Researchers reveal active-layer structure evolution for acidic oxygen

The past years have witnessed numerous attempts and approaches in developing a low-iridium loading but efficient oxygen evolution reaction (OER) electrocatalyst, most of which failed to exhibit efficient yet stable OER catalysis in acidic media.

Prof. YAN Wensheng’s research group from National Synchrotron Radiation Laboratory (NSRL), University of Science and Technology of China (USTC), cooperating with Prof. JIN Song’s group from the University of Wisconsin-Madison (UWM), jointly synthesized highly-active 1 nm IrO_x particles anchored on 9R-BaIrO₃ (IrO_x/9R-BaIrO₃) via solution calcination followed by strong acid treatment. The results revealed the structure of the active layer of IrO_x/9R-BaIrO₃ and its evolvement amid electrolyzing. This work was published in Journal of the American Chemistry Society on October 25.

The electrolysis of water plays a significant role in developing renewable clean energy technology. Compared with conventional alkaline electrolyzers, proton exchange membrane-based water electrolysis have more advantages. Iridium oxides-based electrocatalysts have become the prior material for the anodes of water electrolyzers in acidic conditions, for their excellent activity and stability. However, the high-cost and scarcity of iridium oxide greatly hinder the practical application of these precious catalysts. Therefore, finding stable electrocatalysts that provide higher activity per unit iridium mass has become the main focus.

Utilizing scanning transmission electron microscopy (STEM), synchrotron radiation-based X-ray absorption spectroscopy (XAS), and X-ray photoelectron spectroscopy (XPS), researchers found that during the electrocatalytic process, before evolving into amorphous Ir⁵⁺O_x/IrO₆ octahedrons on the surface, the initial 1 nm IrO_x nanoparticles/9R-BaIrO₃ first evolved into amorphous Ir⁴⁺O_xH_y/IrO₆ octahedrons. The high relative content of amorphous Ir⁵⁺O_x species derived from trimers of face-sharing IrO₆ octahedrons in 9R-BaIrO₃ and the enhanced metallic conductivity of the Ir⁵⁺O_x/9R-BaIrO₃ catalyst are responsible for the excellent acidic OER activity.

The results revealed the surface active-layer structure evolution in iridium-based perovskite electrocatalysts, providing new approaches for engineering superb acidic OER nanocatalysts.