Semi-artificial Photosynthesis: Sunlight Turned Into Fuel in 'Milestone' for Solar Energy

An international team of researchers has demonstrated a new technique, inspired by the process of photosynthesis in plants, which could one day be used to produce hydrogen fuel—a clean and practically unlimited source of renewable energy.

In a paper published in the journal Nature Energy, scientists from the University of Cambridge and the Ruhr University Bochum have outlined a proof-of-principle method to split water molecules into their constituent parts, hydrogen and oxygen, using sunlight.

Plants also "split" water molecules when they convert sunlight into energy during photosynthesis. While artificial photosynthesis techniques have been around for decades, they have not been adapted to produce renewable energy because these methods require the use of catalyst materials which have several drawbacks.

According to Erwin Reisner, Professor of Energy & Sustainability from Cambridge and lead author of the study, the new research is a “milestone” in the emerging field of “semi-artificial photosynthesis.” This approach harnesses the abilities of natural enzymes and combines them with artificial technology in an attempt to overcome some of the limitations of purely artificial photosynthesis techniques.

“Solar energy conversion to produce renewable fuels and chemicals—i.e., solar fuel synthesis—is an important strategy for powering our society in a post-fossil era,” Reisner told Newsweek. “Natural photosynthesis has evolved to store solar energy and to ‘fix’ the greenhouse gas carbon dioxide (CO2) into sugars, but this process is not very energy efficient.

“Artificial photosynthesis mimics natural photosynthesis and aims to produce sustainable hydrogen from water through water-splitting or carbon-based fuels from CO2 fixation, but is commonly hampered by expensive, toxic or inefficient catalysts,” he said. “We try to establish a new line of research by combining the best of the natural and artificial worlds and take highly efficient and abundant biological catalysts, such as enzymes, and combine them with synthetic materials in solar devices for efficient solar fuel synthesis.”

The team’s technique employs a key enzyme present in algae, known as hydrogenase, in addition to synthetic pigments, to achieve unassisted solar-driven water-splitting into hydrogen and oxygen. The prototype system is capable of absorbing more solar light than natural photosynthesis.

“Compared to the natural pathway, this new system makes wider use of the solar spectrum, delivers high conversion yields, and bypasses several competing metabolic steps, which is not achievable using synthetic biology or materials science alone,” Reisner said.

179563_web Experimental two-electrode setup showing the photoelectrochemical cell illuminated with simulated solar light. Katarzyna Sokól

According to the researchers, the work overcomes many difficult challenges associated with the integration of biological and organic components into inorganic materials “and as a result widens the toolbox for developing future semi-artificial systems for energy conversion.”

Reisner emphasizes that the new technique is still just a proof-of-principle and is still too fragile to be used in real-world applications in its current state. However, the researchers hope to refine the concept and demonstrate its wide applicability in the near future.

Hydrogen has been touted as the fuel of the future by many and is already being used in some vehicles and other contexts. Unlike fossil fuels, hydrogen is incredibly abundant given that it can be extracted from any water body—the oceans, for example. Furthermore, it does not produce greenhouse gases or other pollutants. The only byproducts of hydrogen fuel cells are water and heat.

However, at present, fossil fuels are being burnt to provide the large amounts of energy needed to create hydrogen fuels, highlighting the need for a scalable and affordable zero-emissions solution for producing hydrogen from renewable sources. The latest semi-artificial photosynthesis technology is one of several different approaches proposed by scientists around the world in a bid to address this issue.

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