Architecting One-Dimensional Hierarchical Porous Carbon Nanofibers via NaHCO ₃ -Mediated Activation: Mechanism Elucidation of Tunable Micro/Mesoporous Structure

Achieving precise control over the pore architecture of carbon nanofibers (CNFs) remains a significant challenge in materials science for applications in the fields of energy storage and environmental remediation. This study introduced an innovative template-free approach for systematically engineering hierarchical porous carbon nanofibers (PCNFs) through the copyrolysis of the preoxidized polyacrylonitrile/polyvinylpyrrolidone nanofiber with a NaHCO₃ activator at 700-900 °C. The Brunauer-Emmett-Teller specific surface area of the PCNF exhibited a significant enhancement from 739 to 3574 m² g^-1 with elevated thermal treatment temperatures. These values substantially exceeded those of the pristine CNF with a relatively low surface area of 11.3 m² g^-1. Moreover, the mesopore density in PCNF correlated positively with pyrolysis temperature, accompanied by tunable pore sizes. Powder X-ray diffraction, Raman spectroscopy, and thermogravimetric-mass spectrometry analyses elucidated the intricate pore formation mechanisms. The NaHCO₃ activator demonstrated dual functionality in generating CO₂/H₂O vapor phases and facilitating carbon matrix rearrangement, enabling precise tuning of micro- and mesoporous structures through controlled pyrolysis. Comparative experiments with different activating agents confirmed the unique role of NaHCO₃. This work will provide insight into NaHCO₃-mediated activation mechanisms and guide future developments in hierarchical PCNF-based materials for energy and environmental applications.