Nitrogen-doped nanotube production using hematite-quartz-nickel as catalysts and their application in hydrogen generation

Abstract

Nitrogen-doped multiwalled carbon nanotubes (N-MWCNTs) were synthesized via aerosol-assisted catalytic chemical vapor deposition (AAC-CVD) using earth-abundant catalysts composed of hematite, quartz, and varying amounts of nickel. The effects of nickel concentration and synthesis temperature (750–950 °C) were systematically evaluated to optimize the structural, morphological, and electrochemical properties of the resulting nanomaterials. The CT2-Ni catalyst (9 wt % Ni) demonstrated the highest production efficiency, reaching ∼280 %, and promoted the growth of thin entangled nanotubes with average diameters as low as 35.5 nm. Raman spectroscopy revealed significant structural disorder at lower temperatures (I_D/I_G = 0.93 for CT1-750), which correlated with enhanced catalytic activity. Electrochemical measurements showed that N-MWCNTs synthesized at 750 °C delivered high current densities of >100 mA cm⁻² at −0.6 V vs. RHE, supported by favorable electrochemical parameters such as low charge-transfer resistance (22.9 Ω) and high double-layer capacitance (5.25 mF cm⁻²). These results highlight the synergistic effect between Ni doping and defect engineering in optimizing the HER activity. The materials developed in this study offer a scalable and cost-effective alternative to noble-metal-based catalysts, bridging the gap between fundamental research and industrial hydrogen production. This study confirms that a strategic catalyst design using common oxides can drive sustainable energy solutions.