In his 2003 State of the Union address, President George W. Bush touted fuel cell technology and hydrogen-powered cars as the solution to the United States' 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. 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 the stars, and the engineering community hasn't yet developed any "solar mining" techniques. Hydrogen does not exist freely and is only produced from other sources of energy.
Also, hydrogen has very high energy for its weight but very low energy for its volume, presenting challenges to store and transport it. And fuel cell technology still needs improvements in efficiency and durability.
Most hydrogen production today is by steam reforming natural gas. But it is a fossil fuel, so the carbon dioxide released in the reformation process adds to the greenhouse effect. While using fossil fuels for fuel cells is much cleaner and more efficient than burning them, fossil fuels are nonetheless not sustainable in the long run.
Hydrogen can be extracted from water through electrolysis -- passing electricity through water to break it into its constituent components of hydrogen and oxygen -- 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 (1,333 watts per square meter) than the Earth's surface (1,000 W/s-m), and it has NASA's budget.
Credit: U.S. Department of Energy
Developing technology to efficiently and cost-effectively make hydrogen is thus a big goal. With that said, many researchers are looking for better ways to extract hydrogen from renewable sources to use in fuel cells.
Engineers at Duke University have developed a hydrogen extraction method
that uses a catalyst made of gold and iron oxide nanoparticles. Whereas previous methods produced carbon monoxide as a byproduct, the new method produces hydrogen with carbon dioxide as its byproduct. The researchers call the byproduct harmless, assuming the CO2 is not being released into the air.
Not to be outdone by their Duke rivals, a team from University of North Carolina and North Carolina State University is 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.
Researchers at Virginia Tech have a sweet idea: extracting hydrogen from sugar
. All plants are rich in starches, and Percival Zhang, professor of bioengineering at VT, 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 it 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 said to be 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, the team at VT is 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, but the technology is promising; Zhang and his colleagues have 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 U.S. dependence on fossil fuels. Battery-powered electric vehicles are leading the charge right now, but hydrogen could soon rise to the occasion and has better long-term potential.
Top photo credit: ponsulak at FreeDigitalPhotos.net
This article was originally published on Engineering.com and is adapted with permission. For more stories like this please visit Engineering.com.