Electrochemical reduction of CO 2 on CoNi nanoparticles supported on different carbon matrixes

Electrochemical reduction of CO 2 on CoNi nanoparticles supported on different carbon matrixes | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Electrochemical reduction of CO 2 on CoNi nanoparticles supported on different carbon matrixes Jhon Faber Zapata Cardona, Julieta Carballo, Gonzalo Montiel, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6823214/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract CoNi nanoparticles were deposited over two different carbon supports. A mesoporous carbon obtained from a resorcinol formaldehyde resin, and commercial carbon nanotubes. The metal nanoparticles were evaluated for the electrochemical reduction of CO 2 in aqueous media. X-ray diffraction and transmission electron microscopy measurements show differences in the nanoparticle’s morphology. The electrochemical determinations presented different results for the CO2 electroreduction. Formic acid was formed at different potentials on each catalyst as indicated by chromatography. CoNi over mesoporous carbon showed a faradaic efficiency of 32.9% at -0.9 V vs SHE while the metal nanoparticles over nanotubes presented an efficiency of 38.9% at -1.1 V vs SHE. Rotating ring disk electrode determinations also showed different behavior for each metal nanoparticulated catalyst. CO2 Electrochemical reduction RRDE Formic Acid Nanoparticles Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 1. Introduction It is widely known that the intensive use of fossil fuels generates an uncontrolled increase in the atmospheric amount of carbon dioxide (CO 2 ), which leads to the current environmental crisis [ 1 ]. This, coupled with the dwindling reserves of fossil fuels, challenges the scientific community to develop methods and technologies that propose options for the use of fossil fuels as an energy source and thus reduce or control CO 2 emissions. Currently, the reduction of CO 2 by electrochemical means presents an attractive method for energy storage and fuel generation [ 2 – 4 ]. For this purpose, is paramount the use of alternative energy sources such as solar and wind, hydroelectric, as well as nuclear power plants, among others C free sources. The reduction (CO 2 RR) and electrochemical reduction (CO 2 ER) of CO 2 is an alternative to solve the environmental and energy problem by storing energy, producing fuel, and conserving a balanced amount of CO 2 in the atmosphere. The reduction of CO 2 may generate different compounds some of which can be used directly as fuels such as methane (CH 4 ) and methanol (CH 3 OH). While other reduction products may function as, raw materials for industrial uses such as formic acid (HCOOH) and formaldehyde (CH 2 O) [ 5 ]. The challenges for CO 2 reduction are in the design of selective, stable, and efficient catalysts that are composed of cheap and abundant materials that allow cost-effective use [ 6 ]. The use of catalysts based on metal composition has been extensively studied in recent years allowing to have a better understanding of the processes involved in the reaction, and thus improving the efficiency and selectivity conversion of CO 2 [ 7 , 8 ]. Among these, there are catalysts based on transition metals such as Cu, Au, Sn, Co, Ni, Fe, and Mo [ 9 – 11 ]. Cu-based catalysts have been widely used producing different products among which hydrocarbons stand out, mainly methane, ethylene, and ethanol [ 12 – 14 ]. However, it presents many challenges to improve its stability, efficiency, and selectivity. In recent years, cobalt-based catalysts have shown increasing attention for their potential to reduce CO 2 . Xiao et al. reported CoAlO x catalysts for the selective electroreduction of CO 2 to ethanol, obtaining an efficiency of 92.1% at 140°C [ 15 ]. Cobalt oxides and porphyrins promote the selective electroreduction of CO 2 to CO with a faradaic efficiency of 75% [ 16 ]. Also, the use of Co nanoparticles stabilized with graphitized carbon was efficient for the production of formic acid and CO [ 17 ]. Nanoparticulate Co dispersion on graphene was used to reduce CO 2 to methanol with an efficiency of 71% [ 18 ]. Ni-based catalysts are also a different alternative to Cu-based materials since Ni also reduces CO 2 to high-energy value products such as CH 4 and C 2 H 4 [ 19 ]. Other studies of Ni as a catalyst showed high efficiency in generating CO, with a maximum value of 97% [ 20 ]. Functionalizing carbon nanotubes with a Ni (Ni-cyclam) complex resulted in a highly efficient catalyst to produce CO with efficiencies above 90% [ 21 ]. A combination of two or more metals has been widely used to improve the catalytic properties of the individual metals. The mixture of two metals can affect the interaction of the reactants, the intermediates, and finally the products generated on the catalyst surface, improving or suppressing some electrocatalytic processes [ 22 – 27 ]. Zhang et al., using Co and Ni nanoalloys supported on nitrogen-doped carbon nanofibers, showed that the electronic distribution of the catalyst is modified by shifting the center of the Co d band. This led to variations in the interaction energies of the key intermediates for CO 2 reduction, such as *CO, *COOH, and *H. They reported a high CO efficiency of 85% at a potential − 0.9 V vs SHE [ 28 ]. In the present work, Co-Ni nanoparticles supported on mesoporous carbon (MC) and carbon nanotubes (CNT) were evaluated as electrocatalysts for the electrochemical reduction of CO 2 . The physicochemical characteristics of the catalysts were studied using different techniques such as powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), porosimetry (adsorption-desorption of N 2 ) and thermogravimetric analysis (TGA). The electrocatalytic properties of the material were investigated by linear scanning voltammetry (LSV), cyclic voltammetry (CV), and chronoamperometry. The products obtained from the potentiostatic electroreduction were quantified by ion chromatography (IC). The rotating ring-disc electrode (RRDE) technique was also used for the identification and quantification of reduction products. 2. Experimental 2.1 Catalyst synthesis 2.1.1 Co-Ni Nanoparticles on Mesoporous Carbon (CoNi/MC) The synthesis of mesoporous carbon (MC) was previously carried out by Montiel et al. [ 29 ]. The MC was obtained by carbonization of a resorcinol-formaldehyde resin. Sodium acetate was used as the catalyst, polydiallyldimethylammonium chloride as the structuring agent, and porous silica as the hard mold. The resin was dried in a vacuum oven at 100°C for 24 h, then carbonized in a tubular oven (Indef model T-150) under N 2 atmosphere with a flow of 1 L min − 1 from 20°C to 1000°C, with a heating rate of 3°C min − 1 , and held at 1000°C for 120 minutes. Co-Ni nanoparticles supported on mesoporous carbon (CoNi/MC) were obtained using NaBH 4 as a reducing agent without adjusting the media pH. NaBH4 was added in a molar ratio of 5:1 (NaBH 4 to metal salt) to a suspension of the carbon support containing NiSO 4 ·6H 2 O and Co(NO 3 ) 2 ·6H 2 O precursors at 0°C. The reaction flask was stirred while the temperature was maintained at 0°C for 6 hours. The powder obtained was filtered, washed with milli-Q water, and finally dried in a vacuum oven at 80°C for 24 hours. The metal-to-carbon support ratio was targeted at 40% w/w. 2.1.2 Co-Ni Nanoparticles on Carbon Nanotubes (CoNi/CNT) Co-Ni nanoparticles supported on carbon nanotubes (CoNi/CNT) were synthesized by using sodium dodecyl sulfate (SDS) as a stabilizer. CNT was purchased from Arkema (Graphistrenght®). They present a diameter between 10 and 15 nm and a purity above 90%. Before use, they were washed with a 50% w/w aqueous solution of HCl for 48 h at room temperature. Following, they were filtered and washed with tridistilled water in a Soxhlet apparatus for 24 hours. NiCl 2 ·6H 2 O and CoCl 2 ·6H 2 O were used as precursor salts. The metal-to-carbon support ratio was 40% w/w, while the Ni:Co:SDS ratio was 1:1:0.05 molar, respectively. The synthesis was carried out in a basic medium, using hydrazine as a reducing agent at 80ºC. Finally, the product was washed and dried for 24 hours at 80°C. 2.2 Physicochemical Characterization Techniques The supported catalysts were characterized by powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), porosimetry (adsorption-desorption of N 2 ), and thermogravimetric analysis (TGA). The diffractograms of the catalysts were obtained with the Panalytical diffractometer model Empyrean 2 with a PixCell3D detector and Cu-Kα source with a range of 10° < 2θ < 90°, step length of 0.02°, and a count of 4 seconds. TEM images were made with a JEOL model 100 CX II microscope operated at 100 kV with magnifications of 100,000 X and 270,000 X. For EDS spectra, a FEI QUANTA 250 field emission microscope was used. Porosimetry analysis was done with the Micromeritics ASAP 2020 system with N 2 at -196.15°C. The specific surface area (SBET) was estimated by the BET method and the pore size distribution by the Barrett-Joyner-Halenda (BJH) method. TGA measurements were recorded in a Shimadzu TGA 50 equipment, using approximately 2.5 mg of the sample with an N 2 flow of 20 mL min − 1 and a heating rate of 10°C min − 1 . 2.3 Electrochemical characterization techniques The electrochemical determinations were carried out in a jacketed glass cell (Vol. 60 cm 3 ) with an Autolab PGSTAT302N potentiostat (Echochemie, The Netherlands). An RRDE system (Pine Research Inst.) with a mounted tip consisting of a vitreous carbon disc electrode (0.196 cm 2 ) and a platinum ring electrode (0.110 cm 2 ) was employed. The carbon disk operated as the working electrode (WE). A coiled Pt wire, 1 mm in diameter and 10 cm in length acted as the counter electrode (CE), while a silver/silver chloride (Ag/AgCl, KCl sat) as the reference electrode (RE). A suspension of the CoNi/MC and CoNi/CNT powders was prepared by weighing 5 mg of the prepared catalyst, 15 mg of 5 wt% PVDF in N-methylpyrrolidone (NMP) as a binding agent, and 30 mg of NMP as a solvent. The components were uniformly mixed for 15 minutes in an ultrasonic bath. A drop of 10 µL was deposited over the carbon disk (WE) and dried in a vacuum oven at 80°C for 30 min. The final weight of the catalyst over the WE was determined to be ca. 5.00 mg cm − 2 . An aqueous solution of 0.1 M KHCO 3 (ACS reagent, Aldrich) in ultrapure water from an Arium Pro system (Sartorius) was used as an electrolyte. Measurements were made after degassing the solution for 20 min. With N 2 (4.0, Indura) or saturating it with CO 2 (3.8, Indura). All measurements were performed at a controlled temperature of 25°C. All potentials were referenced to the standard hydrogen electrode (SHE). Exploratory LSVs were performed by sweeping the potential from 0.3 to − 1.3 V vs. SHE at 10 mV s − 1 . CO 2 electrochemical reduction experiments were carried out potentiostatically (chronoamperometry). Discrete potential values from − 0.9 to − 1.4 V vs. SHE with 0.1 V intervals were applied for 900 s at the electrode. The electrolyte was previously saturated with CO 2 for 20 min, and then a flow rate of 2 mL min − 1 was maintained during the measurements. Soluble products were assessed by IC (DIONEX ICS 5000) with a column ION PACK AS19 - Analytical − 4 × 250 mm, from an aliquot of the electrolyte solution. The faradaic efficiencies ( f ) were calculated from the quantities measured by IC. Electrochemical measurements in an RRDE setup were employed for the determination of CO 2 electroreduction products, particularly low-solubility products such as CO [ 30 ]. The measurements were performed by LSV on the disk electrode while a fixed potential was applied to the ring. While the combined electrodes (disk/ring) rotated at 900 rpm, the disk electrode potential was swept from − 0.8 V to − 1.3 V vs. SHE at 10 mV s − 1 , and the ring electrode was fixed at 0.8 V vs. SHE. The ring electrode current (i ring ) produced during the oxidation process was used for the quantification of the reduced product formed on the disk electrode. To identify the reduction products and their oxidation potentials, two sets of CVs were carried out at the ring electrode. The first set of CVs was performed on the Pt ring electrode in the presence of a standard solution of formic acid, formaldehyde, methanol, CO, and H 2 (SI-Fig. 1). The standard solutions of the aforementioned soluble products were all 0.1 M in a 0.1 M KHCO 3 aqueous solution, while in the case of CO and H 2 CVs the electrolyte was saturated with CO (3.8, Indura) and H 2 (Indura 4.8) gas before the measurements. The ring potential was cycled between 0.0 and 1.0 V vs. SHE at 50 mV s − 1 while the disk potential was turned off and the electrode rotated at 900 rpm. CVs were carried out in the ring electrode at the same conditions as described for the standards, while the disk potential was set between − 0.9 and − 1.4 V vs. SHE with 0.1 V intervals for 180 s in 0.1 M KHCO 3 saturated with CO 2 . In other words, voltammograms were performed in the ring electrode while CO 2 reduction was carried out in the disk electrode. To quantify the product collected at the ring by RRDE, the rotating setup requires a calibration of the electrode by obtaining the collection efficiency (N) [ 31 ]. The calibration was carried out by measuring the electrode disk (i disk ) and ring (i ring ) currents of a 0.005 M K 3 Fe(CN) 6 in a 0.1 M K 2 SO4 aqueous electrolyte solution. The disk potential was cycled between 0.0 and 1.0 V at 5 mV s − 1 , while the ring potential was fixed at 1.4 V to oxidize the Fe(CN) 6 4− generated at the disk electrode. The procedure was repeated at different rotation speeds, and N was determined from the slope of i disk vs. i ring plots. Faradaic efficiencies were calculated as previously described [ 30 , 32 ]. 3. Results and Discussion 3.1 Catalyst Morphology Characterization The PXRD patterns of the metal catalyst supported over MC and CNT are presented in Fig. 1 . The plot shows the position of the peaks labeled (211), (310), (301), and (321) associated with the characteristic planes of Co in its trigonal phase (P42/mnm) [ 33 ], the peaks (10–15), (10–16), (10–17) characteristic of Ni in its hexagonal phase (P6/mmm) [ 34 ], and the peaks (111), (200), (220), and (311), corresponding to the bimetallic alloy of Co and Ni [ 35 – 37 ]. Both catalysts show a wide diffraction peak around 20° belonging to the carbonaceous compound of the supports. For the CoNi/CNT catalyst, the main diffraction peaks are observed at approximately 31°, 36°, 38°, and 43° associated with the Co signal corresponding to (211), (310), (301), and (321) as well as peaks at 56° and a broad peak at 59° with a shoulder at 61° aligning with Ni (10–16), (10–15), and (10–17) reflections. In addition, there are peaks at 45°, 51, and 75°, matching closely with the CoNi (111), (200), and (220) reflections. On the other hand, CoNi/MC shows a broad peak at 34° corresponding to Co (310), a broad peak at 60° aligning with Ni (10–15), and small peaks at 45° and 75° corresponding to the (111) and (220) CoNi signals, respectively. Throughout the patterns, the experimental peak positions generally match the expected positions. Both samples show broad peaks indicating small crystallite sizes or partial amorphous content. Importantly, the peak positions associated with pure metallic Ni and Co are shifted relative to their reference positions, suggesting that the samples do not necessarily contain separate nanoparticles of pure Co or pure Ni. Instead, this shifting might imply particles with a higher content on one of the metals. There are also differences between the MC and CNT samples in peak intensities and widths, reflecting variations in crystallinity or phase composition. Overall, both samples exhibit diffraction features consistent with mixtures of Co, Ni, and CoNi phases, and their comparison highlights subtle yet important variations in crystalline structure, alloying, and phase distribution. Based on the peaks identified for each sample, the crystallite size of the nanoparticles was calculated using the Scherrer equation [ 38 ]. CoNi/CNT gave nanoparticle sizes of 6.92 nm for Co, 9.3 nm for Ni and 22 nm for the bimetallic peaks. For CoNi/MC the crystallite size was determined to be 2.69 nm for Co, 5.54 nm for Ni, and 9.7 nm corresponding to the CoNi signals. The dispersion and size of metallic nanoparticles in the support were evaluated by TEM images. TEM images of the CoNi/MC catalyst are shown in Fig. 2 . The mesoporous carbon support shows a high concentration of homogeneously distributed particles with a circular geometry and an average size of 4.4 nm. The TEM images of CoNi/CNT are shown in Fig. 3 . The sample presented tubes of various thicknesses, with large particles homogeneously distributed throughout the structures. The particles have an elongated morphology and blunt edges, in addition to particles with a circular morphology with an average size of 10.7 nm. To determine the atomic ratio of Co and Ni over the MC and CNT supports, the study of the elemental composition was carried out through EDS (Figure SI-2 and SI-3). The atomic composition presented for each catalyst resulted in 45.5% Co to 54.5% Ni over MC and 48.4% to Co 51.6% Ni over CNT. The composition result is consistent with the 1:1 Co-Ni intended ratio, although needs to be remembered that this is the average composition across the beam area. The nitrogen absorption-desorption isotherms of the CoNi catalysts supported on MC and CNT are shown in Fig. 4 A. In both systems, the isotherms are type IV and hysteresis loop type H3 according to the classification of the International Union of Pure and Applied Chemistry (IUPAC) [ 39 ]. Increased N 2 absorption at low pressures and hysteresis loop formation at high pressure are characteristic of mesoporous structures and multilayer formation. The specific surface area of the samples was 265.7 cm 2 g − 1 and 115.8 cm 2 g − 1 for CoNi/MC and CoNi/CNT, respectively. The pore size distributions obtained through the BJH model (dV/dlog(d)) are shown in Fig. 4 B. Both catalysts show a monomodal distribution of pores between 3 and 62 nm with a maximum value of 35 nm for CoNi/CNT and 40 nm for the CoNi/MC sample. The plots show the presence of pores around 4 nm whose origin is typically interstitial space in sphere clusters [ 40 ]. The metal content was determined by thermogravimetric analysis, and the results are shown in Fig. 5 . The TGA curves in both catalysts show an initial mass loss between 90 and 250°C that corresponds to the evaporation of H 2 O, up to approximately 300°C and 400°C for CoNi/MC and CoNi/CNT, respectively. From these temperatures a more pronounced process is observed that goes up to 700°C and is mainly due to the loss of mass due to the calcination of the supports and their elimination in the form of CO 2 . The metal amount determined in the final catalyst was 35.26% for CoNi/MC and 34.68% for CoNi/CNT. 3 Electrochemical Characterization The LSVs obtained for CoNi over the two carbon matrixes are shown in Fig. 6 (A and B). The voltammetries show a continuous increase of a reduction in current density ( j ) from the beginning of the experiments. In the presence of N 2 and CO 2 , the curves present similar features with minor differences. For both catalysts, the LSV in the degassed electrolyte (N 2 ) shows a sharp increase of the reduction j at around − 1.1V vs SHE. Also, there is a small depression at ca. -0.2V vs SHE. The main difference is the presence of another depression at -0.95V vs SHE for CoNi/CNT. For the electrolyte saturated with CO 2 , both catalysts present the increase of the reduction j at around − 0.85V vs SHE. The main difference observed is that CoNi/MC j stabilizes and then increases again at ca -1.1V vs SHE while for CoNi/CNT the j keeps increasing with a change of rate of lower pace at around − 0.95V vs SHE. The onset potential for the reduction process in the presence of CO 2 is more anodic compared to degassed electrolytes with a shift of ca. 0.25 V for both catalysts. Moreover, the rate change for the current density below 0.85 V vs SHE indicates a more complex reduction process in the presence of CO 2 . Besides the aforementioned change in the j rate, the other difference between each catalyst is that the current density module in the presence of CO 2 is higher for CoNi/MC compared to the degassed electrolyte. Electroreduction of CO 2 for the quantification of the reduction products was performed potentiostatically at discrete potential values between − 0.8 V and − 1.3 V vs SHE. A set of experiments was carried out to assess soluble reduction products by IC from aliquots taken from the electrolyte media. Formic acid was the only soluble product detected at potentials between − 0.9 V and − 1.1 V vs SHE for both catalysts. No product signal was observed below − 1.1 V vs SHE. The charge applied to the WE was converted to the mass of formic acid to calculate the ƒ based on the experimental concentration obtained by IC. The ƒ have a maximum value of 32.94% at -0.9 V vs SHE in CoNi/MC and 38.98% at -1.1 V vs SHE for CoNi/CNT. Table 1 shows the values of electrochemical charge, the formic acid amount measured by IC, and the calculated values of ƒ. Table 1 Formic acid quantities measured by IC (m IC ), experimental electrode charge ( Q ), and faradic efficiency calculated at different potentials for CoNi/MC and CoNi/CNT. CoNi/MC CoNi/CNT Potential (V vs SHE) m IC (mgL − 1 ) Q (mC) ƒ % m IC (mgL − 1 ) Q (mC) f % -0.9 0.28 ± 0.06 73 32.9 0.14 ± 0.03 90 13.3 -1.0 0.10 ± 0.02 150 5.7 0.25 ± 0.05 140 15.3 -1.1 0.24 ± 0.05 210 5.9 1.0 ± 0.2 220 38.9 As mentioned in the experimental section, the determination and quantification of CO 2 electrochemically reduced products by RRDE were previously shown [ 30 ]. Figure 7 , shows the CVs carried out at the ring electrode for different applied potentials on the disk electrode for both catalyst systems. The CVs were compared with those obtained for the standard solutions of the possible reduction products (Figure SI-1). Both catalysts show an oxidation peak in the forward scan. In the case of CoNi/MC, the peak is quite narrow and emerges when the applied potential is below − 1.0 V vs. SHE. On CoNi/CNT, the peak is broader, and although low, is visible starting from − 0.9 V vs SHE. The reduction peak at the back scan showing below 0.4 V vs SHE for CoNi/MC is assigned to the oxygen reduction reaction. According to the standards CVs, the ORR peak is visible when the only product present is CO. Other products like formaldehyde, methanol, and formic acid require a high potential for complete oxidation [ 41 ], diminishing the oxygen reduction reaction. For the CoNi/CNT, there is an increase in the reduction current for the back scan between 0.2 and 0.5 V vs SHE, which is noticeable as the applied potential increases. The methanol standard CV is the one showing an oxidation peak at that particular potential in the back scan, although formaldehyde and formic acid also possess broad oxidation peaks in the back scan. The analysis of the CVs and the information from the IC would indicate that the only products are formic acid and CO. The RRDE quantification of reduction products was performed by linear voltammetry on the disc electrode while the ring electrode was set at 0.8 V vs SHE. The i disk and i ring electrode currents were used to calculate the faradaic efficiency according to Eq. ( 1 ) [ 30 ]. $$\:f=\frac{{i}_{ring}}{\left|{i}_{disk}\right|N}\times\:100$$ 1 Where N is the collection efficiency of the RRDE. It was shown that the model based on a planar electrode used for the determination of N, also applies to a catalyst deposited on the electrode [ 42 ]. The collection efficiency was determined in each system for the calculation of the f . The values obtained were 0.14 ± 0.03 and 0.16 ± 0.01 for CoNi/MC and CoNi/CNT, respectively (supplementary). The efficiency obtained from Eq. ( 1 ) is presented in Fig. 8 . The i ring detected on the ring electrode arises from the oxidation of different reduction products. The form of Eq. 1 is derived for processes involving 2e - . Therefore, the faradaic efficiency represented in Fig. 8 , is the result of sensing the oxidation current arising from the presence of HCOOH and CO, as revealed by the results of the IC and the CVs from Fig. 7 . Also, contribution to the i ring may arise unavoidably from the H 2 presence generated from the H + reduction, particularly at the lowest potentials. For CoNi/MC at -0.9 V vs SHE, the calculated efficiency of 41.7%, corresponding to the formation of HCOOH indicated by IC to contribute with a 32.9% of faradic efficiency, while the difference of 8.8% should be associated with the formation of CO or H 2 . For − 1.0 V vs SHE the efficiency has contributions from HCOOH and CO according to the results obtained by IC and RRDE. The efficiency calculated by RRDE is 49.2% which corresponds to 5.7% of HCOOH obtained by CI and the efficiency of CO is approximately 43.5%. At -1.1 V vs SHE, there is also a contribution from HCOOH and CO, with a total of 5.8%. Being 5.9% for HCOOH and 46.9% for CO. At potentials of -1.2 V and − 1.3 V vs SHE, the efficiency has no contribution from HCOOH according to IC results, and the current in the ring electrode is mainly assigned to CO formation. Therefore, the efficiency calculated at these potentials corresponds to the production of CO with a value of 48.2% and 32.9% for these potentials, respectively. For CoNi/CNT, at -0.9 V vs SHE in Fig. 8 D, the efficiency is 14.7% which corresponds to the sum of contributions from HCOOH and CO. We obtained by IC 13.3% of HCOOH and the remaining 1.4% is associated with the formation of CO. At a potential of -1.0 V vs. SHE, the efficiency also has two contributions with 15.3% HCOOH and 19.4% CO for a total of 34.7%. For − 1.1 V vs SHE, the total efficiency calculated by RRDE is 44.2%, here the highest efficiency was obtained for HCOOH with 38.9% and the remaining 5.3% corresponds to CO. For potentials of -1.2 V and − 1.3 V vs SHE, the formation of HCOOH is no longer detected by IC and the calculated efficiency corresponds to the formation of CO with values of 48.6% and 54% for the aforementioned potentials. The formation of H 2 can be present to a lesser or greater extent throughout the potential range. 4. Conclusions Electrochemical measurements demonstrate that catalysts based on cobalt and nickel nanoparticles exhibit catalytic activity for the reduction of CO₂. Analytical determinations confirm that HCOOH is produced, with an efficiency of 32.9% on CoNi/MC at -0.9 V vs SHE and 38.9% on CoNi/CNT at -1.1 V vs SHE. The faradaic efficiency measured by RRDE indicates that CoNi/MC achieves a maximum conversion of approximately 53% at -1.1 V vs SHE, while for CoNi/CNT, the conversion increases steadily until reaching 54% at -1.3 V vs SHE. Although the products cannot be accurately identified, these efficiencies are most likely due to the conversion to CO. Statements and Declarations Competing interests: The authors declare no competing interests. This work was supported by Agencia Nacional de Promoción de la Investigación, el Desarrollo Tecnológico y la Innovación Argentina (AGENCIA I+D+i) Grant number PICT 2018–01407. CRediT author statement Formal analysis and investigation, Writing - Original Draft. : Jhon Faber Zapata Cardona. Formal analysis and investigation: Julieta Carballo. Formal analysis and investigation: Gonzalo Montiel . Conceptualization, Writing - review and editing: Mariano M. Bruno. Conceptualization, Visualization, Funding acquisition, Writing - Review & Editing: Federico A. Viva Acknowledgment: The authors thank Ana Larralde and Diego Lamas from the Applied Crystallography Laboratory (UNSAM) for the DRX measurements. In addition to Cecilia Albornoz from the DMFC Chemistry Laboratory for the TG measurements. 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Wang, Bimetallic CoNi Alloy Nanoparticles Embedded in Pomegranate-like Nitrogen-Doped Carbon Spheres for Electrocatalytic Oxygen Reduction and Evolution, ACS Appl. Nano Mater. 3 (2020) 1354–1362. https://doi.org/10.1021/acsanm.9b02201. S. Sargazi, M.R. Hajinezhad, A. Rahdar, M. Mukhtar, M. Karamzadeh-Jahromi, M. Almasi-Kashi, S. Alikhanzadeh-Arani, M. Barani, F. Baino, CoNi alloy nanoparticles for cancer theranostics: synthesis, physical characterization, in vitro and in vivo studies, Appl. Phys. A. 127 (2021) 772. https://doi.org/10.1007/s00339-021-04917-8. D. Feng, H. Yang, Q. Wang, X. Guo, Preparation and characteristic of three-dimensional NiCo alloy/carbon composite monoliths with well-defined macropores and mesostructured skeletons, J. Mater. Sci. 54 (2019) 4719–4731. https://doi.org/10.1007/s10853-018-03224-7. R.S. Bear, X‐ray diffraction procedures for polycrystalline and amorphous materials., J. Polym. Sci. 17 (1955) 274–274. https://doi.org/10.1002/pol.1955.120178412. K.S.W. Sing, Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity (Recommendations 1984), Pure Appl. Chem. 57 (1985) 603–619. https://doi.org/10.1351/pac198557040603. F.A. Viva, M.M. Bruno, M. Jobbágy, H.R. Corti, Electrochemical Characterization of PtRu Nanoparticles Supported on Mesoporous Carbon for Methanol Electrooxidation, J. Phys. Chem. C. 116 (2012) 4097–4104. https://doi.org/10.1021/jp209549g. N. Markovic, Surface science studies of model fuel cell electrocatalysts, Surf. Sci. Rep. 45 (2002) 117–229. https://doi.org/10.1016/S0167-5729(01)00022-X. U.A. Paulus, A. Wokaun, G.G. Scherer, T.J. Schmidt, V. Stamenkovic, V. Radmilovic, N.M. Markovic, P.N. Ross, Oxygen Reduction on Carbon-Supported Pt−Ni and Pt−Co Alloy Catalysts, J. Phys. Chem. B. 106 (2002) 4181–4191. https://doi.org/10.1021/jp013442l. Additional Declarations No competing interests reported. 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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-6823214","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":482680886,"identity":"a3649a24-8d3e-4a89-8a58-4090c1172a16","order_by":0,"name":"Jhon Faber Zapata Cardona","email":"","orcid":"","institution":"Universidad EAFIT","correspondingAuthor":false,"prefix":"","firstName":"Jhon","middleName":"Faber Zapata","lastName":"Cardona","suffix":""},{"id":482680887,"identity":"1d3c76a1-be93-4a76-8ff2-4964646249e0","order_by":1,"name":"Julieta Carballo","email":"","orcid":"","institution":"Centro Científico Tecnológico Conicet","correspondingAuthor":false,"prefix":"","firstName":"Julieta","middleName":"","lastName":"Carballo","suffix":""},{"id":482680890,"identity":"6968c135-57ca-41af-82ed-2625911a7d68","order_by":2,"name":"Gonzalo Montiel","email":"","orcid":"","institution":"Instituto Nacional de Tecnología Industrial (INTI)","correspondingAuthor":false,"prefix":"","firstName":"Gonzalo","middleName":"","lastName":"Montiel","suffix":""},{"id":482680891,"identity":"2acd0c03-57d2-4bc3-9fb0-3520894e88b8","order_by":3,"name":"Mariano M. Bruno","email":"","orcid":"","institution":"Centro Científico Tecnológico Conicet","correspondingAuthor":false,"prefix":"","firstName":"Mariano","middleName":"M.","lastName":"Bruno","suffix":""},{"id":482680893,"identity":"010988ef-dabd-47df-aaa9-1fae0d41c4cd","order_by":4,"name":"Federico A. Viva","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABAElEQVRIiWNgGAWjYBAC9gYGAwYQYmAG4g9QUWZ8WngOIGlhnEG8FphKHqK0sDdvfFxRYCdncJzH8LNNzR05/gb2i48LGOzycWrhOVZseMYg2djgMI+xdM6xZ8YSB3iKjWcwJFs24NBiL5FjJtlgcCBxZjNbgnRuw+HEhgM8adI8DMwGOHQw8Mi/Mf8J1ZL827LhcP18iJZ63FokeMwYQVr6mZmPSTM2HE4wOMB+DKjlMG4tPGnFQIclG/MDtVj2HDtsuPEwD7PxDIPjuLWwH974seGPnRwb/8HmGz9qDsvLHW9/+LigohqnFiyAmQcauSQA9gekqR8Fo2AUjILhDgCsK01ejJP9DwAAAABJRU5ErkJggg==","orcid":"","institution":"Gerencia de Investigaciones y Aplicaciones (GIyA), CNEA-CONICET Centro Atómico Constituyentes, Comisión Nacional de Energía Atómica","correspondingAuthor":true,"prefix":"","firstName":"Federico","middleName":"A.","lastName":"Viva","suffix":""}],"badges":[],"createdAt":"2025-06-04 19:23:22","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6823214/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6823214/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":86487217,"identity":"c9f50a43-ed87-4f62-a930-306d9daad4ab","added_by":"auto","created_at":"2025-07-11 08:26:41","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":87191,"visible":true,"origin":"","legend":"\u003cp\u003eDiffraction patterns of CoNi catalysts on MC (Top) and CNT (Bottom).\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6823214/v1/eab51275fe1f042d896a203a.png"},{"id":86488833,"identity":"27013e61-1db2-430b-8226-48e321ed796e","added_by":"auto","created_at":"2025-07-11 08:42:42","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":511534,"visible":true,"origin":"","legend":"\u003cp\u003eTEM images at different magnifications and histograms of particle size distribution of CoNi/MC.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6823214/v1/b9095b186d6f8fcd8731daf5.png"},{"id":86487220,"identity":"adcc4e63-5991-4c92-a481-a1a94bc575b4","added_by":"auto","created_at":"2025-07-11 08:26:42","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":527052,"visible":true,"origin":"","legend":"\u003cp\u003eTEM images at different magnifications and histograms of particle size distribution of CoNi/MC.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6823214/v1/80aa8199516b25f2bcbbb24c.png"},{"id":86487219,"identity":"6e9e8712-103b-472b-a590-4382e6714b02","added_by":"auto","created_at":"2025-07-11 08:26:42","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":418841,"visible":true,"origin":"","legend":"\u003cp\u003eA) N\u003csub\u003e2\u003c/sub\u003e adsorption/desorption isotherms at -196.15 °C. B) Pore size distributions obtained from the BJH Desorption dV/dlog(d) Pore Volume vs Pore Diameter plots.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6823214/v1/06019b164fbbc083fc454ef5.png"},{"id":86487838,"identity":"f978768e-6941-4c5e-b281-48ae84f9f419","added_by":"auto","created_at":"2025-07-11 08:34:42","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":38721,"visible":true,"origin":"","legend":"\u003cp\u003eThermogram for CoNi on MC and CNT.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-6823214/v1/95319d7231b31210df60579e.png"},{"id":86487840,"identity":"b975e404-d640-4230-ad8b-d58f0662935b","added_by":"auto","created_at":"2025-07-11 08:34:42","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":375575,"visible":true,"origin":"","legend":"\u003cp\u003eLinear sweep voltammetry in 0.1 M KHCO\u003csub\u003e3\u003c/sub\u003e saturated with N\u003csub\u003e2\u003c/sub\u003e and CO\u003csub\u003e2\u003c/sub\u003e at a sweep rate of 10 mV s\u003csup\u003e-1\u003c/sup\u003e. A) CoNi/MC and B) CoNi/CNT.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-6823214/v1/a29a7b1db0924e896bc86ee6.png"},{"id":86487224,"identity":"3fe6499e-0752-428e-878e-eb5d119a12db","added_by":"auto","created_at":"2025-07-11 08:26:42","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":509747,"visible":true,"origin":"","legend":"\u003cp\u003eCyclic voltammetry of the ring electrode between 0.0 V and 1.0 V vs SHE at 900 rpm and a sweeping rate of 10 mV s\u003csup\u003e-1\u003c/sup\u003e at different disk electrode potentials. A) CoNi/MC and B) CoNi/CNT.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-6823214/v1/68422a2d9bc2ce6256f55bfc.png"},{"id":86487844,"identity":"831069ae-4d77-4268-b7dd-d3913ad9cfcf","added_by":"auto","created_at":"2025-07-11 08:34:42","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":163771,"visible":true,"origin":"","legend":"\u003cp\u003eFaradaic efficiency calculated from Eq. 1 for the disk and ring current obtained from the LSV in the RRDE configuration, A) CoNi/MC, C) CoNi/CNT. Bar chart representing the ƒ of the CO\u003csub\u003e2\u003c/sub\u003e reduction products based on the values obtained by analytical and electrochemical techniques, B) CoNi/MC, D) CoNi/CNT.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-6823214/v1/6d36e00911d5e5c72f4d65f7.png"},{"id":88131251,"identity":"ee59f0e8-e87c-4f6b-8b0b-834df1bee9c5","added_by":"auto","created_at":"2025-08-01 19:16:33","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2887332,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6823214/v1/7a0e5ffe-55f9-4622-81d9-dcedd0166fb1.pdf"},{"id":86488834,"identity":"b789ba61-6332-4ffa-aae2-1176b6eaf300","added_by":"auto","created_at":"2025-07-11 08:42:42","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":281429,"visible":true,"origin":"","legend":"","description":"","filename":"SuplementalMaterial.docx","url":"https://assets-eu.researchsquare.com/files/rs-6823214/v1/f7834ec232f6ec997e545fc8.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Electrochemical reduction of CO 2 on CoNi nanoparticles supported on different carbon matrixes","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eIt is widely known that the intensive use of fossil fuels generates an uncontrolled increase in the atmospheric amount of carbon dioxide (CO\u003csub\u003e2\u003c/sub\u003e), which leads to the current environmental crisis [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. This, coupled with the dwindling reserves of fossil fuels, challenges the scientific community to develop methods and technologies that propose options for the use of fossil fuels as an energy source and thus reduce or control CO\u003csub\u003e2\u003c/sub\u003e emissions. Currently, the reduction of CO\u003csub\u003e2\u003c/sub\u003e by electrochemical means presents an attractive method for energy storage and fuel generation [\u003cspan additionalcitationids=\"CR3\" citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. For this purpose, is paramount the use of alternative energy sources such as solar and wind, hydroelectric, as well as nuclear power plants, among others C free sources. The reduction (CO\u003csub\u003e2\u003c/sub\u003eRR) and electrochemical reduction (CO\u003csub\u003e2\u003c/sub\u003eER) of CO\u003csub\u003e2\u003c/sub\u003e is an alternative to solve the environmental and energy problem by storing energy, producing fuel, and conserving a balanced amount of CO\u003csub\u003e2\u003c/sub\u003e in the atmosphere. The reduction of CO\u003csub\u003e2\u003c/sub\u003e may generate different compounds some of which can be used directly as fuels such as methane (CH\u003csub\u003e4\u003c/sub\u003e) and methanol (CH\u003csub\u003e3\u003c/sub\u003eOH). While other reduction products may function as, raw materials for industrial uses such as formic acid (HCOOH) and formaldehyde (CH\u003csub\u003e2\u003c/sub\u003eO) [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. The challenges for CO\u003csub\u003e2\u003c/sub\u003e reduction are in the design of selective, stable, and efficient catalysts that are composed of cheap and abundant materials that allow cost-effective use [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. The use of catalysts based on metal composition has been extensively studied in recent years allowing to have a better understanding of the processes involved in the reaction, and thus improving the efficiency and selectivity conversion of CO\u003csub\u003e2\u003c/sub\u003e [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Among these, there are catalysts based on transition metals such as Cu, Au, Sn, Co, Ni, Fe, and Mo [\u003cspan additionalcitationids=\"CR10\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Cu-based catalysts have been widely used producing different products among which hydrocarbons stand out, mainly methane, ethylene, and ethanol [\u003cspan additionalcitationids=\"CR13\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. However, it presents many challenges to improve its stability, efficiency, and selectivity.\u003c/p\u003e\u003cp\u003eIn recent years, cobalt-based catalysts have shown increasing attention for their potential to reduce CO\u003csub\u003e2\u003c/sub\u003e. Xiao \u003cem\u003eet al.\u003c/em\u003e reported CoAlO\u003csub\u003ex\u003c/sub\u003e catalysts for the selective electroreduction of CO\u003csub\u003e2\u003c/sub\u003e to ethanol, obtaining an efficiency of 92.1% at 140\u0026deg;C [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Cobalt oxides and porphyrins promote the selective electroreduction of CO\u003csub\u003e2\u003c/sub\u003e to CO with a faradaic efficiency of 75% [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Also, the use of Co nanoparticles stabilized with graphitized carbon was efficient for the production of formic acid and CO [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Nanoparticulate Co dispersion on graphene was used to reduce CO\u003csub\u003e2\u003c/sub\u003e to methanol with an efficiency of 71% [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Ni-based catalysts are also a different alternative to Cu-based materials since Ni also reduces CO\u003csub\u003e2\u003c/sub\u003e to high-energy value products such as CH\u003csub\u003e4\u003c/sub\u003e and C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e4\u003c/sub\u003e [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Other studies of Ni as a catalyst showed high efficiency in generating CO, with a maximum value of 97% [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Functionalizing carbon nanotubes with a Ni (Ni-cyclam) complex resulted in a highly efficient catalyst to produce CO with efficiencies above 90% [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. A combination of two or more metals has been widely used to improve the catalytic properties of the individual metals. The mixture of two metals can affect the interaction of the reactants, the intermediates, and finally the products generated on the catalyst surface, improving or suppressing some electrocatalytic processes [\u003cspan additionalcitationids=\"CR23 CR24 CR25 CR26\" citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Zhang et al., using Co and Ni nanoalloys supported on nitrogen-doped carbon nanofibers, showed that the electronic distribution of the catalyst is modified by shifting the center of the Co d band. This led to variations in the interaction energies of the key intermediates for CO\u003csub\u003e2\u003c/sub\u003e reduction, such as *CO, *COOH, and *H. They reported a high CO efficiency of 85% at a potential \u0026minus;\u0026thinsp;0.9 V vs SHE [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eIn the present work, Co-Ni nanoparticles supported on mesoporous carbon (MC) and carbon nanotubes (CNT) were evaluated as electrocatalysts for the electrochemical reduction of CO\u003csub\u003e2\u003c/sub\u003e. The physicochemical characteristics of the catalysts were studied using different techniques such as powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), porosimetry (adsorption-desorption of N\u003csub\u003e2\u003c/sub\u003e) and thermogravimetric analysis (TGA). The electrocatalytic properties of the material were investigated by linear scanning voltammetry (LSV), cyclic voltammetry (CV), and chronoamperometry. The products obtained from the potentiostatic electroreduction were quantified by ion chromatography (IC). The rotating ring-disc electrode (RRDE) technique was also used for the identification and quantification of reduction products.\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n \u003ch2\u003e2.1 Catalyst synthesis\u003c/h2\u003e\n \u003cdiv id=\"Sec4\" class=\"Section3\"\u003e\n \u003ch2\u003e2.1.1 Co-Ni Nanoparticles on Mesoporous Carbon (CoNi/MC)\u003c/h2\u003e\n \u003cp\u003eThe synthesis of mesoporous carbon (MC) was previously carried out by Montiel et al. [\u003cspan class=\"CitationRef\"\u003e29\u003c/span\u003e]. The MC was obtained by carbonization of a resorcinol-formaldehyde resin. Sodium acetate was used as the catalyst, polydiallyldimethylammonium chloride as the structuring agent, and porous silica as the hard mold. The resin was dried in a vacuum oven at 100\u0026deg;C for 24 h, then carbonized in a tubular oven (Indef model T-150) under N\u003csub\u003e2\u003c/sub\u003e atmosphere with a flow of 1 L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e from 20\u0026deg;C to 1000\u0026deg;C, with a heating rate of 3\u0026deg;C min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and held at 1000\u0026deg;C for 120 minutes.\u003c/p\u003e\n \u003cp\u003eCo-Ni nanoparticles supported on mesoporous carbon (CoNi/MC) were obtained using NaBH\u003csub\u003e4\u003c/sub\u003e as a reducing agent without adjusting the media pH. NaBH4 was added in a molar ratio of 5:1 (NaBH\u003csub\u003e4\u003c/sub\u003e to metal salt) to a suspension of the carbon support containing NiSO\u003csub\u003e4\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO and Co(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO precursors at 0\u0026deg;C. The reaction flask was stirred while the temperature was maintained at 0\u0026deg;C for 6 hours. The powder obtained was filtered, washed with milli-Q water, and finally dried in a vacuum oven at 80\u0026deg;C for 24 hours. The metal-to-carbon support ratio was targeted at 40% w/w.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003ch3\u003e2.1.2 Co-Ni Nanoparticles on Carbon Nanotubes (CoNi/CNT)\u003c/h3\u003e\n\u003cp\u003eCo-Ni nanoparticles supported on carbon nanotubes (CoNi/CNT) were synthesized by using sodium dodecyl sulfate (SDS) as a stabilizer. CNT was purchased from Arkema (Graphistrenght\u0026reg;). They present a diameter between 10 and 15 nm and a purity above 90%. Before use, they were washed with a 50% w/w aqueous solution of HCl for 48 h at room temperature. Following, they were filtered and washed with tridistilled water in a Soxhlet apparatus for 24 hours. NiCl\u003csub\u003e2\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO and CoCl\u003csub\u003e2\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO were used as precursor salts. The metal-to-carbon support ratio was 40% w/w, while the Ni:Co:SDS ratio was 1:1:0.05 molar, respectively. The synthesis was carried out in a basic medium, using hydrazine as a reducing agent at 80\u0026ordm;C. Finally, the product was washed and dried for 24 hours at 80\u0026deg;C.\u003c/p\u003e\n\u003ch3\u003e2.2 Physicochemical Characterization Techniques\u003c/h3\u003e\n\u003cp\u003eThe supported catalysts were characterized by powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), porosimetry (adsorption-desorption of N\u003csub\u003e2\u003c/sub\u003e), and thermogravimetric analysis (TGA). The diffractograms of the catalysts were obtained with the Panalytical diffractometer model Empyrean 2 with a PixCell3D detector and Cu-K\u0026alpha; source with a range of 10\u0026deg; \u0026lt; 2\u0026theta;\u0026thinsp;\u0026lt;\u0026thinsp;90\u0026deg;, step length of 0.02\u0026deg;, and a count of 4 seconds. TEM images were made with a JEOL model 100 CX II microscope operated at 100 kV with magnifications of 100,000 X and 270,000 X. For EDS spectra, a FEI QUANTA 250 field emission microscope was used. Porosimetry analysis was done with the Micromeritics ASAP 2020 system with N\u003csub\u003e2\u003c/sub\u003e at -196.15\u0026deg;C. The specific surface area (SBET) was estimated by the BET method and the pore size distribution by the Barrett-Joyner-Halenda (BJH) method. TGA measurements were recorded in a Shimadzu TGA 50 equipment, using approximately 2.5 mg of the sample with an N\u003csub\u003e2\u003c/sub\u003e flow of 20 mL min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and a heating rate of 10\u0026deg;C min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e\n\u003ch3\u003e2.3 Electrochemical characterization techniques\u003c/h3\u003e\n\u003cp\u003eThe electrochemical determinations were carried out in a jacketed glass cell (Vol. 60 cm\u003csup\u003e3\u003c/sup\u003e) with an Autolab PGSTAT302N potentiostat (Echochemie, The Netherlands). An RRDE system (Pine Research Inst.) with a mounted tip consisting of a vitreous carbon disc electrode (0.196 cm\u003csup\u003e2\u003c/sup\u003e) and a platinum ring electrode (0.110 cm\u003csup\u003e2\u003c/sup\u003e) was employed. The carbon disk operated as the working electrode (WE). A coiled Pt wire, 1 mm in diameter and 10 cm in length acted as the counter electrode (CE), while a silver/silver chloride (Ag/AgCl, KCl sat) as the reference electrode (RE). A suspension of the CoNi/MC and CoNi/CNT powders was prepared by weighing 5 mg of the prepared catalyst, 15 mg of 5 wt% PVDF in N-methylpyrrolidone (NMP) as a binding agent, and 30 mg of NMP as a solvent. The components were uniformly mixed for 15 minutes in an ultrasonic bath. A drop of 10 \u0026micro;L was deposited over the carbon disk (WE) and dried in a vacuum oven at 80\u0026deg;C for 30 min. The final weight of the catalyst over the WE was determined to be ca. 5.00 mg cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. An aqueous solution of 0.1 M KHCO\u003csub\u003e3\u003c/sub\u003e (ACS reagent, Aldrich) in ultrapure water from an Arium Pro system (Sartorius) was used as an electrolyte. Measurements were made after degassing the solution for 20 min. With N\u003csub\u003e2\u003c/sub\u003e (4.0, Indura) or saturating it with CO\u003csub\u003e2\u003c/sub\u003e (3.8, Indura). All measurements were performed at a controlled temperature of 25\u0026deg;C. All potentials were referenced to the standard hydrogen electrode (SHE).\u003c/p\u003e\n\u003cp\u003eExploratory LSVs were performed by sweeping the potential from 0.3 to \u0026minus;\u0026thinsp;1.3 V vs. SHE at 10 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. CO\u003csub\u003e2\u003c/sub\u003e electrochemical reduction experiments were carried out potentiostatically (chronoamperometry). Discrete potential values from \u0026minus;\u0026thinsp;0.9 to \u0026minus;\u0026thinsp;1.4 V vs. SHE with 0.1 V intervals were applied for 900 s at the electrode. The electrolyte was previously saturated with CO\u003csub\u003e2\u003c/sub\u003e for 20 min, and then a flow rate of 2 mL min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was maintained during the measurements. Soluble products were assessed by IC (DIONEX ICS 5000) with a column ION PACK AS19 - Analytical \u0026minus;\u0026thinsp;4 \u0026times; 250 mm, from an aliquot of the electrolyte solution. The faradaic efficiencies (\u003cem\u003ef\u003c/em\u003e) were calculated from the quantities measured by IC. Electrochemical measurements in an RRDE setup were employed for the determination of CO\u003csub\u003e2\u003c/sub\u003e electroreduction products, particularly low-solubility products such as CO [\u003cspan class=\"CitationRef\"\u003e30\u003c/span\u003e]. The measurements were performed by LSV on the disk electrode while a fixed potential was applied to the ring. While the combined electrodes (disk/ring) rotated at 900 rpm, the disk electrode potential was swept from \u0026minus;\u0026thinsp;0.8 V to \u0026minus;\u0026thinsp;1.3 V vs. SHE at 10 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and the ring electrode was fixed at 0.8 V vs. SHE. The ring electrode current (i\u003csub\u003ering\u003c/sub\u003e) produced during the oxidation process was used for the quantification of the reduced product formed on the disk electrode. To identify the reduction products and their oxidation potentials, two sets of CVs were carried out at the ring electrode. The first set of CVs was performed on the Pt ring electrode in the presence of a standard solution of formic acid, formaldehyde, methanol, CO, and H\u003csub\u003e2\u003c/sub\u003e (SI-Fig. 1). The standard solutions of the aforementioned soluble products were all 0.1 M in a 0.1 M KHCO\u003csub\u003e3\u003c/sub\u003e aqueous solution, while in the case of CO and H\u003csub\u003e2\u003c/sub\u003e CVs the electrolyte was saturated with CO (3.8, Indura) and H\u003csub\u003e2\u003c/sub\u003e (Indura 4.8) gas before the measurements. The ring potential was cycled between 0.0 and 1.0 V vs. SHE at 50 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e while the disk potential was turned off and the electrode rotated at 900 rpm. CVs were carried out in the ring electrode at the same conditions as described for the standards, while the disk potential was set between \u0026minus;\u0026thinsp;0.9 and \u0026minus;\u0026thinsp;1.4 V vs. SHE with 0.1 V intervals for 180 s in 0.1 M KHCO\u003csub\u003e3\u003c/sub\u003e saturated with CO\u003csub\u003e2\u003c/sub\u003e. In other words, voltammograms were performed in the ring electrode while CO\u003csub\u003e2\u003c/sub\u003e reduction was carried out in the disk electrode. To quantify the product collected at the ring by RRDE, the rotating setup requires a calibration of the electrode by obtaining the collection efficiency (N) [\u003cspan class=\"CitationRef\"\u003e31\u003c/span\u003e]. The calibration was carried out by measuring the electrode disk (i\u003csub\u003edisk\u003c/sub\u003e) and ring (i\u003csub\u003ering\u003c/sub\u003e) currents of a 0.005 M K\u003csub\u003e3\u003c/sub\u003eFe(CN)\u003csub\u003e6\u003c/sub\u003e in a 0.1 M K\u003csub\u003e2\u003c/sub\u003eSO4 aqueous electrolyte solution. The disk potential was cycled between 0.0 and 1.0 V at 5 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, while the ring potential was fixed at 1.4 V to oxidize the Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e generated at the disk electrode. The procedure was repeated at different rotation speeds, and N was determined from the slope of i\u003csub\u003edisk\u003c/sub\u003e vs. i\u003csub\u003ering\u003c/sub\u003e plots. Faradaic efficiencies were calculated as previously described [\u003cspan class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e32\u003c/span\u003e].\u003c/p\u003e"},{"header":"3. Results and Discussion","content":"\u003ch2\u003e3.1 Catalyst Morphology Characterization\u003c/h2\u003e\n\u003cp\u003eThe PXRD patterns of the metal catalyst supported over MC and CNT are presented in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. The plot shows the position of the peaks labeled (211), (310), (301), and (321) associated with the characteristic planes of Co in its trigonal phase (P42/mnm) [\u003cspan class=\"CitationRef\"\u003e33\u003c/span\u003e], the peaks (10\u0026ndash;15), (10\u0026ndash;16), (10\u0026ndash;17) characteristic of Ni in its hexagonal phase (P6/mmm) [\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e], and the peaks (111), (200), (220), and (311), corresponding to the bimetallic alloy of Co and Ni [\u003cspan class=\"CitationRef\"\u003e35\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e37\u003c/span\u003e]. Both catalysts show a wide diffraction peak around 20\u0026deg; belonging to the carbonaceous compound of the supports. For the CoNi/CNT catalyst, the main diffraction peaks are observed at approximately 31\u0026deg;, 36\u0026deg;, 38\u0026deg;, and 43\u0026deg; associated with the Co signal corresponding to (211), (310), (301), and (321) as well as peaks at 56\u0026deg; and a broad peak at 59\u0026deg; with a shoulder at 61\u0026deg; aligning with Ni (10\u0026ndash;16), (10\u0026ndash;15), and (10\u0026ndash;17) reflections. In addition, there are peaks at 45\u0026deg;, 51, and 75\u0026deg;, matching closely with the CoNi (111), (200), and (220) reflections. On the other hand, CoNi/MC shows a broad peak at 34\u0026deg; corresponding to Co (310), a broad peak at 60\u0026deg; aligning with Ni (10\u0026ndash;15), and small peaks at 45\u0026deg; and 75\u0026deg; corresponding to the (111) and (220) CoNi signals, respectively. Throughout the patterns, the experimental peak positions generally match the expected positions. Both samples show broad peaks indicating small crystallite sizes or partial amorphous content. Importantly, the peak positions associated with pure metallic Ni and Co are shifted relative to their reference positions, suggesting that the samples do not necessarily contain separate nanoparticles of pure Co or pure Ni. Instead, this shifting might imply particles with a higher content on one of the metals. There are also differences between the MC and CNT samples in peak intensities and widths, reflecting variations in crystallinity or phase composition. Overall, both samples exhibit diffraction features consistent with mixtures of Co, Ni, and CoNi phases, and their comparison highlights subtle yet important variations in crystalline structure, alloying, and phase distribution. Based on the peaks identified for each sample, the crystallite size of the nanoparticles was calculated using the Scherrer equation [\u003cspan class=\"CitationRef\"\u003e38\u003c/span\u003e]. CoNi/CNT gave nanoparticle sizes of 6.92 nm for Co, 9.3 nm for Ni and 22 nm for the bimetallic peaks. For CoNi/MC the crystallite size was determined to be 2.69 nm for Co, 5.54 nm for Ni, and 9.7 nm corresponding to the CoNi signals.\u003c/p\u003e\n\u003cp\u003eThe dispersion and size of metallic nanoparticles in the support were evaluated by TEM images. TEM images of the CoNi/MC catalyst are shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e. The mesoporous carbon support shows a high concentration of homogeneously distributed particles with a circular geometry and an average size of 4.4 nm. The TEM images of CoNi/CNT are shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e. The sample presented tubes of various thicknesses, with large particles homogeneously distributed throughout the structures. The particles have an elongated morphology and blunt edges, in addition to particles with a circular morphology with an average size of 10.7 nm.\u003c/p\u003e\n\u003cp\u003eTo determine the atomic ratio of Co and Ni over the MC and CNT supports, the study of the elemental composition was carried out through EDS (Figure SI-2 and SI-3). The atomic composition presented for each catalyst resulted in 45.5% Co to 54.5% Ni over MC and 48.4% to Co 51.6% Ni over CNT. The composition result is consistent with the 1:1 Co-Ni intended ratio, although needs to be remembered that this is the average composition across the beam area.\u003c/p\u003e\n\u003cp\u003eThe nitrogen absorption-desorption isotherms of the CoNi catalysts supported on MC and CNT are shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eA. In both systems, the isotherms are type IV and hysteresis loop type H3 according to the classification of the International Union of Pure and Applied Chemistry (IUPAC) [\u003cspan class=\"CitationRef\"\u003e39\u003c/span\u003e]. Increased N\u003csub\u003e2\u003c/sub\u003e absorption at low pressures and hysteresis loop formation at high pressure are characteristic of mesoporous structures and multilayer formation. The specific surface area of the samples was 265.7 cm\u003csup\u003e2\u003c/sup\u003e g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 115.8 cm\u003csup\u003e2\u003c/sup\u003e g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for CoNi/MC and CoNi/CNT, respectively. The pore size distributions obtained through the BJH model (dV/dlog(d)) are shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eB. Both catalysts show a monomodal distribution of pores between 3 and 62 nm with a maximum value of 35 nm for CoNi/CNT and 40 nm for the CoNi/MC sample. The plots show the presence of pores around 4 nm whose origin is typically interstitial space in sphere clusters [\u003cspan class=\"CitationRef\"\u003e40\u003c/span\u003e].\u003c/p\u003e\n\u003cp\u003eThe metal content was determined by thermogravimetric analysis, and the results are shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e. The TGA curves in both catalysts show an initial mass loss between 90 and 250\u0026deg;C that corresponds to the evaporation of H\u003csub\u003e2\u003c/sub\u003eO, up to approximately 300\u0026deg;C and 400\u0026deg;C for CoNi/MC and CoNi/CNT, respectively. From these temperatures a more pronounced process is observed that goes up to 700\u0026deg;C and is mainly due to the loss of mass due to the calcination of the supports and their elimination in the form of CO\u003csub\u003e2\u003c/sub\u003e. The metal amount determined in the final catalyst was 35.26% for CoNi/MC and 34.68% for CoNi/CNT.\u003c/p\u003e\n\u003ch3\u003e3 Electrochemical Characterization\u003c/h3\u003e\n\u003cp\u003eThe LSVs obtained for CoNi over the two carbon matrixes are shown in Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e (A and B). The voltammetries show a continuous increase of a reduction in current density (\u003cem\u003ej\u003c/em\u003e) from the beginning of the experiments. In the presence of N\u003csub\u003e2\u003c/sub\u003e and CO\u003csub\u003e2\u003c/sub\u003e, the curves present similar features with minor differences. For both catalysts, the LSV in the degassed electrolyte (N\u003csub\u003e2\u003c/sub\u003e) shows a sharp increase of the reduction \u003cem\u003ej\u003c/em\u003e at around \u0026minus;\u0026thinsp;1.1V vs SHE. Also, there is a small depression at ca. -0.2V vs SHE. The main difference is the presence of another depression at -0.95V vs SHE for CoNi/CNT. For the electrolyte saturated with CO\u003csub\u003e2\u003c/sub\u003e, both catalysts present the increase of the reduction \u003cem\u003ej\u003c/em\u003e at around \u0026minus;\u0026thinsp;0.85V vs SHE. The main difference observed is that CoNi/MC \u003cem\u003ej\u003c/em\u003e stabilizes and then increases again at ca -1.1V vs SHE while for CoNi/CNT the \u003cem\u003ej\u003c/em\u003e keeps increasing with a change of rate of lower pace at around \u0026minus;\u0026thinsp;0.95V vs SHE. The onset potential for the reduction process in the presence of CO\u003csub\u003e2\u003c/sub\u003e is more anodic compared to degassed electrolytes with a shift of ca. 0.25 V for both catalysts. Moreover, the rate change for the current density below 0.85 V vs SHE indicates a more complex reduction process in the presence of CO\u003csub\u003e2\u003c/sub\u003e. Besides the aforementioned change in the \u003cem\u003ej\u003c/em\u003e rate, the other difference between each catalyst is that the current density module in the presence of CO\u003csub\u003e2\u003c/sub\u003e is higher for CoNi/MC compared to the degassed electrolyte.\u003c/p\u003e\n\u003cp\u003eElectroreduction of CO\u003csub\u003e2\u003c/sub\u003e for the quantification of the reduction products was performed potentiostatically at discrete potential values between \u0026minus;\u0026thinsp;0.8 V and \u0026minus;\u0026thinsp;1.3 V vs SHE. A set of experiments was carried out to assess soluble reduction products by IC from aliquots taken from the electrolyte media. Formic acid was the only soluble product detected at potentials between \u0026minus;\u0026thinsp;0.9 V and \u0026minus;\u0026thinsp;1.1 V vs SHE for both catalysts. No product signal was observed below \u0026minus;\u0026thinsp;1.1 V vs SHE. The charge applied to the WE was converted to the mass of formic acid to calculate the \u0026fnof; based on the experimental concentration obtained by IC. The \u0026fnof; have a maximum value of 32.94% at -0.9 V vs SHE in CoNi/MC and 38.98% at -1.1 V vs SHE for CoNi/CNT. Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e shows the values of electrochemical charge, the formic acid amount measured by IC, and the calculated values of \u0026fnof;.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eFormic acid quantities measured by IC (m\u003csub\u003eIC\u003c/sub\u003e), experimental electrode charge (\u003cem\u003eQ\u003c/em\u003e), and faradic efficiency calculated at different potentials for CoNi/MC and CoNi/CNT.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n \u003cth align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eCoNi/MC\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eCoNi/CNT\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003ePotential\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e(V vs SHE)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003em\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003eIC\u003c/strong\u003e\u003c/sub\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e(mgL\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e\u0026minus;\u0026thinsp;1\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eQ\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e(mC)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026fnof;\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e%\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003em\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003eIC\u003c/strong\u003e\u003c/sub\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e(mgL\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e\u0026minus;\u0026thinsp;1\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eQ\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e(mC)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003ef\u003c/em\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e%\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-0.9\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.28\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e73\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e32.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.14\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e90\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e13.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-1.0\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.10\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e150\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.25\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e140\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e15.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-1.1\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.24\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e210\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e220\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e38.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eAs mentioned in the experimental section, the determination and quantification of CO\u003csub\u003e2\u003c/sub\u003e electrochemically reduced products by RRDE were previously shown [\u003cspan class=\"CitationRef\"\u003e30\u003c/span\u003e]. Figure \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e, shows the CVs carried out at the ring electrode for different applied potentials on the disk electrode for both catalyst systems. The CVs were compared with those obtained for the standard solutions of the possible reduction products (Figure SI-1). Both catalysts show an oxidation peak in the forward scan. In the case of CoNi/MC, the peak is quite narrow and emerges when the applied potential is below \u0026minus;\u0026thinsp;1.0 V vs. SHE. On CoNi/CNT, the peak is broader, and although low, is visible starting from \u0026minus;\u0026thinsp;0.9 V vs SHE. The reduction peak at the back scan showing below 0.4 V vs SHE for CoNi/MC is assigned to the oxygen reduction reaction. According to the standards CVs, the ORR peak is visible when the only product present is CO. Other products like formaldehyde, methanol, and formic acid require a high potential for complete oxidation [\u003cspan class=\"CitationRef\"\u003e41\u003c/span\u003e], diminishing the oxygen reduction reaction. For the CoNi/CNT, there is an increase in the reduction current for the back scan between 0.2 and 0.5 V vs SHE, which is noticeable as the applied potential increases. The methanol standard CV is the one showing an oxidation peak at that particular potential in the back scan, although formaldehyde and formic acid also possess broad oxidation peaks in the back scan. The analysis of the CVs and the information from the IC would indicate that the only products are formic acid and CO.\u003c/p\u003e\n\u003cp\u003eThe RRDE quantification of reduction products was performed by linear voltammetry on the disc electrode while the ring electrode was set at 0.8 V vs SHE. The i\u003csub\u003edisk\u003c/sub\u003e and i\u003csub\u003ering\u003c/sub\u003e electrode currents were used to calculate the faradaic efficiency according to Eq. (\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e) [\u003cspan class=\"CitationRef\"\u003e30\u003c/span\u003e].\u003c/p\u003e\n\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e$$\\:f=\\frac{{i}_{ring}}{\\left|{i}_{disk}\\right|N}\\times\\:100$$\u003c/div\u003e\n \u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eWhere N is the collection efficiency of the RRDE. It was shown that the model based on a planar electrode used for the determination of N, also applies to a catalyst deposited on the electrode [\u003cspan class=\"CitationRef\"\u003e42\u003c/span\u003e]. The collection efficiency was determined in each system for the calculation of the \u003cem\u003ef\u003c/em\u003e. The values obtained were 0.14\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03 and 0.16\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01 for CoNi/MC and CoNi/CNT, respectively (supplementary). The efficiency obtained from Eq.\u0026nbsp;(\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e) is presented in Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e.\u003c/p\u003e\n\u003cp\u003eThe i\u003csub\u003ering\u003c/sub\u003e detected on the ring electrode arises from the oxidation of different reduction products. The form of Eq. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e is derived for processes involving 2e\u003csup\u003e-\u003c/sup\u003e. Therefore, the faradaic efficiency represented in Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e, is the result of sensing the oxidation current arising from the presence of HCOOH and CO, as revealed by the results of the IC and the CVs from Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e. Also, contribution to the i\u003csub\u003ering\u003c/sub\u003e may arise unavoidably from the H\u003csub\u003e2\u003c/sub\u003e presence generated from the H\u003csup\u003e+\u003c/sup\u003e reduction, particularly at the lowest potentials. For CoNi/MC at -0.9 V vs SHE, the calculated efficiency of 41.7%, corresponding to the formation of HCOOH indicated by IC to contribute with a 32.9% of faradic efficiency, while the difference of 8.8% should be associated with the formation of CO or H\u003csub\u003e2\u003c/sub\u003e. For \u0026minus;\u0026thinsp;1.0 V vs SHE the efficiency has contributions from HCOOH and CO according to the results obtained by IC and RRDE. The efficiency calculated by RRDE is 49.2% which corresponds to 5.7% of HCOOH obtained by CI and the efficiency of CO is approximately 43.5%. At -1.1 V vs SHE, there is also a contribution from HCOOH and CO, with a total of 5.8%. Being 5.9% for HCOOH and 46.9% for CO. At potentials of -1.2 V and \u0026minus;\u0026thinsp;1.3 V vs SHE, the efficiency has no contribution from HCOOH according to IC results, and the current in the ring electrode is mainly assigned to CO formation. Therefore, the efficiency calculated at these potentials corresponds to the production of CO with a value of 48.2% and 32.9% for these potentials, respectively. For CoNi/CNT, at -0.9 V vs SHE in Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003eD, the efficiency is 14.7% which corresponds to the sum of contributions from HCOOH and CO. We obtained by IC 13.3% of HCOOH and the remaining 1.4% is associated with the formation of CO. At a potential of -1.0 V vs. SHE, the efficiency also has two contributions with 15.3% HCOOH and 19.4% CO for a total of 34.7%. For \u0026minus;\u0026thinsp;1.1 V vs SHE, the total efficiency calculated by RRDE is 44.2%, here the highest efficiency was obtained for HCOOH with 38.9% and the remaining 5.3% corresponds to CO. For potentials of -1.2 V and \u0026minus;\u0026thinsp;1.3 V vs SHE, the formation of HCOOH is no longer detected by IC and the calculated efficiency corresponds to the formation of CO with values of 48.6% and 54% for the aforementioned potentials. The formation of H\u003csub\u003e2\u003c/sub\u003e can be present to a lesser or greater extent throughout the potential range.\u003c/p\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eElectrochemical measurements demonstrate that catalysts based on cobalt and nickel nanoparticles exhibit catalytic activity for the reduction of CO₂. Analytical determinations confirm that HCOOH is produced, with an efficiency of 32.9% on CoNi/MC at -0.9 V vs SHE and 38.9% on CoNi/CNT at -1.1 V vs SHE. The faradaic efficiency measured by RRDE indicates that CoNi/MC achieves a maximum conversion of approximately 53% at -1.1 V vs SHE, while for CoNi/CNT, the conversion increases steadily until reaching 54% at -1.3 V vs SHE. Although the products cannot be accurately identified, these efficiencies are most likely due to the conversion to CO.\u003c/p\u003e"},{"header":"Statements and Declarations","content":"\u003cp\u003eCompeting interests: The authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003eThis work was supported by Agencia Nacional de Promoción de la Investigación, el Desarrollo Tecnológico y la Innovación Argentina (AGENCIA I+D+i) Grant number PICT 2018–01407.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCRediT author statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFormal analysis and investigation, Writing - Original Draft.\u003cstrong\u003e: Jhon Faber Zapata Cardona.\u003c/strong\u003e Formal analysis and investigation: \u003cstrong\u003eJulieta Carballo.\u0026nbsp;\u003c/strong\u003eFormal analysis and investigation: \u003cstrong\u003eGonzalo Montiel\u003c/strong\u003e. Conceptualization, Writing - review and editing: \u003cstrong\u003eMariano M. Bruno.\u003c/strong\u003e Conceptualization,\u0026nbsp;Visualization,\u0026nbsp;Funding acquisition, Writing - Review \u0026amp; Editing: \u003cstrong\u003eFederico A. Viva\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAcknowledgment:\u003c/p\u003e\n\u003cp\u003eThe authors thank Ana Larralde and Diego Lamas from the Applied Crystallography Laboratory (UNSAM) for the DRX measurements. In addition to Cecilia Albornoz from the DMFC Chemistry Laboratory for the TG measurements. The authors also thank Facundo Baraldo, Silvina Martin, and Roberto Servant from the Analytical Chemistry Department (CNEA) for the IC measurements. JFZ thanks Consejo Nacional de Investigaciones Científicas y Técnica Argentina (CONICET) for his doctoral scholarship. MMB and FAV are members of CONICET.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eR.L. Singh, P.K. Singh, Global Environmental Problems, in: Princ. Appl. Environ. Biotechnol. a Sustain. 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Wokaun, G.G. Scherer, T.J. Schmidt, V. Stamenkovic, V. Radmilovic, N.M. Markovic, P.N. Ross, Oxygen Reduction on Carbon-Supported Pt\u0026minus;Ni and Pt\u0026minus;Co Alloy Catalysts, J. Phys. Chem. B. 106 (2002) 4181\u0026ndash;4191. https://doi.org/10.1021/jp013442l.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"CO2, Electrochemical reduction, RRDE, Formic Acid, Nanoparticles","lastPublishedDoi":"10.21203/rs.3.rs-6823214/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6823214/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eCoNi nanoparticles were deposited over two different carbon supports. A mesoporous carbon obtained from a resorcinol formaldehyde resin, and commercial carbon nanotubes. The metal nanoparticles were evaluated for the electrochemical reduction of CO\u003csub\u003e2\u003c/sub\u003e in aqueous media. X-ray diffraction and transmission electron microscopy measurements show differences in the nanoparticle\u0026rsquo;s morphology. The electrochemical determinations presented different results for the CO2 electroreduction. Formic acid was formed at different potentials on each catalyst as indicated by chromatography. CoNi over mesoporous carbon showed a faradaic efficiency of 32.9% at -0.9 V vs SHE while the metal nanoparticles over nanotubes presented an efficiency of 38.9% at -1.1 V vs SHE. Rotating ring disk electrode determinations also showed different behavior for each metal nanoparticulated catalyst.\u003c/p\u003e","manuscriptTitle":"Electrochemical reduction of CO 2 on CoNi nanoparticles supported on different carbon matrixes","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-11 08:26:37","doi":"10.21203/rs.3.rs-6823214/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"eea024a1-f85b-4dba-bb5f-c8bc8dd13bd0","owner":[],"postedDate":"July 11th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-08-01T19:08:24+00:00","versionOfRecord":[],"versionCreatedAt":"2025-07-11 08:26:37","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6823214","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6823214","identity":"rs-6823214","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}