How does metal affect N-doped carbon catalyst for oxygen reduction reaction?

Abstract

N-doped carbon (NC) catalyst for oxygen reduction reaction (ORR) is widely studied. How does metal affect NC catalyst for ORR? In this work, we reveal the real roles of metal, namely providing more active sites to enhance the ORR catalytic activity and reducing the preparation temperature, through comparing NC(0), NC(Fe) and NC(Co), where NC(0) is prepared from pyrolyzing the mixture of carbon and melamine, NC(Fe) and NC(Co) from pyrolyzing Fe(NO3)3 and Co(NO3)2 with carbon and melamine followed by acid-washing, respectively. The best preparation temperature for NC(0) is 900 °C, while for NC(Fe) and NC(Co), they are both 700 °C, much lower than that of NC(0). It is also found that NC(Fe) and NC(Co) exhibit much more positive ORR peak potential (Ep) of 0.88 V and 0.85 V, much more positive half-wave potential (E1/2) of 0.85 V and 0.83 V, than those of NC(0) (0.78 V and 0.75 V), as well as higher electron transfer number, better stability and methanol-tolerance. Based on the results of material characterizations, the better ORR catalytic performances of NC(Fe) and NC(Co) are attributed to the abundant active sites of pyrrolic N species and metal nanoparticles.