Cobalt Nanoparticles Embedded in Porous Carbon Nanofibers As Bifunctional Electrocatalysts for Oxygen Reduction and Evolution Reactions

Abstract

Increasing demand for clean and sustainable energy has accelerated research on alternative energy production and storage systems with high efficiency, low cost, and environmental benignity. Various renewable energy technologies such as fuel cells, metal-air batteries, and water splitting require efficient catalysts for oxygen reduction and evolution reactions. In the past, various precious (expensive) and non-precious metal catalysts have been studied as efficient ORR or OER catalysts, while only a few studies have reported bifunctional catalysts for both ORR and OER. Hence, it is highly challenging and desirable to develop low cost and bifunctional catalyst with high ORR and OER activity. In the present study, cobalt nanoparticles embedded in porous carbon nanofibers have been reported as an efficient bifunctional electrocatalyst for both ORR and OER in alkaline medium. The polymer solution consisting of polyacrylonitrile (as carbon precursor), Nafion (as sacrificial polymer) and cobalt carbonate (as cobalt precursor) in DMF was electrospun to form nanofibers. During pyrolysis to 1000 °C in inert atmosphere, Nafion decomposes out to form porous carbon nanofibers, while cobalt carbonate reduces to cobalt oxide. Cobalt oxide is further reduced to cobalt by reduction in hydrogen at 500 °C. Thus, a stable, synergistic catalyst combining the high ORR activity of porous carbon nanofibers and the excellent OER activity of cobalt nanoparticles is obtained. The electrochemical tests on the fabricated materials were carried out using a rotating disc electrode setup. It was found that the hybrid catalyst exhibits comparable ORR activity to a commercial carbon-supported precious Pt catalyst (20wt% on Vulcan carbon) and improved OER activity than 20wt%Ir/C and 20wt% Ru/C in alkaline solutions. Such a high activity is attributed to the uniform distribution of cobalt nanoparticles within the porous carbon nanofiber matrix providing high surface area and efficient charge transfer ability. Fig. 1. Comparison of ORR and OER activities of cobalt-porous carbon nanofibers (Co-PCNFs) with that of commercial Pt/C. *Singhal, R. and Kalra, V. Electrospun porous carbon nanofibers embedded with cobalt nanoparticles as an excellent bifunctional electrocatalyst for oxygen reduction and evolution reactions, to be submitted . Figure 1