Columbia University engineers make breakthrough in understanding electroreduction of CO2 for conversion to electrofuels
Electrocatalysis and photocatalysis (artificial photosynthesis) are among the most promising ways to achieve effective storage for renewable energy. CO2 electroreduction has been capturing the imagination of researchers for more than 150 years because of its similarity to photosynthesis.
Recent research in electrocatalytic CO2 conversion points the way to using CO2 as a feedstock and renewable electricity as an energy supply for the synthesis of different types of fuel and value-added chemicals such as ethylene, ethanol, and propane. However, scientists still do not understand even the first step of these reactions: CO2 activation, or the transformation of the linear co1 molecule at the catalyst surface upon accepting the first electron.
Knowing the exact structure of the activated CO2 is essential because its structure dictates both the end product of the reaction and its energy cost. This reaction can start from many initial steps and go through many pathways, giving typically a mixture of products. If scientists figure out how the process works, they will be better able to selectively promote or inhibit certain pathways, which will lead to the development of a commercially viable catalyst for this technology.
Researchers at Columbia University have solved the first piece of the puzzle; they have proved that CO2 electroreduction begins with one common intermediate, not two as was commonly thought. Their paper is published in Proceedings of the National Academy of Sciences (PNAS).
They applied a comprehensive suite of experimental and theoretical methods to identify the structure of the first intermediate of CO2 electroreduction: carboxylate CO2- that is attached to the surface with C and O atoms. Their breakthrough came by applying surface enhanced Raman scattering (SERS) instead of the more frequently used surface enhanced infrared spectroscopy (SEIRAS). The spectroscopic results were corroborated by quantum chemical modeling.
Our findings about CO2 activation will open the door to an incredibly broad range of possibilities: if we can fully understand CO2 electroreduction, we'll be able to reduce our dependence on fossil fuels, contributing to the mitigation of climate change. In addition, our insight into CO2 activation at the solid-water interface will enable researchers to better model the prebiotic scenarios from CO2 to complex organic molecules that may have led to the origin of life on our planet.—lead author Irina Chernyshova
The researchers decided to use SERS rather than SEIRAS for their observations because they found that SERS has several significant advantages that enable more accurate identification of the structure of the reaction intermediate. Most importantly, the researchers were able to measure the vibrational spectra of species formed at the electrode-electrolyte interface along the entire spectral range and on an operating electrode.
Using both quantum chemical simulations and conventional electrochemical methods, the researchers were able to get the first detailed look at how CO2 is activated at the electrode-electrolyte interface.
Understanding the nature of the first reaction intermediate is a critical step toward commercialization of the electrocatalytic CO2 conversion to useful chemicals. It creates a solid foundation for moving away from the trial-and-error paradigm to rational catalyst design.
With this knowledge and computational power, researchers will be able to predict more accurately the reaction on different catalysts and specify the most promising ones, which can further be synthesized and tested.—co-author Sathish Ponnurangam
The Columbia Engineering experiments provide such detail that we should be able to obtain very definitive validation of the computational models. I expect that together with our theory, the Columbia Engineering experiments will provide precise mechanisms to be established and that examining how the mechanisms change for different alloys, surface structures, electrolytes, additives, should enable optimization of the electrocatalysts for water spitting (solar fuels), CO2 reduction to fuels and organic feedstocks, N2 reduction to NH3 to obtain much less expensive fertilizers, all the key problems facing society to obtain the energy and food to accommodate our exploding population.—William Goddard, Charles and Mary Ferkel Professor of Chemistry, Materials Science, and Applied Physics at CalTech, who was not involved with the study
The team is now working to uncover the subsequent reaction steps to see how CO2 is further transformed and to develop superior catalysts based on earth-abundant elements such as Cu (copper) and Sn (tin).
Irina V. Chernyshova, Ponisseril Somasundaran, Sathish Ponnurangam (2018) “On the origin of the elusive first intermediate of CO2 electroreduction” Proceedings of the National Academy of Sciences doi: 10.1073/pnas.1802256115