Energy Harvesting

A Metal-Air Scavenger for Powering Robots, Vehicles, and Electronics

The limited capabilities of batteries are a principal barrier to realizing the potential of modern electronic technologies. In many cases, the size and weight of energy storage technologies required to power electronic systems are too large or massive for practical use. This results in compromises where the systems, such as an untethered robot, have limited operational times and are constrained by long battery recharging times over which they remain unused. Energy storage is particularly restrictive for micrometer- to centimeter-scale robots, vehicles, and electronics, as microbatteries dominate the size and mass of the corresponding devices.

To address these limitations, we present a metal-air scavenger (MAS), a device that extracts electrical energy from metal surfaces to power robots, vehicles, and electronics.


The MAS is composed of a thin polymer electrolyte film and flexible carbon electrode. When the electrolyte contacts a metal surface, the MAS extracts energy from the metal by oxidizing it and reducing oxygen in the air surrounding the MAS. Because the metal fuel and oxygen are external to the MAS and the powered devices, they only need to carry the mass of the electrolyte and carbon electrode.

The MAS can operate as a stationary or moving device on zinc, aluminum, and iron surfaces and extract up to 3,097 Wh/kg at 217 W/kg. We have shown that an MAS-powered toy vehicle can travel up to 7.9 mm/s velocity and 5.5 mm/s when carrying a 50g load.

The MAS concept presented here takes advantage of the prolific variety of external metal energy sources available in modern urban environments. We suspect it will find utility in many applications and lead to further unconventional methods and resulting materials development for powering robotic systems.

A principal advantage of the MAS is that it can continue to power a device as it travels across a metal surface. We show how combining metal-air chemistries with a mobile robotics platform can alleviate the near-term challenges in battery energy density by extracting energy from metal surfaces in the robot’s environment. This capability can be utilized by robots for continuous inspection of metal surfaces, recharging using scrap metal, and operation on or near metal surfaces prolific in urban environments.

Hydrogel film close-up
A hydrogel film saturated with an electrolyte conducts electrical energy from the metal surface and powers the moving vehicle.


Watch a video of the Tech Briefing event. (Unfortunately, the recording cuts out before the end of the talk.)