Carbon nanotube formation via catalytic methane pyrolysis over molten NiMoCu-Bi catalysts

Methane is a direct carbon source for carbon nanotube (CNT) growth, yet molten catalytic media in methane pyrolysis have rarely been designed to control carbon morphology, product recovery and graphitic quality. Here we use compositionally tuned NiMoM-Bi molten alloys to direct methane-derived carbon toward recoverable, graphitized CNTs. Screening 29 NiMoM-Bi alloys at 1050 ℃ showed selective CNT formation: only six produced CNTs, whereas most yielded amorphous carbon or graphitic flakes. The six compositions were Ni 9 Mo 3 -Bi, Ni 15 Mo 5 -Bi, Ni 12 Mo 4 Cu 4 -Bi, Ni 9 Mo 3 Mn 3 -Bi, Ni 12 Mo 4 Mn 2 -Bi and Ni 12 Mo 4 Mn 5 -Bi. In follow-up temperature tests, Ni 12 Mo 4 Cu 4 -Bi and three Mn-containing alloys formed CNTs across 800–1050 ℃. Ni 12 Mo 4 Cu 4 -Bi gave the most ordered product at 900 ℃ (I D /I G = 0.31). The CNTs showed diameters of 6–16 nm with a mean value of 10.53 nm, and high-resolution transmission electron microscopy (HRTEM) confirmed hollow graphitic tubes with interlayer spacings of 0.342–0.344 nm. HRTEM, elemental mapping and molecular dynamics simulations support a base-growth mechanism in which Cu-containing alloy particles stabilize the tubular carbon framework and suppress metal encapsulation at tube tips. After acid purification, the recovered CNTs retained 324.12 mAh g −1 after 150 cycles at 0.2 A g −1 as sodium-ion battery anodes. At 900 ℃, Cu addition increased the hydrogen production rate by approximately 39% relative to the matched Cu-free alloy.