Preparation of PVDF nanofiber composites for hydrogen generation from sodium borohydride

Nanofibers are able to form a highly porous mesh and their large surface to volume ratio improves performance for many applications. Organic-inorganic polyvinylidene fluoride (PVDF)-cobalt (II) chloride hexahydrate nanofiber composites were prepared by electrospinning method. The structure and physical-chemical properties of the novel nanofiber composites are characterized by SEM, EDX and FTIR. The SEM results showed the morphology of the fibers and EDX was given the composition of the nanocomposite catalysts. The nanofibers loaded with metal catalysts are used for the hydrogen production by directly mixing with NaBH₄ and water. The novel PVDF nanofiber composites catalyst has shown the stability and given the promising results for the quick production of hydrogen.     

Hydrogen cycle with sodium borohydride

In this paper, we review production of NaBH₄ as hydrogen storage material. Linking this with other processes, we create a system to recycle hydrogen. Difficulties and advantages of NaBH₄ synthesis by natural available boron source colemanite and borax minerals were discussed. We show that basic chemicals suffice for NaBH₄ production in a procedure designed to work below 275 °C. This procedure may be used to compensate for the loss of materials during the recycle. In this procedure, hydrogen including substances have been used to remove oxygen and bond remaining hydrogen to the by-product NaBO₂ of dehydrogenation reaction. The wet and dry applications of producing NaBH₄ have been also discussed. Moreover, a shorter procedure can be proposed to directly obtain NaBH₄ from borax mineral. Among these processes, dehydrogenation is critical but it requires plenty of water. Hence, new types of catalyst are important to reduce the amount of water required during dehydrogenation.     

Alkaline sodium borohydride gel as a hydrogen source for PEMFC or an energy carrier for NaBH4-air battery

In this preliminary study, we tried to use sodium polyacrylate as the super absorbent polymer to form alkaline NaBH₄ gel and explored its possibilities for borohydride hydrolysis and borohydride electro-oxidation. It was found that the absorption capacity of sodium polyacrylate decreased with increasing NaBH₄ concentration. The formed gel was rather stable in the sealed vessel but tended to slowly decompose in open air. Hydrogen generation from the gel was carried out using CoCl₂ catalyst precursor solutions. Hydrogen generation rate from the alkaline NaBH₄ gel was found to be higher and impurities in hydrogen were less than that from the alkaline NaBH₄ solution. The NaBH₄ gel also successfully powered a NaBH₄-air battery.     

Hydrogel assisted nickel nanoparticle synthesis and their use in hydrogen production from sodium boron hydride

In this study, hydrogels were synthesized from 2-acrylamido-2-methyl-1-propansulfonic acid (AMPS) via a photo polymerization technique. Approximately 100 nm Ni metal nanoparticles were generated in situ inside these p(AMPS) hydrogel networks and used as a catalyst in hydrogen production by hydrolysis of sodium boron hydride in a basic medium. The effects of several parameters on the hydrolysis reaction such as the amount of catalyst, the initial concentration of NaBH₄, and the temperature were investigated. The activation energy, activation enthalpy and activation of entropy for the reaction were calculated as 42.28 kJ mol⁻¹, 39.59 kJ mol⁻¹ and −171.67 J mol⁻¹ K⁻¹, respectively.     

Catalytic hydrolysis of sodium borohydride solution for hydrogen production using thermal plasma synthesized nickel nanoparticles

In the present study nickel nanoparticles were synthesized by thermal plasma route. In this method we obtained highly crystalline almost spherical nanoparticles with maximum number of particles having size around 30–50 nm. These nanoparticles were thoroughly characterized and employed as a catalyst for hydrogen production using hydrolysis of sodium borohydride (NaBH₄). The effect of initial concentration of NaBH₄, pH and temperature of solution on the rate of hydrogen production was investigated. Nickel nanoparticles exhibits first order reaction with respect to NaBH₄ concentration at elevated temperatures. After hydrolysis, the nickel nanoparticles showed presences of B–O and B–OH species on the nickel surface. The catalyst was found to be stable during 5 sequential cycles of test.     

Hydrogen production through hydrolysis of sodium borohydride: Highly dispersed CoB particles immobilized in carbon nanofibers as a novel catalyst

Agglomeration of CoB catalysts is a severe problem in hydrogen generation from NaBH₄ hydrolysis. Herein, highly dispersed carbon nanofiber immobilized CoB catalysts (CoB/CN) were synthesized by a combined prereduction and carbonization method, which is used in hydrogen generation from NaBH₄ hydrolysis. Morphological evolution of carbon nanofibers, phase structure and elemental distribution of CoB/CN catalysts are explored by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Compared to Co/carbon nanofiber catalysts (Co/CN) without prereduction, CoB/CN catalysts can afford higher CoB dispersity and specific surface area because the migration rate of cobalt species during carbonization is effectively retarded by prereduction. Hence the agglomeration of magnetic CoB nanoparticles can be effectively inhibited. The hydrogen generation experiment shows that CoB/CN catalysts process higher catalytic activity and lower activation energy than Co/CN.     

Simple and fast fabrication of polymer template-Ru composite as a catalyst for hydrogen generation from alkaline NaBH4 solution

Polymer template-Ru composite (Ru/IR-120) catalyst was prepared using a simple and fast method for generating hydrogen from an aqueous alkaline NaBH₄ solution. The hydrogen generation rate was determined as a function of solution temperature, NaBH₄ concentration, and NaOH (a base-stabilizer) concentration. The maximum hydrogen generation rate reached 132 ml min⁻¹ g⁻¹ catalyst at 298 K, using a Ru/IR-120 catalyst that contained only 1 wt.% Ru. The catalyst exhibits a quick response and good durability during the hydrolysis of alkaline NaBH₄ solution. The activation energy for the hydrogen generation reaction was determined to be 49.72 kJ mol⁻¹.     

Kinetics of hydrolysis of sodium borohydride for hydrogen production in fuel cell applications: A review

Hydrogen generation from the hydrolysis of sodium borohydride (NaBH₄) solution has drawn much attention since early 2000s, due to its high theoretical hydrogen storage capacity (10.8 wt%) and potentially safe operation. However, hydrolysis of NaBH₄ for hydrogen generation is a complex process, which is influenced by factors such as catalyst performance, NaBH₄ concentration, stabilizer concentration, reaction temperature, complex kinetics and excess water requirement. All of these limit the hydrogen storage capacities of NaBH₄, whose practical application, however, has not yet reached a scientific and technical maturity. Despite extensive efforts, the kinetics of NaBH₄ hydrolysis reaction is not fully understood. Therefore, better understanding of the kinetics of hydrolysis reaction and development of a reliable kinetic model is a field of great importance in the study of NaBH₄ based hydrogen generation system. This review summarizes in detail the extensive literature on kinetics of hydrolysis of aqueous NaBH₄ solution.     

Synergistic hydrogen generation from AlLi alloy and solid-state NaBH4 activated by CoCl2 in water for portable fuel cell

Solid-state AlLi/NaBH₄ mixture activated by CoCl₂ salt is fabricated for hydrogen generation via a milling process, providing uniform dispersion of AlLi alloy and CoCl₂ salt among pulverized NaBH₄ particles in order to improve NaBH₄ hydrolysis through the contact of NaBH₄ with active catalytic sites. The active catalytic sites come from Co₂B loaded in Al(OH)₃ (Bayerite) or LiAl₂(OH)₇ hydrate, generated from the reaction of CoCl₂, AlLi alloy, and NaBH₄ in water. The results show that the gravimetric hydrogen storage capacity is as high as 6.4 wt.% and an efficiency of above 90% in 30-min hydrolysis at 323 K could be achieved using the limited amount of water. The hydrogen generation amount and rate could be regulated by changing the composition, mixing style, mixture/water weight ratio, and hydrolysis temperature. The relative mechanism is explored.     

Exploring the technological maturity of hydrogen production by hydrolysis of sodium borohydride

Sodium borohydride NaBH₄ (SB) has been rediscovered in the late 1990s and been presented as a promising hydrogen storage material owing to its high gravimetric hydrogen density of 10.8 wt% and ability to produce H₂ by hydrolysis at ambient conditions. This looked promising, but soon hydrolysis of SB encountered numerous obstacles. In 2015, a progress report (Int J Hydrogen Energy 2015; 40:2673–91) showed that the 2000–2014 research did not overcome all of the obstacles, making SB far from being technologically mature. Eight years have passed since 2015. Have we put more effort into all aspects relating to hydrolysis of SB? If so, do we have produced scaled-up technologies and prototypes, of which we would have a better knowledge? Have we been able to gain in technological readiness level? Answering these questions is the main objective of this article. A secondary objective is to summarize the newly acquired knowledge. Five main observations stand out. First, the 2015–2022 period is regrettably similar to the 2000–2014 since, again, catalysts have dominated the field and the other aspects (e.g. recycling of the by-product to regenerate SB, scale-up and implementation) have received little attention. Second, hydrolysis of SB still runs into numerous obstacles, some of the obstacles being known since a long time and other ones being relatively new and unknown. Third, there has been little gain in terms of technological readiness level while few research groups have shown that there is room for new ideas and innovation. Fourth, energy, exergy and economic analyses are needed to evaluate the overall cost of H₂ from SB. Fifth, SB has not effectively thought from the end user perspective. In conclusion, many obstacles remain to be overcome before hydrolysis of SB can be a commercial solution for carrying and producing H₂. However, all efforts should be dedicated to (i) construct, operate and optimize H₂ production systems (i.e. prototypes and demonstrators), (ii) handle SB at the gram-to-kilogram scale, (iii) make production of SB even more efficient, and (iv) overcome all obstacles while thinking from the end user perspective.     

Advances in catalysts for hydrogen production by methanolysis of sodium borohydride

Fossil energy is a major contributor to global greenhouse gases and air pollutants, causing serious environmental and health issues. In order to develop clean new energy as a substitute, catalytic methanolysis of sodium borohydride (NaBH₄) has become a hot topic in hydrogen energy field. In this work, the latest research development of hydrogen production by NaBH₄ methanolysis is comprehensively reviewed from the perspective of different types of catalysts, furthermore, the merits and demerits of these studies are analyzed, the comparison between various catalysts is also completed from the dimensions of hydrogen generation rate, apparent activation energy as well as durability, and the technical challenges the hydrogen production process may face and the corresponding recommendations are proposed. This review can provide enlightenment for the research and application of novel catalysts for the methanolysis of NaBH₄ and the development of efficient hydrogen production technology.     

Pd-C powder and thin film catalysts for hydrogen production by hydrolysis of sodium borohydride

In this work we study the hydrogen generation by catalytic hydrolysis of alkaline _NaBH4${\mathrm{NaBH}}_4$ solution employing Pd-supported on carbon powder (Pd/C) as well as in form of Pd and Pd–C thin films synthesized by pulsed laser deposition (PLD). Two sets of samples were prepared: (1) pure Pd catalyst films which were bombarded with Ar⁺${\mathrm{Ar}}^{+}$ ions at different ions fluence in order to increase the surface roughness; (2) highly irregular C film were deposited by using different Ar pressure in the PLD chamber prior to deposition of the Pd film to further increase the surface area for the active Pd catalyst. Surface morphology was studied by using scanning electron microscopy (SEM) and atomic force microscopy (AFM) while compositional analysis was performed by using energy dispersive spectroscopy (EDS). Cone like structure on the surface of the Pd film developed by Ar⁺${\mathrm{Ar}}^{+}$ ion bombardment was not efficient to enhance the catalytic activity of the Pd. Pd/C films showed higher catalytic activity in comparison to Pd/C powders when the same amount of catalyst is used. The results are discussed in relation to the morphology of the C-films.     

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.     

Preparation and catalytic activity of PVP-protected Au/Ni bimetallic nanoparticles for hydrogen generation from hydrolysis of basic NaBH4 solution

Poly(N-vinyl-2-pyrrolidone)(PVP)-protected Au/Ni bimetallic nanoparticles (BNPs) were prepared in one-vessel via chemical reduction of the corresponding ions with dropwise addition of NaBH₄, and their catalytic activity in the hydrogen generation from hydrolysis of a basic NaBH₄ solution was examined. The structure, particle size, and chemical composition of the resultant BNPs were characterized by Ultraviolet–visible spectrophotometry (UV–Vis), X-ray photoelectron spectroscopy (XPS), Transmission electron microscopy (TEM) and High-resolution transmission electron microscopy (HR-TEM). The effects of processing parameters such as metal composition, metal ion concentration, and mole ratio of PVP to metal ion on the hydrolysis of a basic NaBH₄ solution were studied in detail. The results indicated that as-prepared Au/Ni BNPs showed a higher catalytic activity than corresponding monometallic NPs (MNPs) in the hydrogen generation from the hydrolysis reaction of a basic NaBH₄ solution. Among all the MNPs and BNPs, Au/Ni BNPs with the atomic ratio of 50/50 exhibited the highest catalytic activity, showing a hydrogen generation rate as high as 2597 mL-H₂ min⁻¹ g-catalyst⁻¹ at 30 °C, which can be ascribed to the presence of negatively charged Au atoms and positively charged Ni atoms. Based on the kinetic study of the hydrogen generation from the hydrolysis reaction of a basic NaBH₄ solution over the PVP-protected Au/Ni BNPs, the corresponding apparent activation energy was determined as 30.3 kJ/mol for the BNPs with the atomic ratio of 50/50.     

Cobalt oxides as Co2B catalyst precursors for the hydrolysis of sodium borohydride solutions to generate hydrogen for PEM fuel cells

Cobalt boride (Co₂B) is an inexpensive catalyst for the hydrolysis of sodium borohydride (NaBH₄) to generate hydrogen (H₂) for PEM fuel cells. Preparation of Co₂B in situ in the H₂ generation vessel as well as in an external reactor was studied using cobalt (III) oxide (Co₃O₄) and lithium cobalt oxide (LiCoO₂) as precursors. The oxide precursors were characterized by XRD and the Co₂B catalysts by XRD and ICP. Co₂B formation from the oxide precursors depends on the crystallinity of the oxides as well as the concentration of NaBH₄ in the solution. During reduction of the oxides to CoB₂, Co(s) metal, Co(BO₂)₂ may also form from competing side reactions, however crystalline oxides react faster leading to higher Co₂B yield and better H₂ generation efficiency. Crystallinity of Co₃O₄ was improved by preparing it at a higher temperature. Co₃O₄ prepared at 600 °C reacts faster leading to enhanced Co₂B formation than Co₃O₄ prepared at lower temperatures (200 °C and 400 °C). The activation energy for the hydrolysis of NaBH₄ by Co₂B formed in situ from Co₃O₄ produced at 600 °C was calculated to be 77.90 kJ mol⁻¹. This activation energy value is found to be slightly higher than that of Pt, Ru-based catalysts.     

Improved hydrogen sorption performance of NbF5-catalysed NaAlH4

The effect of NbF₅ on the hydrogen sorption performance of NaAlH₄ has been investigated. It was found that the dehydrogenation/hydrogenation properties of NaAlH₄ were significantly enhanced by mechanically milling with 3 mol% NbF₅. Differential scanning calorimetry results indicate that the ball-milled NaAlH₄-0.03NbF₅ sample lowered the completion temperature for the first two steps dehydrogenation by 71 °C compared to the pristine NaAlH₄ sample. Isothermal hydrogen sorption measurements also revealed a significant enhancement in terms of the sorption rate and capacity, in particular, at reduced operation temperatures. The apparent activation energy for the first-step and the second-step dehydrogenation of the NaAlH₄-0.03NbF₅ sample is estimated to be 88.2 kJ/mol and 102.9 kJ/mol, respectively, by using Kissinger’s approach, which is much lower than for pristine NaAlH₄, indicating the reduced kinetic barrier. The rehydrogenation kinetics of NaAlH₄ was also improved with 3 mol% NbF₅ doping, absorbing ∼1.7 wt% hydrogen at 150 °C for 2 h under ∼5.5 MPa hydrogen pressure. In contrast, no hydrogen was absorbed by the pristine NaAlH₄ sample under the same conditions. The formation of Na₃AlH₆ was detected by X-ray diffraction on the rehydrogenated NaAlH₄-0.03NbF₅ sample. Furthermore, the structural changes in the NbF₅-doped NaAlH₄ sample after ball milling and the hydrogen sorption were carefully examined, and the active species and mechanism of catalysis in NbF₅-doped NaAlH₄ are discussed.     

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.     

Effects of alkaline treatment of hydrogen storage alloy on electrocatalytic activity for NaBH4 oxidation

Activation of the MmNi_4.03Co_0.42Mn_0.31Al_0.24 hydrogen storage alloy electrode is performed by immersing the electrode in a solution containing 6.0 mol dm⁻³ NaOH and 0.1 mol dm⁻³ NaBH_4. The effects of activation on the electrocatalytic activity of the electrode for NaBH₄ oxidation are investigated by cyclic voltammetry and chronoamperometry. Immersion activation greatly improves the electrocatalytic activity of the alloy electrode. Hydrogen was absorbed in the alloy during the immersion activation treatment and its electrooxidation is responsible for the high initial oxidation current. The stabilized current mainly results from the direct oxidation starting from the borohydride species. The effects of activation on structure and surface chemistry of the alloy are also discussed.     

Photocatalytic hydrogen production over CuO and TiO2 nanoparticles mixture

Cheap and efficient photocatalysts were fabricated by simply mixing TiO₂ nanoparticles (NPs) and CuO NPs. The two NPs combined with each other to form TiO₂/CuO mixture in an aqueous solution due to the opposite surface charge. The TiO₂/CuO mixture exhibited photocatalytic hydrogen production rate of up to 8.23 mmol h⁻¹ g⁻¹ under Xe lamp irradiation when the weight ratio of P25 to CuO was optimized to 10. Although the conduction band edge position of CuO NPs is more positive than normal hydrogen electrode, the TiO₂/CuO mixture exhibited good photocatalytic hydrogen production performance because of the inter-particle charge transfer between the two NPs. The detailed mechanism of the photocatalytic hydrogen production is discussed. This mixing method does not require a complicated chemical process and allows mass production of the photocatalysts.     

Insight into the role of solvents in enhancing hydrogen production: Ru-Co nanoparticles catalyzed sodium borohydride dehydrogenation

Ru-Co nanoparticles prepared in nano-size by combustion derived of citric acid used sol-gel technique followed by calcination process at 450 °C. The external and internal properties of nano-sized catalyst were characterized by XRD, XPS, SEM, TEM, ICP-OES, and N₂ sorption techniques. The characterization results proved that nano-sized catalyst was mixture of cubic Co₃O₄ (18 nm) and tetragonal RuO₂ (40 nm) crystals with mesoporous structure (12.64 m²g^-1). Insight into the role of solvents for enhancing hydrogen production from Ru-Co nanoparticles catalyzed sodium borohydride (NaBH₄, SBH) was systematically studied by altering the dehydrogenation medium with water or methanol. The reaction kinetic performance of nano-sized catalyst was evaluated by performing both hydrogen generation reactions at various reaction temperatures, initial SBH concentration, and catalyst dosage to evaluate the hydrogen generation activity. Ru-Co nanoparticles exhibited exclusive catalytic performance for hydrogen generation by hydrolysis and methanolysis of SBH. The apparent activation energies (E_a) for the catalytic hydrolysis and methanolysis of SBH over Ru-Co nanoparticles were determined to be 20.02 kJ mol⁻¹ and 54.38 kJ mol⁻¹, respectively. Furthermore, Ru-Co nanoparticles also performed satisfied stability for both hydrolysis and methanolysis reactions. Beside both hydrogen generation was achived with fully conversion of SBH, Ru-Co nanoparticles promised good recyclability for at least 5 cycle for methanolysis of SBH.