Researchers from Chung-Ang University are developing a new

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image: Hydrogen fuel cells produce clean electricity, generating only water as a byproduct. Developing efficient and inexpensive catalysts with improved performance in the production of hydrogen from water separation is therefore imperative. Now researchers at Chung-Ang University are using metal-organic structures and transition metal hydroxides for this purpose.
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Credit: AC Transit hydrogen fuel cell bus by Eric Fischer.

Concerns about rising carbon dioxide levels in the atmosphere and global warming have made it an environmental imperative to replace fossil fuels with cleaner, more sustainable alternatives. In this respect, hydrogen, a clean energy source, has emerged as an excellent potential candidate.

Of the many methods available for the generation of hydrogen, the separation of water using electricity in the presence of a catalyst, or “electrocatalytic water separation”, as it is called, is the cleaner. Unfortunately, the process requires expensive and rare noble metal catalysts, such as platinum, to maintain reasonable efficiency. This, in turn, has limited its large-scale industrial applications.

A relatively inexpensive option is catalysts based on transition metals, such as oxides, sulphides, hydroxides of cobalt, nickel, iron, etc. However, there is a catch: the electrocatalytic separation of water consists of two half-reactions, namely the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). In OER, water molecules are oxidized to form oxygen and positive hydrogen ions at the anode (positively charged electrode). The hydrogen ions then travel through the electrolyte to the cathode (the negatively charged electrode), where they are reduced to produce hydrogen (HER). It turns out that most transition metal catalysts reported so far can only catalyze HER or OER. This makes the setup complicated and the overall cost higher.

In this context, researchers from Chung-Ang University in Korea have developed, in a new study, a novel heterostructured catalyst composed of hollow cobalt sulfide (CoSX) and layered nickel-iron (NiFe) double hydroxide (LDH) nanosheets that stimulate both half-reactions simultaneously. This article was posted on March 15, 2022 and was published in Volume 18 Number 16 of the journal Little April 16, 2022.

“A reasonable strategy for fabricating highly efficient catalysts for water splitting is to elaborately integrate active NiFe LDH and HER catalysts into a heterostructure,” says Assistant Professor Seung-Keun Park, who led the study. “Given their large surface area and open structure, hollow HER catalysts are considered ideal for this work. It turns out that metal-organic frameworks (MOFs) are an effective precursor for the fabrication of hollow structures. However, a hollow catalyst based on MOF with NiFe LDH has not been reported so far.

Accordingly, the researchers electrochemically deposited NiFe LDH nanosheets in a controlled manner on the surface of hollow CoSX nanoarrays supported on nickel foam. “The integration of an active HER catalyst, CoSX and an OER catalyst, NiFe LDH, ensures superior bifunctional catalytic activitysays Dr. Park.

And indeed, the catalyst was able to consistently deliver a high current density of 1000 mA cm-2 in both low cell voltage half-reactions, suggesting its feasibility for industrial-scale water separation applications. The researchers attributed this to the presence of numerous active sites on the heterostructure of the catalyst, which allowed electrolyte penetration and gas release during reactions. Additionally, an electrolyzer based on this catalyst demonstrated a high current density of 300 mA cm-2 low cell voltage and 100 hour durability in overall water separation.

“The enhanced electrocatalytic properties of our catalyst are likely due to its unique hierarchical heterostructure and the synergy between its components. We believe that our work will take us one step closer to achieving a zero-emissions society,” says an optimistic Dr. Park.

And we hope that we are not far away!

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Reference

DO I: https://doi.org/10.1002/smll.202200586

Authors: Yun Jae Lee and Seung-Keun Park

Affiliations: Chung-Ang University, Republic of Korea

About Chung-Ang University
Chung-Ang University is a private comprehensive research university located in Seoul, South Korea. It was started as a kindergarten in 1918 and gained university status in 1953. It is fully accredited by the Ministry of Education of Korea. Chung-Ang University conducts research activities under the slogan “Justice and Truth.” Its new vision to end its 100 years is “The world leader in creation”. Chung-Ang University offers undergraduate, postgraduate, and doctoral programs, which encompass a law school, a management program, and a medical school; it has 16 undergraduate and graduate schools each. Chung-Ang University’s cultural and artistic programs are considered the best in Korea.
Website: https://neweng.cau.ac.kr/index.do

About the Assistant Professor Seung Keun Park
Seung-Keun Park is currently an Assistant Professor in the Department of Advanced Materials Engineering, Chung-Ang University, Korea. He got his doctorate. (2016) in Convergence Science from Seoul National University and completed his postdoctoral training at Korea University. His research group develops new approaches for the precise design of nanostructured materials for energy storage and conversion applications. Dr. Park has published over 80 articles in reputable peer-reviewed journals. Currently, it has an ISI citation total of over 3900 and an h-index of 35 (Google Scholar).


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