'Drinking bird' toys upgraded to generate clean energy from water

Scientists have converted a children's "drinking bird" toy into a tool that generates usable amounts of electricity. The generator could one day be utilized to power a wide variety of small electronic devices, both indoors and outside.

First of all, just how does an unmodified drinking bird (aka dipping bird) work?

Well, its vacuum-sealed body consists of two glass bulbs linked by a glass tube, one bulb forming the head and the other one forming the tail. The head bulb incorporates a protruding beak and is covered in an absorbent fabric, whereas the tail bulb is bare.

The body is mounted on a set of plastic legs that serve as a teeter-totter-like fulcrum, and it's filled with a volatile chemical called methylene chloride – some of that chemical is in a liquid state, and some of it's in a vaporous state. A glass of water is placed in front of the toy, set at a height that allows the bird's beak to dip into the liquid.

The user starts by pushing the head into the glass, allowing its fabric covering to draw water in via the beak. Once the head is released, the body swings back to an upright (vertical) orientation, thanks to the weight of the liquid methylene chloride in the tail.

As the water evaporates from the fabric, it produces a cooling effect inside the head bulb. This causes the methylene chloride vapor in the head to condense into a liquid, so it runs down into the tail. Because the pressure in the lower body is now higher than that in the head, the liquid methylene chloride is forced back up the tube and intothe head.

As a result, the toy's center of balance is shifted to the point that its body tilts forward, dipping its beak into the glass so that it can take up more water. At the same time, a clear passage is opened between the head and the lower body, equalizing the pressure. The liquid methylene chloride then runs back down, allowing the process to start again … and to be repeated over and over.

Led by South China University of Technology's Prof. Hao Wu, a team of scientists recently took one of these toys and added two disc-shaped triboelectric nanogenerator modules to either side of it. These devices harness the triboelectric effect, in which certain materials become electrically-charged when they're rubbed against one another – it's what's responsible for the static charge that occurs when you're combing your hair.

The whole rig is thus known as the drinking-bird triboelectric hydrovoltaic generator, or DB-THG.