Redox Additive Electrolyte Research Articles

Enhancement in the Specific Energy of B‐doped Graphene Using Redox Additive Electrolytes

AbstractElectrochemical performance of carbon materials can be enhanced by doping with heteroatoms. Electrochemical investigations suggest that the B‐doped graphene in which B‐source and graphene oxide are in the ratio 1 : 1 demonstrates a highest specific capacitance of 406 F/g at 2 A/g in 1 M H2SO4. The specific capacity of B‐doped graphene in 0.01 M hydroquinone (HQ)/H2SO4 is 2523 C/g in redox additive electrolyte. Performance evaluation of fabricated symmetric supercapacitor cell indicates that the specific capacitance in 0.01 M HQ/H2SO4 and 1 M H2SO4 solution are found to be 440 and 284 F/g at 3 A/g, respectively and greater than EMIMBF4 (97 F/g). The maximum specific energy of the fabricated symmetric cell achieved using 0.01 M HQ/H2SO4 solution is found to be 50 Wh/kg which is comparatively superior than 1 M H2SO4 (14.2 Wh/kg) and EMIMBF4 (30 Wh/kg).

Hydrothermally derived porous carbon and its improved electrochemical performance for supercapacitors using redox additive electrolytes

The N-rich porous carbon with high surface area is derived from the starch of Artocarpus heterophyllus seed (AHS) through hydrothermal carbonization (HTC) followed by KOH chemical activation. The EDLC's are fabricated using nitrogen inherited porous carbon with and without the addition of 0.05 M VOSO4 as redox additive in the pristine 0.5 M H2SO4 electrolyte. The device delivered an ultrahigh specific capacitance of 133 Fg-1 (at a high current of 15 mA) and high specific energy (32 Whkg−1) at a specific power of 936 Wkg−1 in the redox electrolyte when compared with pristine 0.5 M H2SO4 (92 Fg-1). Similarly, the symmetric redox-mediated EDLC exhibited extended cyclic stability up to 10,000 cycles with a coloumbic efficiency of 97%. These outstanding performance of the fabricated EDLC is due to the excellent faradaic interaction between N-rich, surface-functionalized porous carbon electrode with the redox electrolyte at the electrode-electrolyte interface through the redox reaction between VO2+/VO2+ species. The present work corroborates that the combination of hydrothermal derived porous carbon (HPAC) and redox additive electrolyte is a promising way to enhance the specific capacitance of the electric double-layer capacitors.

Improved ion-diffusion assisted uniform growth of 1D CdS nanostructures for enhanced optical and energy storage properties

The defect-free growth of 1D CdS nanostructure faces serious setback since other techniques heavily bank on high-temperature growth, use of organic solvents, catalyst, seed layer, and expensive electrodes. Over and above, the organic ligand passivates the surface defect states that obstruct the optical pathway of 1D nanostructures; and make them unsuitable for device applications. Amidst all these shortcomings, low-cost ion-diffusion is one such technique which is simple, reproducible and eco-friendly for the synthesis of defect-free pure CdS nanotubes (NTs) through AAO membrane; reported here with strong merits, unlikely not possible with the conventional approaches. Aligned CdS NTs with tapered diameter at the bottom were fabricated for its possible incorporation into nanoscale photonic devices. The synthesized NTs showed strong photoluminescence (PL) near-band-edge emission and third order multiphonon LO mode in resonant Raman scattering (RRS); due to its small crystalline grain size. In addition, the well-aligned hollow CdS NTs on AAO membrane proved to be an excellent energy electrode material with a specific capacitance of 1207 F g−1 at a scan rate of 5 mV s−1 in 6 mol L−1 KOH with 10−4 mol L−1 of K3Fe(CN)6 as redox additive electrolyte.

The fascinating supercapacitive performance of activated carbon electrodes with enhanced energy density in multifarious electrolytes

The effect of electrolytes on activated porous carbon was extensively studied using different electrolytes. A symmetric supercapacitor cell in redox additive electrolyte delivered a high energy (58.5 W h kg−1) and power density (9 kW kg−1).

Effect of Redox Additive Electrolyte on the Electrochemical Performance of MnO2 Nanorods for Supercapacitor Application

Pure MnO2 nanorods were synthesized by hydrothermal method and characterized by different techniques to analyze their crystalline nature, surface morphology, functional groups, and optical properties. XRD analysis confirms that the prepared nanorods possess a tetragonal crystalline structure. The occurrence of nanorods was confirmed by SEM analysis and its elemental composition was studied by elemental mapping. MnO2 nanorods modified working electrode was fabricated by the deposition of prepared nanorods on nickel foil. Electrochemical performance of the MnO2 nanorods modified working electrode was studied using redox additive based electrolyte containing 0.1M K4 [Fe(CN)6 ] in 1M KOH solution. The maximum specific capacitance of the prepared nanorods in 1M KOH electrolyte was 89 Fg-1 and it is greatly enhanced by the addition of 0.1M K4 [Fe(CN)6 ] redox additives (634 Fg-1 ).

Enhanced electrochemical performance of Ti3C2Tx MXene film based supercapacitors in H2SO4/KI redox additive electrolyte

The introduction of redox additives into the electrolyte is considered to be an effective and facile approach to increase the specific capacitance of supercapacitors (SCs), as these additives facilitate redox reactions at the electrode/electrolyte interfaces. Herein, a freestanding titanium carbide Ti3C2Tx (MXene) film was prepared through lithium fluoride/hydrochloric acid (LiF/HCl) etching method and subsequent vacuum filtration process. Subsequently, the electrochemical behavior of freestanding Ti3C2Tx film based symmetric SCs was improved via the addition of potassium iodide (KI), as a redox additive. The optimized Ti3C2Tx//H2SO4/KI//Ti3C2Tx redox additive electrolyte SCs (RAESs) assembled using Ti3C2Tx film as both positive and negative electrodes and H2SO4/KI as electrolyte show a volumetric capacitance of 601 F cm−3 and a volumetric energy density of 83.5 Wh L–1 at a power density of 1800 W L–1. These results suggest the importance of KI redox additive electrolyte in developing Ti3C2Tx based SCs.

Structural analysis and redox additive electrolyte based supercapacitor performance of ZnO/CeO2 nanocomposite

The ZnO/CeO2 nanocomposite material has been successfully synthesized through a simple chemical precipitation method and calcinated at 750 °C. The calcinated sample has been characterized by powder X-ray diffraction analysis to confirm the crystalline nature of the material. The atomic positions and structural parameters were calculated by Rietveld refinement process from the observed diffraction pattern. The prepared nanocomposite was also characterized by SEM, FT-IR, and UV–Vis diffuse reflectance spectroscopy techniques to understand the surface morphology, functionality and optical properties of the prepared sample, respectively. The ZnO/CeO2 nanocomposite used to modify electrode to investigate the electrochemical performance towards supercapacitor application using 3 M KOH and 0.2 M K4[Fe(CN)6] redox additive based electrolyte. The ZnO/CeO2 nanocomposite delivered a maximum specific capacitance of 1069 Fg-1 at a scan rate of 5 mVs−1 and the maximum energy density of 39.6 Whkg−1 at 3 Ag-1 current density.

Improved surface charge storage properties of Prosopis juliflora (pods) derived onion–like porous carbon through redox-mediated reactions for electric double layer capacitors

Abstract Turning trash into treasure, the present work divulges the preparation of onion-like porous carbon derived out of the most malignant invasive weed, the Prosopis juliflora. The pods of the Prosopis juliflora are treated hydrothermally and chemically activated using KOH. The effect of activation temperature on the pore formation is investigated to obtain the desired porous carbon. The prepared porous carbon (J–800) has a significant specific surface area of 967 m2 g−1 with unique morphology of onion-like nanostructures and provided a sensible specific capacitance of 274 F g−1 at 1.3 A g−1 in H2SO4 electrolyte. Further, the performance of the device is effectually enhanced by adding KI as redox additive. Interestingly, the increased cell voltage (1.4 V) and improved cell capacitance of 588 F g−1 is obtained. Ultimately, a superior energy density of 35.7 Wh kg−1 at an enhanced power density of 971 W kg−1 is also obtained in the redox additive based aqueous electrolyte. A detailed investigation of the surface storage mechanism is discussed, and the stability of the prepared supercapacitors is also demonstrated. Thus, the most eradicable eco-threat P. juliflora is successfully reformed into an efficient electrode material for the energy storage application.

Significantly enhanced performance of rGO/TiO2 nanosheet composite electrodes based 1.8 V symmetrical supercapacitor with use of redox additive electrolyte

The role of redox additive electrolytes in supercapacitors is gaining an increased significance. The present research work, for the first time, investigates the supercapacitor performance of a rGO/TiO2 nanosheet composite (prepared via facile one step hydrothermal reaction route) electrode in combination with a redox additive electrolyte, i.e., 0.2 M K3[Fe(CN)6] in 1 M Na2SO4. The synergistic effects between the porous rGO/TiO2 nanosheet electrode and the optimized redox electrolyte have helped to achieve a significantly high specific capacitance of 1565 F/g at a current density of 3 A/g (working potential window = −0.1–0.5 V). This value of specific capacitance is much higher than achievable with the application of a plain aqueous electrolyte (e.g., 1 M Na2SO4). Furthermore, rGO/TiO2 nanosheet electrodes have been used to fabricate a symmetrical supercapacitor device which has delivered an excellent specific capacitance value of 204.5 F/g at a current density of 1.5 A/g. The device also yielded promising values of energy density (15.5 Wh/kg) and power density (1.1 kW/kg) apart from showing a long-term cyclic stability (∼87%) even after 1000 continuous charge-discharge cycles.

Redox Additive Electrolyte Study of Mn–MOF Electrode for Supercapacitor Applications

AbstractThe selection of appropriate electrode materials and electrolytes in addition to optimization of their combinations is a key to improve the performance of supercapacitors. Among the new electrode materials, metal‐organic frameworks (MOFs) based electrodes are attracting attention in energy storage devices, including supercapacitors and batteries. In recent years, the redox additive electrolytes have been projected as efficient options over simple aqueous electrolytes. The present work reports the synthesis of a layered MOF, i. e., manganese‐1,4‐ benzene dicarboxylate (Mn‐BDC) and explores its utility as a supercapacitor electrode in the presence of an optimized redox additive electrolyte (0.2 M K3[Fe(CN)6] in 1 M Na2SO4 (0.2 M KFCN)). As demonstrated for the first time in this study, the combined use of the porous Mn‐BDC electrode and KFCN electrolyte has provided a synergistic enhancement in the supercapacitor performance. The present Mn‐BDC/KFCN combination has delivered a high specific capacitance of 1590 F/g at a current density of 3 A/g. Furthermore, the Mn‐BDC electrode could retain around 82% of its initial specific capacitance even after 3000 continuous charge‐discharge cycles. In view of its encouraging electrochemical performance parameters, the proposed system can be touted as an efficient supercapacitor assembly.

Self‐Nitrogen‐Doped Porous Biocarbon from Watermelon Rind: A High‐Performance Supercapacitor Electrode and Its Improved Electrochemical Performance Using Redox Additive Electrolyte

Self‐nitrogen‐doped biocarbons are obtained from the watermelon rind via an easy one‐step pyrolysis‐activation process. Porous biocarbon ACW‐2, obtained with a watermelon/potassium hydroxide (KOH) mass ratio of 1:2 at 700 °C, exhibits a large specific surface area of 1303.3 m2 g−1 and is decorated with abundant nitrogen/oxygen‐containing functional groups. When ACW‐2 is used as a supercapacitor electrode, a high specific capacitance of 260 F g−1 is achieved at a current density of 1 A g−1. ACW‐2 also exhibits an ultrahigh cycling stability, and its retention rate is maintained at 93.8% even after 5000 cycles at a scan rate of 100 mV s−1. Furthermore, ACW‐2 acquires a supramaximal specific capacitance (852 F g−1) and a high energy density (12.9 Wh kg−1) when p‐phenylenediamine redox additive is added into the KOH electrolyte. Therefore, the watermelon rind can be used as a promising biomass precursor, and the as‐prepared porous biocarbon is expected to be an outstanding comprehensive electrode material for electrochemical supercapacitors.

Performance enhancement approach for supercapacitor by using mango kernels derived activated carbon electrode with p-hydroxyaniline based redox additive electrolyte

Abstract Mango kernel is utilized for the synthesis of activated carbon as an electrode material for supercapacitors application. The synthesized active material is characterized by using the X-ray diffraction, Raman spectroscopy, scanning electron microscopy and fourier transform infrared spectroscopy techniques that confirm its well porous structure in graphitic conducting phase. Electrochemical testing of this material as an electrode for supercapacitor is carried out in 1M sulphuric-acid and sulphuric-acid added p-hydroxyaniline (redox additive) electrolytes by using impedance spectroscopy, cyclic voltammetry and charge-discharge techniques. We find that the fabricated supercapacitor with sulphuric-acid exhibits specific capacitance of 157.5 F g−1 and energy density of 11.8 Wh kg−1 at a current density of 1 A g−1, whereas by adding p-hydroxyaniline in sulphuric-acid, these values shows remarkable enhancement of 587.1 F g−1 and 34.3 Wh kg−1, respectively. The credit for remarkable enhancement is given to the hydroxyl and amine groups present in p-hydroxyaniline that initiates faradic redox reaction within the system and is also confirmed through the observed cyclic voltammetry pattern. Cyclic stability test shows 85.3% capacitance retention for almost 5000 cycles. Effect of temperature variation on the diffusion process, resistance and capacitance are also studied for the optimized cells.

Fabricating a high-energy-density supercapacitor with asymmetric aqueous redox additive electrolytes and free-standing activated-carbon-felt electrodes

Aqueous carbon-based supercapacitors are now reaching the energy density limits set by electric double layer mechanism and water decomposition voltage window. Here, we construct a high-energy-density carbon-based supercapacitor with a new strategy of asymmetric electrolyte design by adding K3[Fe(CN)6] and 2,6-dihydroxyanthraquinone (2,6-DHAQ) as positive and negative redox additives in 2 M KOH solution respectively. Modified activated carbon felt (ACF) serves as low-cost free-standing electrodes with no binders and conductive additives, porous structure of which facilitates excellent electrolyte permeability and fast ion transport. And it shows great potential for large-scale energy storage due to unique flexible and scalable properties. The corresponding supercapacitor integrating the advantages of redox activity of K3[Fe(CN)6] in positive potential and 2,6-DHAQ in negative potential achieves higher ion utilization, extended operation window to 2 V, high cell capacitance of 79 F g−1 and excellent cycling performance with 84% capacitance retention after 5000 cycles. Most importantly, it delivers high energy density of 39.1 Wh kg−1 maintaining superior power density, much higher than those of previously reported supercapacitors with symmetric aqueous redox electrolytes. The asymmetric redox additives in aqueous electrolytes for ACF-based supercapacitors may represent a new approach to high-performance energy storage.

High-performance quasi-solid-state asymmetric supercapacitors based on BiMn2O5 nanoparticles and redox-additive electrolytes

The investigation of nanomaterials with improved energy storage performance is essential in the development of high energy density supercapacitors.

High-Performance Symmetrical Supercapacitor with a Combination of a ZIF-67/rGO Composite Electrode and a Redox Additive Electrolyte.

The synthesis of a highly porous composite of ZIF-67 and reduced graphene oxide (rGO) using a simple stirring approach is reported. The composite has been investigated as an electrode to be assembled in a supercapacitor. In the presence of an optimized redox additive electrolyte (RAE), that is, 0.2 M K3[Fe(CN)6] in 1 M Na2SO4, the ZIF-67/rGO composite electrode has combined the properties of improved conductivity, high specific surface area, and low resistance. The proposed composite electrode in the three-electrode system shows an ultrahigh specific capacitance of 1453 F g–1 at a current density of 4.5 A g–1 within a potential window of −0.1 to 0.5 V. Further, the ZIF-67/rGO composite electrode was used to fabricate a symmetrical supercapacitor whose operation in the presence of the RAE has delivered high values of specific capacitance (326 F g–1 at a current density of 3 A g–1) and energy density (25.5 W h kg–1 at a power density of 2.7 kW kg–1). The device could retain about 88% of its initial specific capacitance after 1000 repeated charge–discharge cycles. The practical usefulness of the device was also verified by combining two symmetrical supercapacitors in series and then lighting a white light-emitting diode (illumination for 3 min). This study, for the first time, reports the application of a ZIF-based composite (ZIF-67/rGO) in the presence of an RAE to design an efficient supercapacitor electrode. This proposed design is also scalable to a flexible symmetric device delivering high values of specific capacitance and energy density.

Regulating Fast Anionic Redox for High-Voltage Aqueous Hydrogen-Ion-based Energy Storage.

The ionic conductivity and small size of the hydrogen ion make it an ideal charge carrier for hydrogen-ion energy storage (HES); however, high-voltage two-electrode configurations are difficult to construct as the result of the lack of efficient cathodic energy storage. Herein, the high potential fast anionic redox at the cathode of reduced graphene oxide (rGO) was applied by introducing redox additive electrolytes. By coupling the storing hydrogen ion in the Ti3 C2 Tx at the anode, a HES with a voltage of 1.8 V and a plateau voltage at 1.2 V was constructed. Compared with 2.2 Wh kg-1 for the low-voltage Ti3 C2 Tx //Ti3 C2 Tx , the specific energy of asymmetric rGO//Ti3 C2 Tx reaches 34.4 Wh kg-1 . Furthermore, it possesses an energy density of 23.7 Wh kg-1 at high power density of 22.5 kW kg-1 . Thus, this study provides a novel guideline for constructing high-voltage fast HES full cells.

Regulating Fast Anionic Redox for High‐Voltage Aqueous Hydrogen‐Ion‐based Energy Storage

AbstractThe ionic conductivity and small size of the hydrogen ion make it an ideal charge carrier for hydrogen‐ion energy storage (HES); however, high‐voltage two‐electrode configurations are difficult to construct as the result of the lack of efficient cathodic energy storage. Herein, the high potential fast anionic redox at the cathode of reduced graphene oxide (rGO) was applied by introducing redox additive electrolytes. By coupling the storing hydrogen ion in the Ti3C2Tx at the anode, a HES with a voltage of 1.8 V and a plateau voltage at 1.2 V was constructed. Compared with 2.2 Wh kg−1 for the low‐voltage Ti3C2Tx//Ti3C2Tx, the specific energy of asymmetric rGO//Ti3C2Tx reaches 34.4 Wh kg−1. Furthermore, it possesses an energy density of 23.7 Wh kg−1 at high power density of 22.5 kW kg−1. Thus, this study provides a novel guideline for constructing high‐voltage fast HES full cells.

A phenylenediamine-mediated organic electrolyte for high performance graphene-hydrogel based supercapacitors

We prepare a novel redox-additive organic electrolyte containing phenylenediamine for a graphene-hydrogel supercapacitor. By adopting this electrolyte, significant capacity enhancement (47–596% increase) is achieved. At the concentration of 0.02 mol l−1, the specific capacity value of the graphene-hydrogel electrode reaches 171 mAh g−1, 287 mAh g−1, and 353 mAh g−1 at 1 A g−1 for o-phenylenediamine (OPD), m-phenylenediamine (MPD), and p-phenylenediamine (PPD), respectively. The enhancement by PPD is more significant than OPD and MPD at concentrations higher than 0.02 mol l−1. This behavior is likely caused by the para-amino groups, which exhibits less stereo-hindrance during the absorption of phenylenediamine onto the graphene surface. In the electrolyte containing 0.04 mol l−1 of PPD, specific capacity of 516 mAh g−1 at 1 A g−1 and energy density of 143 Wh kg−1 with power density of 1.11 kW kg−1 are achieved. Meanwhile, 93.8% of the electrode's initial capacity (433 mAh g−1) is retained after 5000 cycles at 2 A g−1, demonstrating its excellent cycling stability.

Improving the electrochemical performances of active carbon-based supercapacitors through the combination of introducing functional groups and using redox additive electrolyte

High-performance and low-cost electrochemical capacitors (ECs) are essential for large-scale applications in energy storage. In this work, the specific capacitance of active carbon (AC) electrode was significantly improved through the combination of introducing functional groups on the surface of AC and adding redox-active molecules (K3Fe(CN)6) into 2 M KOH aqueous electrolytes. The surface-oxygen functionalized AC (FAC) was synthesized using HNO3 echoed as the electrode and 2 M KOH with 0.1 M K3Fe(CN)6 as the electrolyte. The surface functional groups of the AC not only contribute to the pseudocapacitance but also increase the active sites of the electrode/electrolyte interface, which enhances the electrochemical activity of the Fe(CN)63−/Fe(CN)64− redox pair, thus leading to high capacitance. In the redox electrolyte, the specific capacitance was much higher in 229.17 F g−1 (1 A g−1) achieved for those FAC than in raw AC (only 147.06 F g−1). Similarly, the FAC electrode suggested high energy density and extended cycling stability in the KOH + K3Fe(CN)6 electrolyte.

Enhanced electrochemical performance of in situ reduced graphene oxide–polyaniline nanotubes hybrid nanocomposites using redox-additive aqueous electrolyte

Reduced graphene oxide (RGO)–polyaniline nanotubes (PAniNTs) nanocomposites have been synthesized by in situ reduction of GO. The morphology and structure of the nanocomposites are characterized by HRTEM, XRD and micro-Raman spectroscopy. The electrical and electrochemical performances of the nanocomposites are investigated for different RGO concentrations by conductivity measurements, cyclic voltammetry, charge-discharge and electrochemical impedance spectroscopy. Highest gravimetric specific capacitance of 448.71 F g−1 is obtained for 40 wt.% of RGO-PAniNTs nanocomposite as compared to 194.92 F g−1 for pure PAniNTs in 1 M KCl electrolyte. To further improve the electrochemical performance of the nanocomposite electrode, KI is used as redox-additive with 1 M KCl electrolyte. Highest gravimetric specific capacitance of 876.43 F g−1 and an improved cyclic stability of 91% as compared to 79% without KI after 5000 cycles is achieved for an optimized 0.1 M KI concentration. This is attributed to the presence of different ionic species of I− ions that give rise to a number of possible redox reactions improving the pseudocapacitance of the electrode. This improved capacitive performance is compared with that of catechol redox-additive in 1 M KCl electrolyte, and that of KI and catechol redox-additives added to 1 M H2SO4 electrolyte.