Metal Air Scavenger System "Eats" Aluminum to Power Robots and Other Electronic Devices
By turning its environment into a battery, the metal-scavenging MAS system boasts impressive energy density.
A team of engineers at the University of Pennsylvania has published details of what it describes as a "metal air scavenger" system for powering robots and other electronics by giving them the ability to "eat" metal.
"[The] inverted relationship between computing performance and energy storage makes it very difficult for small-scale devices and robots to operate for long periods of time," claims Assistant Professor James Pikul of the team's research. "There are robots the size of insects, but they can only operate for a minute before their battery runs out of energy.
"Harvesters, like those that collect solar, thermal, or vibrational energy, are getting better. They're often used to power sensors and electronics that are off the grid and where you might not have anyone around to swap out batteries. The problem is that they have low power density, meaning they can't take energy out of the environment as fast as a battery can deliver it."
The "metal air scavenger" system, or MAS, aims to solve that problem. "Our MAS has a power density that's ten times better than the best harvesters, to the point that we can compete against batteries," Pikul claims. "It's using battery chemistry, but doesn't have the associated weight, because it's taking those chemicals from the environment."
The system works by wiring a cathode to the robot or other electronic device to be powered, then placing it on top of a slab of hydrogel — a spongy network of polymer chains designed to conduct electrons using water molecules. The hydrogel serves as an electrolyte — turning any metal surface the robot touches into the anode and completing the battery.
"Energy density is the ratio of available energy to the weight that has to be carried," Pikul explains. "Even factoring in the weight of the extra water, the MAS had 13 times the energy density of a lithium ion battery because the vehicle only has to carry the hydrogel and cathode, and not the metal or oxygen which provide the energy."
While the process is, effectively, having the robot "eat" the metal, the engineers claim it's unlikely to cause structural damage to any surfaces over which it travels: The process causes oxidization, making the metal rust, but only to a thickness of around 100 microns; at that point, the bonds available to the MAS system are exhausted, and if it doesn't move to a fresh piece of metal the power ceases to flow.
"As we get robots that are more intelligent and more capable, we no longer have to restrict ourselves to plugging them into a wall. They can now find energy sources for themselves, just like humans do," says Pikul. "One day, a robot that needs to recharge its batteries will just need to find some aluminum to 'eat' with a MAS, which would give it enough power to for it work until its next meal."
The team's work has been published in the journal ACS Energy Letters under closed-access terms.