Self-assembled monolayers (SAM) and mixed monolayers of a redox-active nickel(LI) azamacrocyclic complex 1 show an efficient electrocatalytic activity toward the oxidation of H2O2. The cyclic voltammograms recorded at stationary and rotating disk electrodes for the electrocatalytic oxidation of H2O2 exhibit unique sharp anodic peaks of inverted "V" shape in both anodic and cathodic scans, largely depending on the concentration of the supporting electrolyte NO3- anion. The electrocatalytic oxidation of H2O2 is found to proceed via an inner-sphere electron-transfer mechanism. The local concentration of NO3- anions at the monolayer-solution interface is investigated in situ as a function of applied potential by subtractively normalized interfacial infrared reflection spectroscopy. The potential-dependent increase in the local concentration of NO3- anion at the interface, which could lead to the stabilization of the intermediates involved in the electrocatalytic oxidation of H2O2, has been speculated as the cause for the unique cyclic voltammetric behavior observed in the electrocatalytic oxidation of H2O2.