Highly nitrogen-doped graphitic carbon fibers from sustainable plant protein for supercapacitor

Abstract

In this research, a novel biomass-based, highly nitrogen-doped carbon fiber material has been synthesized from electrospun plant protein fibers by one-step carbonization. The material fibrous structure was well maintained during pyrolysis by incorporating Ca2+ in the protein fiber matrix, since Ca2+ increased the thermal stability of the protein and the calcium salt/oxide provided a solid support during pyrolysis. In addition, the calcium salt served as a template to generate pores on the carbon samples. X-ray photoelectron spectra showed that the fibrous carbon materials possessed large nitrogen content (7.5%), mainly in the form of pyridonic/pyrrolic and pyridinic nitrogen. The optimized sample P-10% Ca-CL exhibited an interconnected carbon fiber network with meso and micropores on the fiber surface. Moreover, the well aligned granular graphitic structure observed embedded within the carbon fibers, which has been found for the first time from biomass derived carbon fiber materials. The optimized carbon fibers (P-10% Ca-CL) showed an exceptional areal specific capacitance of 64 μF/cm2 at 0.5 A/g. This is attributed to the large number of N functional groups which induced a pseudocapacitance and improved the wettability of the carbon surface. The carbon fibers also exhibited excellent cyclic stability with 98% retention after 5000 cycles at a current density of 10 A/g. This research is the first publication of highly N-doped carbon fibers derived from plant proteins and show potential to be used as a supercapacitor electrode. Additionally, these materials were prepared by a convenient and environmentally-friendly method, not requiring a large energy input or corrosive chemicals.