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

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. [Display omitted] •An ionic cyclization is realized by introducing carboxyl groups via hydrolysis.•The stabilization becomes more efficient, with a cyclization degree higher than 60 %.•Fiber breakage phenomenon is greatly suppressed to ensure high mechanical properties.•The highest tensile strength of carbon nanofiber films is up to 70.4 MPa.