Nanoparticles of CoFeZn Supported on N-Doped Carbon as Bifunctional Catalysts for Oxygen Reduction and Oxygen Evolution

Abstract

Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are two important reactions in clean energy conversion devices. It is necessary to develop nonprecious metal-based bifunctional catalysts for ORR and OER. In this work, a multimetal bifunctional catalyst, nanoparticles of trimetallic CoFeZn supported on N-doped carbon (CoFeZn/NC), is prepared by one-step carbonizing the mixture of M-ZIFs (M = Fe, Co, and Zn), carbon black, and melamine. CoFeZn/NC has a more mesoporous structure and a higher specific surface area of 1029.6 m²/g compared to FeCo/NC, which is attributed to the easy volatilization of Zn at high temperatures. It also has high contents of pyridinic N (35.8%) and pyrrolic N (31.1%), abundant metal active sites, and exhibits strong synergistic effects between these nanoparticles of metals. Better than the single-metal catalysts (Co/NC, Fe/NC, and Zn/NC) and bimetallic catalysts (CoFe/NC, FeZn/NC, and CoZn/NC), CoFeZn/NC has an ORR peak potential of 0.90 V (vs. RHE) and a half-wave potential of 0.87 V (vs. RHE) in 0.1 M KOH solution, and exhibits excellent stability and methanol resistance. For OER, CoFeZn/NC has the lowest overpotential of 319.9 mV at a current density of 10 mA/cm² and a Tafel slope of 82.47 mV dec^–1.