Development of Next-Generation Water Electrolysis Catalyst by surface restructuring of Low-Dimensional Semiconductor 'Tungsten Disulfide (WS2)'

A joint research effort by Professors Lee Wonkyu (Department of Materials Science and Engineering) and Song Bonggeun (Department of Chemical Engineering) from Hongik University, along with Senior Researcher Kim Insoo from the Korea Institute of Science and Technology (KIST), has been published as an important breakthrough in the prestigious international academic journal Advanced Materials.

Recently, amid growing concerns over carbon emissions due to air pollution, there is increasing interest in environmentally friendly energy production methods. In particular, hydrogen fuel is gaining attention as an ideal clean energy source because it can produce chemical energy equivalent to fossil fuels without generating carbon dioxide during combustion. Hydrogen fuel is categorized into gray hydrogen, blue hydrogen, and green hydrogen based on its production methods. Gray and blue hydrogen have limitations as they are based on fossil fuels, leading to the production of carbon dioxide as a byproduct.  Green hydrogen is considered the ultimate energy production method pursued by hydrogen energy systems. It utilizes electrolysis technology to chemically decompose water molecules into oxygen and hydrogen without generating carbon dioxide.  In this case, the development of electrochemical catalysts/electrode materials to lower the power required for the electrolysis of water is a key technology at the national level for the mass production of water electrolysis. However, to date, most catalysts are based on platinum, which is scarce and expensive globally. Research is ongoing to develop electrochemical catalysts with high stability and reliability to replace platinum-based catalysts.

The Hongik University-KIST research team focused on the development of next-generation catalysts that can achieve platinum or higher water electrolysis efficiency and stability through surface restructuring of tungsten disulfide (WS2) as a low-dimensional semiconductor material. The team mechanically exfoliated and transferred multilayer WS2, sequentially exposing it to argon (Ar) and oxygen (O2) plasma to form nano-domains with extremely high electrochemical reactivity and activity on the material surface. Using various analytical techniques such as X-ray Photoelectron Spectroscopy (XPS), Raman spectroscopy, Atomic Force Microscopy (AFM), and Transmission Electron Microscopy (TEM), the team experimentally observed that the surface structure of WS2 was restructured into a collective of partially amorphized nano-domains. Subsequently, the team demonstrated through electrochemical characterization, that the collective composite nanostructures formed by plasma surface treatment can sustain ultra-high efficiency water electrolysis for a long time in the ultra-low voltage range. The team also succeeded in calculating the electrochemical reactivity of the individual domains and the increase in their activity at the atomic level using density functional theory, thereby theoretically proving the catalytic reactivity observed experimentally.

The lead researcher, Professor Lee Wongyu, emphasized the significance of this study, stating, "This research is meaningful in presenting a methodology to synthesize highly efficient electrochemical catalysts on a large scale through simple plasma treatment. Typically, plasma treatment is widely used in semiconductor processes for purposes such as impurity removal and etching of surfaces. However, this study is novel in that it repurposes the plasma process as part of a templated synthesis method that uses the structure of existing materials as a framework to form new nanostructures from the bottom-up".  "Materials engineering is a discipline that deals with the relationships among structure, property, and process of materials. In conducting this research, many relationships between structure and property within materials formed by very simple processes remain poorly understood. In particular, selective amorphisation and disorder control of low-dimensional semiconductor structures will be crucial to the design of next-generation catalytic materials for water electrolysis and fuel cells. Establishing theoretical and experimental methodologies that can systematically analyse the structure of amorphous materials is essential," Professor Lee said, expressing his opinions on the subject.

This research was co-first authored by Park Jiheon, a master's student in the Department of New Materials Engineering, Jo Yian, a doctoral student in the Department of Chemical Engineering, and Jeon Hotae, a master's student in the Department of New Materials Engineering at Hongik University. The study received support from Hongik University's Academic Research Promotion Fund and the National Research Foundation of Korea’s Excellent New Research Project.

Title of paper : Conversion of Layered WS2 Crystals into Mixed-Domain Electrochemical Catalysts by Plasma-Assisted Surface Reconstruction

Research Paper DOI: 10.1002/adma.202314031

Figure 1. 

(Left) Schematic diagram of the fabrication process of multilayer WS2-based catalysts, 

(Top right) Catalyst structure and composition distribution as viewed by transmission electron microscopy (TEM), 

(Bottom right) Comparison table of water electrolysis performance with conventional WS2-based catalysts.

Figure 2.

(Left) Theoretical model of nanodomains formed on the WS2 surface, 

(Right) Calculated hydrogen adsorption free energy and theoretical exchange current density for each reaction site on the domain.

From left to right: Park Jiheon (first author), Jo Yian (first author), Jeon Hotae (first author), Professor Lee WoonKyu, Department of New Materials Engineering, Hongik University (corresponding author), Senior Researcher Kim Insoo, KIST (corresponding author), Professor Song Bonggeun, Department of Chemical Engineering, Hongik University (corresponding author).

Online Communications Reporter, Kwon Seoyoon