Pseudocapacitor Applications Research Articles

Structure and morphology modification of ZnO nanocrystals via substitutional cobalt doping for enhanced electrochemical activity

This study investigated the electrochemical performance of the morphologically and structurally modified Co-doped ZnO nanocrystals synthesized via the chemical co-precipitation method. The structural properties were characterized by XRD, where the lattice parameters and volume got smaller with the increasing amount of Cobalt doping. The compositional analyses showed that 1.5 and 2.5 at% of Cobalt was present in the Co-doped ZnO nanocrystals. The FT-IR analyses showed that Zn–O (tetrahedral) and Zn–O (octahedral) vibrational modes are present for the precipitated ZnO-based nanocrystals. Besides that, the characteristic Raman spectra mode for ZnO displayed redshift, and more modes were activated, which showed a change in the defect chemistry after the cobalt substitution into the ZnO host lattice. A significant change was observed in morphology where the pristine ZnO formed nanoflower composed of nanoflakes and the Co-doped ZnO nanoparticles formed nanospheres. Lastly, cyclic voltammetry was performed at different scan rates where typical Faradaic peaks were observed for all the samples, and the electrochemical performance was increased with the small amount of Co doping into the ZnO lattice. The samples showed improved pseudocapacitive behavior, suggesting that Cobalt doped ZnO nanoparticles synthesized via the chemical co-precipitation method can be a potential electrode material for pseudocapacitor applications.

Facile hydrothermal synthesis of a tri-metallic Cu-Mn-Ni oxide-based electrochemical pseudo capacitor.

Transition metal oxide nanocomposites with heterostructures have gained a lot of attention for use in supercapacitors owing to their low cost, high surface area, fast transport of ions and electrons and high specific capacitance due to efficacious interplay between the electrode and the electrolytes. In this study, we fabricated tri-metallic Cu, Mn, Ni(CMNO), bi-metallic Mn, Ni(MNO) and mono-metallic Ni(NO) oxides through a facile hydrothermal route. All the fabricated materials were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and energy dispersive spectroscopy (EDX), and their electrochemical properties were studied using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge (GCD). The CMNO material showed remarkable electrochemical performance with a specific capacitance of 790.63 F g-1 at a current density of 1 A g-1, surpassing the performance of MNO (438.4 F g-1) and NO (290.82 F g-1). Furthermore, CMNO showed high cycling stability with a retention of 96.7% specific capacitance after 8000 cycles. Based on remarkable and unique properties, the CMNO material is regarded as a promising material for new-generation pseudo-capacitor applications.

Role of walnut ac-based Si-ZrO2: investigation of rietveld refinement, optical and electrochemical properties for pseudo-capacitor applications

In this current project, silicon substituted zirconia matrixes with the general formula of SixZr(1-x)O2 at x = 0.1–0.6, step size 0.1 have been fabricated through powder metallurgy route. All the samples have been sintered at 1200 °C for four hours in an air furnace. The structural, refinement, 3-dimensional view, functional groups, optical and electrochemical properties have been investigated using x-ray diffractometer (XRD), Rietveld refinement, diamond and Vista software, Fourier Infrared spectroscopy (FTIR), Diffuse reflectance spectroscopy (DRS), and Cyclic voltametric (CV) respectively. The XRD and Rietveld refinement exhibit sharp peaks which are matched with JCPD card no 07-0343, the single monoclinic phase is achieved in all samples. The goodness of fit clarifies the proper growth of the crystal. Furthermore, the theoretical evaluation is cross-matched with refinement data. The ATR-FTIR analysis indicates the characteristic bands of monoclinic zirconia. Due to the creation of active sites on the electrode surface, the average surface area of these oxides as determined by SEM is in the range of 58–63 m2 g−1. The lowest band gap and higher ionic conductivity values reveal the higher compatibility rate of charge carriers. The maximum specific capacitance (Csp) obtained from CV, GCD, and EIS analyses using walnut shell a.c is 903.1 A g−1, which are excellent materials for pseudocapacitive electrodes.

Advances in WO3-Based Supercapacitors: State-of-the-Art Research and Future Perspectives.

Electrochemical energy storage devices are one of the main protagonists in the ongoing technological advances in the energy field, whereby the development of efficient, sustainable, and durable storage systems aroused a great interest in the scientific community. Batteries, electrical double layer capacitors (EDLC), and pseudocapacitors are characterized in depth in the literature as the most powerful energy storage devices for practical applications. Pseudocapacitors bridge the gap between batteries and EDLCs, thus supplying both high energy and power densities, and transition metal oxide (TMO)-based nanostructures are used for their realization. Among them, WO3 nanostructures inspired the scientific community, thanks to WO3's excellent electrochemical stability, low cost, and abundance in nature. This review analyzes the morphological and electrochemical properties of WO3 nanostructures and their most used synthesis techniques. Moreover, a brief description of the electrochemical characterization methods of electrodes for energy storage, such as Cyclic Voltammetry (CV), Galvanostatic Charge-Discharge (GCD), and Electrochemical Impedance Spectroscopy (EIS) are reported, to better understand the recent advances in WO3-based nanostructures, such as pore WO3 nanostructures, WO3/carbon nanocomposites, and metal-doped WO3 nanostructure-based electrodes for pseudocapacitor applications. This analysis is reported in terms of specific capacitance calculated as a function of current density and scan rate. Then we move to the recent progress made for the design and fabrication of WO3-based symmetric and asymmetric supercapacitors (SSCs and ASCs), thus studying a comparative Ragone plot of the state-of-the-art research.

Boron nitride/polyaniline composite-based hybrid electrode for pseudocapacitor application

Boron nitride/polyaniline composite-based hybrid electrode for pseudocapacitor application

Facile synthesis of porous transition metal hydroxides from a poly(4-vinyl pyridine) film by controlling pH.

Non-noble transition metal hydroxides have been widely used in electrochemical devices because of low cost and multiple redox states. In particular, self-supported porous transition metal hydroxides are used to improve the electrical conductivity, as well as achieving fast electron and mass transfer and a large effective surface area. Herein, we introduce facile synthesis of self-supported porous transition metal hydroxides using a poly(4-vinyl pyridine) (P4VP) film. We used metal cyanide as a transition metal precursor capable of forming metal hydroxide anions in aqueous solution, which is the seed for transition metal hydroxides. To increase the coordination between P4VP and the transition metal cyanide precursors, we dissolved the precursors in buffer solutions with various pH. When the P4VP film was immersed in the precursor solution with lower pH, the metal cyanide precursors were sufficiently coordinated with the protonated nitrogen in P4VP. When reactive ion etching was performed on the precursor-containing P4VP film, the P4VP region without coordination was etched out and became pores. Then, the coordinated precursors were aggregated as metal hydroxide seeds and became the metal hydroxide backbone, resulting in the formation of porous transition metal hydroxide structures. We successfully fabricated various self-supported porous transition metal hydroxides (Ni(OH)2, Co(OH)2, and FeOOH). Finally, we prepared a pseudo-capacitor based on self-supported porous Ni(OH)2, which showed a good specific capacitance (780 F g-1 at 5 A g-1).

Facile in-situ synthesis of MnO2-ITO NWs composite for electrochemical supercapacitors

MnO2 is a promising material for pseudocapacitor applications due to its high specific capacity and low cost, while MnO2 electrodes suffer from their low electrical and ionic conductivities. Herein, a facile and low-cost method is adopted to synthesize MnO2 - tin-doped indium oxide nanowires (ITO NWs) composite with highly ordered network structures for electrochemical supercapacitors. Such network structure can effectively decrease the ion diffusion and charge transport resistance in the electrode. The specific capacitance of bare ITO NWs is only 2.83 F g−1, thus the contribution of the matrix material to capacitance can be ignored, and the optimized MnO2 possesses a high specific capacitor of 508.54 F g−1 at the scan rate of 5 mV s−1. It is anticipated that the synthesized MnO2-ITO NWs composite will find wide applications in supercapacitors (SCs) and other devices in virtue of their outstanding characters of good conductivity, convenient synthesis.

Pseudocapacitive Effects of Multi-Walled Carbon Nanotubes-Functionalised Spinel Copper Manganese Oxide.

Spinel copper manganese oxide nanoparticles combined with acid-treated multi-walled carbon nanotubes (CuMn2O4/MWCNTs) were used in the development of electrodes for pseudocapacitor applications. The CuMn2O4/MWCNTs preparation involved initial synthesis of Mn3O4 and CuMn2O4 precursors followed by an energy efficient reflux growth method for the CuMn2O4/MWCNTs. The CuMn2O4/MWCNTs in a three-electrode cell assembly and in 3 M LiOH aqueous electrolyte exhibited a specific capacitance of 1652.91 F g−1 at 0.5 A g−1 current load. Similar investigation in 3 M KOH aqueous electrolyte delivered a specific capacitance of 653.41 F g−1 at 0.5 A g−1 current load. Stability studies showed that after 6000 cycles, the CuMn2O4/MWCNTs electrode exhibited a higher capacitance retention (88%) in LiOH than in KOH (64%). The higher capacitance retention and cycling stability with a Coulombic efficiency of 99.6% observed in the LiOH is an indication of a better charge storage behaviour in this electrolyte than in the KOH electrolyte with a Coulombic efficiency of 97.3%. This superior performance in the LiOH electrolyte than in the KOH electrolyte is attributed to an intercalation/de-intercalation mechanism which occurs more easily in the LiOH electrolyte than in the KOH electrolyte.

Low-Cost, High-Yield ZnO Nanostars Synthesis for Pseudocapacitor Applications.

Energy storage devices based on earth-abundant materials are key steps towards portable and sustainable technologies used in daily life. Pseudocapacitive devices, combining high power and high energy density features, are widely required, and transition metal oxides represent promising building materials owing to their excellent stability, abundance, and ease of synthesis. Here, we report an original ZnO-based nanostructure, named nanostars (NSs), obtained at high yields by chemical bath deposition (CBD) and applied as pseudocapacitors. The ZnO NSs appeared as bundles of crystalline ZnO nanostrips (30 nm thin and up to 12 µm long) with a six-point star shape, self-assembled onto a plane. X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence spectroscopy (PL) were used to confirm the crystal structure, shape, and defect-mediated radiation. The ZnO NSs, dispersed onto graphene paper, were tested for energy storage by cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) analyses, showing a clear pseudocapacitor behavior. The energy storage mechanism was analyzed and related to oxygen vacancy defects at the surface. A proper evaluation of the charge stored on the ZnO NSs and the substrate allowed us to investigate the storage efficiency, measuring a maximum specific capacitance of 94 due to ZnO nanostars alone, with a marked diffusion-limited behavior. The obtained results demonstrate the promising efficacy of ZnO-based NSs as sustainable materials for pseudocapacitors.

MnO2 core-shell type materials for high-performance supercapacitors: A short review

Energy storage systems have gotten a lot of attention in recent decades, especially in industries like hybrid electric vehicles and smart portable electronics. MnO2 based materials have been extensively studied for application in pseudocapacitors due to their high theoretical specific capacitance, high power density, fast charge/discharge capability, strong chemical and thermal stability, long cycling life, natural abundance, environmental friendliness, and inexpensive cost. The material's core/shell structure is one of the most effective techniques to create high surface area and high conductivity for providing more Faradaic reaction sites and accelerating charge transfer, respectively, and thus to improve supercapacitors performance. This review paper examines the morphology and synthesis to better comprehend the MnO2 core–shell type materials. The electroactive materials applied in the core/shell structure include metal oxides, metal hydroxides, metal chalcogenides, carbon materials, conducting polymers etc. Finally, the challenges and next steps in developing MnO2 core–shell type materials for high-performance supercapacitors (SCs) are discussed.

Nanoporous Silicon with Graphene-like Coating for Pseudocapacitor Application.

This paper presents the results of studies of the nanoporous silicon structure, both with different pore depths (up to 180 μm) and with layers in which a graphene-like coating was synthesized on the inner surface of the pores. The nanoporous layers were characterized by SEM as well as IR and Raman spectroscopy. Cyclic voltammetry and galvanostatic charge–discharge data in 3 M H2SO4 are presented as well as the results of the cyclic stability of these characteristics for the nanoporous structure. It was found that the degree of electrolyte pre-impregnation significantly affected the electrochemical processes, and the capacitance values depended on the depth (thickness) of the nanoporous layer. Increasing the thickness of the porous layer led to an increase in area-normalized pseudocapacity and was limited only by the mechanical strength of the structure. Performance improvement was also achieved by synthesis of the graphene-like layer in the volume of the nanoporous structure. The electrodes (composite materials) proposed in the work showed one of the best capacitive characteristics (87 mF/cm2 with 100% capacity retention after 15,000 cycles) in comparison with the data reported in the literature at present.

Direct SILD synthesis of efficient electroactive materials based on ultrathin nanosheets of amorphous CoCr-LDH

In this work, we present a novel facile route to direct the synthesis of amorphous CoCr-LDH nanosheets via the Successive Ionic Layer Deposition (SILD) method. The results showed that the as-synthesized product is formed as ultrathin amorphous CoCr-LDH nanosheets with a thickness of 6–8 nm. Electrochemical characterization of the electrode based on the CoCr-LDH nanolayers deposited on nickel foam shows a pseudocapacitive behavior with the high specific capacity (1080F/g at a current density of 1 A/g) and also low hydrogen evolution reaction (HER) overpotential (-175 mV at 10 mA/cm2) in alkaline media. We believe that these nanomaterials are can be promising candidates for application in high-effeciency pseudocapacitors and electrocatalysts for water splitting in alkaline media.

Facile hydrothermal synthesis of α-MnO2 and δ-MnO2 for pseudocapacitor applications

Facile hydrothermal synthesis of α-MnO2 and δ-MnO2 for pseudocapacitor applications

Characterization of nickel sulfide and zinc sulfide nanostructures

The present work reports the synthesis of nanoparticles of nickel sulfide (NiS), zinc sulfide (ZnS), and NiS/ZnS nanocomposites using hydrothermal method followed by their analytical characterizations. Field emission scanning electron microscopic survey confirms the star-like, spherical and mixture of both shapes for the NiS, ZnS and NiS/ZnS nanocomposites, respectively, whereas EDX spectrum corroborates the chemical purity of as-synthesized nanomaterials. Optical band gap of NiS, ZnS and nanocomposite, as determined by the tauc’s plot method, were found 4 eV, 3.8 eV, and 4.2 eV, respectively. Cyclic voltammetry and galvanostatic charge-discharge have been measured and a maximum specific capacitance of 1594.68 F/g is observed at a scan rate of 5 mV/S for the composite material with a charging/discharging time of 461.97sec. Owing to Conducive performance and potential of the as-synthesized NiS/ZnS nanocomposite for electrochemical studies, suggests their appropriateness for pseudo-capacitor application

Influence of electrolyte and redox active electrode materials properties on working mechanism and performance of manganese oxide-based supercapacitors

In this work the pseudocapacitors based on graphite foil/manganese oxide powder electrodes, CelgardTM separator foil, and different water-based electrolytes were manufactured. Commercially available MnO2 (Sigma-Aldrich) with average grain size of 10 µm, milled – 0.1 µm, milled and reduced in 5vol.% of H2 in Ar atmosphere (10 h at 600 °C) were used for electrode formation. The influence of electrolytes on the performance of pseudocapacitors was tested using cyclic voltamperometry. The electrolytes were based on cations with different: valence (Na+, K+, Ca2+ and Al3+), activity (a), hydrated ion size (rh), specific ionic conductivity of electrolyte (λ), diffusion coefficient (D) and these parameters were correlated with determined capacitances. The highest capacitances were observed for K+-based electrolytes, which can be explained by the smallest rh and the highest D for this cation. Such direct explanation was not possible for other cations as the parameters describing the electrolyte properties are depends on each other and should be analyzed in conjunction. The observed correlations shows that the diffusion coefficient is the most valuable parameter for selection of the electrolyte for pseudocapacitor applications. The influence of electrode materials properties must be also taken into account, as the crystal structure, grain size, morphology or electrical properties influence the mechanism of charge accumulation of different ions, as it was simultaneously observed in this work.

Synthesis, Characterizations, and Electrochemical Performances of Highly Porous, Anhydrous Co0.5Ni0.5C2O4 for Pseudocapacitive Energy Storage Applications.

Electrochemical energy storage relies essentially on the development of innovative electrode materials with enhanced kinetics of ion transport. Pseudocapacitors are excellent candidates to bridge the performance gap between supercapacitors and batteries. Highly porous, anhydrous Ni0.5Co0.5C2O4 is envisaged here as a potential electrode for pseudocapacitor applications, mainly because of its open pore framework structure, which poses inherent structural stability due to the presence of planar oxalate anions (C2O42–), and active participation of Ni2+/3+ and Co2+/3+ results in high intercalative charge storage capacity in the aqueous KOH electrolyte. The Ni0.5Co0.5C2O4 electrode shows specific capacitance equivalent to 2396 F/g at 1 A/g in the potential window of 0.6 V in the aqueous 2 M KOH electrolyte by galvanostatic charge/discharge experiments. Predominant pseudocapacitive mechanism seems to operative behind high charge storage due to active participation of Ni2+/3+ and Co2+/3+ redox couple as intercalative (inner) and surface (outer) charges stored by porous anhydrous Co0.5Ni0.5C2O4 were close to high 38 and 62% respectively. Further, in full cell asymmetric supercapacitors (ASCs) in which porous anhydrous Co0.5Ni0.5C2O4 was used as the positive electrode and activated carbon (AC) was utilized as the negative electrode, in the operating potential window 1.6 V, the highest specific energy of 283 W h/kg and specific power of ∼817 W/kg were achieved at 1 A/g current rates. Even at a very high power density of 7981 W/kg, the hybrid supercapacitor still attains an energy density of ∼75 W h/kg with high cyclic stability at a 10 A/g current rate. The detailed electrochemical studies confirm higher cyclic stability and a superior electrochemical energy storage property of porous anhydrous Co0.5Ni0.5C2O4, making it a potential pseudocapacitive electrode for large energy storage applications.

Fabrication of Graphene-Fe3O4-Polypyrrole based ternary material as an electrode for Pseudocapacitor application

An attempt has been made to prepare Graphene-Fe3O4-polypyrrole (GFP) based ternary material as an electrode for pseudocapacitors. The GFP nanocomposite materials were fabricated well by a simple hydrothermal route. The as-prepared materials were well characterized by conventional analytical techniques. Polypyrrole helps the Fe3O4 nanoparticles to anchor on the graphene oxide surface and inhibits the aggregation of sheets of graphene as well as Fe3O4 particles. It also improves the electrochemical performance to estimate the performance of electrochemical behavior of the prepared ternary electrode material for cyclic voltammetry (CV), galvanostatic charge–discharge, and Electrochemical impedance spectroscopy (ESI) in which a three-electrode system has been used at room temperature in an aqueous electrolyte. The effect of scan rate and current density has also been studied on electrochemical performance. At a constant current density of 2.5 A/g, the maximum specific capacitance 180.18F/g is found and the specific capacitance is 204F/g in 1 M KOH solution of the ternary composite at a 5 mV/s scan rate. Furthermore, the energy density of 140.76 Wh/kg exhibited by the capacitor at a reasonable high-power density of 5680 W/kg, which is appreciably greater than parent materials.

Hydrothermal Synthesis of Co3O4/ZnCo2O4 Core-Shell Nanostructures for High-Performance Supercapacitors

Supercapacitive properties of Co/ZnCo oxide composite with a core–shell nanostructure (Co3O4/ZnCo2O4) prepared directly onto a nickel foam substrate by a two-step hydrothermal method were investigated. The synthesized core–shell structure consisted of some ∼40–100 nm in thick flaky ZnCo2O4 deposits coated onto the surface of Co3O4 nanorods measuring ∼150 nm in diameter. The specific capacitance value of the Co3O4/ZnCo2O4 core–shell nanostructure synthesized by hydrothermal at 130 °C for a ZnCo2O4 deposition time of 2 h can attain 1804 F g−1 at a scan rate of 5 mV s−1. Furthermore, the core–shell structured electrode still exhibited a relatively good capacitance retention of more than 93% after 3000 CV cycles due to the superior structural support of Co3O4 scaffolds. The Co3O4/ZnCo2O4 core–shell structure exhibits excellent electrochemical performances and, as such, is one of the more promising active materials in pseudocapacitor applications.

One-Step Hydrothermal Synthesis of Nitrogen-Doped Reduced Graphene Oxide/Hausmannite Manganese Oxide for Symmetric and Asymmetric Pseudocapacitors.

In this paper, the pseudocapacitive performance of nitrogen-doped and undoped reduced graphene oxide/tetragonal hausmannite nanohybrids (N-rGO/Mn3O4 and rGO/Mn3O4) synthesized using a one-pot hydrothermal method is reported. The nanohybrid electrode materials displayed exceptional electrochemical performance relative to their respective individual precursors (i.e., reduced graphene oxide (rGO), nitrogen-doped reduced graphene oxide (N-rGO), and tetragonal hausmannite (Mn3O4)) for symmetric pseudocapacitors. Among the two nanohybrids, N-rGO/Mn3O4 displayed greater performance with a high specific capacitance of 345 F g–1 at a current density of 0.1 A g–1, excellent specific energy of 12.0 Wh kg–1 (0.1 A g–1), and a high power density of 22.5 kW kg–1 (10.0 A g–1), while rGO/Mn3O4 demonstrated a high specific capacitance of 264 F g–1 (0.1 A g–1) with specific energy and power densities of 9.2 Wh kg–1 (0.1 A g–1) and 23.6 kW kg–1 (10.0 A g–1), respectively. Furthermore, the N-rGO/Mn3O4 nanohybrid exhibited an impressive pseudocapacitive performance when fabricated in an asymmetric configuration, having a stable potential window of 2.0 V in 1.0 M Na2SO4 electrolyte. The nanohybrid showed excellent specific energy and power densities of 34.6 Wh kg–1 (0.1 A g–1) and 14.01 kW kg–1 (10.0 A g–1), respectively. These promising results provide a good substance for developing novel carbon-based metal oxide electrode materials in pseudocapacitor applications.

Facile microwave synthesis of Sn-doped WO3 for pseudocapacitor applications

Facile microwave synthesis of Sn-doped WO3 for pseudocapacitor applications