TWICE as far on a single tank of fuel? That鈥檚 the implication of a breakthrough in fuel-cell technology announced last week that promises to deliver almost twice the efficiency of today鈥檚 most efficient cars. But while its makers hope the cell will help the world to use its oil more efficiently, others say it is a distraction from the real goal of weaning us off the black stuff entirely.
Fuel cells combine hydrogen and oxygen to make water and electricity, and are seen by many as the only long-term alternative to the internal combustion engine. But while the oxygen is freely available in the atmosphere, hydrogen must be prepared in advance. The hydrogen-fuelled dream is that we will break down water into hydrogen and oxygen using electricity from renewable sources such as the wind or sunshine.
But the technology and the infrastructure to make and distribute renewable hydrogen on the scale required for widespread use are still decades away. And with few hydrogen cars on the road, there is little incentive to build a network of hydrogen filling stations. What is more, the lack of demand means there is little immediate prospect that fuel cells will benefit from the economies of scale that could make them affordable. It鈥檚 one chicken-and-egg problem after another.
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If hydrogen is to become the fuel of the future, a stepping-stone technology will be needed to break the deadlock by making hydrogen some other way. Till now, nobody has been able to make such a stepping stone work efficiently. But researchers at Northwestern University in Chicago may have come up with a solution. It鈥檚 a fuel cell that runs on octane, the major component of petrol, so a car running on such a fuel cell should in principle be able to fill up anywhere.
It鈥檚 not the first attempt to tap into the existing petroleum-based infrastructure. Many teams have experimented with in-car devices that use a catalyst to convert the hydrocarbons in petrol, diesel or natural gas into hydrogen, a process called reforming. But combined with the fuel cell, reforming suffers from 鈥渃oking鈥�, in which the breakdown process creates carbon that builds up on the fuel cell鈥檚 anode. This dramatically reduces its efficiency. In addition, reforming only works at a high temperature, and the energy needed to heat the reformers reduces the efficiency of these systems to a mere 29 per cent.
The new system, developed by materials scientist Scott Barnett and his graduate student Zhongliang Zhan, avoids this. Rather than running a separate reformer and fuel cell, they have combined the two and use the waste heat from the power-generating process to help power the production of hydrogen. 鈥淲e have bypassed these technological hurdles by basically bringing the hydrogen plant inside,鈥� Barnett says. Their system promises an overall efficiency of 50 per cent. That not only beats today鈥檚 fuel cells, it would even beat petrol-electric hybrid vehicles, which have an efficiency of 32 per cent.
Barnett and Zhan beat the coking problem by coating the anode with zirconium oxide sandwiched between layers of ruthenium cerium oxide. This catalyses the reaction between carbon and oxygen to form carbon dioxide, preventing solid carbon deposits. In lab tests using iso-octane 鈥� which is similar to petrol but without the usual additives 鈥� the catalytic layer completely eliminated the coking problem, the team has reported in Science (DOI: 10.1126/science.1109213).
There are still problems, however. The system is based on a solid-oxide fuel cell that operates at temperatures of up to 800 掳C and needs time to warm up before it can be used. This means that these units are likely to be used first as secondary power supplies. They could also be incorporated into hybrid vehicles that run on battery power for the first few minutes of driving while the fuel cell warms up.
鈥淓ven if they only served as secondary power units, the cells could have a big impact on efficiency and emissions鈥�
But even if they only served as secondary power units, the cells could have a big impact on efficiency and emissions. 鈥淚f you鈥檝e ever been to a truck stop, it鈥檚 a nightmare,鈥� Barnett says. It is common to find the huge diesel engines of trucks running for hours just to provide power for a few accessories.
The US military, which has funded much of the research through the Pentagon鈥檚 research arm DARPA, is also interested in the fuel cells because they provide quiet, limited-emission power that would make military vehicles harder to detect. The hope is that between them, these customers could provide the all-important demand to kick-start the fuel cell market.
鈥淭he US military is also interested in the fuel cells because they would make its vehicles harder to detect鈥�
David Friedman of the Union of Concerned 杏吧原创s agrees that such applications could save enormous amounts of wasted fuel, but cautions that solid-oxide fuel cells remain at an early stage of development.
Closer to fruition for primary power is a type of hydrogen fuel cell called a polymer-electrolyte membrane (PEM) being developed by Ballard Power Systems of Vancouver, Canada, the world鈥檚 leading producer of fuel cells for vehicles. But the widespread use of PEMs will depend on a reliable source of hydrogen, either from on-board reforming of hydrocarbons or the widespread distribution of hydrogen.
Friedman warns that these projects could distract effort from more immediate problems. He says other strategies should be a priority, such as the development of lightweight frames, low-resistance wheels and improved aerodynamics, which could double fuel efficiency in conventional cars, and the development of better hybrid vehicles that could double it again. 鈥淎ll these developments in the short term also make it easier for fuel cells to succeed in the long run,鈥� he says. 鈥淚t鈥檚 about balance.鈥�
