The effects of operating conditions on hydrogen production from sodium borohydride using Box-Wilson optimization technique

Sodium borohydride is the most investigated boron compound among hydrogen-carrier materials by researchers because of its stable structure, relatively high hydrogen storage capacity (NaBH₄, 10.8% hydrogen by weighing), comparatively cost-efficiency, and non-flammability. This study aims to produce hydrogen from sodium borohydride solution whose hydrolysis was carried out both in the absence of any catalysts at above 100 °C. In order to increase the rate of hydrogen production using NaBH₄ solution, the initial concentration of HCl and temperature were optimized using the Box- Wilson method. The field of the highest dehydrogenation yield was shown by drawing contour plot for the second order model. As a result of the experiments, the highest dehydrogenation yield (100%) of this solution was achieved in 3.76 M HCl concentration and at 157 °C; besides, the reaction time was the least under these conditions.     

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.     

Aluminum chloride for accelerating hydrogen generation from sodium borohydride

The present research paper reports preliminary results about the utilization of anhydrous aluminum chloride (AlCl₃) for accelerating hydrogen generation through hydrolysis of aqueous solution of sodium borohydride (NaBH₄) at 80 °C. To the best of our knowledge, AlCl₃ has never been considered for that reaction although many transition metal salts had already been assessed. AlCl₃ reactivity was compared to those of AlCl₃·6H₂O, AlF₃, CoCl₂, RuCl₃ and NiCl₂. With AlCl₃ and a NaBH₄ solution having a gravimetric hydrogen storage capacity (GHSC) of 2.9 wt.%, almost 100% hydrogen was generated in few seconds, i.e., with a hydrogen generation rate (HGR) of 354 L min⁻¹ g⁻¹(Al). This HGR is one of the highest rates ever reported. Higher HGRs were obtained by mixing AlCl₃ with CoCl2, RuCl₃ or NiCl₂. For example, the system RuCl₃:AlCl₃ (50:50 mass proportion) showed a HGR > 1000 L min⁻¹ g⁻¹(Ru:Al). The hydrolysis by-products (once dried) were identified (by XRD, IR and elemental analysis) as being Al(OH)₃, NaCl and Na₂B(OH)₄Cl and it was observed that even in situ formed Al(OH)₃ has catalytic abilities with HGRs of 5 L min⁻¹ g⁻¹(Al). All of these preliminary results are discussed, which concludes that AlCl₃ has a potential as accelerator for single-use NaBH₄-based storage system.     

Fluorinated cobalt for catalyzing hydrogen generation from sodium borohydride

The present paper reports preliminary results relating to a search for durable cobalt-based catalyst intended to catalyze the hydrolysis of sodium borohydride (NaBH₄). Fluorination of Co [Suda S, Sun YM, Liu BH, Zhou Y, Morimitsu S, Arai K, et al. Catalytic generation of hydrogen by applying fluorinated-metal hydrides as catalysts. Appl Phys A 2001; 72: 209–12.] has attracted our attention whereas the fluorination of Co boride has never been envisaged so far. Our first objective was to compare the reactivity of fluorinated Co with that of Co boride. We focused our attention on the formation of Co boride from fluorinated Co. Our second objective was to show the fluorination effect on the reactivity of Co. Our third objective was to find an efficient, durable Co catalyst. It was observed a limited stabilization of the Co surface by virtue of the fluorination, which made the formation of surface Co boride more difficult while the catalytic activity was unaltered. The fluorination did not affect the number of surface active sites. Nevertheless, it did not prevent the formation of Co boride. The fluorination of Co boride was inefficient. Hence, fluorination is a way to gain in stabilization of the catalytic surface but it is quite inefficient to hinder the boride formation. Accordingly, it did not permit to compare the reactivity of Co boride with that of Co.     

Influences of sodium borohydride concentration on direct borohydride fuel cell performance

In this work, the effects of sodium borohydride concentration on the performance of direct borohydride fuel cell, which consisted of Pd/C anode, Pt/C cathode and Na⁺ form Nafion^® membrane as the electrolyte, have been investigated in steady state/steady-flow and uniform state/uniform-flow systems. The experimental results have revealed that the power density increased as the sodium borohydride concentration increased in the SSSF system. Peak power densities of 7.1, 10.1 and 11.7 mW cm⁻² have been obtained at 0.5, 1 and 1.5 M, respectively. However, the performance has decreased when the sodium borohydride concentration has been increased, and the fuel utilization ratios of 29.8%, 21.6% and 20.4% have been obtained at 0.5, 1 and 1.5 M, respectively in the USUF system.     

Thermochemical production of sodium borohydride from sodium metaborate in a scaled-up reactor

Sodium borohydride (NaBH₄) is a safe and practical hydrogen storage material for on-board hydrogen production. However, a significant obstacle in its practical use on-board hydrogen production system is its high cost. Hence, the reproduction of NaBH₄ from byproducts that precipitate after hydrolysis is an important strategy to make its use more cost effective. In this work, we focused on the optimization of thermochemical NaBH₄ reproduction reaction in a large-scaled reactor (∼100 ml), and we investigated the effects of the reaction temperature (400–600 °C) and H₂ pressure (30–60 bar) on the NaBH₄ conversion yield using Mg as a reducing agent. The conversion yield of NaBO₂ to NaBH₄ increased with an increase in H₂ pressure to 55 bar and then decreased slightly at 60 bar. The yield increased with an increase in the reactor temperature from 400 to 600 °C. The maximum yield was 69% at 55 bar and 600 °C using homogenized reactants by ball-milling for 1 h under an Ar atmosphere. Though Ca as a reducing agent makes the thermochemical reproduction reaction more favorable, the NaBH₄ yield was low after 1 h of production at 55 bar and 600 °C. This result may be due to the fact that Ca is not as effective as Mg in catalyzing the conversion of hydrogen gas to protide (H⁻), which can substitute oxygen actively in NaBO₂.     

Apparatus for the production of hydrogen from sodium borohydride in alkaline solution

Extended application of hydrogen as energy carrier demands an economical, safe and reliable technology for storage. In particular, chemical hydrides appear as capable and promising to overcome the issues related to hydrogen safety and handling and to be considered competitive with respect to conventional fuels.     

Synergistic hydrogen generation from aluminum, aluminum alloys and sodium borohydride in aqueous solutions

A new method to produce high purity hydrogen using reactions of aluminum and sodium borohydride with aqueous alkaline solutions is described. This process mainly consumes water and aluminum (or its alloys) which are cheaper raw materials than the borohydride. As a consequence, this process could be competitive for in situ production of hydrogen. Moreover, a synergistic effect has been observed in hydrogen production rates and yields combining aluminum or aluminum alloys with sodium borohydride in aqueous solutions. Good results have been obtained for powders of Al, Al/Si and Al/Co alloys. The development of this idea could improve yields and reduce costs in power units based on fuel cells which use borohydride as raw material for hydrogen production.     

Hydrogen generation from sodium borohydride using microreactor for micro fuel cells

A microreactor for hydrogen generation from sodium borohydride was designed and fabricated in the present study. The microreactor has three photosensitive glasses, including the cover, the reactor layer and the base. A nickel form was inserted in the reactor layer as a catalyst support. A Co-P-B catalyst for sodium borohydride hydrolysis was coated on the nickel form by electroless plating. The characteristics of the catalyst were studied using SEM and EDS analysis. The hydrogen generation rate of the microreactor was measured under a variety of conditions and made up 15.6 ml/min at a temperature of 40 °C. The generated hydrogen was supplied to a micro fuel cell with a maximum power output of 157 mW at a current of 0.5 A.     

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.     

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.     

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.     

Acetic acid, a relatively green single-use catalyst for hydrogen generation from sodium borohydride

Acid-catalyzed hydrolysis of sodium borohydride (NaBH₄) has been studied (reactivity and kinetics) at high acid concentration (0.32 M). A mineral (hydrochloric acid, HCl) and an organic benign (acetic acid, CH₃COOH) acid have been chosen. Our study has three distinct objectives, namely: (i) combining the simplicity of the storage of solid NaBH₄ with the simplicity of the aqueous solution of acid; (ii) showing CH₃COOH can be as reactive as HCl in specific well-chosen operating conditions; and (iii) emphasizing the relative greenness of the CH₃COOH-based process. All of these objectives have been fulfilled and show that CH₃COOH is a benign relatively green acid catalyst of choice for catalyzing hydrogen generation from NaBH₄, the acid–water–NaBH₄ system being quite simple.     

Hydrogen production from solid sodium borohydride

A system for a controlled production of hydrogen from solid NaBH₄ has been designed and built. Cartridges of catalysed or non-catalysed NaBH₄ in powder form are fed by water or catalyst solution into a reactor; the reaction is started and tuned by controlling the input water (or water/catalyst solution) flow. We designed, built and tested different reactor layouts and geometries. Tests have been carried out in order to monitor operative parameters (i.e., water flow, reactor temperature) and to evaluate their influence on hydrolysis performance. The facility allows hydrogen flow in the 5–30 L/h range for several hours. The paper reports on the experimental runs and on the main achieved goals.     

Hydrogen production from solid sodium borohydride with hydrogen peroxide decomposition reaction

This study investigates hydrogen production from solid sodium borohydride with hydrogen peroxide decomposition reaction for a fuel cell based air-independent propulsion system in space and underwater applications. Sodium borohydride in the solid state was used as a hydrogen source in the present study. Pure hydrogen could be generated by a catalytic hydrolysis reaction in which the water source was obtained from the hydrogen peroxide decomposition. Hydrogen peroxide was selected as an oxidizer, being decomposed catalytically to generate oxygen and water. The pure oxygen was provided to a fuel cell and the water was stored separately for the hydrolysis reaction. A fuel cell system was fabricated to validate the fuel cell based air-independent power system proposed in the present study. Two catalytic reactors were prepared; one for the solid sodium borohydride hydrolysis reaction and the other for the hydrogen peroxide decomposition reaction. The hydrogen and oxygen generation rate were measured based on the various conditions. The performance evaluation of a fuel cell system proposed in the present study was carried out.     

Electrooxidation of hydrogen peroxide and sodium borohydride on Ni deposited carbon fiber electrode for alkaline fuel cells

In this study, Ni deposited carbon fiber electrode (Ni/CF) prepared by electroless deposition method was examined for their redox process and electrocatalytic activities during the oxidation of hydrogen peroxide and sodium borohydride in alkaline solutions. The Ni/CF catalyst was characterized by X-ray diffraction (XRD), energy dispersive X-ray analysis (EDAX), scanning electron microscopy (SEM) and electrochemical voltammetry analysis. The electrocatalytic activity of the Ni/CF for oxidation of hydrogen peroxide and sodium borohydride in alkaline solutions was investigated by cyclic voltammetry. The anodic peak current density is found to be three times higher on Ni/CF catalyst for sodium borohydride compared to that for hydrogen peroxide. Preliminary tests on a single cell of a direct borohydride/peroxide fuel cell (DBPFC) and direct peroxide/peroxide fuel cell (DPPFC) indicate that DBPFC with the power density of 5.9 mW cm⁻² provides higher performance than DPPFC (3.8 mWcm⁻²).     

Thermo-economic analysis of a hydrogen production system by sodium borohydride (NaBH4)

In the spectrum of current energy possibilities, hydrogen represents a solution of great interest toward a future sustainable energy system. No single technology can sustain the energy needs of the whole society, but integration and hybridization are two key strategic features for viable energy production based in hydrogen economy.In the present work, a hydrogen energy model is analyzed. In this model hydrogen is produced through the electrolysis of water, taking advantage of the electrical energy produced by a renewable generator (photovoltaic panels). The produced hydrogen is chemically stored by the synthesis of sodium borohydride (NaBH₄). NaBH₄ promising features in terms of safety and high volumetric density are exploited for transportation to a remote site where hydrogen is released from NaBH₄ hydrolysis and used for energy production.This model is compared from an economic standpoint with the traditional hydrogen storage and transportation technology (compressed hydrogen in tanks).This paper presents a thermodynamic and economic analysis of the process in order to determine its economic feasibility. Data employed for the realization of the model have been gathered from recent important progresses made on the subject.The innovative plant including NaBH₄ synthesis and transportation is compared from an economic standpoint with the traditional hydrogen storage and transportation technology (compressed hydrogen in tanks). As a final point, the best technology and the components' optimal sizes are evaluated for both cases in order to minimize production costs.     

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.