The electrochemical reduction of manganese dioxide in acidic solutions: Part III. voltammetric peak 3

Abstract

Linear sweep voltammetry in 0.0125–1.25 M H 2SO 4 on thin MnO 2 films electrodeposited onto a smooth glassy carbon (GC) substarte reveals two cathodic current peaks. The first peak, peak 1, is terminated by loss of electrical conductivity of the deposit which remains essentially as γ-MnO 2. Peak 2 occurs ≈1000 mV negative to peak 1 on a GC substrate. In 3.75–7.5 M H 2SO 4 a further peak, peak 3, previously unreported in acidic solutions is observed on GC between peaks 1 and 2. Peak 3 arises according to the following cyclic scheme: 1/2MnO 2 + 1/2Mn 2++2H +Mn 3++H 2O Mn 3++ eMn 2+ The reaction is instigated by the presence of small amounts of Mn 2+ generated previously during peak 1. The charge-transfer reaction proceeds on the GC substrate and not the MnO 2 deposit as the latter has a very low electrical conductivity after peak 1. Some thermodynamic measurements on H 2SO 4 solutions are appended to supplement the general literature.