Tailoring the Structure of Chitosan-Based Porous Carbon Nanofiber Architectures toward Efficient Capacitive Charge Storage and Capacitive Deionization

High Resolution Image Download MS PowerPoint Slide Carbon nanoarchitectures derived from biobased building blocks are potential sustainable alternatives to electrode materials generated with petroleum-derived resources. We aim at developing a fundamental understanding on the connection between the structure and electrochemical performance of porous carbon nanofiber (PCNF) architectures from the polysaccharide chitosan as a biobased building block. We fabricated a range of PCNF architectures from the chitosan carbon precursor and tailored their structure by varying the amount and molecular weight of the sacrificial pore-forming polymer poly(ethylene oxide). The morphology (high-resolution scanning electron microscopy), carbon structure (X-ray diffraction, transmission electron microscopy), pore network (N 2 gas adsorption, small-angle X-ray scattering), and surface/bulk composition (X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy) were studied in detail together with a comprehensive electrochemical analysis on the fabricated electrodes. In supercapacitor devices, the best-performing freestanding electrode had (1) a high accessible surface area ( a s,BET ≈ 700 m 2 g –1 ) and hierarchical pore network (micro- and mesopores) providing a fast ion diffusion process, high specific capacitance, and rate capability, (2) surface chemistry allowing a high Coulombic efficiency by avoiding parasitic Faradaic side reactions, and (3) a unique turbostratic carbon nanostructure leading to low charge transfer resistance while keeping good electrical conductivity. This electrode exhibited good stability over 2000 cycles (at 2 A g –1 ) with high capacitance retention (>80%) and charge efficiency (>90%). In the capacitive deionization (CDI) device, our electrode demonstrated an ultrahigh salt adsorption capacity of 23.6 mg g –1, which is among the state-of-the-art values reported for a biobased carbon. A high charge efficiency (85%) was achieved during the CDI process using low-cost materials, in contrast to similarly performing devices fabricated with expensive ion exchange membranes or petroleum-based carbon precursors. Our results demonstrate that inexpensive chitosan-based materials can be readily transformed in one carbonization step without any aggressive activating chemicals into tailor-made hierarchically ordered state-of-the-art carbon materials for charge storage devices.