Development of a “Natural Energy Harvesting Wall” That Generates Electricity from Raindrops on Building Exteriors
Published in the international academic journal *Chemical Engineering Journal*
 
A research team led by Professor Kang Bongchul from the Department of Mechanical Engineering at Kookmin University has developed “Natural Energy Harvesting Walls (NEHW),” which generate electricity every time raindrops fall by directly engraving power-generating devices onto marble—a material commonly used for building walls—using a laser. Simply put, this technology allows building walls to generate electricity on their own as they are exposed to rain. This research was published in *Chemical Engineering Journal* (IF: 12.5, top 4.0%), a prestigious international journal in the fields of chemical and environmental engineering. Dr. Baek Seung-hyun, a graduate of the program, served as the first author, while master’s students Choi Min-chang and Choi Jong-moon participated as co-authors, and Professor Kang Bong-cheol served as the corresponding author.
 
Nowadays, many buildings generate electricity by installing solar panels on their rooftops or windows. However, since solar panels require sunlight to function, they produce almost no electricity on cloudy or rainy days, or at night. The research team focused precisely on these “times when solar power is inactive.” This is because if electricity can be generated from raindrops falling during a rainstorm, buildings can be supplied with electricity regardless of the weather.
 
The principle behind generating electricity from raindrops is similar to the static electricity “zap” you feel when taking off winter clothes. Electricity is generated the moment a water droplet hits a special surface and bounces off; to effectively collect this electricity, a metal layer with a very large surface area—created by countless micro- and nano-sized pores—is required. The problem was that stones like marble have rough surfaces and contain many impurities, making it difficult to deposit electrodes using the precision equipment typically used in semiconductor manufacturing. Furthermore, while aluminum—the electrode material—is inexpensive and has excellent electrical properties, it oxidizes easily when exposed to heat during the manufacturing process, leading to a decline in electrical performance.
 
The research team solved this problem by using a method that involves “sintering aluminum particles by firing a pulsed laser at them.” They rapidly repeated a process in which the aluminum particles were instantly melted by a laser for a very short duration of about 50 nanoseconds (5 hundred-millionths of a second) and then cooled for a much longer period of about 20 microseconds. This process allows the aluminum to melt and agglomerate gradually without having time to react with oxygen, creating a porous electrode filled with small clumps and microscopic pores—much like a rural gravel road. A major advantage of this technology is that it enables the fabrication of electrodes directly on stone surfaces without the need for complex vacuum equipment or cleanrooms typically used in conventional semiconductor processes.
 
Experimental results showed that the electrodes produced in this way demonstrated power generation performance more than twice as high as that of conventional methods. They continued to function normally even after being exposed to water droplets for extended periods in high-humidity environments or after the surface was rubbed or tapped, confirming their high stability and durability. Notably, when used in conjunction with solar panels, they generated additional electricity equivalent to approximately 21.7% of the solar power output, and were even capable of generating electricity solely from raindrops at night when sunlight was unavailable.
 
The eco-friendly design is also noteworthy. Once the device has served its purpose, simply sanding the surface restores it to its original marble state, allowing for reuse. In essence, it is a “recyclable power-generating device” that minimizes waste.
 
This research is significant in that it demonstrates the potential to transform bricks and stones—which previously merely clad buildings—into “energy-producing spaces” capable of generating electricity on their own. It is expected to be applied not only to building exteriors but also to roads, bridges, and other urban areas to generate eco-friendly energy. This research was conducted with support from the National Research Foundation of Korea (Mid-Career Researcher Program, Key Research Institute) and the Ministry of Trade, Industry and Energy.
 
Meanwhile, the research paper, titled “Natural energy harvesting walls: Laser-sintered porous Al electrodes on natural stone for triboelectric rain energy harvesting” by Back, S., Choi, M., Choi, J., and Kang, B., was published in the October 2026 issue of *Chemical Engineering Journal*.

(Photo: From left) Dr. Baek Seung-hyun (alumnus), Choi Min-chang (master’s student), Choi Jong-mun (master’s student), and Professor Kang Bongchul