Researchers create dual purpose fire sensor

Various clean energy technologies have been developed to meet the rapidly intensifying energy demand and dwindling fossil fuel reserves. However, many of these technologies are hindered by low efficiency and high costs.

Hydrovoltaic (HV) mechanisms, in which electricity is generated by the direct interaction of nanostructured materials and water molecules, have recently emerged as promising, cost-efficient alternatives. HV systems show particular promise for powering electrical sensors, including fire sensors.

Traditional fire sensors rely on batteries to operate during power outages, but these batteries can explode during fires. In contrast, HV systems draw energy from water, where the device is partially immersed in it, making them a safer alternative.

Additionally, traditional fire sensors face challenges such as false alarms triggered by cooking smoke, steam, or dust, along with high maintenance needs and limited lifespans. HV systems overcome these limitations by responding only to evaporation-driven changes to water flow, such as those caused by fire. Despite their potential, no studies have yet explored the integration of HV systems in fire-sensing applications.

In a recent study, a research team led by Associate Professor Byungil Hwang from the School of Integrative Engineering at Chung-Ang University developed an innovative HV device that doubles as a fire sensor.

“Our hydrovoltaic system can produce up to a few tens of microwatts, making it perfect for small-scale applications like fire detectors and health monitoring systems. This system is self-reliant, requires only a few milliliters of water, and has a fast response time,” explains Prof. Hwang. Their study is published in the Chemical Engineering Journal.

HV systems consist of hydrophilic substrates covered with a nanoporous layer with a highly charged surface capable of attracting protons from water. When immersed in water, protons are drawn to the negatively charged surface of the nanostructure, forming an electrical double layer (EDL). The EDL consists of two parallel layers of opposite charges on either side of a surface, in this case, the HV system’s nanostructure.

Evaporation, caused by increased temperature from visible light or infrared light or a fire, acts as a driving force, causing water to flow from this immersed region to the non-immersed region via capillary action. This flow of water generates an asymmetry of proton densities, causing a potential difference along the direction of flow, known as the streaming potential, which can then be harnessed to produce electricity.

The device proposed in the study utilizes waste cotton integrated with Triton X-100 and PPy, collectively termed CPT, as the nanoporous layer. This CPT layer is placed into a cylindrical tube with corrosion-resistant aluminum electrodes at both ends, part of which is immersed in water.

The black color of PPy enhances light absorption and therefore evaporation on the non-immersed end, while Triton X-100 induces a high surface charge in the EDL, facilitating a high voltage generation. This design allows electricity generation simply by shining light onto the device.

Testing revealed that the device can generate a maximum voltage of 0.42 Volts and 16–20 microamperes of current under infrared light. As a fire-sensing device, it exhibits a fast response time of 5–10 seconds. Furthermore, it maintained excellent stability over 28 days of continuous testing, with no corrosion or degradation in performance, indicating long-term viability. It also performed robustly under varying environments.

“This is the first demonstration of using a hydrovoltaic system in a fire sensing application,” notes Prof. Hwang. “Our HV system has the potential to be a sustainable power source for various sensor systems, such as health and environmental monitoring systems that require uninterrupted operation.”

This innovative device demonstrates how sustainable small-scale energy systems can revolutionize applications like fire detection, health monitoring, and environmental sensing.

Provided by
Chung Ang University