Efficient artificial photosynthesis to generate hydrogen

Researchers develop a new way to harness sun’s energy for clean, storable, efficient fuel

July 29, 2021
The Scitech

Humans might soon acquire the capacity for photosynthesis as explained by Yulia Puskhar, a biophysicist and professor of physics in Purdue’s College of Science. 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. The closest process to artificial photosynthesis humans have today is photovoltaic technology, where a solar cell converts the sun’s energy into electricity. That process 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 – 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.

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 Catalysis: 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. Progress in artificial photosynthesis is complicated, though, by the fact that photosynthesis is so multifaceted, a fact bemoaned by biochemistry students everywhere. “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.

Source: Purdue University news release