Engineers in the United States have built a wallpaper that makes electricity from the humidity in the air. The invention could one day power small home devices without batteries.

Researchers at Binghamton University, led by Professor Seokheun Choi, published the work in the journal Advanced Energy Materials. Each unit is a 2 by 2 centimetre square of paper divided into three zones.

The edge of each square carries glycerol, which grabs water vapour from the air. The middle zone holds a plastic-like material called PVP that pulls the liquid inward. The centre is treated with wax, which lets vapour escape.

This one-way flow of moisture creates an imbalance of charged particles, producing an electric current. A single unit makes about 0.34 volts at 80 per cent humidity, with a power density of 2.2 microwatts per square centimetre.

The team built a panel of 1,596 units that ran a wireless keyboard. The wallpaper also works as a passive dehumidifier, cutting room humidity from 38 to 32 per cent in 15 minutes. The power is still tiny, so it suits only low-energy devices like sensors and smart thermostats.