Groundbreaking Discovery Enables Cost-Effective and Eco-friendly Green Hydrogen Production

Abstract
Despite intensive studies over decades, the development of electrocatalysts for acidic water splitting still relies on platinum group metals, especially Pt and Ir, which are scarce, expensive, and poorly sustainable. Because such problems can be alleviated, Ru-based bifunctional catalysts such as rutile RuO2 have recently emerged. However, RuO2 has a relatively low activity for hydrogen evolution reactions (HER) and low stability for oxygen evolution reactions (OER) under acidic conditions. In this study, the synthesis of a RuOx-based bifunctional catalyst (RuSiW) for acidic water splitting via the electrochemical evolution from Ru-based polyoxometalates at cathodic potentials is reported. RuSiW consists of the nanocrystalline RuO2 core and Si,W-codoped RuOx shell. RuSiW exhibits outstanding HER and OER activity comparable to Pt/C and RuO2, respectively, with high stability. Computational analysis suggests that the codoping of RuOx with W and Si synergistically improves the HER activity of otherwise poor RuO2 by shifting the d-band center and optimizing atomic configurations beneficial for proper hydrogen adsorption. This study provides insights into the design and synthesis of unprecedented bifunctional electrocatalysts using catalytically inactive and less explored elements, such as Si and W.

A breakthrough technology has been developed that enables the production of green hydrogen in a more cost-effective and environmentally friendly manner, bringing us closer to a carbon-neutral society by replacing expensive precious metal catalysts.

Led by Professor Jungki Ryu in the School of Energy and Chemical Engineering at UNIST and Professor Dong-Hwa Seo from the Department of Materials Science and Engineering at KAIST, a joint research team has successfully developed a bifunctional water electrolysis catalyst for the high-efficiency and stable production of high-purity green hydrogen.

The newly-developed catalyst exhibits exceptional durability even in highly corrosive acidic environments. By utilizing ruthenium, silicon, and tungsten (RuSiW), the catalyst is more cost-effective compared to conventional platinum (Pt) or iridium (Ir) catalysts. Furthermore, it emits significantly fewer greenhouse gases, making it an eco-friendly alternative.

Figure 1. Schematic image, showing the characteristics of RuSiW. (Left) Dark-field STEM, (Center) EDX elemental mapping images of RuSiW, and (Right) High-resolution bright-field TEM image of RuSiW.

Water electrolysis is a cutting-edge technology that produces hydrogen through the process of electrolyzing water. It is considered a key technology for achieving a carbon-neutral society as it enables the production of environmentally friendly hydrogen without carbon emissions.

The research team focused on finding alternatives to precious metal catalysts like platinum and iridium, which exhibit stability in acidic conditions. Ruthenium has gained attention as an eco-friendly metal due to its relatively low production cost and significantly lower greenhouse gas emissions compared to platinum and iridium. However, it faced challenges in commercialization due to its lower catalytic activity compared to platinum and lower stability compared to iridium.

To overcome these limitations, the research team developed a catalyst based on ruthenium, silicon, and tungsten. By enhancing the function of the ruthenium catalyst, which has lower stability in both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), the team demonstrated the catalyst’s potential as a bifunctional catalyst.

Figure 2. Overall water splitting using RuSiW as a bifunctional HER and OER catalyst. a) Experimental scheme. b) Polarization curves of the full cells: RuSiW on CFP as an anode, RuSiW on Ti mesh as a cathode, and 0.5 m H2SO4 as an electrolyte. c) Chronopotentiograms of the corresponding full cells at 10 mA cm−2.

The developed catalyst features a structure doped with tungsten and silicon around a ruthenium atom. The catalyst’s reaction acceleration ability was enhanced by increasing the adsorption intensity of protons on the catalyst surface. It exhibits higher activity in the hydrogen evolution reaction compared to commercially available platinum catalysts. Additionally, a thin tungsten film with a thickness of 5~10 nm protects the catalytic site of ruthenium, thereby improving its stability.

The research team conducted a stability experiment on the catalyst. Using an acidic electrolyte (with an acidity of 0.3), they injected 10 mA of current into a 1 ㎠ electrode. The developed catalyst demonstrated stable performance even after running for over 100 hours.

Figure 3. Long-term stability of the corresponding catalysts during OER at 10 mA cm−2.

Professor Ryu stated, “The development of this three-element catalyst is significant as it has the potential to replace expensive platinum and iridium simultaneously. It is expected to be applied to high-purity green hydrogen production systems, such as PEM electrolyzers, as it can be easily and stably synthesized even in highly corrosive acidic conditions.”

The research involved the collaboration of Dr. Dasom Jean (School of Energy and Chemical Engineering, UNIST), Dr. Dong Yon Kim (Department of New Materials Engineering, KAIST), and Dr. Hyongoo Kim (School of Energy and Chemical Engineering, UNIST) who participated as the first authors.

This research received support from the Korea Research Foundation of the Ministry of Science and ICT, the Regional Innovation Leading Research Center (RLRC) project, and the National Supercomputing Center (KISTI). The research findings have been published in Advanced Materials on January 4, 2024.

Journal Reference
Dasom Jeon, Dong Yeon Kim, Hyeongoo Kim, et al., “Electrochemical Evolution of Ru-Based Polyoxometalates into Si,W-Codoped RuOx for Acidic Overall Water Splitting,” Advanced Materials, (2023).