Uncovering the power of chemistry to mitigate climate change

Title: Room temperature CO2 reduction to solid carbon species on liquid metals featuring atomically thin ceria interfaces

Authors: Dorna Esrafilzadeh, Ali Zavabeti, Rouhollah Jalili, Paul Atkin, Jaecheol Choi, Benjamin J. Carey, Robert Brkljača, Anthony P. O’Mullane, Michael D. Dickey, David L. Officer, Douglas R. MacFarlane, Torben Daeneke & Kourosh Kalantar-Zadeh

Journal: Nature Communications

Year: 2019

Article: https://www.nature.com/articles/s41467-019-08824-8

Cover image: Image by PIRO4D from Pixabay

Carbon dioxide is the largest contributor to anthropogenic climate change. It has very high concentrations in the atmosphere and these are continuing to increase. While many researchers and policymakers discuss reducing our CO2 emissions, we also need to draw down the current concentration in the atmosphere if we want to reverse the changes to climate already occurring. This calls upon carbon-capture devices which are developing methods to store the CO2 in a form that is not present in the atmosphere, stable over the long term, and cost and space effective. This study describes a new technology that has the power to do just that! Researchers have developed a way to turn carbon dioxide into storable and stable solid graphite.

The new liquid-metal catalyst described here uses cerium oxide to perform room temperature continuous electrocatalytic reduction of CO2. Reduction is a chemical reaction where the atom gains electrons, changing its oxidation state. Here, when the CO2 is converted to graphite, two electrons are gained by the carbon atom, changing its valence state from 2+ to 0. When this system is driven by a renewable energy source such as solar or wind power, it is a negative CO2 emission technology.

Carbon dioxide is a very stable molecule, which means that systems require a large amount of energy input in order to convert CO2 to a different, usable product. These researchers have developed a way to dissolve gaseous CO2 in a liquid and then use an electrical potential to convert it into graphite. The problem with electrocatalysis is that the metal surface often gets coated in the solid that is formed, graphite, which reduces the efficiency of the catalyst. To overcome this issue researchers created a new electrode made of metallic cerium mixed into a liquid metal mixture of gallium, indium, and tin (called galistan, Figure 1). This electrode produces a high potential when CO2 is dissolved in the electrolyte due to the following series of reactions:

Figure 1: Schematic of the catalytic cycle.

As a control, researchers also ran their electrode setup in a nitrogen only environment and did not observe a potential. This means that the CO2 was in fact the driving force for the potential. Another control test was done by using a different solution, replacing the solvents involved in the mixture. The same results were produced indicating the CO2 was reacting rather than the components of the solution.

Researchers collected the solid that was formed through the electrocatalysis and analyzed it to determine its chemical nature. They performed tests such as Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), Raman spectroscopy, and elemental analysis (Figure 2). This allows them to determine that the product was amorphous carbon sheets with a few oxygen impurities.

Figure 2: Characterization results of the solid product. (a) FTIR spectrum showing many carbon functional groups (b) TEM image and elemental analysis results (c/d) Raman shift results showing peaks characteristic of carbon sheets.

This research provides exciting scientific steps forward in fighting climate change. While we will have to reduce our CO2 emissions as a global community, this would help reverse the effects that are already being observed with increased concentrations and help ease the transition to renewable energy. It provides a room temperature solution, that requires little energy input, and creates a stable, storable product. In continuing work, researchers are working to run

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