In-Situ and Real-Time Monitoring of Oxygen Evolution during Kolbe Reaction by Scanning Electrochemical Microscopy

Abstract

In this study, the oxygen evolution during the Kobe reaction was in-situ and real-time monitored by scanning electrochemical microscopy (SECM) in tip-generation substrate-collection (TG/SC) mode. A typical Kolbe reaction involving the acetate electro-oxidation was used as a study model. To this end, the TG/SC method of acetate electro-oxidation was performed at a 10 μm-diameter tip Pt disk microelectrode positioned ~1.2 μm away from a 50 μm-diameter substrate Pt disk microelectrode. The substrate Pt was employed as an efficient catalyst to monitor the byproduct O2 produced at the tip by the catalytic reduction at an appropriate electrode potential. The linear scanning voltammetry (LSV) results indicated that O2 evolution during acetate oxidation depended on both the electrode potential and acetate concentration. At low potentials (<2.4V vs. Ag/AgCl), the current of O2 evolution dominated the acetate oxidation reaction in 0.1 M HClO4 electrolyte, while O2 evolution was inhibited at the joint condition of higher potentials (>2.4V) and elevated concentrations of acetate, resulting in better current efficiencies of acetate oxidation. The inhibition effect of O2 evolution was also confirmed in alkaline electrolytes, consistent with the reported literature dealing with other traditional detection techniques. In sum, the proposed detection technique based on in-situ and real-time dynamic monitoring of oxygen evolution was accurate and sensitive, thereby promising for the study of broad range of reactions involving the generation of oxygen species.