Bionic Leaf that Converts Sunlight into Liquid Fuel

Bionic Leaf
Image courtesy of Jessica Polka/Silver Lab image source

Generally, Photosynthesis process is used to convert solar energy into chemical energy. It is the process used by the plants and other organisms to convert light energy normally from the sun into chemical energy that can be later released to fuel the organism’s activities.

In plants, some bacteria, and some Protestants uses the energy from sunlight to generate glucose from carbon dioxide and water. This glucose can be converted into Pyruvate which releases Adenosine triphosphate (ATP) by cellular respiration. Oxygen is also created. (ATP is a nucleoside triphosphate used in cells as a Coenzyme of intracellular energy transfer.)

A new method has been cultivated by Harvard Scientists. They have developed a ‘bionic leaf’ that converts solar energy into a liquid fuel. The work in the new field ‘bio-manufacturing’ is the fruit of co-operation between the laboratories of Adams, professor of biochemistry and systems biology Pamela Silver at Harvard Medical School(HMS) and Patterson Rockwood, a professor at energy Daniel Nocera in the faculty of Arts and Sciences.

Labelling by silver, the system is called ‘bionic’ because it connects the biological system to a clever piece of artificial chemistry known as an artificial leaf. An artificial leaf converts solar energy into hydrogen fuel developed by Nocera. This artificial leaf plays an important role in bionic leaf, It act as a fuel of bionic leaf, works by interposing a photo-voltaic cell between two thin metal oxide catalysts. When it is deep inside a glass of water at room temperature and normal atmospheric pressure, the artificial leaf processes photosynthesis. From the silicon solar, the wafer is delivered to the catalysts, which splits water molecules. Oxygen bubbles rise on the one side of the wafer while hydrogen rises from the catalyst on the other side of the wafer. It is more effective than the field- grown plant, which catches 1 percent of sunlight energy.

Nocera said that “he can reach efficiencies of 70 to 80 percent of the underlying solar-wafer technology, which is improving constantly. The hydrogen generated by it is a versatile fuel at a chemical standpoint and can easily become the basis of a fuel cell.”

In part of the gas, the artificial leaf is not widely adaptable. Hence, the bionic leaf is important because liquid fuels are much easier to handle and store.

In bionic leaf, hydrogen gas is delivered to Rastonia eutropha. Rastonia eutropha is a metabolically engineered version of a bacterium. The bacteria integrates the hydrogen with carbon dioxide as they split to develop more cells. After that, through isopropanol, they are burned in an engine most likely to the gasoline additive ethanol. Isopropanol is a rubbing alcohol, a trick developed by Anthony Sinskey, professor of microbiology and of health, sciences and technology at MIT.

Brendan Colón, a graduate student in systems biology in the Silver lab and a co- author of the Proceedings of the National Academy of Sciences paper, said, “The advantage of interfacing the inorganic catalyst with biology is you have an unprecedented platform for chemical synthesis that you don’t have with inorganic catalysts alone.”

“Life has evolved for billions of years to produce catalysts capable of making chemical modifications on complicated molecules with surgical precision, many times at room temperature,” Colón explains.

“If you can use enzymes for building chemicals, you open the door to making many of the natural compounds we rely on every day, such as antibiotics, pesticides, herbicides, fertilizer, and pharmaceuticals”, she continued.

For perfection of the complicated interface between the catalyst and bacteria, so that they develop and grow optimally, members of Silver’s lab are still working on it. In its first test, bionic leaf matched the effectiveness of photosynthesis in plants. It is far below the effectiveness of Nocera’s artificial leaf.

Now the team has been working on surpassing blue-green algae which have 5 percent efficiency to do better photosynthesis than plants.

Colon is developing a strain of the bacterium that grows well at lower voltages. It may emit by solar wafer at the system’s core on a cloudy day. For example, this cloud severely enhances overall efficiency.

Colon says, “Silver’s goal is not to create fuels from this work, but “high-value commodities” in remote places. Fuel is cheap because we fight for it and developing a system that could make fuel at a price lower than gasoline would, therefore, be very difficult. Drugs, on the other hand, are high-value commodities, so engineering a bacterium to produce not isopropanol but a vitamin or a drug may be her next goal for this system.”

Nocera said, “Modern society, has created an entire manufacturing economy based not only on burning fossil fuels but on using petroleum to make things such as rubber and plastics. A lot of chemistry was done which set that up. The present system makes sense now because petroleum costs so little; a sustainable system like the artificial or bionic leaf can’t compete with that. But when oil becomes scarce.”

He says, “We might want to redo everything in terms of manufacturing. In the future, you might want to make everything renewably.”