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University of Toronto scientists solve puzzle of converting CO₂ emissions to fuel

Saving the planet from climate change with a grain of sand

Photo of a thick blanket of hazardous smog over Tokyo

A thick blanket of hazardous smog over Tokyo, Japan. Photo: © | t_kimura.

Every year, humans advance climate change and global warming and quite likely our own eventual extinction by injecting about 30 billion tonnes of carbon dioxide (CO₂) into the atmosphere.

A team of scientists from the University of Toronto believes they’ve found a way to convert all these emissions into energy-rich fuel in a carbon-neutral cycle that uses a very abundant natural resource: silicon. Silicon, readily available in sand, is the seventh most-abundant element in the universe and the second most-abundant element in the earth’s crust.

The idea of converting CO₂ emissions to energy isn’t new: there’s been a global race to discover a material that can efficiently convert sunlight, carbon dioxide and water or hydrogen to fuel for decades. However, the chemical stability of CO₂ has made it difficult to find a practical solution.

“A chemistry solution to climate change requires a material that is a highly active and selective catalyst to enable the conversion of CO₂ to fuel. It also needs to be made of elements that are low cost, non-toxic and readily available,” said Geoffrey Ozin, a chemistry professor in U of T’s Faculty of Arts & Science, the Canada Research Chair in Materials Chemistry and lead of U of T’s Solar Fuels Research Cluster.

Converting greenhouse gas emissions into energy-rich fuel using nano silicon (Si) in a carbon-neutral carbon-cycle Image: Chenxi Qian

Converting greenhouse gas emissions into energy-rich fuel using nano silicon (Si) in a carbon-neutral carbon-cycle. Image: Chenxi Qian.

In an article published this week in Nature Communications, Ozin and colleagues report silicon nanocrystals that meet all the criteria.

The hydride-terminated silicon nanocrystals nanostructured hydrides for short have an average diameter of 3.5 nanometres and feature a surface area and optical absorption strength sufficient to efficiently harvest the near-infrared, visible and ultraviolet wavelengths of light from the sun together with a powerful chemical-reducing agent on the surface that efficiently and selectively converts gaseous carbon dioxide to gaseous carbon monoxide. The potential result: energy without harmful emissions.

“Making use of the reducing power of nanostructured hydrides is a conceptually distinct and commercially interesting strategy for making fuels directly from sunlight,” said Ozin.

The U of T Solar Fuels Research Cluster is working to find ways and means to increase the activity, enhance the scale, and boost the rate of production. Their goal is a laboratory demonstration unit and, if successful, a pilot solar refinery.

Collaborators on the paper include:

  • Le He, Chenxi Qian, Laura Reyes, Wei Sun and Annabelle Wong of U of T’s Department of Chemistry, Faculty of Arts & Science;
  • Abdinoor Jelle and Jia Jia, both cross-appointed in U of T’s Department of Chemistry and Department of Materials Science & Engineering;
  • Kulbir Kaur Ghuman, Department of Materials Science & Engineering, Faculty of Applied Science & Engineering;
  • Chandra Veer Singh of U of T’s Department of Materials Science & Engineering and Department of Mechanical & Industrial Engineering
  • Charles A. Mims, Paul G. O’Brien and Thomas E. Wood of U of T’s Department of Chemical Engineering & Applied Chemistry and the Solar Fuels Research Cluster;
  • Amr S. Helmy of the Edward S. Rogers Sr. Department of Electrical & Computer Engineering, U of T.