As more and more industries and governments invest in projects to achieve this goal, the potential for hydrogen energy to play an important role in the global search for clean and safe energy is increasing. Out of concerns about climate change, investors and policy makers are pushing for aggressive carbon emissions reductions. Although hydrogen has received attention as a clean energy in the past, the current momentum driven by decarbonization goals and improved technology shows greater hope for realizing its potential.
As a fuel, hydrogen has the advantage of not producing carbon dioxide when burned. However, most of the world's hydrogen supply is currently produced from fossil fuels, and it is mainly used industrially in the petroleum refining and fertilizer industries. According to the International Energy Agency (IEA; The Future of Hydrogen: Seizing Today’s Opportunities, June 2019, www.iea.org), hydrogen production generates approximately 830 million metric tons of carbon dioxide emissions each year. However, there has been a surge in projects to produce "green" hydrogen from water through electrolysis.
The hydrogen produced by water electrolysis only produces hydrogen and oxygen, so it does not cause greenhouse gas emissions. Renewable energy sources such as wind and solar energy can be used to produce hydrogen, making it an attractive option for storing variable output from these sources. According to the International Energy Agency’s report, “it’s time to harness the potential of hydrogen to play a key role in a clean, safe and affordable energy future”.
The following two articles discuss some of the activities centered on promoting the production and industrial use of "green" hydrogen as a next-generation fuel. The first article focuses on electrolysis cell technology, while the second article briefly introduces activities such as hydrogen production and its application in transportation.
-Dorothy Lozowski, Editorial Director of Chemical Engineering and Power
Figure 1. Electrolyzer manufacturers are expanding production capacity to meet growing global demand
Figure 1. Electrolyzer manufacturers are expanding production capacity to meet growing global demand
Technological and economic advancements have brought hydrogen to the forefront of sustainable development strategies in many industries, and end users hope to take advantage of the promise of significantly reducing or completely eliminating carbon dioxide emissions.
Most of the activity surrounding hydrogen today involves electrolyzers, which are modular processing units in which electrical current is applied to break water molecules into hydrogen and oxygen. When powered by renewable energy sources such as wind or solar energy, the electrolyzer produces no-emission or "green" H2.
In recent years, the output of electrolyzers has increased significantly to meet the global demand for green H2. In June 2020, thyssenkrupp Industrial Solutions AG (Essen, Germany; www.thyssenkrupp-industrial-solutions.com) cooperated with De Nora SpA (Milan, Italy; www.denora.com) to expand the manufacturing capacity of electrolyzer devices (Figure 1). "We are now able to build an electrolysis plant with an annual capacity of 1 GW, and we will further expand our capacity," explains Christoph Noeres, head of energy storage and hydrogen at ThyssenKrupp. These electrolyzers are provided in the form of prefabricated skid-mounted modules (Figure 2), which can be combined to easily expand production capacity. Noeres said that expanding the capacity of the electrolyzer will help realize an economically promising value chain, not only for the large-scale production of green H2, but also for the subsequent production of sustainable chemicals such as ammonia and methanol. "Green H2 will play a central role in achieving greenhouse gas neutralization and building a closed-loop economy," Noeres added. Recently, ThyssenKrupp has focused its development projects on areas with favorable conditions for Power-to-x applications. Earlier this year, the company announced that its electrolysis plant will be able to connect to the German electricity market through E.ON's virtual power plant, effectively acting as a large-scale buffer for stabilizing the grid. For this ambitious milestone, electrolyzers must meet several eligibility criteria for load changes detailed in the grid specifications of transmission operators, proving that they have sufficient response speed and flexibility to participate in the energy balance market.
There are two main types of electrolysis cells on the market-alkaline and proton exchange membrane (PEM). Other emerging electrolysis technologies that are still mainly in the development stage include anion exchange membranes (AEM), solid oxide electrolyzers (SOEC), and photoelectrochemical (PEC) water splitting. In an alkaline electrolytic cell, in the presence of an alkaline electrolyte solution (usually potassium hydroxide (KOH)), water is broken down into its components. The water splitting reaction in the PEM electrolyzer collects its electrolyte from the catalyst applied to the polymer membrane.
Alkaline electrolysis is a more mature technology. Alkaline electrolysis cells are generally more affordable, but PEM electrolysis cells bring some added value through faster response to power changes. In addition, PEM is generally regarded as a safer option because the membrane provides a physical barrier between the H2 and O2 produced.
Figure 2. Their modular nature makes electrolyzers suitable for large and small installations
Figure 2. Their modular nature makes electrolyzers suitable for large and small installations
David Bow, senior vice president of corporate business development and strategy, said that although electrolyzers are not new, recent development work and industry trends have made them compared to the traditional method of producing hydrogen from natural gas through steam-methane reforming (SMR). More attractive, Nel Hydrogen (Wallingford, Connecticut; www.nelhydrogen.com). "In the past 2 to 3 years, the capital cost of the electrolyzer industry has decreased by 75%, mainly due to market demand for larger systems and innovations in system design and manufacturing," Bao explained. The popularization of low-cost renewable energy is also a huge driving force, and it also brings pressure to achieve sustainable development goals for enterprises and governments. "SMR produces 10 to 12 tons of carbon dioxide for every ton of hydrogen produced. Now, low-cost renewable electricity can be provided to produce green H2 with zero carbon dioxide emissions," Bow said. One of the main goals of electrolyzer suppliers is to achieve "fossil parity"-this means that electrolyzers can produce green H2 at the same price as using SMR and natural gas ("ash" hydrogen).
Figure 4. AEM electrolyzer is ready to combine the advantages of alkaline electrolyzer and PEM electrolyzer, which is currently the dominant technology on the market
Figure 4. AEM electrolyzer is ready to combine the advantages of alkaline electrolyzer and PEM electrolyzer, which is currently the dominant technology on the market
After achieving considerable cost reductions, Nel now focuses more development efforts on improving the efficiency and performance of electrolyzers, including reducing the content of precious metals (such as platinum and iridium) in PEM catalysts, and alkaline system electrode technology improvement.
When comparing the economics of SMR and electrolyzers, geographic location is an important factor. In some areas, the natural gas feedstock for the SMR device is scarce and natural gas needs to be transported; or H2 transported in a tube trailer or in a liquid form in a tanker truck, which is very inefficient and CO2 intensive. "Because H2 is such a light molecule, a full tube trailer can only carry about 350 kg. In addition, storing hydrogen in liquid form will cause considerable losses because it will be discharged with temperature changes. "Bow explained. This makes on-site H2 generation a more attractive proposal for major hydrogen consumers, such as ammonia plants, methanol plants, and refineries.
Although SMR is the dominant technology so far, many chemical processing sites are turning to electrolyzers to help increase SMR capacity and increase plant flexibility, because electrolyzers can operate efficiently at large turndown ratios and are easy to expand. Bow cited an example. A large chemical manufacturer purchased H2 from a nearby SMR unit and found that their demand exceeded the capacity of the SMR. "They considered buying another SMR unit, rather than transitioning to an electrolyzer or transporting liquid H2 in a tanker truck, and found that series electrolyzers provide higher efficiency at a lower cost," Bow said.
Nel has conducted various pilot tests for different H2 applications to help the site transition from gray H2 to green H2. "Many (if not all) major ammonia producers are considering some degree of electrolysis testing. We have a wind energy ammonia project in Minnesota that has been in operation for several years, and there are more projects in the pipeline. We Many large alkaline electrolyzers for the production of ethylene and sugar alcohols are also sold, and both processes consume large amounts of H2 in the process," Bow said.
Nel Hydrogen is the Hydrogen and Fuel Cell Technology Office (HFTO) of the United States Department of Energy (DOE; Washington, DC; www.doe.gov) through the Office of Energy Efficiency and Renewable Energy (EERE). In July, 18 projects to support H2@Scale's goal of advancing the hydrogen economy in the United States received US$64 million in funding. Nearly US$15 million in the latest round of financing was used for a project specifically aimed at manufacturing electrolytic cells. "One of the advantages of electrolyzers is that they are suitable for intermittent renewable energy sources such as wind and solar energy. HFTO Director Sunita Satyapal explained that electrolyzers are not used to cut electricity, but to produce hydrogen for energy storage or other value-added end uses. Applications, such as manufacturing chemicals or steel.
For electrolyzers, H2@Scale's main goals include improving efficiency and durability, while reducing overall costs. With the advancement of electrolyzer technology, Satyapal pointed to a trend towards more comprehensive and collaborative development projects. "Most of the current work is not focusing on specific components, such as catalysts or membranes, but on the integration of materials and manufacturing processes, and how we can integrate them into large-scale manufacturing," she said. "An example of a unique area that we have been funding is quality control methods. Ideally, if we are to upgrade the electrolyzer to the gigawatt level, the components will not be manufactured in batches, so we are looking for higher throughput High-volume continuous processes, such as roll-to-roll and high-speed inspection of large-area components to find defects that may affect durability." Other major development areas include: membrane coating technology and simplified membrane manufacturing; optimization of porous transport layers; and reduction of precious metals content. In addition, H2@Scale is carrying out two first-of-its-kind nuclear hydrogen production projects in the United States
H2@Scale focuses on a variety of hydrogen production, storage, distribution, and utilization requirements, including PEM electrolyzers. These requirements are becoming more and more popular in the market, but there is still the potential to significantly reduce costs. Satyapal said that water quality is another emerging research area for the project. "We have some early projects researching the ability to use dirty water or salt water instead of requiring high-purity water for electrolysis," she added. "We also have a pioneering project in the United States. We are using electrolyzers to produce H2, and using biological systems to produce renewable methane from H2 and CO2," Satyapal said.
Synergy with natural gas is another area of great significance, especially in mixing hydrogen and natural gas, it is possible to inject hydrogen into natural gas pipelines. However, for H2 mixing, material compatibility may be a major issue, depending on the materials used, and many research activities involve the effect of hydrogen on embrittlement and its effect on metals and polymers, just like DOE’s H-Mat The consortium resolved it.
An important milestone for the H2 mix occurred in July 2020, when Baker Hughes (Houston; www.bakerhughes.com) and Snam (San Donato Milan, Italy; www.snam.it) completed the world’s first " The test of "hybrid" hydrogen turbines is designed for natural gas networks, with the ultimate goal of injecting H2 and natural gas into Snam's current transmission infrastructure.
Figure 3. These compact electrolyzer units are designed to be installed in challenging locations, such as the head of a wind turbine, to achieve streamlined energy storage
Figure 3. These compact electrolyzer units are designed to be installed in challenging locations, such as the head of a wind turbine, to achieve streamlined energy storage
Hoeller Electrolyzer GmbH (Wismar, Germany; www.hoeller-electrolyzer.com) has developed an optimized battery surface technology for compact PEM electrolyzers (Figure 3), which reduces the amount of precious metals required and increases working pressure. Hoeller considered demanding installations when designing the PEM battery stack, such as integrating the battery stack directly into the head of the wind turbine. "The main advantage of PEM electrolysis is that the output of H2 almost changes with the energy provided, so the process with changing H2 requirements is an ideal match," said Matthias Kramer, Hoeller's Chief Financial Officer. According to Hoeller, its stack can handle load changes from 0 to 100% of the nominal load in a few seconds. Although PEM has versatility in the face of changing needs, Kramer also emphasizes its ability to operate continuously. In addition, the stack can be pressurized to 50 bar or higher, making direct storage more convenient. Hoeller’s proprietary PEM technology was demonstrated in the proof-of-concept of the Fraunhofer Institute for Solar Energy Systems (ISE; Freiburg im Breisgau, Germany; www.ise.fraunhofer.de). Kramer stated that the company hopes to install a prototype by the end of 2020. The pilot project of the new PEM reactor for the Schleswig-Holstein wind farm in Germany will be discussed.
Figure 5. Molecular sieve device can be installed downstream of the electrolytic cell for dehydration
Figure 5. Molecular sieve device can be installed downstream of the electrolytic cell for dehydration
An emerging technology for hydrogen production is anion exchange membrane (AEM) electrolysis (Figure 4). Oliver Conradi, who specializes in membrane research at Evonik Industries AG (Essen, Germany; www.evonik.com), explained that AEM is to some extent a hybrid solution that combines the advantages of PEM and traditional diaphragm alkaline electrolysis. "Alkaline electrolysis obviously involves very alkaline conditions, while PEM involves an acidic environment. These respective pH values require certain materials. Under alkaline conditions, you can use cheaper materials such as stainless steel and nickel, while for PEM , You must use platinum or other precious metals as catalysts, and electrochemical cells must be based on titanium, so the investment cost of PEM is much higher,” Conrad explained. However, the PEM system overcomes some basic limitations of traditional alkaline electrolysis-due to the specific electrolytic cell design in the alkaline system, the current density and efficiency are limited, and the alkaline system is more difficult to pressurize, which means that an additional compression step is usually need. "In the PEM device, the dense membrane makes the entire system easier to pressurize. With AEM, you can fundamentally combine the advantages of the two most advanced technologies while making up for their shortcomings," Conrad said, noting that the development is effective The main obstacle of the AEM system is the development of suitable polymer membrane materials that can withstand alkaline conditions.
One area of particular concern is the cation part, which is responsible for transporting hydroxide ions from the cathode to the anode. In addition to stability in alkaline environments, polymers must also provide high ionic conductivity and stability under pressurized electrolytic cell conditions. Inspired by existing gas separation membrane technology, Evonik has developed a new polymer chemistry with a proprietary ion-conducting cationic part. As part of the Channel consortium focused on AEM, Evonik is expanding the production of polymers and expanding film manufacturing on the pilot coating line. "The consortium is building an AEM electrolyzer to prove that membranes and other components work under challenging conditions," Conrad explained. The team’s first AEM demonstrator unit is on a laboratory scale and is running a test protocol to reflect real-world conditions. "The next milestone will be to prove the reliability of the system and expand the stack size, while expanding the membrane handling," he continued.
Although electrolyzers have made considerable progress in terms of efficiency and cost, the H2 produced still often requires post-processing steps such as compression, dehydration, or purification. "Electrolysis reactors usually do not produce hydrogen that is directly suitable for use. If you want to store, distribute, or use the generated hydrogen, you need to remove contaminants," Frames Group (Alfing Arndenlein, Netherlands; www.frames-group .com) said Jordi Zonneveld, hydrogen product portfolio manager. "Because the PEM technology only uses ultrapure water, the only pollutant is water, and there may be a very small amount of oxygen. Alkaline electrolysis uses KOH solution as the process fluid, so it is also necessary to remove the trace KOH in the generated hydrogen."
Depending on the gas flow and purity requirements, preparing hydrogen for end-use applications may require several steps. For example, Zonneveld said, separator tanks with defogging internals and optional gas cooling equipment are often used as the first step to increase hydrogen purity to 99.9%. Then, if higher purity is required, a molecular sieve device may be required (Figure 5). He also mentioned that dehydration using triethylene glycol (a common technology for natural gas processing) has shown the potential to purify hydrogen, but there has not yet been any large-scale hydrogen application.
The compression of H2 also brings unique challenges. Stefanie Peters, managing partner of Neuman & Esser Group (NEA; Übach) said: “H2 has a very high energy density per unit mass, but a very low density. Therefore, a compressor is required downstream of the electrolyzer to compress H2 for efficient storage and transportation. -Palenberg, Germany; www.neuman-esser.de). The low molecular weight of H2 also poses a problem. "The turbomachinery faces major problems in capturing H2 in the compression chamber. Only positive displacement machines such as pistons and diaphragm compressors It is suitable for effective compression to the required H2 discharge pressure," Peters added. For example, a dry-running piston compressor can achieve a discharge pressure of up to 300 bar. With a lubricated cylinder, the discharge pressure may be as high as 700 bar, but This option introduces a small amount of oil pollution, so oil-free diaphragm compressors are the preferred high-pressure option when no pollution is acceptable, because they can reach discharge pressures above 5,000 bar.
As the demand for electrolyzers and green H2 continues to grow, technological improvements, not only in the electrolyzer itself, but also in post-processing, will continue to be an important area of R&D work.
According to the International Energy Agency (IEA; Paris, France; www.iea.org) on the occasion of the G20 Energy and Environment Ministers Meeting held in Karuizawa, Japan from June 15 to 16, 2019.
"Clean hydrogen is currently receiving strong support from governments and companies around the world, and the number of policies and projects is increasing rapidly," the study said. The study titled "The Future of Hydrogen: Seize Today’s Opportunities" initiated by Fatih Birol, Executive Director of the International Energy Agency and Hirsunari Seko, Minister of Economy, Trade and Industry of Japan, stated that hydrogen provides a wide range of industries. Methods of decarbonization include chemical manufacturing and iron and steel production, which can be converted into fuel for cars, trucks, trains, ships, and airplanes.
"The world should not miss this unique opportunity to make hydrogen an important part of our clean and safe energy future," Birol said.
However, some people believe that H2 fuel cells will never be widely used, because compared with batteries such as lithium ion batteries (LIB), H2 fuel cells have high cost, low efficiency, and it takes a long time to overcome technical difficulties. The issues involved. Nevertheless, people are still trying to improve the technology and economics of hydrogen-based economy.
As a fuel system for cars, buses, trains, etc., hydrogen is stored in storage tanks in vehicles. H2 is sent to the fuel cell, which generates electricity for the electric motor that drives the vehicle. Unlike fossil fuels, hydrogen combustion does not produce carbon dioxide or other pollutants—just water vapor. As far as automotive fuel systems are concerned, the main competitor of H2 fuel cells is LIB. Today, most electric vehicles use batteries, usually based on lithium ion or lead acid chemistry. Each individual fuel cell generates low current and voltage, and like LIB, the batteries need to be stacked together to reach the target voltage and maximum current required by the vehicle. One of the advantages of H2 for fuel cells is that its energy-to-weight ratio (specific energy) is much greater than that of LIB. The specific energy of LIBs is 0.36～0.875 MJ/kg, and the specific energy of hydrogen is 120～142 MJ/kg. Therefore, the H2 in the fuel cell allows a greater range while being lighter and smaller. Another major advantage of H2 fuel cells is that they can be charged within minutes. In contrast, the full charging time of LIB electric vehicles is usually measured in hours. However, H2 also brings serious shortcomings. One of them is that it combines well with other elements, so it must be isolated through an expensive and energy-consuming process before it can be used as a fuel. In addition, storing hydrogen is expensive and energy consuming, whether it is stored in gaseous form at high pressures or in liquid form at low temperatures. H2 is also highly flammable, difficult, dangerous and expensive to produce, store and transport. Despite the problems with H2 fuel cells, and despite the negative predictions made by some experts, there are still a large number of projects in progress around the world, and a large amount of research and development funds are being invested in H2 fuel cells. There are already many vehicles using hydrogen fuel cells, including cars, buses, and trains, although they have not yet gained widespread market acceptance. According to the International Energy Agency, there are currently approximately 11,200 H2-powered cars on the roads of the world. The oldest hydrogen-powered cars commercially available in certain markets are: Toyota Mirai, Hyundai Nexo and Honda Clarity. In 2013, Hyundai Tucson Fuel Cell Electric Vehicle (FCEV) was the world's first H2 FCEV to be mass-produced commercially. It has a range of nearly 600 kilometers. Hyundai Nexo (Figure 1) achieved success in 2018. Toyota launched Mirai at the end of 2014. Its cruising range is about 500 kilometers, and it takes about 5 minutes to fill the H2 tank. Although many car companies have launched a limited number of demonstration models, many of them have turned to pure electric vehicles. At the end of last year, the world's first passenger train powered by H2 fuel cells started operating in Germany (Figure 2). It is called Coradia iLint and was developed by Alstom (Paris, France; www. alstom.com). The maximum speed of the train can reach 140 km/h.
Figure 1. Hyundai Nexo is one of the latest hydrogen fuel vehicles
Figure 1. Hyundai Nexo is one of the latest hydrogen fuel vehicles
Figure 2. The world's first hydrogen-fueled passenger train started operation in Lower Saxony, Germany in September last year
Figure 2. The world's first hydrogen-fueled passenger train started operation in Lower Saxony, Germany in September last year
Figure 3. Based on mature technology in the chlor-alkali industry, the water electrolysis system can be scaled up to 10 MW
Figure 3. Based on mature technology in the chlor-alkali industry, the water electrolysis system can be scaled up to 10 MW
At present, almost all H2 in the world is supplied by fossil raw materials in the process of CO2 emission, unless the CO2 is fully captured and stored. Clean hydrogen production is achieved by electrolyzing water using electricity derived from renewable energy sources such as solar and wind energy. However, currently only about 5% of the hydrogen in the world is produced through water splitting. The process in a fuel cell is basically the opposite of the electrolysis process that produces H2 from water.
Recently, thyssenkrupp AG (Essen, Germany; www.thyssenkrupp.com; Figure 3) and Siemens AG (Erlangen, Germany; www.siemens.com) have developed a new type of large-scale electrolyzer to realize H2 (Chem. Eng. , January 2019, pages 14-17).
Siemens’ electrolyzer was initially capable of converting kilowatt-level renewable energy into clean hydrogen, and now the company is building larger-scale equipment. Siemens will soon deliver a 1.25 MW unit to the Townsley Innovation District in South Australia. It also provides a device that can be expanded to 10 MW, and plans to further expand by another order of magnitude.
The world's largest solar green hydrogen power plant is planned to be built in the Burrup Peninsula of Western Australia during the Yala Pilbara era. The fuel cell microgrid demonstration project will be operated by the company in the Boston area. Recently, the company developed what is said to be the world's first integrated H2 tanker.
In October last year, a Japanese consortium started the construction of the Fukushima Hydrogen Energy Research Field (FH2R; Chem. Eng., October 2018, p. 10). FH2R will produce (using renewable energy) and store up to 900 tons/year of H2. A new type of control system will be adopted to coordinate the overall operation of the hydrogen energy system, grid control system and hydrogen demand forecasting system to optimize hydrogen production, hydrogen power generation and hydrogen supply.
The system will use H2 to offset the grid load and deliver H2 to the Northeast and other regions, and will seek to demonstrate the advantages of H2 as a grid balancing solution and as a H2 gas supply. The compressed hydrogen will be transported in trailers and provided to users.
The U.S. Department of Energy (DOE; Washington, DC; www.energy.gov) hydrogen and fuel cell plans to conduct research and development in H2 production, transportation, storage, and fuel cells. Its technical goals are: biomass-derived liquid reforming, electrolysis, biomass gasification, thermochemical water splitting, photoelectrochemical water splitting, photobiological processes and microbial biomass conversion. At the same time, a water purification plant in Sendai, Miyagi Prefecture, Japan is conducting research to incorporate H2 into the renewable energy system. Fukuoka City is carrying out a project to use biogas extracted from sewage sludge to produce H2. The hydrogen produced will be used in fuel cell vehicles.
"Sewage treatment plants across the country have the potential to provide hydrogen to as many as 1.86 million fuel cell vehicles," said Masaki Tajima, professor of environmental energy at Tottori University (Tottori-u.ac.jp, Japan).
Also in Japan, Toshiba Corporation (Tokyo; www.toshiba.com) has developed its 100-kilowatt H2 Rex pure hydrogen cascade fuel cell to increase the utilization rate of hydrogen. Fuel cells can generate electricity at a temperature of 80°C, which is much lower than the operating temperature of other types of fuel cells, and does not require a heating process.
Researchers at the Center for Sustainable Chemistry Technology at the University of Bath (UK; www.bath.ac.uk) have developed an improved method of using sunlight to split water. They use perovskite solar cells. Because these batteries are unstable in water, which limits their use to directly produce clean hydrogen fuel, the researchers used a graphite waterproof coating. Although the voltage generated by perovskite solar cells is higher than that of silicon cells, the voltage is still not enough to split water. To solve this problem, the researchers added a catalyst.
A team from the Catalan Institute of Chemistry (Tarragona, Spain; www.iciq.org) recently discovered another way to improve hydrogen production by electrolysis. The team is led by José Ramón Galón-Mascarós. The researchers achieved H2 production at low voltage only by placing the permanent magnet close to the anode, thus immediately saving energy. The team also used catalysts based on the earth's abundant metals such as nickel and iron. The team claims that the use of electrolyzers can increase the efficiency of hydrogen production by 100%. In an industrial environment, the team expects to increase efficiency by 30% to 40% (Chem. Eng., July 2019, page 12).
Researchers at the Indian Institute of Science (Bangalore, India; www.iisc.ac.in) led by Professor Prabeer Barpanda have developed a low-cost catalyst to accelerate the rate of water splitting to produce H2.
One of the two main reactions involved in the process-the oxygen evolution reaction-is slow, which limits the overall efficiency of the process. The most effective catalysts commonly used are made of expensive metals such as Pt and Ru. Indian researchers developed a catalyst by combining cobalt oxide with sodium phosphate (metaphosphate). Researchers claim that this catalyst is more than two hundred times cheaper than the current state-of-the-art RuO2 catalyst, and the reaction speed is faster.
To make the catalyst, the researchers calcined sodium metaphosphate and cobalt oxide in an argon atmosphere. This creates a piece of partially burned carbon with cobalt oxide crystals made of sodium metaphosphate scattered on it. Metaphosphate forms a strong framework to maintain the integrity of cobalt oxide, showing high stability. This treatment allows the catalyst to maintain its activity through multiple cycles.
A team from the University of Michigan (Ann Arbor; www.umich.edu), led by Professor Don Siegel, has identified a method to pack more H2 into the metal organic framework (MOF) than ever before, thereby increasing energy density and therefore fuel The estimated mileage of a battery car.
The team created a database of MOFs and used computer simulations to screen nearly 500,000 MOFs to find the ones most suitable for storing H2. Three MOFs have been identified, which will exceed the previous H2 storage records. Siegel said that by increasing the amount of H2 that can be stored in the MOF adsorbent, the pressure required to store it can be reduced, and the size of the tank can also be reduced.
As another way to store and transport H2, Chiyoda Corp. (Yokohama, Japan; www.chiyodacorp.com) has developed the SPERA Hydrogen system in cooperation with JXTG Nippon Oil & Energy Corp., the University of Tokyo, and Queensland University of Technology. The system remains liquid under ambient temperature and pressure, so it can be stored in existing tanks for long-term storage and transported by existing tankers. The system is a liquid called methylcyclohexane (MCH). It is produced using the organic chemical hydride (OCH) method, in which toluene and hydrogen undergo a catalytic reaction. The volume of MCH is a fraction of the volume of gaseous H2. Although the OCH method using MCH has been known for a long time, no commercial catalyst has been developed for the production of H2 from MCH in the dehydrogenation process. Chiyoda has developed a dehydrogenation catalyst that can continuously provide more than 10,000 hours of stable high performance on a laboratory scale. In another method, a team at Newcastle University (Newcastle upon Tyne, UK; www.ncl.ac.uk) led by Professor Ian Metcalfe developed what is said to be the first to be able to produce H2 in the form of a pure product stream. .
The reactor transfers oxygen between reactant streams through a solid oxygen reservoir, thereby avoiding mixing of reactant gases. The reservoir is designed to maintain close equilibrium with the reactant gas flow when it follows its reaction trajectory, thereby retaining the "chemical memory" of its exposure conditions. H2 is therefore produced as a pure product stream, eliminating the need for expensive separation of the final product. "Traditional H2 production requires two reactors and a separator, while our reactor completes all steps in one unit," Metcalf said.
Researchers at Pohang University of Science and Technology (Pohang, South Korea; www.postech.ac.kr) and Colorado School of Mines (Golden, Colorado; www.mines.edu) led by Kun-Hong Lee and Bo Ram of Pohang Lee introduced a new concept to improve the hydrogen storage capacity inside structures formed by water molecules called gas hydrates. Gas hydrates are ice-like solid compounds including gas. The main problem with storing hydrogen in natural gas hydrates is to reduce the energy required. The researchers studied the metastable state of gas hydrates, which is determined by a stable state that can be changed by adding a small amount of energy. They succeeded in maintaining the stability of the hydrogen hydrate under very mild pressure (0.5 to 1 MPa) and demonstrated that the H2 storage in the hydrate was increased (up to 52%).
"If a proper process is designed to trap the system in this metastable state with a high concentration of gas, coupled with the self-preservation benefits of hydrates, then a new paradigm for gas storage in clathrate hydrates will be born," Kun-Hong said plum. At the same time, CSIRO (Melbourne, Australia; www.csiro.au) carried out a study on the "round-trip efficiency of ammonia as a renewable energy transportation medium". The study shows that NH3 is an excellent solution for converting renewable energy into H2, transporting it to areas with low renewable energy intensity, and converting NH3 into H2 for local consumption. According to the study, the round-trip efficiency of electrical energy storage can be higher than 80%.