The quest to make hydrogen the fuel of the future
Key text
This topic is sponsored by the Australian Research Council Linkage Learned Academies Special Project Grant.
Australia and many other countries around the world are preparing for hydrogen to take over from fossil fuels such as oil and natural gas, and move to what's being called the 'hydrogen economy'. But there are some big hurdles to overcome before it can happen.
You may not realise it, but scientists, the energy industry, governments and climate change experts around the world have joined forces and are on a global quest - and a race against time. Their goal is to find an economical, practical and safe form of energy to replace our reliance on fossil fuels.
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.
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), and there is no infrastructure yet to ensure that it can be supplied cheaply, conveniently and safely (Box 2).
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.
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.
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'.
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.
Boxes
1. Storing and distributing hydrogen
2. Hydrogen – too hot to handle?
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Posted September 2008.