System to convert carbon dioxide into electricity and hydrogen developed by UNIST scientists

Hybrid Na-CO2 system based on using dissolved carbon dioxide in the water to start an electrochemical reaction

A group of scientists from Ulsan National Institute of Science and Technology (UNIST) in South Korea have developed Hybrid Na-CO2 system that, they claim, is capable of producing electricity and hydrogen from carbon dioxide (CO2) dissolved in aqueous solution.

Carbon dioxide is the most significant greenhouse gas emitted as a result human activities. It enters the atmosphere through burning of fossil fuels, trees, solid waste and also as a result of some specific chemical reactions. The emissions of this greenhouse gas have dramatically increased over the past five decades and continue to increase every year.

A large amount of CO2 emitted due to human activities also enters oceans, where it is dissolved in water. It reacts with seawater and creates carbonic acid, thereby increasing the acidity of the water.

The Hybrid Na-CO2 system developed by UNIST researchers is based on the idea of using dissolved CO2 in the water to start an electrochemical reaction. The CO2 dissolved in water increases the acidity of the solution, which increases the number of protons.

More protons in the solution means there is more power to attract electrons. Researchers suggest a battery system based on the phenomenon can be used to produce electricity by removing CO2 from such an aqueous solution.

"Carbon capture, utilisation, and sequestration (CCUS) technologies have recently received a great deal of attention for providing a pathway in dealing with global climate change," says Professor Guntae Kim from the School of Energy and Chemical Engineering at UNIST, and the lead researcher of the study.

"The key to that technology is the easy conversion of chemically stable CO2 molecules to other materials."

The hybrid Na-CO2 system functions in similar way to a fuel cell. It features a cathode (sodium metal), anode (catalyst) and separator (NASICON). In the system, catalysts are contained in water, and a lead wire connects them to a cathode. The electrochemical reaction starts when CO2 is injected into the water. The reaction starts eliminating CO2 and produces electricity and hydrogen (H2).

The researchers claim the conversion efficiency of the system is about 50 per cent. It is also stable and able to operate for more than 1,000 hours without any damage to electrodes.

"This research will lead to more derived research and will be able to produce H2 and electricity more effectively when electrolytes, separator, system design, and electrocatalysts are improved," said Professor Kim.

The findings of the study are published in journal Science Direct.