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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

On the production of hydrogen via alkaline electrolysis during off-peak periods

This article studies the opportunity for producing hydrogen via alkaline electrolysis from electricity consumption during off-peak periods. Two aspects will be discussed: electricity spot markets and nuclear electricity production in France.

From a market point of view, when there is a significant fluctuation in electricity prices, the use of an electrolysis installation during off-peak periods makes it possible to make quite considerable savings in production costs. Savings vary enormously from one market to the next; some highly fluctuating markets offer very low off-peak prices and allow for viable hydrogen production, even if average electricity prices first appear to be quite high. Very fluctuating spot prices market may be difficult to predict and makes operations of an electrolysis installation more complicated and risky. For other more stable markets, the use of an electrolysis installation during off-peak periods does not appear to be a relevant proposition.

From the point of view of French electricity production, the availability of current nuclear power plants and the estimation of available energy for mass production of hydrogen show that the installations studied would not be viable. For “peak period” use, it would certainly be more useful to have electrolysers with a lower investment proportion, even if this means slightly higher operating costs. Research into large-capacity electrolysers should, therefore, both develop low-production-cost electrolysers, for use in base load mode where dedicated production means are concerned, and highly flexible electrolysers, with low investment costs, which could easily be viable with low rates of use.     

Two-dimensional simulation and critical efficiency analysis of high-temperature steam electrolysis system for hydrogen production

High-temperature steam electrolysis (HTSE) is a promising method for highly efficient large-scale hydrogen production. The HTSE process not only reduces the amount of thermodynamic electrical energy requirement but also decreases the polarization losses, which improves the overall efficiency of hydrogen production.In this paper, a two-dimensional simulation method of the efficiency of the HTSE system integrated with high-temperature gas-cooled nuclear reactor (HTGR), which changes two parameters simultaneously in a reasonable range while keeping one parameter constant, was presented. Compared with one-dimensional analysis method, the effects of electrical efficiency (η_el), electrolysis efficiency (η_es,), and thermal efficiency (η_th) on overall efficiency (η_overall) were investigated more objectively and accurately. Moreover, the critical concepts of η_es and η_th were put forward originally, which were very important to determine the optimum electrolysis voltages and operation temperatures in the actual HTSE processes. The calculated critical value of η_es was ΔG(T)/ΔH(T) and the actual η_es should be higher than the theoretically calculated one in order to maintain the high hydrogen production efficiency of HTSE system. Also, it was very interesting to find that the critical η_es was the theoretical maximum efficiency in SOFC mode. Furthermore, the critical value of η_th was equal to the value of η_el, which means the overall efficiency decreases with the η_es increasing if the η_th in the actual HTSE process is less than the critical value of η_th. Therefore, it is very important to control the η_th higher than the critical value in the actual HTSE process to get high overall system efficiency.     

Intermetallics as advanced cathode materials in hydrogen production via electrolysis

Intermetallics phases along Mo–Pt phase diagram have been investigated as cathode materials for the production of hydrogen by electrolysis from water KOH solutions, in an attempt to increase the electrolytic process efficiency. These materials were compared with conventional cathodes (Fe and Ni), often used in the alkaline electrolysis, and also with the intermetallic Ti–Pt. An significant upgrade of the electrolytic efficiency using intermetallics in pure KOH electrolyte was achieved in comparison with conventional cathode materials.     

Viability analysis of centralized hydrogen generation plant for use in mobility sector

Nowadays, the use of renewable energy sources is one of the keys to achieve the sustainable development of societies. The intensive use of fossil fuels has caused effects in the environment and the human health. Greenhouse gas emissions and the carcinogenic effect of diesel are widely demonstrated. The production of clean energy based on renewable sources and the use of hydrogen as an energy vector in general and as an alternative fuel in particular represent a technically feasible reality. However, it is necessary to study the economic variables of centralized or distributed production of hydrogen as an alternative fuel. The aim of this paper is to analyze the technical and economic viability of a centralized generation hydrogen plant for mobility use. It was performed a sensitivity analysis of main parameters such as size of hydrogen production plant, operating hours of the plant, investment costs of the main equipment and electricity price. A NPV of 1,272,692 and a 9-year pay-back were obtained for a centralized hydrogen production plant of 2 MW, considering commercial values of the main evaluation parameters. The sensitivity analysis determines that the main variables affecting the NPV are the price of electricity and the operating hours of the plant. With 95% of confidence, the NPV will be positive with an 80.19% of certainty. Therefore, centralized hydrogen production represents a technically viable, environmentally friendly and economically attractive process that can rapidly position hydrogen as an alternative fuel for mobility.     

Evaluation and calculation on the efficiency of a water electrolysis system for hydrogen production

With the help of the typical model of a water electrolysis hydrogen production system, which mainly includes the electrolysis cell, separator, and heat exchangers, three expressions of the system efficiency in literature are compared and evaluated, from which one reasonable expression of the efficiency is chosen and directly used to analyze the performance of a water electrolysis hydrogen production system under different operation conditions. Several new configurations of a water electrolysis system are put forward and the problem how to calculate the efficiencies of these configurations is solved. Moreover, a solid oxide steam electrolyzer system (SOSES) for hydrogen production is taken as an example to expound that the different configurations of a water electrolysis system should be adopted for different operation conditions. The results obtained here may provide some guidance for the optimum design and operation of water electrolysis systems for hydrogen production.     

One-dimensional dynamic modeling of a high-pressure water electrolysis system for hydrogen production

Research on high-pressure water electrolyzers is under way worldwide as the economic production of hydrogen from renewable energy sources becomes more important. With increases in operating pressures, new safety issues have emerged, for which a reliable dynamic model of the electrolyzers is important for predicting their behavior. In this paper, a one-dimensional dynamic model of a high-pressure proton exchange membrane water electrolyzer is proposed. The model integrates various important physico-chemical phenomena inside the electrochemical cell that have been investigated individually into a dynamic model framework. Water transport, gas permeation, gas volume variation in anode/cathode channels, gas compressibility, and water vaporization are considered to formulate the model. Numerical procedures to handle and solve the model and the model performance for the prediction of steady and dynamic state behaviors are also presented.     

On-board hydrogen storage and production: An application of ammonia electrolysis

On-board hydrogen storage and production via ammonia electrolysis was evaluated to determine whether the process was feasible using galvanostatic studies between an ammonia electrolytic cell (AEC) and a breathable proton exchange membrane fuel cell (PEMFC). Hydrogen-dense liquid ammonia stored at ambient temperature and pressure is an excellent source for hydrogen storage. This hydrogen is released from ammonia through electrolysis, which theoretically consumes 95% less energy than water electrolysis; 1.55 Wh g⁻¹ H₂ is required for ammonia electrolysis and 33 Wh g⁻¹ H₂ for water electrolysis. An ammonia electrolytic cell (AEC), comprised of carbon fiber paper (CFP) electrodes supported by Ti foil and deposited with Pt-Ir, was designed and constructed for electrolyzing an alkaline ammonia solution. Hydrogen from the cathode compartment of the AEC was fed to a polymer exchange membrane fuel cell (PEMFC). In terms of electric energy, input to the AEC was less than the output from the PEMFC yielding net electrical energies as high as 9.7 ± 1.1 Wh g⁻¹ H₂ while maintaining H₂ production equivalent to consumption.     

The exploitation of hydrogen sulfide for hydrogen production in geothermal areas

Hydrogen is a valuable energy resource and it is widespread in nature. As a matter of fact, researches on hydrogen production are currently experiencing an increasing interest from scientists around the world since this resource is clean and renewable. Several methods of producing hydrogen have been developed in industrialized countries such as the United States of America and Germany.This paper is interested in the process by which hydrogen sulfide of geothermal areas is exploited for hydrogen production. In fact, research advances in this field have concluded that hydrogen sulfide of geothermal resources can contribute significantly and economically in the process of hydrogen generation.The present paper was principally conducted from a literature study and a synthesis of works achieved in recent years in order to highlight the various aspects of hydrogen production from hydrogen sulfide and particularly to study the possibility of the exploitation of Algeria’s thermal resources in this field.