Their work was published in the Feb. 13 issue of Science.
According to the research team, the new technology is poised to remove a major stumbling block to the "hydrogen economy" - no free hydrogen exists, except what is made at high cost from fossil fuels.
The researchers see an early use for their invention in remote areas, where the installation of new power lines is not feasible. People could buy ethanol and use it to power small hydrogen fuel cells in their basements. The process could also be extended to biodiesel fuels, the researchers said. Its benefits include reducing dependence on imported fuels, reducing carbon dioxide emissions (because the carbon dioxide produced by the reaction is stored in the next year's corn crop), and boosting rural economies.
Hydrogen is now produced by a process called steam reforming, which requires high temperatures and large furnaces - in other words, a large input of energy. It's unsuitable for any application except large-scale refineries, said Lanny Schmidt, Regents Professor of Chemical Engineering, who led the research effort. Working with him were scientist Gregg Deluga, first author of the Science paper, and graduate student James Salge. All three are in the university's department of chemical engineering and materials science.
"The hydrogen economy means cars and electricity powered by hydrogen," said Schmidt. "But hydrogen is hard to come by. You can't pipe it long distances. There are a few hydrogen fueling stations, but they strip hydrogen from methane - natural gas - on site. It's expensive, and because it uses fossil fuels, it increases carbon dioxide emissions, so this is only a short-term solution until renewable hydrogen is available."
Ethanol is a renewable fuel source produced from corn, and it is used in car engines. But used to generate hydrogen for fuel cells, the process would be nearly three times as efficient. Said Schmidt, "Ethanol in car engines is burned with 20 percent efficiency, but if you used ethanol to make hydrogen for a fuel cell, you would get 60 percent efficiency."
The difference, Deluga explained, is due in large part to the need to remove all the water from ethanol before it can be put in an automobile gas tank - and the last drops of water are the hardest to remove. But the new process doesn't require pure ethanol; in fact, it strips hydrogen from both ethanol and water, yielding additional hydrogen.
The invention rests on two innovations: a catalyst based on the metals rhodium and ceria, and an automotive fuel injector that vaporizes and mixes the ethanol-water fuel. The vaporized fuel mixture is injected into a tube that contains a porous plug made from rhodium and ceria. The fuel mixture passes through the plug and emerges as a mixture of hydrogen, carbon dioxide, and minor products. The reaction takes 50 milliseconds and eliminates the flames and soot that commonly accompany ethanol combustion.
The work was supported by the University of Minnesota's Initiative on Renewable Energy and the Environment, the National Science Foundation, and the U.S. Department of Energy (DOE).
Publication date: 02/16/2004