Techsplanations: Fuel Cell

To scientists, running vehicles on hydrogen makes all the sense in the world. Hydrogen can be derived from so many different things, including water, and constitutes roughly 75 percent of the universe's chemical elemental mass.

Consumers, however, often shy up when presented with the option of a hydrogen-powered vehicle. They think of "H-bombs," or the explosion of the Hindenburg. But that's pretty silly when you consider we handle 15 to 25 gallons of highly volatile gasoline in our vehicles now.

As the U.S. struggles politically and culturally to map out a logical energy future, hydrogen doesn't get a lot of attention. Most of the talk is about battery-powered electric vehicles and gas-electric hybrids that can run on either gasoline, electricity, or a combination of both simultaneously. But to mark Earth Day 2012, we want to shed some light on perhaps the most abundant energy solution of all for our vehicles – hydrogen.

What is it?

A fuel-cell vehicle is a type of electric vehicle. Like the Nissan Leaf and other EVs, it uses an electric motor to drive the wheels. But rather than draw electricity from heavy batteries that take time to recharge, a fuel cell generates electricity as needed by creating a chemical reaction using hydrogen and oxygen. The hydrogen is stored onboard the car in tanks as a compressed gas and the oxygen comes from the air. A fuel-cell vehicle can be refueled by pumping hydrogen into its tank at a hydrogen refueling station, similar to a regular gas station.

While fuel cell vehicles are still considered advanced technology, the science is not new. Fuel cells were developed in the NASA space program in the 1960's and the first fuel-cell vehicle, the Chevrolet Electrovan, was built by General Motors in 1966. At the time, the fuel cells were too big and costly to even dream of deploying in a production version. But much has changed in the past five decades, as sophisticated computer control systems have allowed the size of fuel cells to shrink along with the costs. Modern demonstration vehicles have been logging miles since the 1990s, though automakers' interest in the technology has waxed and waned over the ensuing years.

Techsplanation recently drove a Mercedes-Benz F-Cell fuel-cell vehicle (See video). The system is built into the Mercedes B-Class. This F-Cell has an electric engine rated at 100 kW (134 horsepower), and a range of about 250 miles. This improvement in range over an earlier version is due in part to the B-Class's greater space for holding the compressed hydrogen tanks and higher storage pressure.

We so enjoyed driving the F-Cell around Los Angeles, with such ease of refilling the tank when we needed, that we keep asking ourselves: Why can't we have this now in larger numbers?
How does it work?

A fuel cell works by catalyzing hydrogen, a fancy way of saying a chemical reaction breaks down hydrogen atoms into their atomic components: electrons and protons. The electrons create an electric current – that's where the electric power comes from – before they're recombined with the protons and oxygen from the air to create water, the fuel cell's only emission.

A fuel cell is comprised of several hundreds of these cells, wired together to create the full system large enough to power the vehicle's electric motor, just like a battery.

Fuel cell cars have an actual battery in them as well, usually a lithium-ion one like in your laptop computer. The vehicle uses this battery to store energy from regenerative braking, just as in a battery electric vehicle or a hybrid like the Toyota Prius. Because the fuel cell vehicle is powered by an electric motor, that motor can regenerate electricity any time the vehicle is decelerating. It does this by allowing the wheels to spin the electric motor, rather than the other way around. The motor then acts like a generator, returning electric current to the battery. Of course, a computer controls this entire process, as well as deciding when the motor should draw its power from the fuel cell, the battery, or both.

Why would I want it?

The big reason to want fuel cell vehicles is it doesn't produce any harmful emissions. That's right, no carbon monoxide, no carbon dioxide, no nitrogen oxides, none of the traditional tailpipe emissions associated with internal combustion engines. Zip. Nada.

Fuel-cell vehicles improve upon battery electrics because they are theoretically just as convenient to operate as a gasoline- or diesel-powered vehicle. When a battery EV runs low on charge, it can take quite some time – often hours – to recharge. But a hydrogen fuel cell vehicle can have its tanks refilled in a matter of minutes, just like a gasoline engine.

Is there any downside?

The biggest issue facing fuel-cell adoption is there's virtually no hydrogen refueling infrastructure anywhere in the world. We filled up our tank at a station in Los Angeles as part of a pilot program. While we have more than 100,000 gas stations in the United States, you can count the number of hydrogen refueling stations on your fingers.

There's also the question of where the hydrogen would come from. Hydrogen needs to be manufactured by extracting it from other substances, like water, natural gas or coal. Heck, you can even crack hydrogen from gasoline, but we don't want to go down that road. These processes have their own energy cost and associated emissions that can blur the picture of just how "green" fuel-cell vehicles are. However, given that the U.S. has abundant stores of natural gas, it is the most logical fuel stock for hydrogen in the near term.

Then there's cost. Estimates have pegged the cost to build each 2008 Honda FCX Clarity fuel cell vehicle in the six figures. While the FCX Clarity is a first-generation purpose-built fuel cell vehicle, Mercedes has recently stated its expectation that costs of so-called second-generation hydrogen fuel cell vehicles will come down. Mercedes forecasts that by 2014 they might be comparable to the cost of diesel hybrids, which while still expensive, would be feasible for carmakers to build and sell at a profit.

What vehicles offer it?

The thing about cars powered by fuel cells is that there aren't many of them. Honda launched the first purpose-built, publicly available fuel cell car in 2007, the FCX Clarity. But only a handful of cars have been sold – just 30 to date – and their availability has been restricted to leases in Southern California. Honda did this because the cars cost far more to build than the $600/month lease price will cover, and the limited number of hydrogen refueling stations means the cars can't be sold just anywhere.

The Mercedes-Benz F-Cell was launched in late 2010, and used a similar leasing program to put its cars in the hands of the public. These cars, based on a European model called the B-Class, were also restricted to California customers, for similar reasons. Mercedes has said it plans to lease a total of 200 F-Cell cars globally, although through 2011, 20 cars had been delivered here in the U.S.

These two car programs are only a small step beyond experimental, but that's not deterring car-makers from moving forward with plans to put more fuel cell vehicles on the road. General Motors, Toyota, and Hyundai have all announced plans to start producing fuel-cell vehicles within the next two to three years. The technology is just too smart for them not to keep pushing the costs down. And there is widespread agreement – outside the oil industry – the U.S. must, for the sake of its environment and national security, diversify our transportation fuel stock beyond oil.

Bottom line

Hydrogen fuel cell vehicles have been perpetually a decade away from the mainstream for 20 years. That could change, as automakers have gotten serious about developing alternatives to the internal combustion engine in recent years.

If you get a chance to drive a fuel-cell vehicle, take it. You will be driving the future, and you may just be part of a wave that brings the future a bit closer to the present.