Effect of carbonization conditions of polyaniline on its catalytic activity towards ORR. Some insights about the nature of the active sites

Abstract

N-doped carbon materials were obtained using polyaniline (PANI) as precursor. Heat treatment of PANI and de-doped PANI (PANId) was performed using different temperatures −600 and 800 °C–. Two different atmospheres were used during the treatment: an inert atmosphere (N2) and another one consisting on a slightly oxidizing mixture of gases (3000 ppm O2 in N2). The prepared materials at 800 °C showed high values of capacitance, up to 170 and 255 F g−1 in basic and acid electrolytes, respectively, in spite of their low surface area. The electrocatalytic activity towards oxygen reduction reaction (ORR) of all materials was studied in basic and acid media. The heat treated materials at 600 °C did not show a good electrocatalytic activity due to their poor electrical conductivity. On the other hand, heat-treated materials at 800 °C showed an enhanced catalytic activity due to their higher conductivity and the presence of nitrogen and oxygen functionalities in the carbon surface. Interestingly, the heat treatment at 800 °C using a slightly oxidant atmosphere produces carbon materials with much higher ORR activity which seems to be related to the larger amount of N-edge and O-edge sites. Preliminary computational studies suggest that the presence of these nitrogen and oxygen functionalities in the vicinities of the carbon atom improves the catalytic performance of N-doped carbon materials in the ORR and that two adjacent active sites can produce the O2 reduction to H2O through a 4 electrons pathway.