The quest to make hydrogen the fuel of the future

Key text

Hydrogen, the most abundant element in the Universe, is one potential candidate. Many regard it as the ultimate 'clean, green' fuel because when it burns in oxygen, only heat and water are created.

Related site: Fuelling the 21st century Describes the use of hydrogen fuel cells for generating power. (Nova: Science in the news, Australian Academy of Science)

In the years and decades to come, we could convert to what's called a 'hydrogen economy' where hydrogen would become the dominant energy carrier. It could power our cars, trains and spaceships, even our appliances such as mobile phones and laptops. In fact, scientists can do all that now. Fuel cells based on hydrogen are becoming widespread as reliable, more efficient power sources, and hydrogen cars are already appearing on our roads.

But one major obstacle to overcome is finding a cheap, efficient way of producing large supplies of hydrogen — hydrogen does not occur freely in nature. A 2005 study showed that in Australia, production of hydrogen can cost between $8 and $58 per gigajoule – generally much more expensive than alternatives such as coal ($1-3), natural gas ($5) and petrol ($10).

Another complication is there are several competing technologies to produce hydrogen – some old, some very expensive, and some so new they're still being developed. Currently, the cheapest method of making hydrogen uses natural gas – a method that also creates carbon dioxide, increasing our greenhouse gas emissions. The way to the future might be uncertain, but already there is general agreement that using fossil fuels to produce hydrogen is not a long-term solution.

So the search is also focusing on finding 'greener' methods of producing hydrogen that rely on renewable sources of energy, such as solar, wind or geothermal energy (which do not contribute to greenhouse gas emissions). That's a tough challenge in itself. But there are two other significant hurdles to overcome. Storing hydrogen is problematic (Box 1: Storing and distributing hydrogen), and there is no infrastructure yet to ensure that it can be supplied cheaply, conveniently and safely (Box 2: Hydrogen - too hot to handle?).

And it’s a race against time because there are other competing energy carriers. Bringing together all those loose ends is a big task. But scientists, industry, and governments are working towards solving the hydrogen economy puzzle.

Making hydrogen from fossil fuels

No matter what fuel we adopt to replace fossil fuels in the future, we're going to need lots of it. Australia's current energy demand is around 5600 petajoules (5600 000 000 000 000 000 joules), with about 95 per cent of that coming from oil, gas and coal. By 2030, it's estimated we will need nearly 50 per cent more.

Related site: Capturing the greenhouse gang Provides information on greenhouse gas capture and storage. (Nova: Science in the news, Australian Academy of Science)

But supplies of liquid fossil fuels are dwindling and are often found in regions of political and/or economic instability and fossil fuels add to environmental problems including air pollution and increased greenhouse gas levels. Research is underway in Australia to develop ways of reducing greenhouse gas emissions from fossil fuels by making energy production more efficient and developing carbon capture and storage technologies.

There are several ways to produce hydrogen using fossil fuels. This would still produce carbon dioxide and be energy intensive, but it would allow countries to begin phasing in the use of hydrogen as a major fuel source. And as researchers develop and perfect better ways of producing hydrogen using sustainable energy sources, the use of fossil fuels would be phased out. Ultimately, the goal would be to stop using fossil fuels altogether and instead shift to methods of making hydrogen that rely on renewable energy.

But that's still some way off.

Currently, the cheapest and most widely used means for manufacturing hydrogen is to react natural gas (mostly methane) with steam over a catalyst at high temperature (900ºC) — so-called 'steam reforming'. The resulting mixture of hydrogen and carbon monoxide — known as 'syngas' — is then reacted with further steam and a catalyst at a lower temperature to convert the carbon monoxide to carbon dioxide and produce more hydrogen.

Related site: Solar thermal project Provides information on the National Solar Energy Centre. (CSIRO Energy Technology, Australia)

A more interesting technology is solar-thermal reforming, which uses solar energy to generate steam. This then reacts with methane to form hydrogen and carbon dioxide. The CSIRO's National Solar Energy Centre in New South Wales has been hailed for its work in this field, which is considered highly relevant to Australian conditions.

Another method involving natural gas is partial oxidation which involves burning methane in oxygen to produce hydrogen. Again, greenhouse gases are created.

Coal can also be used to make hydrogen. With gasification, one of the oldest methods of making hydrogen, coal is heated under high pressures with steam and oxygen to convert it into a gas mixture containing hydrogen. But other undesirable compounds are also produced, including carbon dioxide, carbon monoxide, sulphur and nitrogen compounds. Hydrogen can be separated from these other compounds, but at a cost.

Comparison of different processes for hydrogen production

Making hydrogen using greener alternatives

There is also a range of production methods that are friendlier to the environment.

Many high school science students will be familiar with producing hydrogen by electrolysis, where you use an electric current to split water into hydrogen and oxygen. There's no carbon dioxide given off, but this method is not as efficient when it comes to producing large amounts of hydrogen. It's energy intensive, and if you use electricity generated from fossil fuels, carbon dioxide is produced at an earlier stage in the process.

In Tasmania, researchers are using wind power to provide the electricity for electrolysis. The hydrogen produced is then used in a car with an engine adapted to run on hydrogen instead of petrol. Its advocates say the end result is to have vehicles that basically run on 'wind and water'. Likewise, other renewable energy sources such as solar and geothermal can be used for electrolysis to make hydrogen.

Biomass gasification involves heating biomass (eg. crop waste, wood or newspapers) with steam and oxygen to produce hydrogen. Carbon dioxide is also produced, but the plants take in carbon dioxide while they're alive, so the overall effect on greenhouse gas release is reduced.

As an abundant and clean source of energy, solar energy is being investigated for several methods of hydrogen production. The promising thermochemical process uses solar energy to heat water to around 1000ºC to drive a series of chemical reactions that produce hydrogen. An alternative technology, thermolysis uses solar energy to heat water to more than 2000ºC, causing the water to break down directly to hydrogen and oxygen.

At the University of Queensland, researchers are producing hydrogen using biophotolysis. Certain strains of microscopic algae that have been deprived of sulfur, switch from their normal photosynthesis pathway to one that produces hydrogen, which literally bubbles to the top of ponds for collection. Researchers say it could supply Queensland's future chemical energy needs using a system of 33 square kilometres of algal ponds. Although it has potential as a cheaper, 'greener' source of hydrogen, this method is currently not efficient enough to be economically viable.

Another method involves using sunlight to split water, producing hydrogen and oxygen. But unlike conventional electrolysis this method doesn't need separate production of electricity. lnstead, the sun's energy is harnessed by a photoelectrochemical cell then used to drive the electrolysis of water. The University of New South Wales is investigating the photo-electrochemical approach using titanium oxide cells.

Piecing the puzzle together

Converting Australia to a hydrogen economy has been talked about for more than two decades. What's different now is that all the years of research and collaboration on the various technologies are coming together. Researchers are piecing the puzzle of the hydrogen economy together making it easier to visualise the end result or 'big picture'.

Related site: Australian hydrogen activity Provides information on hydrogen research and technology in Australia. (Department of Resources, Energy and Tourism, Australia)

The 2003 National Hydrogen Study sets out the case for Australia to become a key player in the move to hydrogen and a series of recommendations on how to achieve it. A 2008 report suggests research and development should occur in three stages over the next three decades. Despite Australia having more than 120 hydrogen-related research projects underway, it's likely we will have to depend on fossil fuels for at least the next 20 years.

Conversion to a hydrogen economy won’t happen overnight but the quest to make hydrogen the fuel of the future is well underway. Perhaps it's only a matter of time before all the pieces of the puzzle come together and the hydrogen economy is not science fiction, but science fact.

Related Nova topics:

Which way ahead for hydrogen cars?

Fuelling the 21st century

Box 1: Storing and distributing hydrogen

Over the 192 kilometre stretch of road, you'll find the 'hydrogen highway' project being set up by the government of British Columbia. The road will have a series of hydrogen refuelling stations, as well as demonstration projects highlighting hydrogen and fuel cell technologies.

The aim of the project is to have the highway up and running for hydrogen vehicles by 2010, when the eyes of the world will be on Vancouver as it hosts the Winter Olympics. Once completed, you'll be able to fill up your hydrogen vehicle when you want and drive on, almost as easily as if you had a petrol vehicle.

Hydrogen highways and demonstration projects like the hydrogen bus trials (Ecobus) in Western Australia are important prototypes to help address the storage and distribution issues associated with hydrogen. Without the right infrastructure, hydrogen won't catch on as a replacement fuel, simply because people won't be able to access it easily.

Currently, hydrogen is mostly made for industrial purposes such as fertilisers, plastics and petroleum products. It can be transported to end users via pipelines – which is the cheapest method – but there are relatively few existing pipelines compared with natural gas systems. Installing new pipelines can be costly at between $300 000 and $600 000 per kilometre.

Compressed hydrogen gas can be transported via roads, but the required trailers with high-pressure storage tubes are expensive, especially for long distances.

Liquid hydrogen, or cryogenic hydrogen, can be produced by cooling the gas to –253ºC. Liquid hydrogen takes up 1/700th of its normal gaseous volume and can be trucked long distances. But this is also expensive, as you need strong, well-insulated tanks; in addition, cooling hydrogen to a liquid uses a lot of energy.

However, getting hydrogen to fuelling stations isn't the only storage issue. You also have to find a way of storing it in your vehicle. Even compressed to a liquid, hydrogen provides only a quarter of the energy of the same volume of petrol. That means you would need a tank four times the size of a petrol vehicle tank to drive a fuel cell vehicle the same distance. Although it is used in larger vehicles, the large tanks required to carry hydrogen are currently a major obstacle to its widespread use in cars.

But there are more ingenious ways of storing hydrogen involving advanced (solid state) materials. By associating hydrogen with these solid materials inside a tank, more hydrogen can be stored than in liquid hydrogen tanks.

Some of these materials – such as metal hydrides and complex chemical hydrides – can store hydrogen atoms by absorbing them into their framework, where they bond with the host material. Metal hydrides store reasonable amounts of hydrogen but many need high temperatures to release the hydrogen when needed and refuelling can be slow. Complex chemical hydrides store more hydrogen but can be costly and need to be regenerated with hydrogen in a processing plant. Although advanced materials are very promising in terms of the amount of hydrogen that can be stored, the challenge remains to ensure that the hydrogen can be quickly released on demand to cope with, say, the extra energy needed at a moment's notice to accelerate a vehicle.

Other more futuristic materials – such as carbon nanotubes – store hydrogen by having hydrogen simply 'stick' to their surface in a process called adsorption. These materials work by increasing the surface area available for the hydrogen to 'stick' to. Hydrogen can also be stored by this method in metal-organic frameworks (being investigated at the University of Sydney) but they have the drawback of needing very low temperatures and high pressures to be effective.

Related sites

• Hydrogen energy: Challenges and prospects (The Royal Society of Chemistry, UK)

• Hydrogen highway (Canada)

• Fill her up with caged hydrogen (New Scientist, 24 May 2003)

• US Department of Energy
  • Hydrogen storage
  • Hydrogen distribution and delivery infrastructure

• Solid (state) progress (Scientific American, 13 June 2005)

• Australian Academy of Science
  • Hydrogen storage in nanoporous materials
  • Hydrogen storage: Status and prospects

Box 2: Hydrogen – too hot to handle?

For instance, some people believe that hydrogen is not a safe fuel. This attitude was probably formed over many years by incidents such as the Hindenburg disaster in the 1930s, when a hydrogen-filled airship burst into flames in the USA and killed more than 30 people. The incident is memorable because it was filmed and has been shown in countless newsreels, newspapers and television programs. But hydrogen wasn't the culprit. It's now believed that the flammability of a coating on the airship's fabric was the main cause of the inferno.

Likewise, some people wrongly blamed hydrogen fuel for the 1986 Challenger space shuttle disaster, rather than the faulty o-rings later identified by investigators.

Like other fuels, such as petrol and gas, hydrogen is very flammable. But refineries and industrial sites have been producing, storing and using hydrogen safely for a long time. In fact, a hydrogen pipeline has been operating in Germany's Ruhr Valley since 1938 with no apparent problems.

But like any fuel, hydrogen has to be treated with respect, with appropriate storage and handling guidelines. What's different is that because hydrogen is not widely used, people are unfamiliar with how to handle it. But that's changing as more countries draw up appropriate safety frameworks.

Surprisingly, you might actually be better off in the vicinity of a hydrogen spill rather than a petrol or gas accident. Hydrogen is the lightest known element. Gaseous hydrogen has 1/14th the density of air, so when released it disperses quickly and has a strong tendency to rise up. If there's a leak, it doesn't hang around for long so the risk of fire is brief. Even liquid hydrogen, if spilled, evaporates almost instantaneously on account of its low boiling point and diffuses rapidly away.

When it burns, the pale flames tend to shoot upwards (rather than outwards) and there is less radiant heat to burn bystanders, damage property or cause secondary fires. BMW, which has produced a car with an internal combustion engine that uses liquid hydrogen or petrol, has not found safety concerns to be an overwhelming issue. Other factors in hydrogen's favour are that it's non-toxic to the environment, non-corrosive, has no disadvantageous physiological effects, and won't pollute waterways if there is a leak.

But it's not all good news. Hydrogen is colourless, odourless and tasteless. If there's a leak, you won't notice it unless there is a sensor or safety system to alert you. In addition, when hydrogen burns the flames are less obvious than flames of other fuels, posing a further safety risk.

Research at the University of Sheffield in the United Kingdom indicates that hydrogen cars could be a problem if they were involved in an accident in a tunnel, where any fire could reach up to the roof in a 'jet flame' and possibly damage ceilings, sensors and sprinkler systems.

Despite the bad image it might have developed over the years, there seems to be a general consensus that hydrogen is as safe as other fuels such as petrol – if you understand its properties and follow appropriate handling and storage guidelines. Development of such frameworks is underway as researchers pursue the quest to develop a universal hydrogen economy.

Related sites

• US Department of Energy
  • Hydrogen safety
  • Fuel cell engine safety

• Australian fuel cells and safety (National Hydrogen Institute of Australia)

• Hydrogen cars pose tunnel fire risk (New Scientist, 14 November 2007)

Activities

• EcoBus education modules
  • Electrochemical cells experiment – students make an electrochemical cell to power a light bulb.
  • Making H₂ with acid and metal – students make hydrogen by reacting several metals with acid.
  • Make H₂ by electrolysis – students design an experiment to collect hydrogen gas produced by electrolysis.
  • Properties of hydrogen. Treasure hunt – students use the internet to find answers to a series of questions on the properties of hydrogen.
  • EcoBus web quest – a web quest investigating a range of issues associated with using hydrogen vehicles (for younger students).

• US Department of Energy
  • Welcome to hydrogen and fuel cells: A middle school activity guide – contains an extensive range of clear resources and activities on hydrogen production, storage and safety.
  • Hydrogen and fuel cells: How is hydrogen produced, delivered and stored – a clear PowerPoint presentation on hydrogen production, storage and delivery (worksheets are available in the activity guide above).

Further reading

Useful sites

• Australian hydrogen activity
  A comprehensive report on the status of hydrogen as an energy carrier in Australia.
  http://www.ret.gov.au/energy/Documents/facts%20statistics%20publications/aust_hydro_activity_report.pdf

• National hydrogen study
  A comprehensive report assessing the role of hydrogen as an energy carrier in Australia.
  http://www.ret.gov.au/energy/clean_energy_technologies/energy_technology_framework_and_roadmaps/
  hydrogen_technology_roadmap/Pages/HydrogenTechnologyRoadmap.aspx

Australian Broadcasting Corporation

• Hydrogen production from algae (Science Show, 26 April 2008)
  Outlines research into the production of hydrogen from algae.
  http://www.abc.net.au/rn/scienceshow/stories/2008/2224016.htm

• Hydrogen HWY (Catalyst, 4 October 2007)
  Discusses Australian research into the production and use of hydrogen.
  http://www.abc.net.au/catalyst/stories/s2050132.htm

• Tasmanian enviro car nears completion (AM, 10 September 2005)
  Reports on research into cars that run on hydrogen produced by electrolysis from wind energy.
  http://www.abc.net.au/am/content/2005/s1457459.htm

How the hydrogen economy works (HowStuffWorks, USA)

Explains various aspects of the hydrogen economy including production, distribution and storage.
http://auto.howstuffworks.com/hydrogen-economy.htm

Hydrogen fact sheets (The National Hydrogen Association, USA)

Provides clearly written hydrogen "fact sheets" on various topics including hydrogen production and storage.
http://www.hydrogenassociation.org/general/factSheets.asp

US Department of Energy

• Technologies
  Outlines technologies for hydrogen production, storage, delivery and fuel cells.
  http://www1.eere.energy.gov/hydrogenandfuelcells/technologies.html

• Hydrogen production
  Provides a clear overview of methods of hydrogen production.
  http://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/doe_h2_production.pdf

• Hydrogen fuel cell engines and related technologies course manual
  A detailed manual for hydrogen fuel cells.
  http://www1.eere.energy.gov/hydrogenandfuelcells/tech_validation/h2_manual.html

• Today's hydrogen production industry
  Describes hydrogen production in the USA
  http://www.fossil.energy.gov/programs/fuels/hydrogen/currenttechnology.html

Australian Academy of Science

• The two hydrogen economies
  Justifies the need for alternatives to the carbon economy and outlines the state of the hydrogen economy.
  http://www.science.org.au/sats2006/crabtree.htm

• Towards development of an Australian scientific roadmap for the hydrogen economy
  Proposes roadmap for development of an Australian hydrogen economy.
  http://www.science.org.au/reports/hydrogen.pdf

Hydrogen energy: Challenges and prospects (The Royal Society of Chemistry, UK)

A book which includes discussion of the challenges and prospects for achieving a hydrogen economy.
http://www.rsc.org/publishing/ebooks/2007/9780854045976.asp

BMW Hydrogen 7: A sedan fueled by the future (New York Times, USA)

Describes the BMW hydrogen cars in the USA.
http://www.nytimes.com/2008/07/20/automobiles/autosreviews/20AUTO.html?pagewanted=1&_r=4&ei=5087&em&en=b9849f46f5a2a47e&ex=1216699200

Glossary

algae. A large group of simple organisms, ranging from single celled phytoplankton to the larger seaweeds. Like plants they are photosynthetic, but they generally have a simpler structure than plants. Algae are found in water as well as on land.

biomass. Plant or animal matter (including agricultural waste) used as a fuel or energy source. Alternatively, the total mass of living matter within a given environmental area.

complex hydrides. Complex hydrides combine hydrogen with metals and other substances; they typically contain more than one type of metal or metalloid (eg. sodium aluminium hydride).

cryogenic. Relating to very low temperatures.

electrolysis. Chemical reactions brought about by passing electricity through a solution. The following equation illustrates the process of the electrolysis of water (H₂O).

gasification. The conversion of a substance into a gas. The conversion of coal, petroleum or biomass into a gas mixture containing carbon dioxide, carbon monoxide and hydrogen in the presence of oxygen. The gas mixture produced (syngas) can then be treated with steam to produce more hydrogen. Gasification occurs through chemical reactions at high temperature and often at high pressure.

geothermal. Related to the heat emitted from the Earth; for example, hot springs are heated by geothermal sources. Geothermal energy is generated from natural steam, hot water, hot rocks or lava in the Earth's crust.

gigajoule. The joule (J) is a unit for measuring energy.  A gigajoule is one thousand million (10⁹) joules. It is defined as the work done, or energy expended, by a force of one newton moving one metre in the direction of the force.

metal hydrides. Compounds in which hydrogen is bonded chemically to a metal or metalloid (eg. boron or silicon).

metal-organic frameworks (MOFs). Compounds consisting of metal ions associated with organic (carbon-containing) molecules that form three dimensional porous structures. The pores allow storage of gases such as hydrogen by adsorption.

nanotubes. Extremely small tubes that can be made from pure carbon. For more information see IPE nanotube primer (Institut de Physique des Nanostructures, Switzerland).

photoelectrochemical cell. Light (eg. solar) cells that use semiconductors to capture light energy and convert it into electrical energy. The electrical energy is then used directly to produce hydrogen in a process similar to the electrolysis of water.

photosynthesis. The process in which green plants and some other organisms such as algae use energy from light to synthesise carbohydrates from carbon dioxide and water. Photosynthesis can be shown as: