A whole lot of planet Earth’s problems could be solved if we had some easy way of recapturing carbon dioxide from the atmosphere and converting it into readily usable fuel. Obviously.
There exists a hard way of doing this involving the usage of prohibitively expensive catalysts to flip carbon dioxide into carbon monoxide, which can then be combined with hydrogen resulting in everyday fuels like kerosene and gasoline. Via this hard way, the nature of the required catalysts—extra stuff needed to make reactions occur more quickly—makes it so that you’re putting in more energy to break down the CO2 than you’re getting in return.
In a paper published Monday in Nature Energy, researchers from École polytechnique fédérale de Lausanne (EPFL) describe a new catalyst for splitting carbon dioxide that, in their words, is the foundation for the first ever low-cost carbon-dioxide splitting system. It relies on two materials, tin oxide and copper oxide, both of which are readily abundant on Earth, and offers a CO2 to CO conversion efficiency of nearly 14 percent.
The CO2 splitting process here is electrolysis, generally. An anode (positively charged wire) and cathode (negatively charged) are dunked in a liquid solution with some CO2 as some current is passed between them, with the result being the decomposition of the CO2 into carbon monoxide and oxygen. It sounds easy, but the challenge is in not putting more energy into the process than you’re getting out in return in the form of broken down CO2. This is where catalysts come in.
The catalyst used in the new process consists of an atomic layer of tin oxide deposited on copper oxide nanowires, which form the anode and cathode. Copper, as a classic electrical conductor, is natural enough for usage in an electrolytic system, but it suffers from something called overpotential when used as electrodes in a system like this. Basically, energy winds up going “missing” in the process and escapes as heat. Efficiency is lost.
The EPFL researchers have gotten around this by doping the wires with tin oxide. The liquid bath the electrodes are then placed needs to be then finely tuned in terms of pH and ion gradients, which is tough. They managed to maintain this fine tuning by way of a thin membrane placed in the solution between the two wires.
Even with the help of catalysts, splitting CO2 is still an “uphill” process. It takes energy to accomplish. Here, that energy is supplied via solar cells. So, none of this is magic—we still owe the process an energy input, but solar energy plus the careful tweaking described above gives us something that looks like a relatively free transaction.
“This is the first time that such a bi-functional and low-cost catalyst is demonstrated,” offers EPFL researcher Marcel Schreier in a statement. “Very few catalysts—except expensive ones, like gold and silver—can selectively transform CO2 to CO in water, which is crucial for industrial applications.”