Abstract
The growing adoption of biobased materials for electronic, energy conversion, and storage devices has relied on high-grade or refined cellulosic compositions. Herein, lignocellulose nanofibrils (LCNF), obtained from simple mechanical fibrillation of wood, are proposed as a source of continuous carbon microfibers obtained by wet spinning followed by single-step carbonization at 900 °C. The high lignin content of LCNF (∼28% based on dry mass), similar to that of the original wood, allowed the synthesis of carbon microfibers with a high carbon yield (29%) and electrical conductivity (66 S cm–1). The incorporation of anionic cellulose nanofibrils (TOCNF) enhanced the spinnability and the porous morphology of the carbon microfibers, making them suitable platforms for electrochemical double layer capacitance (EDLC). The increased loading of LCNF in the spinning dope resulted in carbon microfibers of enhanced carbon yield and conductivity. Meanwhile, TOCNF influenced the pore evolution and specific surface area after carbonization, which significantly improved the electrochemical double layer capacitance. When the carbon microfibers were directly applied as fiber-shaped supercapacitors (25 F cm–3), they displayed a remarkably long-term electrochemical stability (>93% of the initial capacitance after 10 000 cycles). Solid-state symmetric fiber supercapacitors were assembled using a PVA/H2SO4 gel electrolyte and resulted in an energy and power density of 0.25 mW h cm–3 and 65.1 mW cm–3, respectively. Overall, the results indicate a green and facile route to convert wood into carbon microfibers suitable for integration in wearables and energy storage devices and for potential applications in the field of bioelectronics.
Highlights
Renewable resources are attractive alternatives for the growing demand of carbon fibers (CFs).[1]
Recent studies indicated cellulose nanofibrils (CNF) as possible precursors that require no dissolution for wet spinning, representing a simple, low cost, and eco-friendly technique.[5−8] In this process, aqueous suspensions of CNF are extruded into a coagulation bath comprising either an organic solvent or aqueous solutions.[9]
The present work is motivated by the fact that a high lignin concentration facilitates high carbonization yield while hemicelluloses and cellulose introduce porosity features in the resultant carbon microfibers and remove the need for thermal stabilization
Summary
Renewable resources are attractive alternatives for the growing demand of carbon fibers (CFs).[1]. Supercapacitors store energy either by electrochemical double layer capacitance (EDLC), via reversible ion adsorption/desorption or by pseudocapacitance (PC), via surface redox reactions Owing to their high conductivity and porous morphology, the LCNF/ TOCNF-derived carbon microfibers are suitable for EDLC. Coupling the synthesized, porous carbon microfibers with conductive polymers or metal-oxides in core−shell device configurations is expected to lead to gains in pseudocapacitance
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