Suppressed boron doping in electrospun carbon webs from polyacrylonitrile-based polymer blends

Abstract

Boron- and nitrogen-codoped porous carbon materials derived from polyacrylonitrile-based polymer blends are of broad interest for a range of applications, from batteries to carbon capture. However, the influence of different fabrication routes, including film- and fiber-based architectures and thermal treatment conditions, on the final pore morphology, carbon structure, and heteroatom composition in direct pyrolysis remains underexplored. In this work, we investigate how fabrication approaches modulate the coupled effects of polymer blend phase separation, carbon framework evolution, and dopant incorporation on the resulting materials. Using a poly(butadiene-co-acrylonitrile) (BAN)/poly(styrene-co-acrylonitrile) (SAN) precursor system with benzene-1,4-diboronic acid (BDBA) as the boron source, we compare spin-coated films and electrospun fibers while varying thermal processing conditions through rapid thermal annealing. This approach enables systematic deconvolution of how different fabrication routes and thermal processing together govern the structural and compositional outcomes. We find that during the stabilization stage, polyacrylonitrile (PAN) cyclization establishes a kinetic competition with both phase separation and dopant incorporation in the polymer blend, which strongly influences the pore morphology and heteroatom incorporation. Meanwhile, differences in sample geometry between films and fibers contribute to higher boron concentration in film, which could result from distinct dopant condensation behaviors. Specifically, BDBA can undergo condensation reactions (e.g. boroxine-like network formation) that may reduce the amount of boron available for incorporation, while the resulting network can simultaneously reduce structural collapse and retain better fibrous architecture. Our findings highlight the need to carefully consider processing conditions, as they play a critical role in shaping the final structure and dopant incorporation during pyrolysis, thereby providing guidelines for rational design of multicomponent polymer-derived porous carbons.