Abstract
The growing need for efficacious, affordable, and sustainable energy storage devices has intensified research into supercapacitors (SCs). SCs, proposed as a replacement for lithium-ion batteries, can supply high power density (Pd) with quick charge/discharge. These energy storage devices rely on electrode materials to deliver excellent electrochemical results. While nickel oxide/carbon nanotubes (NiO/CNT) composites have been comprehensively studied, many prior works utilized complex and/or expensive synthesis techniques. This study bridges this gap by employing spray pyrolysis (SP), an affordable and mass-producible approach, to synthesize NiO/CNT electrodes for SC applications. The samples were annealed at 350, 400, and 500 ℃ after deposition on glass substrates. Characterization techniques, including X-ray diffraction (XRD), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), N2 adsorption/desorption, X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS), were used to analyze the structural, morphological, and electrochemical properties of the synthesized materials. XRD data verified the formation of crystalline cubic NiO in the pristine and composite materials. CNT’s graphitic plane was present in all composites, confirming the successful composite formation. SEM revealed that the NiO/CNT nanocomposites possessed a uniform, crack-free morphology with interconnected and compact NiO/CNT nanoparticles, in contrast to the sparse and rough surfaces of NiO nanoparticles with apparent voids. FTIR peaks showed the presence of Ni-O bonds with carbon functional groups, indicating the successful blend of the metal oxide and carbon material. The materials’ pseudocapacitive properties were validated by CV findings. Notably, the NiO and NiO/CNT materials annealed at 400 ℃ (400-NiO and 400-NiO/CNT) showcased superior electrochemical energy storage capabilities amongst the fabricated electrodes. At 5 A g-1, 400-NiO/CNT delivered larger specific capacitance (Cm) of 745 F g-1, improved capacitance preservation (30.7% at 30 A g-1), and excellent cycle life (109% @ 30 A g-1 after 1,000 cycles) than 400-NiO (16.20 F g-1 at 5 A g-1, 26% rate retention, and 21% stability @ 2 A g-1 after 1,000 cycles). EIS results portrayed a lesser charge transfer resistance (Rct) in the nanocomposite (0.16 Ω) than pure NiO (1.58 Ω), demonstrating improved conductivity and ion diffusion. Furthermore, the Brunauer-Emmett-Teller (BET) results revealed that the mean pore volume and specific surface area of the 400-NiO/CNT (0.43 cm3 g-1 and 93.82 m2 g-1) were larger than those of 400-NiO (0.13 cm3 g-1 and 35.63 m2 g-1). Besides, the pore size distribution was
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within 2-40 nm, indicating the mesoporous nature of the prepared materials. The BJH mean pore size for 400-NiO was 14.90. In comparison, it was 19.51 nm for 400-NiO/CNT. The enhanced pore size/volume and surface area observed from BET analysis improve ion diffusion, contain volume variations during long charge/discharge cycles, and provide more active sites for enriched electrochemical charge storage. XPS survey spectrum reveals three strong peaks ascribed to the presence of three elements: carbon, nitrogen, and oxygen, confirming the successful formation of the composites. Summarily, the results indicate that the spray-deposited NiO/CNT materials, across all temperatures, exhibited improved electrochemical behavior; larger Cm, better capacitance retention, and superb cycle life, compared to pure NiO. In particular, the 400-NiO/CNT sample delivered optimal performance. Given these results, spray pyrolysis offers an affordable and sustainable alternative while maintaining superior performance. These findings align with the SDG7 goal of promoting affordable and efficient energy storage solutions, thereby enhancing the commercial viability of SCs. Moreover, the results of this study are relevant to several industries that rely on efficient and affordable energy storage devices for their products, including the automotive industry, electronics industry, and telecommunications industry.