Innovative Cell Powers Remote IoT Devices

Internet of Things (IoT) technologies show great promise for monitoring remote environments and transmitting the data back to a remote server. While IoT will be crucial for automating sensing and monitoring approaches, it can’t be powered by mains electricity, and finding efficient ways of powering these systems has always presented a challenge.

Nanogenerators, such as triboelectric nanogenerators (TENG), have gathered much interest in powering small-scale devices. However, battery and capacitor architectures are a much more recognizable technology and offer more scope for large-scale commercialization.

Power substation in remote mountains. Image used courtesy of Wikimedia Commons

Researchers from the University of Utah's College of Engineering have developed a pyroelectrochemical (PEC) cell based on supercapacitor architecture that can harvest heat from the surroundings to power IoT sensors in remote environments.

Limitations of TENGs 

Because IoT sensors tend to be used in remote environmental or health monitoring environments, powering them via mains electricity is not feasible. While conventional batteries can be a popular option due to their availability, they are not suitable for many IoT applications, which are often placed in locations where human operators cannot change the batteries.

One technology that has gathered attention over the years is nanogenerators, such as TENGs, that harvest motion from their surroundings to charge the sensors. However, despite academic interest, nanogenerator technologies have fallen flat commercially, and there’s never been much interest beyond academia. Solar cells are another option, but they tend to get dirty in remote environmental monitoring settings, which affects their PEC and charging capabilities.

Developing a Supercapacitor Solution

In the Energy & Environmental Science journal, researchers reported a new PEC cell that converts thermal energy into stored electrochemical energy. The PEC is not too dissimilar to nanogenerators in the ability to harvest from the surroundings, but it is based on a more commercially feasible and recognizable architecture.

PEC structure. Image used courtesy of the University of Utah

The cell facilitates energy transfer using a porous, pyroelectric separator within a supercapacitor. When exposed to temperature, the pyroelectric separator induces an electric field, which drives ions into electric double layers (EDL). The charge is stored in positive and negative layers of ions. This process charges the cell and provides a low level of energy harvesting that can power dedicated sensors and accompanying components in IoT setups. 

PEC Properties and Features 

The pyroelectric separator is the key part of the cell. It is a composite material of porous polyvinylidene fluoride and barium titanate nanoparticles. The researchers chose this combination of materials because its electrical properties change when heated or cooled, changing the separator's polarization.

Various simulations and experimental approaches were used to determine the cell’s properties. Some key features identified in these tests include:

• A 155% increase in measured current upon heating compared to a 35% increase in measured current for a non-pyroactive separator
• Charging by 0.65 mV after four applications of a 20-30-20°C low-temperature thermal cycle under open circuit conditions
• A predicted energy generation of >100 μJ cm−2 from temperature fluctuations commonly found in natural and built environments—enough to power small-scale IoT sensors
• An orientation within the cell that enables the ion’s travel direction to be reversed by reversing the separator’s orientation
• Heating and cooling of the PEC changes the amount of positive and negative ions stored in the EDL.

Real-World Potential for Powering Remote Devices

This research into PEC offers an alternative to other options floated for IoT sensors. The PEC is essentially a specialized supercapacitor that can store electrochemical energy using temperature rather than an applied electrical current from a power source. Naturally, this is more useful for remote monitoring applications because enough energy can be harvested from the surroundings to power small-scale IoT sensors. Given the commercial relevance of supercapacitors and the number of systems on the market/in products today, these cells should be more commercially feasible than nanogenerators and other small-scale energy harvesters in recent years.