Over the next 10–20 years, motor vehicles and trains powered by carbon-free hydrogen fuel cells could become commonplace. With limits on greenhouse gas emissions looming and with their streets choked with exhaust, Japan and other energy-importing East Asian nations are already searching abroad for sources of readily usable hydrogen.
If renewable energy is to supplant fossil fuels on a global scale, wind and solar power from nations with abundant resources will need to be moved across oceans to energy-poor countries. Hydrogen, which can be cleanly burned or used to generate electricity in fuel cells, is a convenient energy carrier—a clean alternative to liquefied natural gas.
Despite its huge, largely unpopulated land mass and abundant sunshine, Australia has been slow to capitalize on its vast solar and wind energy potential. But policymakers are beginning to recognize the economic development potential of exporting cleanly generated hydrogen gas. Federal and state governments are backing demonstration projects. Hydrogen is an issue in the parliamentary election due to take place this month: The Labor opposition party has pledged to invest Aus$1 billion ($711 million) to develop and deploy a hydrogen export industry.
The ruling coalition government has not proposed a similar plan. Instead, it promised that by the end of the year it would develop a national hydrogen strategy that will consider both export and domestic uses. The plan is to be developed by a task force headed by Alan Finkel, the country’s chief scientist. A 68-page white paper he prepared for the government stated that hydrogen exports could generate Aus$1.7 billion annually and a total of 2800 new jobs by 2030.
Hydrogen itself, however, may not be the ideal shipping or storage medium. California has most of the 6100 fuel-cell vehicles (FCVs) on US roads today. The majority of the cost of hydrogen, currently about $14 per kilogram at the pump in California, comes from compressing, transporting, and storing it at pressure. Liquefying hydrogen requires temperatures below −253 °C and heavily insulated storage containers. The US Department of Energy says that to compete with gasoline, hydrogen should be priced down at $6/kg.
Various inorganic and organic compounds could carry hydrogen in a more concentrated or convenient fashion. None are quite ready to challenge compressed hydrogen, but two—borohydride compounds and ammonia—are prominent candidates. Australia is playing an outsized role in both.
An Australian–Israeli company, Electriq Global, says it is on the cusp of commercializing a mixture of potassium borohydride and water to power fuel-cell buses and trucks. The company claims its KBH4 fuel will deliver twice the range of the same volume of gasoline for half the price: $4/kg at the pump, says CEO Guy Michrowski. A kilogram of hydrogen will propel a car about 60 km.
In February, Electriq announced an agreement with the Dutch company Eleqtec to commercialize the fuel technology in trucks, buses, barges, and mobile generators. The first applications are expected to debut next year in the Netherlands, where tightened tailpipe standards are due to take effect in 2025. Michrowski says a separate partnership with a UK firm to demonstrate the technology on a double-decker bus will be announced within weeks.
Borohydrides are energy dense, nonflammable, and stable at ambient temperature. In Electriq’s case, releasing hydrogen at the point of use is done on demand by way of an onboard proprietary catalyst. As with conventionally fueled FCVs, the hydrogen reacts with oxygen in a proton-exchange-membrane fuel cell to produce electricity that drives the wheels. In Electriq’s process, depleted fuel will be pumped out of the vehicle at a refueling station and trucked back to a recycling plant.
Electriq’s low cost is largely because half the hydrogen extracted onboard the FCV is from the water that constitutes 60% of the fuel’s volume, Michrowski says. It’s also because of low capital and operating costs, since hydrogen does not need to be stored and transported at high pressures, nor does energy need to be expended to keep the hydrogen compressed at 700 times normal atmospheric pressure, which is how it currently is dispensed into FCV tanks.
An uphill process
Regeneration is where borohydride encounters its major drawback: Hydrogenating borate to borohydride requires so much energy that the fuel is likely to be uneconomic, says Zhenguo Huang, leader of the research group on boron for energy storage and transfer at the University of Technology Sydney. Staff scientist Thomas Autrey, in the catalysis group at Pacific Northwest National Laboratory, is also skeptical. “My first question would be, How are they going to do the regeneration? It’s thermodynamically uphill.” Replenishing the spent fuel isn’t as simple as applying hydrogen to the borate under pressure. Multiple chemical reactions driven by temperatures of 300 °C or more are required, says Huang.
Michrowski, however, says Electriq’s multiple catalysts provide a high conversion efficiency with a reduced energy input. The cost of replenishing the fuel is included in his $4/kg estimate, he notes. If Electriq’s claim holds up, it could be a “game changer,” says Huang.
So far, Electriq has demonstrated its processes only at lab scale and with a fuel-cell-powered bike. A pilot regeneration plant in Israel aims to demonstrate the technology at an industrial scale this summer, Michrowski says. Similar pilot plants are planned in China, where Electriq has an agreement with that country’s largest FCV manufacturer to demonstrate the fuel on a long-haul truck. A plant is also planned somewhere in Europe; Michrowski wouldn’t say where, nor would he provide capacities for any of the pilot plants. The company has received grants from Israel and other governments, the amount of which he declined to specify.
Electriq is developing an improved fuel that will double the hydrogen-carrying capacity, says Michrowski. The company’s current formulation holds 40 grams of hydrogen per liter, about the same as compressed hydrogen at 700 bars. Liquid hydrogen, used in a few places in Germany, has a density of 70 g/L.
Others who have worked with borohydrides are skeptical of their usefulness in mass-market applications. In the US, Ballard Unmanned Systems in Massachusetts has built demonstrations of sodium borohydride–powered fuel-cell soldier power packs and underwater and aerial unmanned vehicles. Unlike KBH4, NaBH4 is a reducing agent used by chemical companies and manufactured in quantity. Phil Robinson, Ballard’s vice president, says that although the compounds could be useful for niche applications, “I’m not sure that any borohydride makes sense for automotive use.” The growing infrastructure for compressed hydrogen in California, parts of the East Coast, and East Asia, he argues, “negates the need for more complex, more expensive hydrogen storage means for vehicles.”
Borohydrides are perhaps better suited to provide energy storage in stationary applications that don’t require frequent regeneration and are too big for batteries, says Autrey. Examples include backup power for data centers and for seasonal storage of excess hydroelectricity.
Ammonia is favored in Oz
In Australia, interest in hydrogen carriers has focused on ammonia. Because it has a long-established global production and transportation infrastructure, primarily for fertilizer production, ammonia has a head start over other carrier candidates. The second-most-synthesized chemical on the planet, ammonia has a hydrogen content of 130 g/L, nearly twice that of liquid hydrogen. It becomes liquid at −23 °C, well above hydrogen’s boiling point. And there is no need for regeneration.
Japan presents the most immediate export opportunity. Importing 94% of its energy, Japan aspires to a hydrogen-fueled economy. The Japanese government has set a goal of having 800 000 FCVs on the road by 2030, from 25 000 currently. More than 250 000 homes in Japan today are powered with residential fuel cells, and 5.3 million are projected by 2030.
The 30 million tons of hydrogen Japan looks to import annually by the late 2020s is nearly equivalent to the energy content of all Australian thermal coal exports, says David Harris, director of research for low-emissions technologies at CSIRO Energy, a branch of the federal Commonwealth Scientific and Industrial Research Organisation. (Australia is the world’s largest coal exporter by value.) South Korea, which plans to deploy 20 000 fuel-cell buses by the mid 2020s, is another upcoming hydrogen market.
Ammonia has drawbacks. Exposure to high concentrations will cause burning of the eyes and the respiratory tract. Temperatures of around 500 °C are required to break the chemical bonds and separate the hydrogen from nitrogen. But by burning ammonia in an engine or turbine, a portion of the released energy could be used to provide the heat.
The ammonia synthesis process, known as Haber–Bosch, currently accounts for between 1% and 2% of global energy consumption, according to DOE, and produces a similar proportion of the world’s carbon emissions. First, hydrogen is stripped by steam from natural gas or coal. It is then combined with atmospheric nitrogen at high temperature and pressure. Fossil-fuel combustion is typically the source of the required energy.
Electrolysis powered with renewable energy can decarbonize the hydrogen production step. Norwegian ammonia producer Yara is designing a solar-powered electrolysis facility that will eliminate half of the carbon dioxide emitted by its Western Australia ammonia plant. The government of South Australia has funded another solar-powered electrolysis demonstration plant that will begin operations in 2020. Part of that plant’s hydrogen output will be used to make ammonia; the rest will be used to generate power, both via combustion and by fuel cell.
Researchers at Monash University in Melbourne are working to decarbonize the other half of the ammonia synthesis process. With a grant of Aus$2.6 million from the Australian Renewable Energy Agency, they are using ionic liquids to synthesize ammonia directly from air and hydrogen. Douglas MacFarlane, who leads the Monash group, says tuning catalysts and electrode structures will get their devices close to 100% faradaic efficiency (a measure of the efficiency with which charge is transferred in an electrochemical reaction). That compares with the 50% efficiency of the Haber–Bosch process. “Efficiency is a vital aspect of the process as it has a massive impact on overall energy cost of the nitrogen to ammonia process,” he says. Although output of devices currently being designed is small—100 g/day—scaling to larger amounts should be straightforward, he adds.
CSIRO is addressing another challenge for ammonia: Palladium membranes commonly used to separate hydrogen from ammonia are too expensive for high volumes. Last fall, the organization demonstrated a vanadium-based membrane in a portable hydrogen fueling station that separated 20 kg of pure hydrogen. After filling the tanks of their cars, says Harris, FCV manufacturers Hyundai and Toyota both were satisfied that the hydrogen contained no ammonia, which would damage or destroy proton-exchange-membrane fuel cells. CSIRO has partnered with Fortescue Metals Group, an iron-ore producer, to build a 200 kg/day demonstration of its membrane system that’s expected to be finished next year, says Harris.
Decomposing ammonia would best occur at a central location in major population centers, says Harris, followed by delivery of compressed gas to individual service stations.
Alternative carriers
The first hydrogen supply chain to be demonstrated internationally will use neither ammonia nor borohydride. Japan’s Chiyoda Corp is leading a partnership that will begin in Brunei, where the hydrocarbon solvent toluene (C6H5CH3) will be hydrogenated with natural gas to become methylcyclohexane (MCH; C6H11CH3). The compound will be shipped by tanker to Kawasaki, Japan, where the hydrogen will be extracted and mixed into the natural-gas supply system. The spent toluene will be shipped back to Brunei for a reload. For MCH, hydrogen loading is thermodynamically downhill, says Autrey. The reverse process requires a lot of heat, and Chiyoda says a proprietary catalyst is key to the economics.
A research group headed by chemist Gábor Laurenczy at Switzerland’s École Polytechnique Fédérale de Lausanne last year demonstrated the use of formic acid (CH2O2) as a hydrogen carrier. Researchers there said they had built the world’s first integrated power supply employing a formic-acid fuel cell. The simplest combination of hydrogen and CO2, formic acid is liquid at room temperature, making it easy to store, transport, and handle. It is widely used in agriculture and several other industries.
Formic acid, however, is a by-product of petrochemical manufacturing, and its manufacture “has nothing to do with CO2 and hydrogen,” says Huang. Combining CO2 and hydrogen directly is at best 2% efficient, he says. Autrey, however, says that “on paper,” at least, producing formic acid should require less energy than producing borohydrides.