Dude, Where's My Hydrogen Car?

Image: US Department of Energy

In his 2003 State of the Union Address, President George W. Bush touted fuel cell technology and hydrogen powered cars as the solution to our energy, environmental, and economic woes. Hydrogen is powerful, clean, and abundant. But over a decade later, there’s hardly a mention of fuel cells as a power source for automobiles. Why is that?

Proton Exchange Membrane (PEM) fuel cells - the kind that operate at relatively low temperatures, making them suitable for cars - produce energy by combining hydrogen and oxygen. Their only byproduct is water. Clean chemicals go in, clean chemicals come out, and energy is produced. It doesn’t get much better than that. But there’s a complication: although hydrogen is the most abundant element in the universe, most of it is concentrated in stars, and the engineering community hasn’t yet developed any “solar mining” techniques. (There are unconfirmed reports of an engineering school dropout who tried to mine the Sun by going at night, but I have yet to see a peer-reviewed paper showing his results!)

Hydrogen can be extracted from water through electrolysis, but breaking the covalent bonds that hold water molecules together requires putting energy into the system - considerably more energy than you’ll get out of the resulting hydrogen. The energy could be produced by photovoltaic cells, as is done on the International Space Station (ISS), but that’s very inefficient. The ISS has several advantages in this regard: it’s above the atmosphere so it receives a lot more direct sunlight (1333 w/m²) than the Earth’s surface (1000 w/m²), and it has a NASA budget that allows it to buy expensive technology. (I’m not suggesting that NASA spends wastefully - it’s just the best technology for the job and it happens to be expensive.) Other methods of hydrogen extraction involve non-renewable fossil fuels. To be fair, I should note that using fossil fuels for fuel cells is much cleaner and more efficient than burning the fossil fuels. Nonetheless, fossil fuels are not sustainable in the long run, so I won’t discuss them further.

With that said, many researchers are searching for better ways to extract hydrogen from renewable sources to use in fuel cells. Let’s look at some of the more promising methods...

Engineers at Duke University have developed a hydrogen extraction method that uses a catalyst made of gold and iron oxide nanoparticles. Where previous methods produced CO as a byproduct, the new method produces hydrogen with CO₂ as its byproduct. The researchers call the byproduct harmless - I assume they’re not releasing the CO₂ - a greenhouse gas - into the air.

Not to be outdone by their Duke rivals, a team from University of North Carolina and North Carolina State University are developing a dye-sensitized photoelectrosynthesis cell (DSPEC) that uses sunlight to split hydrogen and oxygen from water. The researchers think that the same technology can be used to convert CO₂ into a carbon-based fuel such as methane. Maybe they can get the CO₂ from their neighbors at Duke.

Researchers at Virginia Tech Institute have a sweet idea: extracting hydrogen from sugar. All plants are rich in starches, and Percival Zhang, professor of bioengineering at VTI, has developed a combination of enzymes that efficiently separate hydrogen from sugar molecules. He and his colleagues dubbed the project “Sweet Hydrogen.” The beauty of this is twofold: it uses a renewable source (biomass), and it eliminates the problem of transporting and storing hydrogen, a flammable and explosive gas. The biomass can come from waste material like corn stalks, grass clippings, and wood chips. The hydrogen extraction process is clean and inexpensive. Zhang believes that extraction can take place either in the car or at the service station, so instead of large tanker trucks filled with petroleum, you might someday see sugar trucks heading to your nearest fueling station. At the moment they’re working on optimizing the reaction for greater efficiency. The next step will be to build a functional reactor that’s small enough to fit in a car. The technology is promising; they’ve even received financial backing from an oil company.

On the opposite coast, chemists at the University of California, Santa Cruz have developed a hydrogen extraction process using sunlight and sewage. The organic matter in wastewater becomes the fuel in a microbial fuel cell (MFC), which generates a small amount of electricity. The photoelectrochemical cell (PEC) converts sunlight to electricity. Combining the two provides enough energy to perform electrolysis with no additional energy added. The process not only extracts hydrogen, it also cleans wastewater.

Alternative fuel vehicles will help reduce greenhouse gases and decrease our dependence on fossil fuels. Battery powered electric vehicles are leading the charge right now, but hydrogen could soon rise to the occasion, and I think it has better long-term potential.