○ Principles of water activation confirmed through real-time Raman spectroscopy and theoretical calculations... Published in the international journal *Carbon Energy*

A research team led by Professor Lee Chan woo of the Department of Chemistry at Kookmin University (President Jeong Seung Ryul) has developed a ruthenium-titania (RuO₂/TiO₂) heterostructure catalyst that highly efficiently promotes the hydrogen evolution reaction (HER) in alkaline water electrolysis, and elucidated its core operating principle through real-time Raman spectroscopy and theoretical calculations. The research team created a heterogeneous interface that rapidly promotes the water splitting reaction by uniformly depositing ruthenium oxide nanoparticles, approximately 2 nm in size, onto a titania support measuring 25 nm.

Anion-exchange membrane water electrolysis (AEMWE) is gaining attention as a next-generation hydrogen production technology that operates in an alkaline environment, reducing dependence on expensive platinum-group catalysts and corrosion-resistant components. However, under alkaline conditions, the initial step of breaking the O–H bond in water molecules to form hydrogen intermediates proceeds slowly, leading to high overpotential in the hydrogen evolution reaction and reduced energy efficiency. Consequently, for the commercialization of water electrolysis, it is crucial to design catalysts that can lower the activation energy barrier of water and to gain a direct understanding of the interfacial reaction mechanisms.

The research team designed a RuO₂/TiO₂ heterostructure catalyst by combining ruthenium-based materials—which are attracting attention as platinum substitutes—with titania, which possesses water-activating properties. RuO₂ nanoparticles were deposited via hydrothermal synthesis using a RuCl₃ precursor onto anatase TiO₂ nanoparticles with surface defects introduced by hydrogen peroxide treatment, forming a heterogeneous interface where ruthenium oxide and titania were in close contact without the need for separate high-temperature heat treatment. During the electrochemical hydrogen evolution process, the catalyst surface is partially reduced and reconfigured into an active interface of the form Ru/RuO₂/TiO₂₋ₓ(OH)y. It was confirmed that the reduced titania and Ti–OH functional groups formed during this process promote the adsorption and decomposition of water molecules.

The developed RuO₂/TiO₂ catalyst required an overpotential of only 6.6 mV to reach a current density of 10 mA cm⁻² in a 1 M KOH electrolyte. This performance is superior not only to that of pure RuO₂ (79 mV) but also to that of the commercial reference catalyst Pt/C (43 mV). Furthermore, it exhibited a low Tafel slope of 36.7 mV dec⁻¹, demonstrating a significant improvement in the kinetics of the alkaline hydrogen evolution reaction. It also recorded a high turnover frequency (TOF) of 25.07 s⁻¹ at a 100 mV overpotential, indicating excellent active site utilization even among reported ruthenium-based alkaline hydrogen evolution catalysts. The mass activity was also approximately 10 times and 6.4 times higher than that of RuO₂ and Pt/C, respectively.

△ Schematic diagram of the hydrogen production performance and reaction mechanism of a ruthenium-titania heterojunction catalyst

This study is particularly significant not only for improving catalyst performance but also for directly confirming how water is activated at the heterointerface. The research team applied shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) to track changes in interfacial water molecules, adsorbed hydrogen (*H), and hydroxyl intermediates (*OH) under actual HER operating conditions. The results showed that on the RuO₂/TiO₂ catalyst, highly reactive interfacial water species—such as water coordinated with K⁺ (K⁺-H₂O) and weakly hydrogen-bonded water (2-HB-H₂O)—increased, and Ti–OH signals were also observed. This demonstrates that the titania interface attracts water molecules and facilitates the cleavage of O–H bonds.

DFT calculations also supported these experimental results. In a model where reduced and hydroxylated titania clusters were bound to the Ru surface, water molecules were preferentially adsorbed near the Ti–OH functional group, and the activation barrier for water splitting was found to be significantly lower compared to the bare Ru surface. Charge density analysis confirmed that charge redistribution occurs at the Ru–TiO₂ interface, stabilizing water adsorption, and that Ru provides a cooperative reaction pathway responsible for the adsorption of hydrogen intermediates and the formation of hydrogen molecules. These results demonstrate at the molecular level that the ruthenium-titania heterojunction goes beyond simply modulating the electronic structure to actually promote water activation, which is the bottleneck step in alkaline HER.

△ (From left) Professor Lee Chan-woo of the Department of Chemistry at Kookmin University, Ph.D. candidate Dwi Sakti Aldianto Pratama, and Ph.D. candidate Andi Haljanto

Professor Lee Chan woo said, stated, “This study is significant because it not only developed a highly active catalyst but also directly observed the process by which a heterogeneous interface activates water molecules under actual operating conditions.” He added, “Based on the principle that water activation and hydrogen intermediate formation occur separately and cooperatively at the ruthenium-titania interface, we will be able to propose a high-efficiency catalyst design strategy applicable to next-generation alkaline and anion-exchange membrane electrolysis systems.”

This research was conducted with support from the Ministry of Science and ICT through the Excellent Young Researcher Program (RS-2023-00210114), the Green Hydrogen Technology Self-Reliance Project (RS-2025-02304646), and the Global TOP Strategic Research Group Support Program (GTL25021-210). The research findings were published in the international journal Carbon Energy (IF 24.2, top 2.9% in the JCR) under the title “Ruthenium-Titania Interface-Mediated Water Activation for High Turnover Frequency in Alkaline Hydrogen Evolution.”