Researchers find new catalyst to make hydrogen generation cheaper
Hydrogen is often touted as one of the best potential candidates for a cleaner, more sustainable alternative to fossil fuels.
The cleanest way to produce it is with "electrocatalytic water splitting" - a process where the water molecule is split into oxygen and hydrogen gas using electricity. However, the need for expensive and rare metal catalysts has so far made the process unfeasible for large-scale industrial use.
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Another relatively inexpensive option is transition metal-based catalysts, such as oxides, sulfides, hydroxides of cobalt, nickel, iron etc. However, there is a catch: the electrocatalytic water splitting consists of two half-reactions, namely the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER).
In OER, water molecules are oxidised to form oxygen and positive hydrogen ions at the anode (positively charged electrode). The hydrogen ions then move across the electrolyte to the cathode (the negatively charged electrode), where they are reduced to produce hydrogen (HER). Most transition metal-based catalysts reported so far can only catalyse either HER or OER. This makes for a complicated configuration and a higher overall cost.
A study by South Korea's Chung-Ang University could end that, however, because researchers have developed an inexpensive catalyst composed of a transition metal hydroxide-sulfide heterostructure that makes for highly efficient overall water splitting.
"A reasonable strategy for fabricating highly efficient catalysts for water splitting is to elaborately integrate OER-active NiFe LDH and HER-active catalysts into a heterostructure," said Assistant Professor Seung-Keun Park, who headed the study.
"Given their high surface area and open structure, hollow HER catalysts are believed to be ideal for this job. It turns out that metal-organic frameworks (MOFs) are an efficient precursor for fabricating hollow structures. However, an MOF-based hollow catalyst with NiFe LDH has not been reported so far."
The researchers then 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, guarantees a superior bifunctional catalytic activity," added Dr. Park.
The resulting catalyst was able to consistently deliver a high enough current density in both half-reactions at low cell voltages, which the team says suggests it is feasible for industrial-scale water-splitting applications. The researchers attributed this to the presence of ample active sites on the catalyst heterostructure, which enabled electrolyte penetration and gas release during the reactions.
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"The enhanced electrocatalytic properties of our catalyst is likely due to its unique hierarchical heterostructure and the synergy between its components. We believe that our work will take us one step closer towards realizing a zero-emission society," added Dr. Park.
- The paper was published online on 15 March 2022 and was published in Volume 18 Issue 16 of the journal Small on 16 April 2022.
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