Technology developments are progressing towards large-scale production of ‘green’ hydrogen, along with improved methods for storage and transportation
The world has an important opportunity to tap into hydrogen’s vast potential to become a critical part of a more sustainable and secure energy future,” according to an in-depth study launched by the International Energy Agency (IEA; Paris, France; www.iea.org) on the occasion of the meeting of G20 energy and environment ministers in Karuizawa, Japan, on June 15–16. “Clean hydrogen is currently receiving strong support from government and businesses around the world, with the number of policies and projects expanding rapidly,” the study says. Titled The Future of Hydrogen: Seizing Today’s Opportunities, and launched by the IEA’s executive director Fatih Birol, and Japan’s minister of economy, trade and industry Hiroshige Seko, the study says hydrogen offers ways to decarbonize a range of sectors, including chemicals manufacturing and iron and steel production, and it can be transformed into fuels for cars, trucks, trains, ships and aircraft. “The world should not miss this unique chance to make hydrogen an important part of our clean and secure energy future,” Birol says.
There are, however, people who believe H 2 fuel cells will never be widely used, because they present high costs and low efficiencies when compared with batteries, such as lithium-ion batteries (LIBs), and it would take too long to overcome the technical issues involved. Nevertheless, efforts are ongoing to improve the technology and economics of a hydrogen-based economy.
H2 for transportation
As a fuel system for cars, buses, trains and so on, hydrogen is stored in a tank within the vehicle. H2 is fed to a fuel cell, which produces electricity for an electric motor that moves the vehicle. Unlike fossil fuels, hydrogen combustion produces no CO2 or other pollutants — just water vapor.
As far as a fuel system for motor cars is concerned, the main contender of H2 fuel cells is LIBs. Today most electric vehicles use batteries, often based on Li-ion or lead-acid chemistry. Each individual fuel cell produces low currents and voltages and, like LIBs, the cells need to be stacked together to reach the target voltage and maximum current required by the vehicle.
One of the advantages of H2 used in fuel cells is that it has an energy-to-weight ratio (specific energy) much greater than that of LIBs. The specific energy of LIBs is 0.36 to 0.875 MJ/kg, and the specific energy of hydrogen is 120 to 142 MJ/kg. H2 in fuel cells thus permits much greater range while being lighter and occupying smaller volumes. Another major advantage of H2 fuel cells is that they can be recharged in a few minutes. In contrast, full charge times for LIB electric vehicles is typically measured in hours.
However, H2 also entails serious drawbacks. One of them is that it combines well with other elements and therefore has to be isolated, before being usable as fuel, by means of processes that are expensive and energy consuming. Also, storing H2 is expensive and energy intensive, either when it is stored as a gas at high pressure, or even more so, as a liquid at cryogenic temperatures. H2, which is also highly flammable, is difficult, dangerous and expensive to produce, store and transport.
In spite of the problems presented by H2 fuel cells, and in spite of the negative predictions by some experts, a large number of projects are ongoing and a significant amount of R&D dollars are being invested in H2 fuel cells around the world. There are already many vehicles running on hydrogen fuel cells, including motor cars, buses and trains, although they have not yet attained wide market acceptance. According to the IEA, there are currently about 11,200 H2-powered cars on the roads worldwide.
The oldest hydrogen cars commercially available in selected markets are: the Toyota Mirai, the Hyundai Nexo and the Honda Clarity. In 2013 the Hyundai Tucson fuel-cell electric vehicle (FCEV) was the first commercially mass-produced H2 FCEV in the world. It had a range of nearly 600 km. Hyundai Nexo (Figure 1) succeeded it in 2018. Toyota launched its Mirai at the end of 2014. It has a range of about 500 km and it takes about 5 min to refill its H2 tank.
Although many automobile companies have introduced demonstration models in limited numbers, many of those companies have switched to battery electric vehicles.
Late last year, the world’s first passenger train powered by H2 fuel cells began operating in Germany (Figure 2). Called Coradia iLint, it was developed by Alstom (Paris, France; www.alstom.com). The train is capable of maximum speeds of 140 km/h.
Currently, almost all of the world’s H2 is supplied from fossil feedstocks in processes that emit CO2, unless the CO2 is adequately captured and stored. Clean H2 production is achieved by the electrolysis of water using electricity obtained from renewable sources, such as solar and wind. Presently, however, only about 5% of the world’s H2 is produced via water splitting. The process within the fuel cell is essentially the reverse of the electrolytic process for producing H2 from water. In the H2 fuel cell, the H2 reacts with oxygen from the air, and the only byproduct is clean water.
Recently, thyssenkrupp AG (Essen, Germany; www.thyssenkrupp.com; Figure 3) and Siemens AG (Erlangen, Germany; www.siemens.com) have developed new, large-scale electrolyzers in order to decarbonize the production of H2 (Chem. Eng., January 2019, pp. 14–17; www.chemengonline.com/power-x-batteries-not-required).
Siemens’ electrolyzers were initially capable of turning kilowatts of renewable energy into clean H2, and the company is now building larger scale devices. Siemens will soon deliver a 1.25-MW unit to the Tonsley Innovation District of South Australia. It is also offering a unit capable of scaling up to 10 MW, with plans to scale further by another order of magnitude.
The largest solar-powered green hydrogen plant in the world is planned for the Burrup Peninsula in Western Australia by Yara Pilbara (Burrup, Western Australia; www.yara.com.au) and French energy company Engie (Paris, France; www.engie.com). It will be a full-scale 100-MW plant with a 66-MW electrolyzer.
In January, Air Liquide (Paris, France; www.airliquide.com) invested $20 million in Hydrogenics Corp. (Mississauga, Ontario; www.hydrogenics.com), a leader in electrolysis H2 production equipment and fuel cells. Air Liquide and Hydrogenics have also entered into a technology and commercial agreement to jointly develop proton exchange membrane (PEM) electrolysis technologies for the rapidly growing H2 energy markets around the world.
Meanwhile, Angstrom Advanced, Inc. (Stoughton, Mass.; www.verdellc.com), which offers renewable H2-generation systems, says the state government of Massachusetts confirmed, in 2016, that the world’s first commercialized renewable energy H2 production, storage, refueling, and fuel cell microgrid demonstration project would be operated by the company in the Boston area. More recently, the company has developed what it claims to be the world’s first all-in-one H2 refueler.
Last October, a Japanese consortium started construction of the Fukushima Hydrogen Energy Research Field (FH2R; Chem. Eng., October 2018, p. 10; www.chemengonline.com/japan-takes-major-step-toward-h2-based-economy). FH2R will produce (using renewable energy) and store up to 900 ton/yr of H2. It will use a new control system to coordinate overall operation of the H2 energy system, the power grid control system, and the H2-demand-forecast system, so as to optimize H2 production, H2-based electricity generation and H2 gas supply.
The system will use H2 to offset grid loads, and deliver H2 to locations in Tohoku and beyond, and will seek to demonstrate the advantages of H2 as a solution in grid balancing and as a H2 gas supply. Compressed H2 will be transported in trailers and supplied to users.
The U.S. Dept. of Energy (DOE; Washington, D.C.; www.energy.gov)Hydrogen and Fuel Cell Program conducts research and development in H2 production, delivery, storage and fuel cells. Its technical targets are: biomass-derived liquid reforming, electrolysis, biomass gasification, thermochemical water splitting, photoelectrochemical water splitting, photobiological processes, and microbial biomass conversion.
Meanwhile, research is being conducted at a water purification plant in Sendai, Miyagi Prefecture, Japan to incorporate H2 into renewable energy systems. The city of Fukuoka is engaged in a project to produce H2 with biogas extracted from sewage sludge. The H2 produced will be used for fuel cell vehicles.
“Sewage treatment plants across the nation have the potential to power up to 1.86 million fuel cell vehicles with hydrogen,” says Masaki Tajima, a professor of environmental energy at Tottori University (Tottori City, Japan; www.tottori-u.ac.jp).
Also in Japan, Toshiba Corp. (Tokyo; www.toshiba.com) has developed its 100-kW H2Rex pure hydrogen cascading fuel cells, which increases the utilization rate of hydrogen. The fuel cells can generate power at a temperature of 80°C, which is much lower than the operating temperature of other types of fuel cells, eliminating the need for a heating process.
Researchers at the Center for Sustainable Chemical Technologies at the University of Bath (U.K.; www.bath.ac.uk), have developed an improved method for using sunlight to split water. They used perovskite solar cells. Since these cells are unstable in water, which limits their use for the direct generation of clean H2 fuels, the researchers used a waterproof coating from graphite. While perovskite solar cells produce a higher voltage than silicon cells, the voltage is still not enough to split water. To solve this problem, the researchers added catalysts.
Another way to boost H2 production from electrolysis has been recently discovered by a team from the Institute of Chemical Research of Catalonia (Tarragona, Spain; www.iciq.org), led by José Ramón Galón-Mascarós. The researchers achieved H2 production at low voltages just by approaching a permanent magnet to the anode, which results in immediate energy savings.
The team also used catalysts based on earth-abundant metals like nickel and iron. The team claims it can increase the H2-producing efficiency using an electrolyzer by 100%. In an industrial setting the team would expect efficiency gains of 30 to 40% (Chem. Eng., July 2019, p. 12; www.chemengonline.com/magnetism-gives-water-splitting-a-big-boost).
Researchers at the Indian Institute of Science (Bengaluru, India; www.iisc.ac.in), led by professor Prabeer Barpanda, have developed a low-cost catalyst to speed up the splitting of water to produce H2.
One of the two major reactions involved in this process — the oxygen evolution reaction — is slow, limiting the process’ overall efficiency. The most efficient catalysts normally used are made of expensive metals, such as Pt and Ru. The Indian researchers have developed a catalyst by combining cobalt oxide with phosphate salts of sodium (metaphosphates). The researchers claim this catalyst is more than two hundred times less expensive than the current state-of-the-art RuO2 catalyst, and the reaction rate is also faster.
To make the catalyst, the researchers roasted sodium metaphosphate and cobalt oxide in an argon atmosphere. This creates a sheet of partially burned carbon onto which crystals made of cobalt oxide framed by sodium metaphosphate are spread out. The metaphosphates form a strong framework to hold the cobalt oxides intact, showing high stability. This treatment allows the catalyst to retain its activity over multiple cycles.
A team from the University of Michigan (Ann Arbor; www.umich.edu), led by professor Don Siegel, has identified ways to cram more H2 than ever before into metal-organic frameworks (MOFs), increasing the energy density, and therefore the projected driving range of fuel cell vehicles.
The team created a database on MOFs, and used computer simulations to screen nearly 500,000 MOFs for those best suited to store H2. Three MOFs were identified that would surpass previous records for H2 storage. Siegel says that by increasing the quantity of H2 that can be stored in a MOF adsorbent, the pressure needed to store it can be reduced, and the size of the tank can also be reduced.
In another way to store and transport H2, Chiyoda Corp. (Yokohama, Japan; www.chiyodacorp.com), in association with JXTG Nippon Oil & Energy Corp., the University of Tokyo and Queensland University of Technology, has developed the SPERA Hydrogen system. This system is kept in a liquid state at ambient temperatures and pressures, and can therefore be stored in existing tanks for a long time and transported by existing tankers.
The system is a liquid called methylcyclohexane (MCH). It is produced using the organic chemical hydride (OCH) method, whereby toluene and hydrogen are catalytically reacted. The volume of MCH is a small 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 producing H2 from MCH in the dehydrogenation process. Chiyoda developed a dehydrogenation catalyst that continuously delivers stable high performance for more than 10,000 h at the laboratory scale.
In yet another approach, a team from the University of Newcastle (Newcastle-upon-Tyne, U.K.; www.ncl.ac.uk), led by professor Ian Metcalfe, has developed what it claims is the first thermodynamically reversible chemical reactor capable of producing H2 as a pure product stream.
The reactor avoids mixing reactant gases by transferring oxygen between reactant streams via a solid-sate oxygen reservoir. The reservoir is designed to remain close to equilibrium with the reacting gas streams as they follow their reaction trajectory and thus retains a “chemical memory” of the conditions to which it was exposed. The H2 is thus produced as a pure product stream, eliminating the need for costly separation of the final products. “Whereas conventional H2 production requires two reactors and a separation, our reactor accomplishes all the steps in one unit,” Metcalfe says.
Researchers from Pohang University of Science and Technology (Pohang, South Korea; www.postech.ac.kr) and the Colorado School of Mines (Golden, Colorado; www.mines.edu), led by Pohang’s Kun-Hong Lee and Bo Ram Lee, have introduced a new concept for improving hydrogen storage capacity inside the structure formed by water molecules called gas hydrates.
Gas hydrates are ice-like solid compounds including gas. The main problem in storing hydrogen in gas hydrates has been lowering the energy required. The researchers studied the metastability of gas hydrates, which is determined by a stable state that can be changed by the addition of a small amount of energy. They succeeded to keep the hydrogen hydrates stable at very mild pressure (0.5 to 1MPa) and demonstrated increased H2 storage in the hydrates (up to 52% larger amount).
“If an appropriate process is designed to trap the system in this metastable state with a high concentration of gas, coupled with the benefits of hydrate self-preservation, a new paradigm will be born for gas storage in clathrate hydrates,” says Kun-Hong Lee.
Meanwhile, the CSIRO (Melbourne, Australia; www.csiro.au) has conducted a study on the “Round-trip Efficiency of Ammonia as a Renewable Energy Transportation Medium.” The study says that NH3 is an excellent proposition for converting renewable energy to H2, transporting it to locations with low renewable energy intensity and converting the NH3 back to H2 for local consumption. The round-trip efficiency of electrical energy storage can be higher than 80%, the study says.
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