Energizing sensors and other electronic systems that typically require battery power can be a dirty business, requiring the use of scarce or hazardous chemicals and metals and adding to the growing volume of electronic waste. However, dirt can be a solution to these issues: researchers have developed fuel cell technology that harvests energy from soil-dwelling microbes.

Soil-based microbial fuel cells, which harvest electricity from bacteria that naturally donate electrons to nearby conductors to produce an electric current, are not new. What differentiates this new approach from existing devices is its geometry: a perpendicular cell replaces the more traditional architecture with cathode and anode in parallel. A carbon felt-based anode is horizontal to the ground’s surface and is topped with the vertical cathode assembled with an inert, conductive metal. Part of the cathode is coated with a waterproofing material, so that during flood conditions a hydrophobic section of the cathode is supplied with oxygen to keep the fuel cell running.

The vertical design ensures that the top end is flush with the ground’s surface, and a 3D-printed cap placed at the top prevents debris from falling inside. Consistent airflow is provided by a hole on top and an empty air chamber running alongside the cathode.

The fuel cell described in the Proceedings of the Association for Computing Machinery on Interactive, Mobile, Wearable and Ubiquitous Technologies generated 68 times more power than needed to operate onboard soil moisture sensors. Researchers from Northwestern University, University of California San Diego, Georgia Institute of Technology and University of California Santa Cruz also equipped the soil-powered sensor with a tiny antenna to wirelessly transmit data to a neighboring base station by reflecting existing radio frequency signals.