Green hydrogen has gained significant importance in recent years as part of efforts to achieve a decarbonized economy. It is produced without the use of fossil fuels or carbon dioxide emissions. However, the high production cost of water electrolysis devices, which are used to produce green hydrogen, has hindered its economic feasibility.
Addressing this challenge, a research team led by Dr. Hyun S. Park and Sung Jong Yoo from the Hydrogen and Fuel Cell Research Center at the Korea Institute of Science and Technology (KIST) has made a breakthrough. They have developed a technology that significantly reduces the reliance on precious metals like platinum and iridium in the electrode protection layer of polymer electrolyte membrane water electrolysis devices, while maintaining performance and durability.
Unlike previous studies that focused on reducing the amount of iridium catalyst while still using substantial amounts of platinum and gold in the electrode protection layer, the researchers replaced the precious metal with a cost-effective alternative: iron nitride. This material has a large surface area, and a small amount of iridium catalyst is uniformly coated on top of it. This innovation greatly enhances the economic efficiency of the electrolysis device.
The polymer electrolyte membrane water electrolysis device is responsible for producing high-purity hydrogen and oxygen by decomposing water using electricity from renewable sources like solar power. It plays a crucial role in supplying hydrogen to various industries, including steelmaking and chemicals. Moreover, it enables the conversion and storage of renewable energy as hydrogen, making the economic efficiency of this device vital for the realization of a green hydrogen economy.
In a typical electrolysis device, two electrodes are responsible for producing hydrogen and oxygen. The oxygen-generating electrode, which operates in a harsh and corrosive environment, is typically coated with 1 mg/cm2 of gold or platinum as a protective layer to ensure durability and efficient production. On top of that, 1-2 mg/cm2 of iridium catalyst is applied. However, the scarcity and limited production of these precious metals pose a significant challenge for the widespread adoption of green hydrogen production devices.
To address this issue and improve the cost-effectiveness of water electrolysis, the research team devised a solution. They replaced the precious metals, gold and platinum, used as a protective layer for the oxygen electrode in polymer electrolyte membrane hydrogen production devices with a more affordable alternative: iron nitride (Fe2N).
The team developed a composite process for this purpose. Initially, the electrode is uniformly coated with iron oxide, which has lower electrical conductivity. Then, the iron oxide is converted to iron nitride, thereby enhancing its conductivity. Additionally, the team devised a method to uniformly apply a 25-nanometer-thick iridium catalyst layer on top of the iron nitride protective layer. This resulted in a significant reduction in the amount of iridium catalyst required, bringing it down to less than 0.1 mg/cm2. As a result, the electrode demonstrated high efficiency in hydrogen production and durability.
By replacing the gold or platinum protective layer with non-precious metal nitrides while maintaining similar performance to existing commercial electrolysis units, and reducing the iridium catalyst amount to just 10% of the current level, the team achieved a notable breakthrough. Furthermore, the new components were subjected to over 100 hours of operation to verify their initial stability.
According to Dr. Hyun S. Park from KIST, it is crucial to reduce the amount of iridium catalyst and explore alternative materials for the platinum protective layer in order to make polymer electrolyte membrane green hydrogen production devices economically viable and widely accessible. The substitution of platinum with cost-effective iron nitride holds significant importance in this regard. Dr. Park further added that they will continue to assess the performance and durability of the electrode and aim to implement it in commercial devices in the near future.
The research findings have been published in the online edition of the journal Applied Catalysis B: Environmental.
Source: National Research Council of Science & Technology