Fabrication and characterization of poly(tannic acid) coated magnetic clay decorated with cobalt nanoparticles for NaBH4 hydrolysis: RSM-CCD based modeling and optimization

Hydrogen generation from sodium borohydride (NaBH₄) hydrolysis in the presence of metal catalysts is a frequently used and encouraging method for hydrogen storage. Metal nanoparticle-supported catalysts are better recyclability and dispersion than unsupported metal catalysts. In this study, the synthesis and characterization of a polymer-supported catalyst for hydrogen generation using NaBH₄ have been investigated. For the synthesis of polymeric material, first of all, kaolin (KLN) clay has been magnetically rendered by using the co-precipitation method (Fe₃O₄@KLN) and then coated with poly tannic acid (PTA@Fe₃O₄@KLN). Then, the catalyst loaded with cobalt (Co) nanoparticles have been obtained with the NaBH₄ reduction method (Co@PTA@Fe₃O₄@KLN). The surface morphology and structural properties of the prepared catalysts have been determined using methods such as scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma mass spectrometry (ICP-MS) and vibrating sample magnetometer (VSM). The optimization of the most important variables (NaBH₄ amount, NaOH amount, catalyst amount, and metal loading rate) affecting the hydrolysis of NaBH₄ using the synthesized polymeric catalysts was carried out using response surface methodology (RSM). Depending on the evaluated parameters, the desired response was determined to be hydrogen production rate (HGR, mL/g min). HGR was 1540.4 mL/g_cat. min. in the presence of the Co@PTA@Fe₃O₄@KLN at optimum points obtained via RSM (NaBH₄ amount 0.34 M, NaOH amount 7.9 wt%, catalyst amount 3.84 mg/mL, and Co loading rate 6.1%). The reusability performance of the catalyst used in hydrolysis of NaBH₄ was investigated under optimum conditions. It was concluded that the catalyst is quite stable.     

Kinetics of NaBH4 hydrolysis on carbon-supported ruthenium catalysts

In this work, different shapes (powder and spherical) of ruthenium-active carbon catalysts (Ru/C) were prepared by impregnation reduction method for hydrogen generation (HG) from the hydrolysis reaction of the alkaline NaBH₄ solution. The effects of temperature, amount of catalysts, and concentration of NaOH and NaBH₄ on the hydrolysis of NaBH₄ solution were investigated with different shapes of Ru/C catalysts. The results show that the HG kinetics of NaBH₄ solution with the powder Ru/C catalysts is completely different from that with the spherical Ru/C catalysts. The main reason is that both mass and heat transfer play important roles during the reaction with Ru/C catalysts. The HG overall kinetic rate equations for NaBH₄ hydrolysis using the powder Ru/C catalysts and the spherical catalysts are described as r = A exp (−50740/RT) [catalyst]^1.05 [NaOH]^−0.13 [NaBH₄]^−0.25 and r = A exp (−52,120/RT) [catalyst]^1.00 [NaOH]^−0.21 [NaBH₄]^0.27 respectively.     

A study on hydrogen generation from NaBH4 solution using Co-loaded resin catalysts

Hydrogen production via chemical processes has gained great attention in recent years. In this study, Co-based complex catalyst obtained by adsorption of Co metal to Amberlite IRC-748 resin and Diaion CR11 were tested for hydrogen production from alkaline NaBH₄ via hydrolysis process. Their catalytic activity and microstructure were investigated. Process parameters affecting the catalytic activity, such as NaOH concentration, Co percentage and catalyst amount, as well as NaBH₄ concentration and temperature were investigated. Furthermore, characteristics of these catalysts were carried out via SEM, XRD and FT-IR analysis. Hydrogen production rates equal to 211 and 221 ml min⁻¹ g_cat⁻¹ could be obtained with Amberlite IRC-748 resin and Diaion CR11 Co based complex catalysts, respectively. The activation energies of the catalytic hydrolysis reaction of NaBH₄ were calculated as 46.9 and 59.42 kJ mol⁻¹ for Amberlite IRC-748 resin and Diaion CR11 based catalysts respectively kJ mol⁻¹ from the system consisting of 3% Co, 10 wt% NaBH₄ and 7 wt% NaOH as well as 50 mg catalyst dosage. It can be concluded that Co-based resins as catalysts for hydrogen production is an effective alternative to other catalysts having higher rate.     

Preparation of CoB catalysts supported on raw and Na-exchanged bentonite clays and their application in hydrogen generation from the hydrolysis of NaBH4

The aim of this work is to prepare CoB catalysts supported on raw bentonite (CoB/bentonite) and Na-exchanged bentonite (CoB/Na-bentonite) by the impregnation and chemical reduction method. The prepared catalysts were characterized using X-ray diffractometry (XRD), X-ray fluorescence spectroscopy (XRF), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR) techniques. The activities of the catalysts were tested in the hydrolysis reaction of sodium borohydride (NaBH₄) in a semi-batch system. The volume of the evolved hydrogen gas was determined by a water displacement method. The effects of catalyst amount, NaOH (a base stabilizer) concentration, NaBH₄ concentration and solution temperature on the hydrogen generation rate were investigated. The maximum hydrogen generation rates were determined as 921.94 mL/min.g_cat for CoB/bentonite and 1601.45 mL/min.g_cat for CoB/Na-bentonite when the 5 wt % NaBH₄ and 10 wt % NaOH solutions were used at 50 °C. The activation energies (E_a) of the hydrolysis reaction over CoB/bentonite and CoB/Na-bentonite were determined as 55.76 and 56.61 kJ/mol, respectively.     

Nickel modified dolomite in the hydrogen generation from sodium borohydride hydrolysis

Hydrogen is expected to play an important role as an energy carrier in the world's future energy systems, as it is environmentally friendly and flexible in use. Hydrolysis of NaBH₄ is a promising and effective method, especially for fuel cells and other portable devices, thanks to hydrogen release. Therefore, catalyst research is of great importance in the development of this technology. In this study, Ni/Dolomite catalyst was synthesized by wet impregnation method and used in hydrolysis process. Additionally, the effects of reaction temperature (30–60 °C), nickel content (10–40 wt%), catalyst amount (25–125 mg), NaOH concentration (0.10–0.75 M), and an initial amount of NaBH₄ (25–125 mg) on hydrogen yield were investigated. Eventually, the catalyst with 40 wt% Ni content was assigned as the most suitable catalyst, attaining H₂ production of 100% with a rate of 88.16 mL H₂/g_cat.min at 60 °C with 5 mL of 0.25 M NaOH, NaBH₄, and Ni/Dolomite catalyst (100 mg).     

The use of metallurgical waste sludge as a catalyst in hydrogen production from sodium borohydride

In this study, the metallurgic sludge which contained oil and was obtained as waste of grinding, sharpening and milling parts was used in the production of hydrogen (H₂) from sodium borohydride (NaBH₄). The hydrolysis of NaBH₄ with the metallurgic sludge catalyst was investigated depending on several parameters such as sodium hydroxide (NaOH) concentration, catalyst amount, NaBH₄ concentration and temperature. The obtained metallurgic sludge catalyst was characterized by the XRD, FT-IR and SEM techniques and was evaluated for its activity in the H₂ generation from NaBH₄ hydrolysis. The maximum H₂ production rate from the hydrolysis of NaBH₄ with the metallurgic sludge catalyst was calculated as 9366 ml min⁻¹.g_cat⁻¹. The value of activation energy was found as 48.05 kJ mol⁻¹.     

Stability and kinetic studies of MOF‐derived carbon‐confined ultrafine Co catalyst for sodium borohydride hydrolysis

A mesoporous carbon‐confined cobalt (Co@C) catalyst was fabricated by pyrolysis of macroscale Co‐metal–organic framework (MOF) crystals and used to catalyze NaBH₄ hydrolysis for hydrogen production. To reveal the structural changes of cobalt nanoparticles, we characterized the fresh and used Co@C catalysts using X‐ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), and N₂ adsorption. This MOF‐derived Co@C exhibits high and stable activity toward NaBH₄ hydrolysis. No obvious agglomeration of Co nanoparticles occurred after five consecutive runs, implying good resistance of Co@C composite to metal aggregation. The kinetics of NaBH₄ hydrolysis was experimentally studied by changing initial NaBH₄ concentration, NaOH concentration, and catalyst dosage, respectively. It was found that the hydrogen generation rate follows a power law: r = A exp (?45.0/RT)[NaBH₄]^0.985[cat]^1.169[NaOH]^?0.451 .     

The effects of plasma treatment on electrochemical activity of Co–W–B catalyst for hydrogen production by hydrolysis of NaBH4

A plasma treatment of Co–W–B catalyst increases the rate of hydrogen generation from the hydrolysis of NaBH₄. The catalytic properties of Co–W–B prepared in the presence of plasma have been investigated as a function of NaBH₄ concentration, NaOH concentration, temperature, plasma applying time, catalyst amount and plasma gases. The Co–W–B catalyst prepared with cold plasma effect hydrolysis in only 12 min, where as the Co–W–B catalyst prepared in known method with no plasma treatment in 23 min. The activation energy for first-order reaction is found to be 29.12 kJ mol⁻¹.     

Superporous P(2-hydroxyethyl methacrylate) cryogel-M (M:Co,Ni, Cu) composites as highly effective catalysts in H2 generation from hydrolysis of NaBH4 and NH3BH3

Highly porous p(2-hydroxyethyl methacrylate) p(HEMA) cryogels were synthesized via cryopolymerization technique and used as template for Co, Ni, and Cu nanoparticle preparation, then as composite catalyst systems in H₂ generation from hydrolysis of both NaBH₄ and NH₃BH₃. Due to their highly porous and open microstructures, p(HEMA)-Co cryogel composites showed very effective performances in H₂ production from hydrolysis of both chemical hydrides. The characterization of p(HEMA) cryogels, and their metal composites was determined via various techniques including swelling experiments, digital camera images, SEM and TEM images, AAS and TGA measurements. The effect of various parameters on the hydrolysis reaction of NaBH₄ such as metal types, concentration of chemical hydrides, amounts of catalyst, alkalinity of reaction medium and temperature were investigated in detail. It was found that Co nanoparticles are highly active catalysts in H₂ generation reactions from both hydrides. The hydrogen generation rate (HGR) of p(HEMA)-Co was 1596 (mL H₂) (min)⁻¹ (g of Co)⁻¹ which is quite good in comparison to reported values in the literature. Furthermore, kinetic parameters of p(HEMA)-Co metal composites such as energy, enthalpy and entropy were determined as Ea = 37.01 kJmol⁻¹, ΔH# = 34.26 kJmol⁻¹, ΔS# = −176,43 Jmol⁻¹ K⁻¹, respectively.     

Monodispersed p(2-VP) and p(2-VP-co-4-VP) particle preparation and their use as template for metal nanoparticle and as catalyst for H2 production from NaBH4 and NH3BH3 hydrolysis

The monodispersed poly(2-vinyl pyridine) (p(2-VP)) and poly(2-vinyl pyridine-co-4-vinyl pyridine) (p(2-VP-co-4-VP)) particles of different compositions were synthesized by a surfactant-free emulsion polymerization system using divinyl benzene (DVB) as cross-linker. The diameter of p(2-VP) and p(2-VP-co-4-VP) particles were measured between 370 and 530 nm. Co, Ni and Cu metal nanoparticles were prepared inside these microgels after quaternization with HCl and loading of metal salts, such as CoCl₂, NiCl₂, and CuCl₂, in ethyl alcohol followed by reduction with NaBH₄. The prepared metal nanoparticles within these particles were used as catalyst for H₂ production via hydrolysis of NaBH₄ and NH₃BH₃. Various parameters of the polymeric microgels such as template, metal types, reuse, the amount of NaOH, and temperature were investigated. From hydrolysis reactions the activation energy (E_a), enthalpy (ΔH), and entropy (ΔS) were calculated for Co metal nanoparticles as catalyst for the NaBH₄ hydrolysis reaction in the temperature range of 0–50 °C. The activation parameters of NaBH₄ hydrolysis catalyzed by Co nanoparticle composite systems were calculated as 46.44 ± 1.1 kJ mol⁻¹ for E_a, 36.39 ± 6.5 kJ mol⁻¹ for ΔH and −170.56 ± 20.1 kJ mol⁻¹ K⁻¹ for ΔS.     

Synthesis of Ni/TiO2 catalyst by sol-gel method for hydrogen production from sodium borohydride

Hydrogen is a sustainable, renewable and clean energy carrier that meets the increasing energy demand. Pure hydrogen is produced by the hydrolysis of sodium borohydride (NaBH₄) using a catalyst. In this study, Ni/TiO₂ catalysts were synthesized by the sol-gel technique and characterized by X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) methods. The effects of Ni loading ratio (20–40%), catalyst amount (75–200 mg), the concentration of sodium hydroxide (NaOH, 0.25–1 M), initial amount of NaBH₄ (75–125 mg) and the reaction temperature (20–60 °C) on hydrogen production performance were examined. The hydrogen yield (100%) and hydrogen production rate (110.87 mL/g_cat.min) were determined at the reaction conditions of 5 mL of 0.25 M NaOH, 100 mg NaBH₄, 100 mg Ni/TiO₂, 60 °C. Reaction order and activation energy were calculated as 0.08 and 25.11 kJ/mol, respectively.     

Effective TiO2 supported Cu-Complex catalyst in NaBH4 hydrolysis reaction to hydrogen generation

This paper reports the experimental results on using TiO₂ based Cu(II)-Schiff Base complex catalyst for hydrolysis of NaBH₄. In the presence of Cu-Schiff Base complex which we reported in advance [1] and with titanium dioxide supports a novel catalyst named TiO₂ supported 4-4′-Methylenbis (2,6-diethyl)aniline-3,5-di-tert-buthylsalisylaldimine-Cu complex is prepared, successfully. The synthesized catalyst was characterized by means of X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), Brunauer-Emmett-Teller Surface Area Analysis (BET) and Fourier Transform Infrared Spectroscopy (FT-IR). The as prepared catalyst was employed to generate hydrogen through hydrolysis reaction of NaBH₄. Effects of different parameters (e.g. amount of Cu-Schiff Base complex in all catalyst, percentage of NaBH₄, percentage of NaOH, amount of TiO₂ supported Cu-Schiff Base complex catalyst and different temperatures) are also investigated. A high apparent activation energy (Ea), 25,196 kJ.mol^-1 is calculated for hydrolysis of NaBH₄ at 20–50 °C. Hydrogen generation rate was 14,020 mL H₂/g_cat.min and 22,071 mL H₂/g_cat.min in order of 30 °C and 50 °C.     

High-capacity hydrogen release through hydrolysis of NaB3H8

NaB₃H₈ has advantages over NaBH₄ and NH₃BH₃, two most widely studied chemical hydrides for hydrogen storage via hydrolysis. NaB₃H₈ has an extraordinary high solubility in water and thus possesses a high theoretical capacity of 10.5 wt% H via hydrolysis, in contrast to 7.5 wt% for NaBH₄ and 5.1 wt% for NH₃BH₃. NaB₃H₈ is reasonably stable in water which makes it unnecessary to add corrosive NaOH as a stabilizer as the case for NaBH₄. Furthermore, hydrolysis of NaB₃H₈ can be catalyzed by a Co-based catalyst with fast kinetics that is comparable to Ru-based catalysts. Therefore, cost-effective hydrolysis of NaB₃H₈ is possible for practical applications. A high capacity of 7.4 wt% H was achieved when water was included in the materials weight.     

Synthesis of cobalt-doped catalyst for NaBH4 hydrolysis using eggshell biowaste

In the present study, a cobalt-doped catalyst was prepared from chicken eggshell powder (CEP) biowaste to be used in the hydrolysis of sodium borohydride (NaBH₄). In the presence of the prepared catalyst (CEP_cat), possible effects of the parameters of NaOH concentration (%), catalyst amount (g), NaBH₄ concentration (%), process temperature (^oC) and reusability affecting the hydrolysis of sodium borohydride were examined. The CEP_cat obtained was characterized with FT-IR, TGA, XRD, SEM and EDX analyses. The hydrogen generation rate (HGR) was determined as 432 mL g_Co⁻¹ min⁻¹ in the presence of 1 g CEP_cat, a CoO/CaO ratio of 10/90 and 1% NaBH₄ concentration. The activation energy of the NaBH₄ hydrolysis reaction was calculated as 16.78 kJ mol⁻¹. After 16 reuses of the CEP_cat there was no significant decrease in the hydrogen volume. Compared to the first use while there was an increase in the HGR. These results showed that the CEP_cat prepared has a significant advantage over other catalysts for use in NaBH₄ hydrolysis.     

Catalytic hydrolysis of NaBH4 over titanate nanotube supported Co for hydrogen production

A Co/HTNT catalyst is developed by immobilizing Co on the surface of titanate nanotubes. The microstructure and composition of the catalyst are investigated with atomic absorption spectroscopy (AAS), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Fourier transform infrared spectrometer (FT-IR) and X-ray photoelectron spectroscopy (XPS). The developed Co/HTNT catalyst shows great performance in catalyzing NaBH₄ hydrolysis. The hydrolysis of 25 mg NaBH₄ catalyzed by 50 mg Co/HTNT in 10 g NaOH solution (12.5 wt%) provides a hydrogen production rate of 1.04 L min^?1 g_Co^?1 at 30 °C, and the activation energy of the reaction is 29.68 kJ mol^?1. The high catalytic activity and economical property make this catalyst a promising choice for on-site hydrogen production from NaBH₄ hydrolysis.     

Catalytic hydrolysis of sodium borohydride by a novel nickel–cobalt–boride catalyst

With the aim of designing an efficient hydrogen generator for portable fuel cell applications nickel–cobalt–boride (Ni–Co–B) catalysts were prepared by a chemical reduction method and their catalytic hydrolysis reaction with alkaline NaBH₄ solution was studied. The performance of the catalysts prepared from NaBH₄ solution with NaOH, and without NaOH show different hydrogen generation kinetics. The rate of hydrogen generation was measured using Ni–Co–B catalyst as a function of the concentrations of NaOH and NaBH₄, as well as the reaction temperature, in the hydrolysis of alkaline NaBH₄ solution. The hydrogen generation rate increases for lower NaOH concentrations in the alkaline NaBH₄ solution and decreases after reaching a maximum at 15 wt.% of NaOH. The hydrogen generation rate is found to be constant with respect to the concentration of NaBH₄ in the alkaline NaBH₄ solution. The activation energy for hydrogen generation is found to be 62 kJ mol⁻¹, which is comparable with that of hydrogen generation by a ruthenium catalyst.     

The on demand generation of hydrogen from Co-Ni bimetallic nano catalyst prepared by dual use of hydrogel: As template and as reactor

We report the preparation of metal nanoparticles in various formulations inside p(2-acrylamido-2-methyl-1-propansulfonic acid; p(AMPS)) hydrogels and their utilization as a catalyst in hydrolysis of NaBH₄. The swollen, flexible p(AMPS) network was used for metal ion loading and reduction in situ for the preparation of Co:Ni nanoparticles as bimetallic clusters in various formulation, and Co and Ni bimetallic catalysts as Co + Co, Co + Ni, Ni + Co and Ni + Ni. In addition to utilization of hydrogels as support materials, the p(AMPS)-metal nanoparticle system was used as catalyst to generate hydrogen in the hydrolysis of NaBH₄ with very high yield. Various parameters for the hydrolysis reaction were determined and the activation parameters were calculated. For the first time, inclusion of ferrite magnetic particles to control hydrogen generation on demand by using an externally applied magnetic field to remove the hydrogel-catalyst system from the hydrolysis medium is reported.     

Hydrogen generation by hydrolysis of sodium borohydride on CoB/SiO2 catalyst

Generation of hydrogen by hydrolysis of alkali metal hydrides has attracted attention. Unsupported CoB catalyst demonstrated high activity for the catalytic hydrolysis of NaBH₄ solution. However, unsupported CoB nanoparticles were easy to aggregate and difficult to reuse. To overcome these drawbacks, CoB/SiO₂ was prepared and tested for this reaction. Cobalt (II) acetate precursor was loaded onto the SiO₂ support by incipient-wetness impregnation method. After drying at 100 °C, Co cations were deposited on the support. The dried sample was then dispersed in methanol/water solution and then fully reduced by NaBH₄ at room temperature. The catalyst was characterized by N₂ sorption, XRD and XPS. The results indicated that the CoB on SiO₂ possessed amorphous structure. B and Co existed both in elemental and oxidized states. SiO₂ not only affected the surface compositions of CoB, but also affected the electronic states of Co and B. B⁰ could donate partial electron to Co⁰. The structure effect caused by the SiO₂ support helped to prevent CoB nanocluster from aggregation and therefore the activity increased significantly on hydrolysis of alkaline NaBH₄ solution. The CoB/SiO₂ catalyst showed much higher activity than the unsupported CoB catalyst. At 298 K, the hydrogen generation rate on CoB/SiO₂ catalyst was 4 times more than that on the unsupported CoB catalyst. The hydrogen generation rate was as high as 10,586 mL min⁻¹ g⁻¹ catalyst at 298 K. CoB/SiO₂ is a very promising catalyst for this reaction.     

Metal ion-imprinted hydrogel with magnetic properties and enhanced catalytic performances in hydrolysis of NaBH4 and NH3BH3

Metal ion-imprinted (IIH) poly(2-acrylamido-2-methyl-1-propansulfonic acid) p(AMPS) hydrogels were prepared by using a free-radical polymerization technique in the presence of metal ions (M = Co (II) or Ni (II)). Using metal ion-imprinted hydrogels (IIHs), and non-metal ion-imprinted (NIH) hydrogels as template for the preparation of Co and Ni catalyst systems, the hydrolysis kinetics of NaBH₄ and NH₃BH₃ were investigated. The catalytic performances of IIHs and NIHs were compared in terms of effect on hydrolysis kinetics of NaBH₄ and NH₃BH_3. To increase the amounts of Co nanoparticles within p(AMPS) hydrogel for better catalytic activity, several reloading and reduction cycles of Co (II) ions were carried out, and the prepared p(AMPS)-Co composite catalyst systems were tested for hydrogen generation from the hydrolysis of NaBH₄. As the number of Co (II) loading and reduction cycles increased, the amount of metal catalysts and the catalytic performance of composites increased. Kinetics studies were carried out on three times Co (II) ion loaded and reduced p(AMPS)-Co catalyst systems (containing 36.80 mg/g Co). Three time Co (II)-loaded catalyst systems provided very fast hydrolysis kinetics for NaBH₄, and provided magnetic field responsive behavior. The hydrolysis reaction of NaBH₄ was completed within 50 s, under the described conditions at 60 °C. It was demonstrated that the synthesized catalyst systems can be used ten times repetitively without significant loss of catalytic activity (86.5%).     

Hydrogen generation from sodium borohydride solution using a ruthenium supported on graphite catalyst

The catalyst with high activity and durability plays a crucial role in the hydrogen generation systems for the portable fuel cell generators. In the present study, a ruthenium supported on graphite catalyst (Ru/G) for hydrogen generation from sodium borohydride (NaBH₄) solution is prepared by a modified impregnation method. This is done by surface pretreatment with NH₂ functionalization via silanization, followed by adsorption of Ru (III) ion onto the surface, and then reduced by a reducing agent. The obtained catalyst is characterized by transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). Very uniform Ru nanoparticles with sizes of about 10 nm are chemically bonded on the graphite surface. The hydrolysis kinetics measurements show that the concentrations of NaBH₄ and NaOH all exert considerable influence on the catalytic activity of Ru/G catalyst towards the hydrolysis reaction of NaBH₄. A hydrogen generation rate of 32.3 L min⁻¹ g⁻¹ (Ru) in a 10 wt.% NaBH₄ + 5 wt.% NaOH solution has been achieved, which is comparable to other noble catalysts that have been reported.