Rising atmospheric CO2 levels can generally be tackled in three ways: developing alternative energy sources with lower emissions; carbon capture and storage (CCS); and capturing carbon and repurposing it. Researchers at Princeton University are claiming to have developed a technique that ticks two of these three boxes by using solar power to convert CO2 into formic acid.

With power from a commercially available solar panel provided by utility company Public Service Electric and Gas (PSE&G), researchers in the laboratory of Princeton professor of chemistry Andrew Bocarsly, working with researchers at New Jersey-based start-up Liquid Light Inc., converted CO2 and water to formic acid (HCOOH) in an electrochemical cell.

Made from easily obtained machined parts, the electrochemical cell consists of liquid-carrying channels surrounded by metal plates the size of rectangular lunchboxes. Through an optimization process known as impedance matching, the team was able to match the power generated by the solar panel to the amount of power the electrochemical cell can handle so as to maximize the efficiency of the system.

According to the researchers, in this way they were able to approach an energy efficiency of 2 percent by stacking three of the electrochemical cells together. They claim that this is twice the efficiency of natural photosynthesis and the best energy efficiency achieved to date using a man-made device.

Formic acid, which is found in the venom of ants, currently has a wide variety of applications, such as a preservative and antibacterial agent in livestock feed and for producing formate salt, which is used as a de-icing agent for airport runways. However, it also has potential for storing solar energy within fuel cells.

The approach shares some similarities with an artificial photosynthesis system developed by Panasonic. However, that system, which used hydrogen formed by splitting water by way of a nitride semiconductor to create formic acid, achieved an efficiency of 0.2 percent.

The team's study is published in the Journal of CO2 Utilization.