Reviewed by Lexie CornerJan 24 2025
A research team led by Associate Professor Byungil Hwang from Chung-Ang University’s School of Integrative Engineering has developed a novel device that combines energy generation through hydrovoltaic (HV) processes with fire-sensing capabilities.
The growing demand for renewable energy has driven the development of various solutions, many of which face challenges such as low efficiency and high costs. HV systems, which generate energy from the interaction between nanostructured materials and water molecules, have emerged as a promising and cost-effective alternative. These systems hold particular potential for powering electrical sensors, including fire sensors.
Traditional fire sensors rely on batteries to operate during power outages, but these batteries pose risks of explosion during fires. In contrast, HV systems harvest energy from water when partially immersed, offering a safer alternative.
Conventional fire sensors also face issues such as false alarms caused by cooking smoke, steam, or dust, along with high maintenance costs and limited lifespans. HV systems address these limitations by responding specifically to evaporation-induced changes in water flow, such as those caused by fire. Despite this potential, little research has been conducted on integrating HV systems into fire-sensing applications.
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.
Byungil Hwang, Associate Professor, School of Integrative Engineering, Chung-Ang University
HV systems consist of hydrophilic substrates coated with a nanoporous layer featuring a highly charged surface that attracts water protons. 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 the surface—here, the nanostructure of the HV system.
Evaporation induced by increased temperatures from visible light, infrared light, or fire drives water movement from the immersed region to the non-immersed region via capillary action. This movement creates an asymmetry in proton densities, resulting in a potential difference along the flow direction, known as the streaming potential, which can be harnessed to generate electricity.
The nanoporous layer in the device described in the study is composed of waste cotton mixed with Triton X-100 and polypyrrole (PPy), referred to as CPT. This CPT layer is housed within a cylindrical tube with corrosion-resistant aluminum electrodes at both ends, partially submerged in water. The black color of PPy enhances light absorption, increasing evaporation at the non-immersed end, while Triton X-100 generates a significant surface charge in the EDL, enabling high voltage production. This setup produces power simply by exposing the device to light.
Tests showed that the device generates 16–20 microamperes of current and a maximum voltage of 0.42 volts under infrared light. It responds quickly as a fire sensor, with reaction times of 5–10 seconds. Long-term stability was demonstrated over 28 days of continuous operation, with no corrosion or performance degradation. Additionally, the device performed reliably across various environmental conditions.
“This is the first demonstration of using a hydrovoltaic system in a fire sensing application. 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.” Added Prof. Hwang.
This device demonstrates the potential for environmentally sustainable small-scale energy systems to advance applications in environmental sensing, health monitoring, and fire detection.
Journal Reference:
Lal, S., et al. (2025) Photo-sensitive hydrovoltaic energy harvester with fire-sensing functionality. Chemical Engineering Journal. doi.org/10.1016/j.cej.2025.159281