Even though it is always better to reuse and recycle, many simple, low-power, small electronic gadgets are often single-use. However, a novel paper battery activated by water and biodegrades once discarded could make them more environmentally friendly.
The battery was created by researchers at the Empa institute in Switzerland and is meant for use in disposable medical diagnostic equipment, “smart” shipping labels, and environmental sensors.
The battery has one or more linked cells in its current proof-of-concept design. Each cell has one centimeter (0.4 in) square surface area and is saturated with sodium chloride on its paper substrate (also known as table salt). It has a wax covering on one end, and two wires are joined.
Graphite flakes-containing ink, acting as the cathode, is printed on one side of the paper. The opposing side is printed with ink that contains zinc powder, which acts as the anode. Finally, a third ink, which connects the cathode and anode to the two wires at one end, covers both inks on both sides of the paper and contains graphite flakes and carbon black.
The salt in the paper dissolves when a small amount of water is introduced to the battery, releasing charged ions. These ions cause the zinc in the anode to oxidize, liberating electrons as they move through the electrolyte in the wet paper.
“These electrons can then be transferred from the zinc-containing anode – via the graphite- and carbon black-containing ink, the wires and the device – to the graphite cathode, where they are transferred to – and hence reduce – oxygen from ambient air. These redox reactions (reduction and oxidation) thus generate an electrical current that can be used to power an external electrical device.”
Using a two-cell version of the battery, the researchers successfully powered a small alarm clock with a liquid crystal display in a lab test. It was also discovered that two drops of water were enough to activate one cell instantly. In addition, that cell could generate 1.2 volts when it wasn’t attached to a power source. As the paper dried out, the cell’s performance began to decline after one hour, but after adding two more drops of water, it could sustain an operational voltage of 0.5 volts for an additional hour.
Prof. Gustav Nyström, the lead scientist and inventor of a biodegradable mini-capacitor, thinks that with improved engineering, drying of the paper shouldn’t be as much of a barrier. An article detailing the study was released on July 28, 2022, in the journal Scientific Reports.