Hydrogen production through solar energy water electrolysis

Various methods of making hydrogen from water have been proposed, but at the present time the only practical way to make hydrogen from water without fossil fuel is electrolysis. The development of a new, advanced, water electrolyser has become necessary for use in hydrogen energy systems and in electricity storage systems. All the new possible electrolysis processes, suitable for large-scale plants, are being analysed, in view of their combination with solar electricity source. A study of system interactions between large-scale photovoltaic plants, for electrical energy supply, and water electrolysis, is carried out. The subsystems examined include power conditioning, control and loads, as they are going to operate. Water electrolysis systems have no doubt been improved considerably and are expected to become the principal means to produce a large amount of hydrogen in the coming hydrogen economy age. Thus, the present paper treats the subject of hydrogen energy production from direct solar energy conversion facilities located on the earth's oceans and lakes. Electrolysis interface is shown to be conveniently adapted to direct solar energy conversion, depending on technical and economical feasibility aspects as they emerge from the research phases. The intrinsic requirement for relatively immense solar collection areas for large-scale central conversion facilities, with widely variable electricity charges, is given. The operation of electrolysis and photovoltaic array combination is verified at different insolation levels. Solar cell arrays and electrolysers are giving the expected results during continuously variable solar energy inputs. Future markets will turn more and more towards larger scale systems powering significantly bigger loads, ranging from hundreds of kW to several MW in size. Detailed design and close attention to subsystem engineering in the development of high performance, high efficiency photovoltaic power plants, are carried out. An overall design of a 50 MWp photovoltaic central station for electricity and hydrogen co-generation is finally discussed.     

Exploration of catalytically active materials for efficient electrochemical hydrogen and oxygen evolution reactions

Hydrogen, an efficient and clean energy source has the potential to power our energy systems of the future. Electrochemical water splitting as a hydrogen evolution source has acquired great interest in related research and technology. Noble metal-based electrode materials were previously utilized for water decomposition, but their low abundance and high cost have limited their practical applications. Recently, earth-abundant transition metal sulfides and phosphides/phosphates are employed as an electrode material in water electrolysis. These materials are emerging as promising electrode materials and are preferably integrated into electrochemical water splitting owing to their extremely stronger redox chemistry, permanence and incredible electronic conductivity. Therefore, a comprehensive report is highly desired to provide an overview of the current state of the field. Herein, we report the thermodynamics of both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) mechanisms that helps us to understand the water electrolysis in detail. Furthermore, the attractive transition metal sulfides, phosphates and phosphides-based electrode materials are discussed and presented in a detailed manner to summarize their performance for hydrogen and oxygen evolution water electrolysis.     

Electrocatalysts for the generation of hydrogen,oxygen and synthesis gas

Water electrolysis is the most promising method for efficient production of high purity hydrogen (and oxygen), while the required power input for the electrolysis process can be provided by renewable sources (e.g. solar or wind). The thus produced hydrogen can be used either directly as a fuel or as a reducing agent in chemical processes, such as in Fischer–Tropsch synthesis. Water splitting can be realized both at low temperatures (typically below 100 °C) and at high temperatures (steam water electrolysis at 500–1000 °C), while different ionic agents can be electrochemically transferred during the electrolysis process (OH⁻, H⁺, O²⁻). Singular requirements apply in each of the electrolysis technologies (alkaline, polymer electrolyte membrane and solid oxide electrolysis) for ensuring high electrocatalytic activity and long-term stability. The aim of the present article is to provide a brief overview on the effect of the nature and structure of the catalyst–electrode materials on the electrolyzer's performance. Past findings and recent progress in the development of efficient anode and cathode materials appropriate for large-scale water electrolysis are presented. The current trends, limitations and perspectives for future developments are summarized for the diverse electrolysis technologies of water splitting, while the case of CO₂/H₂O co-electrolysis (for synthesis gas production) is also discussed.     

Potential methods for geothermal-based hydrogen production

In this study, four potential methods are identified for geothermal-based hydrogen production, namely, (i) directly from the geothermal steam, (ii) through conventional water electrolysis using the electricity generated from geothermal power plant, (iii) using both geothermal heat and electricity for high temperature steam electrolysis and/or hybrid processes, (iv) using the heat available from geothermal resource in thermochemical processes to disassociate water into hydrogen and oxygen. Here we focus on relatively low-temperature thermochemical and hybrid cycles, due to their greater application possibility, and examine them as a potential option for hydrogen production using geothermal heat. We also present a brief thermodynamic analysis to assess their performance through energy and exergy efficiencies for comparison purposes. The results show that these cycles have good potential and become attractive due to the overall system efficiencies over 50%. The copper–chlorine cycle is identified as a highly promising cycle for geothermal hydrogen production. Furthermore, three types of industrial electrolysis methods, which are generally considered for hydrogen production currently, are also discussed and compared with the above mentioned cycles.     

Hydrogen production by methanol aqueous electrolysis using photovoltaic energy: Algerian potential

Hydrogen is considered as the most promising energy carrier for providing a clean, reliable and sustainable energy system. It can be produced from a diverse array of potential feed stocks including water, fossil fuels and organic matter. Electrolysis is the best option for producing hydrogen very quickly and conveniently. Water electrolysis as a source of hydrogen production has recently gained much attention since it can produce high purity hydrogen and can be compatible with renewable energies. Besides the water electrolysis, aqueous methanol electrolysis has been reported in several studies. The aqueous methanol electrolysis proceeds at much lower voltage than that with the water electrolysis. As a result of the substantially lower operating voltage, the energy efficiency for methanol electrolysis can be higher than that for water electrolysis. In this paper, we are interesting to methanol electrolysis in order to produce hydrogen. The relation linking hydrogen production rate to the power needed to electrolyse a unit volume of aqueous methanol solution has been determined. Using this relation, the potential of hydrogen from aqueous methanol solution using a PV solar as the energy system has been evaluated for different locations in Algeria.     

Water management in membrane electrolysis and options for advanced plants

The development of polymer electrolyte membrane electrolysis (PEMEL) is driven by increasing performance to decrease the costs of electrolysis systems. One option for increasing power density is decreasing the Ohmic losses within the cell. This can be enabled by using thinner membranes, although the disadvantage of thin membranes is their lower diffusion resistivity for water, hydrogen and oxygen what influences the efficiency and the operating conditions. In this paper the water transport and the Ohmic resistance of catalyst coated membranes with different thickness are analyzed. The disadvantage of high water permeability in thin membranes can be used to change the feed configuration in stacks and systems. It is possible to feed the electrolysis only from the cathode, which simplifies the mass transport (single phase) in the anode's porous transport layer and reducing stack and system dimensions, as well as costs.     

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.     

高浓重水电解过程中杂质氢的动态变化方程与计算方法

电解重水制氘是生产高纯氘的重要方法之一。而氘中氢(氕)含量是评价氘纯度的一个重要指标。因此，为了弄清高浓重水电解过程中杂质氢的变化行为，作者以电解反应与气、液相氢同位素交换反应平衡方程为基础，建立了杂质氢的动态方程。并结合工程应用实际，推导出间断定量加水电解过程中，氢杂质的计算公式、计算步骤以及各参数的计算方法。为研究重水电解及高纯氘的制取奠定了必要的理论基础。     

Hydrogen from solar energy,a clean energy carrier from a sustainable source of energy

Solar energy is going to play a crucial role in the future energy scenario of the world that conducts interests to solar-to-hydrogen as a means of achieving a clean energy carrier. Hydrogen is a sustainable energy carrier, capable of substituting fossil fuels and decreasing carbon dioxide (CO₂) emission to save the world from global warming. Hydrogen production from ubiquitous sustainable solar energy and an abundantly available water is an environmentally friendly solution for globally increasing energy demands and ensures long-term energy security. Among various solar hydrogen production routes, this study concentrates on solar thermolysis, solar thermal hydrogen via electrolysis, thermochemical water splitting, fossil fuels decarbonization, and photovoltaic-based hydrogen production with special focus on the concentrated photovoltaic (CPV) system. Energy management and thermodynamic analysis of CPV-based hydrogen production as the near-term sustainable option are developed. The capability of three electrolysis systems including alkaline water electrolysis (AWE), polymer electrolyte membrane electrolysis, and solid oxide electrolysis for coupling to solar systems for H₂ production is discussed. Since the cost of solar hydrogen has a very large range because of the various employed technologies, the challenges, pros and cons of the different methods, and the commercialization processes are also noticed. Among three electrolysis technologies considered for postulated solar hydrogen economy, AWE is found the most mature to integrate with the CPV system. Although substantial progresses have been made in solar hydrogen production technologies, the review indicates that these systems require further maturation to emulate the produced grid-based hydrogen.     

Performance evaluation of hydrogen production based on off-peak electric energy of the nuclear power plant

The article investigates the efficiency of commercial hydrogen production by water electrolysis on the base of NPP excess energy with its additional purification higher than 99.9999%, considering its transport. The competitive high purity hydrogen release price has been determined as compared to the market price. Besides, the use of high duty electrolysis plants has been suggested. Moreover, the advantages of water electrolysis cyclic operation while consuming electric energy from NPP as compared to the continuous mode have been presented in the paper.     

Hydrogen electrolyser technologies and their modelling for sustainable energy production: A comprehensive review and suggestions

The advancement of hydrogen technology is driven by factors such as climate change, population growth, and the depletion of fossil fuels. Rather than focusing on the controversy surrounding the environmental friendliness of hydrogen production, the primary goal of the hydrogen economy is to introduce hydrogen as an energy carrier alongside electricity. Water electrolysis is currently gaining popularity because of the rising demand for environmentally friendly hydrogen production. Water electrolysis provides a sustainable, eco-friendly, and high-purity technique to produce hydrogen. Hydrogen and oxygen produced by water electrolysis can be used directly for fuel cells and industrial purposes. The review is urgently needed to provide a comprehensive analysis of the current state of water electrolysis technology and its modelling using renewable energy sources. While individual methods have been well documented, there has not been a thorough investigation of these technologies. With the rising demand for environmentally friendly hydrogen production, the review will provide insights into the challenges and issues with electrolysis techniques, capital cost, water consumption, rare material utilization, electrolysis efficiency, environmental impact, and storage and security implications. The objective is to identify current control methods for efficiency improvement that can reduce costs, ensure demand, increase lifetime, and improve performance in a low-carbon energy system that can contribute to the provision of power, heat, industry, transportation, and energy storage. Issues and challenges with electrolysis techniques, capital cost, water consumption, rare material utilization, electrolysis efficiency, environmental impact, and storage and security implications have been discussed and analysed. The primary objective is to explicitly outline the present state of electrolysis technology and to provide a critical analysis of the modelling research that had been published in recent literatures. The outcome that emerges is one of qualified promise: hydrogen is well-established in particular areas, such as forklifts, and broader applications are imminent. This evaluation will bring more research improvements and a road map to aid in the commercialization of the water electrolyser for hydrogen production. All the insights revealed in this study will hopefully result in enhanced efforts in the direction of the development of advanced hydrogen electrolyser technologies towards clean, sustainable, and green energy.     

碳中和愿景下绿色制氢技术发展趋势及应用前景分析

围绕目前主流的绿色制氢技术,综述国内外“绿氢”技术的最新研究进展,重点阐述电解水制氢技术（碱性电解水法、质子交换膜电解水法、固体氧化物电解水法）、太阳能分解水制氢技术（光催化法、光热分解法、光电化学法）以及生物质制氢技术（热化学转化法、微生物法）的产氢原理、技术难点和改进方法等,讨论比较各类“绿氢”技术的优缺点,分析未来绿色制氢技术的应用前景和发展方向。     

Conceptual design of large scale water electrolysis plant using solid polymer electrolyte technology

In an energy conscious environment, the key to the applicability of water electrolysis as a means for generation of hydrogen in bulk quantities is the achievement of high efficiencies (i.e. over 90%) at high enough current densities to keep the capital costs within economic bounds. The solid polymer electrolyte (SPE) water electrolysis technology developed by the General Electric Company is now demonstrating these efficiencies at current densities up to 500 A ft⁻², and the results of recent laboratory testing show a potential for increasing this to 2000 A ft⁻² within the next 10 years. This capability now makes water electrolysis one of the most promising methods for generating hydrogen from nuclear, solar or other non-fossil fuel energy sources.

The performance and life test results are shown including laboratory cells on which future performance projections are based. The design and development status of a scaled-up electrolysis cell suitable for large-sized hydrogen generation plants is described. Estimated capital costs and operating costs are projected from which the resultant hydrogen costs are calculated.     

Proposal for a new system for simultaneous production of hydrogen and hydrogen peroxide by water electrolysis

Authors have proposed a new hydrogen production system that simultaneously produces hydrogen and hydrogen peroxide by water electrolysis. Experimental apparatus of the system is composed of a hydrogen electrode with platinum meshes, a hydrogen peroxide electrode with carbon material and an electrolyte with Nafion^®. In this paper, the superiority of the system is outlined, and the experimental results of the electrolytic synthesis of hydrogen and hydrogen peroxide from water are reported. Hydrogen peroxide is synthesized at the high efficiency when some kinds of carbon material are used as the hydrogen peroxide electrode. Furthermore, the possibility of applying the solar energy to this system is also discussed.     

Configuration design and performance optimum analysis of a solar-driven high temperature steam electrolysis system for hydrogen production

A new solar-driven high temperature steam electrolysis system for hydrogen production is presented, in which the main energy consumption processes such as steam electrolysis processes, heat transfer processes, and product compression processes are included. The detailed thermodynamic-electrochemical modeling of the solid oxide steam electrolysis (SOSE) is carried out, and consequently, the electrical and thermal energy required by every energy consumption process are determined. The efficiency of the system is derived, from which the effects of some of the important parameters such as the operating temperature, component thickness of the SOSE, leakage resistance, effectiveness of heat exchangers, and inlet rate of water on the performance of the system are discussed. It is found that the efficiency attains its maximum when a proper current density is chosen. The ratio of the required electric energy to the total energy input of the system is calculated, and consequently, the problem how to rationally operate the solar concentrating beam splitting device is investigated. The results obtained will be helpful for further understanding the optimal design and performance improvement of a practical solar-driven high temperature steam electrolysis system for hydrogen production.     

Recent progress on tungsten oxide-based materials for the hydrogen and oxygen evolution reactions

As a form of clean and renewable energy, hydrogen has received much attention recently. However, industrial hydrogen production is primarily via conversion of natural gas, which consumes a large amount of energy and emits large volumes of greenhouse gases. Electrochemical water electrolysis is a promising, pollution-free method for the production of hydrogen from water. Efficient, cost-effective, stable and abundant catalysts that can drive hydrogen production in water with minimal electrical bias are a major goal towards achieving electrolysis on a large scale. Recently, tungsten oxide-based materials have emerged as one of the most promising electrocatalytic compounds, due to their activity, low cost and durability in both acid and base conditions. There are often oxygen vacancies in metal oxides, whether intentional or not, which can potentially promote the water electrolysis. In this review, we provide an overview of tungsten oxide-based materials used for electrocatalytic water splitting. In addition, mechanisms to improve the electrocatalytic activities of oxygen vacant tungsten oxide are summarized and discussed, with proposals for future research. This review article will provide a valuable resource for scientists pursuing materials for electrochemical water splitting.     

Comparison of thermochemical,electrolytic, photoelectrolytic and photochemical solar-to-hydrogen production technologies

Hydrogen produced from solar energy is one of the most promising solar energy technologies that can significantly contribute to a sustainable energy supply in the future. This paper discusses the unique advantages of using solar energy over other forms of energy to produce hydrogen. Then it examines the latest research and development progress of various solar-to-hydrogen production technologies based on thermal, electrical, and photon energy. Comparisons are made to include water splitting methods, solar energy forms, energy efficiency, basic components needed by the processes, and engineering systems, among others. The definitions of overall solar-to-hydrogen production efficiencies and the categorization criteria for various methods are examined and discussed. The examined methods include thermochemical water splitting, water electrolysis, photoelectrochemical, and photochemical methods, among others. It is concluded that large production scales are more suitable for thermochemical cycles in order to minimize the energy losses caused by high temperature requirements or multiple chemical reactions and auxiliary processes. Water electrolysis powered by solar generated electricity is currently more mature than other technologies. The solar-to-electricity conversion efficiency is the main limitation in the improvement of the overall hydrogen production efficiency. By comparison, solar powered electrolysis, photoelectrochemical and photochemical technologies can be more advantageous for hydrogen fueling stations because fewer processes are needed, external power sources can be avoided, and extra hydrogen distribution systems can be avoided as well. The narrow wavelength ranges of photosensitive materials limit the efficiencies of solar photovoltaic panels, photoelectrodes, and photocatalysts, hence limit the solar-to-hydrogen efficiencies of solar based water electrolysis, photoelectrochemical and photochemical technologies. Extension of the working wavelength of the materials is an important future research direction to improve the solar-to-hydrogen efficiency.     

Valuation and development of the solar hydrogen production

This article considers Algeria as a case study for the evaluation of the solar hydrogen production potential. The study relates to the design of a hydrogen generating station by water electrolysis whose energy resources are solar. The electricity supply is done by a solar tower power plant. The numerical simulation of the hydrogen production for the installation proposed is made while being based on the characteristic equations governing the electrolysis of water, hydraulic pumping system and the solar tower. The hydrogen production rate is given for various values of the solar radiation and several sites of Algeria. The results obtained by the established computer code, and of which the required goal is the determination of the most favorable conditions for a better production of hydrogen, are presented and discussed.     

Comparative study of anion exchange membranes for low-cost water electrolysis

Various anion-exchange membranes (AEMs) were studied in the electrolysis cell using the non-precious metal-based catalysts showing the good potential of selected AEMs in low-cost water electrolysis application. The 0.1–1 M potassium hydroxide electrolyte is applied for high performance electrolysis process, whereas the usage of pure water leads to the significant AEM resistance increase. The post mortem MEA analysis, using SEM is performed to study the structure and morphology of catalyst layers transferred from the electrodes prepared by catalyst coated substrate approach. The importance of the catalyst layer–membrane interface and the binder used to bond the catalyst layer is discussed. AEM electrolysis safety aspect in terms of the hydrogen crossover through the 28 μm thin A-201 membrane is studied. The linear dependency of the permeated hydrogen flux on current density is shown. Hydrogen content in the anode outlet gas is less enough to ensure high safety of the AEM electrolysis technology in the operating currents range.     

A techno-economic appraisal of hydrogen generation and the case for solid oxide electrolyser cells

There is significant interest in alternatives to fossil fuels in order to reduce carbon dioxide emissions. One option is the use of hydrogen in applications such as fuel cells. There are various routes to the production of hydrogen, one being via the electrolysis of water. Water electrolysers are already operational within industry on a small-scale, accounting for 4% of world hydrogen production. These electrolysers operate at low temperatures and require electrical power input that has been shown to be costly due to the limited efficiency of the electrolysis process. However, the use of high temperature solid oxide electrolyser cells (SOECs) has the potential to generate hydrogen with a higher electrical efficiency which may allow electrolysis to become cost competitive with steam methane reforming (SMR), depending on where the heat and electrical power to service the SOEC comes from.This paper examines the various routes to hydrogen production and, in particular electrolysis technologies. The cost of hydrogen production is examined in the context of the source of the electricity and the efficiency of the electrolysis process compared to SMR generation. It is found that to become cost competitive with SMR, the lowest cost electricity is required, sourced either from nuclear or combined cycle gas turbine plants with electrolysis efficiency as high as possible, meaning that SOEC technology is particularly attractive.