Rice University has come up with an invention that converts carbon dioxide into valuable fuels. Carbon Dioxide was turned to liquid fuel in an environment-friendly manner by using an electrolyzer and renewable energy. The catalytic reactor was developed by Haotian Wang, a chemical and biomolecular engineer at Rice University.
It uses carbon dioxide as feedstock and the latest prototype produces highly purified concentrated formic acid. Traditional ways of producing formic acid are costly and require energy-intensive purification steps. The direct production of pure formic acid will help in promoting commercial carbon dioxide conversion technologies. The work appears in Nature Energy journal.
Wang and his group pursue all those technologies that convert greenhouse gases into useful products. In experiments, the electrocatalyst reached an energy conversion efficiency of nearly 42%. So almost half the electrical energy can be stored as liquid fuel in the formic acid. Formic acid an energy carrier and a fuel cell that can generate electricity and emit carbon dioxide which can be recycled again. It is a fundamental unit in chemical engineering as a feedstock for other chemicals and also a storage material for hydrogen that can hold 1000 times the energy of the same amount of hydrogen gas, which is also difficult to compress.
Chuan Xia, postdoc researcher at Rice said that this was possible due to two advancements. The first being the development of robust, two-dimensional bismuth catalysts and the second, a solid-state electrolyte which eliminates the need for salt in the reaction. Bismuth is a heavy atom with lower mobility and stabilizes the catalyst. The structure of the reactor prevents contact of water from the catalyst. Currently, catalysts are produced on a milligram or gram scale but Xia and his team have developed a way to produce them in the kilograms thus scaling up the industry.
The polymer-based electrolyte is coated with sulphonic acid ligands to conduct positive charge or amino functional groups for negative ions. Carbon dioxide is usually reduced in a liquid electrode using salty water and for the conduction of electricity, pure water is too resistant. Salts like sodium chloride or potassium bicarbonate have to be added so that ions can move freely.
Formic acid generated in this manner mixes with salts. But for most of the applications, salts have to eliminated from the end product which consumes energy and cost. Instead, solid electrolytes made up of insoluble polymers, inorganic compounds were used thus cancelling the need for salts.
The rate of water flow through the chamber determines the concentration of the solution. Researchers have expectations to achieve higher concentration from next-generation reactors accepting gas flow to generate pure formic acid.
The Rice lab worked with Brookhaven National Laboratory to view the process in progress. “X-ray absorption spectroscopy, a powerful technique available at the Inner Shell Spectroscopy (ISS) beamline at Brookhaven Lab’s National Synchrotron Light Source II. It enables us to probe the electronic structure of electrocatalysts during the actual chemical process.
They followed the bismuth’s oxidation states at different potentials and were able to identify the catalyst’s active state during the reduction process of carbon dioxide. The reactor can generate formic acid for 100 hours without any degradation of its components. Carbon dioxide reduction is a big step towards the effect of global warming and with renewable energy, we can make a loop that turns carbon dioxide to useful products without emitting it.
Journal Reference: Nature Energy