Researchers from the Swiss Institute Empa have developed a water-activated paper battery. The purpose? solve the inadequacy of low-power disposable electronics. The team believes the invention could be used in place of current, expensive smart trackers, environmental sensors and diagnostic medical equipment.
How is the Empa paper battery made?
The battery contains at least one small cell, with three different inks printed on a rectangular paper strip. The paper is then sprinkled with salt and immersed in wax: finally, ink with graphite flakes (which acts as a positive pole) and ink with zinc powder (which acts as a negative pole) are placed on both sides of the paper. Finishing touch: Another ink mix with graphite and carbon black is printed on both sides of the strip finishing everything off.
And how does it work? Just add a small amount of water. The salts coating the paper dissolve, releasing charged ions to make the strip conductive. As the ions disperse, the zinc in the ink oxidizes and releases electrons, which are then transferred via the inks to the graphite cathode. The resulting reaction with oxygen in the air generates an electrical current that can be used to power external devices.
During the study, the team successfully combined two cells to initiate a liquid crystal display alarm clock, reaching a stable voltage of 1,2 volts, just below the 1,5 volts of a standard AA alkaline battery.
After an hour, when the experimental battery's performance dropped dramatically due to the paper drying out, the scientists simply added more water, allowing the cell to maintain a stable operating voltage of 0,5 volts for another hour.
“The peculiarity of our new paper battery,” he explains Guastav Nystrom, who conducted the study, “is its extreme versatility. It allows us to add only the amount of zinc needed for the specific application to the ink.”
What about the problem of drying paper? The scientist is confident: the team will make the design improvements necessary to circumvent the problem, which however only occurs in particular wet conditions.
Could this paper battery be the key to reducing low-power e-waste? It sure looks promising.