Which way ahead for hydrogen cars?Rising petrol prices and diminishing oil supplies may drive motorists to demand alternative forms of fuel – such as hydrogen.
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Back to basics You will get more from this topic if you have mastered the basics of energy – this link will take you to an annotated list of sites with helpful background information. Key textCompetitors in the men's and women's marathons at the 2000 Sydney Olympics had an exciting glimpse of the future. The pace vehicle that led them round the 42-kilometre circuit looked like a typical family wagon, but looks were deceptive. Under the bonnet was a stack of fuel cells, not an internal combustion engine. And as the car glided silently forward it emitted no smelly fumes or greenhouse gases – just a little water vapour.The car was powered by hydrogen, the simplest and most abundant of all chemical elements. The fuel cells under the bonnet converted the hydrogen directly into electricity. Many experts think hydrogen will replace petrol, diesel and natural gas as the main fuel for cars, buses and trucks over the next few decades. Already car manufacturers around the world have invested billions of dollars in research and development. The advantages of hydrogen are enormous: no more smog-forming exhaust gases, no more carbon dioxide emissions that contribute to global warming, no more worries about diminishing oil supplies and rising prices. But some tricky questions need to be answered before mass-produced hydrogen cars start appearing on the streets:
The choice – combustion or fuel cells? Two kinds of engines can use hydrogen as a fuel – those that have an internal combustion engine converted to use hydrogen and those that are made up of a stack of fuel cells. Internal combustion engines BMW successfully demonstrated this technology in a fleet of 15 sedans used to ferry people to and from EXPO 2000, the world fair in Hanover, Germany. The fact that no major changes need to be made to the basic internal combustion engine design is a major attraction. Fuel cell engines Unlike batteries, which store electricity, fuel cells make electricity as they go. Recent developments in technology have greatly increased the amount of power that a stack of cells – small enough to fit under a car’s bonnet – can provide. This has opened up the prospect of non-polluting electric cars with the levels of performance we expect from conventional vehicles. Fuel cell technology sounds simple. The hydrogen fuel reacts with oxygen from the air to produce water and electricity – the reverse of the familiar electrolysis process that releases oxygen and hydrogen from water. In reality it’s much more complicated. Box 1: Plenty of power from fuel cells outlines how fuel cells will power our cars. The big advantage of a fuel cell engine over an internal combustion engine running on hydrogen is its greater efficiency. The same amount of hydrogen will take a fuel cell car at least twice as far as one with a converted internal combustion engine.
Fill ‘er up please
Hydrogen has many advantages as a fuel for vehicles, but a big disadvantage is that it is difficult to store. This is because at normal temperatures hydrogen is a gas. The hydrogen must be packed tightly into a car’s tank, otherwise a filling stop will be needed every few kilometres. The obvious solution is to strongly compress the hydrogen, or liquefy it. However, large amounts of energy are needed for this – an estimated 20–40 per cent of the energy content of the fuel. Also, tanks designed to hold hydrogen at extremely high pressures, or at temperatures approaching absolute zero, are heavy and expensive. A futuristic filling station kept EXPO 2000's fleet of converted BMWs running. Drivers pulled up at the pump, pressed a button on their dashboard, and watched from inside the car as a laser-guided robotic arm connected the store of liquid hydrogen to their tank. Filling took about 3 minutes. It was wise to keep well out of the way – at minus 253ºC, liquid hydrogen is unimaginably cold. The special insulated tanks in the BMWs held 140 litres of hydrogen, enough to drive at least 300 kilometres. (That’s a reasonable range, although a 95 litre tank of petrol would take the same cars twice as far.) The hydrogen-powered marathon car at the Sydney Olympics also ran on liquid hydrogen. Its much smaller tank (75 litres) gave it a range of about 400 kilometres, a sign of the greater efficiency of fuel cell cars. High cost and the large amount of energy needed to liquefy the fuel are likely to be the main problems with refuelling with liquid hydrogen. Filling up with compressed hydrogen gas will probably prove more practical, even though it may reduce the distance between fills. Cars could store the hydrogen in high pressure tanks similar to those used for compressed natural gas. Or, if current research proves successful, some high-tech alternatives could be employed. Scientists have found that various metals can absorb up to a thousand times their own volume of hydrogen gas. Specially treated carbon may also hold large amounts. These discoveries could shape the fuel tanks of the future (Box 2: Alternative hydrogen storage systems).
But where will the hydrogen come from?
There’s no risk that we’ll ever run out of hydrogen, it's by far the most plentiful element in the universe. On Earth, however, it exists naturally only in chemical compounds, not as hydrogen gas. Water and the main components of coal, oil and natural gas are prime examples of these compounds. Natural gas currently provides most of the hydrogen used in industry. The relatively simple technology employed – steam reforming – could also produce hydrogen gas for cars at central plants or filling stations. Alternatively fuel tanks could be filled with petrol or methanol, with the cars using on-board ‘reformers’ to generate hydrogen for their fuel cells. This shows promise as a transitional measure while research proceeds on the problems of storing hydrogen. In steam reforming the hydrocarbon fuel reacts with water at high temperatures to produce hydrogen gas. A major drawback is that carbon dioxide and smog-causing gases such as nitrogen oxides are given off too, although emissions per kilometre of car travel would be less than from petrol-burning vehicles. An alternative approach now under development, autoreforming, should increase the attractiveness of on-board hydrogen production. Use of a catalyst will allow the reforming to occur at much lower temperatures – too low for the production of nitrogen oxides. Water is the only potentially pollution-free source of hydrogen. Researchers are looking at new ways of producing hydrogen – using algae, bacteria or photovoltaic cells to absorb sunlight and split water into hydrogen and oxygen. But the technology most likely to be adopted on a large scale is electrolysis, which uses an electric current to split water into oxygen and hydrogen.
Is it safe?
‘Remember the Hindenburg’ – that’s a phrase often heard when hydrogen is discussed. This German passenger airship, kept aloft by hydrogen, crashed in flames as it came in to land at Lakehurst, New Jersey, USA in May 1937. Thirty-five people died. Nowadays helium, which can’t burn, is the gas of choice for lighter-than-air craft. Hydrogen is highly flammable, but recent research has indicated that the airship’s fabric, not hydrogen, was the culprit in the Hindenburg disaster. Properly handled, there’s no reason to think hydrogen is any more dangerous as a fuel than petrol, the explosive liquid now carried safely in the tanks of untold millions of motor vehicles.
Looking forward
Recent technological advances, particularly in fuel cell design, have made hydrogen-powered cars a practical proposition, and car makers expect to start mass-producing them within the next decade or so. Their power and acceleration should match those of today’s petrol-powered vehicles, but they may have to be refuelled more often. The best ways to produce, distribute and store the hydrogen still have to be sorted out. In the short term fossil fuels may remain in demand as a hydrogen source. However, the idea that in the not too distant future most of us will be driving non-polluting cars fuelled by hydrogen from a clean, renewable source is no longer a flight of fantasy. Related Nova topic:
Fuel cells have been around for a long time – Sir William Grove, a Welsh physicist, invented one that ran on hydrogen way back in 1839 – but their potential as a commercial power source is only now beginning to be realised. With different applications in mind (from large-scale power generation to electricity for portable electronic devices), researchers are working on many types of cells – alkaline, phosphoric acid, molten carbonate and proton exchange membrane (PEM). In Australia, CSIRO and industry researchers are collaborating in developing a solid oxide fuel cell.
A fuel cell for vehicles
For vehicles, attention has focused on the PEM fuel cell. Its key component, the membrane, is a sheet of rubbery plastic coated with a platinum catalyst. The catalyst splits hydrogen gas into protons and electrons (a hydrogen atom comprises just one proton and one electron). The protons pass through the membrane and the electrons leave the cell along wires; this is the electric current generated by the cell. When the protons and electrons meet again on the other side of the membrane, they combine with oxygen to form water. As long as hydrogen is supplied the cycle continues, with hydrogen and oxygen being turned into water while generating electricity. A great advantage of this type of fuel cell is that it operates at 60-90ºC whereas other types require temperatures of 500-1000ºC. The breakthroughs that turned stacks of PEM cells into suitable power packs for cars came in the 1990s. Ballard Power Systems of Canada, whose two largest shareholders are DaimlerChrysler and Ford, discovered a way to multiply a stack’s power output per litre from less than 200 to more than 1300 watts. With such a stack under the bonnet, an electric car can match the performance of petrol-powered models.
Trials of PEM fuel cell buses in Perth
Trials of Mercedes-Benz buses powered by Ballard’s PEM fuel cells have been conducted successfully over the past few years in Chicago and Vancouver, and Perth is one of eleven cities around the world to host a bigger series of trials. Beginning in 2002, these trials involve a total of 33 fuel cell powered buses. The three buses in Perth slot into the regular commuter fleet and are fuelled by hydrogen produced at the BP petroleum refinery at Kwinana. Related sites
In one approach, hydrogen combines with a pure or alloyed metal to produce a metal hydride. Heating the hydride releases the hydrogen. Studies have shown that this system can store hydrogen at higher densities than simple compression. The challenge remains, though, to identify a metal that will store and release sufficient hydrogen at temperatures suited to a practical system. Very small glass spheres are the basis of another approach. During filling, hydrogen passes through the glass at high temperatures. Cooling stops this movement, trapping the gas at high pressures inside the ‘microspheres’. Another technology uses carbon nanotubes – tiny fibres of graphite. Research has shown that these can absorb very large amounts of hydrogen, storing much more fuel per litre than is possible with either liquefied or compressed hydrogen. As with the other approaches though, substantial problems need to be solved before a practical storage system emerges.
Australasian Science May 2008, pages 20-22 Just add water (by Peter Pockley) Proposes a new source of hydrogen using aluminium.
March 2008, pages 30-32 The road to the hydrogen economy (by Cameron Kepert and Vanessa Peterson) Describes developments in the storage of hydrogen gas.
August 2002, pages 22-26 Hydrogen – Australia's energy future (by Julian Cribb) An interview with two of Australia's leading energy scientists.
Winter 1996, pages 51-53 Sydney 2000 and the electric car (by Simon Tonkin and Paul Tonkin)
Ecos No. 117, 2003, pages 20-24 Towards the forever fuel (by Steve Davidson) Looks at the problems to be overcome before a hydrogen fuel economy can be realised.
No. 116, 2003, page 6 Perth’s hydrogen bus trial (by Steve Davidson) Describes trials in Perth and ten European cities of hydrogen powered buses.
Nature 28 April 2010, pages 1262-1264 Hydrogen vehicles: Fuel for the future? (by Jeff Tollefson) Assesses the main challenges facing adoption of hydrogen cars.
13 August 2009, pages 809-811 Technology: Hydrogen-fuelled vehicles (by Louis Schlapbach) Answers a series of frequently asked questions about hydrogen on its use, safety and storage.
New Scientist A collection of articles on cars and motoring is available.
29 November 2008, pages 40-43 Hydrogen’s long road to nowhere (by David Strahan) Describes progress made towards establishing a hydrogen economy.
10 November 2007, page 29 Hydrogen cars pose tunnel risk Discusses the potential risks of hydrogen cars in road tunnels.
29 July 2006, pages 35-37 Power on tap (by David Adam) Looks at research into making hydrogen on demand to fuel cars.
25 February 2006, pages 37-39 Green gold (by Peter Aldhous) Looks at the possibility of using photosynthetic algae to produce hydrogen.
1 October 2005, page 24 Hydrogen power brewed on the go (by Helen Knight) Describes a device made to generate hydrogen for micro fuel cells for electronic gadgets.
9 April 2005, page 6 Fuel cell squeezes more from petrol (by David Chandler) Describes a high octane burning fuel.
15 November 2003, pages 6-7 Reality bites for the dream of a hydrogen economy (by Anil Ananthaswamy) Discusses possible problems associated with the use of hydrogen.
16 August 2003, pages 8-9 The clean green energy dream (by James Randerson) A report on the use of hydrogen as an energy source.
24 May 2003, page 18 Fill her up with caged hydrogen (by Nicola Jones) Describes a new way of storing hydrogen gas for electric cars powered by fuel cells.
25 November 2000, pages 35-42 Kicking the habit (by Fred Pearce) Describes the advantages of hydrogen as a clean, green fuel.
RTD Info August 2004 Hydrogen is on the way Reviews the various alternatives to fossil fuels and looks at the ‘production-storage-transport’ chain envisaged as part of the hydrogen economy.
August 2004 Fuel cells Summarises the range of fuel cells with a variety of potential applications from vehicles to power stations.
August 2004 H2 hour Looks at options for the production, storage and distribution of hydrogen.
Science 24 June 2005, pages 1901-1905 Cleaning the air and improving health with hydrogen fuel-cell vehicles (by MZ Jacobson, WG Colella and DM Golden) This technical article estimates the impact of changing all vehicles in the USA to hydrogen fuel-cell vehicles, in terms of air quality, health and climate.
Scientific American 3 June 2008 Gassing up gas-free (by Eliot Caroom) A slide show which looks at the infrastructure necessary for hydrogen hybrid cars.
April 2007, pages 62-69 Gassing up with hydrogen (by Sunita Satyapal, John Petrovic and George Thomas) Looks at research into ways for fuel cell vehicles to store hydrogen needed for long distance travel.
September 2006, pages 70-77 High hopes for hydrogen (by Joan Ogden) Looks at options for a hydrogen infrastructure, advances in fuel cells, and some of the hurdles to be overcome in the technology towards the use of hydrogen as an energy source.
July 2006, pages 59-65 A power grid for the hydrogen economy (by Paul Grant, Chauncey Starr and Thomas Overbye) Summarises a network of infrastructure to transport both electricity and hydrogen.
May 2004, pages 40-47 Questions about a hydrogen economy (by Matthew L. Wald) Looks at the use of hydrogen fuel cells to power cars and other devices, comparing fuel cells with conventional petrol-fuelled vehicles.
October 2002, pages 40-49 Vehicle of change (by Lawrence D. Burns, J. Byron McCormick and Christopher E. Borroni-Bird) Discusses fuel cell vehicles and explains that they could motivate a shift to an energy economy based on hydrogen.
Dawn of the hydrogen age (Wired, October 1997, USA)
A readable account of the use of hydrogen as a fuel, concentrating on its use in transportation. The article highlights the importance of using cleaner fuels, but notes the difficulties involved in switching to hydrogen power. Explores some alternatives to an immediate switch to hydrogen as a transportation fuel.
Hydrogen: Fuel of the future (American Society for the Advancement of Science, USA)
Thorsteinn Sigfusson, professor of physics at the University of Iceland in Reykjavik and chairman of Iceland New Energy, says that Iceland is set to become birthplace of the hydrogen economy -- providing electricity, heating its buildings through the long winters, and running its buses, trucks, cars and even trawlers.
Harnessing hydrogen: the key to sustainable transportation (INFORM, USA)
Covers different aspects of the advantages and challenges of hydrogen as a transportation fuel. It also presents the ways that vehicles could use the hydrogen (eg, internal combustion engines, fuel cells and hybrid vehicles).
The hydrogen economy (Physics Today, USA)
Describes the basic research that is required in materials and design to make hydrogen-based energy a viable proposition.
Australian Broadcasting Corporation
How a fuel cell works (Union of Concerned Scientists, USA)
A very brief illustrated introduction to a hydrogen car's fuel cell.
How Stuff Works (USA)
Fuel cells (Fuel Economy, Department of Energy and Environmental Protection Agency, USA)
Explains the difference between a fuel cell and a battery, and includes an annotated diagram of a proton exchange membrane (PEM) fuel cell.
Melbourne University's hydrogen car (University of Melbourne, Australia)
Explains the problem of using hydrogen as a fuel in an internal combustion engine (and provides a solution). Includes animated diagrams.
Hydrogen is on the way (RTD Info, European Union)
The concept of the hydrogen economy has become one of the fundamental elements on which the European Union is focusing its sustainable energy policy for the decades to come.
element. A substance made up of only one type of atom. For more information see our Back to basics topic, Atoms and molecules. fuel cell. A device that converts energy from chemical reactions directly into electrical energy. The simplest fuel cell 'burns' hydrogen in a flameless chemical reaction to produce electricity. In order to 'burn' the hydrogen a fuel cell needs a source of oxygen and this is usually obtained from air. The only by-product from this type of fuel cell is water. For more information about fuel cells see Fuelling the 21st century (Nova: Science in the news, Australian Academy of Science). nanotubes. Extremely small tubes made from pure carbon. For more information see IPE nanotube primer (Institut de Physique des Nanostructures, Switzerland). photovoltaic (PV) cells. Also known as solar cells. A photovoltaic cell is made of thin wafers of two slightly different types of silicon. One, doped with tiny quantities of boron, is called P-type (P for positive) and contains positively charged 'holes', which are missing electrons. (Electrons are negatively charged particles that orbit the nuclei of atoms.) The other type of silicon is doped with small amounts of phosphorus and is called N-type (N for negative). It contains extra electrons. Putting these two thin P and N materials together produces a junction which, when exposed to light, will produce a movement of electrons – and that constitutes an electric current. Photovoltaic cells thus convert light energy into electrical energy.
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