Power/Performance Bits: Aug. 5

Biofuels from microorganisms; non-toxic solar cells.


Biofuels from microorganisms
Researchers at Uppsala University are working on adapting microorganisms to be capable of producing useful biofuels out of carbon dioxide and solar energy.

The team is focused on a series of modified cyanobacteria that produces the alcohol butanol, said Pia Lindberg, Senior Lecturer at the Department of Chemistry Ångström Laboratory, Uppsala University. “When the best cells are used in long-term laboratory experiments, we see levels of production that exceed levels that have been reported in existing articles. Furthermore, it is comparable with indirect processes where bacteria are fed with sugar.”

Butanol can be used as an environmentally friendly fuel for automobiles, and it can also be used as a component of rubber for tires.

While this cyanobacteria has been shown to produce butanol before, the amounts have been limited. Now, the team says they’ve found that more butanol is formed as more is removed from the cyanobacteria, enough for the produced fuel to be commercially viable.

“Microscopic cyanobacteria are the most efficient photosynthetic organisms on earth. In this study, we utilise their ability to efficiently capture the sun’s energy and bind to carbon dioxide in the air, alongside with all the tools we have to modify cyanobacteria to produce desirable products. The results show that a direct production of carbon-neutral chemicals and fuels from solar energy will be a possibility in the future,” said Peter Lindblad, Professor at the Department of Chemistry Ångström Laboratory at Uppsala University.

The researchers say that industries that currently produce high greenhouse gas emissions could use cyanobacteria to bind carbon dioxide, reducing their emission. The work is part of a larger project pn photofuels coordinated by VW.

Non-toxic solar cells
Researchers at the Washington University in St. Louis, Australian National University, Oak Ridge National Laboratory, and Los Alamos National Laboratory investigated a new material for solar cells that combines the benefits of perovskite cells while being non-toxic.

Lead-halide perovskites, one the most common types, suffer from both instability and the potential health and environmental hazards of lead.

The team’s new semiconductor is  made up of potassium, barium, tellurium, bismuth and oxygen (KBaTeBiO6). The team used materials informatics and quantum mechanical calculations on the supercomputer at Oak Ridge to analyze an initial 30,000 potential bismuth-based oxides, finding KBaTeBiO6 to be the most promising.

“We found that this looked to be the most stable compound and that it could be synthesized in the lab,” said Rohan Mishra, assistant professor of mechanical engineering & materials science at WashU. “More importantly, whereas most oxides tend to have a large band, we predicted the new compound to have a lower band gap, which is close to the halide perovskites, and to have reasonably good properties.”

The most promising compounds for solar cell applications have a band gap of about 1.5 eV, or electronvolt, Mishra said. Once the new material was synthesized, it was stable and had a band gap of 1.88 eV, which is what was predicted.

Mishra noted that these are first-generation solar cells that need more fine tuning of the band gap, but said it is a good first step toward nontoxic solar cells. “This shows that we can go away from these lead-halide perovskites. This opens up a really big space for designing semiconductors not just for solar cell applications but also for other semiconductor applications, such as LCD displays.”

The team plans to continue the work by studying the role of any defects in the new semiconductor and looking into more advanced synthesis techniques such as aerosol.

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