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Cobalt ferrites have attracted extraordinary attention due to their high coercivity, chemical stability, and mechanical hardness. Lanthanum doped-cobalt ferrites having chemical formula CoLaxFe2-xO4 with composition x = (0.00, 0.015, 0.045, 0.060) were synthesized by chemical co-precipitation method. The prepared samples were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, and current-voltage (I-V) technique. The structure of the crystal was analyzed by X-ray diffraction. The crystallite size of nanoparticles was examined in the range of 21–25 nm, and a fluctuating trend was found with the inclusion of La3+ cations. The X-ray diffraction patterns verify the contraction of lattice constant and unit cell volume with the substitution of La3+ cations except for the concentration of x = 0.060. Lattice constant was in the range of 8.34 A–8.41 A while unit volume cell was in the range of 580 A3–596 A3. The resistivity of all samples was calculated by the application of two probes I-V technique. The maximum resistivity of the order of 81.129 × 105 Ω cm was found for the concentration of x = 0.060 at 723 K which makes it useful for high-frequency gimmicks applications. The resistivity and drift mobility were found inversely related to each other. The inverse relation low-frequency absorption band and high-frequency absorption bands were analyzed by Fourier-transform infrared spectroscopy technique.

Optimization of suitable electrode material flashing high electrochemical performance is the main hindrance in energy storage applications. Metal oxide-based electrode materials are promising candidate which greatly promotes the sustainable development. Herein, strontium oxide (SrO) is synthesized from sonochemical method followed by calcination. Incorporating polyaniline (PANI) and graphene (Gr) intensify the materials performance. Three asymmetric devices are designed using SrO, its composites (SrO/PANI and SrO/PANI/Gr) and activated carbon (AC) as an electrode and electrolyte-soaked separators are sandwiched in solidly packed cell assembly. Electrochemical measurements are performed to scrutinize the inherent properties. After that, Dunn’s model is applied to evaluate the capacitive and diffusion-controlled contributions. The obtained result divulges that SrO/PANI/Gr//AC exhibits more diffusive-controlled contribution and reveals a battery type behavior due to the contribution of PANI in redox reactions. Thus, this work delivers a route to synthesize metal oxides-based composites and a systematic approach to analyze the charge storage mechanism in asymmetric supercapacitors.

The transition metal sulfides have gained extensive interest in energy storage devices owing to their unique features. However, the research-based on cobalt, copper and manganese sulfide composites is limited while they are considered as promising contenders for supercapacitor electrodes. The simplest and facile one-step electrodeposition technique was adopted for the direct growth of CuMnS and CoMnS on a Ni-substrate. The electrochemical properties of CuMnS and CoMnS electrodes were investigated and maximum specific capacitances of 1691 and 2290 F/g, respectively, were obtained at 10 A/g current density. Further, these electrodes are investigated with activated carbon (AC) electrode to fabricate asymmetric supercapacitor devices where CoMnS//AC exhibited superior energy density values than CuMnS//AC device. However, both the devices show a relatively uniform capacitance retention rate (~94%) after 2500 charging-discharging cycles. Furthermore, the role of capacitive- and diffusive-controlled contributions in the charge storage phenomenon of supercapacitor devices are explicitly scrutinized by employing Dunn's model. Co-electrodeposition of transition metal sulfides has great potential as electrode material for highly effective supercapacitor devices.

Charge carrier modulation of graphene-based field effect transistors (GFETs) is the key factor to utilize and enhance its fascinating properties for technological applicability. Here, we have demonstrated the gate-dependent tweaking of electrical properties of graphene devices by application of honey as a top gate dielectric. Electrical characterization of dual-gated GFET is elucidated at different top and back-gate voltages. A charge neutrality point is fine-tuned by varying the top gate voltage (Vtg) from + 3 to − 4 V. The change in carrier density is clearly observed from 3.66 × 1012 to 2.15 × 1011 cm−2 at + 3 to − 4 Vtg. The charge carrier mobility of gel-gated GFET is increased significantly to 5376 cm2/V ⋅ sec by increasing top-gate voltages up to − 4 V. Result demonstrates a cost-effective, facile and rapid fabrication of top-gated devices and suggest natural dielectric materials as good candidate to replace conventionally available gate dielectrics in FET technology.

The versatile importance of hybrid supercapacitors in energy storage applications craves the outstanding electrochemical behavior of electrode material. In this study, we have grown several electrode of cobalt-copper-manganese sulfide (CCMS) with different concentration of cobalt and copper on a current collector (Ni foam) by espousing one-step co-electrodeposition approach. The morphological aspects of contrived electrodes have been characterized by FESEM to examine the growth mechanism. Electrochemical characterization reveals the substantial performance of S2 electrode (Co25Cu75MnS) as compared to other compositions. After the experimental investigation, the dependence of inherent charge storage mechanism of CCMS on the concentration of Co and Cu have been scrutinized thru stimulating theoretical approaches. Different mathematical models employed to ascertain the dominant charge storage mechanism involved during electrochemical charge storage and scrutinizing their redox reaction stability. The finding illumines the enhanced electrochemical performances of electrodes with prevalent battery-type charge storing phenomenon which support for the construction of advance hybrid energy storage devices.

A series of cobalt manganese sulfide (CoMnS) grown directly on Ni foam substrate via co-electrodeposition technique to study an appropriate choice of deposition cycle numbers of cyclic voltammetry at a fixed scan rate. The binder free electrodes have been fabricated from a quick synthesis methodology by evaluating the binary metal sulfides for achieving an extremely high energy storage. By carefully selecting the synthesis methodology and ingredients, CoMnS displayed an excellent electrical conductivity and low internal resistance, which makes them a promising contender for energy storage applications. S2 electrode having 12 number of deposition cycles portrayed high electrochemical performance enactment by means of 2297 F/g specific capacitance from cyclic voltammetry (CV) at 3 mV/s, while 2291 F/g from galvanostatic charge discharge (GCD) at 10 A/g. The S2 electrode have smaller ESR value calculated from EIS analysis that elucidated high conductance. Furthermore, the hybrid supercapacitor device was formed by sandwiching activated carbon (negative electrode) with S2 electrode (positive electrode) detached thru 1 M KOH electrolyte drenched permeable membrane. The electrochemical characterizations of device resulted an outstanding specific energy of 106 Wh/kg at 5 A/g, specific power of 24,000 W/kg at 30 A/g and reveals an excellent capacitance retentivity of 94% at room temperature after 2500 GCD cycles. This study suggested that 12 cycle numbers for deposition are optimized as an appropriate mass loaded for superior electrochemical energy storage applications.

Asymmetric devices are fabricated by cramming the active material Co3O4/C composite (positive electrode) with activated carbon (negative electrode). Devices are examined under aqueous and gelled electrolyte. The theoretical model is adopted to study the charge storage mechanism in two devices. It has been observed that the capacitive and diffusion-controlled contribution of electrode material is affected by the phase change of electrolyte. Diffusive contribution is prominent in case of 1 M KOH aqueous electrolyte while more capacitive contribution has been noticed in PVA-KOH-C gelled electrolyte. By changing the phase of electrolyte, the potential window is enhanced which upsurges the energy density of device. For commercial applications, solid state device exhibits more energy storage and have high safety standards than aqueous electrolyte-based devices.

A facile methodology has been adopted for the synthesis of cobalt oxide (Co3O4) by wet chemical technique followed by the calcination and prepared Co3O4/C composite for energy storage devices. Initially, SEM and XRD are carried out to analyze the surface characterizations of electrode material. The electrochemical properties of synthesized material has been investigated and the maximum specific capacitance of 567 F/g is achieved for Co3O4/C composite at 3 mV/s scan rate. Co3O4/C composite and activated carbon (AC) are sandwiching and separated with PVA-KOH-C gel electrolyte. The device has been examined at several scan rates and current densities demonstrating better performance with maximum energy density of 63 Wh/kg at 0.7 A/g. The capacitive retentivity is 82 % after 6000 charge/discharge cycles. The solid-state devices are showing a tremendous performance with high energy and power density and are safe to handle due to no seepage which can be utilized for the next generation.

Two dimensional (2D) layered materials such as graphene and transition metal dichalcogenides (TMDCs) have gain profound attention owing to their unique electrical, optical, structural and mechanical properties . These novel features make them promising candidate for the next generation optoelectronic and photonic devices . Here, we demonstrated the gate-voltage dependent current modulation of vertical Au/WS 2 /Gr Schottky barrier . A clear rectification is observed in J-V characteristic curves at different gate-voltage due to asymmetric barriers Au/WS 2 and WS2/Gr. The current modulation is obtained by varying the gate-voltage and the extracted rectification ratios ranging from 2.25 × 103 at −60 V to 1.65 × 103 at +60 V, respectively. Furthermore, the junction is utilized for the photo response at several drain to source and gate voltages which reveals modulation in the photocurrent . The photocurrent detected at V ds 0.5 V is ~24 μA that is enhanced to ~52 μA upon varying the Vds to 1 V. Gate tunable photoresponse of the junction depicts that the photocurrent is enhanced from 16 μA at Vg 20 V to ~17 μA at Vg 60 V. Our results demonstrate an effective way to modulate the current of Schottky junction (Au/WS2 /Gr) by employing gate voltage whereas the tunability in the photocurrent unveil its potential applications in next generation photodetectors .

Novel and unique characteristics of graphene have received much attention in energy conversion and storage devices. Graphene based hybrid structures have been employed for a wide variety of efficient and durable fuel cell energy systems. Here, the review focuses on the components of fuel cell device and utilization of graphene in modern fuel cell technology such as graphene based electrodes, electro-catalysts, electrolyte membrane and bipolar plates. Dispersion of graphene over conductive electrodes provide electrochemically active sites to improve the electrocatalytic activity towards oxidation reduction reaction and fuel oxidation. The main issue regarding the degradation of fuel cell is corrosion of bipolar plates which is also discussed and can be reduced by incorporating graphene based metal composites. Various electrical transport measurements and electrochemical parameters were also studied to evaluate the fuel cell performance. Incorporation of graphene in fuel cell technology exhibit excellent catalytic performance in potential applications of fuel cell devices.

Electrochemical energy storage devices such as supercapacitors attracting a significant research interest due to their low cost, highly efficient, better cyclic stability and reliability. The charge storage mechanism in supercapacitors are generally depends upon absorption/desorption of charges on electrode-electrolyte interface while the pseudocapacitive phenomenon is due to fast redox reactions. Electrochemical performance of the supercapacitors can be enhanced by optimizing the key parameters such as electrode material, activation agent, potential window, type and molar concentration of the electrolytes. Here, we have reported a thorough investigation about the impact of aqueous electrolytes on the performance of energy storage in electrochemical supercapacitors. To the best of our knowledge, aqueous electrolytes have shown a prominent impact on the capacitance of materials. In light of the reported articles, supercapacitor electrode materials have shown high performance in aqueous acidic electrolyte due to their high ionic conductivity. In contrast, electrode materials for supercapacitors have demonstrated low capacitance in neutral aqueous electrolytes due to low molar ionic conductivity. The choice of electrolyte is an important parameter to achieve high performance energy storage devices for future technological applications.

A systematic approach has been employed to statistically analyze the Faradaic and non-Faradaic mechanism on electrodes. Two strategies have been adopted for device design, i.e. symmetric and asymmetric, by using the metal oxide synthesized via sonochemical method and activated carbon electrode. Structural and electrochemical characterization have been performed to investigate the morphological and electrochemical properties of electrode material. Both devices are electrochemically examined by using cyclic voltammetry (CV) and Galvanostatic charge discharge (GCD) measurements to evaluate the electrochemical performance. CV curves are further explored to study the capacitive and diffusive contribution in both devices. The diffusive-controlled contribution at low scan rate in asymmetric device is about 65% which is suitable for supercapattery applications while the symmetric device shows 91% diffusive contribution presenting better performance for battery applications. The strategy unveils the high capacitive and diffusive contribution in asymmetric and symmetric devices, respectively. Results reveal that same material can be exploited for supercapattery and battery applications by implementing different device architectures.

The excellent solution-processability of polymers have provoked the interest for their potential applications in cost-effective electronic devices. However, these devices usually have low mobility. The study manifests an innovative approach to enhance the mobility of polymer-based field effect transistors (FETs) by incorporating graphene as an intervening layer between poly [4-(4,4-dihexadecyl-4H-cyclopenta [1,2-b:5,4b′] dithiophen-2-yl)-alt-[1,2,5] thiadiazolo [3,4-c] pyridine] (PCDTPT) channel and dielectric layer dielectric. An intentional discontinuity in the graphene layer was introduced to affirm the role of polymer as channel and graphene as carrier injector. The results divulge the enhancement in the performance of PCDTPT-graphene and PCDTPT-graphene (discontinuous) device as compare to pristine PCDTPT based FET. A significantly high mobility i.e. 13.08 cm2/V.sec is achieved for PCDTPT-graphene hybrid device which is 32 times higher than that of pristine PCDTPT based FET (0.41 cm2/V.sec). These results signify that the incorporation of atomically thin graphene layer is a novel route for fabrication of high mobility solution-processed polymer-based FETs for next generation cost effective and high performance electronic devices.

Two dimensional (2D) materials based heterostructures have gained profound interest in optoelectronics and electronic technology due to additional functionalities over the individual structures. This study demonstrates the fabrication and characterization of van der Waal heterostructure by selective coverage of graphene (Gr) with tungsten disulfide (WS2). The electrical transport measurements divulge the tweaking of charge carriers in graphene after WS2 coverage. Such architecture provides route towards the formation of heterojunction within graphene FET based on surface charge transfer between Gr/WS2 heterointerface. Furthermore, the exposure of device towards deep ultraviolet light (DUV) enhances the charge transfer mechanism and as a result more pronounced junction is observed. The photoelectrical characterization of heterostructure is also investigated by calculating detectivity (D*), external quantum efficiency (EQE) photoresponsivity (Rλ). Our results suggest that 2D heterostructures in combination with DUV irradiations are more efficient and suitable choice to selectively tune the properties of 2D material-based optoelectronic devices.

An upsurge in sustainable energy demands has ultimately made supercapattery one of the important choice for energy storage, owing to highly advantageous energy density and long life span. In this work, novel strontium based mixed phased nanostructures were synthesized by using probe sonicator with sonication power 500 W at frequency of 20 kHz. The synthesized material was subsequently calcined at different temperature ranging from 200 to 800 °C. Structural and morphological analysis of the synthesized materials reveals the formation of mixed particle and rod like nanostructures with multiple crystal phases of strontium oxides and carbonates. Crystallinity, grain size and morphology of grown nanomaterials significantly improved with the increase of calcination temperature due to sufficient particle growth and low agglomeration. The electrochemical performance analysis confirms the redox activeness of the Sr-based electrode materials. Material calcined at 600 °C show high specific capacitance of 350 F g−1 and specific capacity of 175 C g−1 at current density of 0.3 A g−1 due to less particle agglomeration, good charge transfer and more contribution of electrochemical active sites for redox reactions. In addition, the developed supercapattery of Sr-based nanomaterials//activated carbon demonstrated high performance with maximum energy density of 21.8 Wh kg−1 and an excellent power density of 2400 W kg−1 for the lower and higher current densities. Furthermore, the supercapattery retain 87% of its capacity after continuous 3000 charge/discharge cycles. The device characteristics were further investigated by analyzing the capacitive and diffusion controlled contributions. The versatile strategy of developing mixed phased nanomaterials pave the way to synthesize other transition metal based nanomaterials with superior electrochemical performance for hybrid energy storage devices.