Hydrogen is considered a promising clean energy carrier for sustainable energy systems. Catalytic methane decomposition (CMD) provides a COx-free pathway for hydrogen production while simultaneously generating valuable carbon nanostructures. In this study, Ni-supported activated carbon (AC) catalysts were synthesized using three different preparation methods: wet impregnation (WI), sonicated wet impregnation (SWI), and hydrothermal (H) synthesis. The catalytic performance of the prepared catalysts (30Ni/AC) was evaluated in a fixed-bed reactor at 850 °C with 40% methane (CH4) at a gas hourly space velocity (GHSV) of 12,000 mL/h.gcat. Structural and morphological properties of fresh and spent catalysts were investigated using XRD, SEM, TEM, EDX, and Raman spectroscopy. The hydrothermal catalyst exhibited the smallest Ni crystallite size (~20 nm) and the highest initial methane conversion (~77%), followed by the SWI catalyst (~73%). Both catalysts demonstrated higher hydrogen production rates and improved catalytic stability compared with the WI catalyst, which showed rapid deactivation due to larger crystallite size and carbon encapsulation. Structural analyses confirmed the formation of graphitic carbon nanotubes with varying degrees of crystallinity. Overall, the study highlights the strong influence of catalyst preparation method on metal dispersion, catalytic activity, and carbon quality during methane decomposition.
Coal tar pitch, a low-cost industrial byproduct with high carbon yield, is a superior precursor for hard carbon. Pre-oxidation and carbonization are two core procedures for pitch-derived hard carbon, yet most previous works focus on pre-oxidation while neglecting carbonization optimization. Conventional slow carbonization using a muffle furnace lacks flexibility in tailoring interlayer spacing, intrinsic defects, and closed pores, thus limiting the improvement of electrochemical performance of hard carbon. Herein, Joule heating flash carbonization is employed to treat pre-oxidized coal tar pitch at 1300 °C. This strategy effectively immobilizes pyrolytic free radicals and promotes ester group formation, meanwhile increasing structural defects, expanding the carbon interlayer spacing, enlarging the closed pore size (from 1.69 to 1.97 nm) and increasing the closed pore volume (from 0.037 to 0.122 cm3 g−1). These structural advantages collectively accelerate Na+ diffusion, enrich active adsorption sites and boost pore-filling capacity. The increased surface activity also induces more electrolyte decomposition and forms a thicker solid electrolyte interphase (SEI), leading to a slight decline in initial Coulombic efficiency (ICE). The resultant HC@F delivers a reversible specific capacity of 328.4 mAh g−1 at 0.1 C with an ICE of 83.9%, and an excellent rate performance of 245.4 mAh g−1 at 4 C, while maintaining good capacity retention of 84.3% over 2500 cycles. Multiple in-situ and ex-situ characterizations verify the “adsorption-intercalation-pore filling” sodium storage mechanism. This work reveals that flash carbonization regulates pitch-based hard carbon, offering a facile thermal strategy for high-performance, low-cost anodes in practical sodium-ion batteries.
