So how was your workout today? How many steps did you walk today? How’s your heart rate? All good? We take for granted the amazing functions of our smartwatch. Wearable tech has come a long way to the point that our watches function like miniature super computers.
The main problem with these devices is that they run on batteries which have a limited life. So what if there was a solution for energy in our body heat? Can the heat from our bodies be used to generate power for wearable devices? Indeed there is. This can be done using what is known as thermoelectric (TE) devices.
Thermoelectric devices can convert temperature differences into electrical energy. Hence, they are a potential technology for sustainable waste heat recovery applications. They also do not create any hazardous byproduct.
A good thermoelectric device must have high electrical conductivity and Seebeck coefficient (a measure of the magnitude of an induced thermoelectric voltage in response to a temperature difference) and low thermal conductivity.
The usual thermoelectric materials such as bismuth telluride are not suitable for wearable devices as they are brittle and non-flexible. Tellurium can be toxic as well.
Silver selenide materials have shown potentials as thermoelectric materials and can be used as a replacement for bismuth telluride.
Silver selenide has to be combined with a polymer in order to be used as a wearable device. Many techniques such as vacuum filtration method, vacuum thermal evaporation, and printing techniques have been done to combine inorganic thermoelectrics onto a nonconducting flexible substrate like nylon.
In this study, the authors Mr. Santosh Kumar, Ms. Minati Tiadi, and Prof. Dillip K. Satapathy from the Soft Materials Laboratory, Department of Physics, Indian Institute of Technology Madras, Chennai, India, and Mr. Vikrant Trivedi and Dr. Manjusha Battabyal from the International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Chennai, India, have processed flexible silver selenide/nylon and silver selenide-copper silver selenide/nylon by cold pressing technique.
Thermoelectric performance of silver selenide/nonconducting polymer film using the cold pressing technique has hardly been reported.
The thermoelectric properties of the silver selenide and silver selenide-copper silver selenide on a nylon substrate were studied. It was found that the cold pressed thermoelectric films could almost retain the thermoelectric properties of bulk samples.
For silver selenide-copper silver selenide/nylon, the output voltage was found to be 9 millivolts, and output power was 110 nanowatts.
When the prototype was contacted with a human wrist, it produced a 1.2 millivolts output voltage at a temperature difference of less than or equal to 5 Kelvins.
To conclude, the thermoelectric prototype synthesized in this study had excellent flexibility and had high output voltage at a low temperature gradient using human body heat.
This study paves the way to fabricate a cost-effective, flexible thermoelectric film through cold pressing that can be potentially used for energy harvesting in near-ambient temperature and wearable applications.
Dr. Suresh Perumal from the Department of Materials Science and Metallurgical Engineering, Indian Institute of Technology Hyderabad, Telangana, India, acknowledged the significance of the work done by the authors with the following comments: “In this study, scientists from IIT Madras and ARCI-Chennai demonstrated high-performance selenide-based flexible thermoelectric films using a seemingly facile and novel fabrication technique. Notably, they showcased a flexible thermoelectric generator that can produce power even with temperature gradients as small as a few Kelvin, especially generates the power by capturing the heat from the human body. This development holds the key to fabricating cost-effective and flexible thermoelectric films for harvesting untapped waste-heat near ambient temperatures, particularly suitable for integration into wearable electronics and small-scale electronic devices.”
Article by Akshay Anantharaman
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