Scientists have developed a new way to capture and store carbon. The negative emission technology uses a liquid-metal electrocatalyst to transforms carbon dioxide gas into carbon-containing solids at room temperature. Details of the method were published on 26 February in Nature Communications (1).
The new type of catalyst was first proposed by researchers from the University of Erlangen-Nuremberg in Germany (2). Based on the same idea, the team of scientists from Australia and Germany created a similar metal alloy ― gallium, indium, and tin ― that is liquid at room temperature and conducts electricity. The metal mixture was “doped” with cerium and a small amount of water. A metal wire was then placed in the liquid to generate electricity. Finally, when CO2 gas is passed through the liquid, the CO2 reacts with the cerium in the presence of electricity and is converted to solid carbon.
The carbon forms as flakes on the surface of the liquid metal that can be easily removed. Importantly, the gallium alloy prevents solid carbon from sticking to the catalyst surface, referred to as “coking.” But the next question is what to do with the carbon. Newly formed carbon could possibly be used in battery electrodes, materials, or buried in the ground ― in some ways, reversing emissions. An interesting ancillary benefit of the new method is that the carbon can hold an electrical charge, thereby acting as a supercapacitor, that could potentially be used in vehicles. In addition, the process produces synthetic fuel as a byproduct, with possible industrial applications.
One of the most important aspects of this new development is that the reaction takes place at room temperature. Other methods used to solid carbon must take place at extremely high temperatures, which can make the process itself energy-intensive and not commercially viable. Furthermore, strategies that compress CO2 into a liquid and inject it underground are expensive and have environmental safety issues, such as the possibility of CO2 leaking from storage sites.
However, the research is only a small step. To have any significant effect on global warming, the technique will have to be scaled up massively, which poses an enormous challenge. The global population generated nearly 30 billion tonnes of CO2 in 2017 alone, according to the International Energy Agency. Converting this much CO2 would result in mountains of solid carbon.
Meeting the targets set out in the Paris Climate Agreement will require novel strategies to both curb and capture greenhouse gas emissions. According to the latest UN climate report, the world will need to triple its efforts to keep warming below the 1.5 degrees Celcius target. This will certainly require removing some of the existing greenhouse gases from the environment. But while carbon capture can and should be part of the overall climate change strategy, reducing emissions should remain at the top of the agenda. Nonetheless, this is an important first step towards solid storage of carbon.
(1) Esrafilzadeh, D. et al. Room temperature CO2 reduction to solid carbon species on liquid metals featuring atomically thin ceria interfaces. Nature Communications (2019). DOI: 10.1038/s41467-019-08824-8
(2) Taccardi, N. et al. Gallium-rich Pd–Ga phases as supported liquid metal catalysts. Nature Chemistry (2017). DOI: 10.1038/nchem.2822