Introducing new inexpensive materials for supercapacitors application with high energy density and stability, is the current research challenge. In this work, Silver doped carbon xerogels have been synthesized via a simple sol-gel method. The silver doped carbon xerogels are further surface functionalized with different loadings of nickel cobaltite (1 wt.%, 5 wt.%, and 10 wt.%) using a facile impregnation process. The morphology and textural properties of the obtained composites are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and nitrogen physisorption analysis. The silver doped carbon xerogels display a higher surface area and larger mesopore volume compared to the un-doped carbon xerogels and hierarchically porous structure is obtained for all materials. The hybrid composites have been utilized as electrode materials for symmetric supercapacitors in 6 M KOH electrolyte. Among all the hybrid composites, silver doped carbon xerogel functionalized with 1 wt.% nickel cobaltite (NiCo1/Ag-CX) shows the best supercapacitor performance: high specific capacitance (368 F g−1 at 0.1 A g−1), low equivalent series resistance (1.9 Ω), high rate capability (99% capacitance retention after 2000 cycles at 1 A g−1), and high energy and power densities (50 Wh/Kg, 200 W/Kg at 0.1 A g−1). It is found that the specific capacitance does not only depend on surface area, but also on others factors such as particle size, uniform particle distribution, micro-mesoporous structure, which contribute to abundant active sites and fast charge, and ion transfer rates between the electrolyte and the active sites.

The demand for high-performance supercapacitors (SCs) and non-conventional energy harvesting systems that possess the requirements of high power density and long lifetime is an essential need for future applications. Despite the usage of carbon material in commercial SCs, reduced graphene oxide (RGO) attracted great concerns due to its unique properties such as superior chemical and thermal stability, high surface area, 2D structure, and high electrochemical performance. In this work, reduced graphene oxide (RGO) was synthesized chemically by the reduction of graphene oxide prepared by improved Hummer method then modified by thermal reduction. After that, a symmetric supercapacitor electrodes were prepared by the coating of RGO paste on graphite substrates to reduce contact resistance and promote electrochemical stability. The CR2032 coin-cell was used as the standard cell package and KOH (6M) as a strong alkaline electrolyte. The electrochemical behavior of the cell was investigated by using Bio-Logic VSP-300 where high specific capacitance of 158 F/g was achieved at 5 mv/s scan rate. Interestingly, retention obtained was about 95% after 1000 cycles coupled with power and energy densities and 2000W/Kg and 14.4Wh/Kg at 1A, respectively. On the other hand, the microstructure and surface morphology of RGO was investigated using scanning electron microscopy (SEM) and X-Ray diffraction.

Flexible supercapacitor (SC) that possess high pulse power and energy density with long lifetime is an essential need for future applications. Moreover, gel polymer liquid-based SC presents many superior advantages over aqueous organic/inorganic electrolytes such as safety, long operation temperature range, solid-state appearance and relatively high voltage window. Therefore, Silver decorated reduced graphene oxide (RGO) coupled with developed (H 3 PO 4 /PVA/GO/ polyaniline) gel polymer were used to fabricate the SCs, which offers flexibility, durability, safety and ability to apply high scan rates. Influence of different ratios of silver to GO weight on specific capacitance and performance were studied. The SCs were prepared by printing technique (layer by layer) then peeled of the basic plastic substrate. After that, silver thin films were sputtered on both sides of the printed SCs as the current collectors using a shadow mask. Interestingly, a specific capacitance of about 164 F/g correlated with 29.5 Wh/Kg energy were achieved correlated with using H 3 PO 4 that is considered to be a weak electrolyte. Moreover, 0.5 ohm represents the smallest electric series resistance that would directly affect the power of the fabricated solid-state SC. The composite was studied using Raman spectroscopy, TEM and XRD, whereas, The VSP-300 potentiostat/galvanostat was used for extensive electrochemical characterizations of the prepared asymmetric SCs.