Humidity electricity generation could turn walls into power sources
Future homes could regulate indoor humidity while producing electricity rather than consuming it, reversing the approach taken by today’s air-conditioning and dehumidification systems. This is the prospect opened up by an innovative “hygroelectric” wallpaper developed by researchers at Binghamton University, State University of New York.
Engineers Guangya Yuan, Yang Gao and Seokheun Choi have investigated a new practical application for so-called moist-electric generators (MEGs), energy conversion devices that have attracted growing research interest in recent years. Their work focuses not only on improving the technology itself, but also on finding a way to make humidity electricity generation useful in everyday indoor environments.
When indoor humidity becomes a problem
Managing humidity inside homes requires a careful balance. Keeping indoor relative humidity between 40% and 60% generally provides the most comfortable conditions. Higher levels can accelerate material deterioration and affect indoor environmental quality by encouraging the growth of bacteria and fungi. Exposure to these contaminants is associated with the development or worsening of respiratory symptoms, allergies, asthma and immune reactions.
Children are particularly vulnerable. The World Health Organization has linked 13% of chronic childhood asthma cases in European countries to excessive dampness in buildings.
The problem is also significant in Italy. According to a recent Saint-Gobain analysis based on data from ISTAT, the country’s national statistics institute, 16.3% of Italian households, equivalent to around 9.4 million people, live in homes with excessive humidity. In Sardinia, the proportion rises to 25.7%.
Solutions already exist. Alongside good household hygiene and passive measures such as moisture-absorbing salts, electric dehumidifiers and controlled mechanical ventilation can play an important role. However, these systems consume energy. This is where the MEG wallpaper developed by the three engineers could offer a different approach.
How does humidity electricity generation work?
MEG technology uses functional groups in hygroscopic materials to capture water vapour from the air and condense it into liquid form. This process releases chemical energy contained in the water molecules, causing mobile ions to separate from their bonds with the material. Driven by deliberately engineered humidity and ionic concentration gradients, the ions move in a single direction, generating an electrical voltage.
The principle is promising, but practical performance remains limited. Moist-electric generators generally suffer from low output and poor stability. Over the past decade, most MEG devices have shown low ion migration efficiency, with electrical performance typically limited to a short-circuit current density of 100 μA/cm².
One consequence is that these devices cannot currently be used outdoors as a general power source. Indoor environments, however, offer more favourable conditions. Humidity tends to be relatively stable, while low-power electronic devices require only microwatt to milliwatt-scale power supplies, making indoor applications, in the researchers’ words, “a more realistic opportunity”.
Most MEGs use vertical or horizontal structures with an asymmetric distribution of hygroscopic materials. One region preferentially absorbs moisture, while another promotes desorption or evaporation. This creates a continuous gradient in humidity and ionic concentration, driving charge separation.
Hygroelectric wallpaper: how the prototype performs
The challenge was therefore to scale this architecture across a large surface area while making efficient use of the available space. According to Chris Kocher of Binghamton University, the researchers drew on Choi’s pioneering work in papertronics to develop a new MEG architecture resembling a microchip on a printed circuit board.
Around the edges, glycerol captures moisture from the air. In the intermediate region, a raised polyvinylpyrrolidone structure acts as a reservoir, while a wax layer at the centre controls water release.
This peripheral absorption and central evaporation design enables controlled, unidirectional moisture transport across a single sheet of paper.
“It wasn’t easy to integrate three different regions into a single document, but I wanted everything to be printable so that it could be mass-produced and scaled up,” Choi said.
To improve its appearance, all the MEG wiring was placed on the back of the wallpaper.
For now, performance remains modest, although the results are notable. A single unit produces around 0.34 V and approximately 2.2 µW/cm² at 80% relative humidity, maintaining a stable output for more than 90 minutes.
A panel containing 1,596 units can power a wireless keyboard while simultaneously reducing indoor humidity from 38% to 32%, effectively turning passive wall surfaces into self-powered interfaces that respond to indoor climatic conditions.
The next goal is to further improve the technology so that it can generate larger amounts of electricity.