A collaborative research team led by Professor Taesung Kim (Departments of Mechanical Engineering, Nanoscience and Technology, and Semiconductor Convergence Engineering) and Professor Pil J. Yoo (Departments of Chemical Engineering, Nanoscience and Technology, and SKKU Institute of Energy Science and Technology) at Sungkyunkwan University, together with Dr. Hyeong-U Kim from the Korea Institute of Machinery and Materials, has successfully developed a high-efficiency, stable hydrogen production electrode material utilizing a low-temperature plasma polarization-field-embedded two-dimensional (2D) heterojunction structure.

In recent years, transition metal dichalcogenide (TMD) thin films have gained attention for their tunable hydrogen ion adsorption energies, which vary with crystal structure, providing a basis for designing hydrogen evolution reaction (HER) electrodes with controllable morphologies. The 2H phase, characterized by semiconducting properties, exhibits lower charge transfer capacity compared to the metallic 1T phase. Although efforts to produce 1T-phase TMDs have been ongoing, the strong adsorption in the 1T phase has resulted in desorption-related challenges. Thus, research focused on tuning material properties to address these limitations has become essential.

To overcome these obstacles, the research team devised a novel approach that leverages a heterojunction interface with embedded polarization fields, introducing interfacial vacancies that liberate electrons previously constrained by sulfur. This structural innovation facilitates enhanced charge transfer to the electrode surface, ultimately enabling a system capable of rapidly reducing adsorbed hydrogen ions to molecular hydrogen.

The team demonstrated that a polarization field formed at the tungsten-graphene interface due to differences in work functions, acting as an internal barrier that prevents the penetration of ionized hydrogen sulfide ions, achieved under low-temperature plasma conditions. This configuration induces sulfur vacancies at the bottom layer, thereby generating free electrons that enhance charge transfer to the surface, surpassing the performance of conventional 2D thin-film-based hydrogen production electrodes.

The team demonstrated that a polarization field formed at the tungsten-graphene interface due to differences in work functions, acting as an internal barrier that prevents the penetration of ionized hydrogen sulfide ions, achieved under low-temperature plasma conditions. This configuration induces sulfur vacancies at the bottom layer, thereby generating free electrons that enhance charge transfer to the surface, surpassing the performance of conventional 2D thin-film-based hydrogen production electrodes.

Experimental validation, conducted via spherical aberration-corrected transmission electron microscopy, revealed the formation of nanocrystalline atomic layers under hydrogen sulfide ion penetration resulting from ion collision reactions in low-temperature plasma. Additionally, X-ray photoelectron spectroscopy and X-ray diffraction analyses elucidated the mechanism by which hydrogen sulfide ions infiltrate the lattice structure to facilitate the crystallization of amorphous WS₂, enabling in-situ synthesis of 1T-phase lattice through excessive ion injection at the lattice interface.

The significance of this work is underscored by its publication in Advanced Materials, a leading journal in multidisciplinary materials science, on September 9, 2024.

Publication Details

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• Journal: Advanced Materials
• Article Title: Electron Release via Internal Polarization Fields for Optimal S-H Bonding States
• DOI: 10.1002/adma.202411211
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※Authors

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• Corresponding Authors: Professor Taesung Kim (Sungkyunkwan University, Departments of Mechanical Engineering, Nanoscience and Technology, and Semiconductor Convergence Engineering), Professor Pil J. Yoo (Sungkyunkwan University, Departments of Chemical Engineering, Nanoscience and Technology, and SKKU Institute of Energy Science and Technology), Dr. Hyeong-U Kim (Korea Institute of Machinery and Materials)
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• First Authors: Hyunho Seok (Integrated Master-PhD Program, Department of Nanoscience and Technology, Sungkyunkwan University), Minjun Kim (Integrated Master-PhD Program, Department of Nanoscience and Technology, Sungkyunkwan University), Jinil Cho (Department of Mechanical Engineering, Sungkyunkwan University)