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.     

Investigation of hydrogen production performance of chlor-alkali cell integrated into a power generation system based on geothermal resources

In present study, hydrogen production performance of chlor-alkali cell integrated into a power generation system based on geothermal resource is studied. The basic elements of the novel system are a separator, a steam power turbine, an organic Rankine cycle (ORC), an air cooled condenser, a saturated NaCl solution reservoir tank and a chlor-alkali cell. To enhance the performance of the cell, the saturated NaCl solution is heated by the waste heat from the ORC. So, this integrated system generates significant amount of electricity for the city grid and also yields three main products those are hydrogen, chlorine and sodium hydroxide. According to the parametric study, when the temperature of a geothermal resource varies from 140 to 155 °C, the electrical power generation increases from nearly 2.5 MW to 3.9 MW and hydrogen production increases from 10.5 to 21.1 kg-h. Thus, when the geothermal resource temperature of 155 °C, the energy efficiency of the system is 6.2% and the exergetic efficiency is 22.4%. As a result, the geothermal energy potential plays a key role on the integrated system performance and the hydrogen production rate.     

Chlorine-free alkaline seawater electrolysis for hydrogen production

A new process for chlorine-free seawater electrolysis is proposed in this study. The first step of the process is separation of Mg²⁺ and Ca²⁺ ions from seawater by nanofiltration. Next, the NF permeate is dosed into the electrochemical system. There it is completely split into hydrogen and oxygen gases and NaCl precipitate. The electrochemical system comprises an electrochemical cell operated at elevated temperatures (e.g. ≥ 50 °C) and a settling tank filled with aqueous NaOH solution (20–40 %wt) that operates at lower temperatures (e.g. 20–30 °C). High concentration of hydroxide ions in the electrolyzed solution prevents anodic chlorine evolution, while the accumulated NaCl precipitates in the settling tank. Batch electrolysis tests, performed in NaCl-saturated NaOH solutions, showed absolutely no chlorine formation on Ni200 and Ti/IrO₂RuO₂TiO₂ anodes at [NaOH] > 100 g/kgH₂O. Three long-term operations (9, 12 and 30 days) of the electrochemical system showed no Cl₂ or chlorate (ClO₃^?) production on both electrodes operated at current densities of 93–467 mA/cm². The Ni200 anode was corroded in the continuous operation that resulted in formation of nickel oxide on the anode surface. On the other hand, the system was successfully operated at 467 mA/cm² with Ti/IrO₂RuO₂TiO₂ electrodes in NaCl-saturated solution of NaOH (30 %wt) for 12 days. During this period no formation of Cl₂ and ClO₃^? has been observed and precipitation of NaCl occurred only in the settling tank. The performance of the system was stable during the operation as indicated by the insignificant fluctuations in the applied cell potentials and measured constant concentrations of NaOH_(aq) and NaCl_(aq) in the electrolyte solution. During 12 days of operation at ≈ 470 mA/cm² about 1.2 m³ of H₂ and ≈150 g of solid NaCl were produced in the system. Electrical energy demand of the electrolysis cell was 5.6–6.7 kWh/m³H₂ for the current density range of 187–467 mA/cm².     

Thermo-economic and thermo-environmental assessment of hydrogen production,an experimental study

Nowdays, the topic involvement of green hydrogen in energy transformation is getting attention in the world. The current research examined, thermo-economic and thermo-environmental analyses of the organic Rankine cycle (ORC) system and the hydrogen production system integrated into the solar collector with medium temperature density are investigated. The presented study is a holistic evaluation of experimentally solar-assisted electricity and hydrogen production. The studied model is comprised of an evacuated tube solar collector for thermal energy generation, ORC system for electricity generation and proton exchanger membrane electrolyzer (PEMe) for hydrogen production. According to the results of the thermodynamic analysis, the energy and exergy efficiency of the whole system are calculated as 39.01% and 17.37%, respectively. Also exergoenviroeconomic and exergoenviromental analysis of the whole system is found as 71.48 kgCO₂/kWh and 0.139 $/kgCO₂, respectively. In addition, the sustainability index of the presented system is obtained as 1.21. In this study, in addition to thermodynamic analysis, parameters such as energy and exergy affecting environmental and economic efficiency, are explained. Ambient temperature plays a prominent role in energy-based environmental analysis. On the contrary, the ambient temperature did not cause a significant change in the exergy-based environmental analysis.     

Thermodynamic analysis of the efficiency of high-temperature steam electrolysis system for hydrogen production

High-temperature steam electrolysis (HTSE), a reversible process of solid oxide fuel cell (SOFC) in principle, is a promising method for highly efficient large-scale hydrogen production. In our study, the overall efficiency of the HTSE system was calculated through electrochemical and thermodynamic analysis. A thermodynamic model in regards to the efficiency of the HTSE system was established and the quantitative effects of three key parameters, electrical efficiency (η_el), electrolysis efficiency (η_es), and thermal efficiency (η_th) on the overall efficiency (η_overall) of the HTSE system were investigated. Results showed that the contribution of η_el, η_es, η_th to the overall efficiency were about 70%, 22%, and 8%, respectively. As temperatures increased from 500 °C to 1000 °C, the effect of η_el on η_overall decreased gradually and the η_es effect remained almost constant, while the η_th effect increased gradually. The overall efficiency of the high-temperature gas-cooled reactor (HTGR) coupled with the HTSE system under different conditions was also calculated. With the increase of electrical, electrolysis, and thermal efficiency, the overall efficiencies were anticipated to increase from 33% to a maximum of 59% at 1000 °C, which is over two times higher than that of the conventional alkaline water electrolysis.     

Aspen Plus model of an alkaline electrolysis system for hydrogen production

A model of an alkaline electrolysis plant is proposed in this paper, including both stack and balance of plant, with the objective of analyzing the performance of a complete electrolysis system. For this purpose, Aspen Plus has been used in this work due to its great potential and flexibility. Since this software does not include codes for modelling the electrolysis cells, a custom model for the stack has been integrated as a subroutine, using a tool called Aspen Custom Modeler. This stack model is based on semi-empirical equations which describe the voltage cell, Faraday efficiency and gas purity as a function of the current. The rest of the components in the electrolysis plant have been modelled with standard operation units included in Aspen Plus. Simulations have been carried out in order to evaluate and optimize the balance of the plant of an alkaline electrolysis system for hydrogen production. Also, a parametric study has been conducted. The results show that increasing the operation temperature and reducing the pressure can improve the overall performance of the system. The proposed model in this work for the alkaline electrolyzer can be used in the future to develop a useful tool to carry out techno-economic studies of alkaline electrolysis systems integrated with other process.     

Direct electrolysis of bunsen reaction product for hydrogen production: The continuous-flow operation

Hydrogen sulfide (H₂S) emitted from oil industry's hydrotreating processes can be converted into hydrogen and used back to the same processes through a H₂S splitting cycle, where the Bunsen reaction and HI decomposition are two participating reactions. To overcome the difficulties and complications posted in the scaling up of the cycle, direct electrolysis of the Bunsen reaction product solution was proposed and has been studied in a batch electrolysis cell in our earlier work. This paper studies the direct electrolysis using a customer-made, continuous-flow electrolysis cell. The effects of the operating parameters including the current density, the entering HI concentration and flow rate of the anolyte, the toluene to aqueous phase ratio and stirring speed in anolyte cell, the H₂SO₄ concentration and circulation rate of the catholyte on the performing parameters such as the conversion of iodide ions, the yield of iodine transferred to toluene, and the anodic and cathodic current efficiencies for iodide conversion and hydrogen production were carefully investigated. The results show that the cathodic current efficiency for hydrogen production is nearly 100% for all the runs and that the anodic current efficiency for iodide ion conversion to iodine is relatively low (20%–70%) and varies with the changes in operating parameters. Running at high levels of the current density, the volumetric ratio of toluene to aqueous phase in anolyte, or the stirring speed in anolyte, and low levels of the entering concentration of I^? in anolyte or the flow rate of anolyte in electrolysis operation are in favor of having a high iodide conversion and high I₂-toluene yield. Iodide anions at a few mmol L^?1 level (a few thousandths of the entering concentration) are found in the cathodic chamber caused by its diffuse against the electric field and the proton exchange membrane. The continuous, direct electrolysis of the Bunsen product solution can be considered being adapted in the sulfur-iodine (S–I) water splitting cycle for hydrogen production.     

Recent development in electrocatalysts for hydrogen production through water electrolysis

Hydrogen is a carbon-free alternative energy source for use in future energy frameworks with the advantages of environment-friendliness and high energy density. Among the numerous hydrogen production techniques, sustainable and high purity of hydrogen can be achieved by water electrolysis. Therefore, developing electrocatalysts for water electrolysis is an emerging field with great importance to the scientific community. On one hand, precious metals are typically used to study the two-half cell reactions, i.e., hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). However, precious metals (i.e., Pt, Au, Ru, Ag, etc.) as electrocatalysts are expensive and with low availability, which inhibits their practical application. Non-precious metal-based electrocatalysts on the other hand are abundant with low-cost and eco-friendliness and exhibit high electrical conductivity and electrocatalytic performance equivalent to those for noble metals. Thus, these electrocatalysts can replace precious materials in the water electrolysis process. However, considerable research effort must be devoted to the development of these cost-effective and efficient non-precious electrocatalysts. In this review article, we provide key fundamental knowledge of water electrolysis, progress, and challenges of the development of most-studied electrocatalysts in the most desirable electrolytic solutions: alkaline water electrolysis (AWE), solid-oxide electrolysis (SOE), and proton exchange membrane electrolysis (PEME). Lastly, we discuss remaining grand challenges, prospect, and future work with key recommendations that must be done prior to the full commercialization of water electrolysis systems.     

Study on POM assisted electrolysis for hydrogen and ammonia production

Introducing silicotungstic acid as e⁻ carrier, it was found that the yield of H₂ can improve 35.31%. Compared to the results without addition of silicotungstic acid, the NH₃ production rate and Faradaic Efficiency were increased by 10.5 and 13.3 times, respectively.     

The stability of MEA in SPE water electrolysis for hydrogen production

Membrane electrode assemblies (MEAs) for water electrolysis were prepared by decal transferring an Ir black anode and a Pt black cathode on the two sides of a perfluorosulfonate solid polymer electrolyte (SPE) Nafion112 membrane. Performance stability of an MEA with 4 cm² effective electrode area was tested for 208 h in a single cell water electrolysis setup. The catalysts of both electrodes on the MEAs were characterized by means of XPS and XRD. Samples of feed water were analyzed by using conductivity meter, inductance coupling plasma optical emission spectroscopy (ICP-OES), ionic chromatography and total organic carbon (TOC) analyzer. Surface oxidation of the anodic Ir catalyst was evidenced, from the original metal Ir to 71.5% Ir₂O₃ and 28.5% IrO₂ after 208 h of electrolysis. While the metallic state of Pt on the cathode did not change during the same period of operation, the crystallite size of the Pt catalyst increased from 9.1 nm to 9.8 nm. Water analysis shows there is significant accumulation of impurities in the feed water, which can contaminate the MEA. Fortunately, the MEA restored more than 98% of its original performance after a simple treatment with 1 mol/L H₂SO₄ solution. This indicates the short period performance decline of the MEA is mainly caused by a recoverable contamination.     

Dispersion and behavior of hydrogen for the safety design of hydrogen production plant attached with nuclear power plant

Development of nuclear energy and hydrogen energy both as renewable energy open up a vast range of prospects. The scheme for hydrogen generation station in nuclear power plant has been carried out in china. However, Nuclear Energy is expected to encourage a safety culture that prevents serious accidents while dispersion of hydrogen from a container produces a risk of combustion. The dispersion and behavior of hydrogen production plant attached with nuclear power plant are still poorly understood. In this paper, a dispersion of hydrogen model is established and is calculated under two typical condition with corrected ideal gas state equation. The flammability of hydrogen after dispersion is studied. The range of flammability of dispersion of hydrogen production plant with different pressures, positions and temperatures is obtained. This work could contribute to the marginal hydrogen safety design for hydrogen production station and lay the foundation for the establishment of a safe distance standard that it's necessary to prevent hydrogen explosion.     

Biochar sacrificial anode assisted water electrolysis for hydrogen production

Carbon-assisted water electrolysis uses carbon oxidation reaction replacing oxygen evolution reaction to decrease the anode potential and the energy consumption for water electrolysis hydrogen production. However, the mass transfer between carbon particle-electrolyte-anode limits its energy saving effect. Based on the principle of self-corrosion/oxidation of carbon-based electrode materials, the biochar sacrificial anode was proposed and investigated to solve the mass transfer issue in carbon slurry assisted water electrolysis for hydrogen production. Results showed that the activity and stability of sacrificial anode could be improved simultaneously in high concentration alkaline electrolyte using pinewood char as active substance, graphite as conductive agent and coal liquefying residue as binder. The biochar anode produced less oxygen than Pt anode, and the anode potential of biochar was 60–76% of that Pt anode. The application of biochar as sacrificial anode offers an industrial clean, scalable and sustainable idea to obtain green hydrogen.     

Investigation of multi-metal catalysts for stable hydrogen production via urea electrolysis

It has been shown that urea electrolysis is a viable method for wastewater remediation and simultaneous production of valuable hydrogen. Inexpensive nickel catalyst is optimal for the oxidation of urea in alkaline media but improvements are needed to minimize surface blockage and increase current density. Multi-metal catalysts were investigated by depositing platinum group metals on a nickel substrate. Rhodium and nickel proved synergistic to reduce surface blockage and increase catalyst stability. Rh-Ni electrodes reduced the overpotential for the electro-oxidation of urea and improved the current density by a factor of 200 compared to a Ni catalyst.     

Manipulating the hydrogen production from acetate in a microbial electrolysis cell-microbial fuel cell-coupled system

A biological hydrogen-producing system is configured through coupling an electricity-assisting microbial fuel cell (MFC) with a hydrogen-producing microbial electrolysis cell (MEC). The advantage of this biocatalyzed system is the in-situ utilization of the electric energy generated by an MFC for hydrogen production in an MEC without external power supply. In this study, it is demonstrated that the hydrogen production in such an MEC-MFC-coupled system can be manipulated through adjusting the power input on the MEC. The power input of the MEC is regulated by applying different loading resistors connected into the circuit in series. When the loading resistance changes from 10 Ω to 10 kΩ, the circuit current and volumetric hydrogen production rate varies in a range of 78 ± 12 to 9 ± 0 mA m⁻² and 2.9 ± 0.2 to 0.2 ± 0.0 mL L⁻¹ d⁻¹, respectively. The hydrogen recovery (RH₂), Coulombic efficiency (CE), and hydrogen yield (YH₂) decrease with the increase in loading resistance. Thereafter, in order to add power supply for hydrogen production in the MEC, additional one or two MFCs are introduced into this coupled system. When the MFCs are connected in series, the hydrogen production is significantly enhanced. In comparison, the parallel connection slightly reduces the hydrogen production. Connecting several MFCs in series is able to effectively increase power supply for hydrogen production, and has a potential to be used as a strategy to enhance hydrogen production in the MEC-MFC-coupled system from wastes.     

Optimization of NiMo catalyst for hydrogen production in microbial electrolysis cells

Non-platinum based cathodes were recently developed by electrodepositing NiMo on carbon cloth, which demonstrated good electrocatalytic activity for hydrogen evolution in microbial electrolysis cells (MECs). To further optimize the electrodeposition condition, the effects of electrolyte bath composition, applied current density, and duration of electrodeposition were systematically investigated in this study. The developed NiMo catalysts were characterized with scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) and evaluated using chronopotentiometry and in MECs. The optimal condition for electrodeposition of NiMo on carbon cloth was determined as: a Mo/Ni mass ratio of 0.65 in electrolyte bath, an applied current density of 50 mA/cm² and electrodeposition duration of 10 min. Under this condition, the NiMo catalyst has a formula of Ni₆MoO₃ with a nodular morphology. The NiMo loading on the carbon cloth was reduced to 1.7 mg/cm² and the performance of MEC with the developed NiMo cathode was comparable to that with Pt cathode with a similar loading. This result indicates that a much lower cathode fabrication cost can be achieved compared to that using Pt catalyst, and thereby significantly enhancing the economic feasibility of the MEC technology.     

Modelling of hydrogen production from hydrogen sulfide in geothermal power plants

Geothermal power plants emit high amount of hydrogen sulfide (H₂S). The presence of H₂S in the air, water, soils and vegetation is one of the main environmental concerns for geothermal fields. There is an increasing interest in developing suitable methods and technologies to produce hydrogen from H₂S as promising alternative solution for energy requirements. In the present study, the AMIS technology is the invention of a proprietary technology (AMIS^® - acronym for “Abatement of Mercury and Hydrogen Sulfide” in Italian language) for the abatement of hydrogen sulphide and mercury emission, is primarily employed to produce hydrogen from H₂S. A proton exchange membrane (PEM) electrolyzer operates at 150 °C with gaseous H₂S sulfur dimer in the anode compartment and hydrogen gas in the cathode compartment. Thermodynamic calculations of electrolysis process are made and parametric studies are undertaken by changing several parameters of the process. Also, energy and exergy efficiencies of the process are calculated as % 27.8 and % 57.1 at 150 °C inlet temperature of H₂S, respectively.     

Pt-WC/C as a cathode electrocatalyst for hydrogen production by methanol electrolysis

A novel tungsten carbide promoted Pt/C (Pt-WC/C) was prepared by an intermittent microwave heating (IMH) method and used for the cathode electrocatalyst in an electrolyser for hydrogen production by methanol electrolysis. The electrolyser showed better performance for hydrogen production using the Pt-WC/C cathode electrocatalyst than using a commercial Pt/C cathode electrocatalyst. The single cell electrolyser gave reasonable current at voltages lower than 0.4 V. The novelty of this technique is the inherent simplicity and substantially lowered cost.     

Heat management for hydrogen production by high temperature steam electrolysis

Many research and development projects throughout the world are devoted to sustainable hydrogen production processes. Low-temperature electrolysis, when consuming electricity produced without greenhouse gas emissions, is a sustainable process, though having limited efficiency.