A simple and low‐cost and highly calibrated probe sonication method was used to prepare bismuth oxide nanoparticles (Bi₂O₃ NPs). The formation of a well‐crystalline sample at the end of the product has been further calcined at 600°C for 2 hrs. The powder X‐ray diffraction (PXRD) patterns of the NPs substantiated the monoclinic structure (space group P2₁/c), and the average crystallite size was found to be 60 nm, which was also confirmed by transmission electron microscopic (TEM) studies. Scanning electron microscopic (SEM) images depicted highly porous Bi₂O₃ NPs with little agglomeration. Utilizing diffused reflectance spectra (DRS) data, the energy bandgap (E_g) value of 3.3 eV was deduced for Bi₂O₃ NPs, and their semiconductor behavior has been confirmed. Two dyes, methylene blue (MB) and acid green (AG) were utilized for degradation studies using Bi₂O₃ NPs under UV light irradiation (from 0 to 120 min). The photocatalytic degradation was found to be maximum for MB (93.45%) and AR (97.80%) dyes. Cyclic voltammetric (CV) and sensor studies using the electrochemical impedance spectroscopy (EIS) were performed. The specific capacitance value of 25.5 Fg^-1 was deduced from the cyclic voltammograms of the Bi₂O₃ electrode in 0.1 N HCl with a scan rate of 10 to 50 mV/s. From the obtained EIS data, the Bi₂O₃ electrode showed pseudocapacitive characteristics. The prepared electrodes also exhibited high sensitivity towards the detection of ascorbic acid and lead. Hence, sonochemically synthesized Bi₂O₃ NPs are possibly hopeful for excellent photocatalytic and electrochemical sensing of biomolecules.

Nanostructured NiO and Li-ion doped NiO have been synthesized via a facile microwave technique and simulated using the first principle method. The effects of microwaves on the morphology of the nanostructures have been studied by Field Emission Spectroscopy. X-ray diffraction studies confirm the nanosize of the particles and favoured orientations along the (111), (200) and (220) planes revealing the cubic structure. The optical band gap decreases from 3.3 eV (pure NiO) to 3.17 eV (NiO doped with 1% Li). Further, computational simulations have been performed to understand the optical behaviour of the synthesized nanoparticles. The optical properties of the doped materials exhibit violet, blue and green emissions, as evaluated using photoluminescence (PL) spectroscopy. In the presence of Li-ions, NiO nanoparticles exhibit enhanced electrical capacities and better cyclability. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) results show that with 1% Li as dopant, there is a marked improvement in the reversibility and the conductance value of NiO. The results are encouraging as the synthesized nanoparticles stand a better chance of being used as an active material for electrochromic, electro-optic and supercapacitor applications.

Metal/metal oxide nanocomposites (NCs) have been attracting significant attention in recent times because of their applications in the fields of energy and environment. In the present work, we investigate the photocatalytic and electrochemical performances of Ni/NiO NCs synthesized by a facile and cost-effective reduction method using lithium salt as the dopant. Lithium influences the size, morphology and structural constitution of the final product. A variation in the lithium percentage was seen to have a direct effect on the Ni content. The structural conformation of the samples has been analyzed by XRD and further confirmed by XPS. A low optical energy bandgap (∼3.7 eV) and a mesoporous structure of the as-prepared samples were seen to play a crucial role in achieving the photocatalytic degradation of the cationic organic dyes concomitant to its electrochemical activity. On illumination with UV light, the Li-doped Ni/NiO NCs demonstrated rapid degradation of crystal violet and methyl violet 2B dyes. The synergism arising due to the substitutional doping of lithium and the presence of metallic nickel leads to efficient photodegradation of the dye pollutants by the catalysts. Further, the Li-doped Ni/NiO NCs displayed a better electrochemical performance than the undoped samples. The NC with 1 wt% Li exhibited the best values of specific capacitance (276.2 F g⁻¹ at 5 A g⁻¹) with an excellent cycling ability (<1% capacitance loss after 2000 cycles). The enhanced electrochemical and photocatalytic results suggest the dual activity of these nanocomposites in energy storage and water treatment applications.

The use of nonrenewable fossil fuels for energy has increased in recent decades, posing a serious threat to human life. As a result, it is critical to build environmentally friendly and low-cost reliable and renewable energy storage solutions. The supercapacitor is a future energy device because of its higher power density and outstanding cyclic stability with a quick charge and discharge process. Supercapacitors, on the other hand, have a lower energy density than regular batteries. It is well known that the electrochemical characteristic of supercapacitors is strongly dependent on electrode materials. The current review highlights advance in the TMOs for supercapacitor electrodes. In addition, the newly discovered hybrid/pseudo-supercapacitors have been discussed. Metal oxides that are employed as electrode materials are the focus of this study. The discovery of nanostructured electrode materials continues to be a major focus of supercapacitor research. To create high-performance electrode materials from a morphological standpoint, various efforts have been attempted. Lastly, we analyze the supercapacitor’s evolving trend and our perspective for the future generations of supercapacitors.