Boosting the Mars Immigration Program, Yang Peidong ’s “Artificial Photosynthesis” System Enters Version 2.0, Turning CO2 into organic product is Just Around the World

If mankind conducts "interstellar migration" in the future, then Mars will undoubtedly be the first target. Silicon Valley "Iron Man" Elon Musk has always had the goal of "colonizing Mars" and plans to build a self-sustainable city on Mars. However, all materials needed for human life, such as oxygen, fuel, food, and medicine, are all unrealistic to rely on rockets to transport from the earth; even though SpaceX's rocket carrying capacity is constantly improving. However, Professor Yang Peidong of the University of California, Berkeley has a more long-term and simpler plan, or it will help the "Mars Immigration Plan" to be realized as soon as possible.

In the past ten years, researchers in Yang Peidong's laboratory have been studying a "circulatory system" that combines microorganisms with non-biological materials. The system can convert carbon dioxide and water into the basic components of organic molecules by absorbing solar energy-this is also known as "artificial photosynthesis". In 2015, Yang Peidong Lab successfully developed the first generation of "artificial photosynthesis" system, and just recently, they launched a more excellent "2.0 version". According to Yang Peidong, the silicon nanowires in this system are essentially similar to antennas-they capture solar photons like solar panels. These silicon nanowires then generate electrons and provide them to the attached microorganisms. Finally, microorganisms absorb carbon dioxide, perform chemical reactions, and produce acetate.

The paper about the study was published in the journal Joule on March 31, Yang Peidong's "Artificial Photosynthesis System Version 2.0" set a new record of conversion efficiency: up to 3.6% of solar energy absorption in a week Conversion efficiency, complete the conversion from solar energy to chemical energy, and finally stored in the form of acetate. In addition, oxygen can also be produced.

Figure | "Artificial photosynthesis system version 2.0": a device that captures carbon dioxide from the air and converts it into a practical organic matter; on the left is the space containing the combined system of microorganisms and nanowires, where carbon dioxide is converted to acetic acid Salt, on the right is the space where oxygen is produced (Source: Yang Peidong / UC Berkeley)

Nature-like "dynamic circulation system"

"96% of the Martian atmosphere is carbon dioxide." Yang Peidong said, "our system absorbs solar energy through silicon semiconductor nanowires and passes them to the microbes on the nanowires to carry out chemical reactions."

For space missions, people need to consider the weight of the payload, and the advantage of biological systems is that they can replicate themselves. In this way, people do not have to rely on rockets to launch more things, so this is precisely the attractive advantage of the "biological / abiotic combined system". Even if interstellar immigration is not considered, it can help solve problems such as energy shortages and global warming caused by carbon dioxide emissions.

"In addition to sunlight, our artificial photosynthesis system requires only another substance-water." Yang Peidong said, "The polar ice caps on Mars are relatively rich, and most of the planet's underground is likely to freeze a lot Water. "Similarly, more than 70% of our planet is covered by sea water.

The "artificial photosynthesis" system designed by his laboratory combines silicon semiconductor nanowires with microorganisms that can use their own enzymes to convert carbon dioxide into specific multi-carbon products, thereby achieving the conversion process from solar energy to chemical energy. When the system first came out in 2015, it attracted widespread attention. But at that time, its conversion efficiency was relatively low, only 0.4%.

"The first-generation mainly proved that our design is feasible from the concept." Yang Peidong said. Then in the past five years, they continued to optimize it until it increased to 3.6% today-and this is close to the conversion efficiency of the "champion" sugarcane in nature, which converts carbon dioxide into sugar and other substances, 4% ~ 5%."We have spent a lot of thoughts on this, and probably experienced 3 or 4 waves of graduate students."

Because of the survival time of microorganisms, the self-replication ability of microorganisms is very strong and frequent. As a catalyst for conversion, it takes a while A batch will die afterward, but then a second batch will be generated. It will have a self-regeneration process, so the durability of the system has no problem. "

Figure | Scanning electron microscopy image of the microbe-nanowire combination system: Under the optimal pH environment, the microbes will tightly wrap the nanowires; this close packing will make solar energy more effectively converted into carbon bonds (source: Yang Peidong)

As the 2.0 version of the "artificial photosynthesis" system, Yang Peidong's laboratory mainly studied and optimized the interface between microorganisms and nanowire electrodes.

The researchers initially tried to fill the nanowires with more microorganisms to improve efficiency, and when electrons were directly transferred to the microorganisms through the nanowires for chemical reactions, the microorganisms would fall off the nanowires, damaging the circuit. After repeated experiments, they found that these microorganisms reduced the acidity of the surrounding water during the production of acetic acid, thus causing them to separate from the nanowires.

Yang Peidong and his students eventually found a way to control the acidity of the water in the environment, thereby counteracting the effect of the continuous increase in pH caused by acetic acid. This allows them to put more microorganisms into the nanowires, increasing the conversion efficiency by nearly 10 times. The system can carry out the carbon dioxide reduction reaction stably and efficiently for a week without supplementing microorganisms.

Under continuous sunlight, the average energy conversion efficiency of the "Artificial Photosynthesis System Version 2.0" within a week of "solar to acetic acid" reached 3.6%; at the same time, the daily acetic acid production in this week can also reach 44.3 g / m2 (Or 0.3 g / L). In addition, they used the isotope labeling method to confirm the reaction trajectory of carbon, and used dark control experiments to prove that light energy is the only energy source for carbon dioxide conversion.

The generated acetate molecules can be used as a part of a series of organic molecules, including fuels, plastics and drugs. At the same time, many other organic products can also be made from acetate in genetically modified organisms, such as bacteria or yeast. In addition, Yang Peidong's laboratory is also studying the use of solar energy and carbon dioxide to produce sugar and carbohydrate systems, which may further solve the food problem of interstellar immigrants.

Oxygen is a side benefit, which may help humans create a 21% oxygen environment that mimics the Earth on Mars.

"IIn summary, the silicon nanowires in this system are similar to antennas in nature-they capture solar photons like solar panels. These silicon nanowires then generate electrons and provide them to the attached microorganisms. Finally, the microorganisms absorb carbon dioxide, Carry out a chemical reaction and produce acetate. "Yang Peidong said.

Scientific research focuses on "original", the results come from accumulation

"Artificial photosynthesis system" has been developed to this day, and has achieved such remarkable results, thanks to Yang Peidong's accumulation of knowledge in many fields for many years, and his "original" design thinking.

As a pioneer in the field of nanowires, Yang Peidong worked with his mentor Charles Lieber, an academician of the US Three Academy of Sciences and a nanoscience scientist at Harvard University, when he was studying about Semiconductor nanowires for  a doctorate at Harvard University 25 years ago . This is a very thin silicon wire with a diameter of only one percent of human hair. It can be used to convert thermal energy, light energy into electrical energy, or It is widely used as an electronic component in sensors and solar cells and has great potential.

In 2001, semiconductor nanowire electronic devices were selected as the top ten breakthroughs by Science magazine. In addition, the technology was also rated as one of the "Top Ten Breakthrough Technologies Affecting the Future" by the MIT Technology Review in 2004. In 2006, "Nature" magazine listed semiconductor nanowire research as one of the top ten research hotspots in physics.

After developing the nanowires, Yang Peidong came to the University of California, Berkeley, and began to conduct research on the photonics of nanowires and solar cells related to nanowires. With the development of fields such as genetic engineering, biosensors, and biofuel cells, hybrid functional materials that combine biological and non-biological materials have received extensive attention. Subsequently, the scientific research community turned its attention to the use of microorganisms to achieve efficient reduction of carbon dioxide in the aqueous phase.

Around 2010, Yang Peidong began the research on "artificial photosynthesis" based on the interface between microorganisms and non-biological materials. Due to his pioneering advantages in semiconductor nanowires, coupled with his continuous learning and in-depth investment in the fields of chemistry and microbiology, Yang Peidong's laboratory has always been in a leading position in the field of artificial photosynthesis.

"This is a relatively 'niche' field." Yang Peidong said, "Because it requires a relatively large subject span and high requirements for scientific research conditions and technology accumulation. Not many laboratories can do this."

But "niche" does not mean that research in this field is not important enough. In September 2018, NASA released a "CO2 Conversion Challenge" for space: providing a prize of 1 million US dollars, hoping that participants can find a new method of CO2 conversion and convert it into useful compounds such as glucose. NASA will reward 5 teams, and each team will receive US $ 50,000. The results will be announced in April 2019. After that, the selected team will enter the second stage-build a conversion system and display it. The bonus in the second stage is up to 750,000 USD.

As expected, the research team of Yang Peidong's laboratory successfully entered the "Final 5" in the first phase. "We are currently in the second phase of this challenge." However, the NASA challenge is not the same as the artificial photosynthesis system we are talking about.