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Abstract

Synthesis of carbon nanofibers suffers in classical approaches from either costs or the introduction of metallic impurities, and a more simple method of synthesis based on affordable and accessible educts would be highly welcomed. For that, we rationally designed a metal-free approach based on ketene chemistry using phosphorus pentoxide (P₂O₅) and vegetable oil. Based on the characterization of intermediates, P₂O₅-oil reaction yielded most possibly alkylketenes, which polymerized into poly(ketene) with abundant enol groups. The enol groups further reacted with P₂O₅, forcing the poly(ketene) to assemble into a nano-sized preassembly structure. Moderate heating transforms these soft assembly structures into carbonaceaus nanofibers. Moreover, this approach is applicable to other chemicals with similar structure to vegetable oil, which demonstrates the generality of methodology. The carbon nanofibers with P-O-C functionalization show relatively high graphitization degree and promising textural properties (e.g., well-developed porosity, negatively-charged surface). The C-O-P environment accounts for 66 at% of the total P and create a superior thermal stability of carbon nanofibers as compared with unfunctionalized all-carbon nanotubes. As a model application, a CDI system built of a carbon nanofibers-based electrode countered by an activated carbon-based electrode exhibited exceptional performance: a NaCl adsorption capacity ~30 mg g^-1 at applied voltage of 1.2 V was reached, with very stable adsorption-desorption cycles. This research opens a promising path to large-scale and low-cost synthesis of 1-dimensional carbon nanofibers from sustainable carbon sources without using metal catalysts or expensive equipment.