Nitrogen-Doped Carbon Electrodes: Influence of Microstructure and Nitrogen Configuration on the Electrical Conductivity of Carbonized Polyacrylonitrile and Poly(ionic liquid) Blends

Abstract

In this paper, the preparation of nitrogen-doped carbon fibers and thin films from mixtures of polyacrylonitrile (PAN) and a poly(ionic liquid) (PIL) by electrospinning and dip-coating is presented, respectively, followed by carbonization at distinct temperatures. The poor processability of the PIL into sub-micrometer fibers by electrospinning—originating from its high charge density and meanwhile low glass transition temperature—is successfully circumvented by using blends of PAN and PIL. The electrospun fiber mats exhibit a high surface-to-volume-ratio with an intrinsically macroporous through-pore structure and a uniform fiber diameter after carbonization. Physicochemical characterization of the N-doped carbons by means of scanning electron microscopy, algorithmic X-Ray diffraction analysis, nitrogen physisorption, thermogravimetry, elemental analysis, energy-dispersive X-ray, and X-ray photoelectron spectroscopy gives insight into their physical and electrical structures. Impedance measurements on carbonized PIL/PAN-blends reveal high electrical conductivities up to 320 S cm−1, which are attributed to the incorporation of predominantly quaternary-graphitic nitrogen atoms into the carbon network during carbonization. The results indicate that the electrical conductance of the N-doped carbons strongly depends on the chemical environment of the inserted nitrogen atoms, the microstructural evolution of π-conjugated carbon network—which in turn correlate with the carbonization temperature—and the chemical composition.