COx-free hydrogen production from ammonia decomposition over sepiolite-supported nickel catalysts

Sepiolite, a clay mineral, was utilized as a support for nickel-based catalysts for CO_x-free hydrogen production from ammonia decomposition. First, the physical and chemical properties of sepiolite were changed by calcining it at temperatures varying from 500 to 1000 °C, then nickel was impregnated on these calcined supports and tested for ammonia decomposition at various temperatures following reduction at 650 °C. Results indicated that even though the catalysts contained almost the same amount of nickel, they showed different hydrogen production performance. Detailed characterization of the catalysts before and after reaction illustrated that the support obtained by calcining sepiolite at 700 °C shows good basic properties with a high surface area offering a high degree of nickel dispersion. These properties lead to promising hydrogen production rates which are on par, if not higher, than most of the nickel-based catalysts prepared on supports, which are either not cheap or require tedious preparation procedures.     

Hydrogen production system combined with a catalytic reactor and a plasma membrane reactor from ammonia

Ammonia is a 1promising raw material for hydrogen production because it may solve several problems related to hydrogen transport and storage. Hydrogen can be effectively produced from ammonia via catalytic thermal decomposition; however, the resulting residual ammonia negatively influences the fuel cells. Therefore, a high-purity hydrogen production system comprising a catalytic decomposition reactor and a plasma membrane reactor (PMR) has been developed in this work. Most of the ammonia is converted to hydrogen and nitrogen by the catalytic reactor. After the product gas containing unreacted ammonia is introduced to the PMR, unreacted ammonia is decomposed and hydrogen is separated in the PMR. Based on these processes, hydrogen with a purity of 99.99% is obtained at the output of the PMR. Optimal operation conditions maximizing the hydrogen production flow rate were investigated. The gap length of the PMR and the gas differential pressure and applied voltage of the plasma influence the flow rate. A pure hydrogen flow rate of ∼120 L/h was achieved using the current operating conditions. The maximum energy efficiency of the developed hydrogen production system is 28.5%.     

Pulsed current water splitting electrochemical cycle for hydrogen production

A pulsed current 3 D MnO₂ electrode water splitting electrochemical cycle is being proposed for hydrogen production. In 3D MnO₂ electrochemical cycle, the reactions take place at the solid/liquid and solid/gas two phase boundaries. Also, this electrochemical cycle should be able to generate hydrogen and oxygen gas separately at different periods of time. Here, we applied an interrupted pulsed current to reduce the overpotential caused by diffusion layers in conventional direct current electrolysis. The pulsed current, which disturbs the formation of the ion diffusion layer in the vicinity of the electrodes, is observed to be effective above 50 Hz. The best electrolysis performance was recorded at a current density of 0.2 A cm^?2, and the observed cell voltage was 1.69 V at 25 °C for a pulse frequency of 500 Hz, which is less than the corresponding conventional alkaline electrolysis.     

Highly purified hydrogen production from ammonia for PEM fuel cell

Liquid ammonia is an attractive hydrogen carrier because of high storage capacity. According to ISO14687-2, an acceptable ammonia concentration in hydrogen for polymer electrolyte membrane (PEM) fuel cell vehicles is 0.1 ppm. When ammonia is used as the hydrogen carrier, about 1000 ppm of ammonia included in gas generated by ammonia decomposition at 773–823 K and 0.1 MPa has to be reduced to less than 0.1 ppm. Although several types of ammonia absorption materials are investigated as ammonia remover, the target value cannot be achieved by static adsorption methods. However, we have succeeded in that the ammonia concentration is reduced down to 0.01–0.02 ppm by using Li-exchange X-type zeolite (Li-X) as the absorbent and dynamic adsorption methods. Furthermore, Li-X is simply recycled by heating at 673 K. Therefore, Li-X is a durable and recyclable ammonia removal material for the highly purified hydrogen production from ammonia for PEM fuel cells.     

Enhancing the ammonia to hydrogen (ATH) energy efficiency of alternating current arc discharge

In order to enhance the ammonia to hydrogen (ATH) energy efficiency, systematic study was carried out with atmospheric pressure alternating current arc discharge reactor (using a pair of stainless steel (SS) tube electrodes). Results showed that, using small-diameter SS tube electrodes with small discharge gaps forced more ammonia molecules to go through the effective plasma volume and obtained high electrodes temperature. Adopting low discharge frequency increased the discharge time, the effective plasma volume and the electrode temperature. These changes can enhance both the gas-phase plasma decomposition and the electrode-surface catalytic decomposition of ammonia. Insulating the reactor significantly increased the electrode temperature in small-diameter reactor, so as to enhance the electrode-surface catalytic decomposition of ammonia. In large-diameter reactors, however, the electrodes temperature increased less rapidly and more ammonia bypass of the effective plasma volume occurred. A 12.5 mol/kW h ATH energy efficiency was reached when ammonia was completely converted under the conditions of electrode diameter 3 mm, electrode gap 4 mm, discharge frequency 5 kHz, reactor diameter 8 mm, NH₃ flow rate 150 ml/min and input power 48 W. The ATH energy efficiency was further enhanced under similar conditions when incomplete ammonia conversion was allowed.     

Hydrogen production by a low-cost electrolyzer developed through the combination of alkaline water electrolysis and solar energy use

Electrolysis is a relatively simple process for obtaining hydrogen and can be combined with use of renewable energy sources, such as solar photovoltaic energy, for clean, sustainable gas production. This study designed a cylindrical electrolytic cell made of acrylic and 304 stainless steel electrodes to produce hydrogen. The electrolyte used was sodium hydroxide (NaOH 2–5 mol L^?1), and the direct current voltages applied were 2.0, 2.7, and 3.4 V. The maximum hydrogen production was achieved with 5.0 mol L^?1 NaOH and 3.4 V electric voltage. The system was connected to a photovoltaic panel of 20 W and exposed to solar radiation from 10 a.m. to 2 p.m. Approximately 2 L of hydrogen was produced within a period, and an average irradiance of 800.0 W m^?2 ± 60 W m^?2 was achieved. The system was stable throughout the tests.     

Hydrogen gas production from food wastes by electrohydrolysis using a statical design approach

Hydrogen gas production was investigated by electrohydrolysis of food waste due to its high organic content. Different voltages generated by DC power supply were applied to food waste in order to produce hydrogen gas. Effects of the DC voltage, reaction time and initial solid content on cumulative hydrogen gas production, hydrogen gas content in the gas phase and total organic carbon (TOC) removal were investigated by using a Box-Behnken statistical experiment design approach. The most suitable voltage/reaction time/solid content values resulting in the highest hydrogen gas content (99%), the highest cumulative hydrogen gas formation (7000 mL) and total organic carbon removal (33%) were determined as 5 V/75 h/20%. The results indicated that food wastes constitute a good source for H₂ gas production by electrohydrolysis. Hydrogen gas produced by electrohydrolysis of food waste can be directly used in fuel cells due to its high putrity.     

Modifying the structure of red mud by simple treatments for high and stable performance in COx-free hydrogen production from ammonia

Red mud (RM) modified by various treatments was used as a catalyst for ammonia decomposition. Catalytic activity measurements performed at 500 °C and differential conversions illustrated that the rate increases with a decrease in the size of Fe₃N_y nanoparticles formed during activation in NH₃ flow. Measurements at 700 °C showed that a catalyst prepared by digesting RM in 6 M HCl followed by calcination at 900 °C provides a stable ammonia conversion of 98.8 ± 0.5% for more than 70 h at a space velocity of 120 000 cm³ NH₃ h^?1 g_cat^?1. This rate is premier among all iron-based catalysts in terms of both activity and stability and even on par with the performance of other non-noble metal catalysts. Detailed characterization indicated Fe₃N_y species readily available on the surface as the active species. Results provided here enable the utilization of RM as an environmentally-friendly, highly efficient, and almost cost-free catalyst for CO_x-free hydrogen production.     

High pressure membrane separator for hydrogen purification of gas from hydrothermal treatment of biomass

For hydrogen purification and green hydrogen production in the context of biomass hydrothermal gasification, a palladium membrane system with microchannels on feed and permeate side was studied. The high pressure in the product gas of the hydrothermal process could potentially be used to generate pressurized pure hydrogen on the permeate side. Stabilizing the membrane by an additional porous metal support, experimental verification of the concept was done at feed pressure up to 50 bar and permeate pressure up to 20 bar. The temperatures were varied between 370 °C and 425 °C. The device was found to be highly selective and efficient for pure hydrogen separation. The membrane was characterized regarding the hydrogen flux and a deviation of the permeation from Sievert's law above 30 bars feed pressure was found. Generally, the microchannels on the feed side minimized concentration polarization effects, leading to high hydrogen fluxes with hydrogen feed mixtures and with real gas samples from hydrothermal gasification.     

Assessment of an integrated solar hydrogen system for electrochemical synthesis of ammonia

In this paper, a solar based electrochemical system is designed, built and tested to synthesize ammonia and hydrogen from nitrogen and saturated steam. Ammonia can serve as a sustainable fuel and is in heavy demand by the fertilizer industry. However, the conventional methods rely on hydrogen produced from fossil fuels. Hydrogen can be supplied back by implementing fuel cells and feeding electricity back to the system, directed to the conventional ammonia production methods as a reactant, or sold as a fuel. A simple and direct system is studied to pose a sustainable option for ammonia and hydrogen production. Very high concentrations of Nano iron catalyst are used to promote the concentration of ammonia at the output. The reactor is designed for continuous flow and can be disassembled for varying tests and scenarios. The maximum concentration of ammonia is found to be 950 ppm measured with excess reactant supply. Increasing nitrogen flow rates along with decreasing steam flow rates render increasing concentration results. The system at optimum conditions consumes 650 mA at 1.7 V. The low power requirements and valuable products of the system encourage further studies. Additionally, a solar energy based system is proposed as a renewable approach to ammonia synthesis with a fuel cell component to increase the efficiency by reducing the power consumption to 60% of its original value.     

Numerical modeling of a bayonet heat exchanger-based reactor for sulfuric acid decomposition in thermochemical hydrogen production processes

Sulfur-based thermochemical hydrogen production cycles represent one of the most appealing options to produce hydrogen from water on a large scale. The Hybrid Sulfur is one of the most advanced thermochemical cycles. The high temperature section of the process, common to all sulfur-based cycles, operates the sulfuric acid thermal decomposition reaction at temperatures on the order of 800 °C. The paper shows and discusses the modeling results obtained for a bayonet heat exchanger based high temperature reactor that decomposes the sulfur compounds into sulfur dioxide and oxygen. A detailed transport phenomena model, including suitable decomposition kinetics, has been set up using a finite volume numerical approach. A preliminary configuration of the reactor, established based on process simulation results and on the initial reactor prototype developed at Sandia National Laboratory, has been examined and simulated. Results, obtained for a reactor driven by thermal power provided by helium flow, demonstrate the effective decomposition performance at maximum temperatures on the order of 800 °C and pressures of 14 bar. For a laminar flow configuration a sulfur dioxide production yield of about 28 wt% (with sulfur trioxide reduction from 69 wt% to approximately 33 wt%) has been achieved, representing decomposition rates practically equal to the corresponding equilibrium values. Limited pressure drops of approximately 2500 Pa have also been achieved in the sulfur mixture region.     

Preparation,characterization and hydrogen production performance of MoPd deposited carbon felt/Mo electrodes

Mo-coated carbon felt (C) supporting material modified by electrochemical deposition of trace amounts of MoPd binary composites having various metal ratios and characterized using various techniques. To our best knowledge, these materials is being reported firstly. The hydrogen evolution activity of the electrodes tested in 1 M KOH solution using electrochemical techniques. It shown that MoPd modified electrodes have large surface area, which is very beneficial for the rate of hydrogen evolution reaction (HER). Pd and Mo metals almost homogeneously distributes over the surface and no local aggregations are appeared. The loading of MoPd binary deposits over the Mo-coated C supporting material enhances the rate of the HER more and more when compared to the base substrate. The hydrogen evolution performance of the composites is depending on the metal ratios. The enhanced current density at the C/Mo-Mo₅₀Pd₅₀ electrode at ?1.60 V(Ag/AgCl) is 79.1% with respect to the C felt and 48.1% with respect to the C/Mo modified supporting material. The reduction in resistance related to hydrogen gas releasing at 100 mV overpotential was 97.2% and 58.6% with respect to bare C felt and C/Mo supporting material. The high hydrogen releasing performance of the PdMo-modified electrocatalysts related to intrinsic catalytic activities of Pd and Mo, a possible synergism between these metals and enhanced real surface area of the electrode. The C/Mo-Mo₅₀Pd₅₀ electrode has excellent electrochemical and physical stability during the long time electrolysis. Therefore, it is expected that the procedure applied here contribute to literature since the modifying C support by an active metal provides activation of electrocatalysts. Due to superior properties, we can suggest C/Mo-Mo₅₀Pd₅₀ electrode as promising cathode material for industrial water electrolysis which can reduces the energy input.     

Design study of an AnSBBR for hydrogen production by co-digestion of whey with glycerin: Interaction effects of organic load,cycle time and feed strategy

An anaerobic sequencing batch biofilm reactor (AnSBBR) treating a mixture of dairy industry wastewater and biodiesel production wastewater (co-digestion of whey with glycerin) was applied to hydrogen production. The influence of fed-batch and batch mode, cycle time and interactions effects between influent concentration and cycle time (2, 3 and 4 h) over the organic loading rate were assessed in order to obtain a sensitivity analysis for important operational variables to the reactor. It was possible to find an optimal cycle time of 3 h with an influent concentration of 7000 mgCOD L^?1 (molar productivity 129.0 molH₂ m^?3 d^?1 and yield 5.4 molH₂ kgCOD^?1). Reactor operation in fed-batch mode allowed higher hydrogen production rates. Increasing the influent concentration (with a constant cycle time) was better for the hydrogen production process than decreasing the cycle length (with a constant influent concentration), which means that these two parameters have different weights in the organic loading rate. The best operational conditions produce hydrogen via acetic, butyric and valeric acids similarly. The system is able to produce 1.3 kJ per gram of COD applied.     

Experimental investigation of various copper oxide electrodeposition conditions on photoelectrochemical hydrogen production

In this study, an experimental investigation of photosensitive material copper oxide electrodeposition on various substances is performed under different experimental conditions in order to evaluate the effects on photoelectrochemical hydrogen production system. The experimental setup consists of solar simulator, electrodeposition chemicals, hydrogen sensor, pH meter, graphite and platinum electrodes, heating plate, stirrer, temperature sensors, cathode and anode plates, concentrating lens and potentiostat. The overall aim is to optimize the efficiencies by generating higher currents and eventually hydrogen as light enhances the separation of water process. The results obtained in this study are promising for photoelectrochemical hydrogen production under the solar simulator and concentrated light irradiation conditions. Furthermore, an electrolysis setup using the coated metals and graphite rod is built to investigate the amount of photocurrent production. The characterization is also conducted under light and no-light conditions, where the amount of produced current and hydrogen increased in light compared to no-light condition. At the applied voltage of ?0.6 V and ?0.4 V vs. Ag/AgCl, the photocurrent densities of 0.8 mA/cm² and 0.27 mA/cm² are obtained with a solar conversion efficiency of 0.86% and 0.24%, respectively.     

Hydrogen production from the methanolysis of ammonia borane by Pd-Co/Al2O3 coated monolithic catalyst

The aim of this study is to enable high hydrogen production yield from catalytic methanolysis of ammonia borane (AB) in the presence of a cordierite type ceramic monolithic. The monolithic channel surfaces were coated with Al₂O₃ by wash-coating method and then this layer was impregnated with 1 wt%Pd-2 wt%Co bimetallic catalyst. SEM-EDX and multi-point BET analysis were used in order to characterize the catalyst. The experimental studies were conducted in a continuous flow type reactor, which was used for the first time in this study. The reactions were carried on low temperature (40 °C), and with various AB feed concentrations and flow rates. It was found that the highest hydrogen production yield (88.5%) was obtained from AB flow rate of 3.3 mL/min, and AB feed concentration of 0.1 wt%. It was concluded that Pd-Co/Al₂O₃ coated monolithic, which is a stable, active and low-cost catalyst, was a very promising catalyst for on-board hydrogen production from the methanolysis of ammonia borane.     

Ammonia fuel cell using doped barium cerate proton conducting solid electrolytes

Proton-conducting solid electrolytes composed of gadolinium-doped barium cerate (BCG) or gadolinium and praseodymium-doped barium cerate (BCGP) were tested in an intermediate-temperature fuel cell in which hydrogen or ammonia was directly fed. At 700 °C, BCG electrolytes with porous platinum electrodes showed essentially no loss in performance in pure hydrogen. Under direct ammonia at 700 °C, power densities were only slightly lower compared to pure hydrogen feed, yielding an optimal value of 25 mW cm⁻² at a current density of 50 mA cm⁻². This marginal difference can be attributed to a lower partial pressure of hydrogen caused by the production of nitrogen when ammonia is decomposed at the anode.A comparative test using BCGP electrolyte showed that the doubly doped barium cerate electrolyte performed better than BCG electrolyte. Overall fuel cell performance characteristics were enhanced by approximately 40% under either hydrogen or ammonia fuels using BCGP electrolyte. At 700 °C using direct ammonia feed, power density reached 35 mW cm⁻² at a current density of approximately 75 mA cm⁻². Minimal loss of performance was noted over approximately 100 h on-stream in alternating hydrogen/ammonia fuels.     

The Hydroloysis of ammonia borane by using Amberlyst-15 supported catalysts for hydrogen generation

Resin catalysts have the advantage of having various properties and long lifetime due to their ability to be regenerated easily, which makes them attractive supports. In this paper, a comparative study was conducted to optimize the dehydrogenation reaction condition using two different types of support materials: alumina (Al₂O₃), and Amberlyst-15 and to improve the catalytic activity as well as preparing an efficient and low-cost system for practical application, ruthenium metal catalyst was incorporated on Amberlyst-15 resin (a sulfonic acid type based upon a styrene-divinylbenzene copolymer) to release H₂ via hydrolytic dehydrogenation of ammonia borane. Using ruthenium (Ru) catalysts based on Amberlyst-15 support material and comparing the results with Al₂O₃ as the common supporting material is considered to be studied for the first time. The effect of temperature (20–50 °C), the initial ammonia borane concentration (0.05–0.5 %wt), and catalyst amount (0.2–0.5 g) on the produced H₂ yield was also investigated. Ru@Amberlyst-15 nanoparticle was discovered to be an effective catalyst for hydrogen evolution via the hydrolysis of ammonia borane with a turnover frequency value (TOF) of 343.3 min^?1, while Ru@Al₂O₃ yielded a TOF of 87.5 min^?1 at the room temperature. Therefore, it can be concluded that the Amberlyst-15 supporting effect on ruthenium metal leads an increase in the hydrogen production rate.     

Kinetic model of homogeneous thermal decomposition of methane and ethane

In this paper, the homogeneous decomposition of methane and ethane is modeled in a well stirred flow reactor. The kinetics of this process is represented by a reaction mechanism of 242 reactions and 75 species, based on a mechanism developed for hydrocarbon combustion and soot formation. It is shown that this model correctly predicts the hydrogen yield from pyrolysis in a temperature range of 600–1600 °C, and pressure range of 0.1–10 atm. Furthermore, the effect of temperature, pressure and residence time on the amount of hydrogen produced from the decomposition of methane, ethane, natural gas, and a mixture of methane and argon is studied. The model predicts that the use of ethane or its addition to methane increases the speed of hydrogen production at low temperatures and pressures. The addition of a noble gas like argon also increases the yield of hydrogen at high pressures.     

One-step synthesis of Ni/yttrium-doped barium zirconates catalyst for on-site hydrogen production from NH3 decomposition

On-site produced hydrogen from ammonia decomposition can directly fuel solid oxide fuel cells (SOFCs) for power generation. The key issue in ammonia decomposition is to improve the activity and stability of the reaction at low temperatures. In this study, proton-conducting oxides, Ba(Zr,Y) O_3-δ (BZY), were investigated as potential support materials to load Ni metal by a one-step impregnation method. The influence of Ni loading, Ba loading, and synthesis temperature, of Ni/BZY catalysts on the catalytic activity for ammonia decomposition were investigated. The Ni/BZY catalyst with Ba loading of 20 wt%, Ni loading of 30 wt%, and synthesized at 900 °C attained the highest ammonia conversion of 100% at 600 °C. The kinetics analysis revealed that for Ni/BZY catalyst, the hydrogen poisoning effect for ammonia decomposition was significantly suppressed. The reaction order of hydrogen for the optimized Ni/BZY catalyst was estimated as low as ?0.07, which is the lowest to the best of our knowledge, resulting in the improvement in the activity. H₂ temperature programmed reduction and desorption analysis results suggested that a strong interaction between Ni and BZY support as well as the hydrogen storage capability of the proton-conducting support might be responsible for the promotion of ammonia decomposition on Ni/BZY. Based on the experimental data, a mechanism of hydrogen spillover from Ni to BZY support is proposed.     

Test of conductor and semiconductor electrocatalysts in high voltage alkaline electrolyzer as production media for green hydrogen

Despite the restricted success of conductor and semiconductor electrodes in solving hydrogen production problems, they provide a promising alternative to expensive conventional electrodes in water electrolysis investigations. Titanium dioxide (TiO₂) and silver (Ag) are widely used as photocatalysts in water splitting systems for hydrogen generation. Though TiO₂ is an inactive chemical semiconductor with poor conductivity, it has not been entirely investigated as an electrocatalyst yet. Two criteria were used to achieve this target: supplying high voltage to overcome the TiO₂ large band gap and immersing it in an alkaline solution to activate its inert surface. For comparison study, Ag noble metal nanoparticles coating was employed as a competitive electrocatalyst. In this regard, the application of Ag and TiO₂ coated on Ti electrodes in a hydrogen production system operated under high voltage was reported. The nanoparticles were synthesized using cost-effective and simple methods based on UV-deposition for Ag nanoparticles and the chemical precipitation method for TiO₂ nanoparticles. Then the synthesized nanoparticles were deposited on the Ti electrodes by simple immersion. The synthesized nanoparticles and coated electrodes were tested by XRD, SEM, and EDS to study their morphology, structure, particle size, and surface composition. Based on these results, TiO₂ nano-powder and coated electrodes exhibited homogenous spheres with a mixture of rutile and anatase phases, the majority being the anatase phase. The Ag-coated Ti substrate possessed a smaller crystallite size compared to TiO₂ coated substrate. To evaluate the performance of Ag/Ti and TiO₂/Ti electrodes toward hydrogen production, H₂ flow rates were measured in a 3.6 M KOH electrolytic solution at 6 V. Hydrogen flow rates obtained for pure Ti, Ag, and TiO₂ electrodes at a steady state were 21, 35, and 37 SCCM (standard cm³/min), respectively. Also, it was found that energy consumption was reduced when the electrodes were coated with nanoparticles. Furthermore, the electrolyzer's performance was assessed by calculating the hydrogen production efficiency and the voltage efficiency. The results showed that using TiO₂ electrodes gave the best hydrogen production and voltage efficiencies of 27% and 23%, respectively. This study brings new insights about Ag and TiO₂ coated electrodes in alkaline water electrolysis at high voltage regarding nanoparticle performance, hydrogen production, system performance, and energy consumption. In addition, minimizing the fabrication and operation costs of hydrogen production is the major enabler for the broad commercialization of water electrolysis devices.