Facile binder free synthesis of NiO–Cr₂O₃ composite coatings for high performance symmetric supercapacitor

The spray pyrolysis technique was used to prepare NiO, Cr₂O₃ and Ni Cr composite thin films on a glass substrate of soda lime and nickel foam. The high crystallinity of pure NiO and Cr₂O₃ was identified by X-ray diffraction (XRD), whereas the composites had partial crystallinity and the appearance of a cubic spinel NiCr₂O₄ phase. The spinel structure was further confirmed by Raman and FTIR analyses by the appearance of characteristic Ni O, Cr O, and Ni–O–Cr vibrational bands. SEM showed that the films had uniform and crack-free structures with fine grains, suggesting that they were densely and uniformly formed in their surfaces. Electrochemical studies (CV, GCD, and EIS) revealed that NC3 composite (Cr/Ni = 1:1) had showed excellent performance with specific capacitances of 1371 F g −1 at 2 mV s −1 and 1451 F g −1 at 1.5 A g −1 , and a low equivalent series resistance (1.27 Ω). Symmetric supercapacitor based on NC3 electrode provided 99.7 F g −1 at 1.33 A g −1 , and maintained 89 % capacitance after 9000 cycles, and an energy density of 19.95 Wh kg −1 at 800 W kg −1 . These results show the excellent electrochemical activity and stability of the Ni Cr composite thin films for advanced energy storage applications. • NiO, Cr₂O₃, and Ni Cr films were synthesized by spray pyrolysis. • XRD, Raman, and FTIR confirmed the cubic spinel NiCr₂O₄ phase. • SEM showed uniform, dense, and crack-free film surfaces. • The Cr/Ni (1:1) composite showed excellent capacitance of 1451 F g −1 at 1.5 A g −1 . • The NC3-based supercapacitor showed 99.7 F g −1 at 1.33 A g −1 , retaining 89 % after 9000 cycles.