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Germinating the Seeds of Solar-Hydrogen Fuel Trees, Orchards and Gardens

“Green” energy innovators have been striving to emulate nature, and more specifically plant photosynthesis, in bids to address climate change and fuel the transition to a healthier, more vital and more equitable sustainable energy future. 

Recent news reports highlight the advances that have been taking place. Participating in last October’s Discovery Education 3M Young Scientist Challenge, a 13 year-old from Ohio, Maanasa Mendu won the title of “Amercia’s Top Young Scientist,” and the contest’s $25,000 grand prize. 

Working with her 3M mentor, Mendu built a prototype that uses solar PV and piezoelectric ribbons to convert and harvest solar energy, as well as the energy in vibrations caused by wind and precipitation. All this in a working device that cost $5 to create, according to a news report.

As encouraging as this and other related advances are, so-called “solar leaf” and artifical photosynthesis technologies are still years away from prospective commercial application. At least one exception exists, however. U.K.-based SolarBotanic is touting its “Energy Tree” as a robust, scalable and economic “net zero” emissions energy production and storage system for remote communities in the EU (European Union). 

SolarBotanic's "Energy Tree"

SolarBotanic’s “Energy Tree” is said to efficiently and cost-effectively convert solar and wind energy to electricity, then convert that electrical energy for household use, electric vehicle charging, sale to the utility grid or stored longer term as hydrogen fuel.

Akin to Mendu’s grand prize-winning 3M Young Scientist Challenge prototype, the piezoelectric solar energy conversion technology incorporated in SolarBotanic's Energy Tree sways with winds and rain, harvesting and converting the kinetic energy to electricity. More specifically: 

“Nanoleaves, composed of nantenna electromagnetic collectors, convert both ‘visible’ and ‘invisible’ radiation into electricity. This sophisticated approach allows for energy to be gathered at a high efficiency even after the sun has set, or on a cloudy day,” management explains in a news release.

The next step in the process is key: SolarBotanic employs regenerative, or reverse, hydrogen fuel cells (RHFC) to convert and store the electricity as hydrogen gas, making it a readily available source of energy for residential, commercial, industrial or transportation applications. 

As the moniker indicates, RHFCs work in reverse of standard hydrogen fuel cells, which typically use inorganic chemical catalysts in an electrolytic solution separated by thin, selectively permeable membranes to drive a reaction that converts the chemical energy contained in hydrogen and oxygen gas to produce electricity and water. RHFCs, on the other hand, use a combination of water and electricity to produce oxygen and a hydrogen gas fuel resource.

Going the Extra Mile

Furthermore, SolarBotanic appears to have gone the extra mile to assure that its Energy Tree technology is as environmentally friendly as possible. Besides emissions-free electricity, the entire process of fabricating them – from raw materials to final product – is environmentally low-impact as well. According to management:

“The stronger the wind and the more powerful the sun, the more electricity is produced. By utilizing high-quality thermoplastics from renewable resources such as lignin, SolarBotanic achieves an outstanding level of efficiency while furthering its ecological mission.”

If all this proves true, critical questions regarding the Energy Tree’s efficiency, robustness, scalability, and net economic benefits need to be answered.

Other cutting-edge solar leaf, tree and artificial photosynthesis research groups are taking different tacks. Rather than looking for new, better inorganic chemical catalysts that can be used in fuel cells and artificial photosynthesis, they’re identifying, and in some instances fabricating, new living organisms, i.e. bacteria, that serve as catalysts in driving chemical reactions that convert a mix of solar energy, water and CO2 into hydrogen fuels and other useful hydrocarbon chemicals. 

Chasing Artificial Photosynthesis

Last June, Harvard University professor of energy science Daniel Nocera announced that he and his colleague Pamela Silver had devised “a system that completes the process of making liquid fuel from sunlight, carbon dioxide, and water.” 

Nocera has been pioneering artificial photosynthesis, “solar leaf” and solar fuel R&D since joining MIT’s faculty in 2007 and taking up the helm of MIT’s Solar Revolution Project in 2008. In 2009, Nocera founded Sun Catalytix, a startup with the aim of further developing and producing market-ready versions of artificial leaf technology. Lockheed Martin bought the company in 2014.

In natural photosynthesis, plants are able to harvest solar energy, CO2 and water to produce energy-storing carbohydrates at about 1 percent energy efficiency. Significantly, Nocera and Silver’s new process reportedly does so with 10 percent energy efficiency when pure CO2 is used and 3-4 percent when CO2 is harvested from the atmosphere. 

Furthermore, it does so more cheaply and at lower temperatures than alternatives, according to an MIT Technology Review news announcement. Nocera and Silver use a pair of catalysts to convert water into oxygen and hydrogen (a well-known process known as hydrolysis) then  feed the hydrogen along with CO2 to genetically engineered bacteria that can “digest” the gas mixture and produce a liquid hydrocarbon fuel. 

The new process, details of which have been published in a peer-reviewed research paper in Science, “could be a milestone in the shift away from fossil fuels,” MIT Technology Review reports.

A New Milestone

Just this past month, an international team of research scientists led by Indiana University, Bloomington’s Liang-shi Li reportedly created a bacteria that reduces carbon dioxice (CO2) to carbon monoxide (CO), which is used as a fuel in a wide range of industrial processes. 

The advance, according to a university news press release, represents “a new milestone in the quest to recycle carbon dioxide in the Earth’s atmosphere into carbon-neutral fuels and others materials.”

As explained in the press release, burning a fuel, such as carbon monoxide, produces carbon dioxide and releases energy. At least the equivalent amount of energy input is needed to reverse the process and convert CO2 back into CO, which can then be recycled and used in an artificial photosynthesis process to produce liquid biofuel from solar-powered processes. Scientists around the world are searching for ways to reduce the additional energy needed.

"If you can create an efficient enough molecule for this reaction, it will produce energy that is free and storable in the form of fuels," said Li, an associate professor in the IU Bloomington College of Arts and Sciences' Department of Chemistry. "This study is a major leap in that direction."

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