A new electrochemical process uses nano spikes of carbon and copper to convert carbon dioxide into ethanol, thanks to a chance finding by a team at Oak Ridge National Laboratory.
According to team member Adam Rondinone, the researchers were trying to study the first step of a particular reaction that might convert the greenhouse gas into a useful fuel when they realized that the catalyst was facilitating the entire reaction on its own. The carbon, copper and nitrogen catalyst works with an applied current and triggers a convoluted chemical reaction that in effect reverses the combustion of ethanol. The nanoscopic spikes provide a vast number of reaction sites in a tiny area allowing carbon dioxide from aqueous solution to be reduced to ethanol in a yield of approximately 63%. Conventional electrochemical reactions of this kind lead to multiple products in much lower yields. [AJ Rondinone et al., Chem Select (2016), DOI: 10.1002/slct.201601169]
"We're taking carbon dioxide, a waste product of combustion, and we're pushing that combustion reaction backwards with very high selectivity to a useful fuel," Rondinone explains. "Ethanol was a surprise," he adds. Until now it has been "extremely difficult to go straight from carbon dioxide to ethanol with a single catalyst." It is the nanoscale structure that seems to be key to their serendipitous success. The catalyst is made up of copper nanoparticles embedded in carbon spikes giving a high surface area nano-textured material that precludes the need for expensive or rare metals such as platinum that often limit the economic viability of many chemical processes.
"By using common materials, but arranging them with nanotechnology, we figured out how to limit the side reactions and end up with the one thing that we want," Rondinone adds. The spikes act as 50-nanometer lightning rods to concentrate electrochemical reactivity at the tip of the spike, Rondinone adds. The approach the team has hit on uses relatively inexpensive materials and operates at room temperature in water rather than a volatile organic solvent. As such, they anticipate it could be scaled up for industrial applications and perhaps as a way to use electricity generated by solar or wind power to store that energy as chemical fuel as well as using what is normally considered to be a worrying waste product.
"As for the next step, our strength is basic science so we will continue research into understanding the mechanism of the reaction, then using that understanding to improve the performance," Rondinone told Materials Today. "While the yield is quite good, the overall efficiency hasn't been thoroughly investigated or optimized. I'm also optimistic that others will be interested in the applications side."
David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the popular science book "Deceived Wisdom".