Power/Performance Bits: Sept. 24

Generating electricity from sewage
Stanford University researchers have come up with a new way to generate electricity from sewage using naturally-occurring “wired microbes” as mini power plants, producing electricity as they digest plant and animal waste.

Calling their invention a ‘microbial battery,’ the researchers hope one day it will be used in places such as sewage treatment plants, or to break down organic pollutants in the “dead zones” of lakes and coastal waters where fertilizer runoff and other organic waste can deplete oxygen levels and suffocate marine life.

At the moment their laboratory prototype is about the size of a D-cell battery and looks like a chemistry experiment, with two electrodes, one positive, the other negative, plunged into a bottle of wastewater.

Inside the murky vial, attached to the negative electrode like barnacles to a ship’s hull, an unusual type of bacteria feast on particles of organic waste and produce electricity that is captured by the battery’s positive electrode.

The tubular growth depicted here is a type of microbe that can produce electricity. Its wire-like tendrils are attached to a carbon filament. This image is taken with a scanning electron microscope. More than 100 of these “exoelectrogenic microbes” could fit side by side in a human hair. (Source: Stanford Engineering)

New materials improve oxygen catalysis

MIT researchers have found a new family of materials that provides what they say is the best-ever performance in a reaction called oxygen evolution, a key requirement for energy storage and delivery systems such as advanced fuel cells and lithium-air batteries.

The materials — called double perovskites — are a variant of a mineral that exists in abundance in the Earth’s crust and they have a remarkable ability to promote oxygen evolution in a water-splitting reaction, which breaks water molecules into oxygen and hydrogen.

The performance of this family of materials is a step forward from the previous record-holder for a catalyst that promotes electrochemical water-splitting — a material that these researchers reported two years ago. In addition, while the earlier material quickly changes structure during water-splitting, the new material is stable.

Splitting water into its constituent elements could be a significant boon for renewable energy sources, such as wind and solar, whose output is highly variable. Using a catalytic system, electricity from a solar panel or wind turbine can be fed into a container of water, and the streams of oxygen and hydrogen produced by splitting the water molecules can be collected in separate tanks. Then, when the power is needed, the two gases can be recombined, such as in a fuel cell, to produce water and electricity, the researchers explained.

To make this economically viable researchers must find catalysts that are inexpensive, easily manufactured and efficient enough to carry out the conversion without losing too much of the original power. The new finding could be a significant step in that direction, the MIT researchers said.

~Ann Steffora Mutschler