There is plenty of moisture in the air — Professor Swee Ching Tan wants to harvest the humidity and put it to good use.
Tan, along with fellow researchers from the National University of Singapore (NUS), has invented a novel gel-like material that dehumidifies ambient air to improve thermal comfort.
After taking in water from the environment, the zinc-oxide hydrogel becomes opaque and lowers infrared transmission by about 50 percent, reducing ambient temperature by more than seven degrees Celsius.
The hydrogel also generates about 1.8 volts of electricity – similar to the energy output of a AA battery.
The university team has filed a patent for their invention, and the researchers will study how the hydrogel’s properties can be put to use.
Professor Tan spoke to Tech Briefs about the applications that, at the moment, are still up in the air.
Tech Briefs: What was the inspiration for this work?
Prof. Swee Ching Tan: A major fact unknown to most people is that high levels of humidity – more than heat – causes the greatest discomfort.
I had spent almost seven years in the US and UK where the levels of humidity are quite low. The summer temperatures are very similar to Singapore, but I did not feel any discomfort. In Singapore, however, the levels of relative humidity (RH) are very high – about 70% to 80% throughout the year.
This causes sweat to evaporate more slowly from our body, making us feel hotter and uncomfortable. In Singapore, there is heavy reliance on air-conditioners and dehumidifiers, which are energy-intensive. Thus, we are looking to effectively dehumidify the ambient air at zero energy expense, thereby enhancing thermal comfort.
Tech Briefs: How does the gel absorb water?
Tan: The structure of the hydrogel is quite similar to zeolites such as silica gel – it has a very open and porous structure, which makes its affinity towards moisture extremely high. The gel can absorb water more than 250% of its own weight, making it the best available drying agent we know so far.
Moisture in the air is the primary cause for high levels of relative humidity (RH), and it results in thermal discomfort. Absorption of water is a valuable property because the gel can effectively dehumidify enclosed spaces at zero energy expense and provide enhanced thermal comfort.
Tech Briefs: In a common application, where exactly would you place the hydrogel?
Tan: The hydrogel can be coated on any surface – walls, facades, window panes, decorative items, etc.
Tech Briefs: What are the properties of the hydrogel?
Tan: The hydrogel is a form of zinc oxide – a compound commonly found in sunscreen lotions. The most striking feature of this hydrogel is its enormous capacity to absorb water. Additionally, water absorbed by the hydrogel can be desorbed easily by just exposing it to sunlight; this makes the hydrogel reusable.
Apart from this, the hydrogel also exhibits interesting changes in optical, electrical, and electrochemical properties on absorption of moisture. For instance, it is transparent in dehydrated state and becomes opaque when it absorbs water, thereby opening up the possibilities of constructing a thermo-hygroscopic privacy window.
When fully saturated with water, the gel blocks out about 50% of the incoming infrared radiation, thus making our rooms cooler. It also acts as a conducting path in hydrated state and functions as an electrolyte for batteries.
Tech Briefs: How does the gel generate electricity?
Tan: A simple electrochemical cell was constructed with the hydrogel as the electrolyte between the electrodes. As the hydrogel absorbs water, the ionic properties change thereby leading to electricity generation.
Tech Briefs: There are plenty of applications for the hydrogel. Which is the one that will be the most practical? And which of the application possibilities are most exciting to you?
Tan: The most practical and easiest form of commercial application for the hydrogel is for it to function as a desiccant/drying agent to remove moisture from an enclosed area. The applications that are most exciting will be as coatings for windows where it can double up both as a privacy window and an IR blocking windscreen. Serving as a battery is another valuable application for emergency situations.
Where do YOU see the hydrogel being most useful? Share your comments (and questions) below.