Electrochemical Oscillation during H₂O₂ Reduction in Basic Solutions

Abstract

A new type of electrochemical oscillation has been found to appear as a current oscillation in the H 2 O 2 -NaOH-Pt system. The oscillation, named oscillation I, appears within the potential region where an N-shaped negative differential resistance (N-NDR) is observed. The N-NDR is attributed to the formation of under-potential deposited hydrogen (upd-H) which suppresses the reduction of HO 2 - produced from H 2 O 2 . Moreover, oscillation I also appears in the H 2 O 2 -H 2 SO 4 -Pt system when the salts such as Na 2 SO 4 and K 2 SO 4 are added to electrolytes, because the local pH at the electrode surface even in H 2 SO 4 solutions becomes basic during the H 2 O 2 reduction. Electrochemical impedance measurements indicate that oscillation I is classified into an NNDR oscillator, and also that the N-NDR plays a crucial role in the positive feedback loop in oscillation I. The surface concentration of HO 2 - plays a role as the slow process in the negative feedback loop.