Often, when the subject of global warming is discussed, attention quickly turns to our automobile habits, and rightly so: they account for almost 20% of global carbon dioxide emissions. If that figure isn’t shocking enough, it is generally agreed that it will rise far above its current level as lesser economically developed countries begin to follow our lead. A pivotal point has been reached, as manufacturing methods become cost-effective enough to market cars to these massive populations. Although these cars are smaller, and therefore more fuel-efficient, there will soon be vast numbers of them adding to the automobile industry’s CO2 output. So, what are our options?

An oft-vaunted panacea is the idea of hydrogen-fuelled vehicles; burning hydrogen in air produces only water, as the hydrogen and oxygen molecules combine into their most natural state. More often than not, the fact that hydrogen can be obtained from water itself is thrown around in conversation. So, what could be wrong with a fuel obtained from water, which burns to form water? For those of you familiar with energy conservation laws, alarms should already be ringing. The concept of hydrogen fuel seems like a squeaky clean solution to the problem, but many, many factors are being ignored. Where, exactly, does our hydrogen come from? Often glossed over with a reference to its derivation from water, this question is a difficult one to answer, and so very rarely in the spotlight. Currently, the most efficient method of hydrogen extraction we have is chemical extraction from hydrocarbons, the technical name given to the family of chemicals which our current fossil fuels fall into. This, however, raises the now-common problem of sustainability, as natural gas deposits are increasingly hard to find. More damningly, it also results in large quantities of CO2 and carbon monoxide being released.

The claims of hydrogen being obtainable from water are, in fact, technically founded and valid. The process of electrolysis, applying huge voltages across water to split water into hydrogen and oxygen, has an efficiency of around 70%. This means that of the electrical energy used in electrolysis, around 70% can be retrieved by the combustion of the resulting hydrogen gas. However, this ignores the energy production method. Even our arguably most efficient and viable method for electrical energy production, nuclear fission, results in a net loss of around 65% of the energy released from plutonium. A lot of this inefficiency arises from the nuclear reactor system, however – the heat given off by nuclear fission is transferred by liquid of a high latent heat to a vast quantity of water, which expands into superheated steam as this heat is transferred to it, driving turbines. Inefficiency arises in the both the transport of heat, and the generation of electromotive force (voltage) in the turbine generators. It has been demonstrated in the laboratory that using high temperatures (of around 900C), to split water molecules is almost twice as efficient. These temperatures could only realistically be achieved on a large scale as part of a nuclear reactor, but there is one massive advantage: power stations could feed the national power grid during the daytime, and at times of low demand, such as night, generate hydrogen gas.

Once gas has been produced, there is the problem of storage. Being a gas, hydrogen is much less dense than conventional fuels, requiring huge tanks to compete in terms of vehicle range. Compression is a way around this, but requires extreme pressures or incredibly low temperatures. There are also major safety concerns – hydrogen combusts much more rapidly than conventional fuels. If petrol is set alight in an open space, it simply burns; the only reason cars are capable of explosion is the confinement of petrol tanks combined with rapid expansion. If hydrogen is set alight, even in an open space, it will expand forcibly enough to be classed as an explosion. If confined to a tank, the results could be devastating. Cooling the gas to liquid has little effect, and is hugely expensive, both in terms of equipment and energy. A research unit under the banner of United Nuclear, based in New Mexico, has recently successfully employed a very different method of storage. By chemically binding hydrogen to metal hydrides inside their tanks, the hydrogen storage can be even denser than water, and completely safe; their research website states that one “could even fire incendiary bullets through the tank and the Hydride would only smoulder like a cigarette”. To release the hydrogen from its bonds, heating elements can be used to release hydrogen as and when required. These tanks are still being tested, and as yet are still unavailable for purchase.

The most important aspect of hydrogen fuel technology, however, is its direct usage in a vehicle to produce forwards motion. When people talk of hydrogen “fuel cells”, they are referring to a still fairly experimental device that combines hydrogen and oxygen to form water, using the reaction to directly produce electricity to turn a large electric motor, providing force for locomotion. Although this method is hypothetically highly efficient, we are a long way off having it stable or cheap enough to make available commercially. There is also the difficulty in getting rid of and replacing every single internal combustion engine powered car that is currently in use. These shortcomings have led to a different approach being explored. Again, a major research area of the aforementioned company, many are turning to the idea of adapting conventional internal combustion engines to burn hydrogen in place of fossil fuels. The replacement is surprisingly simple, with the correct electronics regulating release and flow of hydrogen to the cylinders. There are a few stumbling blocks in terms of compression ratios and “knocking” – fuel beginning to combust too early in a cylinder’s stroke, damaging the engine – but trials have been mostly successful. The major advantage of the concept is that a car could store both hydrogen fuel and petrol, as a backup fuel, leaving the driver’s options open. A knock on effect of this is an increased range for the vehicle.

So where do we stand? Is hydrogen as a fuel a viable and sensible possibility? Overall, I would say yes, it is – with the exception of production. The most effective method available seems to be using a nuclear fission reactor’s heat during the nighttime, but there are negatives associated with the nuclear fission process. Using hydrogen as a fuel is not the panacea it is often held aloft as, but may be part of the overall solution.

Copyright Ethan Fowler, 2008

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