Mimicking nature has long been part of human evolution. Researchers at Harvard have designed a system that mimics the process of Photosynthesis, the process by which plants convert solar energy into chemical energy that is later used to fuel the plant. The idea is not new though. The innovation, nicknamed "Bionic leaf," which was considered too good to be true, has now become a reality.
In 2011, Daniel Nocera, Professor of Energy at Harvard, demonstrated an artificial leaf that uses the Sun to produce energy. Like all great innovations, the idea is simple: Capture energy from the Sun and turn it into hydrogen and oxygen, mimicking the photosynthesis process in plants.
Sunlight to Isopropanol
The leaf was made from a silicon strip coated with catalysts on the sides. The strip, when placed in water and exposed to sunlight, released hydrogen and oxygen by splitting the water molecules.
Nocera's latest creation, in collaboration with the Harvard University's Faculty of Arts and Sciences, Harvard Medical School and the Wyss Institute for Biologically Inspired Engineering at Harvard University, is a specially engineered bacteria called Ralstonia eutropha that converts hydrogen into alcohol-based liquid fuel. This leaf works the same way as Nocera's leaf, the only difference being the channeling of hydrogen through a chamber filled with the genetically modified bacterium which produced isopropanol (a potential substitute for petrol) by absorbing the hydrogen.
The engineering method was discovered by Anthony Sinskey, Professor of Microbiology and Health Sciences and Technology at MIT. The method is detailed in the Proceedings of the National Academy of Sciences.
The Problem with Hydrogen
Though the idea is simple, it has its own share of challenges. "The problem with the artificial leaf," Nocera says, is that "it makes hydrogen. You guys don't have an infrastructure to use hydrogen."
Why? Because hydrogen is extremely unstable. The smallest stable molecule, it tries to escape into the atmosphere. Hydrogen must be compressed first before it can be contained which may be way expensive. Gasoline and diesel have an advantage over hydrogen in that they are stable and the most convenient.
The artificial leaf addresses this problem with the specially engineered bacterium which converts hydrogen into a liquid fuel.
Death of bacteria: the eluding challenge
Keeping the bacteria alive requires high-voltage current, which makes the process less efficient. During the initial stages, the bacteria died. Reactive oxygen was identified as the culprit. But more interesting is the source: the reactive oxygen was coming out of the hydrogen side, not the oxygen side.
"We were shocked," Nocera says. "That confused us for a while." Keeping the bacteria alive requires high-voltage current, making the process far less efficient. Nocera's team solved this problem and were able to produce fuel more efficiently.
Improving the Efficiency
"We're almost at a 1 per cent efficiency rate of converting sunlight into isopropanol," Professor Nocera said. "There have been 2.6 billion years of evolution, and Pam and I working together a year and a half have already achieved the efficiency of photosynthesis." Their goal is 5% efficiency, compared to nature's 1% efficiency rate for photosynthesis.
