Experimental and DFT studies of oxygen reduction reaction promoted by binary site Fe/Co–N–C catalyst in acid

Abstract

• The Fe–Co bimetallic sites were confirmed in FeCo–N–C by one-step pyrolysis. • The as-prepared catalyst achieves high ORR performance in acidic electrolytes. • The bimetallic site can result in facile cleavage of the O–O bond and thus a direct 4e − ORR process. • The FeCoNC-10 exhibits remarkable performance in DMFCs with superior methanol tolerance. The cost and efficiency issues of cathodic electrocatalyst for oxygen reduction reaction (ORR) hinder a broad application of fuel cells. Therefore, it is necessary to develop highly efficient and sustainable ORR electrocatalysts of platinum group metal-free (PGM-free). The atomically dispersed FeCoNC-10 electrocatalysts were constructed by incorporating Fe phthalocyanine (FePc) molecules into bimetallic metal–organic frameworks (BMOF) followed by one-step pyrolysis. It showed remarkable ORR activity in acidic medium compared with FeNC and CoNC catalysts. The Fe–Co bimetallic sites were confirmed in FeCo–N–C, together with abundant isolated FeN 4 and CoN 4 sites. Theoretical study revealed that the bimetallic site can enhance O 2 adsorption and elongate O–O bond length rather than FeN 4 and CoN 4 . This can result in facile cleavage of the O–O bond and thus a direct 4e − ORR process. FeCoNC-10 catalyst showed enhanced ORR stability, due to very weak Fenton-type reaction related to Co species. Membrane electrode assemblies (MEAs) consisted of the FeCoNC-10 was applied in the cathode. It showed a peak power density of 100 mW cm −2 in a direct methanol fuel cells (DMFCs) with superior methanol tolerance. This work sheds light on the mechanism of atomically dispersed Fe/Co dual-doped carbon in enhancing ORR activity and stability, which enables the cost-effective ORR electrocatalyst design to achieve robust fuel cell performance.