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ZnWO 4 nanoparticles were synthesized by a hot injection method using different zinc precursors (zinc nitrate, zinc acetate, zinc sulphate and zinc chloride) with sodium tungstate. Similarly, the ZnWO 4 particles were prepared by co-precipitation and solid-state method for comparative analysis. The phase formation temperature of ZnWO 4 was identified through thermal analysis. X-Ray diffraction (XRD) analysis enumerates that the formation of a single-phase monoclinic wolframite structure with the space group P2/c. The characteristic functional groups of Zn-O, Zn-O-W, and W-O were identified through Fourier Transform Infrared Spectroscopy (FTIR). The microscopic images revealed that the formation of spherical shape particles in size range between 60 and 100 nm. The room temperature electrical conductivity was measured using LCR meter, and it shows that the conductivity is in the range of 2.2 × 10 −5 to 6.2 × 10 −6 S.cm −1 . The calculated corrosion rate of ZnWO 4 using Tafel Polarization curve in 1 M H 2 SO 4 at 1 mV s −1 was 0.2554 mmpy. The electrocatalytic activity towards the hydrogen evolution reaction (HER) was studied using linear sweep voltammogram in 1 M H 2 SO 4 solution at a scan rate of 1 mV s −1 . Further, the zinc acetate precursor assisted particles have shown a low onset potential (0.42 V) and higher current density (−228.52 mA cm −2 ) in the potential range of 0 to −1.0 V compared with other samples.

For the fabrication of aqueous Li-ion hybrid supercapacitor, carbon coated LiCo1/3Ni1/3Mn1/3O2 (or LiCo1/3Ni1/3Mn1/3O2@C composite) is synthesized by polymeric precursor method with subsequent thermal decomposition procedures for carbon coating. Graphene like porous carbon is obtained by chemical activation from the biomass of Agave Americana. The XRD analysis reveals that LiCo1/3Ni1/3Mn1/3O2 is having a hexagonal layered structure and activated carbon exists in both amorphous and graphitic nature. The TEM image infers that LiCo1/3Ni1/3Mn1/3O2 particles having the non-uniform shape with sub-micron size and the LiCo1/3Ni1/3Mn1/3O2 particles are embedded into amorphous carbon cloud in the composite. The activated carbon shows the specific surface area of 1219 m2 g−1. Finally, the fabricated aqueous LiCo1/3Ni1/3Mn1/3O2@C‖AC hybrid supercapacitor delivers the specific capacitance of 56 F g−1 with good capacity retention even after 5000 cycles.

To realize the ideal electrode material for supercapacitors, the scientific community has been prompted to investigate a variety of materials. This study deals with the hydrothermal synthesis of NiSb2O4 for the first time for application to hybrid supercapacitors. First-principles density functional theory (DFT) calculations are employed to study the electronic structure of synthesized NiSb2O4. The single phase tetragonal structure NiSb2O4 is revealed from X-ray diffraction (XRD) analysis. Rod-like micron-sized structures are revealed through field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) analysis. Structural parameters and unit cell dimensions are deduced from Rietveld refinement analysis. The comparative effects of various K+ electrolytes (1 M KOH, 1 M KCl, 1 M KNO3 and 0.5 K2SO4) on the NiSb2O4 negative electrode material are studied. Cyclic voltammogram (CV) showed greatest specific capacitance of 758 F g−1 at 2 mV s−1 in 1 M KOH. Galvanostatic charge-discharge analysis (GCD) exhibited capacitance of 382 F g−1 at 1 A g−1. The asymmetric supercapacitor is assembled with synthesized Ni3(Fe(CN)6)2(H2O) as positive electrode and the device exhibits a specific capacitance of 344 F g−1 at 1 mV s−1 in 1 M KOH in the wider potential window of 1.6 V, suggesting its potential application as an energy storage device.

Nitrogen-doped Multi-walled Carbon Nanotubes (N-doped MWCNT)/MnCo 2 O 4 hybrid is synthesized by a facile hydrothermal method. The X-ray diffraction studies revealed the single phase formation of cubic spinel structured MnCo 2 O 4 and their composites. The presence of D and G band of MWCNT is identified through Raman spectral analysis. The elemental oxidation state and nitrogen content is obtained using X-ray photoelectron spectroscopy, which elucidates that Co and Mn exists in multivalence state and the nitrogen functional groups are in pyrolytic and pyridinic-type. FE-SEM shows the microsphere formation of MnCo 2 O 4 and size exhibits in the range of 6–9 μm. The N-doped MWCNT/MnCo 2 O 4 hybrid catalyst exhibits an improved oxygen reduction electrocatalytic activity in an aqueous alkaline medium when compared with pristine MnCo 2 O 4 .

Lithium-ion battery (LIB) is an essential energy storage device in numerous applications such as electronic devices and electric vehicles. Nevertheless, LIBs cannot meet some requirements, such as high energy and power density. To achieve these goals, the development of an electrode material with high capacity and fast kinetics is needed. Here, we report on Cu2SnSe4 nanoparticles embedded with N-doped carbon (Cu2SnSe4@N-C) as a new anode material. The cycling tests revealed that the Cu2SnSe4@N-C delivered a higher discharge capacity of 788.6 mAh g−1 than the pristine Cu2SnSe4 (14.8 mAh g−1) after 100 cycles at 100 mA g−1. It also exhibited a better long term cycling stability (365 mAh g−1 after 200 cycles at 2000 mA g−1) and excellent rate performance at a high current density. Such a superior performance is associated with the surface coating of N-doped carbon on the Cu2SnSe4 nanoparticles. It can accommodate the volume strain during charge-discharge cycles and enhance ionic and electronic transport within the electrode material. The N-doped carbon can also act as a fence that strongly suppresses the dissolution of polyselenide into the electrolyte solution through strong chemical adsorption.

Because of a high global energy demand and challenging sustainability requirements, hydrogen has been promoted as a clean and green energy carrier allowing the potential replacement of nonrenewable fossil fuels. Hydrogen is a renewable energy carrier that does not contribute to CO2 emissions, and it holds the highest gravimetric energy density. It can be produced by the electrochemical splitting of water into hydrogen and oxygen molecules. Herein, we investigate the bifunctional activity of bimetallic oxide, sulfide, and selenide nanostructures in water electrolysis. Spinel-type, phase-pure NiCo2O4, NiCo2S4, and NiCo2Se4 with comparable morphological properties were synthesized by a hydrothermal method. The electrocatalytic characterization of NiCo2Se4 was found to demonstrate higher oxygen and hydrogen evolution reaction activities (245 mV and 122 mV @ 10 mA cm−2, respectively) compared to those of NiCo2O4 and NiCo2S4. Furthermore, a lab-scale water-splitting system was fabricated to examine the bifunctional properties of bimetallic nanostructures. A NiCo2Se4-based water-splitting system was found to require a cell voltage of 1.58 V, which is lower than that required by NiCo2S4 (1.64 V)- and NiCo2O4 (1.75 V)-based systems. In summary, this study explores bimetallic NiCo2Se4 as an efficient electroactive material that can be employed in various electrochemical energy systems.

In this work, we demonstrate the FeS2/MoS2 composite embedded in rGO nanosheets (FeS2/MoS2-rGO composite) as an anode material for sodium-ion battery. The FeS2/MoS2 composite material was synthesized by one step hydrothermal method, and the prepared particles were wrapped by reduced graphene oxide (rGO) nanosheets, which facilitated the electronic transport between the particles, and suppressed the volume expansion of active materials as well as the polysulfide dissolution into the electrolyte during cycling. The FeS2/MoS2-rGO composite electrode delivered a high initial discharge capacity of 468.0 mA h g−1 and exhibited good cycling stability at a current density of 100 mA g−1. Due to the pseudocapacitive behavior of FeS2/MoS2-rGO electrode, a high reversible capacity of 346.5 mA h g−1 was achieved at 3000 mA g−1, which was much higher than those of FeS2, MoS2 and FeS2/MoS2 composite electrodes. The sodium-ion full cell assembled with FeS2/MoS2-rGO composite anode and Na3V2(PO4)2F3 cathode exhibited a high reversible capacity with good cycling stability, which demonstrates that the prepared FeS2/MoS2-rGO composite can be used as a promising anode material for sodium-ion batteries.

Spinel Co2TiO4 is synthesised using a polymeric precursor method and used as an efficient negative electrode for Li-ion batteries. Precise full-profile Rietveld refinement proves the formation of a single-phase cubic spinel structure with a lattice parameter of a = 8.4190(9) A, which corresponds to the sample composition of Co2.05Ti0.95O4. Subsequently, a carbon coating around Co2TiO4 is achieved through a simple hydrothermal method. TGA analysis implies that Co2TiO4@C consists of 17 wt% carbon, and the presence of D and G bands was confirmed through Raman analysis. Transmission electron microscopy (TEM) is employed to probe the morphological features, as well as to confirm the carbon coating on Co2TiO4. It shows non uniform shape particles with sizes in the range of 400–750 nm and that the thickness of the carbon coating is 10 nm. The superior electrochemical performance of Co2TiO4@C is confirmed by a higher initial discharge–charge capacity (1283/418 mA h g−1), high diffusion coefficient (1.76 × 10−10 cm2 s−1/2) and lower Rct (after 50 cycles). This is attributed to the increased electrical conductivity and the creation of new active sites due to the synergistic effect of the carbon matrix on Co2TiO4, thereby making it a promising candidate for lithium ion battery applications.

Energy-storage devices are state-of-the-art devices with many potential technical and domestic applications. Conventionally used batteries do not meet the requirements of electric or plug-in hybrid-electric vehicles due to their insufficient energy and power densities. Graphite is used for the conventional anodes of Li-ion batteries. However, the specific capacity (372 mA h g−1) of a graphite electrode is not sufficient for high-power applications. Therefore, Co-, Ni-, Mn-, and Zn-based simple oxides have been investigated as anode components due to their high specific capacities (500–1000 mA h g−1). Among these, Co-based anodes have demonstrated the best electrochemical performances; however, Co's high cost and toxicity limit its use as an ideal anode component. Recently, mixed-metal oxides with AB2O4 (A = Cu, Co, Ni, Mn, and Zn; B = Co, Mn, and Fe) and A2BO4 (A = Co, Mn, and Fe; B = Sn, Si, Ti, and Ge) structures have received much interest, and their electrochemical performances have been extensively studied. This type of mixed-metal oxide affords the following main advantages: they store charge through conversion as well as alloying–dealloying processes, and they exhibit higher electronic conductivities than that obtained with simple metal oxides. The above points indicate the importance of AB2O4- and A2BO4-structured materials. The present review emphasizes the recent literature on the electrochemical performance of AB2O4- and A2BO4-structured materials and their composites and feasible ways to implement these materials in Li-ion batteries in the near future.