In situ ESR spectro-electrochemical investigation of the superoxide anion radical during the electrochemical O2 reduction reaction in aprotic electrolyte

For the first time, electrochemically generated superoxide ions on a porous carbon electrode are investigated by means of in situ electrochemical ESR technique at ambient conditions. Superoxide ions (O2·−) are detected as the product of the electrochemical O2 reduction reaction. The redox couple (O2/O2·−) is reversible in DMSO electrolyte. The superoxide ions are believed to be absorbed and de-mobilized on the carbon surface. Overlapping a symmetric carbon ESR signal, the anisotropic signal of the superoxide is observed. The g-factor of the carbon ESR spectra is found to be 2.0025, which is almost identical to that of a free electron; Anisotropic g-factors for the O2·− are g⊥ = 2.0031, g// = 2.0750.