Strengthening polyacrylonitrile-based carbon nanofibers via a hydrolysis-induced low-energy-barrier cyclization reaction

Abstract

Electrospun polyacrylonitrile (PAN) nanofibers have been widely used as a precursor to fabricate high-quality carbon nanofibers (CNFs). However, the low degree of cyclization and breakage of fibers during the stabilization process severely restrict the mechanical properties of the final CNFs. In this work, we propose a novel strategy to enhance the cyclization by introducing carboxyl groups via hydrolysis. This treatment significantly reduces the cyclization energy barrier by facilitating an ionic pathway rather than a radical pathway. As a result, the degree of stabilization effectively increases from ∼45% to over 60%. Simultaneously, the cyclization temperature also reduces from 288 to 260 °C, corresponding to a gentler cyclization reaction, that can avoid stress concentration and thus eliminate the fiber breakage during heat treatments. These features lead to a remarkable enhancement on the tensile strength for CNF films, from 26.0 to 70.4 MPa. This hydrolysis-based stabilization optimization provides a straightforward method to strengthen CNFs, thereby extending their applications.