Recycling CO₂ with water to liquid solar fuels

South Africa has enormous untapped renewable energy supplies of sunlight, on par with the best in the world, in large, low-populated areas. At the same time, the country is one of the largest polluters of the atmosphere with greenhouse gases, with an annual carbon dioxide emission of 10 tonnes per capita. 65% of it is emitted at point sources and is due to electricity production in 14 coal-fired power plants and in another major industrial installation.

The continuous drop of prices for photovoltaic modules over the past years lead to lower cost of solar than coal-based electricity. In order to reduce the country’s contribution to global warming, we have started a programme that intends to convert CO₂ to liquid fuels such as methanol, using solar energy. Liquid fuels are suitable for storage of large amounts of energy in chemical form, much more so than batteries or other means of energy storage, to cope with the asynchronous daily cycles of energy demand and renewable energy supply. These fuels can also be transported over large distances by rail, road or sea with existing infrastructure and may thus even be lucrative for export. Recycled methanol is a carbon-neutral fuel for use in internal combustion engines or turbines, or in fuel cells for direct back-conversion to electricity. An efficient means of solar energy storage can cope with the energy demand at any time of day and in any weather [1]

In collaboration with a group at the University of Poitiers in France we have at first converted formic acid (nominally the first intermediate of the recycling reaction) on an indium oxide catalyst with high efficiency to a mixture of methanol, ethanol and iso-propanol [2].

Diffuse Reflection Fourier-Transform Infrared Spectroscopy as a function of applied cell voltage in the oxidative regime showing the vibrational bands of formic acid (FA) to disappear and those of CO₂ to appear.

The studies will be extended to the full coelectrolysis reaction of CO₂ gas with liquid water. This fundamental research aiming at novel electrochemical processes could later be scaled up for industrial applications.

[1] E. Roduner,* E.R. Rohwer, Technical principles of atmospheric carbon dioxide reduction and conversion
      – economic considerations for some developing countries. Clean Technol. Environ. Policy
     (https://doi.org/10.1007/s10098-020-01889-w)

[2] K.A. Adesina, S. G. Radhakrishnan, C. L. Gray, B. Sowa, C. Morais, P. Rayes,
      E. R. Rohwer, C. Comminges,* K. Boniface Kokoh, E. Roduner.*
      Highly efficient formic acid and carbon dioxide electroreduction to alcohols
      on indium oxide electrodes (https://doi.org/10.1039/D0SE00623H)       

Have a look at our new book chapter: Carbon Dioxide Activation
In: Carbon Dioxide Utilisation: Volume 1. Fundamentals
https://doi.org/10.1515/9783110563191 (pp. 227-248)

Contacts: Dr. Shankara Radhakrishnan, Prof. Egmont Rohwer and Prof. Emil Roduner