Making ethanol without corn or other plants

“Most materials are incapable of reducing carbon monoxide and exclusively react with water,” Kanan said. “Copper is the only exception, but conventional copper is very inefficient.”

In the Nature experiment, Kanan and Li used a cathode made of oxide-derived copper. When a small voltage was applied, the results were dramatic.

“The oxide-derived copper produced ethanol and acetate with 57 percent faradaic efficiency,” Kanan said. “That means 57 percent of the electric current went into producing these two compounds from carbon monoxide. We’re excited because this represents a more than 10-fold increase in efficiency over conventional copper catalysts. Our models suggest that the nanocrystalline network in the oxide-derived copper was critical for achieving these results.”

Carbon neutral
The Stanford team has begun looking for ways to create other fuels and improve the overall efficiency of the process. “In this experiment, ethanol was the major product,” Kanan said.

“Propanol would actually be a higher energy-density fuel than ethanol, but right now there is no efficient way to produce it.”

In the experiment, Kanan and Li found that a slightly altered oxide-derived copper catalyst produced propanol with 10 percent efficiency. The team is working to improve the yield for propanol by further tuning the catalyst’s structure.

Ultimately, Kanan would like to see a scaled-up version of the catalytic cell powered by electricity from the sun, wind or other renewable resource.

The release notes that for the process to be carbon neutral, scientists will have to find a new way to make carbon monoxide from renewable energy instead of fossil fuel, the primary source today. Kanan envisions taking carbon dioxide (CO2) from the atmosphere to produce carbon monoxide, which, in turn, would be fed to a copper catalyst to make liquid fuel. The CO2 that is released into the atmosphere during fuel combustion would be re-used to make more carbon monoxide and more fuel — a closed-loop, emissions-free process.

“Technology already exists for converting CO2 to carbon monoxide, but the missing piece was the efficient conversion of carbon monoxide to a useful fuel that’s liquid, easy to store and nontoxic,” Kanan said. “Prior to our study, there was a sense that no catalyst could efficiently reduce carbon monoxide to a liquid. We have a solution to this problem that’s made of copper, which is cheap and abundant. We hope our results inspire other people to work on our system or develop a new catalyst that converts carbon monoxide to fuel.”

The Nature study was coauthored by Jim Ciston, a senior staff scientist with the National Center for Electron Microscopy at Lawrence Berkeley National Laboratory.

The research was supported by Stanford University, the National Science Foundation and the U.S. Department of Energy.

— Read more in C. Li et al., “Electroreduction of CO to Multi-Carbon Oxygenates on Oxide-Derived Nanocrystalline Cu,” Nature (forthcoming)