SEOULSouth Korea , June 13, 2022 /PRNewswire/ — Concerns about rising carbon dioxide levels in the atmosphere and global warming have made it environmentally 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 document has been posted on March 15, 2022 and was published in volume 18 issue 16 of the journal Little on 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,” explains the assistant professor Seung Keun Parkwho conducted the study. “Given their large surface area and open structure, hollow HER catalysts are considered ideal for this work. Metal-organic frameworks (MOFs) are found to be an effective precursor for fabricating 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 activity“, says 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 realizing a zero-emissions society,” says an optimistic Dr. Park.
And we hope that we are not far away!
DO I: https://doi.org/10.1002/smll.202200586
Title of the original article: Metal–Organic Framework-Derived Hollow CoSX Nanoarray Coupled with NiFe Layered Double Hydroxides as Efficient Bifunctional Electrocatalyst for Global Water Splitting
About Chung-Ang University
Seong Kee Shin
SOURCE Chung-Ang University