Step-by-step synthesis of a heteroatom-doped carbon-based electrocatalyst for the oxygen reduction reaction

A heteroatom-doped carbon-based electrocatalyst for the oxygen reduction reaction (ORR) was prepared from a hybrid zeolitic imidazolate framework (ZIF) using a step-by-step approach. A bimetallic Co,Zn-ZIF was synthesized by a microwave-assisted method and then enriched with Fe and N. The resulting ZIF was pyrolysed at 700 degrees C in an inert atmosphere, producing a complex morphology including an amorphous carbon matrix, cobalt nanoparticles and bamboo-like nanotubes. A range of techniques were used to characterize the initial ZIF and the resulting catalyst. The catalytic activity and stability of the carbon-based electrocatalyst towards the ORR were investigated by cyclic voltammetry and chronoamperometry using a rotating disc electrode (RDE) in an acidic medium. The highest electrocatalytic activity for the ORR was reached when an equal weight of commercial carbon black (Vulcan XC-72) was added to the composite. Analysis of Koutecky-Levich plots showed that the reaction followed a four-electron transfer mechanism. A durability test over 1000 cycles showed no signs of decreasing catalytic activity. This catalyst appears to be a promising material for application in fuel cells.