Scientists have built a microbial fuel cell that runs withou

For the first time, scientists have built a microbial fuel cell that produces an electrical current without any external power, which means it's now possible to use bacteria that poop electricity as an energy source.

The 3D fuel cell is made out of paper, and is only a a proof-of-concept at this stage. But it suggests that the batteries of the future could be powered by microbes instead of rare earth metals like lithium.

Microbial fuel cells use the activity of bacteria to effectively break down chemical energy (food) and poop out electrons. Those pooped out electrons can be turned into electrical power, which is pretty awesome.

But in order to ensure a continuous supply of food, scientists currently need to actively pump it to the microbes. If the food stops, the electrons stop too, so for years scientists have had to use external power to keep these microbial fuel cells running, and that kind of defeats the purpose of generating electricity in the first place.

Now a team from Iowa State University have created a 3D paper fuel cell that automatically keeps supplying food - in this case, potassium ferricyanide - to the microbes, without any pumping required.

Using their new set-up, the team showed that a microbial fuel cell could continue to generate an electrical current for five days, without any external power or human interference.

"All power created in this device is useable because no electricity is needed to run the fluids through the device," said lead researcher Nastaran Hashemi. "This is crucial in the advancement of these devices and the expansion of their applications."

To understand how the new microbial fuel cell works, you first need to know how a regular fuel cell works.