As the level of carbon dioxide (CO2) in the atmosphere continues to rise, scientists and engineers around the world are searching for ways to remove it—either by sequestering it in liquid form deep within the Earth or by turning it into a useful product. The latter approach is what plants do through the process of photosynthesis—combining carbon dioxide and water and using energy from the sun to produce the roots, stems, leaves, and flowers. They are all made from combinations of primarily carbon, oxygen, and hydrogen atoms as building blocks.
Scientists have had some limited success using expensive rare-earth or noble metal catalysts (such as ruthenium and rhenium) to achieve artificial photosynthesis. The goal, however, has been to find a way to mimic plants, which are capable of converting CO2 into useful materials using only earth-abundant materials. Now, a report on the research from a group at Tokyo Institute of Technology indicates good progress in carbon capture using earth-abundant materials in a photocatalytic system.
A photocatalytic system refers to a light-driven process that can accelerate a particular reaction of interest.
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The photocatalytic system in this study consists only of earth-abundant materials such as CuPS, the copper complex that behaves as a redox photosensitizer, and a manganese-based catalyst. (Image source: Tokyo Institute of Technology) |
The new process uses a copper-based organic compound (called CuPS) that behaves as a redox photosensitizer—a component that initiates the photochemical one-electron transfer from a reductant to a catalyst. A manganese-based catalyst compound, Mn(4OMe), uses the electrons to convert CO2 into carbon monoxide (CO) and a hydrocarbon (HCOOH).
It should be noted that both copper and manganese, as well as the organic molecules used to create the photosensitizer and the catalyst, are inexpensive and readily available.
The CuPS proved to be both stable and efficient. The team reported a total yield of CO2 reduction product of 57%—similar to the levels reached by rare-earth and noble metal catalysts. This level is remarkable, which led the researchers to note, "To the best of our knowledge, this is the highest quantum yield for CO2 reduction using abundant elements and the yield would be comparable to that obtained with rare metals." It was also noted that CuPS exhibited a much stronger reduction capability compared to other photosensitizers investigated to date.
Senior Editor Kevin Clemens has been writing about energy, automotive, and transportation topics for more than 30 years. He has masters degrees in Materials Engineering and Environmental Education and a doctorate degree in Mechanical Engineering, specializing in aerodynamics. He has set several world land speed records on electric motorcycles that he built in his workshop.
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