- Precise control of atomic-layer Pd shells minimizes hot charge loss; demonstrated performance of antenna–reactor structure nanocatalyst 

- Research published in leading international journal JACS; core source technology for clean energy transition secured 

A research team led by Prof. Hyosun Lee of the Department of Materials Science and Engineering at the University of Seoul has announced next-generation eco-friendly photoelectrochemical catalyst technology developed using solar energy through research conducted jointly with Profs. Jeong Young Park and Hyotcherl Ihee of the KAIST Department of Chemistry.

The team implemented a new catalytic technology that maximizes the utilization of hot charges in plasmonic metals. The novel technology significantly improves the efficiency of solar water splitting achievable with existing technologies.

Because plasmonic metals can utilize the visible light region, which accounts for approximately 47% of sunlight, they are considered promising next-generation eco-friendly water-splitting catalysts. However, their performance has been limited by the rapid recombination of high-energy (hot) charges generated during sunlight absorption, which reduces reaction efficiency.

▶ Schematic diagram of the photoelectrochemical oxygen evolution reaction of Au@Pd nanoparticles

To address this, the researchers fabricated core–shell nanoparticles with a gold–palladium (Au@Pd) “antenna–reactor” structure and systematically compared reactivity by precisely controlling palladium shell thickness in the atomic layer. The Au core functions like an antenna that effectively absorbs visible light and generates plasmonic hot charges, while the Pd shell in the atomic layer functions like a reactor that rapidly transfers hot charges to the surface to participate in chemical reactions.

▶ Photoelectrochemical reactivity graph of Au@Pd/TNAs

Following the combination of Au@Pd nanoparticles with titanium dioxide (TiO2) nanotube electrodes, hot electrons quickly migrated into the metal particles and TiO2 nanotubes to participate in hydrogen evolution at the counter electrode (a platinum coil), while the high density of the hot holes remaining on the Pd surface of the nanoparticles promoted an oxygen evolution reaction. The Schottky barrier formed at the nanoparticle–TiO2 nanotube interface suppressed hot charge recombination, minimizing losses, and the single-layer Pd shell maximized hot hole utilization, greatly enhancing reaction efficiency.

The team also employed ultrafast laser spectroscopy (femtosecond transient absorption spectroscopy) to directly capture hot charge dynamics on the femtosecond timescale. Analysis clearly demonstrates that as the coverage of the Pd shell of Au@Pd nanoparticles expands in the atomic layer, the speed of migration of the plasmon-induced hot electrons and hot holes generated in the Au core increases, reducing losses due to hot charge recombination and thus improving reaction efficiency.

▶ Observation of hot carrier dynamics using ultrafast laser spectroscopy

The significance of this research lies in its proposal of a new strategy for controlling hot charge dynamics by precisely tuning the plasmonic antenna–reactor structure in the atomic layer. The study clarifies the operating mechanism of this structure, providing a design principle for next-generation solar-driven eco-friendly photocatalysts that can minimize hot charge loss. This approach can be used to develop highly efficient photocatalysts through the further optimization of plasmonic metal structures. Its numerous applications in the energy and environment fields include clean hydrogen production and carbon dioxide conversion.

The research was co–first authored by Hyewon Park of the KAIST Department of Chemistry, Seunghyun Chun of the University of Seoul Department of Materials Science and Engineering, and Jeong Hoon Lee of the KAIST Department of Chemistry. The research article was published on September 17 in the prestigious Journal of the American Chemical Society. 

* Paper title: “Impact of Hot Carrier Dynamics on Photoelectrocatalytic Activity on Au@Pd Antenna–Reactor Nanoparticles”

DOI: 10.1021/jacs.5c12825

This research was supported by the National Research Foundation of Korea (funded by the Ministry of Science and ICT), the Institute for Basic Science, and the University of Seoul.

▶ (L-R) Prof. Jeong Young Park, Prof. Hyosun Lee, Prof. Hyotcherl Ihee