Scientists have transformed a children's drinking bird toy into a tool that can generate usable electricity. One day, the generator could power a variety of small electronic devices both indoors and out. First, how do unmodified waterbirds (aka dipbirds) work? Its vacuum-sealed body consists of two glass bulbs connected by a glass tube, one forming the head and the other the tail. The bulb-shaped portion of the head has a protruding beak and is covered with absorbent fabric, while the tail bulb is exposed.

The Water Bird's body is mounted on a set of plastic legs that serve as a seesaw-like fulcrum, and is filled with a volatile chemical called methylene chloride - some of which are in a liquid state, while others are in a gaseous state. Place a glass of water in front of the toy at a height that allows the bird's beak to be immersed in the liquid.

The user first pushes the head into the glass, allowing its fabric covering to draw water in through the beak. Once the head is released, the waterbird's body swings back to an upright (vertical) orientation due to the weight of the liquid methylene chloride in its tail.

As water evaporates from the fabric, it creates a cooling effect inside the head bubble. This causes the methylene chloride vapor in the head to condense into a liquid so it flows downward into the tail bubble section. Since the pressure in the lower body is now higher than the pressure in the head, the liquid methylene chloride is forced back into the tube and into the head.

As a result, the toy's center of balance shifts to a position where its body leans forward, dipping its beak into the glass, which absorbs more water. At the same time, a clear channel opens between the head and lower body, equalizing pressure. The liquid methylene chloride then flows back down, allowing the process to begin again...and repeat over and over again.

A team of scientists led by Professor Wu Hao from South China University of Technology recently added two disk-shaped triboelectric nanogenerator modules to one of the toys' sides. These devices exploit the triboelectric effect, where certain materials become charged when they rub against each other—which is why you create an electrostatic charge when you comb your hair. Therefore, the entire device is called the "Drinking Bird" triboelectric hydroelectric generator (DB-THG).

DB-THG powering the calculator – the two discs on both sides are triboelectric nanogenerator module devices, Wu Zhengqin et al.

In laboratory testing at room temperature 24ºC (75ºF) and relative humidity 20% ±5%, the unit ran for 50 hours using only 100ml (3.4oz) of water. It also achieves a voltage output of up to 100 volts, enough to power devices such as calculators, temperature sensors and 20 linked LCD screens.

Scientists are now developing a specially designed successor to the DB-THG that will perform significantly better than existing improved toys.

"The Waterbird triboelectric hydroelectric generator provides a unique way to use water as a readily available fuel source to power small electronic devices under ambient conditions," Wu said. "I'm still surprised and excited when I see the actual results."

A paper on the research was recently published in the journal Device. You can see the DB-THG's LCD power supply in action in the video below.

DB-THG powers 20 LCDs (Image source: Device, WuZhuangqin, et al.)