Electrospun Polyacrylonitrile, Styrene–Acrylonitrile Copolymer and Carbon Nanotube Composite Fiber Based Oxygen Reduction Catalysts

Abstract

An ever increasing worldwide energy demand drives the need for the development of more efficient and greener energy production and storage technologies.1 In recent years, one-dimensional nanofibrous materials (NFMs) have drawn a lot of attention and been widely studied to address these topical problems. For example, the electrospun NFMs can be employed as an oxygen reduction reaction (ORR) catalyst at the fuel cell cathode. The NFMs are appealing because of their attractive properties e.g. high specific surface area, high length/diameter ratio, specific porosities and multiple functionalities. For the preparation of NFMs, a simple and versatile technique called electrospinning can be applied.2 In our previous study of NFMs, we investigated pyrolyzed electrospun multiwall carbon nanotube (MWCNT) and styrene-acrylonitrile copolymer (SAN) fiber materials as ORR catalysts in alkaline solution. It was found that during the thermal decomposition of SAN, the ORR-active N-functionalities can be embedded into the carbon nanomaterial.3 For further optimization of the catalyst material ORR activity, another nitrogen-containing polymer (polyacrylonitrile, PAN) was incorporated into the NFM composition to study the ORR performance of three-component composite material (SAN/PAN/MWCNT) in our latest work regarding NFMs.4 The ORR performance of SAN/PAN/MWCNT-based catalysts was evaluated in 0.1 M KOH solution by rotating disk electrode and linear sweep voltammetry methods. The catalyst with the highest activity toward the ORR was prepared via pyrolysis at 1100 °C (SAN/PAN/MWCNT-1100) and this material outperformed the best electrospun two-component, SAN and MWCNT, composite fiber-based catalyst from our previous study.3 For physical characterization of the materials, scanning electron microscopy (SEM), X–ray photoelectron spectroscopy (XPS), Raman spectroscopy and N2 adsorption-desorption studies were performed. The structure of the catalysts is nanofibrous with visible MWCNTs according to the SEM images (Figure 1a). The high ORR activity of the catalysts prepared in this work is most likely attributed to the nitrogen species as determined by XPS. The catalyst SAN/PAN/MWCNT-1100 also showed good stability during long-term testing in 0.1 M KOH solution (Figure 1b).4 The material with the highest ORR performance used in the present study (SAN/PAN/MWCNT-1100) is a promising catalyst for the development of efficient cathode catalysts for low-temperature fuel cells.4