Mechanistic Insights into Surfactant-Modulated Electrode-Electrolyte Interface for Steering H₂O₂ Electrosynthesis

Area of Science:

• Electrochemistry
• Surface Science
• Materials Chemistry

Background:

• Electrocatalytic reactions rely on proton-coupled electron transfer at the electrode-electrolyte interface.
• Interfacial proton transfer is typically mediated by a water-dominated hydrogen-bond network.
• Modulating this hydrogen-bond network offers a novel strategy for controlling electrocatalytic pathways.

Purpose of the Study:

• To investigate the use of quaternary ammonium salt cationic surfactants as electrolyte additives.
• To enhance the selectivity of the oxygen reduction reaction (ORR) towards hydrogen peroxide (H2O2) production.
• To understand the role of the interfacial hydrogen-bond network in this process.

Main Methods:

• In situ vibrational spectroscopy to probe interfacial species and interactions.
• Molecular dynamics calculations to simulate interfacial behavior and hydrogen-bond network dynamics.
• Electrochemical measurements to assess ORR selectivity and kinetics.

Main Results:

• Quaternary ammonium salt surfactants adsorb irreversibly on the electrode surface under applied bias.
• Surfactant adsorption weakens the interfacial hydrogen-bond network.
• This weakening decreases interfacial proton transfer kinetics, particularly at high potentials.
• The 4-electron ORR pathway is suppressed, favoring the 2-electron pathway to H2O2.

Conclusions:

• Modulating the interfacial hydrogen-bond network using surfactant additives is an effective strategy to enhance H2O2 selectivity in ORR.
• Surface adsorption of surfactants can tune interfacial proton transfer kinetics.
• This approach offers a new avenue for controlling water-involved electrochemical reactions.