Carbon dioxide , a product of burning fossil fuels and the most prevalent greenhouse gas, has the potential to be sustainably converted back into useful fuels.
In previous studies, the researchers had established the precise conditions that gave the best electrical and chemical environment for creating commercially interesting carbon-rich products.
To pinpoint a design that could be used in the aqueous environment of fuel cells, Bell and his team, as part of the Department of Energy’s Liquid Sunlight Alliance Energy Innovation Hub project, turned to thin layers of ionomers, polymers that allow certain charged molecules to pass through while excluding others.
These effects combined with a pulsed voltage result in substantially enhanced rates of CO2 conversion to valuable carbon-rich products.
Chanyeon Kim, a postdoctoral researcher in Bell’s group and the lead author on the paper, proposed to coat the surface of the copper catalyst with two common ionomers, Nafion and Sustainion.
The researchers applied a thin layer of each ionomer, as well as a bilayer of both ionomers, to copper films supported by a polymer material, forming membranes that they could insert near one end of a hand-sized electrochemical cell.
“This sandwich coating gives the best of both worlds: high product selectivity and high activity,” said Bell.
The researchers concluded that the improved reaction was a consequence of the high CO2 concentration that built up in the coating layer immediately on top of the copper.
To increase the reaction efficiency even further, the researchers turned to a technique that had been demonstrated before, without ionomer films, as another way to increase CO2 and pH: pulsing the voltage.
The Berkeley Lab team’s initial experiments involved small, flat model systems, which are far simpler to work with compared with the high-area, porous structures necessary for commercial applications.
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