Development of Self-Penetrating 'Liquid Metal'... Conducting Hydrogen Catalyst Current

UNIST Professors Hye-Sung Park, Geon-Tae Kim, and Sang-Kyu Kwak Develop Synthesis Method for Transition Metal Chalcogenides
Using Liquid Alkali Metals to Achieve Over 90% Phase Purity and Stability, Anticipated for Catalytic Applications

Professor Park Hyesung (left) and Researcher Park Sanghyun at UNIST.

[Asia Economy Yeongnam Reporting Headquarters Reporter Kim Yong-woo] A technology has been developed that synthesizes liquid-state metals that naturally penetrate well to improve the electrical conductivity of hydrogen evolution catalysts. This technology compensates for the weakness of catalysts that do not conduct electricity well.

A research team at Ulsan National Institute of Science and Technology (UNIST) has developed a technology that dramatically improves the performance of 'Transition Metal Dichalcogenides (TMDs)', which are attracting attention as next-generation hydrogen evolution catalysts, by using liquid alkali metals.

The new synthesis method that allows liquid metal to penetrate the catalyst structure can easily and quickly increase the electrical conductivity, which has been pointed out as a weakness of the catalyst.

The joint research team of Professors Park Hye-sung, Kim Geon-tae, and Kwak Sang-gyu from the Department of Energy and Chemical Engineering at UNIST developed a synthesis method that converts transition metal dichalcogenides into a metallic phase (1T phase) by using an 'alkali molten metal (liquid metal similar to molten steel) intercalation method.'

Transition metal dichalcogenides, which are attracting attention as hydrogen evolution catalysts, perform better as their electrical conductivity improves. This technology converts the semiconductor phase into a highly electrically conductive metallic phase in a short time using a simple synthesis method.

A conceptual diagram of converting transition metal compounds in a semiconductor phase to a metallic phase using liquid alkali metals.

Transition metal dichalcogenides are materials composed of metal elements such as tungsten (W) or molybdenum (Mo) combined with chalcogen elements such as sulfur (S). Due to their low cost and durability, they are used as catalysts for the 'water electrolysis reaction' (a reaction that produces hydrogen from water) as alternatives to platinum (Pt).

However, at room temperature, their electrical conductivity, which is one of the indicators of catalyst performance, decreases. This material contains both semiconductor and metallic properties within a single substance, but at room temperature, it mainly exists in the semiconductor phase, which has lower electrical conductivity. Although there are methods to synthesize the metallic phase, they take a long time and the synthesized material tends to revert to the semiconductor phase.

The joint research team succeeded in synthesizing 'metallic dichalcogenides' in just one hour (compared to the conventional 48 to 72 hours) by inserting liquid alkali metal into transition metal dichalcogenides using capillary action.

The transition of molybdenum disulfide, a transition metal chalcogenide compound, from the semiconductor phase (green) to the metallic phase (black).

At this time, the alkali metal supplies the electrons needed for the dichalcogenides to convert into the metallic phase. Because the capillary action, where liquid is naturally drawn into a thin tube, was used, the liquid alkali metal was well delivered inside the dichalcogenides. In the synthesized dichalcogenides, the metallic phase accounted for 92% of the entire compound.

First author Park Sang-hyun, a master's course researcher in the Department of Energy and Chemical Engineering at UNIST, said, "The conventional synthesis method takes 2 to 3 days to produce metallic transition metal dichalcogenides, but the newly developed synthesis method is shorter and simpler," and added, "We confirmed a high phase purity of over 92% through X-ray photoelectron spectroscopy and other analyses."

In particular, the metallic transition metal dichalcogenides synthesized this time have the advantage of very high stability. The metallic phase was maintained without reverting to the semiconductor phase even under high heat and strong light.

The research team also revealed the reason why the metallic phase can be stably maintained through theoretical analysis. During the synthesis process, the bonding between the alkali metal and the chalcogen material lowers the energy barrier required for the semiconductor phase to convert into the metallic phase and maintains the electronic structure. Furthermore, when the newly synthesized dichalcogenides were applied to an actual water electrolysis system, they showed excellent performance even after more than 100 hours of operation.

Professor Park Hye-sung of the research team said, "We have discovered a new synthesis method for transition metal dichalcogenides, which are attracting attention as next-generation hydrogen evolution catalysts," and added, "This not only provides clues to elucidate the physical properties of two-dimensional materials but also will greatly help in developing hydrogen evolution catalysts by effectively utilizing the characteristics of metallic transition metal dichalcogenides."

This research was published online on July 6 in the prestigious international journal Advanced Materials. The research was supported by the Ministry of Education's 'Basic Research Support Project for Individual Science and Engineering Researchers' and the Ministry of Science and ICT's 'Mid-career Researcher Program.'

This content was produced with the assistance of AI translation services.