On February 5, Professor Kim Byung-hyun of the Department of Chemical and Molecular Engineering at Hanyang University ERICA and a joint research team led by Doctor Lee Young-jun and Lee Sung-ho of Korea Institute of Science and Technology (KIST) announced that they developed a high-performance catalyst that enables more economical and efficient production of carbon-free "clean hydrogen."

The conventional alkaline water electrolysis method had advantages such as lower equipment costs and a simple structure compared to an acidic environment (PEM water electrolysis), yet it faced limitations due to the slow formation of hydrogen ions (H+) through water dissociation and the limitations in hydrogen evolution reaction speed. To overcome these challenges, the joint research team between KIST and Hanyang University developed a catalyst (Rh-TiO2/CNF) that maximizes reactivity by embedding titanium oxide into carbon nanofibers (CNF) and strategically positioning dual-type rhodium single atoms.

The research team facilitated hydrogen evolution on the catalyst surface while reducing the energy barrier of the water dissociation step by anchoring rhodium (Rh) single atoms in a binary phase of nitrogen (Rh-Nx) and oxygen (Rh-Ox) by leveraging the interaction between the carbon nanofiber (CNF) support and titanium oxide (TiO2). As a result, they achieved high-efficiency hydrogen production in an anion exchange membrane water electrolyzer (AEMWE).

The catalytic performance was validated through various experimental and computational chemistry analyses, and the research team found that the combination of Rh-Nx and Rh-Ox significantly enhances hydrogen evolution reaction and water dissociation, while titanium oxide and carbon nanofibers maintain the stable electronic structure of rhodium single atoms to ensure long-term high-efficiency reactions.

In the study, the research team successfully maintained a stable current density of 1 A cm-2 per unit cell for over 225 hours in continuous high-power operation, and they demonstrated excellent stability and high efficiency by constructing a 2-cell AEMWE stack that took the industrialization stage into account. The newly developed catalyst can either replace or complement conventional high-cost precious metal catalysts (Pt, Ir), and it's expected to be a viable alternative with economic competitiveness as it significantly reduces the required amount of noble metals.

By improving the slow Hydrogen Evolution Reaction (HER) kinetics in alkaline conditions, this study is projected to mark a major milestone in next-generation clean hydrogen production considering that it can be directly applied to large-scale industrial electrolyzer stacks (cell stacks).

Dr. Lee Young-jun of KIST, who led the study, said, "This binary rhodium single-atom catalyst will contribute to the realization of a next-generation clean hydrogen economy by dramatically improving hydrogen production efficiency under alkaline conditions."

Professor Kim Byung-hyun of Hanyang University ERICA stressed, "By employing computational chemistry, we successfully identified key factors that enhance the performance of water electrolysis catalysts, and this will play a pivotal role in designing future catalyst materials."

This study was supported by the Convergence Research Group Program for Future-leading Research of the National Research Council of Science and Technology and the STEAM Research Program, and the research findings were published on January 20 in Advanced Science, an internationally renowned journal in the field of materials science. The paper, titled Synergistic Configuration of Binary Rhodium Single Atoms in Carbon Nanofibers for High-Performance Alkaline Water Electrolyzer, was authored by Doctor Natarajan Logeshwaran, KIST, and Kim Gyu-chan, a doctoral student at Hanyang University ERICA, with Professor Kim Byung-hyun of Hanyang University ERICA, Doctor Lee Young-jun of KIST, Doctor Lee Sung-ho of KIST serving as corresponding authors.