcohol is oxidized and the metal species returns to its original state, M(OH): Step II = Reaction with methanol and ethanol: \(\:M\left(OH\right)2+{HCOO}^{-}+2{e}^{-}+\:2{H}_{2}O\rightleftharpoons\:MOOH+{CH}_{3}OH\:\:\:\:\:\:\:\:\:\:\:\) for methanol \(\:M\left(OH\right)2+{{CH}_{3}OO}^{-}+2{e}^{-}+\:2{H}_{2}O\rightleftharpoons\:MOOH+{{C}_{2}H}_{5}OH\:\:\:\:\:\:\:\:\:\:\:\) for ethanol In general: $$\:M\left(OH\right)2+Products\to\:MOOH+{CH}_{3}OH/{C}_{2}{H}_{5}OH$$ In this mechanism, oxidizing intermediate species such as CuOOH and CoOOH react with methanol or ethanol and lead to their oxidation, while themselves being converted to higher oxide forms such as CuO(OH). OH⁻ ions present in alkaline medium play a very important role in activating the electrode surface, because by forming active metal species, they provide the necessary conditions for initiating and accelerating oxidation reactions. This proposed pathway is consistent with previous reports in scientific literature [ 67 , 68 ] and shows that copper and cobalt nanoparticles, together with the conductive structure of f-MWCNT, play a fundamental role in improving the charge transfer process, catalytic stability and increasing the electrooxidation rate of both fuels. These factors enhance the performance of the modified Cu-Co/f-MWCNT/CPE electrode in alcohol fuel cell applications in alkaline environments. 3.6. Study of electrocatalytic oxidation of methanol and ethanol by chronoamperometry To evaluate and estimate the diffusion coefficient (D, in cm²/s) of methanol and ethanol, chronoamperometric analyses were done. These experiments were performed on the Cu-Co/f-MWCNT/CPE in 0.1 M NaOH solution and by applying a potential of 1289 mV with respect to the reference electrode. The resulting chronoamperograms for different concentrations of methanol and ethanol are shown in Fig. 12A for methanol and 12 B for ethanol. Then, the current (I) plots were plotted in terms of the inverse square root of time (t − 1/2 ). It was observed that the anodic current has a linear relationship with t − 1/2 , indicating that the mass transfer process is controlled by diffusion. Based on the Cottrell equation, the current resulting from the electrochemical reaction of the electrostatically active species is expressed as follows [ 69 ]: $$\:I=nFA{D}^{1/2}C/{\pi\:}^{1/2}{t}^{1/2}$$ in which, C is the concentration of the electroactive species in mol.cm − 3 , and D is the diffusion coefficient in cm 2 s − 1 . If for a chronoamperogram, the current changes are plotted in terms of the square root of time, the slope of the graph will be equal to nFAD 1/2 C/π 1/2 , and by knowing n, F, A, and C, the diffusion coefficient can be calculated. Given the linearity of the flow diagram in terms of t − 1/2 , the slope of this diagram is proportional to the value of the diffusion coefficient. The slopes of the lines obtained from Fig. 12 were plotted against different concentrations of methanol and ethanol (insets), and based on them, the diffusion coefficient for methanol and ethanol was calculated to be 9.36 ×10 –6 and 7.90×10 –6 cm 2 /s, respectively. 3.7. Study of the stability of electrocatalyst The stability of the Cu-Co/f-MWCNT/CPE, as one of the key factors in electrocatalytic applications, was investigated using the cyclic voltammetry technique in alkaline medium. For this purpose, the experiments were performed in 0.1 M NaOH solution containing 0.3 M methanol and ethanol. Potential scans were performed at a rate of 100 mV/s in a certain potential range. The results (anodic peak current vs scan numbers) showed that by increasing the number of potential cycles to 200 cycles, the anodic current from methanol (Fig. 13A) and ethanol oxidation (Fig. 13B) experienced only a very slight decrease (less than 5%). Also, the location of the oxidation and reduction peaks remained almost unchanged during the cycles and no significant shift in the peak voltage was observed. The stability of the anodic peak currents and the lack of change in the voltammetric behavior indicate the structural and chemical stability of the modified electrode surface in alkaline medium. The good stability of the electric current over time indicates that the Cu-Co/f-MWCNT nanohybrid is well immobilized in/on the surface of the CPE and is resistant to degradation or passivation during successive cycles. This property is very crucial for the use of this modified electrode in alcohol fuel cell systems. Overall, the cyclic voltammetric behavior shows that the modified electrode is electrocatalytically stable and reliable and can be suitable for long-term applications in alkaline environments. 4. Conclusion The Cu-Co/f-MWCNT/CPE was synthesized and investigated as a novel and efficient electrocatalyst for the oxidation of methanol and ethanol in alkaline medium. This nanohybrid was prepared by a simple method at room temperature; in fact, Cu and Co nanoparticles are well-settled on f-MWCNT. Using various techniques such as SEM, TEM, XRD and EDX, the structure and composition of nanohybrid were fully characterized and it was confirmed that the metals were uniformly dispersed on the nanotubes. This feature increases the active surface area and better charge transfer in the modified electrode. Electrochemical experiments such as cyclic voltammetry and Tafel analysis showed that the Cu-Co/f-MWCNT/CPE has significant electrocatalytic activity for the oxidation of methanol and ethanol. This modified electrode showed a significant decrease in the reaction onset potential and a significant increase in the oxidation current compared to unmodified CPE, and f-MWCNT/CPE, Co/f-MWCNT/CPE, Cu-Co/CPE, Cu/f-MWCNT/CPE. This improvement in performance is due to the synergistic effect between Cu and Co nanoparticles as well as the high conductivity of f-MWCNT, which accelerates electron transfer and creates more active sites. Chronoamperometric analyses confirmed the stability of the modified electrode in alkaline media; so that after 200 continuous cycles, the oxidation current decreased by less than 5%, indicating the high durability of the electrode. Also, Tafel analyses and calculation of diffusion coefficients showed that the oxidation process is controlled by mass transfer and the transfer of one electron plays a role in the rate-determining step. According to the results obtained, the Cu-Co/f-MWCNT/CPE can be introduced as an effective, stable and economical catalyst for application in direct methanol and ethanol fuel cells in alkaline environments. This study is an important step towards the development of advanced high-performance catalytic materials for clean and renewable energies. Declarations Funding: No Funding. Author Contribution Credit author statementBiuck Habibi: Supervision, Monitoring, Editing, Discussing and Revising.Sepideh Khalili: All practical works in lab, Visualization, Investigation, Writing- Reviewingand Editing and Data curation.Sara Pashazadeh: All practical works in lab, Visualization, Investigation, Writing- Reviewingand Editing and Data curation.Younes Bahadori: Visualization, Investigation, Writing- Reviewing and Editing and Data curation.Ali Pashazadeh: Visualization, Investigation, Writing- Reviewing and Editing and Data curation. Acknowledgments The authors gratefully acknowledge the Research Council of Azerbaijan Shahid Madani University for its financial support. Also, the authors sincerely thank the Central Laboratory of Azarbaijan Shahid Madani University for conducting the SEM and EDX experiments (Phenom ProX Desktop SEM) as part of this study. Data Availability All data generated or analysed during this study are included in this published article [and its supplementary information files]. References Aminzadeh, S., Dehghani, M. R. & Taleb, N. Energy consumption, fossil fuel dependence, and sustainability challenges in the context of climate change mitigation. J. Clean. Prod. 412 , 137589. https://doi.org/10.1016/j.jclepro.2023.137589 (2023). Duan, L., Khanna, M. & Li, X. Transitioning from Fossil Fuels to Renewable Energy: A Global Assessment of Challenges and Opportunities. Renew. Sustain. Energy Rev. 174 , 113095. https://doi.org/10.1016/j.rser.2022.113095 (2023). Singh, A. 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Rep., vol. 14, Art. no. 5222, (2024). 10.1038/s41598-024-55770-7 Tables Table 1: Electrochemical parameters of methanol electrooxidation at the different electrocatalysts. Fuel Electrocatalyst Onset Potential, E onset (mV) Peak Potential, E pf (mV) Peak Current, I pf (µA) Methanol CPE 709 1289 1696.53 Methanol f-MWCNT/CPE 696 1259 2802.69 Methanol Cu-Co/CPE 569 1299 5808.86 Methanol Co/f-MWCNT/CPE 519 1239 4176.58 Methanol Cu/f-MWCNT/CPE 549 1249 6775.80 Methanol Cu-Co/f-MWCNT/CPE 499 1249 8998.42 Table 2: Electrochemical parameters of ethanol electrooxidation at the different electrocatalysts. Fuel Electrocatalyst Onset Potential, E onset (mV) Peak Potential, E pf (mV) Peak Current, I pf (µA) Ethanol CPE 729 1309 1749.73 Ethanol f-MWCNT/CPE 709 1289 2482.67 Ethanol Cu-Co/CPE 589 1299 4679.09 Ethanol Co/f-MWCNT/CPE 509 1259 3982.63 Ethanol Cu/f-MWCNT/CPE 599 1279 6261.21 Ethanol Cu-Co/f-MWCNT/CPE 569 1269 8251.13 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 20 Nov, 2025 Reviews received at journal 20 Nov, 2025 Reviews received at journal 19 Nov, 2025 Reviewers agreed at journal 19 Nov, 2025 Reviewers agreed at journal 19 Nov, 2025 Reviews received at journal 18 Nov, 2025 Reviewers agreed at journal 18 Nov, 2025 Reviewers agreed at journal 18 Nov, 2025 Reviews received at journal 18 Nov, 2025 Reviewers agreed at journal 17 Nov, 2025 Reviewers agreed at journal 17 Nov, 2025 Reviews received at journal 17 Nov, 2025 Reviewers agreed at journal 17 Nov, 2025 Reviewers agreed at journal 17 Nov, 2025 Reviewers agreed at journal 17 Nov, 2025 Reviewers agreed at journal 17 Nov, 2025 Reviewers agreed at journal 16 Nov, 2025 Reviewers agreed at journal 16 Nov, 2025 Reviewers agreed at journal 15 Nov, 2025 Reviewers agreed at journal 15 Nov, 2025 Reviewers agreed at journal 15 Nov, 2025 Reviewers agreed at journal 14 Nov, 2025 Reviewers agreed at journal 14 Nov, 2025 Reviewers agreed at journal 14 Nov, 2025 Reviewers agreed at journal 14 Nov, 2025 Reviewers agreed at journal 14 Nov, 2025 Reviewers agreed at journal 14 Nov, 2025 Reviewers agreed at journal 14 Nov, 2025 Reviewers agreed at journal 14 Nov, 2025 Reviewers agreed at journal 14 Nov, 2025 Reviewers invited by journal 14 Nov, 2025 Editor assigned by journal 14 Nov, 2025 Editor invited by journal 14 Nov, 2025 Submission checks completed at journal 11 Nov, 2025 First submitted to journal 11 Nov, 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. 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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-8058781","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":548434094,"identity":"4b74bad7-68f4-46ed-b3da-eb87081a2893","order_by":0,"name":"Biuck Habibi","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA40lEQVRIiWNgGAWjYBACAwYeBmYGgwM8/FABHpg4YS2SDaRpYTgA1EWsw8wZeA9+Lii4I2N8/PjDz5Vtd2QMDjA//MBQcA+nFssGvmTpGQbPeMzOJCRLnm17xmNwgM1YgsGgGLfDDvAYSPMYHOYxO5BwQLKx7TDIU2ZA8QR8Wox/g7QY9z9s/gnRwv6NkBYzsC0GEslsYFv4GXjw22LZzGNmDfKLxI1nbJYN54BamHmKJRLwaDFn7zG+XfDnjj1/f/rjmw1lh+3Z2Ns3fvjwB7cWUKRgEcGjYRSMglEwCkYBEQAAG8JKltyAxWUAAAAASUVORK5CYII=","orcid":"","institution":"Azarbaijan Shahid Madani University","correspondingAuthor":true,"prefix":"","firstName":"Biuck","middleName":"","lastName":"Habibi","suffix":""},{"id":548434098,"identity":"e24126cc-2e8f-41c2-ac4c-a595975a0662","order_by":1,"name":"Sepideh Khalili","email":"","orcid":"","institution":"Azarbaijan Shahid Madani University","correspondingAuthor":false,"prefix":"","firstName":"Sepideh","middleName":"","lastName":"Khalili","suffix":""},{"id":548434100,"identity":"dc280511-ea21-4d51-b0fb-354ecf9f0847","order_by":2,"name":"Sara Pashazadeh","email":"","orcid":"","institution":"Azarbaijan Shahid Madani University","correspondingAuthor":false,"prefix":"","firstName":"Sara","middleName":"","lastName":"Pashazadeh","suffix":""},{"id":548434102,"identity":"d757a6c3-b3d4-472c-b11c-4042e12a2081","order_by":3,"name":"Younes Bahadori","email":"","orcid":"","institution":"Azarbaijan Shahid Madani University","correspondingAuthor":false,"prefix":"","firstName":"Younes","middleName":"","lastName":"Bahadori","suffix":""},{"id":548434103,"identity":"45abb792-95a9-4994-9962-171813769d8d","order_by":4,"name":"Ali Pashazadeh","email":"","orcid":"","institution":"Azarbaijan Shahid Madani University","correspondingAuthor":false,"prefix":"","firstName":"Ali","middleName":"","lastName":"Pashazadeh","suffix":""}],"badges":[],"createdAt":"2025-11-07 16:08:21","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8058781/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8058781/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":96779782,"identity":"0689d321-f3a5-4d19-b67d-e67276d34f9b","added_by":"auto","created_at":"2025-11-26 04:08:44","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":55117,"visible":true,"origin":"","legend":"","description":"","filename":"Manuscript.docx","url":"https://assets-eu.researchsquare.com/files/rs-8058781/v1/1f21d5f88d76a8f0196e3087.docx"},{"id":96779768,"identity":"65c4e556-e3fe-4d26-a997-0bbc5edb7467","added_by":"auto","created_at":"2025-11-26 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04:08:42","extension":"docx","order_by":3,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":24849,"visible":true,"origin":"","legend":"","description":"","filename":"Tablesandtheircaptions.docx","url":"https://assets-eu.researchsquare.com/files/rs-8058781/v1/2098fffd47c3ebb9de4e1d3d.docx"},{"id":96779766,"identity":"e4e14976-c174-4a5a-990f-cc3dd1311faf","added_by":"auto","created_at":"2025-11-26 04:08:41","extension":"xml","order_by":4,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":157498,"visible":true,"origin":"","legend":"","description":"","filename":"63c044b37a2048ccabb862fc31f72dc71enriched.xml","url":"https://assets-eu.researchsquare.com/files/rs-8058781/v1/88874488fe249f3b36dad4b8.xml"},{"id":96779776,"identity":"7a372ada-af55-4f4a-8b4a-adf5da3759e8","added_by":"auto","created_at":"2025-11-26 04:08:43","extension":"xml","order_by":5,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":154406,"visible":true,"origin":"","legend":"","description":"","filename":"63c044b37a2048ccabb862fc31f72dc71structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-8058781/v1/3b66e2685797504de2d50774.xml"},{"id":96779777,"identity":"02bb1b08-0a11-4ca6-bdf6-bdb9420fdf69","added_by":"auto","created_at":"2025-11-26 04:08:43","extension":"html","order_by":6,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":169544,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-8058781/v1/a80936bc56bc07961049510b.html"},{"id":96779781,"identity":"69bfeac5-71d1-416f-a8c2-9dfd08c23710","added_by":"auto","created_at":"2025-11-26 04:08:43","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":191800,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of f-MWCNT (A) and Cu-Co/f-MWCNT nanohybrid (B).\u003c/p\u003e","description":"","filename":"Figuresandtheircaptions1Copy.png","url":"https://assets-eu.researchsquare.com/files/rs-8058781/v1/a8ece13749f4a171695d6cef.png"},{"id":96779771,"identity":"bc400bad-3148-46bf-9f97-305a490363e3","added_by":"auto","created_at":"2025-11-26 04:08:42","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1235202,"visible":true,"origin":"","legend":"\u003cp\u003eSurface elemental mapping of the Cu-Co/f-MWCNT nanohybrid. Each element was indicated on maps. Final map shows the total elements distribution.\u003c/p\u003e","description":"","filename":"Figuresandtheircaptions1.png","url":"https://assets-eu.researchsquare.com/files/rs-8058781/v1/8ce0460550b9e8b9c8bac9fe.png"},{"id":96779775,"identity":"13495804-d800-4d08-b1b6-722bfb0ff039","added_by":"auto","created_at":"2025-11-26 04:08:43","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":346196,"visible":true,"origin":"","legend":"\u003cp\u003eEDX spectrum of (inset is the percent of atoms) (A) and XRD pattern of Cu-Co/f-MWCNT nanohybrid (B).\u003c/p\u003e","description":"","filename":"Figuresandtheircaptions2.png","url":"https://assets-eu.researchsquare.com/files/rs-8058781/v1/f58702ead984bb288f792881.png"},{"id":96779762,"identity":"b72de2bc-5407-4380-b2b4-d978b4e8747d","added_by":"auto","created_at":"2025-11-26 04:08:41","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":319635,"visible":true,"origin":"","legend":"\u003cp\u003eTEM images of low magnification (A) and high magnification of Cu-Co/f-MWCNT nanohybrid (B).\u003c/p\u003e","description":"","filename":"Figuresandtheircaptions3.png","url":"https://assets-eu.researchsquare.com/files/rs-8058781/v1/ed48b1f82606cf35197bace9.png"},{"id":96779774,"identity":"08f919bb-1c46-47b1-91cd-6333bb27ed70","added_by":"auto","created_at":"2025-11-26 04:08:43","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":360878,"visible":true,"origin":"","legend":"\u003cp\u003eCyclic voltammograms of bare CPE (a), f-MWCNT/CPE (b), Co/f-MWCNT/CPE (c), Cu-Co/CPE (d), Cu/f-MWCNT/CPE (e) and Cu-Co/f-MWCNT/CPE (f) with a potential scanning rate of 100 m V s\u003csup\u003e-1\u003c/sup\u003e in 0.1 M NaOH solution in the potential range of -200 to 1600 mV.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"Figuresandtheircaptions4.png","url":"https://assets-eu.researchsquare.com/files/rs-8058781/v1/794f0973c74376c97d3d3bb0.png"},{"id":96914730,"identity":"abed4a00-f99f-43c7-a138-3134d530d6de","added_by":"auto","created_at":"2025-11-27 14:06:17","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":445425,"visible":true,"origin":"","legend":"\u003cp\u003eCyclic voltammograms of the bare CPE, f-MWCNT/CPE, Co/f-MWCNT/CPE, Cu-Co/CPE, Cu/f-MWCNT/CPE, and Cu-Co/f-MWCNT/CPE with a potential scan rate of 100 m V s\u003csup\u003e-1 \u003c/sup\u003ein 0.1 M NaOH containing 0. 3 M methanol (A) and 0.3 M ethanol (B).\u003c/p\u003e","description":"","filename":"Figuresandtheircaptions5.png","url":"https://assets-eu.researchsquare.com/files/rs-8058781/v1/2bf85739e8aea407ed762bac.png"},{"id":96779763,"identity":"13612e54-048d-44fe-9764-c312213bb8ba","added_by":"auto","created_at":"2025-11-26 04:08:41","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":498519,"visible":true,"origin":"","legend":"\u003cp\u003eCyclic voltammograms of Cu-Co/f-MWCNT/CPE in 0.3 M methanol solution with varying NaOH concentrations at a scan rate of 100 mV/s (A) and inset the anodic peak current versus NaOH concentration. Cyclic voltammograms of same modified electrode in 0.3 M ethanol solution with varying NaOH concentrations at a scan rate of 100 mV/s (B) and inset the anodic peak current versus NaOH concentration.\u003c/p\u003e","description":"","filename":"Figuresandtheircaptions6.png","url":"https://assets-eu.researchsquare.com/files/rs-8058781/v1/d89dd44e4a5b9b477178cab3.png"},{"id":96916105,"identity":"66c5315b-831b-4750-8b29-876b0dabb3d3","added_by":"auto","created_at":"2025-11-27 14:08:01","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":476441,"visible":true,"origin":"","legend":"\u003cp\u003eTafel plots for the electrooxidation of 0.3 M methanol on the surface of the Cu-Co/f-MWCNT/CPE (A) and for the electrooxidation of 0.3 M ethanol in the presence of different concentrations of NaOH at a scan rate of 5 mV/s. The concentrations of NaOH were shown on the pictures.\u003c/p\u003e","description":"","filename":"Figuresandtheircaptions7.png","url":"https://assets-eu.researchsquare.com/files/rs-8058781/v1/db36b37caa263053fda2ef71.png"},{"id":96779773,"identity":"367241b3-2646-4b7d-a552-6e357c78ec35","added_by":"auto","created_at":"2025-11-26 04:08:43","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":312722,"visible":true,"origin":"","legend":"\u003cp\u003eLSV curves of Cu-Co/f-MWCNT/CPE in 0.1 M NaOH at a scan rate of 100 mV/sfor different concentrations methanol (A) (0.3-1.0 M) and ethanol (B) (0.3-1.0 M). Insets show the anodic peak current versus concentration of methanol (A) and ethanol (B).\u003c/p\u003e","description":"","filename":"Figuresandtheircaptions8.png","url":"https://assets-eu.researchsquare.com/files/rs-8058781/v1/59c7ac49516a79aaf97f553a.png"},{"id":96779759,"identity":"85bbd0cd-4bfa-4a27-a68e-1fef84d6b153","added_by":"auto","created_at":"2025-11-26 04:08:40","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":268395,"visible":true,"origin":"","legend":"\u003cp\u003eCyclic voltammograms of the oxidation of methanol (A) and ethanol (B) using the Cu-Co/f-MWCNT/CPE in 0.1 M NaOH and 0.3 M methanol and 0.3 M ethanol solutions at different scan rates from 5 to 150 mV/s. Insets: Variation of the anodic peak current as a function of the square root of the scan rate.\u003c/p\u003e","description":"","filename":"Figuresandtheircaptions9.png","url":"https://assets-eu.researchsquare.com/files/rs-8058781/v1/90e7f0612b6d504f52014046.png"},{"id":96779780,"identity":"bf847e5c-3cc7-4c2e-88d5-14f708d60910","added_by":"auto","created_at":"2025-11-26 04:08:43","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":47438,"visible":true,"origin":"","legend":"\u003cp\u003eTafel plots for the electrooxidation of methanol (A) and ethanol (B) in 0.1 M NaOH solution on the Cu-Co/f-MWCNT/CPE at a scan rate of 5 mV/s\u003c/p\u003e","description":"","filename":"Figuresandtheircaptions10.png","url":"https://assets-eu.researchsquare.com/files/rs-8058781/v1/d1f81b39509d10a9fd9e2f80.png"},{"id":96779783,"identity":"a1fac103-cf8b-455b-91d9-b7d11c87faa8","added_by":"auto","created_at":"2025-11-26 04:08:44","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":543610,"visible":true,"origin":"","legend":"\u003cp\u003eChronoamperograms of the Cu-Co/f-MWCNT/CPE in 0.1 M NaOH containing different concentrations of (A) methanol and (B) ethanol. Insets I: current vs. concentration at \u003cem\u003et\u003c/em\u003e = 10 s; Insets II: variation of the slope of I vs. \u003cem\u003et\u003c/em\u003e\u003csup\u003e-1/2 \u003c/sup\u003eplots with fuel concentration.\u003c/p\u003e","description":"","filename":"Figuresandtheircaptions11.png","url":"https://assets-eu.researchsquare.com/files/rs-8058781/v1/fb6e103aef5447529d7b03a4.png"},{"id":96779770,"identity":"d2c500ed-c62d-42af-be79-02a971cb70fd","added_by":"auto","created_at":"2025-11-26 04:08:42","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":106249,"visible":true,"origin":"","legend":"\u003cp\u003eThe anodic peak currents of cyclic voltammograms to investigate the stability of the modified Cu-Co/f-MWCNT/CPE in 0.1 M NaOH solution containing .0.3 M methanol (A) and 0.3 M ethanol (B) at a scan rate of 100 mV/s over 200 consecutive cycles.\u003c/p\u003e","description":"","filename":"Figuresandtheircaptions12.png","url":"https://assets-eu.researchsquare.com/files/rs-8058781/v1/6a133bca452d406868a64a50.png"},{"id":96922570,"identity":"a99f4534-99f1-496b-ae6e-5a14d59cec69","added_by":"auto","created_at":"2025-11-27 14:19:29","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6211302,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8058781/v1/47d1e262-0019-464a-9df7-eacfa8d3bee8.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Noble-metal-free Cu-Co/f-MWCNT electrocatalyst for methanol and ethanol oxidation reactions","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eHumanity\u0026rsquo;s continuous reliance on fuel and energy resources has long posed a significant challenge to sustainability and environmental stability [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Due to the widespread consumption of fossil fuels and the increase in greenhouse gases, replacing these fuels with other energies is necessary [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Nanoscience researchers have studied various materials using synthetic techniques and have presented materials that have attracted attention for the production and storage of energy in fuel cells, solar cells, batteries, and supercapacitors [\u003cspan additionalcitationids=\"CR4\" citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Fuel cells such as methanol and ethanol fuel cells have gained great popularity among researchers due to the renewable nature of these fuels [\u003cspan additionalcitationids=\"CR7\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Direct alcohol fuel cells (DAFCs) are promising energy sources for portable electronic devices and fuel-cell electric vehicles [\u003cspan additionalcitationids=\"CR10\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. The DAFCs is divided into two types: direct methanol fuel cells (DMFCs) and direct ethanol fuel cells (DEFCs) [\u003cspan additionalcitationids=\"CR13\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. DAFCs has features such as simplicity in the design system, high energy density, low cost, low noise, low thermal impact, lack of toxicity, lack of risks in displacement, easy storage, and lack of pressure and high temperatures [\u003cspan additionalcitationids=\"CR16\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Methanol is the simplest and most electroactive organic fuel that can be produced on a large scale, with lower production cost compared to fossil fuels such as coal and natural gas [\u003cspan additionalcitationids=\"CR19\" citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. The electrochemical activity of methanol is at least three times lower than that of hydrogen, while its reforming temperature (~\u0026thinsp;200 ˚C) is significantly lower than those of other organic fuels such as natural gas and ethanol (~\u0026thinsp;700 ˚C) [\u003cspan additionalcitationids=\"CR22\" citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Despite their advantages over other fuel cell technologies, DMFCs remain underdeveloped. A major contributing factor is the limited progress in synthesizing efficient catalyst materials for both anode and cathode electrodes, which ultimately leads to reduced overall system performance and efficiency [\u003cspan additionalcitationids=\"CR25\" citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Ethanol has been introduced as an alternative and renewable fuel higher energy content compared to some fossil fuels. Using agricultural raw materials to produce ethanol also contributes to reducing greenhouse gas emissions and supports economic growth through sustainable practices and the future of sustainable energy [\u003cspan additionalcitationids=\"CR28\" citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. The interaction of ethanol with fuel cell components with fuel cell components leads to minimal interference with electrocatalytic activity and thus reduces the risk of catalyst poisoning at the anode [\u003cspan additionalcitationids=\"CR31\" citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. The chemical stability and reduced catalyst poisoning during methanol and ethanol oxidation reactions contribute significantly to maintaining high electrochemical efficiency over extended operational periods [\u003cspan additionalcitationids=\"CR34\" citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eDesigning and manufacturing clean energy production, conversion, and storage equipment such as solar photovoltaic systems, geothermal power plants, and wind energy converters is a critical step toward achieving global sustainability goals [\u003cspan additionalcitationids=\"CR37\" citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. Advancements in electrochemistry and the application of diverse electrode materials have significantly enhanced the performance of energy storage and conversion systems such as fuel cells, batteries, and supercapacitors, leading to increased research focus on this field [\u003cspan additionalcitationids=\"CR40\" citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. Various materials, including carbon-based structures, conductive polymers, metal oxides, metal-organic frameworks (MOFs), layered double hydroxides (LDHs) and MXenes, are widely utilized for electrode surface engineering to improve electrochemical activity, stability, and energy storage capacity [\u003cspan additionalcitationids=\"CR43\" citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]. Carbon-based nanomaterials such as carbon nanotubes (CNTs), graphene, carbon black, carbon quantum dots, and fullerenes exhibit excellent electrical, thermal, and mechanical properties, making them promising candidates for application as electrode modifiers. These nanomaterials are widely utilized in fields such as electronics, energy storage, biomedical devices, environmental monitoring, and advanced composites [\u003cspan additionalcitationids=\"CR46\" citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e]. CNTs are cylindrical nanostructures made of carbon atoms include single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). MWCNTs are formed from several nanotubes consist of multiple concentric graphene layers rolled into coaxial cylinders [\u003cspan additionalcitationids=\"CR49\" citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e]. Core-shell structured multi-walled carbon nanotubes (MWCNTs), often combined with metal nanoparticles, demonstrate enhanced electrocatalytic performance. These Core-Shell architectures consist of an inner core material encapsulated by an outer shell layer that provides protection and enhances catalytic activity [\u003cspan additionalcitationids=\"CR52\" citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e]. Modifying the structural and electronic properties as well as the surface morphology of these nanomaterials can significantly enhance their catalytic activity, stability, and selectivity, surpassing the performance of conventional single-component catalysts [\u003cspan additionalcitationids=\"CR55\" citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e]. The rational design and synthesis of composite materials such as metal/metal oxides, bimetallic core-shell architectures, and multifunctional nanocomposites offer enhanced electrocatalytic performance by addressing the limitations of conventional single-component catalysts in electrochemical reaction systems [\u003cspan additionalcitationids=\"CR58\" citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eIn this work, Cu-Co nanoparticles with f-MWCNTs as nanohybrid was used as modifier for the first time. Carbon paste electrode (CPE) modified with Cu-Co/f-MWCNTs (Cu-Co@f-MWCNT/CPE) is investigated as an electrocatalyst for the electrooxidation of methanol and ethanol in an alkaline medium. The physiochemical characterization of the synthesized material and modified electrode were studied step by step using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), elemental mapping, transmission electron microscopy (TEM) and electrochemical techniques. The electrocatalytic activity, stability, and reproducibility in the electrooxidation reactions of methanol and ethanol were investigated by electrochemical techniques including cyclic voltammetry (CV), linear sweep voltammetry (LSV) and chronoamperometry (CA). The experimental results showed that Cu-Co/f-MWCNT/CPE) exhibits excellent performance in the electrocatalytic oxidation of methanol and ethanol in alkaline media.\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1. Materials\u003c/h2\u003e\u003cp\u003eThis study used the chemicals: sodium hydroxide (NaOH), ethanol (C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e6\u003c/sub\u003eOH), methanol (CH\u003csub\u003e3\u003c/sub\u003eOH), cobalt (II) chloride hexahydrate (CoCl\u003csub\u003e2\u003c/sub\u003e.6H\u003csub\u003e2\u003c/sub\u003eO), copper (II) chloride dihydrate (CuCl\u003csub\u003e2\u003c/sub\u003e.6H\u003csub\u003e2\u003c/sub\u003eO), citric acid (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e8\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e), sodium borohydride (NaBH\u003csub\u003e4\u003c/sub\u003e), nitric acid (HNO\u003csub\u003e3\u003c/sub\u003e), potassium chloride (KCl), potassium ferricyanide (K\u003csub\u003e3\u003c/sub\u003e[Fe(CN)\u003csub\u003e6\u003c/sub\u003e]) and graphite powder were all purchased from Sigma Aldrich company with a purity of more than 99% and used without further purification. Multi-walled carbon nanotubes (MWCNT) with a 95% purity (10\u0026ndash;20 nm) and 1\u0026micro;m length were purchased from Nanolab (Brighton, MA, USA). Double-distilled water served as the solvent in all stages of the experiment.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2. Instruments and apparatus\u003c/h2\u003e\u003cp\u003eElectrochemical investigations were conducted using a conventional three-electrode cell system, incorporating a carbon paste or modified carbon paste electrode (2 mm diameter) as the working electrode, a platinum wire as the auxiliary electrode, and an Ag/AgCl (3 M KCl) electrode as the reference electrode. The electrochemical measurements were carried out at room temperature (\u0026asymp;\u0026thinsp;25˚C) using a computer-controlled electrochemical workstation (Atom lab potentiostat/galvanostat, Atom lab. Co., Esfahan, I.R. Iran) and data processing software. The physicochemical characterization of the synthesized materials and modified electrodes was carried out using various analytical techniques. Surface morphology and elemental composition were determined by scanning electron microscopy and energy-dispersive X-ray spectroscopy on a TESCAN MIRA3 instrument. Crystallographic information was collected by X-ray diffraction using a Bruker D8 Advance diffractometer with Cu K\u003csub\u003eα\u003c/sub\u003e radiation having a wavelength of 0.15406 nm. Transmission electron microscopy analysis was carried out on PHILIPS-CM 200 electron microscope with operating voltages of 20\u003cem\u003e\u0026ndash;\u003c/em\u003e200 kV and resolution of 2.4 \u0026Aring;. Microsoft Excel (Version 2021) was employed for data analysis and plotting. Experimental procedures were maintained under regular ambient laboratory conditions.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3. Synthesis of Cu-Co/f-MWCNT nanohybrid and preparation of modified electrode\u003c/h2\u003e\u003cdiv id=\"Sec6\" class=\"Section3\"\u003e\u003ch2\u003e2.3.1. Synthesis of Cu-Co/f-MWCNT\u003c/h2\u003e\u003cp\u003eFor the preparation of functional multi-walled carbon nanotubes (f-MWCNT), the MWCNT were dissolved in the mixture of concentrated H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e and HNO\u003csub\u003e3\u003c/sub\u003e (3:1, v/v), and refluxed for about 5 h to obtain carboxylated MWCNT (f-MWCNT). The resulted f-MWCNT was separated by centrifugation (6000 rpm) and washed with double distilled water until the pH of the resulted f-MWCNT solution became neutral. Then, the Cu-Co/f-MWCNT nanohybrid was prepared by the following process: the f-MWCNTs (1.0 mg mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) in a flask were dispersed in an ultrasonic bath (40 kHz) for about 3 min and then the 10 mL of 30 mM CuCl\u003csub\u003e2\u003c/sub\u003e.6H\u003csub\u003e2\u003c/sub\u003eO and 30 mM CoCl\u003csub\u003e2\u003c/sub\u003e.6H\u003csub\u003e2\u003c/sub\u003eO solution was added and stirred for 30 min at room temperature using a stirrer. Then, the solution of 30 mM sodium borohydride (NaBH\u003csub\u003e4\u003c/sub\u003e) was added dropwise to the solution for 1 h. Finally, the solution of 4.5 M citric acid solution was added to the solution and stirred for 2 h. The final solution was centrifuged and washed with ethanol and double-distilled water (50/50). The obtained precipitate, Cu-Co/f-MWCNT was placed in an oven at 60 ˚C for 1 h. For the synthesis of Cu/f-MWCNT and Co/f-MWCNT, the above process was repeated only with one ion metal solution: 10 mL of 30 mM CuCl\u003csub\u003e2\u003c/sub\u003e.6H\u003csub\u003e2\u003c/sub\u003eO for Cu/f-MWCNT and 10 mL of 30 mM CoCl\u003csub\u003e2\u003c/sub\u003e.6H\u003csub\u003e2\u003c/sub\u003eO solution, while other solutions and concentrations as the same as above.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section3\"\u003e\u003ch2\u003e2.3.2. Preparation of CPE and modified CPE\u003c/h2\u003e\u003cp\u003eTo prepare the electrode, carbon graphite paste (CPE) was mixed with paraffin oil in a ratio of 75:25 (w/w). The prepared paste was molded into a polyethylene syringe with a diameter of 2 mm. For the preparation modified electrode, first, 0.1 g of graphite powder was mixed with 0.01 g of modifier (Cu-Co/f-MWCNT) to obtain uniform particles. Then, paraffin oil was added to a uniform mixture, and a paste state was created. After that, the mixture was molded into a polyethylene tube. The surface of Cu-Co/f-MWCNT/CPE was polished and then used as a working electrode. A copper wire was connected to prepared electrodes for an electrical connection between the electrode and the source of the potential application. The surface of the prepared electrodes was polished on a piece of paper before being used as a working electrode. To clean the electrode surface, it was thoroughly washed with double-distilled water. For the preparation of Cu/f-MWCNT/CPE and Co/f-MWCNT/CPE, the Cu/f-MWCNT and Co/f-MWCNT were as modifiers.\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e3.1. Physicochemical characterization of Cu-Co/f-MWCNT nanohybrid\u003c/h2\u003e\u003cp\u003eSEM was used to characterize the surface morphology of the nanohybrid martials. The surface morphology of the f-MWCNT and Cu-Co/f-MWCNT are shown in Fig.\u0026nbsp;1A-B. The SEM images presented here clearly show the structural changes of the samples from raw carbon nanotubes to metallic and bimetallic nanoparticles on/in the f-MWCNT structure. Image (A) shows the surface structure of f-MWCNTs, which have a tubular morphology, uniform diameter, and relatively smooth surface. In image (B), after adding Cu-Co nanoparticles, larger particles with higher contrast are seen, indicating the formation of Cu-Co nanoparticles on/in the f-MWCNT substrate. The increase in the thickness of the bimetallic shell and the change in the surface morphology compared to the Cu/f-MWCNT and Co/f-MWCNT confirm the successful coating of Cu-Co nanoparticles. On the other hand, image B shows the Cu-Co/f-MWCNT nanohybrid in which Cu and Co nanoparticles are uniformly immobilized on the surface of the f-MWCNT substrate, indicating the successful synthesis and formation of the final structure with high potential for electrocatalytic applications.\u003c/p\u003e\u003cp\u003eElemental mapping of the Cu-Co/f-MWCNT nanohybrid reveals a coherent and engineered distribution of elements in the final structure. The observed pattern indicates that the elements are located in a targeted and spatially ordered manner on the surface and inside the nanohybrid (Fig.\u0026nbsp;2). This uniform distribution indicates proper control over the synthesis process and stability of the resulting nanohybrid. The simultaneous presence of metals along with the carbon substrate indicates the creation of a multicomponent composite with a precise structural arrangement. Such a structure can provide a suitable basis for advanced functions in the field of electrocatalysis. The EDX spectrum of the Cu-Co/f-MWCNT nanohybrid (Fig.\u0026nbsp;3A) clearly confirms the presence of Cu and Co elements. The distinct peaks of Cu and Co have appeared in their specific energy regions, indicating the successful loading of these metals on the surface of the nanotubes. Also, the presence of a peak of carbon element at about 0.27 keV is related to the f-MWCNT substrate. The absence of peaks of interfering elements or impurities indicates the proper purity of the final composition. The relative intensity of the peaks indicates the proper ratio between the two metals in the final structure.\u003c/p\u003e\u003cp\u003eThe XRD pattern of the Cu-Co/f-MWCNT nanohybrid clearly shows the presence of carbon and metal components (Fig.\u0026nbsp;3B). The sharp peak observed at 2θ\u0026thinsp;\u0026asymp;\u0026thinsp;26.76\u0026deg; is related to the (002) bond of graphite and indicates the crystalline structure of multi-walled carbon nanotubes (f-MWCNT) in the nanohybrid matrix. The set of peaks appearing at Bragg angles of 16.65\u0026deg;, 28.24\u0026deg;, 35.43\u0026deg;, 41.65\u0026deg;, 45.97\u0026deg; and 49.79\u0026deg; can be attributed to the electrodeposition of copper, indicating the successful formation of Cu crystalline phases in the final structure. Also, the peaks observed at 21.95\u0026deg;, 34.34\u0026deg;, 38.94\u0026deg;, 42.53\u0026deg;, 49.76\u0026deg; and 57.87\u0026deg; are respectively attributable to Co-related phases, which are probably related to the mixed HCP and FCC phases of Co [\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e]. This peak distribution indicates the simultaneous and structured presence of the two metals in the form of nanoparticles with a well-defined crystal order. The absence of additional peaks due to impurities confirms the phase purity and the success in controlling the synthesis of the nanohybrid structure.\u003c/p\u003e\u003cp\u003eAlso, as can be seen in Fig.\u0026nbsp;4, the TEM images (A low magnification and B high magnification) of Cu-Co/f-MWCNT nanohybrid show the distinct structure of f-MWCNT decorated and covered by the Cu-Co metallic nanoparticles. These nanoparticles are visible with bright contrast around the nanotubes, confirming the formation of a uniform metallic nanoparticles structure on/in the MWCNT surface. This uniform and separable distribution of bimetallic nanoparticles indicates good control in the synthesis and successful formation of the metallic nanohybrid structure. Also, the lack of aggregation of metals and their good dispersion indicates the stability and uniformity of the final nanohybrid. These results are in complete agreement with the EDX spectrum and elemental mapping analysis of nanohybrid.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003e3.2. Investigation of the electrochemical performance of the Cu-Co/f-MWCNT/CPE\u003c/h2\u003e\u003cp\u003eTo investigate the electrochemical behavior of the Cu-Co/f-MWCNT/CPE, the freshly prepared modified electrode was scanned for 10th cycles in the selected potential range from \u0026minus;\u0026thinsp;240 to 1600 mV. The obtained currents from the cyclic voltammetry for the modified electrode gradually increased from the first cycle to the 10th cycles. So that after 10 cycles (as the optimal number of potential cycles), the repeated potential cycle shows almost constant situation in the cyclic voltammogram. Surface coverage (Γ*) which is the number of redox moles per unit area of ​​the modified electrodes, can be calculated using Eq.\u0026nbsp;(1).\u003c/p\u003e\u003cp\u003eΓ\u003csup\u003e*\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;Q/nFA (1)\u003c/p\u003e\u003cp\u003eWhere, F: Faradaic constant (96845C mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), Γ\u003csup\u003e*\u003c/sup\u003e: coverage of redox species (mol cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e), n: number of electrons involved in the redox reaction (n\u0026thinsp;=\u0026thinsp;1), and A: electrode area (cm\u003csup\u003e2\u003c/sup\u003e). Where Q is obtained from the integration of the area under the anode peak from the 10th cycle. The surface coverage of the modified electrode was calculated to be about 2.08\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e mol cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e at a scan rate of 100 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. However, for the investigating the electrochemical behavior of other electrodes; for the bare CPE (curve a), f-MWCNT/CPE (curve b), Co/f-MWCNT/CPE (curve c), Cu-Co/CPE (curve d), Cu/f-MWCNT/CPE (curve e) and Cu-Co/f-MWCNT/CPE (curve f), cyclic voltammograms were recorded in 0.1 M NaOH and shown in Fig.\u0026nbsp;5. Cyclic voltammetry shows that the bare CPE (curve a) has the lowest anodic current, which is due to its low active surface area. The addition of f-MWCNT (curve b) causes a significant increase in the current due to their high specific surface area and effective conductivity. In the Co/f-MWCNT/CPE (curve c), the presence of Co nanoparticles leads to the appearance of quasi-capacitance peaks related to the Co\u003csup\u003e2+\u003c/sup\u003e/Co\u003csup\u003e3+\u003c/sup\u003e transitions [\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e]. In the Cu-Co/CPE (curve d), the synergy between Cu and Co nanoparticles species improves the redox behavior, increases the active sites and increase the current. The electrochemical response of Cu/f-MWCNT/CPE (curve e) also increases significantly due to the redox activity of Cu\u003csup\u003e+\u003c/sup\u003e/Cu\u003csup\u003e2+\u003c/sup\u003e and Cu\u003csup\u003e2+\u003c/sup\u003e/Cu\u003csup\u003e3+\u003c/sup\u003e in alkaline medium [\u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e]. The highest current is observed for the Cu-Co/f-MWCNT/CPE (curve f), which is due to the synergistic combination between active metals, conductive nanotube substrate, and facilitation of electron and OH⁻ ion transport. Comparison between curve d (Cu-Co/CPE) and curve f (Cu-Co/f-MWCNT/CPE) shows an increase in the current in the presence of f-MWCNT, whose presence, in addition to increasing electrical conductivity, increases the electrochemically active surface area of metal nanoparticles in the nanohybrid. These results confirm the role of the proton-electron transfer mechanism and the high potential of this nanohybrid modified electrode in electrochemical applications.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003e3.3. Evaluation of the electrocatalytic activity of the Cu-Co/f-MWCNT/CPE toward the oxidation of methanol and ethanol\u003c/h2\u003e\u003cp\u003eThe electrocatalytic activity of the prepared modified electrode was studied using the cyclic voltammetric technique from \u0026minus;\u0026thinsp;0.5 to 1.6 V. Cyclic voltammograms of the unmodified CPE, f-MWCNT/CPE, Co/f-MWCNT/CPE, Cu-Co/CPE, Cu/f-MWCNT/CPE, and Cu-Co/f-MWCNT/CPE in 0.1 M sodium hydroxide solution containing 0.3 M methanol are shown in Fig.\u0026nbsp;6A. As can be seen, there is no signal for methanol electrooxidation at the bare CPE, indicating that bare CPE is inactive and clearly shows that this electrode does not show any electrocatalytic activity towards methanol oxidation without modification. As can be seen for the f-MWCNT/CPE a minor electrocatalytic property is observed, indicating low electrocatalytic activity of f-MWCNT toward methanol oxidation. However, other metal nanoparticles modified electrode show electrocatalytic activity towards methanol oxidation (Co/f-MWCNT/CPE, Cu-Co/CPE, Cu/f-MWCNT/CPE). For the Cu-Co/f-MWCNT/CPE, the electrooxidation peak current increased from 5808.86 \u0026micro;A for Cu-Co/CPE to 8998.42 \u0026micro;A for the Cu-Co/f-MWCNT/CPE with the presence of nanohybrid as electrocatalyst. On the other hand, for Cu-Co/f-MWCNT/CPE, the methanol oxidation reaction is strongly influenced by the presence of Cu, Co nanoparticles, and f-MWCNT doped in the nanohybrid structure, and as a result, the methanol electrooxidation current increases significantly. In the electrode modified with Cu-Co nanoparticles, the methanol oxidation reaction starts simultaneously with the formation of Cu/Cu(OH)\u003csub\u003e2\u003c/sub\u003e and Co/Co(OH)\u003csub\u003e2\u003c/sub\u003e on the electrode surface [\u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e63\u003c/span\u003e]. The anodic peak potential of methanol oxidation at the modified electrode is much more positive than the potential for the conversion of Cu\u003csup\u003e+\u003c/sup\u003e to Cu\u003csup\u003e+\u0026thinsp;2\u003c/sup\u003e and Co\u003csup\u003e2+\u003c/sup\u003e to Co\u003csup\u003e3+\u003c/sup\u003e in the absence of methanol, and it also has a higher anodic current, which may be due to the increase in electron conductivity due to the presence of f-MWCNT and the electrocatalytic properties of Cu-Co nanoparticles. From the point of peak potential and also the onset potential of methanol oxidation at the surface of Cu-Co/f-MWCNT/CPE are lower than that of the other modified electrodes. The electrochemical parameters for methanol oxidation at the modified electrodes surface are listed in Table\u0026nbsp;1.\u003c/p\u003e\u003cp\u003eFigure\u0026nbsp;6B shows the cyclic voltammograms of bare CPE (curve a), f-MWCNT/CPE (curve b), Co/f-MWCNT/CPE (curve c), Cu-Co/CPE (curve d), Cu/f-MWCNT/CPE (curve e) and Cu-Co/f-MWCNT/CPE (curve f) in the presence of 0.3 M ethanol. As expected, the bare CPE lacks any electrochemical response for ethanol oxidation and therefore has no electrocatalytic activity. In contrast, the electrodes containing Cu, Co and Cu-Co metal nanoparticles, especially in the presence of f-MWCNT, show favorable electrocatalytic activity, indicating the effective role of these components in the facilitating the of ethanol oxidation process. For the Cu-Co/f-MWCNT/CPE, the electrooxidation peak current increased from 3982.63 \u0026micro;A for the Co/f-MWCNTC/CPE to 8251.13 \u0026micro;A with the presence of Cu atoms as electrocatalyst; Cu/f-MWCNTC/CPE. With the presence of f-MWCNT as the electrocatalyst support, it increased from 4679.09 \u0026micro;A for Cu-Co/CPE to 13.8251 \u0026micro;A in Cu-Co/f-MWCNT/CPE. In the Cu-Co/f-MWCNT/CPE, a significant increase in the anodic current due to ethanol oxidation is observed, indicating high electrocatalytic activity and synergistic behavior of its components. This performance improvement can be attributed to the simultaneous presence of Co and Cu metal nanoparticles in the nanohybrid structure and conductive substrate of f-MWCNT. In this system, the proposed mechanism is based on the formation of stable hydroxymetal species such as Cu(OH)\u003csub\u003e2\u003c/sub\u003e and Co(OH)\u003csub\u003e2\u003c/sub\u003e on the electrode surface, which, by facilitating electron transfer and effective absorption of ethanol species, cause the oxidation process to start at lower potentials and higher anodic currents [\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e]. Also, the shift of the oxidation peak potential to more positive regions compared to the equilibrium oxidation potentials of metal ions confirms the active interaction of metals with ethanol molecules. f-MWCNT also plays a key role in improving the electrochemical performance of nanohybrid by increasing the effective surface area, electrical conductivity, and uniform distribution of metal nanoparticles [\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e]. The results show that the peak current of ethanol oxidation in Cu/f-MWCNT/CPE and Cu-Co/f-MWCNT/CPE are significantly higher than that of Cu-Co/CPE without f-MWCNT, which indicates the effective role of f-MWCNT in improving charge transfer and expanding the active surface area. Also, the decrease in the onset potential and peak potential of ethanol oxidation at the Co/f-MWCNT/CPE and Cu-Co/f-MWCNT/CPE compared to Cu-Co/CPE indicates the facilitation of the electrocatalytic process due to the presence of optimized nanostructures. Among them, Co/f-MWCNT/CPE has the lowest values ​​of onset potential and peak potential, which can be due to the high intrinsic activity of cobalt in the ethanol oxidation reaction. The performance of different electrodes in the electrochemical oxidation of ethanol was investigated based on three key parameters including onset potential, anodic peak potential and anodic peak current. The results show that the Cu-Co/f-MWCNT/CPE initiates the oxidation reaction at a lower potential (about 569 mV) than Cu-Co/CPE and also provides the maximum current at a lower potential. Also, the anodic peak current is higher in the presence of f-MWCNT, indicating more efficient charge transfer and increased electrochemical active surface area. This improvement can be attributed to the synergistic role between metal nanoparticles and the conductive and diffusive role of f-MWCNT.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003e3.4. Evaluation and optimal setting of operating conditions to improve the electrocatalytic activity of the Cu-Co/f-MWCNT/CPE\u003c/h2\u003e\u003cdiv id=\"Sec13\" class=\"Section3\"\u003e\u003ch2\u003e3.4.1. Supporting electrolyte concertation\u003c/h2\u003e\u003cp\u003eTo achieve optimal performance in electrocatalytic oxidation reactions of methanol and ethanol, the presence of a suitable concentration of supporting electrolyte in the test solution is essential. The supporting electrolyte facilitates the passage of electric current and improves the transport of ions by increasing the conductivity of the solution and reducing the ohmic resistance [\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e]. Also, increasing the ionic strength of the solution helps to better dissolve the reactant species and provides more favorable conditions for the reaction. In this study, the effect of sodium hydroxide (NaOH) concentration as a supporting electrolyte, in the range of 0.01 to 0.25 M, on the anodic peak current of methanol (Fig.\u0026nbsp;7A) and ethanol (Fig.\u0026nbsp;7B) oxidation reactions at the Cu-Co/f-MWCNT/CPE was investigated. The results showed that by increasing the NaOH concentration to 0.1 M, the anodic current for methanol (inset of Fig.\u0026nbsp;7A) and ethanol (inset of Fig.\u0026nbsp;7B) increase due to the reduction of ohmic resistance and improvement of ion separation, but an excessive increase in the concentration causes a decrease in ion separation and a decrease in the conductivity of the solution, which leads to a decrease in the anodic current. Also, for further investigating the effect of the concentration of the supporting electrolyte at different concentrations, in addition to investigating the effect of its concentration on the anodic peak current of methanol and ethanol oxidation reactions in the cyclic voltammetry method, Tafel analysis was performed at different concentrations of the supporting electrolyte at a scan rate of 5 mV/s in the same method. The results for five concentrations are shown in Fig.\u0026nbsp;7 for methanol (7A) and ethanol (7B). As can be seen, the lowest Tafel slope for both fuels were observed at the concentration of 0.1 M NaOH. In Tafel analysis, a low Tafel slope signifies efficient electrocatalysis, indicating that a small increase in overpotential is required to achieve a large increase in observed anodic currents, thus reflecting faster interfacial kinetics and a highly active catalyst. On the other hand, the obtained results indicate the high kinetics and high anodic currents at the 0.1 M concentration of NaOH. Therefore, 0.1 M NaOH concentration was identified as the optimum point in both methanol and ethanol oxidation reactions.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec14\" class=\"Section3\"\u003e\u003ch2\u003e3.4.2. Amount of modifier material\u003c/h2\u003e\u003cp\u003eThe electrocatalytic performance of the Cu-Co/f-MWCNT/CPE directly depends on the loading the amount of modifier material in the modified electrode structure. In order to determine the optimal composition and achieve the highest electrocatalytic efficiency in the oxidation reaction of alcohols, the effect of different amounts of nanohybrid in the weight range of 5 to 40% relative to graphite (W/W) was investigated. For this purpose, modified electrodes were prepared with a combination of 0.150 g of graphite powder and different amounts of Cu-Co/f-MWCNT nanohybrid and tested in solutions containing 0.3 M methanol and ethanol. The results of the cyclic voltammograms showed that with an increase in the percentage of nanocomposite to about 21% by weight, the anodic peak current increases. This increase indicates an improvement in the number of active sites and an increase in the effective catalytic surface area. However, after this amount, further increase of the modifier (up to 40%) caused a significant decrease in the electrocatalytic performance. This performance loss can be attributed to reasons such as the decrease in the conductivity of graphite powder in the electrode structure and excessive coverage of the active centers, which prevents the access of reactive species to the active surface. Finally, 21 wt% of the Cu-Co/f-MWCNT nanohybrid was selected as the optimal composition to achieve the highest electrocatalytic performance in the oxidation reaction of methanol and ethanol and was used in the following experiments.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec15\" class=\"Section3\"\u003e\u003ch2\u003e3.4.3. Effect of methanol and ethanol concentration\u003c/h2\u003e\u003cp\u003eOne of the important characteristics of an ideal electrocatalyst for fuel oxidation is a linear response and the ability to absorb the maximum amount of fuel to produce the maximum anodic peak current. To investigate the effect of methanol and ethanol concentrations on the anodic peak current generated in the Cu-Co/f-MWCNT/CPE nanocomposite, linear sweep voltammetry (LSV) experiments were performed under optimal conditions. The results of LSV showed that the anodic current density increases significantly with increasing methanol (Fig.\u0026nbsp;9A) concentration in the range of 0.25 to 1.0 M (inset of Fig.\u0026nbsp;9A) and the response of the electrocatalyst in this range is completely linear. This linear response indicates the sensitive and reliable performance of the nanocomposite in sensing methanol concentration. Also, for ethanol (Fig.\u0026nbsp;9B) in the range of 0.25 to 1.0 M (inset Fig.\u0026nbsp;9B), it was observed that the anodic current density also increases linearly with increasing ethanol concentration. This feature indicates the stability and reliability of Cu-Co/f-MWCNT/CPE over a wide range of alcohol fuel concentrations. The plots of anode peak current density versus different methanol and ethanol concentrations also confirm the linearity of the electrocatalyst response in these ranges. These features indicate that our nanocomposite is capable of analyzing a wide range of alcohol fuel concentrations accurately and with high sensitivity. In addition, the linearity of the electrode response in these ranges makes this electrode easily applicable in electrochemical sensors and high-performance fuel cells. Therefore, the Cu-Co/f-MWCNT/CPE nanocomposite is a suitable choice for applications related to the oxidation of alcohol fuels in alkaline environments and also offers remarkable performance under practical conditions.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec16\" class=\"Section3\"\u003e\u003ch2\u003e3.4.4. Effect of potential scan rate\u003c/h2\u003e\u003cp\u003eTo more accurately analyze of the kinetic behavior of the oxidation of methanol and ethanol at the surface of Cu-Co/f-MWCNT/CPE, cyclic voltammetry experiments were performed over a range of scan rates (5 to 150 mV/s) in a solution containing 0.1 M NaOH and 0.3 M of methanol (Fig.\u0026nbsp;10A and its inset) and ethanol (Fig.\u0026nbsp;10B and its inset). With increasing scan rate, it was observed that the anodic peak current increased continuously and, at the same time, the anodic peak potential shifted towards more positive values. This potential shift indicates the existence of kinetic limitations in the oxidation process of methanol and ethanol at higher rates, such that the electron transfer rate from the electrode surface does not keep pace with the increase in scan rate, leading to a delay in the reaction. Furthermore, plotting the anodic peak current intensity against the square root of the sweep rate showed an acceptable linear relationship, indicating that the methanol and ethanol oxidation reactions on the surface of the modified Cu-Co/f-MWCNT/CPE are controlled by a diffusion-type mass transfer process. In other words, the rate of transfer of reactant species from the bulk solution to the electrode surface is the dominant factor in determining the overall reaction rate, and not simply surface electron exchange. These results confirm the appropriate efficiency of this nanocomposite in facilitating electrocatalytic processes under different kinetic conditions.\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e\u003ch2\u003e3.5. Investigating the charge transfer mechanism and determining the number of effective electrons through Tafel analysis\u003c/h2\u003e\u003cp\u003eTo better understand the kinetic behavior of the electrooxidation process of methanol and ethanol and to determine the number of electrons participating in the rate-determining step, Tafel analysis was used. The Tafel diagram, which examines the relationship between current density and applied overpotential, can be obtained by plotting the potential graph in terms of log I (in the ascending part of the voltammogram with a low sweep rate (here 5 mV/s)) and using the slope of this graph, the number of electrons involved in the rate-determining step can be obtained according to the following equation [\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e]:\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:\\left(\\frac{I}{{I}_{0}}\\right)log\\frac{2.303RT}{\\alpha\\:nF}=\\eta\\:$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eIn this relation, R is the gas constant, F is the Faraday number, T is the temperature in Kelvin, α is the reaction charge transfer coefficient, I\u003csub\u003e0\u003c/sub\u003e is the exchange current, n is the number of electrons transferred in the rate-determining step, and η is the overpotential. By analyzing the Tofel diagrams for alkaline solutions containing 0.3 M methanol and ethanol, slopes of about 112 and 92.1 mV/decade were obtained for methanol (Fig.\u0026nbsp;11A) and ethanol oxidation (Fig.\u0026nbsp;11B), respectively. Using the Tafel equation and assuming a charge transfer coefficient of α\u0026thinsp;=\u0026thinsp;0.5, the value of nα for both fuels was calculated to be approximately equal to 1.04 and 1.28 for methanol and ethanol, respectively. This value indicates that the rate-determining step in these processes is probably accompanied by the transfer of one electron. Also, the exchange current density (I\u003csub\u003e0\u003c/sub\u003e) for methanol and ethanol was calculated to be about 2.28\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;8\u003c/sup\u003e and 5.87\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;8\u003c/sup\u003e Acm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, respectively, indicating the suitable electrocatalytic activity of the modified electrode in alkaline medium.\u003c/p\u003e\u003cp\u003eThe electrooxidation process of methanol and ethanol in alkaline medium is carried out through metal oxyhydroxide (MOOH) intermediates. These species are first generated from the reaction of OH⁻ ions with active metal species (Cu and Co) on the electrode surface and then participate in the reaction with the fuel (methanol or ethanol). In other words, in an alkaline environment, hydroxide ions ( OH\u003csup\u003e\u0026minus;\u003c/sup\u003e) react with metal hydroxides (such as Cu(OH) and Co(OH)) and convert them into higher valence metal oxyhydroxy species such as CuOOH and CoOOH:\u003c/p\u003e\u003cp\u003eStep I\u0026thinsp;=\u0026thinsp;Formation of the active metal intermediate:\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$$\\:Cu,\\:Co={e}^{-}\\:\\left(M+{H}_{2}O+MOOH\\rightleftharpoons\\:\\:{OH}^{-}+2M(OH\\right)2)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThese oxyhydroxy species (MOOH) act as strong oxidants and react with alcohols. During this reaction, the alcohol is oxidized and the metal species returns to its original state, M(OH):\u003c/p\u003e\u003cp\u003eStep II\u0026thinsp;=\u0026thinsp;Reaction with methanol and ethanol:\u003c/p\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:M\\left(OH\\right)2+{HCOO}^{-}+2{e}^{-}+\\:2{H}_{2}O\\rightleftharpoons\\:MOOH+{CH}_{3}OH\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\)\u003c/span\u003e\u003c/span\u003e for methanol\u003c/p\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:M\\left(OH\\right)2+{{CH}_{3}OO}^{-}+2{e}^{-}+\\:2{H}_{2}O\\rightleftharpoons\\:MOOH+{{C}_{2}H}_{5}OH\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\)\u003c/span\u003e\u003c/span\u003e for ethanol\u003c/p\u003e\u003cp\u003eIn general:\u003cdiv id=\"Equc\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equc\" name=\"EquationSource\"\u003e\n$$\\:M\\left(OH\\right)2+Products\\to\\:MOOH+{CH}_{3}OH/{C}_{2}{H}_{5}OH$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eIn this mechanism, oxidizing intermediate species such as CuOOH and CoOOH react with methanol or ethanol and lead to their oxidation, while themselves being converted to higher oxide forms such as CuO(OH). OH⁻ ions present in alkaline medium play a very important role in activating the electrode surface, because by forming active metal species, they provide the necessary conditions for initiating and accelerating oxidation reactions. This proposed pathway is consistent with previous reports in scientific literature [\u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e, \u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e68\u003c/span\u003e] and shows that copper and cobalt nanoparticles, together with the conductive structure of f-MWCNT, play a fundamental role in improving the charge transfer process, catalytic stability and increasing the electrooxidation rate of both fuels. These factors enhance the performance of the modified Cu-Co/f-MWCNT/CPE electrode in alcohol fuel cell applications in alkaline environments.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec18\" class=\"Section2\"\u003e\u003ch2\u003e\u003cb\u003e3.6. Study of electrocatalytic oxidation of methanol and ethanol by chronoamperometry\u003c/b\u003e\u003c/h2\u003e\u003cp\u003eTo evaluate and estimate the diffusion coefficient (D, in cm\u0026sup2;/s) of methanol and ethanol, chronoamperometric analyses were done. These experiments were performed on the Cu-Co/f-MWCNT/CPE in 0.1 M NaOH solution and by applying a potential of 1289 mV with respect to the reference electrode. The resulting chronoamperograms for different concentrations of methanol and ethanol are shown in Fig.\u0026nbsp;12A for methanol and 12 B for ethanol. Then, the current (I) plots were plotted in terms of the inverse square root of time (t\u003csup\u003e\u0026minus;\u0026thinsp;1/2\u003c/sup\u003e). It was observed that the anodic current has a linear relationship with t\u003csup\u003e\u0026minus;\u0026thinsp;1/2\u003c/sup\u003e, indicating that the mass transfer process is controlled by diffusion. Based on the Cottrell equation, the current resulting from the electrochemical reaction of the electrostatically active species is expressed as follows [\u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e69\u003c/span\u003e]:\u003cdiv id=\"Equd\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equd\" name=\"EquationSource\"\u003e\n$$\\:I=nFA{D}^{1/2}C/{\\pi\\:}^{1/2}{t}^{1/2}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003ein which, C is the concentration of the electroactive species in mol.cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e, and D is the diffusion coefficient in cm\u003csup\u003e2\u003c/sup\u003es\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. If for a chronoamperogram, the current changes are plotted in terms of the square root of time, the slope of the graph will be equal to nFAD\u003csup\u003e1/2\u003c/sup\u003eC/π\u003csup\u003e1/2\u003c/sup\u003e, and by knowing n, F, A, and C, the diffusion coefficient can be calculated. Given the linearity of the flow diagram in terms of t\u003csup\u003e\u0026minus;\u0026thinsp;1/2\u003c/sup\u003e, the slope of this diagram is proportional to the value of the diffusion coefficient. The slopes of the lines obtained from Fig.\u0026nbsp;12 were plotted against different concentrations of methanol and ethanol (insets), and based on them, the diffusion coefficient for methanol and ethanol was calculated to be 9.36 \u0026times;10\u003csup\u003e\u0026ndash;6\u003c/sup\u003e and 7.90\u0026times;10\u003csup\u003e\u0026ndash;6\u003c/sup\u003e cm\u003csup\u003e2\u003c/sup\u003e/s, respectively.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec19\" class=\"Section2\"\u003e\u003ch2\u003e3.7. Study of the stability of electrocatalyst\u003c/h2\u003e\u003cp\u003eThe stability of the Cu-Co/f-MWCNT/CPE, as one of the key factors in electrocatalytic applications, was investigated using the cyclic voltammetry technique in alkaline medium. For this purpose, the experiments were performed in 0.1 M NaOH solution containing 0.3 M methanol and ethanol. Potential scans were performed at a rate of 100 mV/s in a certain potential range. The results (anodic peak current vs scan numbers) showed that by increasing the number of potential cycles to 200 cycles, the anodic current from methanol (Fig.\u0026nbsp;13A) and ethanol oxidation (Fig.\u0026nbsp;13B) experienced only a very slight decrease (less than 5%). Also, the location of the oxidation and reduction peaks remained almost unchanged during the cycles and no significant shift in the peak voltage was observed. The stability of the anodic peak currents and the lack of change in the voltammetric behavior indicate the structural and chemical stability of the modified electrode surface in alkaline medium. The good stability of the electric current over time indicates that the Cu-Co/f-MWCNT nanohybrid is well immobilized in/on the surface of the CPE and is resistant to degradation or passivation during successive cycles. This property is very crucial for the use of this modified electrode in alcohol fuel cell systems. Overall, the cyclic voltammetric behavior shows that the modified electrode is electrocatalytically stable and reliable and can be suitable for long-term applications in alkaline environments.\u003c/p\u003e\u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eThe Cu-Co/f-MWCNT/CPE was synthesized and investigated as a novel and efficient electrocatalyst for the oxidation of methanol and ethanol in alkaline medium. This nanohybrid was prepared by a simple method at room temperature; in fact, Cu and Co nanoparticles are well-settled on f-MWCNT. Using various techniques such as SEM, TEM, XRD and EDX, the structure and composition of nanohybrid were fully characterized and it was confirmed that the metals were uniformly dispersed on the nanotubes. This feature increases the active surface area and better charge transfer in the modified electrode. Electrochemical experiments such as cyclic voltammetry and Tafel analysis showed that the Cu-Co/f-MWCNT/CPE has significant electrocatalytic activity for the oxidation of methanol and ethanol. This modified electrode showed a significant decrease in the reaction onset potential and a significant increase in the oxidation current compared to unmodified CPE, and f-MWCNT/CPE, Co/f-MWCNT/CPE, Cu-Co/CPE, Cu/f-MWCNT/CPE. This improvement in performance is due to the synergistic effect between Cu and Co nanoparticles as well as the high conductivity of f-MWCNT, which accelerates electron transfer and creates more active sites. Chronoamperometric analyses confirmed the stability of the modified electrode in alkaline media; so that after 200 continuous cycles, the oxidation current decreased by less than 5%, indicating the high durability of the electrode. Also, Tafel analyses and calculation of diffusion coefficients showed that the oxidation process is controlled by mass transfer and the transfer of one electron plays a role in the rate-determining step. According to the results obtained, the Cu-Co/f-MWCNT/CPE can be introduced as an effective, stable and economical catalyst for application in direct methanol and ethanol fuel cells in alkaline environments. This study is an important step towards the development of advanced high-performance catalytic materials for clean and renewable energies.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eFunding:\u003c/h2\u003e\n\u003cp\u003eNo Funding.\u003c/p\u003e\n\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\n\u003cp\u003eCredit author statementBiuck Habibi: Supervision, Monitoring, Editing, Discussing and Revising.Sepideh Khalili: All practical works in lab, Visualization, Investigation, Writing- Reviewingand Editing and Data curation.Sara Pashazadeh: All practical works in lab, Visualization, Investigation, Writing- Reviewingand Editing and Data curation.Younes Bahadori: Visualization, Investigation, Writing- Reviewing and Editing and Data curation.Ali Pashazadeh: Visualization, Investigation, Writing- Reviewing and Editing and Data curation.\u003c/p\u003e\n\u003ch2\u003eAcknowledgments\u003c/h2\u003e\n\u003cp\u003eThe authors gratefully acknowledge the Research Council of Azerbaijan Shahid Madani University for its financial support. Also, the authors sincerely thank the Central Laboratory of Azarbaijan Shahid Madani University for conducting the SEM and EDX experiments (Phenom ProX Desktop SEM) as part of this study.\u003c/p\u003e\n\u003ch2\u003eData Availability\u003c/h2\u003e\n\u003cp\u003eAll data generated or analysed during this study are included in this published article [and its supplementary information files].\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAminzadeh, S., Dehghani, M. R. \u0026amp; Taleb, N. Energy consumption, fossil fuel dependence, and sustainability challenges in the context of climate change mitigation. \u003cem\u003eJ. Clean. 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(2022). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3389/fchem.2021.8056\u003c/span\u003e\u003cspan address=\"10.3389/fchem.2021.8056\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHabibi, B., Pashazadeh, A., Pashazadeh, S. \u0026amp; Saghatforoush, L. A. A new method for the preparation of MgAl layered double hydroxide-copper metal\u0026ndash;organic frameworks structures: application to electrocatalytic oxidation of formaldehyde, Sci. Rep., vol. 14, Art. no. 5222, (2024). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1038/s41598-024-55770-7\u003c/span\u003e\u003cspan address=\"10.1038/s41598-024-55770-7\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003e\u003cstrong\u003eTable 1:\u0026nbsp;\u003c/strong\u003eElectrochemical parameters of methanol electrooxidation at the different electrocatalysts.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"612\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eFuel\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eElectrocatalyst\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eOnset Potential, E\u003csub\u003eonset\u003c/sub\u003e (mV)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003ePeak Potential, E\u003csub\u003epf\u0026nbsp;\u003c/sub\u003e(mV)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003ePeak Current, I\u003csub\u003epf\u0026nbsp;\u003c/sub\u003e(\u0026micro;A)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eMethanol\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eCPE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e709\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" valign=\"top\"\u003e\n \u003cp\u003e1289\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1696.53\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eMethanol\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003ef-MWCNT/CPE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e696\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" valign=\"top\"\u003e\n \u003cp\u003e1259\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e2802.69\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eMethanol\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eCu-Co/CPE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e569\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" valign=\"top\"\u003e\n \u003cp\u003e1299\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e5808.86\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eMethanol\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eCo/f-MWCNT/CPE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e519\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" valign=\"top\"\u003e\n \u003cp\u003e1239\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e4176.58\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eMethanol\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eCu/f-MWCNT/CPE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e549\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" valign=\"top\"\u003e\n \u003cp\u003e1249\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e6775.80\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eMethanol\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eCu-Co/f-MWCNT/CPE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e499\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" valign=\"top\"\u003e\n \u003cp\u003e1249\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e8998.42\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 66px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 15px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 169px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 128px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 18px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 107px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2:\u0026nbsp;\u003c/strong\u003eElectrochemical parameters of ethanol electrooxidation at the different electrocatalysts.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"633\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eFuel\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eElectrocatalyst\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eOnset Potential, E\u003csub\u003eonset\u003c/sub\u003e (mV)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003ePeak Potential, E\u003csub\u003epf\u0026nbsp;\u003c/sub\u003e(mV)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003ePeak Current, I\u003csub\u003epf\u003c/sub\u003e (\u0026micro;A)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eEthanol\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eCPE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e729\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1309\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1749.73\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eEthanol\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003ef-MWCNT/CPE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e709\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1289\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e2482.67\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eEthanol\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eCu-Co/CPE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e589\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1299\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e4679.09\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eEthanol\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eCo/f-MWCNT/CPE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e509\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1259\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e3982.63\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eEthanol\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eCu/f-MWCNT/CPE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e599\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1279\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e6261.21\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eEthanol\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eCu-Co/f-MWCNT/CPE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e569\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1269\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e8251.13\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"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":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Alcohol electrooxidation, Methanol, Ethanol, Cu-Co nanoparticles, f-MWCNT, nanohybrid electrocatalyst","lastPublishedDoi":"10.21203/rs.3.rs-8058781/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8058781/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn this study, the design and preparation of a nanohybrid electrocatalyst; Cu-Co/f-MWCNT was presented. The fabrication of present nanohybrid based electrocatalyst was carried out in two steps: firstly, the copper and cobalt nanoparticles were immobilized on/in functional multi-walled carbon nanotubes (f-MWCNT) by chemical deposition, then the Cu-Co/f-MWCNT nanohybrid was used to modified the carbon paste electrode (CPE). The Cu-Co/f-MWCNT/CPE was comprehensively investigated and confirmed using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, elemental mapping, transmission electron microscopy and electrochemical techniques. The obtained results indicate a uniform distribution of Cu-Co nanoparticles on/in the f-MWCNT structure and the formation of a nanohybrid structure with a high specific surface area and favorable electrical conductivity. The fabricated electrocatalyst; Cu-Co/f-MWCNT/CPE showed excellent electrocatalytic activity for the oxidation of methanol and ethanol in alkaline medium. Linear sweep voltammetry experiments have revealed wide linear ranges for the oxidation of methanol (0.5 to 3.0 M) and ethanol (1.0 to 3.5 M) in this condition. The outstanding performance of this system is due to the synergistic effect between Cu-Co nanoparticles in the nanohybrid structure and the high conductivity of f-MWCNT, which leads to fast electron transfer and an increase in the number of activated sites on the modified electrode surface. These results make Cu-Co/f-MWCNT/CPE a promising candidate for application in direct alcohol fuel cells.\u003c/p\u003e","manuscriptTitle":"Noble-metal-free Cu-Co/f-MWCNT electrocatalyst for methanol and ethanol oxidation reactions","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-11-26 04:08:20","doi":"10.21203/rs.3.rs-8058781/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision 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