Chlorine is an industrial chemical of significant importance, ranking among the top ten chemicals in the world with an annual production of 75 million tons. A breakthrough in chlorine production has been made by Prof. Chang Hyuck Choi's team at Pohang University of Science and Technology and Prof. Sang Hoon Joo's team at Seoul National University. Their study, which focuses on a new catalyst design principle to optimize chlorine production, was published in the journal Nature Communications on June 3, 2023.

Chlorine is primarily produced by an electrochemical process known as the chlor-alkali process. This process uses a dimensionally stable anode (DSA) as a catalyst. However, the DSA contains significant amounts of precious metals such as iridium and ruthenium, which significantly increases the cost of chlorine production.

To reduce production costs, the researchers successfully developed a platinum catalyst characterized by atomically dispersed metal atoms on carbon nanotubes. This catalyst can efficiently facilitate chlorine production even with minimal Pt content. Despite this innovation, the source of the high catalytic performance remained unclear, hindering further progress in developing superior catalysts.

Typically, a transition metal atom is stabilized by four chemical bonds within a planar symmetric structure. However, some theoretical studies have challenged this conventional view, suggesting that a planar symmetric structure is inferior in terms of catalytic performance compared to a broken symmetry structure.

To address this controversy, the researchers synthesized precisely controlled single-atom Pt catalysts. Advanced spectroscopic analyses identified more than two types of active sites: a planar symmetric one with four chemical bonds and a distorted one with three chemical bonds. A combination of electrochemical and theoretical studies revealed that this distorted symmetry significantly enhances catalytic performance. This study provided experimental confirmation of the theoretical hypothesis that broken symmetry is responsible for superior catalytic performance.

Prof. Joo and Prof. Choi said that "broken symmetry is the key to high performance chlorine production". They further emphasized that "these findings provide a key principle for the design of advanced catalytic materials.

Schematic illustrations of symmetric and asymmetric active sites of Pt single-atom catalyst

[Reference] Cho J., Lim, T., Kim, H. et al., Importance of broken geometric symmetry of single-atom Pt sites for efficient electrocatalysis. Nat. Commun. 14, 3233 (2023)

[Main Author]  Mr. Junsic Cho (Pohang University of Science and Technology), Dr. Taejung Lim (Ulsan National Institute of Science and Technology), Dr. Haesol Kim (Pohang University of Science and Technology), Prof. Sang Hoon Joo (Seoul National University), Prof. Chang Hyuck Choi (Pohang University of Science and Technology)

* Contact : Prof. Sang Hoon Joo (shjoo1@snu.ac.kr), Prof. Chang Hyuck Choi (chchoi@postech.ac.kr)