Put bacteria in high-density living to make electricity

Did you know you could generate electricity with bacteria? It’s not yet a commercially viable source, but there are ways to harvest electrons from microbes – particularly if they photosynthesise.

A team of researchers have just found a way to make photosynthetic bacteria more efficient energy producers: give them “tiny skyscrapers” to live in.

Publishing their findings in Nature Materials, the researchers describe 3D-printed grids of electrodes, made from metal-oxide nanoparticles. These grids operate as housing for photosynthesising cyanobacteria, promoting their growth. Rent is free, but you need to supply your own electricity.

“Our approach is a step towards making even more sustainable renewable energy devices for the future,” says senior author Dr Jenny Zhang, bacterial landlord and a researcher at the University of Cambridge, UK.

Researchers have been examining energy-producing bacteria for a couple of years, and finding ways they can extract electricity from photosynthesis. But this research improves on previous levels of energy by an order of magnitude.

“There’s been a bottleneck in terms of how much energy you can actually extract from photosynthetic systems, but no one understood where the bottleneck was,” says Zhang.

“Most scientists assumed that the bottleneck was on the biological side, in the bacteria, but we’ve found that a substantial bottleneck is actually on the material side.”

The researchers’ electrodes improve the bacteria’s performance by giving them more access to sunlight. They’ve been printed as dense, heavily branched columns that give the cyanobacteria plenty of places to hang out.

“The electrodes have excellent light-handling properties, like a high-rise apartment with lots of windows,” says Zhang.

“Cyanobacteria need something they can attach to and form a community with their neighbours. Our electrodes allow for a balance between lots of surface area and lots of light – like a glass skyscraper.”

With their array, the researchers were able to draw 245 micro-amps (µA) of current per square centimetre of bacteria. In their paper, they state that this converts to a potential power output of 541 milliwatts per square metre – not exactly energy-dense, but better than some commercial biofuels.

“I was surprised we were able to achieve the numbers we did – similar numbers have been predicted for many years, but this is the first time that these numbers have been shown experimentally,” says Zhang.

“Cyanobacteria are versatile chemical factories. Our approach allows us to tap into their energy conversion pathway at an early point, which helps us understand how they carry out energy conversion so we can use their natural pathways for renewable fuel or chemical generation.”