Efficient generation of hydrogen from biomass without carbon monoxide at room temperature – Formaldehyde to hydrogen catalyzed by Ag nanocrystals

In this paper, we present a new route for hydrogen generation from biomass at room temperature without any carbon monoxide over nano-metal-catalysts. It has been found that the Ag nanocrystals are highly efficient and stable catalysts for the CO-free hydrogen production from formaldehyde (HCHO), a model compound of biomass, at room temperature and at atmospheric pressure. By optimizing the structure and component of catalysts, reaction parameters such as temperature, catalyst amounts, oxygen, formaldehyde concentrations, and NaOH concentrations, the hydrogen generation rate has been maintained for hours without any decay. Furthermore, the apparent activation energy of the Ag catalyzed hydrogen production reaction is determined to be 11.8 kJ mol⁻¹, which was much lower than that of the literature results (65 kJ mol⁻¹) without catalyst. Because of its high hydrogen generation rate, hydrogen generation efficiency, lower activation energy, and the low cost, we speculate that this novel Ag catalyst based hydrogen generation reaction should be a promising candidate for providing hydrogen in PEMFCs at room temperature.     

Highly efficient hydrogen production from formaldehyde over Ag/γ-Al2O3 catalyst at room temperature

Herein, we demonstrate a simple and efficient process for generating hydrogen from the formaldehyde (HCHO) aqueous solution catalyzed by Ag nanoparticles dispersed on high specific surface area γ-Al₂O₃ at room temperature. Moreover, this Ag/γ-Al₂O₃ catalyst exhibits much higher capability and stability for hydrogen production than unsupported Ag nanoparticles. By further optimizing the structure, component, and amounts of Ag/γ-Al₂O₃ catalysts as well as reaction parameters such as reaction atmosphere, formaldehyde concentrations, and NaOH concentrations, the hydrogen generation rate could be greatly increased and maintained for ten hours without any decay. It may provide a general and favorable strategy for the fabrication of highly reactive and stable metal catalyst for the hydrogen production from organic aldehyde solutions.     

PdZn alloys decorated 3D hierarchical porous carbon networks for highly efficient and stable hydrogen production from aldehyde solution

PdZn alloys and Pd catalyst decorated 3D hierarchically porous carbon (HPC) network catalysts were prepared by a facile and simple impregnation/carbonization process from energetic MOFs of MET-6. Due to the high uniformly dispersion of metal nanoparticles and strong metal-support interactions, the as prepared HPC-PdZn catalysts exhibited highly efficient catalytic hydrogen production from formaldehyde solution at room temperature, which is much higher than that of pure Pd nano-particles. By further optimizing the reaction parameters such as reaction temperature, formaldehyde concentrations, and NaOH concentrations, the hydrogen generation rates could be further increased to unprecedented 572.6 mL·min⁻¹ g⁻¹, which was nearly 4 times as much as the solely Pd nanoparticles counterparts. Owing to its high efficiency and stability at room temperature, the as-prepared HPC-PdZn architectures catalyst based hydrogen generation reaction may serve as state-of-the-art candidate in both hydrogen supply and environmental cleaning.     

Two-step catalytic dehydrogenation of formic acid to CO2 via formaldehyde

Formic acid has been decomposed into hydrogen and carbon dioxide through a two-step process involving the formation of formaldehyde. This allows the formation of carbon dioxide and hydrogen in two different steps, negating the need for gas separation. A novel system for the catalytic disproportionation of formic acid into formaldehyde and carbon dioxide was thus far developed using monoclinic bismuth chromate hydroxide proto-catalyst, m-Bi(OH)CrO₄. The catalytically active species, BiCrO₄, was isolated and its activity assessed for thermal disproportionation of formic acid under mild conditions (200–300 °C, tube furnace). A maximum formaldehyde production rate of 0.065 mmol/mmol catalyst/hour was observed using bismuth chromate at 250 °C. The formaldehyde produced through this method was selectively dehydrogenated to formate by an IrCl₃ catalyst at room temperature under basic conditions, with a dehydrogenation rate of 20.1 mmol of hydrogen/mmole catalyst/hour. This completes a step-by-step and yet efficient cycle of formic acid dehydrogenation.     

Bimetallic PdAu catalysts for formic acid dehydrogenation

A series of monometallic and bimetallic palladium gold catalyst were prepared and studied for the formic acid dehydrogenation reaction. Different Pd/Au compositions were employed (Pd_xAu_100-x, where x = 25; 50 and 75) and their impact on alloy structure, particle size and dispersion was evaluated. Active phase composition and reaction parameters such as temperature, formic acid concentration or formate/formic acid ratio were adjusted to obtain active and selective catalyst for hydrogen production. An important particle size effect was observed and related to Pd/Au composition for all bimetallic catalysts.     

High power density direct formic acid fuel cells

A demonstration of direct formic acid fuel cells (DFAFCs) generating relatively high power density at ambient temperature is reported. The performance of Nafion 112-based DFAFCs with different concentrations of formic acid at different temperatures has been evaluated. DFAFCs operated with dry air and zero back-pressure can generate power densities of 110 and 84 mW cm⁻² at 30 and 18 °C, respectively, which are considerably higher than direct methanol fuel cells (DMFCs) operated under the same conditions. The DFAFCs are especially suited to power portable devices used at ambient temperature because the significant high power density can be achieved with highly concentrated formic acid.     

A mini-type hydrogen generator from aluminum for proton exchange membrane fuel cells

A safe and simple hydrogen generator, which produced hydrogen by chemical reaction of aluminum and sodium hydroxide solution, was proposed for proton exchange membrane fuel cells. The effects of concentration, dropping rate and initial temperature of sodium hydroxide solution on hydrogen generation rate were investigated. The results showed that about 38 ml min⁻¹ of hydrogen generation rate was obtained with 25 wt.% concentration and 0.01 ml s⁻¹ dropping rate of sodium hydroxide solution. The cell fueled by hydrogen from the generator exhibited performance improvement at low current densities, which was mainly due to the humidified hydrogen reduced the protonic resistivity of the proton exchange membrane. The hydrogen generator could stably operate a single cell under 500 mA for nearly 5 h with about 77% hydrogen utilization ratio.     

Hydrogen production via electrolysis of aqueous formic acid solutions

Hydrogen was produced via electrolysis of aqueous formic acid solutions, and the effects of the concentrations of formic acid and NaOH on the electrolytic voltage were systematically investigated. The voltage is found to be related to the actual formic acid concentration. When the actual formic acid concentration is higher than 0.8 × 10⁻⁹ M, the initial electrolytic voltage can be as low as 0.30 V, which is much lower than the open circuit voltage in a proton exchange membrane fuel cell. The electrolytic voltage increases with the increase of the current density. Specifically at 1.0 M NaOH and 4.0 M HCOOH, the steady voltage value increases from 0.62 to 0.70 V as the current density increases from 1.0 to 6.0 mA/cm². At 3.0 M HCOOH and 2.5 M NaOH, the hydrogen production rate is 53 μmol/h under 8.0 mA/cm², which is promising for practical industrial-scale hydrogen production.     

Production of hydrogen via methane reforming using atmospheric pressure microwave plasma

In this paper, results of hydrogen production via methane reforming in the atmospheric pressure microwave plasma are presented. A waveguide-based nozzleless cylinder-type microwave plasma source (MPS) was used to convert methane into hydrogen. Important advantages of the presented waveguide-based nozzleless cylinder-type MPS are: stable operation in various gases (including air) at high flow rates, no need for a cooling system, and impedance matching. The plasma generation was stabilized by an additional swirled nitrogen flow (50 or 100 l min⁻¹). The methane flow rate was up to 175 l min⁻¹. The absorbed microwave power could be changed from 3000 to 5000 W. The hydrogen production rate and the corresponding energy efficiency in the presented methane reforming by the waveguide-based nozzleless cylinder-type MPS were up to 255 g[H₂] h⁻¹ and 85 g[H₂] kWh⁻¹, respectively. These parameters are better than those typical of the conventional methods of hydrogen production (steam reforming of methane and water electrolysis).     

Hydrogen production from formic acid in fluidized bed made out of Ni-cenosphere catalyst

This research presents a method of hydrogen production from formic acid with the use of fluidized bed technology. The core-shell catalyst was developed by applying the Ni layer on cenospheres via a technique of gaseous deposition. The efficiency of the decomposition of formic acid was tested continuously in the range of 200–500 °C. An analytical method, based on infrared spectroscopy, allowing the continuous monitoring of the concentration of products in the gas phase has been developed. A 67% yield of hydrogen was achieved at 233 °C. The proposed solution in a fluidized bed has been compared with other methods of obtaining hydrogen from formic acid. The most important advantages of the proposed solutions are on-demand hydrogen generation; the use of an energy carrier that can be obtained from biomass or CO₂; simplicity of the process including easy control of the process temperature; repeatability; ease of scaling the fluidized process; the possibility of continuous monitoring of the products of the process; high efficiency of hydrogen generation per unit volume of the reactor.     

Mass spectroscopy for the anode gas layer in a semi-passive direct methanol fuel cell using porous carbon plate: Part II. Relationship between the reaction products and the methanol and water vapor pressures

Subsequent to Part I, in situ mass spectrometry using a capillary probe was conducted in order to evaluate the gas condition of the anode gas layer of a semi-passive direct methanol fuel cell (DMFC) employing a porous carbon plate (PCP). Different types of PCPs were used for the DMFC, and the production of intermediates besides CO₂, i.e., methylformate (HCOOCH₃), formaldehyde (HCHO) and formic acid (HCOOH), were investigated. The profiles of the vapor pressures of these products were related to the vapor pressure of methanol and water in the gas layer. The production rate of each intermediate was formulated as a power function of the methanol and water vapor pressure ratio, P_CH3OH/P_H2O, with the power factors of 2.07, 0.47 and −0.57 for methylformate, formaldehyde and formic acid, respectively. Based on these equations of the production rates, the product distribution could be quantitatively estimated.     

Passive direct formic acid microfabricated fuel cells

This paper reports on microscale silicon-based direct formic acid fuel cells (Si-DFAFCs) in which the fuel and the oxidant are supplied to the electrodes in a passive manner. Passive delivery of fuel and oxidant eliminates the need for ancillary components and associated parasitic losses. In this Si-DFAFC, an aqueous solution of formic acid is in direct contact with a Pd- or Pt-based anode and a Pt-based cathode is exposed to either a forced oxygen stream or quiescent air. In the presence of a forced oxygen flow on the cathode side the cell with Pd catalyst on the anode delivers a maximum power density of about 30 mW cm⁻² at room temperature, limited mostly by mass transfer at the anode, while in an all-passive mode (quiescent air on the cathode side) a maximum power density of 12.3 mW cm⁻² is obtained, limited by oxygen transport. This all-passive Si-DFAFC is fabricated using processes that are post-CMOS compatible, and thus can be integrated directly with envisioned MEMS applications, such as small sensors and actuators.     

Investigation of the interaction between intermediates from gasification of biomass in supercritical water: Formaldehyde/formic acid mixtures

Supercritical water gasification (SCWG) is a promising technology for converting wet biomass and waste into renewable energy. While the fundamental mechanism involved in SCWG of biomass is not completely understood, especially hydrogen (H₂) production produced from the interaction among key intermediates. In the present study, formaldehyde mixed with formic acid as model intermediates were tested in a batch reactor at 400 °C and 25 MPa for 30 min. The gas and liquid phases were collected and analyzed to determine a possible mechanism for H₂ production. Results clearly showed that both gasification efficiency (GE) and hydrogen efficiency (HE) increased with addition of formic acid, and the maximum H₂ yield reached 17.92 mol/kg with a relative formic acid content of 66.67% in the mixtures. The total organic carbon removal rate and formaldehyde conversion rate also increased to 67.33% and 89.81% respectively. The reaction pathways for H₂ formation form mixtures was proposed and evaluated, formic acid promoted self-decomposition of formaldehyde to generate H₂, and induced a radical reaction of generated methanol to produce more H₂.     

Influence of NaOH and Ni catalysts on hydrogen production from the supercritical water gasification of dewatered sewage sludge

Dewatered sewage sludge was treated with NaOH additive and Ni catalyst in supercritical water in a high-pressure autoclave to examine the effects of separate and combined NaOH additive and Ni catalyst on hydrogen generation. The effects of Ni/NaOH ratio on hydrogen production were also investigated to identify possible catalytic mechanism and interactions. NaOH and Ni, separately or in combination, improved the hydrogen production and hydrogen gasification efficiency. The addition of NaOH additive not only promoted the water–gas shift reaction, but also favored H₂ generation of Ni catalyst by capturing CO₂. The hydrogen yield of combined catalysts with different Ni/NaOH ratios was higher than the theoretical sum of hydrogen yield from the mixture by 10–33%. The largest hydrogen yield, of 4.8 mol per kilogram of organic matter, which was almost five times as much as without catalyst, was achieved with the addition of 3.33 wt% Ni and 1.67 wt% NaOH. The combined NaOH additive and Ni catalyst also improved the gasification of several other dewatered sewage sludges, increasing the hydrogen yield by four to twelve times that seen without catalyst. Combined NaOH additive and Ni catalyst are effective in dewatered sewage sludge gasification at low temperature.     

Hydrogen generation system using sodium borohydride for operation of a 400 W-scale polymer electrolyte fuel cell stack

Sodium borohydride (NaBH₄) in the presence of sodium hydroxide as a stabilizer is a hydrogen generation source with high hydrogen storage efficiency and stability. It generates hydrogen by self-hydrolysis in aqueous solution. In this work, a Co–B catalyst is prepared on a porous nickel foam support and a system is assembled that can uniformly supply hydrogen at >6.5 L min⁻¹ for 120 min for driving 400-W polymer electrolyte membrane fuel cells (PEMFCs). For optimization of the system, several experimental conditions were changed and their effect investigated. If the concentration of NaBH₄ in aqueous solution is increased, the hydrogen generation rate increases, but a high concentration of NaBH₄ causes the hydrogen generation rate to decrease because of increased solution viscosity. The hydrogen generation rate is also enhanced when the flow rate of the solution is increased. An integrated system is used to supply hydrogen to a PEMFCs stack, and about 465 W power is produced at a constant loading of 30 A.     

Fructose decomposition kinetics in organic acids-enriched high temperature liquid water

Biomass continues to be an important candidate as a renewable resource for energy, chemicals, and feedstock. Decomposition of biomass in high temperature liquid water is a promising technique for producing industrially important chemicals such as 5-hydroxymethylfurfural (5-HMF), furfural, levulinic acid with high efficiency. Hexose, which is the hydrolysis product of cellulose, will be one of the most important starting chemicals in the coming society that is highly dependent on biomass. Taking fructose as a model compound, its decomposition kinetics in organic acids-enriched high temperature liquid water was studied in the temperature range from 180 °C to 220 °C under the pressure of 10 MPa to further improve reaction rate and selectivity of the decomposition reactions. The results showed that the reaction rate is greatly enhanced with the addition of organic acids, especially formic acid. The effects of temperature, residence time, organic acids and their concentrations on the conversion of fructose and yield of 5-HMF were investigated. The evaluated apparent activation energies of fructose decomposition are 126.8 ± 3.3 kJ mol⁻¹ without any catalyst, 112.0 ± 13.7 kJ mol⁻¹ catalyzed with formic acid, and 125.6 ± 3.8 kJ mol⁻¹ catalyzed with acetic acid, respectively, which shows no significant difference.     

Hydrogen generation by glow discharge plasma electrolysis of methanol solutions

This paper investigated the glow discharge plasma electrolysis (GDPE) of methanol solutions for hydrogen generation. It is known that H₂ and HCHO are the dominant products of methanol decomposition during GDPE. The experimental results indicate that high-energy electrons are the most important species to initiate methanol decomposition. Likewise, it was shown that discharged polarity, discharged voltage, and methanol concentration have important influences on hydrogen yield, energy consumption, hydrogen concentration, and hydrogen and formaldehyde output. The hydrogen yield (G(H₂)) of cathodic GDPE (CGDPE) was found to be higher than that of anodic GDPE (AGDPE). In addition, the hydrogen concentration in liberated gas from CGDPE remains above 88% after the separation of HCHO when the applied voltage is higher than 750 V. The energy consumption (W_r) of CGDPE is significantly less than AGDPE. Furthermore, W_r decreased with the increase in discharged voltage, while G(H₂) increased with methanol concentration. The experimental results show that the GDPE of methanol solutions is a promising technique for the simultaneous production of hydrogen and formaldehyde.     

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

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

The role of surface reactions on the active and selective catalyst design for bioethanol steam reforming

In order to study the role of surface reactions involved in bioethanol steam reforming mechanism, a very active and selective catalyst for hydrogen production was analysed. The highest activity was obtained at 700 °C, temperature at which the catalyst achieved an ethanol conversion of 100% and a selectivity to hydrogen close to 70%. It also exhibited a very high hydrogen production efficiency, higher than 4.5 mol H₂ per mol of EtOH fed. The catalyst was operated at a steam to carbon ratio (S/C) of 4.8, at 700 °C and atmospheric pressure. No by-products, such as ethylene or acetaldehyde were observed. In order to consider a further application in an ethanol processor, a long-term stability test was performed under the conditions previously reported. After 750 h, the catalyst still exhibited a high stability and selectivity to hydrogen production. Based on the intermediate products detected by temperature programmed desorption and reaction (TPD and TPR) experiments, a reaction pathway was proposed. Firstly, the adsorbed ethanol is dehydrogenated to acetaldehyde producing hydrogen. Secondly, the adsorbed acetaldehyde is transformed into acetone via acetic acid formation. Finally, acetone is reformed to produce hydrogen and carbon dioxide, which were the final reaction products. The promotion of such reaction sequence is the key to develop an active, selective and stable catalyst, which is the technical barrier for hydrogen production by ethanol reforming.     

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.