Eletrocatalisadores de grafeno dopado com nitrogênio por tratamento térmico aplicados à reação de redução de oxigênio: uma investigação eletroquímica e quimiométrica

Abstract

Nitrogen-doped graphene (N-graphene) has been extensively investigated as an electrocatalyst in the Oxygen Reduction Reaction (ORR) for application in the cathode of oxygen and hydrogen supplied polymer electrolyte membrane fuel cells. Doping can be achieved by thermal treatment, a simple and easily scalable method, however, the conditions employed may affect N-graphene’s electrocatalytic activity. In this work, a central composite design was adopted to evaluate the effect of thermal treatment temperature (varied from 660 °C to 940 °C) and of the mass ratio of graphene and urea precursors (respectively varied from 1:3 to 1:17), on the electron transfer number (n) of the ORR electrocatalyzed in alkaline medium by the prepared N-graphene, and to determine the factor levels in which this response is maximized. There was no interaction effect between the factors, and only the temperature had a positive and statistically significant effect on ORR’s n value. The optimal doping condition was at 940 °C, in any of the studied mass ratios. With N-graphene prepared at this temperature, ORR exhibited n = 4, an onset potential of 0.798 V vs RHE, a half-wave potential of 0.689 V vs RHE, a kinetic current density of -4.01 mA mg-1 and a Tafel slope of 75.53 mV dec-1. This investigation represents an important step in the adoption of multivariate experimentation for the exploration of metal-free electrocatalysts for fuel cell cathodes.