Cation Effects on the Acidic Oxygen Reduction Reaction at Carbon Surfaces

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• Hydrogen peroxide (H2O2) is a key green oxidant, with research focused on catalysts for the two-electron oxygen reduction reaction (2e- ORR).
• Electrolyte effects on 2e- ORR, particularly from alkali metal cations (AMCs), remain poorly understood.
• Understanding these effects is crucial for optimizing H2O2 production.

Purpose of the Study:

• To investigate the significant impact of alkali metal cations (AMCs) on carbon-based electrodes in acidic media for the 2e- ORR.
• To elucidate the mechanism behind the observed cation-induced enhancement of H2O2 production.
• To develop a refined reaction mechanism for H2O2 synthesis in the presence of AMCs.

Main Methods:

• Electrochemical characterization using a glassy carbon electrode in acidic environments.
• In situ X-ray photoemission spectroscopy (XPS) to probe surface changes.
• Density functional theory (DFT) calculations to model reaction mechanisms and intermediate stabilization.

Main Results:

• Alkali metal cations shifted the half-wave potential for 2e- ORR from -0.48 V to -0.22 V vs. RHE.
• A unique on/off switching behavior of the cation-induced enhancement was observed, dependent on the voltammetric protocol.
• Evidence suggests the potential of zero charge (PZC) plays a critical role in controlling the catalytic enhancement.
• DFT calculations indicate stabilization of the *OOH intermediate due to locally induced electric fields from AMCs.

Conclusions:

• Alkali metal cations significantly enhance H2O2 production via 2e- ORR on carbon materials.
• The catalytic enhancement is strongly linked to the potential of zero charge and cation-specific interactions.
• A refined mechanism for H2O2 production involving AMCs has been proposed, paving the way for improved electrochemical synthesis.