Two drops of water, a piece of paper, how to generate electricity for an hour?

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Two drops of water, a piece of paper, how to generate electricity for an hour?

Using more environmentally friendly materials and improving the recovery rate of resources are important methods to solve the problem of e-waste flooding, and biodegradable batteries are the hot spots of battery research.

Now, the scientific research team from the Swiss Federal Laboratory for materials science and Technology (EMPA) has made a new breakthrough in biodegradable batteries – in a proof of concept study, they proposed a disposable paper battery that can be activated by water.

It is reported that with only two drops of water, this new battery can continuously supply power to an alarm clock with LED for one hour. After one hour, add two drops of water, and it can continue to be used. It can be made into any shape and size, and the potential application scenarios are very broad.

The research team said that this paper battery can be used to drive various low-power, disposable electronic devices (such as smart tags for tracking objects, environmental sensors and medical diagnostic devices) and minimize its environmental impact.

How can paper batteries generate electricity?

In recent years, scientists have made important progress in green power technologies such as biodegradable optoelectronic devices, energy collectors and supercapacitors. However, the research of biodegradable disposable battery, as a kind of energy with strong complementarity, higher energy density and more stable operation, is still very limited.

The current research on batteries mainly focuses on the improvement of battery performance, that is, the continuous development towards higher energy and power density, faster charging rate and better operation stability, mainly through the development of new materials that meet the requirements of lithium-ion batteries that currently dominate the market.

However, as people have a better understanding of the harm of E-Waste and the emergence of disposable electronic products for environmental sensing and food monitoring applications, the market demand for environmentally friendly batteries is growing.

The transformation of market demand provides new opportunities for non-traditional materials and design. Aqueous primary batteries based on inorganic materials such as magnesium (mg), iron (FE), tungsten (W) and molybdenum (MO) have become ideal candidates for high-energy density transient batteries, and organic materials have also been proved to be good substitutes.

Although scientists have made some promising progress, the additive manufacturing of biodegradable batteries is still an important scientific challenge.

In the past decade, cellulose, which has existed in the form of paper for thousands of years, has been widely used in biomedical diagnosis, information display and energy storage. However, some unique properties of cellulose, such as its inherent biodegradability and hygroscopicity, have not been well utilized.

In this research work, the paper battery proposed by Nystr ö m is composed of at least one battery unit with a size of 1 square centimeter, which contains three kinds of inks printed on the rectangular paper tape. The paper tape is distributed with sodium chloride salt, and the shorter end is soaked with wax. One kind of ink containing graphite sheet is printed on one side of the paper as the positive pole (cathode) of the battery pack, and the reverse side of the paper is printed with ink containing zinc powder as the negative pole (anode).

In addition, on both sides of the paper, ink containing graphite flakes and carbon black is printed on these two inks. This ink connects the positive and negative poles of the battery pack with two wires, which are located at the end with wax. These inks are ideal for additive manufacturing technologies such as 3D printing.

So how does this paper battery generate electricity?

According to the description of the paper, just add a little water, the salt on the paper will dissolve, thus releasing charged ions. These ions disperse on the paper to activate the battery pack, so that the zinc in the negative ink of the battery pack releases electrons, and the wires connected to the electronic equipment can connect the circuit, so that the electrons can be transferred from the negative to the positive (ink containing graphite) through the ink, wires and equipment containing graphite and carbon black, Where it is transferred to the oxygen in the surrounding air, the current is generated in these reactions.

Two drops of water, a piece of paper, how to generate electricity for an hour?(1)

To demonstrate the ability of this battery to drive low-power electronic devices, the research team combined two battery units into a battery pack to drive an alarm clock with a liquid crystal display.

The performance analysis of single cell battery pack shows that adding two drops of water, the battery pack will activate in 20 seconds. When it is not connected to energy consuming equipment, it can reach a stable 1.2 volts, while the voltage of a standard AA alkaline battery (No. 5 battery) is 1.5 volts.

After one hour, the performance of the single cell battery pack will decline rapidly due to the drying of the paper. However, if two more drops of water are added, it can maintain a stable 0.5V working voltage for more than an hour.

Two drops of water, a piece of paper, how to generate electricity for an hour?(2)

The research team said that the biodegradability of paper and zinc enables the battery to minimize the environmental impact of disposable, low-power electronic devices.

As mentioned above, although this paper battery can power the alarm clock, its power density is relatively limited compared with other types of batteries.

In this regard, the research team believes that this paper battery can be used in low-power electronic products and the Internet of things ecosystem. By minimizing the amount of zinc used in the ink, the sustainability of this battery can be further improved, so that the current generated by the battery can be accurately controlled.

In their future work, they will study how to use green catalysts to improve the rate of oxygen reduction reaction, use organic cathode materials as a substitute for zinc, and evaluate the impact on the environment during the life cycle of the battery.

“Our work has advanced the field of disposable electronic products and proposed a battery technology that balances environmental impact and performance.” The research team said so.