In Switzerland they invented a paper battery that is activated
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In Switzerland they invented a paper battery that is activated by a few drops of water

A group of Swiss scientists occurred environmentally friendly and fully biodegradable low-power battery for wearable electronics and sensors. The battery begins to work after applying a few drops of water to its surface. A prototype of a pair of such elements powered an electronic watch for more than an hour. Such elements are expected to minimize the environmental damage caused by the growing stream of smart electronics.

    Two paper batteries connected in series.  Image source: EMPA

Two paper batteries connected in series. Image source: EMPA

The prototype battery is a simple strip of paper coated with table salt on its surface (see Fig. article in Nature). A layer of graphite flakes has been applied to one side of the paper – this is done with a specially made paint. This gives the battery a cathode. An anode in the form of a layer of a graphite-zinc mixture is applied to the back of the paper. To start the redox reactions in the battery, which lead to the generation of electric current, it is enough to put a few drops of ordinary water on it.

Water dissolves salt and creates ionic conductivity in the paper layer of the battery. In fact, this is equivalent to pouring electrolyte into a battery. The zinc oxidation reaction starts in the anode, which releases electrons. When a load is connected to the battery’s terminals, the electrons travel along the wires to the cathode, where a reduction reaction begins by absorbing oxygen from the air. This starts a cycle of redox reactions, producing electricity as long as zinc remains in the anode to support the reactions, or until the water dries up.

Researchers at the Swiss Federal Laboratories for Materials Science and Technology (EMPA) performed a proof-of-concept by making two elements in the proposed way and connecting them in series to increase the voltage. From two drops of water, the element fed the electronic alarm clock for about an hour. A single cell activated 20 seconds after the application of water and showed a stable voltage of 1.2 V for an hour without a load. When the battery dried up, the scientists added a few more drops and extended the battery life by another hour or so more, although the open circuit voltage was only 0.5 V after reactivation.

    Image source: nature

Image source: nature

The developers believe that such batteries can be automatically activated at high humidity, or after adding water it will be possible to create a battery design for normal use. Engineers will certainly be able to find out in advance how the battery can be prevented from drying out. It works as long as zinc remains in the anode. Therefore, it is easy to calculate the life of such batteries and print them strictly to maintain performance within the specified time limits, which is not possible with alternative technologies, for example, air-metal batteries of a similar implementation.

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Johnson Smith

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