Electrolyte-Dependent Oxygen Evolution Reactions in Alkaline Media: Electrical Double Layer and Interfacial...

Area of Science:

• Electrochemistry
• Materials Science
• Surface Chemistry

Background:

• Traditional electrocatalysis models focus on inner-sphere covalent or electrostatic interactions.
• The alkaline oxygen evolution reaction (OER) is critical for energy conversion technologies.
• Interfacial ion behavior in alkaline electrolytes remains incompletely understood.

Purpose of the Study:

• To investigate the role of interfacial structure and ionic interactions in alkaline OER.
• To elucidate the influence of supporting electrolytes on OER mechanisms.
• To identify reliable methods for quantifying active sites in OER.

Main Methods:

• Electrochemical measurements in varying KOH and NaNO3 concentrations.
• Analysis of interfacial ion adsorption and mobility.
• Comparison of pseudocapacitive and electrical double-layer (EDL) charging for active site quantification.
• Durability testing in a liquid alkaline electrolyzer.

Main Results:

• Iridium oxide (IrO2) activity increases significantly with KOH concentration, highlighting inner-sphere OH- adsorption.
• Na+ in the outer interfacial layer forms stronger noncovalent interactions with OH- than K+, reducing OH- mobility.
• Pseudocapacitive behavior is proposed as a more reliable measure of OER active sites than EDL capacitance.
• Interfacial oxygen transport improves with electrolyte conductivity, suggesting increased accessible active sites.
• Addition of NaNO3 to KOH degrades OER activity and long-term stability.

Conclusions:

• Outer-sphere adsorption plays a critical, often overlooked, role in alkaline OER.
• Pseudocapacitive measurements offer a more accurate assessment of active sites for OER.
• Electrolyte composition and conductivity profoundly affect OER performance and durability.
• These findings advance mechanistic understanding for designing efficient and robust OER electrocatalysts.