Leaf photosynthesis inspires new solar cell design

Taking inspiration from the natural world, scientists are developing new solar panels that use the power of the sun to convert carbon dioxide into a burnable hydrocarbon fuel source.

The power of plants

Photosynthesis is one of the least ecologically harmful fuel production processes on the planet.

Using only the power of sunlight, the chlorophyll in plants turns the carbon dioxide and water molecules which are readily abundant in the atmosphere, into glucose and oxygen.[1]

Although oxygen is the only waste product, photosynthesising plants are actually less efficient than photovoltaic – cells that turn solar power into electrical energy, such as those found on a solar panel.[2]

However, due to the impact fossil fuels are having on the environment, scientists have been pursuing a way to imitate photosynthesis to produce burnable fuels.

Harnessing photosynthesis instead of photovoltaic

 In 2007, British biochemist James Barber proposed that scientists should consider the process of photosynthesis as a method of creating fossil fuels, but it took almost a decade before researchers engineered solar cells that replicated photosynthesis.[3]

Scientists from the University of Illinois at Chicago have developed efficient and cheap solar panel cells that use the power of the sun to create hydrocarbon fuel from atmospheric carbon dioxide.

“The new solar cell is not photovoltaic – it’s photosynthetic,” Amin Salehi-Khojin, assistant professor of mechanical and industrial engineering at UIC and senior author of the study, told the university’s website.[4]

“Instead of producing energy in an unsustainable one-way route from fossil fuels to greenhouse gas, we can now reverse the process and recycle atmospheric carbon into fuel using sunlight,” he continued.

Finding the catalyst

The key component of the cells was the catalyst – the part in the reaction that increased its rate. Up until now, scientists have been reliant on inefficient or expensive materials to act as a catalyst, such as silver.

Salehi-Khojin and his colleagues realised that they needed to combine transition metal dichalcogenides, or TMDCs, with an unconventional ionic liquid as the electrolyte to act as a catalyst.

Eventually, they discovered that the TMDC nanoflake tungsten diselenide and the ionic fluid ethyl-methyl-imidazolium tetrafluoroborate (diluted to half strength with water) was the perfect mix

“The new catalyst is more active; more able to break carbon dioxide’s chemical bonds,” UIC postdoctoral researcher Mohammad Asadi observed to the university’s website.

How does it work?

When subjected to light with a strength of 100 watts per square metre (which is roughly how strong it is at the Earth’s surface), hydrogen and carbon monoxide bubble up from the solar cell’s cathode, freeing up oxygen and hydrogen ions. The hydrogen ions then combine with carbon dioxide to create hydrocarbons.

The new energy-efficient photosynthesising solar cells could be used in both small and large scale fuel production operations, and Salehi-Khojin even believes that it may have applications on Mars.

[1] http://www.rsc.org/Education/Teachers/Resources/cfb/Photosynthesis.htm

[2] http://www.scientificamerican.com/article/plants-versus-photovoltaics-at-capturing-sunlight/

[3] http://rsta.royalsocietypublishing.org/content/365/1853/1007

[4] https://news.uic.edu/breakthrough-solar-cell-captures-co2-and-sunlight-produces-burnable-fuel

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