KAIST advance water electrolysis technology

Hydrogen is gaining attention as a clean energy source that emits no carbon. Among various methods, water electrolysis, which splits water into hydrogen and oxygen using electricity, is recognised 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, existing PEMWE technology has faced limitations in commercialisation due to its heavy reliance on expensive precious metal catalysts and coating materials. Korean researchers have now proposed a new solution to address these technical and economic bottlenecks.

The research team focused on the primary reason why iridium oxide (IrOx), a highly active catalyst for water electrolysis electrodes, fails to perform optimally. They found that this is due to inefficient electron transfer and, for the first time, demonstrated that performance can be maximised simply by controlling the catalyst particle size.

In this study, it was 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 (hereinafter referred to as ionomer), and the Ti (titanium) substrate – core components inherently used together in water electrolysis electrodes.

Specifically, they 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. 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 research team fabricated and compared catalysts of various particle sizes. Through single-cell evaluation and multiphysics simulations, they demonstrated that when iridium oxide catalyst particles with a size of 20 nm or larger are used, the ionomer mixed region decreases, ensuring an electron pathway and restoring conductivity.

Moreover, they optimised the interfacial structure through precise design, simultaneously ensuring both reactivity and electron transport. This achievement demonstrated that the previously unavoidable trade-off between catalyst activity and conductivity can be overcome through meticulous interfacial design.

This breakthrough is expected to be a significant milestone not only for the development of high-performance catalyst materials but also for the future commercialisation of PEMWE systems that can achieve high efficiency while drastically reducing the amount of precious metals used.

Professor 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 realising a hydrogen economy.”

This research, with Jeesoo Park, a Ph.D. student from the Department of Chemical and Biomolecular Engineering at KAIST, as the first author, was published on 7 June 2025 in 'Energy & Environmental Science', an international journal in the energy and environmental fields. (Paper title: On the interface electron transport problem of highly active IrOx catalysts, DOI: 10.1039/D4EE05816J).

This research was supported by the New and Renewable Energy Core Technology Development Project of the Ministry of Trade, Industry, and Energy.

Read the article online at: https://www.globalhydrogenreview.com/hydrogen/12062025/kaist-develop-water-electrolysis-technology/