Chromium induced nickel oxides leads to extraordinary enhancement in the performance of aqueous hybrid supercapacitors

Aqueous hybrid supercapacitors (AHSCs) have great potential in portable devices and other modern electronic products due to their high-power density, long life span, and environmentally friendly. However, compared with traditional Li-ion batteries, they are still not mature enough to meet market requirements due to their low energy density. In this study, we proposed to use nanostructured bi-metallic nickel-chromium oxide as an AHSC cathode. By using the synergetic effect arising from the two metal cations, Ni and Cr-ions, the energy storage performance of AHSCs was expected to be significantly improved. We synthesized the nanostructured bi-metallic nickel-chromium oxide (NiCrO3) with a facile hydrothermal method. The achieved NiCrO3 (NCO) has a sheet-like structure and a hexagonal shape in the nanoscale. The results show that NCO loading on carbon cloth (CC) as the working electrode (NCO@CC) has a high specific capacitance of 2,862 F/g at 1 A/g (corresponding capacity of 1,431 C/g) and a favorable cycling stability of 98.3% after 10,000 cycles at 10 A/g. The specific capacitance is about 2.3 and 5.9 times of pristine Cr2O3 and NiO in the same situation. The storage mechanism of charge was investigated by ex-situ XRD, XPS, and Raman spectroscopy, which reveals that the total stored charge is based on the combination of faradic and pseudocapacitive effects. Furthermore, AHSC was fabricated using the NCO@CC as cathode, activated carbon as anode, which showed promising performance (102.7 F/g at 2 A/g) with excellent rate-capability (58.5% at 20 A/g), long life span (48% after 50,000 cycles). Density function theory calculation reveals that NCO possesses higher conductivity than NiO and Cr2O3, and decreases the electron transport energy, which contributes to the improves the reactions kinetics.