Humans can do lots of things that plants can’t do. We can walk around, we can talk, we can hear and see and touch. But plants have one major advantage over humans: They can make energy directly from the sun.

That process of turning sunlight directly into usable energy – called photosynthesis – may soon be a feat humans are able to mimic to harness the sun’s energy for clean, storable, efficient fuel. If so, it could open a whole new frontier of clean energy. Enough energy hits the earth in the form of sunlight in one hour to meet all human civilization’s energy needs for an entire year.

Yulia Puskhar, a biophysicist and professor of physics in Purdue’s College of Science, may have a way to harness that energy by mimicking plants.

Wind power and solar power, harnessed by photovoltaic cells, are the two major forms of clean energy available. Adding a third — synthetic photosynthesis — would dramatically change the renewable energy landscape. The ability to store the energy easily, without requiring bulky batteries, would dramatically improve humans’ ability to power society cleanly and efficiently.

Both wind turbines and photovoltaics have downside in terms of environmental effects and complicating factors. Pushkar hopes that artificial photosynthesis might be able to bypass those pitfalls.

“We and other researchers around the world are working incredibly hard to try to come up with accessible energy,” Pushkar said. “Energy that is clean and sustainable that we can create with nontoxic, easily available elements. Our artificial photosynthesis is the way forward.”

Fotosynthese is een complexe dans van processen waarbij planten de zonnestraling en watermoleculen omzetten in bruikbare energie in de vorm van glucose. Hiervoor gebruiken ze een pigment, meestal het bekende chlorofyl, maar ook eiwitten, enzymen en metalen.

Het proces dat het dichtst in de buurt komt van kunstmatige fotosynthese die mensen tegenwoordig hebben, is fotovoltaïsche technologie, waarbij een zonnecel de energie van de zon omzet in elektriciteit. Dat proces is beroemd inefficiënt en kan slechts ongeveer 20% van de zonne-energie opvangen. Fotosynthese daarentegen is radicaal efficiënter; het is in staat om 60% van de zonne-energie op te slaan als chemische energie in bijbehorende biomoleculen.

The efficiency of simple photovoltaic cells – solar panels – is limited by semiconductors’ ability to absorb light energy and by the cell’s ability to produce power. That limit is something scientists could surpass with synthetic photosynthesis.

“With artificial photosynthesis, there are not fundamental physical limitations,” Pushkar said. “You can very easily imagine a system that is 60% efficient because we already have a precedent in natural photosynthesis. And if we get very ambitious, we could even envision a system of up to 80% efficiency.

“Photosynthesis is massively efficient when it comes to splitting water, a first step of artificial photosynthesis. Photosystems II proteins in plants do this a thousand times a second. Blink, and it’s done.”

Pushkar’s group is mimicking the process by building her own artificial leaf analog that collects light and splits water molecules to generate hydrogen. Hydrogen can be used as a fuel by itself via fuel cells or be added to other fuels such as natural gas, or built into fuel cells to power everything from vehicles to houses to small electronic devices, laboratories and hospitals. Her most recent discovery, an insight into the way water molecules split during photosynthesis, was recently published in the journal Chem Katalyse: Cell Press.

Scientists in Pushkar’s lab experiment with natural photosystem II proteins and synthetic catalysts combinations in attempts to understand what works best – and why. She also puts a priority on using compounds and chemicals that are readily abundant on Earth, easily accessible and nontoxic to the planet.

Vooruitgang in kunstmatige fotosynthese is echter gecompliceerd door het feit dat fotosynthese zo veelzijdig is, een feit waarover biochemiestudenten overal klagen.

“The reaction is very complex,” Pushkar said. “The chemistry of splitting water molecules is extremely intricate and difficult.”

Scientists have been working on artificial photosynthesis since the 1970s. That’s a long time, but not when you remember that photosynthesis took millions of years to evolve. Not only that, but scientists believe that, unlike flight, communication or intelligence, photosynthesis has evolved only once – about 3 billion years ago, only about 1.5 billion years into Earth’s existence.

Pushkar posits that within the next 10-15 years, enough progress will have been made that commercial artificial photosynthesis systems may begin to come online. Her research is funded by the National Science Foundation.

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