© The Economist, London, March 24th 2001
Motor manufacturers are betting heavily on fuel cells as the engines for tomorrow’s cleaner cars. But how to make and store the hydrogen fuel? This feature, kindly supplied by The Economist, looks at some of the significant technical challenges presented by fuel-cell technology in the automotive application field.
THE thundering tom-toms just might be a sign of big changes ahead. Not long ago, dozens of people from around the world descended upon an idyllic country retreat in Canada for a most energetic pow-wow. The motley crew sat in a giant circle with native drums of every imaginable size and shape, and banged away till green inspiration struck. They then strategised about how to move the energy world beyond the filthy but durable workhorses of today-fossil fuels and internal combustion engines. They agreed that the future belongs to fuel cells, which produce clean energy by combining hydrogen with oxygen without combustion.
Now, here is the weird part: those peculiar percussionists were not wild-eyed greens, but sober technical experts from the world’s biggest car companies, energy firms and research laboratories. Indeed, the whole shindig was organised by the new hydrogen division of BP, an oil giant. The reason for their enthusiasm was that, more than 150 years after its invention, the fuel cell is finally about to become a commercial reality.
BP are amongst many global organisations that support the commercial reality of fuel cells
In simple terms, fuel cells combine hydrogen and oxygen to produce electricity, while avoiding combustion and emissions any nastier than water and heat. Although there are variations on the theme, the most promising type of fuel cell is the “proton-exchange membrane”. This is a sandwich of two electrodes – an anode and a cathode – with a polymer membrane serving as an electrolyte stuck in the middle. At the anode, hydrogen gives up its electron with encouragement from the platinum catalyst. While the hydrogen ions (protons) slip through the membrane, the electrons are forced to travel around an external circuit, producing a current that can power a car or a computer. When the protons reach the cathode, they join with the electrons and combine with oxygen from the air to create water and heat. The result is clean energy with no harmful emissions.
“It is clear that the electricity industry will be turned on its head by fuel-cell micropower”
But some think that fuel cells might even reach hydrogen’s promised land: to become the power source of choice for transport. Nearly all of the world’s leading motor manufacturers are trying to develop fuel-cell cars. Goaded on by government threats of “zero emission vehicle” mandates in California and curbs on carbon emissions in Europe, they are pouring billions of dollars into fuel-cell research. They vow to have fuel-cell cars on the market by 2004.
So the hydrogen revolution is about to transform ground transport? Do not hold your breath. In fact, fuel cells might yet prove to be a costly and humiliating flop in cars, even as they take off in other applications. The reason is that the world is just not set up to deliver hydrogen on demand.
In tackling that slightly awkward problem, fuel-cell fans fall into two camps. One camp thinks that hydrogen infrastructure will be far too costly to build for decades to come, and so wants to use some interim fuel during the transition. Such voices point to studies suggesting that building a hydrogen infrastructure could cost $100 billion or more in America alone. The other camp reckons that the investment needed will be much less, and insists that going direct to hydrogen is the only sensible option. Who is right, never mind who will win, is unclear.
The reform club
Everybody agrees that the greenest and most elegant way to feed fuel cells is using hydrogen fuel directly. Indeed, some day in the future, the hydrogen may even be derived from renewables. Until that Utopia arrives, many firms plan to use interim fuels such as methanol or petrol and extract hydrogen on board the vehicle using a “reformer”. Such cars would not be emission-free, but would still be much cleaner than today’s vehicles.
BMW CleanEnergy 750hl Sedan
The methanol champions argue that, unlike petrol, their fuel can be produced from a variety of sources ranging from natural gas to “biomass” (ie, plant matter, cow dung and such like). This may make methanol attractive in poor countries, which use a lot of biomass. Rich countries may prefer methanol because it would reduce their dependence on OPEC.
Advocates note that there are big plants today producing methanol; indeed, there is a global glut. They suggest that this is enough to feed early fuel-cell cars, and so help to achieve mass-market economies of scale-at which time hydrogen can make a graceful entry. Maybe. The danger is that as methanol fuel cells take off, output will have to be increased and retail distribution expanded, leading eventually to stranded assets. Sceptics argue that it might be cheaper to go straight to hydrogen.
Even so, DaimlerChrysler gushes about its “direct methanol” fuel cell, which needs no reformer at all. It recently demonstrated a 3 kilowatt version which powered a go-kart. If perfected, this would be a genuine breakthrough. However, huge technical hurdles remain and commercialisation looks a decade or two away.
The best argument for methanol reformation is that it clearly works, while petrol reformation remains in doubt. That is chiefly because petrol-a far more complex fuel than methanol-contains carbon-carbon molecular bonds that take a lot of energy to break. Petrol reformers must operate at high temperatures (ie, 800°-900°C), while methanol reformers run at perhaps a third of that temperature. The methanol backers gloat that they have more or less solved the chief technical puzzles: Daimler’s new NECAR5 boasts a reformer that powers a 50 kilowatt fuel-cell stack, while petrol reformation remains stuck in the laboratory.
But the petrol researchers insist they have made great progress in recent months. Bill Innes of Exxon Mobil claims that his firm’s fuel-cell alliance with General Motors and Toyota, which has been spending $100m a year on research, has made a breakthrough with its laboratory reformer. He is hoping to install it in a fuel-cell vehicle by the end of this year.
“With public education and garage-style handling, hydrogen can be at least as safe as today’s fuels.”
For the first time, DaimlerChrysler have introduced a fuel cell car in the U.S – the NECAR
If petrol reformation takes off, methanol will lose out. After all, petrol is ubiquitous and familiar and the world is set up to deal with it on a massive scale. However, there is a wild card that could still cause petrol reformation to fail in the market, argues Robert Williams of Princeton University. That is the recent arrival of highly efficient hybrid cars such as the Toyota Prius and Honda Insight that combine petrol engines with electric motors. He argues that as long as the main competition for the petrol fuel-cell car was the conventional internal combustion engine car, the economic case made some sense. The higher initial cost (an extra $5,000, including the reformer) could be more than offset by the likely doubling of the fuel efficiency plus the environmental benefits. However, these new hybrids achieve levels of fuel efficiency and emissions comparable to those of petrol fuel-cell cars today-but at a much lower cost, even when the manufacturers’ hidden subsidies are discounted. It is quite possible that petrol fuel-cell cars could lose out to hybrids and thus fail to capture the market share needed to succeed.
Encouraged by the clouds hanging over reformers, some argue for a move direct to hydrogen. Before contemplating the economics, however, enthusiasts for such an approach must first surmount three hurdles that opponents claim are insurmountable: safety, storage and supply. The easiest to tackle is safety. Hydrogen is often perceived as dangerous, but that reputation is largely undeserved. It is true that hydrogen is inflammable. But methanol is corrosive and extremely toxic, and petrol is both a carcinogen and easily ignited. A related factor is that hydrogen is a gas at room temperature and disperses rapidly, unlike methanol and petrol. With public education and garage-style handling, hydrogen can be at least as safe as today’s fuels.
A tougher challenge is storage. The problem is that hydrogen has the smallest atomic structure of all elements. That causes two problems when trying to handle it. One is that, being so tiny, hydrogen atoms can wiggle through the crystal lattice of the material used to contain it. The leakage from a pressurised hydrogen tank could be significant. The second problem is a consequence of the fact that, being so small, hydrogen is also exceptionally light. In a typical gaseous storage system, it has only a tenth of the volumetric energy density of petrol.
The obvious answer is to compress the hydrogen. IMPCO, the leader in this field, has devised an ingenious all-composite tank that can hold enough hydrogen at a pressure of 5,000 pounds per square inch (psi) to travel 300 miles. The tank meets stringent safety standards and is expected to cost only about $1,000. Holding more than 40 gallons of hydrogen, it is still far bulkier than the average petrol tank. But the firm is testing a tank capable of storing hydrogen at 10,000psi, which should be much more compact.
Hydrogen is very small and light – making it difficult to store
The best way to store hydrogen, however, may well be in some solid form. That would offer advantages of safety as well as convenience. Some experts point to the promise of so-called carbon nanotubes-a form of carbon that experiments suggest could reversibly store astounding quantities of hydrogen. But that is fantasy for the time being. A more tangible approach involves metal hydrides, which store and release hydrogen in the way that the batteries in some of today’s mobile phones and laptop computers do. The firm that pioneered the rechargeable nickel-metal hydride battery, Energy Conversion Devices (ECD) of Troy, Michigan, claims to have repeated the same trick with fuel cells.
Though rivals are sceptical, ECD’s Alastair Livesey says tests prove that its new metal hydride can be recharged in just a few minutes; will last for over 500,000 miles; and can travel 300 miles without refuelling. The tank will weigh about 220 pounds-twice the weight of a full petrol tank-but be only slightly larger, and drivers could fill it up with hydrogen at filling stations. The firm and its oil industry partner, Texaco, believe they can get this project from the research phase to the mass market within five years.
But what about supply? In itself, hydrogen is just a fuel, not an energy source. Hydrogen is the most abundant element in the universe, but rarely exists in its free state on earth-being found normally in combination with oxygen (as water) or carbon (as methane and other hydrocarbons). As a result, it always takes energy to free it for use, whichever way it is produced.
One approach is to strip hydrogen out of hydrocarbons. Firms already do this today by reforming natural gas at centralised plants. The hydrogen produced in this way is used to make ammonia fertilisers and to “lighten” heavy grades of crude oil. The earth’s vast reserves of coal could also be tapped. The production costs of hydrogen from such centralised approaches could be competitive with that of petrol, but the snag is that an expensive system of pipelines or tankers would still be needed to get that hydrogen to consumers.
Another approach is electrolysis, which zaps hydrogen free from water using electricity. This process is energy intensive, so large-scale electrolysis is likely to take off first in places with cheap, clean sources of hydro-electricity. However, it does benefit from the fact that its two prerequisites, electricity and water, are fairly well distributed around the world.
Crunching the numbers
Even if safety, storage and supply are sorted out, does a direct shift to hydrogen make economic sense? It might, provided three big “ifs” are fulfilled-if the hydrogen is phased in over time, if governments give hydrogen strong regulatory support, and if manufacturers produce hydrogen cars that consumers actually want to buy.
To reduce the cost of manufacturing fuel cells and win public acceptance, central and local authorities will have to encourage a shift to hydrogen for fleet vehicles such as city buses, delivery trucks and so on. Since such vehicles are roomy, compressed hydrogen tanks will not be much of a penalty. Fleets of commercial vehicles have the added advantage of refuelling at central depots. So, setting up the infrastructure for refuelling them will be less of a problem. Already, hydrogen buses have been roaming the streets of Vancouver and Chicago. The World Bank believes such vehicles could play a role in helping to reduce urban smog in poorer parts of the world.
ExxonMobil, GM and Toyota have formed a fuel cell alliance, and have been spending $100m a year on research
“As fuel-cell technology matures, a rising level of efficiency will mean falling operating costs.”
Phasing in hydrogen infrastructure is thus the first part of the puzzle. The oft-cited estimates of $100 billion or more for that are outlandish. That is because duplicating today’s petrol infrastructure, from day one, is simply not necessary. Experience with the introduction of diesel in America and unleaded petrol in Germany shows that even if only 15% of forecourts offer it, a new fuel can become widely accepted.
Directed Technologies, a consultancy based in Arlington, Virginia, argues that hydrogen can be produced in a distributed way economically. One option is to tap into the existing natural-gas grid to reform hydrogen. Firms such as International Fuel Cells of South Windsor, Connecticut, are now developing small reformers to do precisely that. These can be placed at petrol stations, supermarkets or even office blocks. Stuart Energy, a firm based in Toronto, is building tiny electrolysers for a car that can produce hydrogen from off-peak electricity. It aims to sell these for $2,000. Electrolysis is especially suited to the early years of hydrogen-powered cars because it is inherently scalable. Hydrogen electrolysis units make economic sense with only 25-50 cars sharing them. By contrast, the smallest hydrogen reformers need 300 users or so to be cost-effective.
Thus the economics of a hydrogen roll-out are not complete nonsense. Even so, explicit government supportmay still be needed. A new study by Dr Williams and Joan Ogden and Eric Larson, two colleagues at Princeton, suggests that, after the initial introduction, direct hydrogen fuel-cell cars will offer significantly lower costs and greater benefits to their users, as well as to society as a whole, than rival fuel-cell options. Unfortunately, the initial hurdle is so high that market forces alone may not spur the necessary investments. Dr Williams thinks the direct-to-hydrogen route will fail unless governments embrace zero-emission mandates like the Californian initiative. But if they do that, the Princeton group expects hydrogen fuel-cell cars to be successful. Within 20 years, they argue, the world could then enjoy extremely low vehicle emissions-and consumers would pay no more than they do today for transport.
That points to the most crucial factor of all in deciding the fate of fuel cells in transport-the actual consumer benefits. The clearest advantage fuel cells offer over the internal combustion engine is the potential for very low or zero emissions. But that may not be important to consumers. A more meaningful benefit is likely to be the fuel cell’s superior efficiency. Today’s internal combustion engines are notoriously inefficient, converting only about 15% of the heat content of petrol into useful energy. Even in their primitive state, fuel cells can already manage at least twice that efficiency. As fuel-cell technology matures, a rising level of efficiency will mean falling operating costs.
A shift to hydrogen for fleet vehicles such as city buses would reduce manufacturing costs
The switch to fuel-cell cars promises other differences that consumers may find attractive-a much quieter ride, a constant torque regardless of speed, a clean “engine off” energy source for power-guzzling electronics and a simpler transmission system requiring less maintenance. And, maybe, the fuel-cell car could even be a source of revenue for home-owners. Plugging it into the home electricity supply and transmitting the power generated by the car back to the grid while it sits in the garage could earn a profit on the energy market.
Contrary to conventional wisdom, going direct to hydrogen is not necessarily a folly. However, it is still possible that firms betting on such a technically superior option may get trumped in the marketplace by rivals peddling an inferior but more accessible technology-be that fuel cells with reformers in the tank or petrol-engined hybrids. Don Huberts, boss of Royal Dutch/Shell’s hydrogen division, says: “That is why everyone is placing bets on several horses. By no means is it clear today which the winner will be.” The race is on and whichever type of fuel-cell car is the eventual winner, the world will be a cleaner place.
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