Activation of electrospun carbon fibers: the effect of fiber diameter on CO2 and steam reaction kinetics

Abstract

First, we present a fabrication process for electrospun carbon fiber mats with mean fiber diameters between 108 nm and 623 nm. The carbon fiber mats were produced by electrospinning of polyacrylonitrile (PAN) solutions and subsequent carbonization. The fiber mats feature small variations of their properties that are required for parameter studies. Second, we investigate the kinetics of steam and CO2 activation with three different activation temperatures and times. Both activation methods result in a surface area increase depending on activation temperature and time. Detailed analysis of the macroscopic properties burn-off, surface area, and conductivity reveals insights into the microscopic activation kinetics. The different fiber diameters of the carbon fiber mats enable the distinction of surface driven and bulk processes. Our results indicate, that CO2 activation kinetics are mass transport controlled, and that steam activation kinetics are reaction rate controlled. The turbostratic nature of PAN derived carbon and the distinct characteristics of the activation agents could explain the nonlinear behavior of the burn-off and surface area development.