Co supported on Manganese Ferrite for Hydrogen Evolution via Sodium Borohydride Hydrolysis

Co supported on Manganese Ferrite for Hydrogen Evolution via Sodium Borohydride Hydrolysis | 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 Co supported on Manganese Ferrite for Hydrogen Evolution via Sodium Borohydride Hydrolysis atieh ranjbar, amir mosayebi This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6883073/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 29 Sep, 2025 Read the published version in Research on Chemical Intermediates → Version 1 posted 11 You are reading this latest preprint version Abstract The generation of hydrogen gas through the catalytic hydrolysis of sodium borohydride (NaBH 4 ) has garnered significant interest in recent years. The primary research challenge remains the development of effective and reusable catalysts. This research details the development of Co/MnFe 2 O 4 catalysts aimed at facilitating the hydrolysis of sodium borohydride (NaBH 4 ), employing MnFe 2 O 4 as the support material. The support was synthesized through a co-precipitation method, while the catalysts were produced via an impregnation-chemical reduction technique. The characterization of the catalysts was performed using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), vibrating sample magnetometry (VSM), and nitrogen adsorption-desorption measurements. The study initially explored the effects of calcination temperature of the supports and the amount of loaded cobalt on the hydrogen generation process. Notably, catalysts supported on MnFe 2 O 4 calcined at 400°C demonstrated superior activity, with 30% Co/MF-400 catalyst yielding 3533 mL.min − 1 .g cat −1 of hydrogen during NaBH 4 hydrolysis. The enhanced catalytic performance of the MF-400 supported catalysts was attributed to their small crystallite size or prominent number of defects and relatively high magnetic properties. In addition, 30Co-MF400 showed high specific surface area of 120.1 m 2 .g − 1 . Subsequently, various parameters were examined over 30Co/MF-400, including catalyst dosage (10–20 mg), concentrations of NaOH (1–7 wt.%), temperature (25-45 o C), and catalyst reusability. The activation energy (E a ) for the 30% Co/MF-400 catalyst was found to be 27.1 kJ/mol, as determined through the application of the rate expression and the Arrhenius equation. The 30% Co/MF-400 catalyst showed a 44% decline in catalytic performance after being used for four cycles. Cobalt MnFe2O4 Hydrolysis NaBH4 Hydrogen production 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 The rising demand for energy, coupled with the finite availability of fossil fuels, compels us to seek out alternative energy sources [ 1 – 2 ]. These alternative sources are anticipated to possess high energy density and to generate no harmful emissions, such as NO x , SO x , CO, and CO 2 . The detrimental effects of these pollutants, including their contribution to the greenhouse effect, are well recognized [ 3 ]. Hydrogen (H 2 ) has garnered significant interest as a clean, sustainable, and efficient energy carrier. H 2 can be produced through various methods, including high-temperature reforming reactions [ 4 ], water electrolysis [ 5 ], photo-catalytic processes [ 6 ], and the hydrolysis of metal hydrides [ 7 , 8 ]. Metal hydrides like NaH, NaAlH 4 , NaBH 4 , LiH, LiAlH 4 , LiBH 4 , CaH 2 , Ca(BH 4 ) 2 , MgH 2 , Mg(BH 4 ) 2 , KH, KBH 4 can be used to generate hydrogen. Among metal hydrides, sodium borohydride (NaBH 4 ) exhibits a hydrogen storage capacity of 10.8 wt.% [ 9 ]. NaBH 4 meets the technical target of 6 wt% hydrogen capacity set by US Department of Energy (DOE). The hydrogen stored in NaBH 4 can be released via a hydrolysis reaction that produces no harmful byproducts [ 10 ], as illustrated in reaction 1 (R1). This exothermic reaction can generate hydrogen at low temperatures when a catalyst is present. Non-catalytic hydrolysis of NaBH 4 is a slow process and its conversion is very low (7–8%) [ 11 ]. The pure hydrogen produced can be utilized in proton exchange membrane fuel cells (PEMFCs) and hydrogen fuel cell vehicles (HFCVs) [ 12 ]. NaBH₄ + 2 H₂ O → NaBO₂ + 4 H₂ (R1) Both noble and non-noble metal catalysts have been investigated for the hydrolysis of NaBH 4 . Noble metal catalysts, such as platinum (Pt) and ruthenium (Ru), whether supported or un-supported, demonstrate high catalytic activity in this reaction. For instance, Ru nanoclusters stabilized by a ligand and Ru-RuO 2 supported on carbon powders achieved hydrogen generation rates (HGR) of 96800 mL.min − 1 .g cat −1 and 2800 mL.min − 1 .g cat −1 , respectively [ 13 – 14 ]. Ru nanoparticles decorated with CoB 2 O 4 on mesoporous carbon revealed HGR of 8139 mL.min − 1 .g cat −1 at 25 o C [ 15 ]. Additionally, Pt and various combinations of Pt/Pd/Ru/Rh supported on carbon/CNT and ferrites have also shown excellent hydrogen production capabilities [ 16 – 18 ]. However, the high cost of noble metals limits their widespread application. Consequently, there has been a development of cost-effective alternatives using non-noble metal catalysts such as cobalt (Co), nickel (Ni), and iron (Fe). The Pt catalyst promoted by Co supported on carbon spheres exhibited 8943 mL.min − 1 .g cat −1 hydrogen generation rate [ 19 ] Various formulations of Co-based catalysts, including Co [ 20 ], Co-B [ 21 ], Co-Ni-B [ 22 ], Co-P-B [ 23 , 24 ], Co-Mn-B [ 25 ] and Co-Y 2 O 3 -B [ 26 ] have been proposed for this reaction. Addition of promoter to Co-based catalysts enhanced the active surface areas and particle distribution over the catalyst. Active (nano)powders or un-supported catalysts often face issues with particle agglomeration, which reduces specific surface area and subsequently diminishes catalytic activity and recyclability. Cobalt or cobalt-promoted catalysts have been supported on various substrates, including activated carbon [ 27 ], multi-walled carbon nanotubes (MWCNTs) [ 28 ], copper sheets [ 29 ], nickel foam [ 30 , 31 ], alumina, cerium oxide (CeO 2 ), titanium dioxide (TiO 2 ) [ 32 , 33 ], hydrogels [ 34 ], clays [ 35 ], quantum dots [ 36 ], zeolites [ 37 ] and ferrites [ 18 , 38 ]. Ferrites are particularly notable for their unique adsorptive, magnetic, thermal, and electrical properties [ 39 ] and are utilized in various catalytic reactions [40–41], gas sensors [ 42 ], electronic devices, and drug delivery systems [ 43 ]. Cobalt [ 44 – 45 ], nickel [ 46 ], zinc, and copper ferrites [ 38 ] have been applied in the hydrolysis of NaBH 4 . Mirshafiee and Rezaei [ 38 ] synthesized Co/MFe 2 O 4 (where M = Cu, Co, Zn, Ni) catalysts via impregnation reduction and sol-gel methods (for MFe 2 O 4 ). The Co/CuFe 2 O 4 catalyst exhibited the highest hydrogen production rate of 2937 mL.min − 1 .g cat −1 , attributed to its excellent cobalt distribution, large surface area, and high electrical conductivity. The NiB/NiFe 2 O 4 catalyst (where NiFe 2 O 4 was prepared using an EDTA-citric acid complexing method) demonstrated significant activity even at low concentrations of NaBH 4 , with superior performance observed for supported catalysts compared to un-supported one [ 46 ]. An Ag-based/CoFe 2 O 4 -CNT catalyst produced 320 mL.min − 1 .g cat −1 hydrogen due to the high dispersion of Ag nanoparticles and the synergistic effect between Ag nanoparticles and CoFe 2 O 4 -CNT. Other materials such as CuFe 2 O 4 /RGO and CoFe 2 O 4 -modified transition metals showed remarkable activity and recyclability. CuFe 2 O 4 /RGO yielded a hydrogen production rate of 622 mL.min − 1 .g cat −1 , while CoFe 2 O 4 -modified catalysts (Ru, Pt, Pd, Ir, Ag) exhibited turnover frequencies of 421 and 348 mol H2 ·mol cat –1 ·min –1 for Ru and Pd modified catalysts, respectively [ 44 , 47 ]. MnFe 2 O 4 is a spinel ferrite that possesses several beneficial properties, which have yet to be explored in the context of sodium borohydride hydrolysis. Its applications have been well-documented in photocatalytic processes [ 48 ] and in the treatment of water and wastewater [ 49 ]. In this investigation, MnFe 2 O 4 was synthesized through a co-precipitation method and subsequently utilized as a support for a cobalt (Co) catalyst, which was prepared using an impregnation reduction approach. The initial focus was on assessing the influence of the calcination temperature of MnFe 2 O 4 as a support for 20% Co catalysts in the hydrolysis reaction of sodium borohydride (NaBH 4 ). Following this, the effects of varying Co loadings (10%, 20%, and 30%) on the optimally heat-treated MnFe 2 O 4 support were investigated. After determining the ideal calcination temperature and Co loading, additional experiments were performed to investigate the impacts of NaOH concentrations, catalyst loading, and reaction temperature on the overall reaction rate. 2. Experimental 2.1. MnFe 2 O 4 synthesis The synthesis of the MnFe 2 O 4 spinel was accomplished through a co-precipitation method. The precursor materials utilized in this process included manganese nitrate tetrahydrate (Mn(NO 3 ) 2 .4H 2 O, Loba Chemie, 98.5%) and iron nitrate nonahydrate (Fe(NO 3 ) 3 .9H 2 O, Loba Chemie, 98%). For synthesis of 1g MnFe 2 O 4 , 3.57 g iron nitrate and 1.1 g manganese nitrate were dissolved in 100 mL of water. Subsequently, a 0.5 M sodium hydroxide (NaOH, Merck, 99%) solution was added dropwise to the mixture while maintaining the temperature at 60°C until the pH reached 10.5. The resulting solution was subjected to stirring for an additional 2 hours at a temperature of 70°C. Upon cooling, the precipitate was filtered and subsequently washed with distilled water to remove any residual nitrates. The filtered precipitate was then dried overnight at 80°C. The samples were subjected to thermal treatment at varying temperatures, with the sample that was not calcined referred to as MF-80. The samples that underwent calcination at 400°C and 600°C were labeled as MF-400 and MF-600, respectively. 2.2. Catalyst synthesis The catalysts were synthesized through the impregnation-reduction technique, utilizing different cobalt loadings. Specifically, cobalt nitrate hexahydrate (Co(NO 3 ) 2 .6H 2 O) was dissolved in 20 mL of distilled water at concentrations of 10, 20, or 30 wt.%. This solution was combined with an adequate amount of MnFe 2 O 4 . Following this, a 10 mL solution of sodium borohydride (NaBH 4 , Loba Chemie, 98%) was swiftly introduced to the mixture, maintaining a molar ratio of NaBH 4 to cobalt at 4. The resulting solution was mixed for 20 min before being subjected to filtration, washing, and drying at 80°C overnight. 2.3. Characterization To investigate the crystal structure of MnFe 2 O 4 spinel and cobalt, X-ray diffraction (XRD) analysis was conducted using a PANalytical X'Pert Pro apparatus, covering a range from 10° to 80°. The surface area and porosity both supports and catalysts were assessed through N 2 adsorption-desorptiontest, utilizing a BELSORP Mini II device. BET (Brunauer-Emmett-Teller) method was employed to measure the surface area, however; porosity was calculated using desorption branch of isotherm by the BJH method. Morphological and structural characteristics of the samples were examined via field emission scanning electron microscopy (MIRA3TESCAN-XMU model) operating at 30 kV. Additionally, the magnetic properties of the Co/MnFe 2 O 4 catalysts were analyzed using a Vibrating Sample Magnetometer (Magnetic Daneshpajooh Kashan MDKB model), with a maximum field strength of 1.5 Tesla. 2.4. Catalytic activity experiments The generation rate of hydrogen was evaluated utilizing the water displacement technique, as depicted in Fig. 1 . A catalyst weighing 15 mg was introduced into a 250 mL round-bottom three-neck flask, which functioned as the reactor, and was maintained at a stable temperature of 35 ± 0.1°C. Following this, 5 mL of an aqueous solution comprising 3 wt.% sodium borohydride and 3 wt.% NaOH was added to the flask while ensuring continuous and vigorous stirring. The feed was warmed to the required temperature before the injection. Hydrogen production began immediately upon the addition of the aqueous solution. The volume of hydrogen generated was monitored by measuring the water displacement in an inverted graduated cylinder. Each experiment was performed at least twice to guarantee the reliability and reproducibility of the findings. 3. Results and discussions 3.1. Characterization of catalysts 3.1.1. XRD analysis The X-ray diffraction (XRD) patterns for the supports and catalysts produced through co-precipitation and impregnation-chemical reduction techniques are illustrated in Figs. 2 and 3 . The supports were subjected to thermal treatment at different temperatures. Analysis revealed that the sample dried at 80°C and the one calcined at 400°C exhibited the formation of a pure cubic spinel phase of MnFe₂O₄. Characteristic diffraction peaks corresponding to MnFe₂O₄ cubic spinel, as per JCPDS No. 01-074-2403, were identified at angles of 18.33°, 30.3°, 35.1°, 57.8°, 62.7°, and 72.39°. In contrast, the sample calcined at 600°C experienced phase separation, leading to the emergence of Fe₂O₃ and Mn₂O₃. Notably, despite the conversion of MnFe₂O₄ into other phases, a residual quantity of MnFe₂O₄ persisted, maintaining its magnetic characteristics. Peaks associated with α-Fe₂O₃ (rhombohedral) were detected at 24.45°, 35.57°, 49°, 54.45°, 57.99°, 62.8°, 64.35°, 72.33°, and 75.69° (JCPDS No. 00-024-0072). Peaks associated with Mn₂O₃ were detected at 33.5°, 35.9°, and 54.5° (JCPDS No. 01-076-0150). Phase separation of MnFe₂O₄ at temperatures exceeding 400°C has been widely reported in the literature [ 50 , 51 ]. Junlabhut et al. [ 50 ] observed similar phase transitions when MnFe₂O₄ was synthesized from chloride precursors using the co-precipitation method, with phase changes occurring above 400°C. These transformations are not limited to co-precipitation techniques; phase transitions to Fe₂O₃ and Mn₂O₃ have also been reported for non-aqueous microwave synthesis, thermal decomposition, and sol-gel methods [ 51 – 53 ]. The X-ray diffraction (XRD) analysis of the catalysts indicated that the dominant peaks were linked to the MnFe 2 O 4 spinel structure. Specifically, the peaks observed at 43.2° and 74.25° were identified as metallic cobalt, whereas those at 35.4° and 62.9° were related to cobalt oxide compounds, namely Co 3 O 4 and CoO. The literature frequently documents the partial oxidation of cobalt in both supported and unsupported catalyst systems [ 54 – 55 ]. Peaks at 35.5° and 62° are commonly attributed to Co₃O₄. The average crystallite sizes of the supports and catalysts, as determined through the application of the Scherrer equation, are detailed in Table 1 . The MF-80 and MF-400 supports exhibited average crystallite sizes of 13.7 nm and 9.17 nm, respectively, based on measurements from the (311), (333), and (440) planes. In contrast, the MF-600 sample demonstrated an average crystallite size of 30.08 nm, which was calculated using the (012), (104), (110), (113), (024), (116), (214), and (300) planes associated with Fe 2 O 3 , noting that the planes corresponding to Mn 2 O 3 overlap with those of Fe 2 O 3 . The same variation of crystallite size at different calcination temperatures is reported by Simon et al. [ 51 ] and Rana et al. [ 56 ]. The unusual decrease of crystallite size with increase of heat treatment temperature in MF-400 is linked to increased disordered defects and disorderliness that start occurring at temperatures higher than 300 o C as reported by Rana et al. [ 56 ] for MnFe 2 O 4 samples prepared by co-precipitation method. The cobalt crystallite size was measured for the 20%Co catalyst supported on MF-400, yielding a value of 5.6 nm based on the (111) plane. Table 1 The properties of prepared supports and catalysts. Sample Crystallite size a (nm) BET surface area (m 2 /g) Total Pore volume (cm 3 . g − 1 ) Average pore size (nm) MF-80 13.72 210.9 0.279 5.2 MF-400 9.17 89.0 0.2303 18.2 MF-600 30.08 - - - 20Co/MF-80 - 154.3 0.2541 6.5 20Co/MF-400 5.6 b - - - 30Co/MF-400 - 120.1 0.3706 15.0 a calculated from XRD. b cobalt crystallite size is calculated. 3.1.2. N 2 adsorption–desorption analysis The specific surface area, total pore volume and mean pore diameter of supports and their catalysts received from N 2 adsorption/desorption are reported in Table 1 . The MF-80 support, which was not subjected to calcination, exhibited the highest surface area of 210.9 m²g − 1 . However, calcination at 400°C resulted in a reduction of the surface area to 89.0 m²g − 1 . Similarly, the total pore volume in MF-400 also decreased, although to a lesser extent than the surface area. The mean pore diameter exhibited a significant increase after calcination at 400°C, escalating from 5.2 nm in MF-80 to 18.2 nm in MF-400. Following the impregnation of the MF-400 support with 30% cobalt, both the BET surface area and total pore volume saw an enhancement, although the mean pore size reduced to 15 nm. This improvement in specific surface area post-impregnation can be ascribed to the development of dispersed cobalt particles that demonstrate robust interactions with the support [ 55 ]. In contrast, the 20 Co/MF-80 sample exhibited a decrease in specific surface area following the impregnation process, which can be attributed to the blockage or damage of narrow pores caused by this procedure. The nitrogen adsorption/desorption isotherms and pore size distribution profiles are presented in Figs. 4 a and 4 b. The MF-80 sample, which was not calcined, along with its corresponding catalyst, displayed a type IV isotherm characterized by an H4 hysteresis loop, indicative of slit-shaped pores. Similarly, MF-400 and its catalyst also exhibited a type IV isotherm. An H1 hysteresis loop was noted for MF-400, while the 30Co/MF-400 sample revealed both H1 and H3 hysteresis loops. The H1 and H3 loops are associated with cylindrical and wedge-shaped pores, respectively [ 57 ]. The impregnation-reduction of the MF-400 support with cobalt resulted in the transformation of some cylindrical pores into wedge-shaped pores or the introduction of redesigned pores within the catalyst. 3.1.3. The magnetic behavior of catalysts The magnetization curves corresponding to the applied magnetic field for the 20Co/MnFe₂O₄ catalysts are presented in Fig. 5 . The observed hysteresis loops indicate superparamagnetic characteristics at room temperature across all samples, a behavior commonly associated with magnetic nanoparticles. Notably, the 20Co/MF-80 sample demonstrated the highest magnetic saturation, recorded at 21.25 emu/g. Nevertheless, an increase in the calcination temperature of the MnFe₂O₄ support resulted in a deterioration of the catalyst's magnetic properties, with this decline becoming increasingly significant at temperatures above 400°C. A comparable reduction in magnetic saturation with elevated calcination temperatures has also been documented by Simon et al. [ 51 ]. They observed a reduction near to 5 emu/g in magnetic saturation at room temperature as the MnFe₂O₄ heat treatment temperature increased from 80°C to 400°C. The magnetic behavior of the Co/MnFe₂O₄ catalysts follows the order: 20Co/MF-80 > 20Co/MF-400 > 20Co/MF-600. The comparatively low magnetic properties of the 20Co/MF-600 sample are primarily attributed to phase transformations in MnFe₂O₄ that occur at elevated temperatures. 3.1.4. FE-SEM images FE-SEM was utilized to investigate the morphology and particle size of the synthesized catalyst. The images corresponding to the 30%Co/MF-400 catalyst are illustrated in Fig. 6 . Specifically, images 6a and 6b reveal the presence of aggregated, compact polyhedral or nearly spherical nanoparticles. The larger particles, exceeding 60 nm in size, exhibited a polyhedral morphology, whereas the smaller particles appeared predominantly spherical. As depicted in Fig. 6 c, a total of 40 particles were analyzed to assess the particle size distribution using Digimizer software, resulting in an average particle size of 58 nm for the 30%Co/MF-400 catalyst. 3.2. Catalytic activity tests 3.2.1. Effect of MnFe 2 O 4 calcination temperature Hydrogen generation over 20%Co/MnFe₂O₄ catalysts at 35°C was evaluated. The hydrogen generation started instantaneously upon injection of solution for all samples. The MnFe₂O₄ support in these catalysts was heat-treated at varying temperatures (80°C, 400°C, and 600°C). As shown in Fig. 7 , hydrogen generation over time was measured. The MnFe₂O₄ support alone displayed negligible catalytic activity in the aqueous solution. The 20%Co/MnFe₂O₄ catalysts demonstrated significantly higher activity for NaBH₄ hydrolysis. These results suggest that the catalytic activity is entirely reliant on the Co active sites, while the MnFe₂O₄ support enhanced the formation of additional active sites for Co through improved interaction and cobalt dispersion. Among the cobalt catalysts with a composition of 20 wt.%, the 20Co/MF-400 catalyst demonstrated the most significant catalytic performance, generating 402 mL of hydrogen gas within a reaction time of 10 minutes. The observed HGR is ranked as follows: 20Co/MF-400 > 20Co/MF-80 > 20Co/MF-600. The enhanced efficacy of the 20Co/MF-400 catalyst can be linked to its reduced crystallite size, increased pore size distribution, and its polyhedral/spherical morphology. Although the calcination process of MF-400 resulted in a decrease in specific surface area to 89 m²g − 1 , it maintained the smallest crystallite size among the various supports synthesized. This smaller crystallite size in MF-400 contributed to a higher degree of structural defects and disorder [ 53 , 56 ]. The presence of these defects facilitated an increase in the number of active sites, while also promoting metal-support interactions and the dispersion of active metal, as noted in previous studies [ 58 – 59 ]. Large cylindrical pores with average diameter of 18 nm were observed in MF-400. Large pores facilitate the reduction of cobalt species and formation of accessible Co particles during the reduction process, especially when the process takes place in less than 20 min. The Narrow pores like slit shaped pores observed in MF-80 are prone to clogging after impregnation of the support, since the metal loading is quite high and therefore cobalt species are not easily reduced during the reduction process. This phenomenon is confirmed by BET results as surface area reduced more than 50 m 2 .g − 1 after impregnation of the MF-80 support with 20%Co. Additionally, larger pores (and inter-connected pores) are easier for the reactants to reach the active sites of Co particles [ 34 – 60 ], thus higher H 2 generation rate is observed for 20Co/MF-400.Conversely, the 20Co/MF-600 catalyst showed the lowest hydrogen generation rate, attributed to its diminished magnetic properties and probably agglomerated particles after calcination at 600 o C. The decline in magnetic properties is linked to the phase transformation or separation of MnFe₂O₄ into Mn₂O₃ and Fe₂O₃ at temperatures exceeding 400°C, as depicted in Figs. 2 & 5 . 3.2.2. Effect of Co loading The outstanding performance of the 20Co/MF-400 catalyst led to the conclusion that the MnFe 2 O 4 support, calcined at 400°C, serves as the most suitable support for subsequent investigations. Figure 8 illustrates the influence of varying cobalt loadings, from 10 wt.% to 30 wt.%, on the catalytic activity of the MF-400 support. It was observed that the catalytic activity improved with increased cobalt loading, following the sequence: 30% >20% >10%. The 30% Co showed highest hydrogen generation rate of 3533 mL.min − 1 .g cat −1 . This indicates that increasing the cobalt content enhances the number of active sites, thereby improves the hydrogen generation rate. In mechanistic studies performed on hydrolysis of NaBH 4 with Co as the active metal [ 20 , 61 – 63 ], borohydride ion (BH 4 - ) interacts with cobalt by electrostatic interactions and BH 3 - intermediates are formed. OH in H 2 O molecule attacks BH 3 - intermediates and formation of [BH 3 -OH] -1 is observed followed by its desorption from the active site. [BH 3 -OH] -1 reacts with H 2 O to produce [BH 2 -(OH) 2 ] - and H 2 molecule. The [BH 2 -(OH) 2 ] - reacts with H 2 O to produce [BH-(OH) 3 ] - and H 2 molecule. The [BH-(OH) 3 ] - reacts with H 2 O to produce [B-(OH) 4 ] - and H 2 molecule. Finally, [B-(OH) 4 ] - is dissociated to [BO 2 ] - and H 2 O molecule. Thus, the more cobalt active sites, the more borohydride ion interaction and H 2 generation is expected. Notably, the increase in cobalt loading did not adversely affect cobalt dispersion. Similar findings were reported by Niu et al. [ 54 ] observed an increase in hydrogen formation with Co loading rising from 13.7–19% in Co-supported activated carbon catalysts [ 54 ]. In a similar vein, the catalysts Co/Al₂O₃ and Co/CAs (carbon aerogels) demonstrated significant enhancements in hydrogen evolution when cobalt loading was increased from 5 wt.% to 15 wt.% and from 8.48 wt.% to 18.71 wt.%, achieving improvements of over 80% and 35%, respectively [ 55 , 64 ]. Conversely, Liang et al. [ 46 ] identified a critical threshold of 10 wt.% for the active metal loading in NiB/NiFe₂O₄ catalysts synthesized through the impregnation-chemical reduction technique; surpassing this threshold led to a decline in catalytic efficiency. Given the exceptional catalytic performance exhibited by the 30%Co/MnFe₂O₄ catalyst, it is suggested that this catalyst warrants further exploration. 3.2.3 Effect of catalyst dosage The influence of catalyst loading on hydrogen generation is depicted in Fig. 9 , with catalyst amounts ranging from 10 mg to 20 mg. An increase in catalyst loading resulted in enhanced hydrogen evolution. The 20 mg catalyst exhibited the highest hydrogen production, while the 10 mg catalyst showed the lowest. This phenomenon can be attributed to the heightened interaction between sodium borohydride (NaBH₄) and cobalt particles as the quantity of the catalyst is increased. Enhanced interaction facilitates the adsorption of BH₄⁻ ions or their intermediate species onto the surface of the catalyst. The adsorbed BH₄⁻ ions subsequently engage in reactions with adsorbed H₂O molecules, leading to an increase in hydrogen production rate [ 65 – 67 ]. The catalyst with mass of 20 mg showed hydrogen generation rate of 3750 mL.min − 1 .g cat −1 . 3.2.4. Effect of NaOH concentration The influence of different NaOH concentrations on the catalytic performance of the 30Co/MnFe 2 O 4 catalyst is depicted in Fig. 10 . Sodium borohydride experiences self-hydrolysis in aqueous environments, which positions sodium hydroxide as a frequently employed stabilizing agent, particularly since the self-hydrolysis rate of NaBH 4 diminishes at pH levels exceeding 13 [ 67 ]. While the incorporation of NaOH generally enhances catalytic activity, there exists a critical concentration beyond which additional NaOH becomes counterproductive. Specifically, an increase in NaOH concentration from 1 wt.% to 5 wt.% resulted in an enhancement of hydrogen evolution rate up to 4600 mL.min − 1 .g cat −1 . However, concentrations beyond 5 wt.% led to a decline in efficiency. It is noteworthy that different catalysts respond differently to the addition of NaOH; for example, noble metal catalysts such as ruthenium (Ru) exhibited a decrease in hydrogen evolution with the introduction of NaOH [ 68 – 69 ]. In contrast, non-noble catalysts, like Co-catalysts, benefited from NaOH addition, leading to enhanced hydrogen production. Similarly, NaOH concentrations up to 4 wt.% improved catalytic performances in Ni-Fe-B catalysts, while higher concentrations negatively impacted activity [ 70 ]. Overall, an appropriate amount of hydroxide ions (OH⁻) enhances the electronic properties of the catalyst surface, promoting hydrogen generation. However, excessive NaOH concentrations (> 5 wt.%) hinder the hydrolysis of NaBH₄ due to the surplus OH⁻, which interferes with BH₄⁻ adsorption on the catalyst surface [ 64 ]. 3.2.5. Effect of temperature The hydrolysis of sodium borohydride (NaBH₄) exhibits a significant dependence on temperature. An investigation into the influence of temperature on the catalytic performance of the 30Co/MnFe₂O₄ catalyst was conducted across five distinct temperature settings, as illustrated in Fig. 11 . It was observed that hydrogen generation rate escalated with increasing temperatures, a phenomenon that has been extensively documented in prior research [ 67 ]. Although the hydrolysis reaction of NaBH₄ is exothermic, the heightened accessibility and reactivity of the reactants at higher temperatures facilitated an increase in hydrogen output. The maximum hydrogen generation rates of 4330 mL.min − 1 .g cat −1 and 5400 mL.min − 1 .g cat −1 were achieved at 40°C and 45°C, respectively. The hydrogen generation rate (r) is influenced by the concentrations of NaBH₄, NaOH, and catalyst, as well as the reaction temperature. This relationship can be expressed through Eq. 2. The activation energy (E a , kJ/mol) for NaBH₄ hydrolysis over the 30Co/MnFe₂O₄ catalyst is determined by incorporating the Arrhenius relation (Eq. 3) into Eq. 2 and applying a logarithmic transformation. The slope of the resulting linear plot (ln r or ln k versus 1/T) corresponds to -E a /R. \(\:r=k{C}_{NaBH4}^{a}{C}_{NaOH}^{b}{C}_{cat}^{c}\) (Eq. 2) \(\:k={k}_{0}{e}^{-Ea/RT}\) (Eq. 3) In Eq. 2, "k" represents the rate coefficient (mol/min. g cat ), while C NaBH4 , C NaOH and C cat denote the concentrations of NaBH₄, NaOH, and the catalyst weight, respectively. a is order of reaction with respect to concentration of NaBH 4 , b is order of reaction with respect to concentration of NaOH and c is order of reaction with respect to concentration of catalyst. In Eq. 3, k 0 is the frequency factor, "R" is the ideal gas constant (8.314 J·mol⁻¹·K⁻¹), and "T" is the reaction temperature. Figure 12 illustrates the linear regression of ln r in terms of 1000/T, which yields an activation energy (E a ) of 27.1 kJ/mol for the 30Co/MnFe₂O₄ catalyst. A comparison of this E a value with those of other Co-based catalysts is provided in Table 2 . The E a observed for the catalyst in this study is relatively lower compared to other Co supported catalysts in Table 2 . This indicates its excellent catalytic performance. Table 2 The hydrogen formation of different non-noble supported catalysts. Catalyst Temperature (°C) NaBH 4 concentration (wt.%) NaOH concentration (wt.%) HGR (mL/min.g) E a (kJ/mol) Ref. Co/CuFe 2 O 4 35 2 4 2937 18.12 38 Co-B/ carbon black 25 0.75 8 2073 57.8 53 Co-B/CN 25 0.5 0.5 473 47.7 71 Co/Al 2 O 3 -Cu 40 3 1 2700 52 55 Co-Cr-B/γ-Al 2 O 3 30 0.3 3 3260 56.06 72 Co/Carbon 27 1 8 10.92 a 42.19 54 Co-W-B/ Ni foam 30 20 5 15000 29 30 Co/γ-Al 2 O 3 30 1 5 2200 32.63 73 Co/hydroxyapatite 25 150 mM 10 2200 53 ± 2 74 Co/Fe 3 O 4 @C 39.8 5.1 4 6005 44.4 75 NiB/NiFe 2 O 4 25 5 2 299 72.52 46 CNF-NiCo 2 O 4 -CoB 30 1.5 1.5 5225 38.32 76 Present work 35 3 3 3533 27.1 - a mL/min.g cobalt 3.2.7. The recycling stability of 30Co/MnFe 2 O 4 catalyst The stability of the 30Co/MnFe 2 O 4 catalyst was evaluated over four successive cycles, as illustrated in Fig. 13 . Following each cycle, the catalyst was retrieved via vacuum filtration, subsequently washed, and dried for further use. A noticeable decrease in catalytic activity was recorded with each cycle. Specifically, a successive reduction of approximately 13% in the hydrogen generation rate was noted for the second and third cycles. In subsequent, for the fourth cycle a more intense decline of the activity was observed. Cumulatively, this resulted in a total decrease of 44% in the hydrogen formation rate from the first to the fourth cycle. Several factors contributed to this decline in catalytic performance. Losses of catalyst during the recovery and washing procedures led to a reduction in the availability of Co active sites, thereby impairing catalytic efficiency. Furthermore, catalyst agglomeration [ 74 ] and potential phase alterations in Co species during repeated usage and separation processes adversely affected reusability. The reusability and stability of a catalyst are critical for its commercial viability. The catalyst in this study demonstrated relatively high stability compared to catalysts such as Co/CuFe₂O₄[ 38 ] and Co/Al₂O₃ [ 55 ]. 4. Conclusions The Co/MnFe₂O₄ catalysts assessed in this investigation exhibited remarkable catalytic efficacy, particularly the Co catalysts that were supported on MnFe₂O₄ calcined at 400°C (designated as MF-400). The outstanding performance of the catalysts supported on MF-400 can be attributed to several key factors. Notably, MF-400 exhibited the smallest crystallite size and the high density of defects among the various supports prepared. These defects contributed to an increased number of active sites and enhanced the interaction between the metal and the support. Additionally, this support demonstrated a relatively high BET surface area of 89 m²g -1 and super paramagnetic characteristics. The presence of larger pores in MF-400 further facilitated the reduction of active metals and improved the accessibility of reactants to the active sites. In contrast, the catalyst supported on MF-600 exhibited the lowest hydrogen generation, which can be attributed to support phase separations occurring at elevated temperatures, leading to a reduction in magnetic properties. Increasing the 30Co/MF-400 catalyst dosage from 10 mg to 20 mg and the temperature from 25°C to 45°C led to an enhanced H₂ generation rate. Likewise, increasing the concentrations of NaOH to 5 wt.% boosted the hydrogen production rate. The catalyst demonstrated great reusability for up to four cycles. Declarations Author Contribution A. ranjbar has written the original manuscript along with the data validation and ...A. mosayebi has supervised the project and reviewed it. 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Cite Share Download PDF Status: Published Journal Publication published 29 Sep, 2025 Read the published version in Research on Chemical Intermediates → Version 1 posted Editorial decision: Revision requested 11 Aug, 2025 Reviews received at journal 30 Jul, 2025 Reviewers agreed at journal 28 Jul, 2025 Reviewers agreed at journal 26 Jul, 2025 Reviews received at journal 23 Jul, 2025 Reviewers agreed at journal 08 Jul, 2025 Reviewers agreed at journal 07 Jul, 2025 Reviewers invited by journal 07 Jul, 2025 Editor assigned by journal 14 Jun, 2025 Submission checks completed at journal 14 Jun, 2025 First submitted to journal 12 Jun, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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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-6883073","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":482405351,"identity":"ee5cd957-3f9d-48cc-ada6-8f90dfe5692b","order_by":0,"name":"atieh ranjbar","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABBklEQVRIie2Rv2rDMBCHTwjkRaGrgkrzCgqFJiF//Coygq7tmKl4yuQHUKEPkbXQ4YyGLHkAQ7KEgtcauhgytCqZMij1WKg+EByHPv0OHUAk8mfhCJDkAEtfq1NLdFC4A9h2V8ArwpwpYa7y3uHz8Xo/GD1/lE35NktHQpOmhfFDSBGY3ErL6+HLzlCB9X32ajXtFyAmeXAkBpJzR6w0IBt0WlUapH8rOOAAGT16JbV9R1vEr9Qr9HhJUcjYT0pmBWUCEcm60uxiytAxNuW8NpabuzGiydbbw2pSqLBys1nRXa/Yz21SvleIi1RtjKva5VP4s6k/pDhrkbzDdtrfLkQikci/5hu8IVL6270w1AAAAABJRU5ErkJggg==","orcid":"","institution":"Tafresh University","correspondingAuthor":true,"prefix":"","firstName":"atieh","middleName":"","lastName":"ranjbar","suffix":""},{"id":482405355,"identity":"51e61e14-35f1-413a-8aa4-fcc3ec56cd8a","order_by":1,"name":"amir mosayebi","email":"","orcid":"","institution":"Tafresh University","correspondingAuthor":false,"prefix":"","firstName":"amir","middleName":"","lastName":"mosayebi","suffix":""}],"badges":[],"createdAt":"2025-06-12 20:38:13","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6883073/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6883073/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s11164-025-05741-y","type":"published","date":"2025-09-29T15:58:05+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":86353457,"identity":"aded3aef-8270-474e-a281-1b8a93533cad","added_by":"auto","created_at":"2025-07-09 16:26:57","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":317795,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic of the set up used for measuring H\u003csub\u003e2\u003c/sub\u003e evolution via catalytic hydrolysis of NaBH\u003csub\u003e4\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-6883073/v1/fbf356bbaf37515fa32dacc6.png"},{"id":86352736,"identity":"98ec5ccf-64ef-475b-af22-05f5f3aa61df","added_by":"auto","created_at":"2025-07-09 16:18:57","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":601273,"visible":true,"origin":"","legend":"\u003cp\u003eXRD patterns of MnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e supports treated at different temperatures (80 \u003csup\u003e°\u003c/sup\u003eC, 400\u003csup\u003e°\u003c/sup\u003eC and 600\u003csup\u003e°\u003c/sup\u003eC).\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-6883073/v1/690f729ce25e2665f3446483.png"},{"id":86352734,"identity":"98ed1b2e-5aea-4f65-a73c-7f92b979861f","added_by":"auto","created_at":"2025-07-09 16:18:57","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":476698,"visible":true,"origin":"","legend":"\u003cp\u003eXRD patterns of 20% and 30% Co loading supported on MF-400 (MnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e calcined at 400 \u003csup\u003e°\u003c/sup\u003eC).\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-6883073/v1/52c41b7324b68614882d6bc9.png"},{"id":86352741,"identity":"64758996-bf53-4de6-86f5-a972d0bd5754","added_by":"auto","created_at":"2025-07-09 16:18:57","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1471438,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Adsorption/ desorption isotherms \u0026amp; (b) pore size distribution of prepared supports and catalysts.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-6883073/v1/83c4ffa4ecdad0d05a520a5e.png"},{"id":86353703,"identity":"127727bf-8ddc-4f25-ba31-40fdebff920b","added_by":"auto","created_at":"2025-07-09 16:34:57","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":20007,"visible":true,"origin":"","legend":"\u003cp\u003eThe magnetization curves of 20 Co/MnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (MnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e heat treated at different temperatures).\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-6883073/v1/ee588cc15234a28e5be937e8.png"},{"id":86353461,"identity":"1593f635-70d7-40ed-b190-99c188ff8449","added_by":"auto","created_at":"2025-07-09 16:26:57","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":2087407,"visible":true,"origin":"","legend":"\u003cp\u003e(a)\u0026amp;(b) SEM images of fresh 30Co/MF-400 catalyst on scale of 500 nm and 200 nm, respectively (c) particle size distribution of the mentioned catalyst.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-6883073/v1/0263bcc39d4797416dd155ac.png"},{"id":86352747,"identity":"45dcbf1b-f3d1-489d-aa7a-bf971fa144e9","added_by":"auto","created_at":"2025-07-09 16:18:57","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":16968,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of MnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e calcination temperature on catalytic activity of 20%Co/MnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (3wt.% NaBH\u003csub\u003e4\u003c/sub\u003e, 3wt.% NaOH and 15 mg catalyst at 35 °C).\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-6883073/v1/18fd51ded0fdb15d8bf11d2e.png"},{"id":86353705,"identity":"6e064ce5-8cc5-4030-bab4-c42fc45f3781","added_by":"auto","created_at":"2025-07-09 16:34:57","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":17341,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of Co loading on catalytic activity over MF-400 support (MnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e calcined at 400 \u003csup\u003e°\u003c/sup\u003eC); (3wt.% NaBH\u003csub\u003e4\u003c/sub\u003e, 3wt.% NaOH and 15 mg catalyst at 35 \u003csup\u003e°\u003c/sup\u003eC)\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-6883073/v1/ae6e7d6eee4528fe761ef6b2.png"},{"id":86352757,"identity":"0d8ee6fd-d826-4a6f-a144-09ca40795064","added_by":"auto","created_at":"2025-07-09 16:18:57","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":16110,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of catalyst dosage on hydrolysis of NaBH\u003csub\u003e4\u003c/sub\u003e over 30Co/MF-400 catalyst (5mL aqueous solution with 3wt% NaBH\u003csub\u003e4\u003c/sub\u003e and 3wt% NaOH with different catalyst amount).\u0026nbsp;\u003c/p\u003e","description":"","filename":"floatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-6883073/v1/534fe8dd0c0b3e55905e108f.png"},{"id":86352754,"identity":"121ad708-6fe2-4216-90b5-1272730ed4d2","added_by":"auto","created_at":"2025-07-09 16:18:57","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":17627,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of NaOH concentration on hydrolysis of NaBH\u003csub\u003e4\u003c/sub\u003e, using 30Co/MF-400 catalyst (15 mg catalyst with 5 mL solution containing 3 wt.% of NaBH\u003csub\u003e4\u003c/sub\u003e).\u003c/p\u003e","description":"","filename":"floatimage10.png","url":"https://assets-eu.researchsquare.com/files/rs-6883073/v1/992205cc9a84aa81c4c311a7.png"},{"id":86352755,"identity":"9904e207-92bc-4079-8f9c-d4826ec91e9c","added_by":"auto","created_at":"2025-07-09 16:18:57","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":17834,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of temperature on hydrolysis of NaBH\u003csub\u003e4\u003c/sub\u003e (15 mg catalyst with 5 mL solution containing 3 wt.% of NaBH\u003csub\u003e4\u003c/sub\u003e and 3wt% NaOH).\u003c/p\u003e","description":"","filename":"floatimage11.png","url":"https://assets-eu.researchsquare.com/files/rs-6883073/v1/dd7daeb77b855231f7d3a7cd.png"},{"id":86353464,"identity":"42f16af8-d32f-4dec-a410-f49683614cae","added_by":"auto","created_at":"2025-07-09 16:26:57","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":21270,"visible":true,"origin":"","legend":"\u003cp\u003eArrhenius plot of 30Co/MnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e catalyst.\u003c/p\u003e","description":"","filename":"floatimage12.png","url":"https://assets-eu.researchsquare.com/files/rs-6883073/v1/28a2b0d2918b1ddf3f2a4450.png"},{"id":86352750,"identity":"4fe5a5cd-1f22-4808-9f2f-4870fe4ecddd","added_by":"auto","created_at":"2025-07-09 16:18:57","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":17564,"visible":true,"origin":"","legend":"\u003cp\u003eRecycling stability of 30Co/MnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4 \u003c/sub\u003e(15 mg catalyst with 5 mL solution containing 3wt.% of NaBH\u003csub\u003e4\u003c/sub\u003e and 3 wt.% NaOH)\u003c/p\u003e","description":"","filename":"floatimage13.png","url":"https://assets-eu.researchsquare.com/files/rs-6883073/v1/2485a6649c056f40898e3733.png"},{"id":92884010,"identity":"41e06865-9ad5-4596-a7c6-1e7d29ac49d0","added_by":"auto","created_at":"2025-10-06 16:12:04","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":7127386,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6883073/v1/d2a0eac4-aac6-489c-8053-5803ff246b77.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Co supported on Manganese Ferrite for Hydrogen Evolution via Sodium Borohydride Hydrolysis","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe rising demand for energy, coupled with the finite availability of fossil fuels, compels us to seek out alternative energy sources [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. These alternative sources are anticipated to possess high energy density and to generate no harmful emissions, such as NO\u003csub\u003ex\u003c/sub\u003e, SO\u003csub\u003ex\u003c/sub\u003e, CO, and CO\u003csub\u003e2\u003c/sub\u003e. The detrimental effects of these pollutants, including their contribution to the greenhouse effect, are well recognized [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Hydrogen (H\u003csub\u003e2\u003c/sub\u003e) has garnered significant interest as a clean, sustainable, and efficient energy carrier. H\u003csub\u003e2\u003c/sub\u003e can be produced through various methods, including high-temperature reforming reactions [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], water electrolysis [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], photo-catalytic processes [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], and the hydrolysis of metal hydrides [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Metal hydrides like NaH, NaAlH\u003csub\u003e4\u003c/sub\u003e, NaBH\u003csub\u003e4\u003c/sub\u003e, LiH, LiAlH\u003csub\u003e4\u003c/sub\u003e, LiBH\u003csub\u003e4\u003c/sub\u003e, CaH\u003csub\u003e2\u003c/sub\u003e, Ca(BH\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e, MgH\u003csub\u003e2\u003c/sub\u003e, Mg(BH\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e, KH, KBH\u003csub\u003e4\u003c/sub\u003e can be used to generate hydrogen. Among metal hydrides, sodium borohydride (NaBH\u003csub\u003e4\u003c/sub\u003e) exhibits a hydrogen storage capacity of 10.8 wt.% [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. NaBH\u003csub\u003e4\u003c/sub\u003e meets the technical target of 6 wt% hydrogen capacity set by US Department of Energy (DOE). The hydrogen stored in NaBH\u003csub\u003e4\u003c/sub\u003e can be released via a hydrolysis reaction that produces no harmful byproducts [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], as illustrated in reaction 1 (R1). This exothermic reaction can generate hydrogen at low temperatures when a catalyst is present. Non-catalytic hydrolysis of NaBH\u003csub\u003e4\u003c/sub\u003e is a slow process and its conversion is very low (7\u0026ndash;8%) [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. The pure hydrogen produced can be utilized in proton exchange membrane fuel cells (PEMFCs) and hydrogen fuel cell vehicles (HFCVs) [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eNaBH₄ + 2 H₂ O \u0026rarr; NaBO₂ + 4 H₂ (R1)\u003c/p\u003e\u003cp\u003eBoth noble and non-noble metal catalysts have been investigated for the hydrolysis of NaBH\u003csub\u003e4\u003c/sub\u003e. Noble metal catalysts, such as platinum (Pt) and ruthenium (Ru), whether supported or un-supported, demonstrate high catalytic activity in this reaction. For instance, Ru nanoclusters stabilized by a ligand and Ru-RuO\u003csub\u003e2\u003c/sub\u003e supported on carbon powders achieved hydrogen generation rates (HGR) of 96800 mL.min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.g\u003csub\u003ecat\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e and 2800 mL.min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.g\u003csub\u003ecat\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e, respectively [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Ru nanoparticles decorated with CoB\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e on mesoporous carbon revealed HGR of 8139 mL.min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.g\u003csub\u003ecat\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e at 25\u003csup\u003eo\u003c/sup\u003eC [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Additionally, Pt and various combinations of Pt/Pd/Ru/Rh supported on carbon/CNT and ferrites have also shown excellent hydrogen production capabilities [\u003cspan additionalcitationids=\"CR17\" citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. However, the high cost of noble metals limits their widespread application. Consequently, there has been a development of cost-effective alternatives using non-noble metal catalysts such as cobalt (Co), nickel (Ni), and iron (Fe). The Pt catalyst promoted by Co supported on carbon spheres exhibited 8943 mL.min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.g\u003csub\u003ecat\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e hydrogen generation rate [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e] Various formulations of Co-based catalysts, including Co [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], Co-B [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e], Co-Ni-B [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e], Co-P-B [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], Co-Mn-B [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e] and Co-Y\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-B [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e] have been proposed for this reaction. Addition of promoter to Co-based catalysts enhanced the active surface areas and particle distribution over the catalyst. Active (nano)powders or un-supported catalysts often face issues with particle agglomeration, which reduces specific surface area and subsequently diminishes catalytic activity and recyclability. Cobalt or cobalt-promoted catalysts have been supported on various substrates, including activated carbon [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e], multi-walled carbon nanotubes (MWCNTs) [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e], copper sheets [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e], nickel foam [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e], alumina, cerium oxide (CeO\u003csub\u003e2\u003c/sub\u003e), titanium dioxide (TiO\u003csub\u003e2\u003c/sub\u003e) [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e], hydrogels [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e], clays [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e], quantum dots [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e], zeolites [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e] and ferrites [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. Ferrites are particularly notable for their unique adsorptive, magnetic, thermal, and electrical properties [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e] and are utilized in various catalytic reactions [40\u0026ndash;41], gas sensors [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e], electronic devices, and drug delivery systems [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]. Cobalt [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e], nickel [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e], zinc, and copper ferrites [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e] have been applied in the hydrolysis of NaBH\u003csub\u003e4\u003c/sub\u003e. Mirshafiee and Rezaei [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e] synthesized Co/MFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (where M\u0026thinsp;=\u0026thinsp;Cu, Co, Zn, Ni) catalysts via impregnation reduction and sol-gel methods (for MFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e). The Co/CuFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e catalyst exhibited the highest hydrogen production rate of 2937 mL.min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.g\u003csub\u003ecat\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e, attributed to its excellent cobalt distribution, large surface area, and high electrical conductivity. The NiB/NiFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e catalyst (where NiFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e was prepared using an EDTA-citric acid complexing method) demonstrated significant activity even at low concentrations of NaBH\u003csub\u003e4\u003c/sub\u003e, with superior performance observed for supported catalysts compared to un-supported one [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]. An Ag-based/CoFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-CNT catalyst produced 320 mL.min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.g\u003csub\u003ecat\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003ehydrogen due to the high dispersion of Ag nanoparticles and the synergistic effect between Ag nanoparticles and CoFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-CNT.\u003c/p\u003e\u003cp\u003eOther materials such as CuFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/RGO and CoFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-modified transition metals showed remarkable activity and recyclability. CuFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/RGO yielded a hydrogen production rate of 622 mL.min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.g\u003csub\u003ecat\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e, while CoFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-modified catalysts (Ru, Pt, Pd, Ir, Ag) exhibited turnover frequencies of 421 and 348 mol\u003csub\u003eH2\u003c/sub\u003e\u0026middot;mol\u003csub\u003ecat\u003c/sub\u003e\u003csup\u003e\u0026ndash;1\u003c/sup\u003e\u0026middot;min\u003csup\u003e\u0026ndash;1\u003c/sup\u003efor Ru and Pd modified catalysts, respectively [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e, \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e]. MnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e is a spinel ferrite that possesses several beneficial properties, which have yet to be explored in the context of sodium borohydride hydrolysis. Its applications have been well-documented in photocatalytic processes [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e] and in the treatment of water and wastewater [\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eIn this investigation, MnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e was synthesized through a co-precipitation method and subsequently utilized as a support for a cobalt (Co) catalyst, which was prepared using an impregnation reduction approach. The initial focus was on assessing the influence of the calcination temperature of MnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e as a support for 20% Co catalysts in the hydrolysis reaction of sodium borohydride (NaBH\u003csub\u003e4\u003c/sub\u003e). Following this, the effects of varying Co loadings (10%, 20%, and 30%) on the optimally heat-treated MnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e support were investigated. After determining the ideal calcination temperature and Co loading, additional experiments were performed to investigate the impacts of NaOH concentrations, catalyst loading, and reaction temperature on the overall reaction rate.\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1. MnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e synthesis\u003c/h2\u003e\u003cp\u003eThe synthesis of the MnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e spinel was accomplished through a co-precipitation method. The precursor materials utilized in this process included manganese nitrate tetrahydrate (Mn(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e.4H\u003csub\u003e2\u003c/sub\u003eO, Loba Chemie, 98.5%) and iron nitrate nonahydrate (Fe(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e.9H\u003csub\u003e2\u003c/sub\u003eO, Loba Chemie, 98%). For synthesis of 1g MnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, 3.57 g iron nitrate and 1.1 g manganese nitrate were dissolved in 100 mL of water. Subsequently, a 0.5 M sodium hydroxide (NaOH, Merck, 99%) solution was added dropwise to the mixture while maintaining the temperature at 60\u0026deg;C until the pH reached 10.5. The resulting solution was subjected to stirring for an additional 2 hours at a temperature of 70\u0026deg;C. Upon cooling, the precipitate was filtered and subsequently washed with distilled water to remove any residual nitrates. The filtered precipitate was then dried overnight at 80\u0026deg;C. The samples were subjected to thermal treatment at varying temperatures, with the sample that was not calcined referred to as MF-80. The samples that underwent calcination at 400\u0026deg;C and 600\u0026deg;C were labeled as MF-400 and MF-600, respectively.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2. Catalyst synthesis\u003c/h2\u003e\u003cp\u003eThe catalysts were synthesized through the impregnation-reduction technique, utilizing different cobalt loadings. Specifically, cobalt nitrate hexahydrate (Co(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e.6H\u003csub\u003e2\u003c/sub\u003eO) was dissolved in 20 mL of distilled water at concentrations of 10, 20, or 30 wt.%. This solution was combined with an adequate amount of MnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e. Following this, a 10 mL solution of sodium borohydride (NaBH\u003csub\u003e4\u003c/sub\u003e, Loba Chemie, 98%) was swiftly introduced to the mixture, maintaining a molar ratio of NaBH\u003csub\u003e4\u003c/sub\u003e to cobalt at 4. The resulting solution was mixed for 20 min before being subjected to filtration, washing, and drying at 80\u0026deg;C overnight.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3. Characterization\u003c/h2\u003e\u003cp\u003eTo investigate the crystal structure of MnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e spinel and cobalt, X-ray diffraction (XRD) analysis was conducted using a PANalytical X'Pert Pro apparatus, covering a range from 10\u0026deg; to 80\u0026deg;. The surface area and porosity both supports and catalysts were assessed through N\u003csub\u003e2\u003c/sub\u003e adsorption-desorptiontest, utilizing a BELSORP Mini II device. BET (Brunauer-Emmett-Teller) method was employed to measure the surface area, however; porosity was calculated using desorption branch of isotherm by the BJH method. Morphological and structural characteristics of the samples were examined via field emission scanning electron microscopy (MIRA3TESCAN-XMU model) operating at 30 kV. Additionally, the magnetic properties of the Co/MnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e catalysts were analyzed using a Vibrating Sample Magnetometer (Magnetic Daneshpajooh Kashan MDKB model), with a maximum field strength of 1.5 Tesla.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4. Catalytic activity experiments\u003c/h2\u003e\u003cp\u003eThe generation rate of hydrogen was evaluated utilizing the water displacement technique, as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. A catalyst weighing 15 mg was introduced into a 250 mL round-bottom three-neck flask, which functioned as the reactor, and was maintained at a stable temperature of 35\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u0026deg;C. Following this, 5 mL of an aqueous solution comprising 3 wt.% sodium borohydride and 3 wt.% NaOH was added to the flask while ensuring continuous and vigorous stirring. The feed was warmed to the required temperature before the injection. Hydrogen production began immediately upon the addition of the aqueous solution. The volume of hydrogen generated was monitored by measuring the water displacement in an inverted graduated cylinder. Each experiment was performed at least twice to guarantee the reliability and reproducibility of the findings.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Results and discussions","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e3.1. Characterization of catalysts\u003c/h2\u003e\u003cdiv id=\"Sec9\" class=\"Section3\"\u003e\u003ch2\u003e3.1.1. XRD analysis\u003c/h2\u003e\u003cp\u003eThe X-ray diffraction (XRD) patterns for the supports and catalysts produced through co-precipitation and impregnation-chemical reduction techniques are illustrated in Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The supports were subjected to thermal treatment at different temperatures. Analysis revealed that the sample dried at 80\u0026deg;C and the one calcined at 400\u0026deg;C exhibited the formation of a pure cubic spinel phase of MnFe₂O₄. Characteristic diffraction peaks corresponding to MnFe₂O₄ cubic spinel, as per JCPDS No. 01-074-2403, were identified at angles of 18.33\u0026deg;, 30.3\u0026deg;, 35.1\u0026deg;, 57.8\u0026deg;, 62.7\u0026deg;, and 72.39\u0026deg;. In contrast, the sample calcined at 600\u0026deg;C experienced phase separation, leading to the emergence of Fe₂O₃ and Mn₂O₃. Notably, despite the conversion of MnFe₂O₄ into other phases, a residual quantity of MnFe₂O₄ persisted, maintaining its magnetic characteristics. Peaks associated with α-Fe₂O₃ (rhombohedral) were detected at 24.45\u0026deg;, 35.57\u0026deg;, 49\u0026deg;, 54.45\u0026deg;, 57.99\u0026deg;, 62.8\u0026deg;, 64.35\u0026deg;, 72.33\u0026deg;, and 75.69\u0026deg; (JCPDS No. 00-024-0072). Peaks associated with Mn₂O₃ were detected at 33.5\u0026deg;, 35.9\u0026deg;, and 54.5\u0026deg; (JCPDS No. 01-076-0150). Phase separation of MnFe₂O₄ at temperatures exceeding 400\u0026deg;C has been widely reported in the literature [\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e]. Junlabhut et al. [\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e] observed similar phase transitions when MnFe₂O₄ was synthesized from chloride precursors using the co-precipitation method, with phase changes occurring above 400\u0026deg;C. These transformations are not limited to co-precipitation techniques; phase transitions to Fe₂O₃ and Mn₂O₃ have also been reported for non-aqueous microwave synthesis, thermal decomposition, and sol-gel methods [\u003cspan additionalcitationids=\"CR52\" citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e]. The X-ray diffraction (XRD) analysis of the catalysts indicated that the dominant peaks were linked to the MnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e spinel structure. Specifically, the peaks observed at 43.2\u0026deg; and 74.25\u0026deg; were identified as metallic cobalt, whereas those at 35.4\u0026deg; and 62.9\u0026deg; were related to cobalt oxide compounds, namely Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and CoO. The literature frequently documents the partial oxidation of cobalt in both supported and unsupported catalyst systems [\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e]. Peaks at 35.5\u0026deg; and 62\u0026deg; are commonly attributed to Co₃O₄. The average crystallite sizes of the supports and catalysts, as determined through the application of the Scherrer equation, are detailed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The MF-80 and MF-400 supports exhibited average crystallite sizes of 13.7 nm and 9.17 nm, respectively, based on measurements from the (311), (333), and (440) planes. In contrast, the MF-600 sample demonstrated an average crystallite size of 30.08 nm, which was calculated using the (012), (104), (110), (113), (024), (116), (214), and (300) planes associated with Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, noting that the planes corresponding to Mn\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e overlap with those of Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e. The same variation of crystallite size at different calcination temperatures is reported by Simon et al. [\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e] and Rana et al. [\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e]. The unusual decrease of crystallite size with increase of heat treatment temperature in MF-400 is linked to increased disordered defects and disorderliness that start occurring at temperatures higher than 300 \u003csup\u003eo\u003c/sup\u003eC as reported by Rana et al. [\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e] for MnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e samples prepared by co-precipitation method. The cobalt crystallite size was measured for the 20%Co catalyst supported on MF-400, yielding a value of 5.6 nm based on the (111) plane.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eThe properties of prepared supports and catalysts.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"5\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSample\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCrystallite size\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\u003cp\u003e(nm)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eBET surface area (m\u003csub\u003e2\u003c/sub\u003e/g)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eTotal Pore volume\u003c/p\u003e\u003cp\u003e(cm\u003csup\u003e3\u003c/sup\u003e. g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eAverage pore size (nm)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMF-80\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e13.72\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e210.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.279\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e5.2\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMF-400\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e9.17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e89.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.2303\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e18.2\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMF-600\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e30.08\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cb\u003e-\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u003cb\u003e-\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003cb\u003e-\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e20Co/MF-80\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e154.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.2541\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e6.5\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e20Co/MF-400\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e5.6 \u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cb\u003e-\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u003cb\u003e-\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003cb\u003e-\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e30Co/MF-400\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003e-\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e120.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.3706\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e15.0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003csup\u003ea\u003c/sup\u003e calculated from XRD.\u003c/p\u003e\u003cp\u003e\u003csup\u003eb\u003c/sup\u003e cobalt crystallite size is calculated.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec10\" class=\"Section3\"\u003e\u003ch2\u003e3.1.2. N\u003csub\u003e2\u003c/sub\u003e adsorption\u0026ndash;desorption analysis\u003c/h2\u003e\u003cp\u003eThe specific surface area, total pore volume and mean pore diameter of supports and their catalysts received from N\u003csub\u003e2\u003c/sub\u003e adsorption/desorption are reported in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The MF-80 support, which was not subjected to calcination, exhibited the highest surface area of 210.9 m\u0026sup2;g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. However, calcination at 400\u0026deg;C resulted in a reduction of the surface area to 89.0 m\u0026sup2;g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Similarly, the total pore volume in MF-400 also decreased, although to a lesser extent than the surface area. The mean pore diameter exhibited a significant increase after calcination at 400\u0026deg;C, escalating from 5.2 nm in MF-80 to 18.2 nm in MF-400. Following the impregnation of the MF-400 support with 30% cobalt, both the BET surface area and total pore volume saw an enhancement, although the mean pore size reduced to 15 nm. This improvement in specific surface area post-impregnation can be ascribed to the development of dispersed cobalt particles that demonstrate robust interactions with the support [\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eIn contrast, the 20 Co/MF-80 sample exhibited a decrease in specific surface area following the impregnation process, which can be attributed to the blockage or damage of narrow pores caused by this procedure. The nitrogen adsorption/desorption isotherms and pore size distribution profiles are presented in Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea and \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb. The MF-80 sample, which was not calcined, along with its corresponding catalyst, displayed a type IV isotherm characterized by an H4 hysteresis loop, indicative of slit-shaped pores. Similarly, MF-400 and its catalyst also exhibited a type IV isotherm. An H1 hysteresis loop was noted for MF-400, while the 30Co/MF-400 sample revealed both H1 and H3 hysteresis loops. The H1 and H3 loops are associated with cylindrical and wedge-shaped pores, respectively [\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e]. The impregnation-reduction of the MF-400 support with cobalt resulted in the transformation of some cylindrical pores into wedge-shaped pores or the introduction of redesigned pores within the catalyst.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section3\"\u003e\u003ch2\u003e3.1.3. The magnetic behavior of catalysts\u003c/h2\u003e\u003cp\u003eThe magnetization curves corresponding to the applied magnetic field for the 20Co/MnFe₂O₄ catalysts are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. The observed hysteresis loops indicate superparamagnetic characteristics at room temperature across all samples, a behavior commonly associated with magnetic nanoparticles. Notably, the 20Co/MF-80 sample demonstrated the highest magnetic saturation, recorded at 21.25 emu/g. Nevertheless, an increase in the calcination temperature of the MnFe₂O₄ support resulted in a deterioration of the catalyst's magnetic properties, with this decline becoming increasingly significant at temperatures above 400\u0026deg;C. A comparable reduction in magnetic saturation with elevated calcination temperatures has also been documented by Simon et al. [\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e]. They observed a reduction near to 5 emu/g in magnetic saturation at room temperature as the MnFe₂O₄ heat treatment temperature increased from 80\u0026deg;C to 400\u0026deg;C. The magnetic behavior of the Co/MnFe₂O₄ catalysts follows the order: 20Co/MF-80\u0026thinsp;\u0026gt;\u0026thinsp;20Co/MF-400\u0026thinsp;\u0026gt;\u0026thinsp;20Co/MF-600. The comparatively low magnetic properties of the 20Co/MF-600 sample are primarily attributed to phase transformations in MnFe₂O₄ that occur at elevated temperatures.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section3\"\u003e\u003ch2\u003e3.1.4. FE-SEM images\u003c/h2\u003e\u003cp\u003eFE-SEM was utilized to investigate the morphology and particle size of the synthesized catalyst. The images corresponding to the 30%Co/MF-400 catalyst are illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. Specifically, images 6a and 6b reveal the presence of aggregated, compact polyhedral or nearly spherical nanoparticles. The larger particles, exceeding 60 nm in size, exhibited a polyhedral morphology, whereas the smaller particles appeared predominantly spherical. As depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec, a total of 40 particles were analyzed to assess the particle size distribution using Digimizer software, resulting in an average particle size of 58 nm for the 30%Co/MF-400 catalyst.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003e3.2. Catalytic activity tests\u003c/h2\u003e\u003cdiv id=\"Sec14\" class=\"Section3\"\u003e\u003ch2\u003e3.2.1. Effect of MnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e calcination temperature\u003c/h2\u003e\u003cp\u003eHydrogen generation over 20%Co/MnFe₂O₄ catalysts at 35\u0026deg;C was evaluated. The hydrogen generation started instantaneously upon injection of solution for all samples. The MnFe₂O₄ support in these catalysts was heat-treated at varying temperatures (80\u0026deg;C, 400\u0026deg;C, and 600\u0026deg;C). As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, hydrogen generation over time was measured. The MnFe₂O₄ support alone displayed negligible catalytic activity in the aqueous solution. The 20%Co/MnFe₂O₄ catalysts demonstrated significantly higher activity for NaBH₄ hydrolysis. These results suggest that the catalytic activity is entirely reliant on the Co active sites, while the MnFe₂O₄ support enhanced the formation of additional active sites for Co through improved interaction and cobalt dispersion. Among the cobalt catalysts with a composition of 20 wt.%, the 20Co/MF-400 catalyst demonstrated the most significant catalytic performance, generating 402 mL of hydrogen gas within a reaction time of 10 minutes. The observed HGR is ranked as follows: 20Co/MF-400\u0026thinsp;\u0026gt;\u0026thinsp;20Co/MF-80\u0026thinsp;\u0026gt;\u0026thinsp;20Co/MF-600. The enhanced efficacy of the 20Co/MF-400 catalyst can be linked to its reduced crystallite size, increased pore size distribution, and its polyhedral/spherical morphology. Although the calcination process of MF-400 resulted in a decrease in specific surface area to 89 m\u0026sup2;g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, it maintained the smallest crystallite size among the various supports synthesized. This smaller crystallite size in MF-400 contributed to a higher degree of structural defects and disorder [\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e, \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e]. The presence of these defects facilitated an increase in the number of active sites, while also promoting metal-support interactions and the dispersion of active metal, as noted in previous studies [\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e]. Large cylindrical pores with average diameter of 18 nm were observed in MF-400. Large pores facilitate the reduction of cobalt species and formation of accessible Co particles during the reduction process, especially when the process takes place in less than 20 min. The Narrow pores like slit shaped pores observed in MF-80 are prone to clogging after impregnation of the support, since the metal loading is quite high and therefore cobalt species are not easily reduced during the reduction process. This phenomenon is confirmed by BET results as surface area reduced more than 50 m\u003csup\u003e2\u003c/sup\u003e.g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e after impregnation of the MF-80 support with 20%Co. Additionally, larger pores (and inter-connected pores) are easier for the reactants to reach the active sites of Co particles [\u003cspan additionalcitationids=\"CR35 CR36 CR37 CR38 CR39 CR40 CR41 CR42 CR43 CR44 CR45 CR46 CR47 CR48 CR49 CR50 CR51 CR52 CR53 CR54 CR55 CR56 CR57 CR58 CR59\" citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e], thus higher H\u003csub\u003e2\u003c/sub\u003e generation rate is observed for 20Co/MF-400.Conversely, the 20Co/MF-600 catalyst showed the lowest hydrogen generation rate, attributed to its diminished magnetic properties and probably agglomerated particles after calcination at 600\u003csup\u003eo\u003c/sup\u003eC. The decline in magnetic properties is linked to the phase transformation or separation of MnFe₂O₄ into Mn₂O₃ and Fe₂O₃ at temperatures exceeding 400\u0026deg;C, as depicted in Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e\u0026amp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec15\" class=\"Section3\"\u003e\u003ch2\u003e3.2.2. Effect of Co loading\u003c/h2\u003e\u003cp\u003eThe outstanding performance of the 20Co/MF-400 catalyst led to the conclusion that the MnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e support, calcined at 400\u0026deg;C, serves as the most suitable support for subsequent investigations. Figure\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e illustrates the influence of varying cobalt loadings, from 10 wt.% to 30 wt.%, on the catalytic activity of the MF-400 support. It was observed that the catalytic activity improved with increased cobalt loading, following the sequence: 30% \u0026gt;20% \u0026gt;10%. The 30% Co showed highest hydrogen generation rate of 3533 mL.min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.g\u003csub\u003ecat\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e. This indicates that increasing the cobalt content enhances the number of active sites, thereby improves the hydrogen generation rate. In mechanistic studies performed on hydrolysis of NaBH\u003csub\u003e4\u003c/sub\u003e with Co as the active metal [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan additionalcitationids=\"CR62\" citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e63\u003c/span\u003e], borohydride ion (BH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e) interacts with cobalt by electrostatic interactions and BH\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e intermediates are formed. OH in H\u003csub\u003e2\u003c/sub\u003eO molecule attacks BH\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e intermediates and formation of [BH\u003csub\u003e3\u003c/sub\u003e-OH]\u003csup\u003e-1\u003c/sup\u003e is observed followed by its desorption from the active site. [BH\u003csub\u003e3\u003c/sub\u003e-OH]\u003csup\u003e-1\u003c/sup\u003e reacts with H\u003csub\u003e2\u003c/sub\u003eO to produce [BH\u003csub\u003e2\u003c/sub\u003e-(OH)\u003csub\u003e2\u003c/sub\u003e]\u003csup\u003e-\u003c/sup\u003e and H\u003csub\u003e2\u003c/sub\u003e molecule. The [BH\u003csub\u003e2\u003c/sub\u003e-(OH)\u003csub\u003e2\u003c/sub\u003e]\u003csup\u003e-\u003c/sup\u003e reacts with H\u003csub\u003e2\u003c/sub\u003eO to produce [BH-(OH)\u003csub\u003e3\u003c/sub\u003e]\u003csup\u003e-\u003c/sup\u003e and H\u003csub\u003e2\u003c/sub\u003e molecule. The [BH-(OH)\u003csub\u003e3\u003c/sub\u003e]\u003csup\u003e-\u003c/sup\u003e reacts with H\u003csub\u003e2\u003c/sub\u003eO to produce [B-(OH)\u003csub\u003e4\u003c/sub\u003e]\u003csup\u003e-\u003c/sup\u003e and H\u003csub\u003e2\u003c/sub\u003e molecule. Finally, [B-(OH)\u003csub\u003e4\u003c/sub\u003e]\u003csup\u003e-\u003c/sup\u003e is dissociated to [BO\u003csub\u003e2\u003c/sub\u003e]\u003csup\u003e-\u003c/sup\u003e and H\u003csub\u003e2\u003c/sub\u003eO molecule. Thus, the more cobalt active sites, the more borohydride ion interaction and H\u003csub\u003e2\u003c/sub\u003e generation is expected. Notably, the increase in cobalt loading did not adversely affect cobalt dispersion. Similar findings were reported by Niu et al. [\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e] observed an increase in hydrogen formation with Co loading rising from 13.7\u0026ndash;19% in Co-supported activated carbon catalysts [\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e]. In a similar vein, the catalysts Co/Al₂O₃ and Co/CAs (carbon aerogels) demonstrated significant enhancements in hydrogen evolution when cobalt loading was increased from 5 wt.% to 15 wt.% and from 8.48 wt.% to 18.71 wt.%, achieving improvements of over 80% and 35%, respectively [\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e, \u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e]. Conversely, Liang et al. [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e] identified a critical threshold of 10 wt.% for the active metal loading in NiB/NiFe₂O₄ catalysts synthesized through the impregnation-chemical reduction technique; surpassing this threshold led to a decline in catalytic efficiency. Given the exceptional catalytic performance exhibited by the 30%Co/MnFe₂O₄ catalyst, it is suggested that this catalyst warrants further exploration.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec16\" class=\"Section3\"\u003e\u003ch2\u003e3.2.3 Effect of catalyst dosage\u003c/h2\u003e\u003cp\u003eThe influence of catalyst loading on hydrogen generation is depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e, with catalyst amounts ranging from 10 mg to 20 mg. An increase in catalyst loading resulted in enhanced hydrogen evolution. The 20 mg catalyst exhibited the highest hydrogen production, while the 10 mg catalyst showed the lowest. This phenomenon can be attributed to the heightened interaction between sodium borohydride (NaBH₄) and cobalt particles as the quantity of the catalyst is increased. Enhanced interaction facilitates the adsorption of BH₄⁻ ions or their intermediate species onto the surface of the catalyst. The adsorbed BH₄⁻ ions subsequently engage in reactions with adsorbed H₂O molecules, leading to an increase in hydrogen production rate [\u003cspan additionalcitationids=\"CR66\" citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e]. The catalyst with mass of 20 mg showed hydrogen generation rate of 3750 mL.min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.g\u003csub\u003ecat\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec17\" class=\"Section3\"\u003e\u003ch2\u003e3.2.4. Effect of NaOH concentration\u003c/h2\u003e\u003cp\u003eThe influence of different NaOH concentrations on the catalytic performance of the 30Co/MnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e catalyst is depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e. Sodium borohydride experiences self-hydrolysis in aqueous environments, which positions sodium hydroxide as a frequently employed stabilizing agent, particularly since the self-hydrolysis rate of NaBH\u003csub\u003e4\u003c/sub\u003e diminishes at pH levels exceeding 13 [\u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e]. While the incorporation of NaOH generally enhances catalytic activity, there exists a critical concentration beyond which additional NaOH becomes counterproductive. Specifically, an increase in NaOH concentration from 1 wt.% to 5 wt.% resulted in an enhancement of hydrogen evolution rate up to 4600 mL.min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.g\u003csub\u003ecat\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e. However, concentrations beyond 5 wt.% led to a decline in efficiency. It is noteworthy that different catalysts respond differently to the addition of NaOH; for example, noble metal catalysts such as ruthenium (Ru) exhibited a decrease in hydrogen evolution with the introduction of NaOH [\u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e68\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e69\u003c/span\u003e]. In contrast, non-noble catalysts, like Co-catalysts, benefited from NaOH addition, leading to enhanced hydrogen production. Similarly, NaOH concentrations up to 4 wt.% improved catalytic performances in Ni-Fe-B catalysts, while higher concentrations negatively impacted activity [\u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e70\u003c/span\u003e]. Overall, an appropriate amount of hydroxide ions (OH⁻) enhances the electronic properties of the catalyst surface, promoting hydrogen generation. However, excessive NaOH concentrations (\u0026gt;\u0026thinsp;5 wt.%) hinder the hydrolysis of NaBH₄ due to the surplus OH⁻, which interferes with BH₄⁻ adsorption on the catalyst surface [\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec18\" class=\"Section3\"\u003e\u003ch2\u003e3.2.5. Effect of temperature\u003c/h2\u003e\u003cp\u003eThe hydrolysis of sodium borohydride (NaBH₄) exhibits a significant dependence on temperature. An investigation into the influence of temperature on the catalytic performance of the 30Co/MnFe₂O₄ catalyst was conducted across five distinct temperature settings, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e. It was observed that hydrogen generation rate escalated with increasing temperatures, a phenomenon that has been extensively documented in prior research [\u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e]. Although the hydrolysis reaction of NaBH₄ is exothermic, the heightened accessibility and reactivity of the reactants at higher temperatures facilitated an increase in hydrogen output. The maximum hydrogen generation rates of 4330 mL.min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.g\u003csub\u003ecat\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e and 5400 mL.min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.g\u003csub\u003ecat\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e were achieved at 40\u0026deg;C and 45\u0026deg;C, respectively.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe hydrogen generation rate (r) is influenced by the concentrations of NaBH₄, NaOH, and catalyst, as well as the reaction temperature. This relationship can be expressed through Eq.\u0026nbsp;2. The activation energy (E\u003csub\u003ea\u003c/sub\u003e, kJ/mol) for NaBH₄ hydrolysis over the 30Co/MnFe₂O₄ catalyst is determined by incorporating the Arrhenius relation (Eq.\u0026nbsp;3) into Eq.\u0026nbsp;2 and applying a logarithmic transformation. The slope of the resulting linear plot (ln r or ln k versus 1/T) corresponds to -E\u003csub\u003ea\u003c/sub\u003e/R.\u003c/p\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:r=k{C}_{NaBH4}^{a}{C}_{NaOH}^{b}{C}_{cat}^{c}\\)\u003c/span\u003e\u003c/span\u003e (Eq.\u0026nbsp;2)\u003c/p\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:k={k}_{0}{e}^{-Ea/RT}\\)\u003c/span\u003e\u003c/span\u003e (Eq.\u0026nbsp;3)\u003c/p\u003e\u003cp\u003eIn Eq.\u0026nbsp;2, \"k\" represents the rate coefficient (mol/min. g\u003csub\u003ecat\u003c/sub\u003e), while C\u003csub\u003eNaBH4\u003c/sub\u003e, C\u003csub\u003eNaOH\u003c/sub\u003e and C\u003csub\u003ecat\u003c/sub\u003e denote the concentrations of NaBH₄, NaOH, and the catalyst weight, respectively. a is order of reaction with respect to concentration of NaBH\u003csub\u003e4\u003c/sub\u003e, b is order of reaction with respect to concentration of NaOH and c is order of reaction with respect to concentration of catalyst. In Eq.\u0026nbsp;3, k\u003csub\u003e0\u003c/sub\u003e is the frequency factor, \"R\" is the ideal gas constant (8.314 J\u0026middot;mol⁻\u0026sup1;\u0026middot;K⁻\u0026sup1;), and \"T\" is the reaction temperature. Figure\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e illustrates the linear regression of ln r in terms of 1000/T, which yields an activation energy (E\u003csub\u003ea\u003c/sub\u003e) of 27.1 kJ/mol for the 30Co/MnFe₂O₄ catalyst. A comparison of this E\u003csub\u003ea\u003c/sub\u003e value with those of other Co-based catalysts is provided in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The E\u003csub\u003ea\u003c/sub\u003e observed for the catalyst in this study is relatively lower compared to other Co supported catalysts in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. This indicates its excellent catalytic performance.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eThe hydrogen formation of different non-noble supported catalysts.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"7\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCatalyst\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eTemperature (\u0026deg;C)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eNaBH\u003csub\u003e4\u003c/sub\u003e concentration\u003c/p\u003e\u003cp\u003e(wt.%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eNaOH\u003c/p\u003e\u003cp\u003econcentration\u003c/p\u003e\u003cp\u003e(wt.%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eHGR (mL/min.g)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eE\u003csub\u003ea\u003c/sub\u003e (kJ/mol)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eRef.\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCo/CuFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e35\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e2937\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e18.12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e38\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCo-B/ carbon black\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.75\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e2073\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e57.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e53\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCo-B/CN\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e473\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e47.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e71\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCo/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-Cu\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e40\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e2700\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e52\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e55\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCo-Cr-B/γ-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e3260\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e56.06\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e72\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCo/Carbon\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e27\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e10.92 \u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e42.19\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e54\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCo-W-B/ Ni foam\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e15000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e29\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e30\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCo/γ-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e2200\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e32.63\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e73\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCo/hydroxyapatite\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e150 mM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e2200\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e53\u0026thinsp;\u0026plusmn;\u0026thinsp;2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e74\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCo/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@C\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e39.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e5.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e6005\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e44.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e75\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNiB/NiFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e299\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e72.52\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e46\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCNF-NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-CoB\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e5225\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e38.32\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e76\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePresent work\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e35\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e3533\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e27.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003ctfoot\u003e\u003ctr\u003e\u003ctd colspan=\"7\"\u003e\u003csup\u003ea\u003c/sup\u003emL/min.g\u003csub\u003ecobalt\u003c/sub\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tfoot\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec19\" class=\"Section3\"\u003e\u003ch2\u003e3.2.7. The recycling stability of 30Co/MnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e catalyst\u003c/h2\u003e\u003cp\u003eThe stability of the 30Co/MnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e catalyst was evaluated over four successive cycles, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e. Following each cycle, the catalyst was retrieved via vacuum filtration, subsequently washed, and dried for further use. A noticeable decrease in catalytic activity was recorded with each cycle. Specifically, a successive reduction of approximately 13% in the hydrogen generation rate was noted for the second and third cycles. In subsequent, for the fourth cycle a more intense decline of the activity was observed. Cumulatively, this resulted in a total decrease of 44% in the hydrogen formation rate from the first to the fourth cycle. Several factors contributed to this decline in catalytic performance. Losses of catalyst during the recovery and washing procedures led to a reduction in the availability of Co active sites, thereby impairing catalytic efficiency. Furthermore, catalyst agglomeration [\u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e74\u003c/span\u003e] and potential phase alterations in Co species during repeated usage and separation processes adversely affected reusability.\u003c/p\u003e\u003cp\u003eThe reusability and stability of a catalyst are critical for its commercial viability. The catalyst in this study demonstrated relatively high stability compared to catalysts such as Co/CuFe₂O₄[\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e] and Co/Al₂O₃ [\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eThe Co/MnFe₂O₄ catalysts assessed in this investigation exhibited remarkable catalytic efficacy, particularly the Co catalysts that were supported on MnFe₂O₄ calcined at 400\u0026deg;C (designated as MF-400). The outstanding performance of the catalysts supported on MF-400 can be attributed to several key factors. Notably, MF-400 exhibited the smallest crystallite size and the high density of defects among the various supports prepared. These defects contributed to an increased number of active sites and enhanced the interaction between the metal and the support. Additionally, this support demonstrated a relatively high BET surface area of 89 m\u0026sup2;g\u003csup\u003e-1\u003c/sup\u003e and super paramagnetic characteristics. The presence of larger pores in MF-400 further facilitated the reduction of active metals and improved the accessibility of reactants to the active sites. In contrast, the catalyst supported on MF-600 exhibited the lowest hydrogen generation, which can be attributed to support phase separations occurring at elevated temperatures, leading to a reduction in magnetic properties. Increasing the 30Co/MF-400 catalyst dosage from 10 mg to 20 mg and the temperature from 25\u0026deg;C to 45\u0026deg;C led to an enhanced H₂ generation rate. Likewise, increasing the concentrations of NaOH to 5 wt.% boosted the hydrogen production rate. The catalyst demonstrated great reusability for up to four cycles.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eA. ranjbar has written the original manuscript along with the data validation and ...A. mosayebi has supervised the project and reviewed it.\u003c/p\u003e\u003cul\u003e\n \u003cli\u003e\u003cstrong\u003eAtieh ranjbar (Corresponding Author)\u003c/strong\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp dir=\"LTR\"\u003eDepartment of Chemical Engineering, Tafresh University, Tafresh 39518 79611, Iran\u003c/p\u003e\n\u003cp dir=\"LTR\"\u003eEmail: [email protected]\u003c/p\u003e\n\u003cp dir=\"LTR\"\u003eORCID: 0009-0006-2727-2358\u003c/p\u003e\n\u003cul\u003e\n \u003cli\u003e\u003cstrong\u003eAmir Mosayebi\u003c/strong\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp dir=\"LTR\"\u003eDepartment of Chemical Engineering, Tafresh University, Tafresh 39518 79611, Iran\u003c/p\u003e\n\u003cp dir=\"LTR\"\u003eEmail: [email protected]\u003c/p\u003e\n\u003cp dir=\"LTR\"\u003e\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eS. 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Alloys Compd. 911,165069 (2022)\u003c/li\u003e\n\u003c/ol\u003e\n"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"research-on-chemical-intermediates","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"rint","sideBox":"Learn more about [Research on Chemical Intermediates](http://link.springer.com/journal/11164)","snPcode":"11164","submissionUrl":"https://submission.nature.com/new-submission/11164/3","title":"Research on Chemical Intermediates","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Cobalt, MnFe2O4, Hydrolysis, NaBH4, Hydrogen production","lastPublishedDoi":"10.21203/rs.3.rs-6883073/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6883073/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe generation of hydrogen gas through the catalytic hydrolysis of sodium borohydride (NaBH\u003csub\u003e4\u003c/sub\u003e) has garnered significant interest in recent years. The primary research challenge remains the development of effective and reusable catalysts. This research details the development of Co/MnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e catalysts aimed at facilitating the hydrolysis of sodium borohydride (NaBH\u003csub\u003e4\u003c/sub\u003e), employing MnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e as the support material. The support was synthesized through a co-precipitation method, while the catalysts were produced via an impregnation-chemical reduction technique. The characterization of the catalysts was performed using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), vibrating sample magnetometry (VSM), and nitrogen adsorption-desorption measurements. The study initially explored the effects of calcination temperature of the supports and the amount of loaded cobalt on the hydrogen generation process. Notably, catalysts supported on MnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e calcined at 400\u0026deg;C demonstrated superior activity, with 30% Co/MF-400 catalyst yielding 3533 mL.min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.g\u003csub\u003ecat\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003eof hydrogen during NaBH\u003csub\u003e4\u003c/sub\u003e hydrolysis. The enhanced catalytic performance of the MF-400 supported catalysts was attributed to their small crystallite size or prominent number of defects and relatively high magnetic properties. In addition, 30Co-MF400 showed high specific surface area of 120.1 m\u003csup\u003e2\u003c/sup\u003e.g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Subsequently, various parameters were examined over 30Co/MF-400, including catalyst dosage (10\u0026ndash;20 mg), concentrations of NaOH (1\u0026ndash;7 wt.%), temperature (25-45\u003csup\u003eo\u003c/sup\u003eC), and catalyst reusability. The activation energy (E\u003csub\u003ea\u003c/sub\u003e) for the 30% Co/MF-400 catalyst was found to be 27.1 kJ/mol, as determined through the application of the rate expression and the Arrhenius equation. The 30% Co/MF-400 catalyst showed a 44% decline in catalytic performance after being used for four cycles.\u003c/p\u003e","manuscriptTitle":"Co supported on Manganese Ferrite for Hydrogen Evolution via Sodium Borohydride Hydrolysis","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-09 16:18:52","doi":"10.21203/rs.3.rs-6883073/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-08-11T10:01:31+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-31T02:58:55+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"107465061428693441045769634375508075021","date":"2025-07-28T11:27:09+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"40190026291829051175350878974265851891","date":"2025-07-27T03:24:26+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-23T11:40:38+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"31108542352061815587748199734438102673","date":"2025-07-08T12:50:42+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"28052280157039671915906240395926083404","date":"2025-07-08T02:50:05+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-07-08T01:52:00+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-06-14T12:40:26+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-06-14T12:38:14+00:00","index":"","fulltext":""},{"type":"submitted","content":"Research on Chemical Intermediates","date":"2025-06-12T20:29:00+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"research-on-chemical-intermediates","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"rint","sideBox":"Learn more about [Research on Chemical Intermediates](http://link.springer.com/journal/11164)","snPcode":"11164","submissionUrl":"https://submission.nature.com/new-submission/11164/3","title":"Research on Chemical Intermediates","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"ee5c4794-b100-4c0e-94dd-cb9b48374b15","owner":[],"postedDate":"July 9th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-10-06T16:07:37+00:00","versionOfRecord":{"articleIdentity":"rs-6883073","link":"https://doi.org/10.1007/s11164-025-05741-y","journal":{"identity":"research-on-chemical-intermediates","isVorOnly":false,"title":"Research on Chemical Intermediates"},"publishedOn":"2025-09-29 15:58:05","publishedOnDateReadable":"September 29th, 2025"},"versionCreatedAt":"2025-07-09 16:18:52","video":"","vorDoi":"10.1007/s11164-025-05741-y","vorDoiUrl":"https://doi.org/10.1007/s11164-025-05741-y","workflowStages":[]},"version":"v1","identity":"rs-6883073","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6883073","identity":"rs-6883073","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}