Understanding How Heat Treatment Enhances the Oxygen Evolution Fe-based Catalyst “β-FeOOH(Cl)” Activity

A study conducted by Takeshi Uyama et al. in collaboration with Kyushu Institute of Technology was published in Chemistry of Materials.

The oxygen evolution reaction (OER) is an important electrochemical process which drives water splitting for hydrogen production and metal–air battery, and other energy conversion systems.
Iron-based materials are attractive OER catalysts because of the natural abundance of iron, but most of them are only stable under alkaline conditions, limiting their practical applications.
Our group developed β-FeOOH(Cl), a unique Fe-based catalyst that exhibits high activity after heat treatment at approximately 200℃ even in neutral solutions.

To clarify the origin of this activation, we conducted synchrotron-based X-ray diffraction measurements in combination with various spectroscopic analyses.
We found that β-FeOOH(Cl) transforms into a Cl-enriched intermediate phase upon heat treatment.
This phase remains stable during the OER and facilitates smooth transport of electrons and chloride ions, as further supported by theoretical calculations.
This enhanced conductivity is a key factor behind the high performance of β-FeOOH(Cl).
These findings provide important guidelines for designing novel Fe-based catalysts that can operate efficiently in a wide range of conditions. The present study was supported by the Uncharted Territory Challenge 2050 Program of the New Energy and Industrial Development Organization (NEDO), Japan.

Title: Role of Chloride Ions in the Heat Treatment of β-FeOOH(Cl) Catalysts to Enhance the Oxygen Evolution Reaction Activity
Authors: Uyama, T., Noda, Y., Suzuki, M., T., Sekizawa, K., Sakamoto, N., Nonaka, T., Morikawa, T.
Journal Name: Chemistry of Materials
Published: April 21, 2025
https://doi.org/10.1021/acs.chemmater.5c00128