Wind power and solar power, harnessed by photovoltaic cells, are the two major forms of so-called renewable energy available, today. Both wind turbines and photovoltaics have major downsides in terms of environmental effects and other complicating factors. So, adding a third source in the form of synthetic photosynthesis would dramatically improve the renewable energy landscape. And its ability to store the energy easily, without requiring bulky batteries would dramatically improve humans’ ability to power society cleanly and efficiently.

The closest process to artificial photosynthesis humans have today is photovoltaic technology, where a solar cell converts the sun’s energy into electricity. However, photovoltaic technology is famously inefficient, able to capture only about 20% of the sun’s energy. Photosynthesis, on the other hand, is radically more efficient; it is capable of storing 60% of the sun’s energy as chemical energy in associated biomolecules.

The efficiency of simple photovoltaic cells is limited by semiconductors’ ability to absorb light energy and by the cell’s ability to produce power. That limit is something scientists could readily surpass with synthetic photosynthesis. Why? With artificial photosynthesis, there are no fundamental physical limitations. Engineers can very easily imagine a system that is 60% efficient because we already have a precedent in natural photosynthesis. And if they get very ambitious a system of up to 80% efficiency is quite possible.

Photosynthesis is massively efficient when it comes to splitting water, the first step of artificial photosynthesis. Photosystems II proteins in plants do this a thousand times a second.

Photosynthesis is a complex dance of processes whereby plants convert the sun’s radiance and water molecules into usable energy in the form of glucose. To do this, they use a pigment, usually the famous chlorophyll, as well as proteins, enzymes and metals.

According to research recently published in the journal Chem Catalysis researchers are mimicking the process by building an “artificial leaf” analog that collects light and splits water molecules to generate hydrogen. This hydrogen can then be used in fuel cells to power everything from vehicles to houses to small electronic devices, laboratories and hospitals 

The researchers experimented with combinations of natural photosystem II proteins and synthetic catalysts in attempts to understand what works best - and why. They specifically focused on using compounds and chemicals that are readily abundant on Earth, easily accessible and nontoxic to the planet.

Scientists have been working on artificial photosynthesis since the 1970s. The researchers expect that within the next 10-15 years, enough progress will have been made that commercial artificial photosynthesis systems will begin to come online.

- CHEM CATALYSIS, “Do multinuclear 3d metal catalysts achieve O–O bond formation via radical coupling or via water nucleophilic attack? WNA leads the way in [Co4O4]n,” by Roman Ezhov, et al. © 2021 Elsevier B.V. All rights reserved.