A study on maxima and inverted peaks in cyclic voltammetry. Electrochemical reduction of pyridine-4-aldoxime at an HMDE

Anomalous current–potential and –time curves have been observed in the electrochemical reduction of pyridine-4-aldoxime (PA) in acidic buffered solutions on a mercury electrode. Voltammetric profiles under different experimental conditions show a current maximum and/or an inverted peak, i.e. a cathodic peak current during the positive going potential scan. These phenomena, which are a function of the reactant concentration and the scan rate, indicate the occurrence of processes involving adsorption. To explain these features, mechanisms are proposed where a catalytic reduction of the H+ ion takes place via a neutral intermediate of PA adsorbed on the mercury electrode. Capacitance–potential curves and chronoamperometric measurements support the hypothesis.