Nanostructured Carbon Fibers for the Oxygen Reduction Reaction

Abstract

Despite efforts to obtain the optimal carbon electrocatalyst while taking advantage of carbon’s desirable properties, i.e. high conductivity, large surface area, and low cost, the challenge remains to create an ideal material that possesses all required properties such as durability, efficient mass-transport, anchoring sites for nucleation of nanoparticles, and catalytically active sites. In this work, we present the electrocatalytic activity of nanostructured carbon fibers (NCF) for the oxygen reduction reaction. Synthesis of NCF was achieved via a polymer templating technique of nitrogen-rich polymer (PAN) along with a rigid sacrificial polymer (Nafion®). The pyrolysis process of these precursors results in the decomposition of the sacrificial polymer resulting in the formation of intra-fiber micro/mesopores with controllable surface areas ranging from 100-1500 m2/g [1]. Our results show that depending on the porosity and surface area of the NCF, the electrocatalyst exhibits selectivity towards either the two-electron process generating hydrogen peroxide or the four-electron reduction of oxygen to water. In addition to the tunability of these materials, the controlled 3D morphology facilitating reactant and product transport, high electronic conductivity, high double layer capacitance, enhanced durability, and large concentration of heteroatom doped sites which can function as active sites or as anchors for the nucleation of metal catalyst nanoparticles make CNF an attractive alternative to replace precious metal catalysts for hydrogen peroxide production and four-electron oxygen reduction in fuel cells. 1. Tran, C. and V. Kalra, Fabrication of porous carbon nanofibers with adjustable pore sizes as electrodes for supercapacitors. Journal of Power Sources, 2013. 235: p. 289-296.