KAIST researchers have developed a new hydrogen production system that will overcome the limitations of current green hydrogen production. It is expected that stable hydrogen production will be possible by utilizing a water-splitting system using a water-soluble electrolyte and blocking the risk of fire.
KAIST (President Kwang-Hyung Lee) announced on the 22nd that Professor Jeung Ku Kang's research team in the Department of Materials Science and Engineering has developed a self-powered hydrogen production system based on a high-performance zinc-air battery*.
*Air battery: A type of primary battery that absorbs oxygen in the air and uses it as an oxidizer. Its advantage is its long lifespan, but its disadvantage is its low electromotive force.
Hydrogen (H2) is a raw material for the synthesis of high value-added materials and is attracting attention as a clean fuel with an energy density (142 MJ/kg) that is three times higher than that of existing fossil fuels (gasoline, diesel, etc.). However, most current hydrogen production methods have the problem of emitting carbon dioxide (CO2).
In addition, green hydrogen production can be done by splitting water using renewable energy sources such as solar cells and wind power as the power source, but renewable energy-based power sources show low water splitting efficiency due to irregular power generation due to temperature, weather, etc.
To overcome this, air cells that can emit sufficient voltage (1.23 V or higher) for hydrogen production through water splitting are attracting attention as a power source, but precious metal catalysts must be used to achieve sufficient capacity, and there is a limitation that the performance of the catalyst material rapidly deteriorates during long-term charging and discharging.
Therefore, it is essential to develop a catalyst that is effective for water splitting reactions (oxygen generation, hydrogen generation) and a stable material for repeated charge and discharge reactions (oxygen reduction, oxygen generation) of zinc-air battery electrodes.
Accordingly, Professor Kang's research team proposed a method for synthesizing a non-precious metal catalyst material (G-SHELL) that is effective for all three different catalytic reactions (oxygen generation-hydrogen generation-oxygen reduction) by utilizing a nano-sized metal-organic framework grown on graphene oxide.
The research team confirmed that the developed catalyst material was composed of the air electrode material of the air battery, and that it had an energy density (797 Wh/kg) that was about 5 times higher than that of existing batteries, high output characteristics (275.8 mW/cm²), and that it could operate stably for a long time even under repeated charging and discharging conditions.
In addition, the zinc-air battery, which is operated by a water-soluble electrolyte and is safe from the risk of fire, is expected to be applied as an eco-friendly method for hydrogen production by linking it with a water electrolysis system as a next-generation energy storage device.
< Figure 1. Illustrations of a trifunctional graphene-sandwiched heterojunction-embedded layered lattice (G-SHELL) structure. Schematic representation of a) synthesis procedures of G-SHELL from a zeolitic imidazole framework, b) hollow core-layered shell structure with trifunctional sites for oxygen reduction evolution (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER), and c) heterojunctions, eterojunction-induced internal electric fields, and the corresponding band structure. >
Professor Kang said, "The zinc-air battery-based self-generation hydrogen production system, which was implemented by developing a catalyst material with high activity and lifespan in three different electrochemical catalytic reactions at low temperatures and in a simple manner, will be a new breakthrough that can overcome the limitations of current green hydrogen production."
<Figure 2. Electrochemical performance of a ZAB-driven water-splitting cell with G-SHELL. Diagram of a self-driven water-splitting cell integrated by combining a ZAB with an alkaline water electrolyzer.>
The results of this study, in which Dong Won Kim, a Ph.D. candidate, and Jihoon Kim, a Master's candidate of KAIST Department of Materials Science and Engineering participated as co-first authors, were published in the Multidisciplinary Materials Science section of the international academic journal Advanced Science on September 17.
(Paper title: Trifunctional Graphene-Sandwiched Heterojunction-Embedded Layered Lattice Electrocatalyst for High Performance in Zn-Air Battery-Driven Water Splitting)
This study was conducted with the support of the Future Technology Research Lab of the Nano and Materials Technology Development Project of the Ministry of Science and ICT and the National Research Foundation of Korea.
