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).     

Investigation of hydrogen production from boron compounds for pem fuel cells

This paper presents a comprehensive study of hydrogen production from sodium borohydride (NaBH₄), which is synthesized from sodium tetraborate (Na₂B₄O₇) decomposition, for proton exchange membrane (PEM) fuel cells. For this purpose, Na₂B₄O₇ decomposition reaction at 450–500 °C under hydrogen atmosphere and NaBH₄ decomposition reaction at 25–40 °C under atmospheric pressure are selected as a common temperature range in practice, and the inlet molar quantities of Na₂B₄O₇ are chosen from 1 to 6 mol with 0.5 mol interval as well. In order to form NaBH₄ solution with 7.5 wt.% NaBH₄, 1 wt.% NaOH, 91.5 wt.% H₂O, the molar quantities of NaBH₄ are determined. For a PEM fuel cell operation, the required hydrogen production rates are estimated depending on 60, 65, 70 and 75 g of catalyst used in the NaBH₄ solution at 25, 32.5 and 40 °C, respectively. It is concluded that the highest rate of hydrogen production per unit area from NaBH₄ solution at 40 °C is found to be 3.834 × 10⁻⁵ g H₂ s⁻¹ cm⁻² for 75 g catalyst. Utilizing 80% of this hydrogen production, the maximum amounts of power generation from a PEM fuel cell per unit area at 80 °C under 5 atm are estimated as 1.121 W cm⁻² for 0.016 cm by utilizing hydrogen from 75 g catalyst assisted NaBH₄ solution at 40 °C.     

Hydrogen generation from solid state NaBH4 by using FeCl3 catalyst for portable proton exchange membrane fuel cell applications

Being a boron-based compound, sodium borohydride, NaBH₄, is a convenient hydrogen storage material for applications like unmanned air vehicles. There are several concerns behind commercialization of hydrogen gas generator by NaBH₄ hydrolysis systems. This study aims to contribute to the solution of the problems of NaBH₄ hydrolysis system in three main ways. First, the usage of solid state NaBH₄ enables to increase the durability and the gravimetric H₂ storage capacity of the system in order to meet US DOE targets. Second, solid NaBH₄ usage decreases the system's weight since it does not require a separate fuel storage tank, which is very important for portable, on demand applications. Finally, the system's cost is decreased by using an accessible and effective non-precious catalyst such as ferric chloride, FeCl₃. The maximum hydrogen generation rate obtained was 2.6 L/min and the yield was 2 L H₂/g NaBH₄ with an efficiency of 76% at its most promising condition. Moreover, the novel solid NaBH₄ hydrogen gas generator developed in the present work was integrated into a proton exchange membrane fuel cell and tested at the optimum operating conditions.     

Performance of direct alkaline sulfide fuel cell without sulfur deposition on anode

The paper reports the use of alkaline sulfide as a fuel with advantages of low cost, easy storage and transportation, and high electrochemical activity. The fuel cell fueled with alkaline sulfide, named direct alkaline sulfide fuel cell (DASFC), oxidizes sulfide to sulfur oxyanion without electrochemical catalyst, allowing not only to remove H₂S but also to fully recover energy stored in H₂S as electricity. In this study, particular attention was paid to systematic investigation of the effects of various operating parameters on cell performance, such as NaOH concentration, sulfide concentration, temperature, and electro-catalyst. Higher alkalinity and sulfide concentration of the anolyte were found to lead to higher power output, recording maximum power density of 10.69 mW cm⁻² at 1.0 M sulfide, 3.0 M NaOH, and 80 °C, which greatly increased up to 25.86 mW cm⁻² with the aid of Pt/C. During discharge, DASFC with higher alkaline anolyte exhibited higher current density profile, resulting in more oxidized sulfur oxyanions to be dominant. In the SEM analysis, the anode surface after discharge did not show any distinctive change from the original state, indicating that the anode of DASFC is free from sulfur deposition even at ambient temperature. Considering electricity generation, recovery of sulfur oxyanion, and long-term stability, we tend to believe that DASFC is one sustainable, promising way of tackling H₂S problem.     

An alkaline direct NaBH4–H2O2 fuel cell with high power density

A high performance alkaline direct borohydride–hydrogen peroxide fuel cell with Pt–Ru catalyzed nickel foam as anode and Pd–Ir catalyzed nickel foam as cathode is reported. The electrodes were prepared by electrodeposition of the catalyst components on nickel foam. Their morphology and composition were analyzed by SEM–EDX. The effects of concentrations of NaBH₄ and H₂O₂ as well as operation temperature on the cell performance were investigated. The cell exhibited an open circuit voltage of about 1.0 V and a peak power density of 198 mW cm⁻² at a current density of 397 mA cm⁻² and a cell voltage of 0.5 V using 0.2 mol dm⁻³ NaBH₄ as fuel and 0.4 mol dm⁻³ H₂O₂ as oxidant operating at room temperature. Electrooxidation of NaBH₄ on Pt–Ru nanoparticles was studied using a rotating disk electrode and complete 8e⁻ oxidation was observed in 2 mol dm⁻³ NaOH solution containing 0.01 mol dm⁻³ NaBH₄.     

Fully-integrated micro PEM fuel cell system with NaBH4 hydrogen generator

A fully-integrated micro PEM fuel cell system with a NaBH₄ hydrogen generator was developed. The micro fuel cell system contained a micro PEM fuel cell and a NaBH₄ hydrogen generator. The hydrogen generator comprised a NaBH₄ reacting chamber and a hydrogen separating chamber. Photosensitive glass wafers were used to fabricate a lightweight and corrosion-resistant micro fuel cell and hydrogen generator. All of the BOP such as a NaBH₄ cartridge, a micropump, and an auxiliary battery were fully integrated. In order to generate stable power output, a hybrid power management operating with a micro fuel cell and battery was designed. The integrated performance of the micro PEM fuel cell with NaBH₄ hydrogen generator was evaluated under various operating conditions. The hybrid power output was stably provided by the micro PEM fuel cell and auxiliary battery. The maximum power output and specific energy density of the micro PEM fuel cell system were 250 mW and 111.2 W h/kg, respectively.     

Effects of hydrazine addition on gas evolution and performance of the direct borohydride fuel cell

A fuel cell configuration using alkaline NaBH₄–N₂H₄ solutions as the fuel is suggested. Gas evolution behaviors and cell performances of alkaline NaBH₄–N₂H₄ solutions on different catalysts have been studied. It is found that gas evolution behaviors are influenced by the applied anodic catalysts and the concentration of NaBH₄ and N₂H₄. NaBH₄ is mainly electro-oxidized on Pd but N₂H₄ is mainly electro-oxidized on Ni and surface-treated Zr–Ni alloy when using NaBH₄–N₂H₄ solutions as the fuel and a composite of Pd, Ni and surface-treated Zr–Ni alloy as the anodic catalyst. The cyclic voltammetry results show that electrochemical oxidation potential of NaBH₄ is higher than that of N₂H₄. Adding hydrazine into alkaline sodium borohydride solutions can suppress gas evolution and improve the cell performance of the DBFC. The performances of fuel cells using NaBH₄–N₂H₄ solutions are comparable to that of fuel cell using N₂H₄ solution.     

A semi-global reaction rate model based on experimental data for the self-hydrolysis kinetics of aqueous sodium borohydride

This work studied the self-hydrolysis kinetics of aqueous sodium borohydride (NaBH₄) for hydrogen generation and storage purposes. Two semi-global rate expressions of sodium borohydride and hydrogen ion consumption were derived from an extensive series of batch process experiments where the following parameters were systematically varied: solution temperature (298 K–348 K), NaBH₄ concentration (0.5 wt% to 25.0 wt%), and sodium hydroxide (NaOH) concentration (0.0 wt% to 4.0 wt%). Transient hydrogen generation rates and transient solution pH were measured during the hydrolysis experiments. Given initial conditions (temperature, NaBH₄ concentration, and H⁺ concentration), the two coupled semi-global rate equations can be integrated to obtain the transient time history of H₂ generation (or NaBH₄ consumption) and solution pH (or H⁺ concentration). Comparing analytical results of transient hydrogen generation rate and transient solution pH with experimental data, good agreement was reached for many conditions, especially for elevated solution pH values, levels at which NaBH₄ solutions are used practically.     

Life time test in direct borohydride fuel cell system

The electric performances of direct borohydride fuel cells (DBFCs) are evaluated in terms of power density and life time with respect to the NaBH₄ concentration. A DBFC constituted of an anionic membrane, a 0.6 mg_Pt cm⁻² anode and a commercial non-platinum based cathode led to performances as high as 200 mW cm⁻² at room temperature and with natural convection of air. Electrochemical life time test at 0.55 mA cm⁻² with a 5 M NaBH₄/1 M NaOH solution shows a voltage diminution of 1 mV h⁻¹ and a drastic drop of performances after 250 h. The life time is twice longer with 2 M NaBH₄/1 M NaOH solution (450 h) and the voltage decrease is 0.5 mV h⁻¹. Analyses of the components after life time tests indicate that voltage loss is mainly due to the degradation of the cathode performance. Crystallisation of carbonate and borate is observed at the cathode side, although the anionic membrane displays low permeability to borohydride.     

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.     

Effects of NaOH addition on performance of the direct hydrazine fuel cell

In this work, we suggested a figuration of the direct hydrazine fuel cell (DHFC) using non-precious metals as the anode catalyst, ion exchange membranes as the electrolyte and alkaline hydrazine solutions as the fuel. NaOH addition in the anolyte effectively improved the open circuit voltage and the performance of the DHFC. A power density of 84 mW cm⁻² has been achieved when operating the cell at room temperature. It was found that the cell performance was mainly influenced by anode polarization when using alkaline N₂H₄ solutions with low NaOH concentrations. However, when using alkaline N₂H₄ solutions with high NaOH concentrations as the fuel, the cell performance was mainly influenced by cathode polarization.     

Influence of operation conditions on direct NaBH4/H2O2 fuel cell performance

Although hydrogen fuel cells have attracted so much attentions in these years because of the application prospect in electric vehicles, some obstacles have not been solved yet, among which hydrogen storage is one of the biggest. Direct borohydride fuel cell (DBFC) is another choice without hydrogen storage problem because borohydride is used as reactant directly in the fuel cell. In this paper, DBFC performance under different operation conditions was studied including electrolyte membrane type, operation temperature, borohydride concentration, supporting electrolyte and oxidant. Results showed that, with Pt/C and MnO₂ as anode and cathode electrocatalyst, respectively, Nafion^® 117 membrane as electrolyte, 1.0 M, 3.0 M and 6.0 M NaBH₄ and H₂O₂ solution in NaOH as reactant solution, 80 °C operation, the peak power density could reach 130 mW/cm².     

Effect of anode conditions on the performance of direct borohydride–hydrogen peroxide fuel cell system

Direct borohydride–hydrogen peroxide fuel cells (DBHPFCs) are attractive power sources for space applications. Although the cathode conditions are known to affect the system performance, the effect of the anode conditions is rarely investigated. Thus, in this study, a DBHPFC system was tested under various anode conditions, such as electrocatalyst, fuel concentration, and stabilizer concentration, to investigate their effects on the system performance. A virtual DBHPFC system was analyzed based on the experimental data obtained from fuel cell tests. The anode electrocatalyst had a considerable effect on the mass and electrochemical reaction rate of the fuel cell system, but had minimal effect on the decomposition reaction rate. The NaBH₄ concentration greatly influenced the mass and decomposition reaction rate of the fuel cell system; however, it had minimal impact on the electrochemical reaction rate. The NaOH concentration affected the electrochemical reaction rate, decomposition reaction rate, and mass of the fuel cell system. Therefore, the significant effects of the anode conditions on the electrochemical reaction rate, decomposition reaction rate, and mass of the fuel cell system prompt the need for their careful selection through fuel cell tests and system analysis.     

Highly active cobalt-based catalysts in situ prepared from CoX2 (X = Cl,NO3) and used for promoting hydrogen generation from NaBH4 solution

Two kinds of CoX₂ (X = Cl⁻, NO₃⁻) are adopted as the accelerators for the hydrolysis reaction of NaBH₄, which is a promising H₂-supply method for proton exchange membrane fuel cell (PEMFC). In the reactor, the initial H₂ generation is caused by the reaction between pre-infused CoX₂ solution and subsequently imported NaBH₄ solution, and some precipitates are in situ formed on the catalyst bed by this way; and the following H₂ generation is promoted by these precipitates. It is found that there are competitive reactions during H₂ generation from an NaBH₄ to NaOH solution, the anions of CoX₂ are crucial to the reaction pathways, which led to the formation of highly active Co–B or inactive Co(OH)₂. The effects of the CoX₂ concentration, the NaOH concentration, the NaBH₄ feeding rate and the NaBH₄ concentration on H₂ generation performances are discussed and compared.     

A direct NaBH4–H2O2 fuel cell using Ni foam supported Au nanoparticles as electrodes

Au/Ni-foam electrodes with three dimensional network structures are prepared by simple spontaneous deposition of nano-sized Au particles onto nickel foam surface in an aqueous solution of AuCl₃. Their morphology and catalytic performance for NaBH₄ electrooxidation and H₂O₂ electroreduction in NaOH solution are investigated. Au particles with diameters smaller than 100 nm are uniformly deposited on the whole surface of all skeletons of the nickel foam substrate. The onset potential for NaBH₄ electrooxidation and H₂O₂ electroreduction is about −1.2 V and −0.1 V, respectively. A direct liquid feed alkaline NaBH₄–H₂O₂ fuel cell is constructed using Au/Ni-foam electrode as both the anode and the cathode. The effects of the concentration of NaBH₄ and H₂O₂ and operation temperature on the fuel cell performance are investigated. The fuel cell exhibits an open circuit voltage of about 1.07 V and a peak power density of 75 mW cm⁻² at a current density of 150 mA cm⁻² and a cell voltage of 0.5 V operating on 0.2 mol dm⁻³ NaBH₄ and 0.5 mol dm⁻³ H₂O₂ at 40 °C.     

Corrosion inhibition of methanol towards stainless steel bipolar plate for direct formic acid fuel cell

The corrosion properties of AISI316L stainless steel (316 L SS) as bipolar plates are investigated under aqueous acid methanol solutions (0.05 M H₂SO₄ + 2 ppm HF + 10 M HCOOH + x M CH₃OH (x = 0, 3, 6 and 9) solutions at 70 °C) to simulate the varied anodic operating conditions of direct formic acid fuel cells (DFAFCs). When the methanol content is higher, the potentiodynamic, potentiostatic polarisation and EIS tests of the 316 L SS bipolar plates all show excellent corrosion resistance. The surface morphology and the glow discharge mass spectrometer (GDMS) illustrate that the surface corrosion on 316 L SS bipolar plates is slowed down when the methanol concentration is increased. These results indicate the methanol plays the role in retarding the corrosion rate of the 316 L SS in simulated DFAFCs anodic operating conditions by restricting the proton conductivity in the test solutions. The sample tested in higher content methanol solution has smoother corroded surface and thinner passivation film, which contributes to a lower interfacial contact resistances (ICR) value.     

Hydrogen generation from sodium borohydride hydrolysis by multi-walled carbon nanotube supported platinum catalyst: A kinetic study

In this study, it is aimed to investigate hydrogen (H₂) generation from sodium borohydride (NaBH₄) hydrolysis by multi-walled carbon nanotube supported platinum catalyst (Pt/MWCNT) under various conditions (0–0.03 g Pt amount catalyst, 2.58–5.03 wt % NaBH₄, and 27–67 °C) in detail. For comparison, carbon supported platinum (Pt/C) commercial catalyst was used for H₂ generation experiments under the same conditions. The reaction rate of the experiments was described by a power law model which depends on the temperature of the reaction and concentrations of NaBH₄. Kinetic studies of both Pt/MWCNT and Pt/C catalysts were done and activation energies, which is the required minimum energy to overcome the energy barrier, were found as 27 kJ/mol and 36 kJ/mol, respectively. Pt/MWCNT catalyst is accelerated the reaction less than Pt/C catalyst while Pt/MWCNT is more efficient than Pt/C catalyst, they are approximately 98% and 95%, respectively. According to the results of experiments and the kinetic study, the reaction system based on NaBH₄ in the presence of Pt/MWCNT catalyst can be a potential hydrogen generation system for portable applications of proton exchange membrane fuel cell (PEMFC).     

Alkali free hydrolysis of sodium borohydride for hydrogen generation under pressure

The present study is related with the production of hydrogen gas (H₂), at elevated pressures and with high gravimetric storage density, to supply a PEM fuel cell on-demand. To achieve this goal, solid sodium borohydride (NaBH₄) was mixed with a proper amount of a powder reused nickel–ruthenium based catalyst (Ni–Ru based/NaBH₄: 0.2 and 0.4 g/g; ≈150 times reused) inside the bottom of a batch reactor. Then, a stoichiometric amount of pure liquid water (H₂O/NaBH₄: 2–8 mol/mol) was added and the catalyzed NaBH₄ hydrolysis evolved, in the absence of an alkali inhibitor. In this way, this research work is designated alkali free hydrolysis of NaBH₄ for H₂ generation. This type of hydrolysis is excellent from an environmental point of view because it does not involve strongly caustic solutions. Experiments were performed in three batch reactors with internal volumes 646, 369 and 229 cm³, and having different bottom geometries (flat and conical shapes). The H₂ generated was a function of the added water and completion was achieved with H₂O/NaBH₄ = 8 mol/mol. The results show that hydrogen yields and rates increase remarkably increasing both system temperature and pressure. Reactor bottom shape influences deeply H₂ generation: the conical bottom shape greatly enhances the rate and practically eliminates the reaction induction time. Our system of compressed hydrogen generation up to 1.26 MPa shows 6.3 wt% and 70 kg m⁻³, respectively, for gravimetric and volumetric hydrogen storage capacities (materials-only basis) and therefore is a viable hydrogen storage candidate for portable applications.     

A direct borohydride fuel cell employing a sago gel polymer electrolyte

The electrochemistry of a direct borohydride fuel cell based on a gel polymer electrolyte was studied. Sago is a type of natural polymer, was employed as the polymer host for the electrolyte. An electrolyte with a composition of sago + 6 M KOH + 2 M NaBH₄ was prepared and evaluated as a novel gel polymer electrolyte for a direct borohydride fuel cell system because it exhibited a high electrical conductivity of 0.270 S cm⁻¹. The rate at which oxygen was consumed at the cathode can be related to the electric current by comparing the calculated number of electrons reacted per molecule of oxygen for different currents supplied to the fuel cell. From the oxygen consumption data, it was deduced that four electrons reacted per molecule of oxygen. The performance of the fuel cell was measured in terms of its current–voltage, discharge and open circuit voltage measurements. The maximum power density obtained was 8.818 mW cm⁻² at a discharge performance of ∼230 mA h and nominal voltage of 0.806 V. The open circuit voltage of the cells was about 0.900 V and sustained for 23 h.     

Influence of process parameters on enhanced hydrogen evolution from alcoholysis of sodium borohydride with a boric acid catalyst

The hydrogen evolution via alcoholysis reaction of sodium borohydride with an H₃BO₃ catalyst was carried out for the first time. In the process of methanol and NaBH₄ (NaBH₄-MR), the effects of the H₃BO₃ and NaBH₄ concentration, and temperature parameters were examined and evaluated. The hydrogen yields by the NaBH₄-MR, NaBH₄ ethanolysis (NaBH₄-ER) and NaBH₄ hydrolysis reactions (NaBH₄-HR) with 0.2 M H₃BO₃ catalyst are 99, 62, and 88% compared to the theoretical hydrogen yield, respectively. The completion times of the NaBH₄-MR using the H₃BO₃ concentrations of 0.2, 0.4, 0.5, 1 M, and saturated acid solution were about 50, 15, 10, 2 and 1 min, respectively. The hydrogen yields obtained with 50, 15, 10, 2, and 1 min for the same acid concentration values were about 100% compared to the theoretical hydrogen value. By increasing the H₃BO₃ concentration from 0.2 M to the saturated H₃BO₃ concentration, the completion time of this NaBH₄-MR process was reduced by approximately 50 times, resulting in a significant result. The activation energy (Ea) of the NaBH₄-MR with the H₃BO₃ catalyst was 57.3 kJ/mol.