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Ionogels are hybrid materials comprising an ionic liquid confined within a polymer matrix. They have garnered significant interest due to their unique properties, such as high ionic conductivity, mechanical stability, and wide electrochemical stability. These properties make ionogels suitable for various applications, including energy storage devices, sensors, and solar cells. However, optimizing the electrochemical performance of ionogels remains a challenge, as the relationship between specific capacitance, ionic conductivity, and electrolyte solution concentration is yet to be fully understood. In this study, we investigate the impact of electrolyte solution concentration on the electrochemical properties of ionogels to identify the correlation for enhanced performance. Our findings demonstrate a clear relationship between the specific capacitance and ionic conductivity of ionogels, which depends on the availability of mobile ions. The reduced number of ions at low electrolyte solution concentrations leads to decreased ionic conductivity and specific capacitance due to the scarcity of a double layer, constraining charge storage capacity. However, at a 31 vol% electrolyte solution concentration, an ample quantity of ions becomes accessible, resulting in increased ionic conductivity and specific capacitance, reaching maximum values of 58 ± 1.48 μS/cm and 45.74 F/g, respectively. Furthermore, the synthesized ionogel demonstrates a wide electrochemical stability of 3.5 V, enabling diverse practical applications. This study provides valuable insights into determining the optimal electrolyte solution concentration for enhancing ionogel electrochemical performance for energy applications. It highlights the impact of ion pairs and aggregates on ion mobility within ionogels, subsequently affecting their resultant electrochemical properties. [ABSTRACT FROM AUTHOR]

Graphene – a carbon nanomaterial has gained huge research interest due to its intriguing and extraordinary properties such as large surface area, excellent electrical conductivity, ultra-thinness, high electron mobility, and superior mechanical strength. The combination of graphene with other inorganic nanoparticles can significantly boost its physiochemical properties and hence, opens up new frontiers of its utilization. Grapheneis significantly exploited for the energy storage systems due to its great potential for electrochemical energy storage. However, the experimental electrochemical performance of graphene is still far away from the theoretical facts. This study critically evaluated the existing synthesis routes for the production of graphene, graphene-based composites and their utilization in the energy storage applications. Furthermore, the techno-economic analysis of the synthesis methods was undertaken to determine the best routes in terms of sustainability for commercial graphene production. Lastly, the fundamental understanding of graphene growth mechanisms and the overall intricacies of the synthesis processes were highlighted and the possible way forward is proposed. Therefore, in the quest for the development of effective alternative yet sustainable energy storage devices; it is hoped that this research will give useful insights to researchers and key players in the electronics industry. [ABSTRACT FROM AUTHOR]

Electrochemical stability of energy storage devices is one of their major concerns. Polymeric binders are generally used to enhance the stability of the electrode, but the electrochemical performance of the device is compromised due to the poor conductivity of the binders. Herein, 3D binder-free electrode based on nickel oxide deposited on graphene (G-NiO) was fabricated by a simple two-step method. First, graphene was deposited on nickel foam via atmospheric pressure chemical vapour deposition followed by electrodeposition of NiO. The structural and morphological analyses of the fabricated G-NiO electrode were conducted through Raman spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and energy dispersive X-ray spectroscopy (EDS). XRD and Raman results confirmed the successful growth of high-quality graphene on nickel foam. FESEM images revealed the sheet and urchin-like morphology of the graphene and NiO, respectively. The electrochemical performance of the fabricated electrode was evaluated through cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS) in aqueous solution at room temperature. The G-NiO binder-free electrode exhibited a specific capacity of ≈ 243 C g−1 at 3 mV s−1 in a three-electrode cell. A two-electrode configuration of G-NiO//activated charcoal was fabricated to form a hybrid device (supercapattery) that operated in a stable potential window of 1.4 V. The energy density and power density of the asymmetric device measured at a current density of 0.2 A g−1 were estimated to be 47.3 W h kg−1 and 140 W kg−1, respectively. Additionally, the fabricated supercapattery showed high cyclic stability with 98.7% retention of specific capacity after 5,000 cycles. Thus, the proposed fabrication technique is highly suitable for large scale production of highly stable and binder-free electrodes for electrochemical energy storage devices. [ABSTRACT FROM AUTHOR]

Aerogel based on reduced graphene oxide was synthesized using supercritical methods of drying the hydrogel in isopropanol. The synthesis technique involves the deposition of iron hydroxides on graphene layers, then their reduction in supercritical isopropyl alcohol to iron oxides (Fe 3 O 4 and γ-Fe 2 O 3). Results revealed that synthesized adsorbents Graphene aerogel (GA) and GA/Fe show excellent high gravimetric methane adsorption with an achievable capacity of 2.5 g/g and 3.6 g/g, respectively, in the pressure range of 0.5–10 MPa and 298 K, which is more than seven times higher than the requirements established by the US Department of Energy for the gravimetric capacity of a porous material for methane storage. However, at high gravimetric absorption, the volume absorption was 104 m3 (STP)/m3 and 102 m3 (STP)/m3 for (GA) and (GA/Fe), respectively. It should be noted that the performance characteristics of aerogels, in general, are comparable to adsorbents of other classes. A generalized flow-chart for obtaining the graphene aerogel. [Display omitted] [ABSTRACT FROM AUTHOR]

This study aims to optimize the fabrication parameters of nickel‑iron phosphate (NiFe-P) electrode to achieve a high areal capacity electrode for supercapattery. The fabrication of binder-free NiFe-P electrode on nickel foam (NF) employs a one-step hydrothermal synthesis method. Further, central composite design (CCD) under the response surface methodology (RSM) is used to optimize the electrode's performance. The factors evaluated are synthesis temperature (60 to 180 °C), time (6 to 24 h), and the molar ratio of precursor solution (1:3, 1:1, 3:1 of Fe: Ni), whereas the response is the areal capacity of NiFe-P electrode at the scan rate of 3 mV/s in a standard three-electrode cell system. The optimal temperature, time, and molar ratio (Fe:Ni) are determined to be 100 °C, 14 h, and 3:1, respectively. The model is confirmed within the confidence interval and prediction as well as comparable with a 10% percentage error between the experimental and predicted specific capacity. The specific capacity of the optimized electrode is 446 C/g at a scan rate of 3 mV/s using cyclic voltammetry (CV) and 413.75 C/g at a current density of 1 A/g in 1 M KOH using a standard three-electrode cell system. Supercapattery is fabricated by combining NiFe-P and activated carbon electrodes (NiFe-P//AC) as positive and negative electrodes, respectively, to evaluate the two-electrode cell system. The results show the maximum power density of NiFe-P//AC supercapattery is 2250 W/kg at an energy density of 45.6 Wh/kg. Furthermore, the NiFe-P//AC supercapattery demonstrated excellent stability and coulombic efficiency by retaining 87.6% and 98.7% of the initial specific capacity values and coulombic efficiency, respectively. • Binder-free NiFe-P electrode was prepared using hydrothermal synthesis. • The fabrication parameters of the electrode were optimized using DOE. • The electrochemical performance of the electrodes was investigated. • Maximum power density of NiFe-P//AC supercapattery is 2250 W/kg at an energy density of 45.6 Wh/kg. • NiFe-P//AC supercapattery retained 87.6% and 98.7% of the initial specific capacity values and coulombic efficiency. [ABSTRACT FROM AUTHOR]

Herein, a one-step fabrication of three-dimensional (3D) binder-free graphene-nickel foam (G-Ni) electrode via atmospheric pressure chemical vapour deposition (APCVD) is reported. Graphene thin films were deposited on nickel foam under isobaric conditions in an inert environment. The process parameters such as temperature, time, and the gas flow rate were statistically optimised using design of experiment (DOE) to maximise the yield of graphene. The structural and morphological properties of the fabricated graphene electrode were investigated through X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), and energy dispersive X-ray spectroscopy (EDS). The electrochemical investigations were conducted through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. The results confirmed few-layered graphene with good surface morphology, high purity, and crystallinity of a binder-free electrode. The statistical analysis revealed that the optimal graphene electrode fabrication conditions were 900 °C, 10 min, and 100 sccm, respectively. Moreover, the regressed model and experimental results for the graphene growth were determined to be 3.93 mg/cm2, and 4.01 mg/cm2, respectively. Electrochemically, a specific capacitance value of 62.07 F/g was recorded at a scan rate of 3 mV/s showing an excellent performance of the fabricated 3D graphene electrode for energy storage applications. • 3D binder-free graphene electrode exhibits excellent properties. • Rapid and cost-effective fabricating of binder-free electrode • Remarkable electrochemical performance (specific capacitance of 62.07 F/g) • Potential electrode candidate for enhanced electrochemical performance [ABSTRACT FROM AUTHOR]

In this study, NiO was electrodeposited on a 3D graphene electrode to produce a nanocomposite with enhanced electrochemical properties. The electrodeposition process parameters such as electrolyte concentration, deposition time, and deposition potential were statistically optimised using response surface methodology. The statistical analysis showed that the optimal electrodeposition conditions to be 0.3 M, 10 min, and -1.2 V for electrolyte concentration, deposition time, and deposition potential, respectively. Furthermore, the predicted model and experimental results for the specific capacity of G-NiO were determined to be 240.91 C/g and 240.58 C/g at 3 mV/s. The results show that the electrochemical deposition technique can be employed as a fast and reliable synthesis route to develop graphene-based metal oxide nanocomposites. The structural and morphological properties were determined by XRD and FESEM studies. The electrochemical measurements revealed the excellent electrochemical performance of 3D graphene NiO composite (G-NiO) for energy storage applications. • Process optimisation study for the electrodeposition of NiO. • G-NiO binder-free electrode exhibits excellent electrochemical properties. • High specific capacity (240.58 C/g) of G-NiO electrode. • Rapid fabrication and eco-friendly of binder-free electrode. [ABSTRACT FROM AUTHOR]