Electrochemical synthesis of metal–polypyrrole composites and their activation for electrocatalytic reduction of oxygen by thermal treatment

This work presents a new approach for synthesis of oxygen reduction catalysts constituted of a transition metal, nitrogen and carbon, by thermal treatment of electrochemically synthesized metal–polypyrrole (M–PPy) composites on glassy carbon electrodes. The synthesis procedure involves immobilization of PPy on glassy carbon followed by dosing of metal (M = Mn, Fe and Co) particles, alternately, by electropolymerization and electrochemical reduction respectively. Electrochemical characterization by cyclic voltammetry (CV) and hydrodynamic rotating disk electrode (RDE) measurements show that the M–PPy composites inherently catalyse the electroreduction of oxygen under acidic conditions. The activity of the composites is significantly augmented when they are heat treated at high temperatures (450–850 °C) under a continuous flow of nitrogen. The presence of metallic entities within the M–PPy composite structures and in the structures ensuing after heat treatment was confirmed by energy dispersive X-ray (EDX) analysis.