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Instant insight: A bright future
19 September 2007
Andy Benniston at Newcastle University, UK, explains how photocatalysts could provide the answer to the planet's energy crisis, and reduce CO2 emissions while they're at it
Nature is way ahead of us when it comes to using sunlight to produce energy
Although the picture painted may seem all 'doom and gloom', it should not be forgotten that the fuels we burn today come from carbon sources that were, in a simple sense, 'fixed' by nature many millions of years ago. The current situation is only the consequence that we are now using up these sources at an alarming rate and nature cannot keep up!
So how can we solve the energy crisis and reduce CO2 emissions at the same time? The answer is either to find a fuel that does not produce CO2, or to find a process that uses CO2 in fuel production. If the two processes could be coupled together then the cycle set up would clearly be highly beneficial. This may seem far-fetched, but this cycle is almost the same as that used by plants to covert water into oxygen that we breathe, and CO2 into carbohydrates that we eat. We breathe out CO2 completing the cycle. The energy source for all this to operate comes from the sun, which to all intent purposes affords the planet unlimited power.
A major challenge for scientists is to mimic the process that plants successfully use to harness solar energy. We may think that this is a new idea, but back in the late 1970s and 1980s many groups tried to solve the problem, to differing levels of success.
If the above reactions are difficult to achieve then the controlled reduction of CO2 is even more so, since several different products are feasible depending on the number of added electrons and protons. One particularly interesting outcome is the six electron/proton product, methanol, which again is a fuel that can be burned to afford energy. It can be speculated that an ideal scenario would be coupling of the water splitting reaction to the CO2 reduction reaction. The greenhouse gas would be converted to a fuel and sunlight would provide the energy source, thus solving all our problems in one go!
What this idyllic story lacks is the science behind how to achieve some of the reactions needed. The real challenge lies in finding photocatalysts that capture sunlight and drive the chemical transformations.
But this is only part of the story as the synthesis of such catalysts is time consuming, and requires controlled build up of the final structure. Even after careful design and synthesis, detailed photophysical studies can often reveal the system does not behave as expected and it's back to the drawing board.
There is a still a long way to go before an 'artificial leaf' is available and a new generation of scientists is needed to take up the challenge now.
Link to journal article
Porphyrin linked poly(pyridyl)-based conjugates as artificial photosynthetic reaction centre models
Andrew C. Benniston, Phys. Chem. Chem. Phys., 2007, 9, 5739
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