Highly conductive microporous carbon fibers by electrospinning of lignin/phosphoric acid/ethanol solutions

Abstract

This contribution reports the preparation of electrospun lignin-based carbon fibers at different carbonization temperatures and the influence of heat treatments at temperatures ranging from 900 to 1600 ºC. The influence of the addition of phosphoric acid in the initial electrospinning solution on the structural ordering, electrical conductivity and porosity development of the final carbon fibers is studied in detail. Alcell lignin fibers were electrospun using a coaxial electrospinning device following the procedure previously reported by our research group. Electrospun H3PO4-lignin fibers were prepared in the same device by addition of phosphoric acid to the lignin solution using mass ratios of 0.1 and 0.3. The electrospun fibers were stabilized in air at 200 ºC, using a slow heating rate and carbonized under inert atmosphere at temperatures between 500 and 900 ºC. In addition, the fibers carbonized at 900 ºC were heat treated at temperatures between 1200 and 1600 ºC. The high temperature heat treatment removes most of the heteroatoms (O, P) for both carbon fibers. However, the surface area of the phosphorous containing carbon fibers is mostly preserved after the heat treatment, while a large porosity shrinkage is observed for the pure lignin-derived fibers. Thus, microporous carbon fibers with large electrical conductivity values have been obtained by heat treatment at 1600 ºC of P-containing electrospun carbon fibers.