Synthesis and Electrochemical Behavior of Nickel Sulfide-Decorated N-Doped Carbon Nanotubes: Effect of Growth Temperature

Abstract Nitrogen-doped multi-walled carbon nanotube (N-MWCNT) hybrid materials decorated with Ni-based sulfide nanoparticles were synthesized via aerosol-assisted chemical vapor deposition using benzylamine, nickelocene, and thiophene as precursors at 900 °C and 1020 °C. The influence of growth temperature on the morphology, structure, and electrochemical behavior was systematically investigated using SEM, XRD, Raman spectroscopy, and FTIR. At 900 °C, the material consisted of thin (∼40 nm), entangled nanotubes with bamboo-like features and moderate defect density, whereas at 1020 °C, thicker filaments (∼100 nm) with smoother external surfaces and increased structural disorder were obtained. The XRD patterns revealed a broad (002) reflection associated with disordered graphitic carbon, along with Ni3C and weak reflections consistent with the NiS and NiS2 phases, whereas Raman and FTIR analyses confirmed the significant defect density and nitrogen incorporation into the carbon framework. Electrochemical characterization demonstrated that the sample synthesized at 900 °C exhibited predominantly electrical double-layer capacitive (EDLC) behavior with minor faradaic contributions. In contrast, the 1020 °C sample exhibited a shift toward mixed EDLC-pseudocapacitive behavior, associated with increased structural disorder, heterogeneous interfaces, and the presence of Ni-based sulfide nanoparticles. However, higher disorder also leads to increased charge-transfer resistance and reduced overall capacitance. The sample synthesized at 900 °C exhibited a specific capacitance of 19.9 F g−1 at 5 mV s−1 and excellent cycling stability, with an approximate 99% Coulombic efficiency after 10,000 cycles. These results highlight the critical role of synthesis temperature in tuning the balance between structural disorder, conductivity, and interfacial chemistry, providing insights into the design of hybrid carbon-based materials with tailored electrochemical properties for energy storage applications.