A research team led by Hee-Tak Kim of the Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science & Technology (KAIST), in a joint study with Gisu Doo of the Korea Institute of Energy Research (KIER), has developed a platinum-free water electrolysis technology.
Water electrolysis, which splits water into hydrogen and oxygen using electricity, is recognized as an eco-friendly hydrogen production method. Specifically, proton exchange membrane water electrolysis (PEMWE) is considered a next-generation hydrogen production technology due to its ability to produce high-purity hydrogen at high pressure. However, it has faced limitations in commercialization due to its reliance on expensive precious metal catalysts and coating materials. In response, Korean researchers have developed an alternative approach aimed at overcoming these technical and economic limitations.
As disclosed, the researchers focused on the primary reason why iridium oxide (IrOx), a highly active catalyst for water electrolysis electrodes, fails to perform optimally, and found that this is due to inefficient electron transfer. The team reportedly demonstrated that performance can be maximized by controlling the catalyst particle size.
KAIST said that this study revealed that the reason iridium oxide catalysts do not exhibit excellent performance without platinum coating is due to “electron transport resistance” that occurs at the interface between the catalyst, the ion conductor (ionomer), and the titanium (Ti) substrates.
Specifically, the researchers identified that the ‘pinch-off’ phenomenon, where the electron pathway is blocked between the catalyst, ionomer, and titanium substrate, is the critical cause of reduced conductivity, KAIST noted, adding: “The ionomer has properties close to an electron insulator, thereby hindering electron flow when it surrounds catalyst particles. Furthermore, when the ionomer comes into contact with the titanium substrate, an electron barrier forms on the surface oxide layer of the titanium substrate, significantly increasing resistance.”
To address this, the team reportedly fabricated and compared catalysts of various particle sizes, and as claimed, “demonstrated, for the first time globally, that when iridium oxide catalyst particles with a size of 20 nanometers (nm) or larger are used, the ionomer mixed region decreases, ensuring an electron pathway and restoring conductivity.”
It is understood that the researchers also adjusted the interfacial structure through controlled design modifications. KAIST said: “This achievement demonstrated that the previously unavoidable trade-off between catalyst activity and conductivity can be overcome through meticulous interfacial design.”
According to the institute, the findings may represent a step forward “not only for the development of high-performance catalyst materials but also for the future commercialization of proton exchange membrane water electrolysis systems that can achieve high efficiency while reducing the amount of precious metals used.”
Hee-Tak Kim stated: “This research presents a new interface design strategy that can resolve the interfacial conductivity problem, which was a bottleneck in high-performance water electrolysis technology. By securing high performance even without expensive materials like platinum, it will be a stepping stone closer to realizing a hydrogen economy.”