Atmospheric CO2 is a major driver of global warming, but could also serve as a valuable resource. Many researchers are exploring ways to convert it into useful carbon-based chemicals, but efforts have been limited by low efficiencies that restrict the potential for large-scale application.
Postdoc Diego Mateo explained how the team at King Abdullah University of Science and Technology (KAUST), Saudi Arabia, based its approach on the synergistic combination of light and heat - known as the ‘photothermal effect’ - whereby heat is generated by the interaction of light with the catalyst, so the two forms of energy come from absorbed light.
The catalyst is said to be built from nickel nanoparticles on a layer of barium titanate. It captures the light in a way that kicks electrons into high energy states, known as ‘hot electrons’, researchers said. These then initiate the chemical reaction that sends CO2 back into methane.
According to the team, the catalyst generates methane with nearly 100 per cent selectivity and ‘impressive efficiency’ under optimum conditions. While some industrial approaches require heating from external sources to attain temperatures as high as 500 degrees Celsius, the KAUST research shows that the reaction can be achieved using just the photothermal effect of daylight.
A wide range of the spectrum of light is harnessed using the technique, in addition to the ultraviolet rays that many catalysts are restricted to. This was described as ‘hugely significant’ by the researchers, since ultraviolet light comprises only four to five per cent of energy available in sunlight.
“We strongly believe that our strategy, in combination with other existing CO2 capture techniques, could be a sustainable way to convert this harmful greenhouse gas into valuable fuel,” said Mateo.
Fuels made from CO2 would still release that gas when burned, but the CO2 could be repeatedly recycled from the atmosphere to fuel and back again rather than being continually released by burning fossil fuels.
Lead researcher Jorge Gascon said that the researchers are looking to widen the applications of the approach. “One strategy for our future research is to move toward producing other valuable chemicals, such as methanol,” Gascon said. The team also sees potential for using light energy to power production of chemicals that don’t contain carbon, such as ammonia.
The study is published in Advanced Functional Materials.