A Fudan University team built an electrochemical membrane for a microrobot’s feet that generates electricity on contact with zinc or aluminum surfaces, using moisture and oxygen from the air.

Insect-sized robots have a power problem. Their bodies are too small to carry much of a battery, and batteries get worse as they get smaller. According to a new study, a 1.7-gram microrobot running on commercial batteries can crawl for only about two minutes.

Researchers at Fudan University in Shanghai propose a way around that limit: let the robot draw its energy from the ground beneath its feet. In a study published in National Science Review, a team led by Yue Gao of Fudan’s Department of Macromolecular Science describes an electrochemical “skin” for a robot’s feet that generates electricity whenever it touches certain metal surfaces.

Why batteries fall short

The numbers in the release illustrate the challenge. For the 1.7-gram microrobot to run for two hours, its battery would need to make up 94 percent of its mass and store energy at a density of 5,382 watt-hours per kilogram, far beyond what today’s lithium-ion batteries can deliver. And microbatteries lose even more energy density as they shrink below about one cubic centimeter or one gram.

Power has been a central obstacle in microrobotics for years. Harvard’s RoboBee, an insect-sized flying robot, first took to the air in 2013 while tethered to an external power supply, and researchers have spent the years since working to cut such cords. Approaches have included solar cells, wireless power and energy-dense fuels.

Small robots are often imagined inspecting pipes, crawling through machinery or searching collapsed buildings, places where stopping to recharge is difficult. The Fudan team noted that many such environments are full of metals such as aluminum, zinc, silicon, tin and lead, common in pipes, buildings, data centers and equipment.

Turning the floor into fuel

The team’s solution is what they describe as an open electrochemical system. A membrane of crosslinked potassium polyacrylate on the robot’s foot converts chemical energy from the metal surface, along with moisture and oxygen from the air, into electricity.

The arrangement resembles a metal-air battery, in which a metal reacts with oxygen to produce current. Here, though, the metal is not carried by the robot. It is the surface the robot walks across, and a flexible platinum-carbon film on the foot serves as the site where oxygen and water react.

Metal-air batteries are a familiar technology. Zinc-air cells, for example, power many hearing aids, drawing oxygen from the air through small holes in their casing. They can store a lot of energy for their weight, in part because one of their reactants, oxygen, does not need to be carried inside the battery.

The membrane is made in a single step, polymerized directly on the foot from acrylic acid, a crosslinker, an initiator and potassium hydroxide. It can be as thin as 135 micrometers and as small as one square millimeter.

The output is substantial for something so small. The skin produced a power density of 133 milliwatts per square centimeter on zinc and 103 milliwatts per square centimeter on aluminum, roughly an order of magnitude higher than typical microbatteries, according to the release. Its current capability held up even at a volume of 0.0004 cubic centimeters.

Power only on contact

The membrane generates electricity only while the foot is touching an active surface. The reaction starts within about 0.1 milliseconds of contact and stops when the foot lifts off.

That on-off behavior has an advantage. Because the products of the reaction are left behind on the surface rather than building up inside the membrane, the system avoids the gradual performance decay seen in conventional, sealed batteries. According to a summary accompanying the release, the system powered more than 10,000 walking steps and remained stable after one million steps.

The membrane also tolerates harsh conditions. At 20 percent relative humidity, it retained most of its water and kept discharging after 48 hours. At minus 20 degrees Celsius, its voltage dropped by only about 0.2 volts compared with room temperature, and it also worked at 80 degrees Celsius. When water evaporated, adding more restored its performance.

Grip and a sense of touch

The skin also helps the robot move. The membrane resists slipping in the direction of travel but detaches easily when pulled straight up, allowing efficient steps. That combination let the robot crawl up inclined aluminum surfaces.

And it can sense what it is walking on. Different materials produce different reaction rates and movements of potassium ions, which generate distinct, stable square-wave electrical signals. Rough surfaces deform the membrane and produce millivolt-level spikes. Using a grid of electrodes, the system can locate points of contact, which the researchers suggest could help a robot seek out energy-rich paths.

Limits of the approach

The approach depends on suitable surfaces. A robot using it would need to walk on reactive metals such as zinc or aluminum, and each step consumes a tiny amount of that surface. How the system performs on painted, coated or corroded metal, and on longer missions, is not addressed in the release.

The release does not include comments from the researchers, and it does not give the paper’s title, full author list or funding sources. But the work points to a different way of thinking about power for very small machines: instead of carrying energy with them, they could harvest it, one footstep at a time, from the environments they are built to explore.

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Notes

1. National Science Review, 2026. DOI: 10.1093/nsr/nwag529.
2. Science China Press. “No battery needed: Robot skin harvests power as it walks.” EurekAlert!, 30 September 2026. https://www.eurekalert.org/news-releases/1146069.

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