Reactive oxygen species in iridium-based OER catalysts

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• Hydrated amorphous iridium oxyhydroxides (IrO₂) show enhanced activity in the oxygen evolution reaction (OER) compared to crystalline rutile-type IrO₂.
• Previous research focused on the metal oxidation state as the primary reason for this activity difference.

Purpose of the Study:

• To investigate the role of oxygen's electronic structure in the OER activity of amorphous IrO₂.
• To elucidate the nature of the reactive species responsible for the higher catalytic performance.

Main Methods:

• Synchrotron-based X-ray photoemission and absorption spectroscopies.
• Ab initio calculations.
• Microcalorimetry.

Main Results:

• Holes in the O 2p states of amorphous IrO₂ create a weakly bound oxygen species.
• This species is highly susceptible to nucleophilic attack and reacts with CO at room temperature.
• Amorphous IrO₂ exhibits a dynamic framework allowing for flexible Ir oxidation states.

Conclusions:

• The OER activity of amorphous IrO₂ is intrinsically linked to the electronic structure of oxygen, not solely the metal's oxidation state.
• The identified weakly bound oxygen acts as an electrophilic species crucial for O-O bond formation during OER.
• The dynamic Ir framework facilitates the formation of this active electrophilic oxygen species.