NiMn2O4 nano-cotton particles and nanofibers: Exploring structural, magnetic and electrochemical energy storage properties

Abstract

Herein, nickel manganite (NiMn<inf>2</inf>O<inf>4</inf>) was successfully synthesized via glycine-nitrate sol-gel combustion process to obtain nano-cotton particles (SG-800) and electrospinning method to obtain nanofibers (ES-400), both followed by calcination. Synthesized materials were characterized in order to evaluate structural, magnetic and energy storage properties. The X-ray diffraction (XRD) pattern revealed the formation of a cubic spinel structure in both cases. The crystallite size of SG-800 (53 nm) was higher than that of ES-400 (16 nm). X-ray photoelectron spectroscopy showed the presence of Ni²⁺, Mn²⁺, Mn³⁺ and Mn⁴⁺ valence states in both samples. Synthesized materials were paramagnetic at room temperature, turning to ferromagnetic ordering at the critical temperatures of 104 and 95 K, while the appearance of the spin-glass-like state was observed at 65 and 80 K for SG-800 and ES-400, respectively. SG-800 and ES-400 were tested in different electrolytes on a glassy carbon electrode as a substrate and demonstrated potential for energy storage through diffusion-controlled, Faraday redox electrochemical reactions. Carbon aerogel (CA) produced by thermal carbonization of lyophilized sodium-alginate hydrogel exhibited EDLC capacitor-like behavior, as shown by electrochemical characterization. Hybrid supercapacitors were assembled from SG-800 or ES-400 and CA and their performance was evaluated. The SG-800 as an electrode material showed superior capacitance and stability, probably due to higher crystallinity and formation of active sites for electrochemical redox reactions.