Microwave-hydrothermally synthesized RuxNiCo2-xO4 spinel oxide nanoparticles for high-performance pseudocapacitor electrodes

Abstract

Abstract A series of Ru x NiCo 2-x O 4 (RNCO; x = 0.00–0.10) spinel oxides at nanoscale were synthesized using a microwave hydrothermal (M-H) process. Structural, morphological, and electrochemical characteristics were investigated by various characterizations. The X-ray diffraction results confirm the formation of a single-phase cubic spinel structure with an Fd -3 m space group for all compositions. The lattice parameter decreases linearly from 8.089 Å (x = 0.00) to 8.085 Å (x = 0.10). Field emission scanning microscopy images reveal nanoparticles with elongated and spherical morphologies, with average grain sizes ranging from 32 nm (x = 0.06) to 55 nm (x = 0.10). Fourier transform infrared spectra exhibit characteristic metal–oxygen vibrational bands around 656 cm −1 , confirming spinel oxide formation. X-ray photoelectron spectroscopy analysis verifies the presence of mixed valence states of Ni 2+ /Ni 3+ , Co 2+ /Co 3+ , and Ru 3+ /Ru 2+ . Electrochemical studies demonstrate enhanced pseudocapacitive behavior with Ru incorporation. The results were corroborated to Randles’s, Dunn’s and impedance analysis. Notably, the Ru 0.06 NiCo 1.4 O 4 (RNCO-4) electrode delivers a superior specific capacitance of 1541 F g −1 , and an energy density of 53.35 Wh kg −1 at a power density of 2233 W kg −1 . These results indicate that Ru-substituted NiCo 2 O 4 spinel oxides synthesized via the Microwave-Hydrothermal (M-H) route resulted in novel electrode materials for supercapacitor applications.