At least in North America, ethanol is a contentious fuel.
A decade ago, it was seen as a homegrown and carbon-neutral way to use less gasoline—and federal legislation mandated that increasing volumes be blended into U.S. fuel supplies.
Much debate followed over using "food for fuel," its supposed carbon neutrality and the footprint of the agriculture required to produce it, its impact on older engines, and other issues.
But suppose it were possible to produce ethanol chemically, using as a feedstock a substance whose growing emissions are a source of enormous global concern?
That is what researchers at the Oak Ridge National Laboratory suggest they may have discovered—somewhat accidentally.
Scientists at the U.S. Department of Energy-funded facility say they have discovered a process in which tiny spikes made of copper and pure carbon can turn carbon dioxide into pure ethanol.
Researchers Yang Song (seated), Dale Hensley (center), Adam Rondinone [Oak Ridge National Lab]
"We were trying to study the first step of a proposed reaction," Rondinone recounted, "when we realized that the catalyst was doing the entire reaction on its own."
The team had attempted to grow a catalyst based on graphene, but in the end, their equipment didn't permit that.
Instead, the team found they could fabricate tiny carbon spikes with nanoparticles of copper embedded in them.
Compared to rare metals like platinum that are used in other types of catalysts, sources of copper are both widespread and inexpensive.
"By using common materials, but arranging them with nanotechnology," Rondinone explained, "we figured out how to limit the side reactions and end up with the one thing that we want."
Copper nanoparticles (spheres) embedded in carbon nanospikes [Oak Ridge National Lab]
These tiny structures taper down to a tip that's just a few atoms thick (50 nanometers), which produces a high and concentrated electric field at the end.
Applying electricity to carbon dioxide (CO2) along with a source of hydrogen in the presence of these "nanospikes" produces ethanol (C2H6O).
The reaction, Rondinone said, has two advantages.
First, it takes place essentially at room temperature, meaning no extra energy is required to heat or cool it to extreme temperatures before the reaction can occur.
Second, the yield from the catalyst is high, at 63 to 65 percent—the team has seen 70 percent, he said—meaning that little energy is wasted to create ethanol against the energy it embodies as a fuel.
Volkswagen Gol and Saveiro, Brazilian flex-fuel vehicles
That fuel can be used today in vehicles equipped to burn it, whether all-ethanol cars like those in Brazil or Flex-Fuel vehicles in the U.S. that can burn any blend up to E85, a mixture of 85 percent ethanol with 15 percent gasoline.
The researchers also suggested that the electricity for their reaction could come from peaky and unpredictable renewable sources like wind and solar.
One challenge of integrating those into the grid is that sudden fluctuations in supply can destabilize grids that are designed for steady inflow of power from large generating plants.
Many utilities are experimenting with huge bunkers of lithium-ion batteries to store such excess energy, but Rondinone notes that the same energy could be used to produce ethanol.
And that would be a truly carbon-neutral fuel source, minus the agriculture.
As always, there are many long and challenging steps between such a lab discovery and any commercialization—as the slow pace of cellulosic ethanol development has shown.
But the research underscores the essential nature of scientific research into basic chemical reactions as one way to cope with carbon emissions and slow climate change.