Anodic H₂O₂ Generation in Carbonate-Based Electrolytes-Mechanistic Insight from Scanning Electrochemical Microscopy

Area of Science:

• Electrochemistry
• Materials Science
• Chemical Engineering

Background:

• Anodic hydrogen peroxide (H2O2) generation is influenced by electrolyte composition.
• Controversies exist regarding the specific reaction pathways and species involved in H2O2 formation.
• Water oxidation at the anode causes local acidification, potentially altering carbonate species equilibrium.

Purpose of the Study:

• To investigate the role of carbonate species in anodic H2O2 generation.
• To determine the local speciation of carbonate species near an operating anode.
• To elucidate the factors controlling local bicarbonate concentration during H2O2 formation.

Main Methods:

• Utilized shear-force scanning electrochemical microscopy (SECM) with a gold (Au) nanoelectrode for local pH measurements.
• Employed generator-collector SECM with a Au-Pt double barrel microelectrode.
• Analyzed the impact of electrolyte composition, anode potential, and bulk pH.

Main Results:

• Confirmed that bicarbonate (HCO3-) is the predominant anionic species at the anode interface during preferential H2O2 formation.
• Demonstrated that local HCO3- concentration is dependent on oxidation current, buffer capacity, and bulk pH.
• Showed that the main anionic species is HCO3- irrespective of the bulk solution pH.

Conclusions:

• Bicarbonate (HCO3-) plays a crucial role in anodic H2O2 generation.
• Local pH and electrolyte properties significantly modulate the reaction pathway for H2O2 formation.
• Understanding local speciation is vital for optimizing H2O2 production through electrolyte engineering.