Research progress on catalysts for hydrogen generation through sodium borohydride alcoholysis

Hydrogen is a promising energy carrier for realizing the transition from fossil fuels to renewable energy sources. Nowadays, the development of the hydrogen economy faces many challenges connected with its efficient production, storage, distribution, and end-use. During the past decade, the alcoholysis, particularly methanolysis, of sodium borohydride (NaBH₄) has attracted much attention due to the nonflammability, nontoxicity, potential for utilization in cold conditions of the reaction system. Highly efficient catalysts are of great significance to guarantee the efficiency of the reaction and control the hydrogen release. In this review, we summarize recent advances in both metallic and nonmetallic catalysts for the alcoholysis of NaBH₄. This review also summarizes the advantages and disadvantages of various catalysts in the investigations to assess the potential opportunities and challenges for their application in NaBH₄ methanolysis. The catalytic mechanisms related to NaBH₄ methanolysis were also discussed.     

Poly(2-aminoethyl methacrylate) based microgels catalyst system to be used in hydrolysis and methanolysis of NaBH4 for H2 generation

The poly(2-aminoethyl methacrylate) (p(AEM)) microgels were synthesized by microemulsion polymerization technique and used for in situ metal nanoparticle preparation to render as p(AEM)-M (M: Co or Ni) microgel composites and were used in p(AEM) based poly ionic liquid (PIL) microgels. Next, these p(AEM)) based microgel materials were used as catalysts for hydrogen (H₂) production from both hydrolysis and methanolysis reactions of sodium borohydride (NaBH₄). It was found that the catalytic hydrolysis of the NaBH₄ reaction, catalyzed by p(AEM)-Co microgel composite was completed in 140 min, whereas the methanolysis of NaBH₄ methanolysis catalyzed by the PIL of p(AEM)⁺Cl⁻ microgels was completed in 5 min both with 250 ± 2 mL H₂ production. Furthermore, p(AEM)-Co microgel composite catalysts maintained 80% catalytic activity after 5 consecutive uses in NaBH₄ hydrolysis. On the other hand, p(AEM)⁺Cl⁻ microgels were found to afford more than 50% catalytic activity even after 20 repetitive use in NaBH₄ methanolysis due to superior regeneration ability. Moreover, activation energy values for p(AEM)-Co microgel composites catalyzed NaBH₄ hydrolysis reaction were calculated as 38.9 kJ/mol in comparison to 37.3 kJ/mol activation energy of p(AEM)⁺Cl⁻ microgel catalyzed methanolysis reaction.     

Very fast H2 production from the methanolysis of NaBH4 by metal‐free poly(ethylene imine) microgel catalysts

The polyethyleneimine (PEI) microgels prepared via microemulsion polymerization are protonated by hydrochloric acid treatment (p‐PEI) and quaternized (q‐PEI) via modification reaction with methyl iodide and with bromo alkanes of different alkyl chain lengths such as 1‐bromoethane, 1‐bromobutane, 1‐bromohexane, and 1‐bromooctane. The bare p‐PEI and q‐PEI microgels are used as catalysts directly without any metal nanoparticles for the methanolysis reaction of sodium borohydride (NaBH₄). Various parameters such as the protonation/quaternization reaction on PEI microgels, the amount of catalyst, the amount of NaBH₄, and temperature are investigated for their effects on the hydrogen (H₂) production rate. The reaction of self‐methanolysis of NaBH₄ finishes in about 32.5 min, whereas the bare PEI microgel as catalyst finishes the methanolysis of NaBH₄ in 22 min. Surprisingly, it is found that when the protonated PEI microgels are used as catalyst, the same methanolysis of NaBH₄ is finished in 1.5 min. The highest H₂ generation rate value is observed for protonated PEI microgels (10 mg) with 8013 mL of H₂/(g of catalyst.min) for the methanolysis of NaBH₄. Moreover, activation parameters are also calculated with activation energy value of 23.7 kJ/mol, enthalpy 20.9 kJ/mol, and entropy ?158 J/K.mol. Copyright © 2016 John Wiley & Sons, Ltd.     

Phosphorus and oxygen doped carbon-based on Spirulina microalgae as efficient metal-free catalysts to obtain H2 from methanolysis of NaBH4

Metal-free catalysts (SP–KOH–P) doped phosphorus and oxygen as a result of modification with H₃PO₄ to the surface of the activated carbon sample (SP–KOH) obtained by activation of KOH with Spirulina microalgae were used to obtain hydrogen (H₂) from methanolysis of NaBH₄. The characteristic structure of SP-KOH-P and SP-KOH metal-free catalysts were examined by XRD, TEM, elemental analysis, FTIR, and ICP-MS. The effects of the amount of catalyst, NaBH₄ concentration, reusability, and temperature on H₂ production rate from NaBH₄ methanolysis reaction were investigated. The hydrogen production rate (HGR) obtained with 25 mg SP-KOH-P was found to be 19,500 mL min^?1 g^?1. The activation energy (Ea) value of SP-KOH-P metal-free catalyst sample was calculated as 38.79 kJ mol^?1.     

Metal-free catalysts with phosphorus and oxygen doped on carbon-based on Chlorella Vulgaris microalgae for hydrogen generation via sodium borohydride methanolysis reaction

Metal-free catalysts (C–KOH–P) containing phosphorus (P) and oxygen (O) prepared by the modification with phosphoric acid (H₃PO₄) of activated carbon (C–KOH) obtained by activation of Chlorella Vulgaris microalgae with potassium hydroxide (KOH) were investigated for the hydrogen (H₂) generation reaction from methanolysis of sodium borohydride (NaBH₄). Elemental analysis, XRD, FTIR, ICP-MS, and nitrogen adsorption were used to analyze the characteristics of metal-free catalysts. The results showed that groups containing O and P were attached to the carbon sample. In the study, the hydrogen production rates (HGR) obtained with metal-free C–KOH and C–KOH–P catalysts were 3250 and 10,263 mL/min/g, respectively. These HGR values are better than most values obtained for many catalysts presented in the literature. Besides, relatively low activation energy (Ea) of 27.9 kJ/mol was obtained for this metal-free catalyst. The C–KOH–P metal-free catalyst showed ideal reusability with 100% conversion and a partial reduction in the H₂ production studies of NaBH₄ methanolysis after five consecutive uses.     

Metal-organic frameworks (MOFs) and MOFs-derived CuO@C for hydrogen generation from sodium borohydride

Hydrogen gas has been considered as one of the promising sources of energy. Thus, several strategies including the hydrolysis of hydrides have been reported for hydrogen production. However, effective catalysts are highly required to improve the hydrogen generation rate. Two dimensional metal-organic frameworks (copper-benzene-1,4-dicarboxylic, CuBDC), and CuBDC-derived CuO@C were synthesized, characterized and applied as catalysts for hydrogen production using the hydrolysis and methanolysis of sodium borohydride (NaBH₄). CuBDC, and CuO@C display hydrogen generation rate of 7620, and 7240 mlH₂·g_cat⁻¹· min⁻¹, respectively for hydrolysis. While, CuBDC offers hydrogen generation rate of 9060 mlH₂·g_cat⁻¹· min⁻¹ for methanolysis. Both catalysts required short reaction time, and showed good recyclability. The materials may open new venues for efficient catalyst for energy-based applications.     

Oxygen and nitrogen-doped metal-free microalgae carbon nanoparticles for efficient hydrogen production from sodium borohydride in methanol

Here, the oxygen(O) and nitrogen(N) doped metal-free carbon synthesis including potassium hydroxide (KOH) activation of Spirulina Platensis microalgae, followed by nitric acid (HNO₃) activation is reported for the first time. Oxygen and nitrogen-doped metal-free catalysts were investigated for efficient hydrogen (H₂) production from methanolysis of sodium borohydride (NaBH₄). Compared to the catalyst obtained with the KOH activation, the catalytic activity for O and N doped metal-free showed about a four-fold improvement. The catalysts were analysed by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffractometer (XRD), nitrogen adsorption, elemental analysis and Fourier-transform infrared spectroscopy (FTIR). The effects of temperature, NaBH₄ amounts, catalyst loading and reusability experiments on the catalytic performance of obtained metal-free catalysts by H₂ release from NaBH₄ methanolysis were performed. This study can provide a new alternative strategy to produce specific metal-free carbon catalysts doped heteroatom for environmentally friendly conversion to produce H₂ efficiently.     

Poly (acrylic acid)/polysaccharides IPN derived metal free catalyst for rapid hydrogen generation via NaBH4 methanolysis

Polymeric catalysts have displayed great performance for catalytic hydrogen generation. However, the reported metal free polymeric catalysts for NaBH₄ methanolysis are mainly limited to coating strategy where the catalytic activity fade after few cycles. Herein, we report an interpenetrating polymer network (IPN) strategy for rapid and highly recyclable NaBH₄ catalytic methanolysis to produce hydrogen (H₂) gas. In this study, we prepared poly(acrylic acid)/polysaccharide IPN via Pickering tempted polymerization. The hydrogen generation performance was studied employing different parameters where maximum HGR of 8182 mL H₂ min^?1 g^?1 of CAP. The activation energy Ea, enthalpy and entropy were calculated to be 62.99 kJ mol^?1, 32.25 kJ mol and ?130.92 J mol K^?1, respectively. Above all, CAP kept cyclic performance to 100% even at the 7th cycle. We confirmed the reproducibility of approach with other natural polysaccharides. This was due to strong chain entanglement of IPN synthesis which forces the active sites to stay in place during cyclic catalysis reaction. Thus, the IPN strategy ensures longer catalyst life for catalytic methanolysis of NaBH₄ for H₂ generation.     

Exergy and energy analysis of hydrogen production by the degradation of sodium borohydride in the presence of novel Ru based catalyst

Chemically possible hydrogen storage material of the most important and widely used metal hydride compound is sodium borohydride. A current research issue is the development of systems that allow regulated hydrogen generation employing appropriate catalysts for the creation of hydrogen gas from the hydrolysis of sodium borohydride (NaBH₄). In this study, controlled hydrogen production from alkali solution of NaBH₄ was aimed. On hydrogen generation rate (HGR), the effects of NaBH₄ and alkaline solution concentrations, catalyst quantity, and temperature were examined. Considering the energy and exergy analysis, which have gained importance in the international arena in recent years, in this study, the exergy energy analysis of the environment in which the sodium borohydride solution is located was performed. The best one of the Ru-based catalysts synthesized in different atomic ratios was determined as 90:10 RuCr. The surface characterization of the obtained catalyst was carried out using scanning electron microscope (SEM-EDX) and X-ray diffractometer (XRD). In the kinetic calculations, the activation energy was calculated as 35,024 kj/mol and the reaction ordered n was found to be 0,65. By applying exergy and energy analysis to the hydrogen production step, the energy and exergy efficiency of the system were found to be 24% and 7%, respectively.     

Carbon spheres from lactose as green catalyst for fast hydrogen production via methanolysis

Micrometer sized carbon spheres (CSs) are prepared in a single step using lactose precursor via hydrothermal method. These CSs are chemically modified with 3-chloro-2-hydroxypropyl ammonium chloride (CHPACl) and triethylenetetramine (TETA) to generate amine groups on the particle surface. Modified CSs with TETA was protonated with HCl as CSs-TETA-HCl that the zeta potential is increased to +40.3 ± 0.70 from ?51.4 ± 4.66 mV. The catalytic performance of CSs are tested as catalysts in the methanolysis of NaBH₄, and the best catalytic performance as 2586 mL min^?1 g^?1 hydrogen generation rate (HGR) was obtained by CSs-TETA-HCl catalyst at 298 K as metal free catalyst. Furthermore, various parameters such as the amount of NaBH₄, the reaction temperature, and the reusability of CSs-TETA-HCl particles are investigated. More importantly, relatively low activation energy, 23.82 kJ mol^?1 for CSs-TETA-HCl catalyzed NaBH₄ methanolysis reaction is obtained in comparison to metal nanoparticle and metal free catalysts reported for the same purpose in the literature.     

Indirect hydrolysis of sodium borohydride: Isolation and crystallographic characterization of methanolysis and hydrolysis by-products

The use of sodium borohydride as a means for hydrogen generation has focused on the base-stabilized hydrolysis reaction, while literature for the methanolysis of sodium borohydride remains scarce. Sodium borohydride methanolysis is an alternative for hydrogen production from sodium borohydride and has a number of advantages over hydrolysis reactions in terms of by-product handling. Previous studies have shown that the presence of water in methanol significantly retards the rate of hydrogen evolution from NaBH₄. This article reports the production of hydrogen from NaBH₄ using rigorously dried methanol. In addition, the solid-state structure of the methanolysis by-product is reported, which lends pertinent information for its hydrolysis for methanol recovery. Also reported is the solid-state structure of the hydrolysis by-product.     

Evaluating organic waste sources (spent coffee ground) as metal-free catalyst for hydrogen generation by the methanolysis of sodium borohydride

In this study, organic waste sources (spent coffee ground (SCG)) is used as metal-free catalyst in comparison with conventional noble-metal catalyst materials for hydrogen generation based on the methanolysis of sodium borohydride solution. Spent coffee ground (SCG) is used as a metal-free catalyst for the first time as treated with different chemicals. The aim is to synthesize the metal-free catalyst that can be used for the production of hydrogen, a renewable energy source. SCG, which was collected from coffee shops, was used for preparing the catalyst. To produce hydrogen by sodium borohydride (NaBH₄) methanolysis, SCG is pretreated with different chemical agents (H₃PO₄, KOH, ZnCl₂). According to the acid performances, the choice of phosphoric acid was evaluated at different mixing ratios (10%, 20%, 30%, 40%, 50%, 100%) (w/w), different temperatures (200, 300 and 400 °C) and burning times (30, 45, 60 and 90 min) for the optimization of SCG-catalyst. A detailed characterization of the samples were carried out with the aid of FTIR, SEM, XRD and BET analysis. In this study, the experiments were generally carried out effectively under ambient temperature conditions in10 ml methanol solution containing 0.025 g NaBH₄ and 0.1 g of the catalyst. The hydrogen obtained in the experimental studies was determined volumetrically by the gas measurement system. When evaluating the hydrogen volume, different NaBH₄ concentrations, catalyst amount and different temperature effects were investigated. The effect of the amount of NaBH₄ was investigated with 1%, 2.5%, 5%, and 7.5% ratio of NaBH₄ while the influence of the concentration of catalyst was carried-out at 0.05, 0.1, 0.15, and 0.25 g catalysts. Four different temperatures were tested (20, 30, 40, 50 and 60 °C) to explore the performance of the catalyst under different temperatures. The experiments by using SCG-catalyst treated with H₃PO₄ reveal that the best acid ratio was 100% H₃PO₄. The maximum hydrogen production rate with the use of SCG-catalyst for the methanolysis of NaBH₄ was found to be 8335.5 mL min⁻¹gcat⁻¹. Also, the activation energy was determined to be 9.81 kJ mol⁻¹. Moreover, it was discovered that there was no decline in the percentage of converted catalyst material.     

Very efficient dehydrogenation of methanolysis reaction with nitrogen doped Chlorella Vulgaris microalgae carbon as metal-free catalysts

In this study, nitrogen (N) doped metal-free catalysts were obtained as a result of nitric acid (HNO₃) activation of carbon sample (C–KOH–N), which was obtained based on Chlorella Vulgaris microalgae by KOH activation (C–KOH). These catalysts have been effectively used to produce hydrogen (H₂) from the sodium borohydride (NaBH₄) methanolysis reaction. Compared to the C–KOH catalyst, the catalytic activity for C–KOH–N showed a seven-fold improvement. Hydrogen generation rate (HGR) values obtained for the NaBH₄ methanolysis reaction for C–KOH and C–KOH–N metal-free catalysts were 3250 and 20,100 mL min^?1 g^?1. The catalysts were characterized using various analytical techniques such as XPS, XRD, SEM, FTIR, BET, and elemental analysis. This work can provide a new alternative strategy to produce specific heteroatom-doped metal-free carbon catalysts for environmentally friendly conversion to produce H₂ efficiently.     

Poly(acrylic acid)-modified silica nanoparticles as a nonmetal catalyst for NaBH4 methanolysis

In the present work, a SiO₂@PAA catalyst for NaBH₄ methanolysis composed of silica nanoparticles modified with poly(acrylic acid) has been developed. The morphology and composition of the prepared SiO₂@PAA catalyst were analyzed with transmission electron microscopy, Fourier transform-infrared spectroscopy, x-ray photoelectron spectroscopy and thermogravimetric analysis. This catalyst showed excellent catalytic performance for methanolysis of NaBH₄. The NaBH₄ methanolysis reaction catalyzed by SiO₂@PAA showed an average hydrogen generation rate 5.5 times as high as the reaction catalyzed by unmodified SiO₂ and 10.6 times as high as the uncatalyzed reaction, respectively. The activation energy for methanolysis of NaBH₄ catalyzed by this SiO₂@PAA catalyst was 24.03 kJ/mol. Moreover, although the catalytic activity of SiO₂@PAA catalyst partially lost after being used, it could be restored after being regenerated by washing with diluted hydrochloric acid solution.     

PDMA cryogel beads as a catalyst for hydrogen generation from NaBH4 alcoholysis

Poly[2-(dimethylamino)ethyl methacrylate] cryogel beads were prepared under cryogenic conditions via free radical polymerization and used as a catalyst in the production hydrogen (H₂) from NaBH₄ by alcoholysis. The efficiency of the catalyst was investigated in the range of 0–40 °C by both methanolysis and ethylene glycolysis reactions, and its reuse was tested. Accordingly, it was observed that the methanolysis reaction was faster than the ethylene glycolysis reaction. When the hydrogen generation rate (HGR) values between 0 and 40 °C were compared, it was concluded that the methanolysis reaction rate increased from 1550 to 4800 mL.min⁻¹g⁻¹ and the ethylene glycolysis reaction rate increased from 923 to 3551 mL.min⁻¹g⁻¹. In the alcoholysis reaction catalyzed by PDMA cryogel beads, the activation energy was calculated as 19.34 and 22.77 kJ.mol⁻¹ for the methanolysis and ethylene glycolysis reactions, respectively. After six repetitions, the catalyst activity was calculated over 50% for NaBH₄ methanolysis and ethylene glycolysis.     

Carbon-supported cobalt catalyst for hydrogen generation from alkaline sodium borohydride solution

Low cost transition metal catalysts with high performance are attractive for the development of on-board hydrogen generation systems by catalytic hydrolysis of sodium borohydride (NaBH₄) in fuel cell fields. In this study, hydrogen production from alkaline NaBH₄ via hydrolysis process over carbon-supported cobalt catalysts was studied. The catalytic activity of the supported cobalt catalyst was found to be highly dependent on the calcination temperatures. The hydrogen generation rate increases with calcination temperatures in the range of 200–400 °C, but a high calcination temperature above 500 °C led to markedly decreased activity. X-ray diffraction patterns reveal that the catalysts experience phase transition from amorphous Co–B to crystalline cobalt hydroxide with increase in calcination temperatures. The reaction performance is also dependent on the concentration of NaBH₄, and the hydrogen generation rate increases for lower NaBH₄ concentrations and decreases after reaching a maximum at 10 wt.% of NaBH₄.     

Controllable hydrogen production from NaBH4 hydrolysis promoted by acetic acid

Numerous catalysts have been widely investigated for accelerating hydrogen production from NaBH₄ hydrolysis. However, these catalysts are usually complicated in structures, costly in fabrication, and hazardous for environment. In this work, cheap and environment-friendly acetic acid, CH₃COOH, is employed to promote NaBH₄ hydrolysis to produce hydrogen in a considerable rate. The experimental results demonstrate that the addition of suitable amount of CH₃COOH into NaBH₄ solutions stabilized with NaOH could dramatically accelerate the hydrolysis reaction. Additionally, the start/stop of NaBH₄ hydrolysis could be controlled by adding acid or base into the solution to realize “go-as-you-please” on-site hydrogen production.     

Chlorella vulgaris microalgae strain modified with zinc chloride as a new support material for hydrogen production from NaBH4 methanolysis using CuB,NiB, and FeB metal catalysts

This study aims to produce hydrogen (HG) from sodium borohydride (NaBH₄) methanolysis using CuB, NiB or FeB catalysts prepared with a different support material including C. vulgaris microalgae strain modified using zinc chloride (CMS-ZnCl₂). The NaBH₄ concentration, metal percentage in the supported-catalyst, the optimal ZnCl₂ percentage, and temperature effect on the NaBH₄ methanolysis were investigated. X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Transmission electron microscopy (TEM), and Scanning electron microscopy (SEM) analysis were performed for the CMS-ZnCl₂-CuB characterization. Also, the low activation energy (Ea) of 22.71 kJ mol⁻¹ was found with the supported catalyst obtained. Under the same conditions, nearly 100% conversion was achieved in the reusability experiments repeated five times, but a gradual decrease in catalytic activity was observed after each use.     

All-in-one portable electric power plant using proton exchange membrane fuel cells for mobile applications

A portable electric power plant is developed using a NaBH₄ (sodium borohydride)-based proton exchange membrane fuel cell stack. The power plant consists of a NaBH₄-based hydrogen generator, a fuel cell stack, a DC-DC converter, a micro-processed controller and a data monitoring device. The hydrogen generator can produce 5.9 L/min pure hydrogen gas using catalytic hydrolysis of 20 wt% NaBH₄ to feed a 500-W scale fuel cell stack. Thus, the Co/γ-Al₂O₃ and Co-P/Ni foam catalysts in the hydrogen generator play significant roles in promoting hydrogen production rates that are as fast as necessary by enhancing the slow response that is intrinsic to using only Co-P/Ni foam catalysts. Moreover, different hydrogen production rates can easily be achieved during the operation by controlling NaBH₄ solution rates using a fuel pump so that the hydrogen storage efficiency can be improved by supplying required hydrogen gas in accordance with load demands. The specific energy density of the electric power plant was measured 211 Wh/kg. Therefore, the power plant described here can be a power source for mobile applications, such as cars and UAVs, as well as a stationary power supplier when electric energy is required.     

Hydrogen generation from hydrolysis of sodium borohydride using Ni–Ru nanocomposite as catalysts

Magnetic nickel–ruthenium based catalysts on resin beads for hydrogen generation from alkaline NaBH₄ solutions were synthesized with combined methods of chemical reduction and electroless deposition. Factors, such as solution temperature, NaBH₄ loadings, and NaOH concentration, on performance of these catalysts on hydrogen production from alkaline NaBH₄ solutions were investigated. Furthermore, characteristics of these nickel–ruthenium based catalysts were carried out by using various instruments, such as SEM/EDS, XPS, SQUID VSM and BET. These catalysts can be easily recycled from spent NaBH₄ solution with permanent magnets owing to their intrinsic soft ferromagnetism and, therefore, reducing the operation cost of the hydrogen generation process. A rate of hydrogen evolution as high as ca. 400 mL min⁻¹ g⁻¹ could be reached at 35 °C in 10 wt% NaBH₄ solution containing 5 wt% NaOH using Ni–Ru/50WX8 catalysts. Activation energy of hydrogen generation using such catalysts is estimated at 52.73 kJ mol⁻¹.