Three-dimensional interpenetrating carbon pillars via template-free HFCVD: Phase evolution-guided growth mechanism and electron transport performance

Three-dimensional (3D) interpenetrating carbon architectures are essential for high-efficiency electron transport and electrochemical applications, yet their fabrication typically relies on sacrificial templates or complex substrate pre-patterning. In this work, we report a single-step, template-free synthesis of 3D interpenetrating carbon pillars via hot filament chemical vapor deposition (HFCVD) using NiFe2O4 as catalyst. By correlating the phase transitions (probed by XRD, Raman and XPS) with morphological evolution (visualized by SEM and TEM), we demonstrate that the carbothermal reduction of NiFe2O4 proceeds through metastable Fe–Ni phases, triggering progressive catalyst fragmentation. This continuous fragmentation orchestrates a five-stage growth mechanism: (I) catalyst encapsulation and initial fragmentation, (II) base-growth carbon nanotube (CNT) initiation, (III) pillar formation with secondary nucleation, (IV) pillar coalescence and divergence, and (V) the formation of a 3D interpenetrating network. A pivotal finding is that amorphous carbon (α-C), traditionally considered an unwanted byproduct, serves as a functional structural mediator. It facilitates catalyst migration and secondary nucleation while fusing adjacent and diverging CNT-cored pillars into a mechanically robust and electrically continuous framework. Compared to non-interpenetrating controls, the 3D interpenetrating carbon pillars exhibit a lower electron field emission turn-on field and significantly enhanced electrochemical performance, highlighted remarkably by a near two-orders-of-magnitude reduction in charge transfer resistance. These results establish the coupling of progressive catalyst evolution with functional carbon deposition as a versatile principle for designing advanced carbon scaffolds.