An "artificial leaf" that produces hydrogen by absorbing indoor lighting—mimicking how plants convert sunlight into energy—has been developed. The breakthrough opens a path to harvest clean hydrogen by recycling lighting electricity, which accounts for 19% of global power consumption.
A research team led by Professor Jang Ji-hyun at the Ulsan National Institute of Science and Technology (UNIST) Department of Energy and Chemical Engineering announced on the 19th that they developed an artificial leaf that produces hydrogen under LED lighting by combining an efficient photoelectrode with a hydrogen production catalyst.
The most critical component of the artificial leaf is the photoelectrode, which functions like chlorophyll. It absorbs light and generates charge carriers, just as plant chlorophyll does.
The photoelectrode developed by the research team is made of cadmium sulfide (CdS), a material that efficiently absorbs indoor lighting—which is dimmer than sunlight—to generate charge carriers. These carriers pass through a titanium dioxide (TiO₂) layer to reach the hydrogen production catalyst layer on the back. On the surface of the "3D nickel (3D-Ni)" catalyst layer, the charge carriers react with water to produce hydrogen.
Sulfide materials undergo "photocorrosion" when exposed to strong light, but weak indoor lighting minimizes this effect. To compensate for reduced charge carriers due to lower light intensity, the team designed an electrode structure with titanium dioxide bonded to the sulfide. This junction prevents positive and negative charge carriers from recombining and disappearing, allowing all limited charges to be fully utilized for hydrogen production without recombination losses. Additionally, coating the sulfide surface with phosphate (Pi) prevents photocorrosion while increasing charge transfer speed, achieving both durability and efficiency.
The developed artificial leaf recorded a photocurrent of 119-120 microamperes per square centimeter (μA/cm²) using only indoor lighting without external voltage, maintaining 94% of initial performance after 12 hours. This is comparable to using expensive platinum (Pt) catalysts (121 μA/cm²). Photocurrent is an indicator for measuring the hydrogen production capacity of an artificial leaf.
Furthermore, the 3D nickel hydrogen production catalyst is inexpensive and can be printed like ink, enabling easy fabrication at scales needed for commercialization. The research team also built a large module connecting four 85 cm² artificial leaves in series, which recorded a total photocurrent of 5 milliamperes (mA) under indoor lighting.
"Unlike solar power, which is sensitive to weather, indoor lighting has the advantage of being consistent," said Professor Jang Ji-hyun. "This research confirms that light wasted indoors can be utilized as an energy source for hydrogen production. We plan to further develop hydrogen separation and recovery technologies going forward."
The research results were published online on the 16th of last month in the international academic journal "Applied Catalysis B: Environmental and Energy" and are pending formal publication. The research was supported by the ERC project of the "Chemical and Bio Convergence Process Research Center for Microplastics Response," a mid-career research grant, and the Innocore Project.