Science and technology | Difference Engine

Electric vehicles powered by fuel-cells get a second look

They may assuage “range anxiety” better than battery-powered cars

|LOS ANGELES

WITH some 455,000 eager fans having deposited $1,000 to reserve a place in the queue for Tesla’s mid-size Model 3—a battery-powered car for the masses that went on sale in early July—electric vehicles appear poised, at last, to gain some serious traction. General Motors has already sold over 12,000 of its Chevrolet Bolt, a broadly similar model launched late last year. Together, these two represent a new wave of battery cars that come close to rivalling the family saloon (sedan) in terms of price, performance and range. And in October, at least in Japan, they will be joined by much-improved version of Nissan's Leaf, currently the world's best-selling electric vehicle.

The Tesla Model 3 and the Chevy Bolt are capable of travelling 300-500km (200-300 miles) on a single charge—the sort of range conventional cars get from a tankful of fossil fuel. The Leaf, which is cheaper, gets only 250km. But even that should help put to rest the “range anxiety” that has made motorists wary of electric vehicles in the past. With ranges limited to 100-150km, previous electrics (Tesla's luxury models excepted) have been niche vehicles, occupying just 1.5% of the new-car market in America and 1% in the world as a whole. Thanks to the new, longer-range models, Morgan Stanley, an American investment bank, expects electric vehicles to account for between 10% and 15% of the market by 2025. ING, a Dutch investment bank, goes further. It suggests the car market, at least in Europe, will be fully electric by 2035.

This bullishness has been prompted by a dramatic fall in the cost of the lithium-ion batteries that are used to power pure-electric vehicles. (Hybrids favour less powerful, but cheaper, nickel metal-hydride batteries.) Between 2010 and 2015, the price of lithium-ion batteries fell from $1,000 per kilowatt-hour of storage capacity to $350, according to Bloomberg New Energy Finance, a market research firm. Since then, they have tumbled to around $200.

Tesla is driving costs down faster than any other maker. The firm standardised from the beginning on battery packs which incorporate thousands of little AA-type cells that are cheaper and easier to manufacture, while rivals adopted designs that employ smaller numbers of proprietary cell modules. Tesla has also invested heavily in battery-making facilities. When it is in full swing next year, the $5 billion “Gigafactory 1” that Tesla and its battery partner, Panasonic, have built in Nevada will be able to produce 500,000 lithium-ion packs a year. By then, Tesla’s battery costs should be down to $125 per kilowatt-hour. That is tantalisingly close to the point where battery-electrics become as cheap to make as cars with internal combustion engines. Insiders reckon parity comes when batteries cost no more than $100 per kilowatt-hour.

The question is whether the fast-maturing lithium-ion cell can yield enough further improvements (eg, through improved anodes, cheaper catalysts and a better internal architecture) to replace the internal-combustion engine when it is banished from the road—as Britain and France have promised to do by 2040, and China recently announced plans to do likewise. The only motoring option then will be the electric vehicle. The question is whether it will be powered by a battery or by some other source of electricity.

A number of carmakers believe most of the low-hanging fruit in lithium-ion research have been picked already. They suspect future gains in price and performance will come in small, incremental steps, rather than the leaps and bounds of the past two decades. To hedge their bets, Honda, Toyota, Hyundai, General Motors, Mercedes-Benz and Volkswagen have dusted down designs for hydrogen fuel-cells that were put aside when the powerful lithium-ion battery burst on the scene a quarter of a century ago. Three of them already have fuel-cell vehicles on the market—the Honda Clarity, the Toyota Mirai and the Hyundai Tucson FC. Mercedes is planning to introduce a plug-in hybrid SUV that combines a battery pack with a fuel-cell generator rather than an internal-combustion engine.

The fuel-cell’s main attraction is that it can propel an electric vehicle for 500km or more on a tankful of fuel—and then be refilled, like a conventional car, in a matter of minutes rather the hours a battery vehicle needs. Proponents believe drivers will demand a similar convenience when petrol and diesel cars are outlawed. Like its battery-powered equivalent, a fuel-cell vehicle produces no nasty emissions. The only waste that comes out of its exhaust pipe is water vapour.

A fuel-cell functions like electrolysis, only in reverse. Instead of using electricity to split water into hydrogen and oxygen, those two gases are combined to produce water and electricity. Compressed hydrogen from a tank is fed to the anode side of the fuel-cell, while oxygen from the air is pumped to the cathode side. Sandwiched between the two is a catalyst that splits the hydrogen atoms into electrons and protons, and a special membrane that selectively blocks the electrons but lets the protons pass through to the cathode. The electrons are forced to follow an external circuit, where they deliver current to an electric motor, before arriving at the cathode. Here, they rejoin the protons, and combine with oxygen to form water.

Those fuel-cell vehicles on the market today are very much works in progress. For a start, their fuel tanks are considerably larger than those of their petrol equivalents, and are far more expensive. Instead of being a cheap polyethylene moulding or a metal pressing, they are fabricated from filaments of carbon fibre wound around a metal or polymer liner. This high-tech construction is required because the hydrogen fuel has to be stored at pressures of up to 700 atmospheres, if enough is to be crammed in for 500km of motoring.

Prospective owners face other drawbacks. For one thing, fuel-cells do not take kindly to extreme conditions, especially temperatures below the freezing point of water. For another, they are not that durable. While internal-combustion engines can provide anything up to 10,000 hours of service, the best fuel-cells around today are good for little more than 4,000 hours. As for refuelling, there are only 34 hydrogen filling-stations open to the public in the whole of America, all but three being in California.

Most of these problems will be overcome in due course. But two bigger concerns—the cost of the fuel-cell “stack” itself, and the economics of producing, transporting and dispensing hydrogen fuel—could prove tougher nuts to crack.

A typical fuel-cell produces less than one volt. To generate a useful amount of power, hundreds of them have to be connected in series, in the form of a stack. In 2007, Honda reckoned the 100-kilowatt stack in an earlier version of its Clarity fuel-cell car cost $350,000—ie, $3,500 per kilowatt. Little wonder Honda built only 200 test cars for its public trials.

Since then, the cost of fuel-cells has come down by at least an order of magnitude, as researchers have learned how, among other things, to use less platinum in the catalyst. Today’s stacks need only 10 grams (a third of a troy ounce) of platinum. That is down from 29 grams in 2015. Meanwhile, the stack’s weight and size have been almost halved. If such trends continue, the Department of Energy believes stacks could cost as little as $50 per kilowatt, if mass-produced in volumes of 500,000 units a year. That would make them almost as cheap to build as internal-combustion engines of comparable output. But when that might occur is anyone’s guess.

On the fuel side, hydrogen is the most abundant element in the universe, while lithium used in batteries is a strategic material found mainly in Chile and China. On top of that, two-thirds of the world's supply of cobalt, a critical ingredient of lithium-ion cells, comes from the Democratic Republic of Congo, a place with a long history of political instability. However, despite its abundance, hydrogen has to be manufactured. Because of its propensity to combine with other elements to form compounds like water and methane, hydrogen on Earth is rarely found on its own.

The usual way to make hydrogen is to reform natural gas (ie, methane) using high-temperature steam in the presence of a nickel catalyst. The chemical industry makes millions of tonnes of the stuff in this way, largely as an ingredient of ammonia for the fertiliser market. Hydrogen is also used for processing foodstuffs, and for "cracking" large molecules in crude oil to create the smaller ones found in petrol and diesel fuel.

Commercial-grade hydrogen costs $1 to $3 a kilogram, depending on how far it has to be transported. Unfortunately, carbon monoxide is also produced in the steam-reforming process along with other impurities, which render commercial-grade hydrogen unsuitable for fuel-cells. To make so-called technical-grade hydrogen—with the “five nines” purity (ie, 99.999%) needed for fuel-cells—the impurities have to be removed using a separation technique known as pressure-swing absorption. Alternatively, it can be made directly by splitting water into its constituents using electrolysis.

Technical-grade hydrogen costs around $6 per kilogram. Compressing the gas, delivering it to a filling station, and storing it under pressure ready for dispensing doubles the cost. After including taxes and profit, the Department of Energy puts the pump price of hydrogen suitable for fuel-cell vehicles at $13-$15 per kilogram—six times the price of petrol (a kilogram of hydrogen has roughly the same energy density as a gallon of petrol). To be competitive, the cost of technical-grade hydrogen at the pump needs to be less than $4 per kilogram (ie, equivalent to petrol at $4 a US gallon).

Whether by steam reforming or electrolysis, the cheapest way of making hydrogen is to produce it in large quantities in a central plant, and then distribute it by pipeline or special tanker lorries called tube trailers. Unfortunately, the pipelines used for delivering commercial-grade hydrogen to industry would have to be upgraded at considerable expensive to meet the finicky needs of fuel-cells. The alternative—buying fleets of tube trailers for delivering compressed hydrogen by road—involves equally heavy investment. So, why not make the hydrogen locally at filling stations? At least one startup is raising money to develop stand-alone electrolysers for doing precisely that.

Doing so certainly avoids spending heavily on infrastructure. But on-site production has higher costs, because of the much smaller scale of operation. According to Sandia National Laboratories in Albuquerque, New Mexico, making hydrogen at a filling station instead of centrally increases the fuel’s cost by a further $6-$10 per kilogram. But that need not necessarily be so. Typical electrolysers use around 65 kilowatt-hours of electricity to produce a kilogram of pure hydrogen. A stand-alone hydrogen generator, powered by the sun instead of the grid, could save a bundle on electricity—perhaps enough to make even home production economically feasible.

Meanwhile, in a bid to ease the pain at the pump, Toyota salesmen have been offering customers kicking the tyres of its Mirai fuel-cell car the option of having $15,000 worth of hydrogen fuel (covering the first three years of pollution-free motoring) included in the lease agreement. If the vehicles clock up 12,000 miles (20,000km) a year, owners will be paying over 40 cents a mile for the privilege of feeling environmentally virtuous (assuming the carbon produced while making and delivering the hydrogen is captured and sequestered). By way of comparison, a conventional car giving 30 miles per gallon and using petrol at $2.50 per US gallon has a fuel cost of eight cents a mile—but will puff 270 grams of carbon into the atmosphere for every mile traveled. As they say, you pays your money and takes your pick.

Discover more

Antarctica, Earth’s largest refrigerator, is defrosting

The world must pay more attention to its southern pole

Killer whales deploy brutal, co-ordinated attacks when hunting

Their techniques are passed down through the generations


A new generation of music-making algorithms is here

Their most useful application may lie in helping human composers