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Herein, we have successfully demonstrated a nanofiller (such as multiwalled carbon nanotubes (MWCNT)) dispersed in a polymer matrix (such as polyacrylonitrile (PAN)) as an effective pore filling agent to a microporous Daramic membrane for inhibiting bromine diffusion in zinc bromine redox flow batteries. A simple protocol of the MWCNT/PAN-Daramic membrane renders a major benefit for inhibiting bromine diffusion relative to the conventional microporous membrane. As a result, the MWCNT/PAN composite Daramic membrane exhibits remarkable electrochemical performance in zinc bromine redox flow batteries at various current densities. More impressively, the MWCNT/PAN composite Daramic membrane shows a 90% Coulombic efficiency compared to the pristine Daramic membrane and the PAN composite Daramic membrane with only 68.53 and 71.20% efficiencies at 160 mA cm-2, respectively. Moreover, the MWCNT/PAN composite Daramic membrane displays an extraordinary long cycling performance with a >97% Coulombic efficiency, whereas the Daramic membrane withstands only 200 cycles due to severe water transport from the catholyte to the anolyte. The zinc bromine redox flow battery assembled with the MWCNT/PAN composite Daramic membrane significantly reduces the self-discharge rate and retains an open circuit voltage of 1.69 V for 13.40 h in comparison to the Daramic membrane (10.83 h) and the PAN composite membrane (11.13 h). Thus, the extraordinary flow cell performance and stability of the MWCNT/PAN composite Daramic membrane lead to the development of an alternative to the microporous Daramic membrane in zinc bromine redox flow batteries.

Ring-opening metathesis polymerization (ROMP) of buckybowl corannulene-based oxa-norbornadiene monomer is shown to give rise to polymeric nanomaterials with an average pore size of about 1.4 nm and a surface area of 49.2 m2/g. Application in supercapacitor devices show that the corannulene-based nanomaterials exhibit a specific capacitance of 134 F·g–1 (1.0 V voltage window) in a three-electrode cell configuration. Moreover, the electrode assembled from these materials in a symmetric configuration (1.6 V voltage window) exhibits long-term cyclability of 90% capacitance retention after undergoing 10000 cycles. This work demonstrates that ROMP is a valuable method in synthesizing nanostructured corannulene polymers, and that materials based on the nonplanar polycyclic aromatic motif represents an attractive active component for fabrication of devices targeted at electrochemical energy storage applications. Accepted version

Electrochemical energy-storage technologies remain the only key to solve the increasing demands of global energy supply, zero-emission transportation, and grid storage in a greener way. Accordingly, novel strategies and the new promising designs of electrodes attempt to conquer the high energy density of supercapacitors without decreasing their power density and cycle life. In supercapacitors, asymmetric supercapacitors outshine the symmetric supercapacitors ( 2.0 V) in a safer way using aqueous electrolytes. Especially, emerging high energy supercapacitors perfected by suitable low cost-electrode materials are now the crown of energy storage research. Employing battery type Ni(OH)2 as a positive electrode has become a promising approach to building next-generation high energy supercapacitors besides its abundance, cost efficiency, environment friendliness, and high theoretical capacity. This review exclusively elaborates the unnoticed vision into the design, fabrication, mechanism, and investigation of such fascinating Ni(OH)2 based supercapacitors in an asymmetric fashion. Further, this review eventually mitigates the issues associated with the Ni(OH)2 component toward the goal of building next-generation supercapacitors for a sustainable environment.

Flexible all solid-state hybrid supercapacitors (HSCs) are considered to be significant energy storage devices and are used as major power sources in various real-time applications. Herein, we fabricated highly crystalline tungsten trioxide (WO3)‖vanadium pentoxide (V2O5) thin film supercapbatteries in which WO3 and V2O5 showed pseudo-capacitive and battery type behavior, respectively. For the first time, WO3 ‖V2O5 thin film based combination has been investigated in this work. The thin film structured electrodes used in this study were prepared in partially pressured, in situ annealing conditions using the pulsed laser deposition (PLD) technique. The as prepared 1.5 V solid state hybrid device delivered a maximum volumetric capacitance of 40.28 F cm−3 at 0.1 mA cm−2. A maximum specific energy density of approximately 12.58 mW h cm−3 at a specific power density of 0.316 W cm−3 was also achieved. Furthermore, the device showed an excellent round trip efficiency of 99.4%, even after 50 000 cycles, with a capacitance retention of 95.2%. The performance characteristics of the hybrid device were also compared with the V2O5‖V2O5 and WO3‖WO3 symmetric devices which showed a superior performance compared to the symmetric devices. In addition, the functions of the device with regards to various engineering aspects, such as the flexibility, twisting nature, and folded conditions, were demonstrated successfully. Furthermore, light-emitting diodes (LEDs) powered using the HSCs confirmed the potential applications of such devices in wearable and portable devices.

Modern wearable technologies require highly efficient energy storage devices for improving their performance attributing a controlled shape and flexibility. Here, the present study is focused on th...

In recent years, Li-S battery has received much attention owing to its high theoretical specific capacity of 1675 mAh g−1. However, diffusion of the polysulfide across the electrodes during charge-discharge process strictly affects the cell characteristics. To avoid such ion diffusion, usage of an appropriate separator is highly appreciable. A suitable separator, particularly in Li-S system, should act as selective ion diffusion medium and as better electrolyte absorber during the cell operando. Hence, in the present study, polyacrylonitrile-polyethersulfone (PAN/PES) based blend electrospun membrane is developed and employed as separator for the very first time in Li-S system. Physical characteristics such as shrinkage, electrolyte uptake, porosity were studied using various techniques. Concurrently, feasibility of the prepared electrospun membrane in Li-S battery is analysed using various electrochemical studies such cyclic voltammetry, galvanostatic charge-discharge studies and electrochemical impedance spectroscopy. The obtained characteristics of the synthesised membrane were also compared with the commercial Celgard 2320 separator. It is noteworthy to mention that the cell delivered an initial specific capacity of 1175 mAh g−1 at 0.1C for synthesised membrane which surpasses that of commercial one. Upon prolonged cycling, the cell showed more than 90% coulombic efficiency; thus, it clearly reveal the better Li ion diffusivity and control of polysulfide diffusion as compared to commercial separator.

Herein for the first time, we have reported the performance and characteristics of new high-voltage zinc–vanadium (Zn–V) metal hybrid redox flow battery using a zinc bromide (ZnBr2)-based electroly...

Optimization of the cell configuration utilizing various carbon felts for obtaining better performance in zinc-bromine redox flow battery (ZBRFB) system is reported. It is clearly observed that the reaction kinetics of both Zn and Br are enhanced when used in different cell configurations with carbon felts. Redox flow cells having carbon felts on both half-cells showed improved performance thanthe other cell configurations tested in the present study. Further, Rayon based carbon felt is evaluated as an electrode on both sides. It is noted that the Rayon carbon felt based cell exhibited good performance in terms of coulombic (96.26%), voltaic (83%) and energy efficiency (79.4%) at a current density of 20 mA.cm−2. In addition to that, Rayon felt based system showed good performance even at 40 mA.cm−2 (3250 mW h. l−1) which indicates the significance of the flow cell configuration on the overall cell performance.

Mn3O4 nanoparticles were anchored on the surface of oxidised graphite paper via template-free hydrothermal method. Synthesized samples were characterized using different techniques such as X-ray diffraction (XRD), Raman spectroscopy, Field Emission Scanning Electron Microscopy (FE-SEM), High Resolution Transmission Electron Microscopy (HRTEM) and X-ray Photoelectron Spectroscopy (XPS). Electrochemical capacitor behaviour was evaluated using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS). The binder free material was found to exhibit a specific capacitance of 471 F g−1 at a current density of 1 mA cm−2 in 1 M Na2SO4. Conductive additive free, Mn3O4 anchored electrode was used as positive electrode in the asymmetric cell fabrication; the asymmetric cell was tested at a potential window of 1.6 V and its performance characteristics were evaluated. The asymmetric cell delivered a maximum specific energy of 47 Wh kg−1 at a power density of 202.5 W kg−1 which evidenced the superior performance of the synthesized electrode material. Here in the present work, the surface oxidised graphite paper was used as an excellent current collector and active sites for anchoring Mn3O4 due to its desirable properties.

Electrochemical energy storage (EES) devices play an important role in meeting the demand for the electrical energy. Particularly, electrochemical hybrid capacitors (HCs) are considered as one of the potential candidates for fulfilling the energy requirement. In this work, aqueous electrolyte-based high voltage HC is fabricated and its electrochemical characteristics are analyzed. Here, electrochemically prepared NiCo and Bi thin films on stainless steel substrate were used as positive and negative electrodes, respectively. The phase structure and crystalline size of the electrodeposited films are confirmed from XRD and AFM. It is observed that the as prepared NiCo film showed an excellent specific capacitance value of 83.33 mF cm−2 at 0.5 mA cm−2; on the other side, Bi film also showed a good storage capacity of 32.2 μA h cm−2 at 1 mA cm−2; To realize the high energy density, Bi||NiCo combination of the thin film HC is fabricated and the HC devices showed excellent performance at a tested potential window of 1.5 V. The cell plateau voltage is observed at 0.8 V. The maximum specific energy density of 7.3 μW h was achieved at a specific power density is 0.3 mW cm−2. Maximum specific power of 7.5 mW cm−2 at an energy density of 1.875 μW h was obtained from HSC. This indicates the excellent performance of the HC at various conditions. Thus, the binder-free, electrodeposited active electrode materials of the present work will play a significant role in the various electronic applications by supplying the energy demand.

Two-dimensional (2-D) polymer has properties that are attractive for energy storage applications because of its combination of heteroatoms, porosities and layered structure, which provides redox chemistry and ion diffusion routes through the 2-D planes and 1-D channels. Here, conjugated aromatic polymers (CAPs) were synthesized in quantitative yield via solid-state polymerization of phenazine-based precursor crystals. By choosing flat molecules (2-TBTBP and 3-TBQP) with different positions of bromine substituents on a phenazine-derived scaffold, C–C cross coupling was induced following thermal debromination. CAP-2 is polymerized from monomers that have been prepacked into layered structure (3-TBQP). It can be mechanically exfoliated into micrometer-sized ultrathin sheets that show sharp Raman peaks which reflect conformational ordering. CAP-2 has a dominant pore size of ∼0.8 nm; when applied as an asymmetric supercapacitor, it delivers a specific capacitance of 233 F g–1 at a current density of 1.0 A g–1,...

Herein for the first time, we have successfully demonstrated the influence of flow rate on the polarization effect caused by the sluggish kinetics of Br−/Br2 redox couple in zinc-bromine redox flow battery (ZBRFB). Besides, the effect of perchloric acid (HClO4) on Br−/Br2 redox reaction has also been explored. The optimized electrolyte flow rate condition shows significant improvisation on the round-trip efficiency (> 95%) due to the balanced kinetics. Further, the double-layer formation was substantially minimized with the help of HClO4 as evidenced by cyclic voltammetry studies. The electrode kinetics towards Br−/Br2 also was enhanced by increasing the concentration of HClO4. The enhanced voltage efficiency (~85%) of the flow cell employing HClO4 as a supporting electrolyte is mainly accredited to the balanced conductivity of the redox electrolyte. Moreover, optimized flow cell design exhibits good cycle life and improved ohmic region over the prolonged cycle studies in comparison. Thus, the optimistic flow rate and the selection of such an efficient electrolyte additive can be proficient candidates for improving the zinc-bromine battery performances.

A novel high-voltage solid solution of Li2CoxMn1–x(SO4)2 (x = 0–1) was synthesized using a simple solid-state reaction. Single-phase monoclinic crystal structure was identified, and there was no evidence for the presence of an orthorhombic polymorph at a sample preparation temperature of 450 °C. Interestingly, the bimetallic sulfates were found to be thermally stable up to 550 °C, and it was validated through various characterization techniques. Beyond 550 °C, the materials start to decompose and form Li2SO4 and α-CoSO4 in the case of Li2Co(SO4)2, while Li2Mn(SO4)2 decomposes to form Li2Mn2(SO4)3. In addition, an important property called sensitivity toward moisture was also characterized, which plays a critical role in the handling of the sulfate-based cathode during the cell fabrication. Thus, the reaction mechanism involved during the absorption of the atmospheric moisture was also investigated carefully. Finally, for the first time electrochemical activity of both Co and Mn systems was discovered wher...

Activated carbon (AC) with high surface area (1901 m 2 g −1 ) is synthesized from low cost bio-waste orange ( Citrus sinensis ) peel for vanadium redox flow battery (VRB). The composition, structure and electrochemical properties of orange peel derived AC (OP-AC) are characterized by elemental analyzer, field emission-scanning electron microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, cyclic voltammetry (CV), and electrochemical impedance spectroscopy. CV results show that OP-AC coated bipolar plate demonstrates improved electro-catalytic activity in both positive and negative side redox couples than the pristine bipolar plate electrode and this is ascribed to the high surface area of OP-AC which provides effective electrode area and better contact between the porous electrode and bipolar plate. Consequently, the performance of VRB in a static cell shows higher energy efficiency for OP-AC electrode than the pristine electrode at all current densities tested. The results suggest the OP-AC to be a promising electrode for VRB applications and can be incorporated into making conducting plastics electrode to lower the VRB cell stack weight and cost.

In this work, -Co(OH)2 nanosheets are explored as efficient pseudocapacitive material for the fabrication of 1.6 V class high energy supercapacitors in asymmetric fashion. As-synthesized -Co(OH)2 nanosheets displayed an excellent electrochemical performance owing to the unique structure, morphology and reversible reaction kinetics (fast Faradic reaction) in both three electrode and asymmetric configuration (with activated carbon, AC). For example, in three electrode set-up, -Co(OH)2 exhibits a high specific capacitance of ~675 F g-1 at scan rate of 1 mV s-1. In asymmetric supercapacitor, -Co(OH)2||AC cell delivers a maximum energy density of 37.3 Wh kg-1 at a power density of 800 W kg-1. Even at harsh conditions (8 kW kg-1), the energy density of 15.64 Wh kg-1 is registered for -Co(OH)2||AC assembly. Such an impressive performance of -Co(OH)2 nanosheets in asymmetric configuration reveals the emergence of pseudo-capacitive electrode towards the fabrication of high energy electrochemical charge storage systems.

Activated carbon (AC) with high surface area (1,901 m2 g−1) is synthesized from bio-waste orange (Citrus sinensis) peel for fabrication of high specific energy lithium ion capacitors (LICs). The composition, structure and electrochemical properties of orange peel derived AC (OP-AC) are characterized by elemental analyzer, field emission-scanning electron microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, cyclic voltammogram, charge-discharge and impedance studies. Fabricated LIC using the high surface area OP-AC with pre-lithiated graphite (LiC6) delivered specific energy of ∼106 Wh kg−1. In addition, LIC configuration with Li4Ti5O12 was also fabricated and observed to be capable of delivering the specific energy of ∼35 Wh kg−1. Symmetric configuration of OP-AC with aqueous and organic solutions was also made for comparison purpose. A systematic improvement from the specific energy of ∼7 to 106 Wh kg−1 is noted from aqueous to LIC assembly. The findings open up the possibility of developing high specific energy LICs from abundant, low-cost, sustainable biomass waste.

Coconut shell derived mesoporous carbon (CS-AC) is explored as prospective supercapacitor component in Li-ion and Na-ion capacitors (LIC and NIC) along with pre-lithiated/sodiated natural plant derived hard carbon (HC) as battery element. Though, there is no obvious variation from the capacitive properties of CS-AC, but an obvious difference is evident for battery component in single electrode configuration. Based on such performance, the mass loading has been adjusted during the fabrication of LIC and NIC. Prior to this, HC is pre-lithiated/sodiated for LIC/NIC assembly. The CS-AC and pre-treated HC based materials registered the maximum energy density of ∼121 and ∼82 Wh kg−1 for LIC and NIC assemblies, respectively. An excellent long-term cycleability of ∼83% retention is noted for LIC after 8000 cycles, whereas NIC showed inferior performance (∼60%) under similar testing conditions. Multilayer surface film is the main reason for such performance which has been clearly revealed from the impedance measurements. First, the CS-AC is prepared by hydrothermal carbonization and subsequent chemical activation with ZnCl2 to yield high specific surface area and pore volume of 1795 m2 g−1 and 2.2 cm3 g−1, respectively, in which 71% originated from mesoporous region.

We report the fabrication of high energy Li-ion capacitor (LIC) using teak wood sawdust derived mesoporous activated carbon (AC-HBP) with electrochemically pre-lithiated graphite (LiC6). Three interesting supercapacitor assemblies are constructed using AC-HBP to realize the high energy density. Amongst, AC-HBP paired with LiC6 delivered a maximum energy density of ∼111 Wh kg−1 compared to Li4Ti5O12 in LIC (∼53 Wh kg−1) and AC-HBP (∼37 Wh kg−1) in symmetric configurations. This excellent energy density is mainly ascribed to the tailored mesoporous nature (∼67%) of the high surface area activated carbon (2108 m2 g−1) obtained via hydrothermal carbonization process in the presence of processing agent, benzene tetracarboxylic acid followed by physico-chemical activation.

We report on the synthesis of a high rate NaTi2(PO4)3/graphene composite for use as an anode material for high power Na-ion hybrid capacitors with the following characteristics; (1) reduction of the particle size of NaTi2(PO4)3 to the nanometer scale in order to reduce the Na+ ion diffusion length, (2) chemical bonding between NaTi2(PO4)3 nanoparticles and graphene in order to improve electrical conductivity, and (3) interconnected nanoporous structures in order to allow easy access of Na+ ions to NaTi2(PO4)3. For this, the NaTi2(PO4)3/rGO microsphere composite was prepared via a facile spray drying method using a solution mixture of graphene oxide, NaH2PO4·2H2O, Ti(OC2H5)4 and NH4H2(PO4)3, in which all the components of the titanium were present as ionic species in order to facilitate the chemical bonding between NaTi2(PO4)3 and rGO in the composite. The NaTi2(PO4)3/rGO microsphere composite had a Ti–O–C bond between NaTi2(PO4)3 nanoparticles (

Polyhalides based hybrid redox flow batteries are highly appropriated for long term stationary charge storage applications due to their high practical energy density, long cycle life, low cost, etc. Among various metal-halide redox flow batteries, zinc-bromine redox flow battery system received much attention due to its reasonable cell voltage, energy density and life-time. However, the poor kinetics of bromine/bromide redox reaction at the electrodes and bromine vapour formation during the charge process are the major issues associated with this flow system. In the present work, low loading of platinum is used as electrocatalyst for improving the Br2/Br-reaction kinetics where platinum particles are deposited on the graphite felt using pulsed laser deposition. Platinum decorated graphite felt is investigated as an active electrode material in the positive compartment of this flow system to study the improvement in the reaction kinetics of Br2/Br− redox couple reaction. This approach is highly influenced in bromine/bromide redox reaction kinetics, as a result, avg. Coulombic efficiency of 99.96% and ever best avg. energy efficiency of ~88% is observed for the zinc-bromine based flow cell tested at 50 mA cm−2. Thus, graphite felt having low loading platinum is considered as a potential candidate for enhancing the Br2/Br-kinetics at any given condition.

Linear two-dimensional materials have recently attracted an intense interest for supercapacitors because of their potential uses as electrodes in next-generation wearable electronics. However, enhancing the electrochemical properties of these materials without complicated structural modifications remains a challenge. Herein, we present the preparation of a hybrid electrode system via polydiacetylene (PDA) cloaking on the surface of aligned multiwall carbon nanotubes (MWCNTs) through self-assembly based in situ photopolymerization. This strategy eliminates the need for initiators and binders that hinder electrochemical performance in conventional conducting polymer based composite electrodes. As noncovalent PDA cloaking did not alter the chemical structure of MWCNTs, high inherent conductivity from sp2 hybridized carbon was preserved. The resulting hybrid microfiber (MWCNT@PDA) exhibited a significant increase in specific capacitance (1111 F g–1) when compared to bare MWCNTs (500 F g–1) and PDA (666.7 F g–...

In the present report, electrochemical, thermal, mechanical and structural properties of the polymer electrolyte composed of Polyvinylidene fluoride (PVdF)-Bis(trifluoromethane)sulfonimide (LiTFSI) for various concentrations of Sepiolite was investigated. Concentration of Sepiolite was optimised based on the ambient temperature conductivity. It was observed that 10 wt.% of sepiolite incorporated composite polymer electrolyte (CPE) showed a higher ionic conductivity in the order of 3.58 x 10−4 S cm−1. C−C stretching, C−F stretching and very strong -CF2 ring breathing vibrational modes of PVdF and the complexity of the prepared composite electrolyte were studied using FTIR and X-ray diffraction analysis. The as-prepared CPE is thermally stable up to ∼335 °C; the addition of sepiolite filler into the polymer salt matrix increased the storage modulus to 40 x 107 Pa from 12 x 107 Pa until 90 °C. The galvanic charge-discharge performances of the CPE that exhibited high ionic conductivity were evaluated in the Li|PVdF-LiTFSI-Sepiolite|LiFePO4 half cell configuration. The cell showed a reversible capacity of 148 mAh g−1 in the second cycle; and exhibited capacity retention above 75 % even after 100 cycles. It was noted that the incorporation of eco-friendly sepiolite into the polymer electrolyte greatly enhanced the thermal, mechanical, structural and electrochemical properties of the composite electrolytes.

Two-dimensional (2D) graphene oxide/polypyrrole (GO/PPy) hybrid materials derived from in-situ polymerization are used as precursors for constructing functionalized three-dimensional (3D) porous nitrogen-doped carbon nanosheet frameworks (FT-PNCNFs) through a one-step activation strategy. In the formation process of FT-PNCNFs, PPY is directly converted into hierarchical porous nitrogen-doped carbon layers, while GO is simultaneously reduced to become electrically conductive. The complementary functions of individual components endow the FT-PNCNFs with excellent properties for both supercapacitors (SCs) and sodium ion batteries (SIBs) applications. When tested in symmetrical SC, the FT-PNCNFs demonstrate superior energy storage behaviour. At an extremely high scan rate of 3000 mV s −1 , the cyclic voltammetry (CV) curve retains an inspiring quasi-rectangle shape in KOH solution. Meanwhile, high capacitances (∼247 F g −1 at 10 mV s −1 ; ∼146 F g −1 at 3000 mV s −1 ) and good cycling stability (∼95% retention after 8000 cycles) are achieved. In addition, an attractive SIB anode performance could be achieved. The FT-PNCNFs electrode delivers a reversible capacity of 187 mAh g −1 during 160th cycle at 100 mA g −1 . Its reversible capacity retains 144 mAh g −1 after extending the number of cycles to 500 at 500 mA g −1 .

Heterogeneous catalysts that are prepared by immobilizing noble metal nanoparticles (NPs) on solid matrices can serve as efficient catalysts in various catalytic reactions. However, the immobilized NPs usually suffer from detachment or migration during the catalytic process owing to their weak interactions with the matrices. Here, we developed a facile approach for the synthesis of high active and stable heterogeneous catalysts by entrapping Pd and Ru NPs in 3D ordered hierarchically porous inverse opal carbon (IOC). For these catalysts, the 3D open-porous structure on multiple length scales provides the reactants easy access to the catalytically active NPs while the entrapment of NPs inside IOC ensures their high dispersion and stability during the catalysis. As a result, the as-prepared catalysts exhibited both high activity and stability for the oxidation of CO and electrocatalysis of VO 2+ /VO 2 + redox couples. The conversion rate of CO over the IOC-PdNPs catalyst reached >98% at 200 °C, which showed no decrease after reacting for 10 h. The IOC-RuNPs-based working electrode exhibited highly reversible redox potentials at 1.25 V and 0.78 V, respectively, and no change of peak currents and peak potential separation were observed for 200 cycles of cyclic voltammetry (CV) measurements.

Research activities on the development of organic Na-ion hybrid electrochemical capacitors (NICs) are described in this review. In particular, more emphasis is given on the development of battery type electrodes (faradaic mechanism), for example, hard carbons, Na2Ti3O7, etc. Also, equal importance is given for the exploration of non-faradaic type counter electrodes derived from bio-mass and polymer precursors. In the recent past, Mxenes have attracted attention as promising candidates for cathodes and anodes for electrochemical energy storage devices. Accordingly, efficient utilization of such Mxenes as positive and negative electrodes in an NIC assembly is given along with their synthetic procedure. Furthermore, the symmetric configuration of other Na-ion based organic supercapacitor is also given in detail.

We report the fabrication of high energy Li-ion capacitors (LICs) using conversion type Mn3O4 octahedrons anchored to few layer graphene (Mn3O4-G) as the negative electrode with activated carbon (AC) as the positive one. First, the Mn3O4-G composite is prepared via a hydrothermal approach using commercially available graphene nanosheets. Li-storage studies of both electrodes (AC and Mn3O4-G) are conducted in single electrode/half-cell configuration with metallic Li to assess the mass balance. Prior to the fabrication of LICs, Mn3O4-G is pre-lithiated in Swagelok fittings with Li and subsequently paired with the desired loading of AC. The AC/Mn3O4-G based LIC delivered a maximum energy density of ∼142 W h kg−1 with excellent cyclability of 9000 cycles with ∼80% retention. This result certainly provides new avenues for the development of high energy LICs using conversion type negative electrodes rather than traditional insertion type anodes.

Graphene quantum dots (GQD) have been used in various potential applications due to their range of attractive properties such as high conductivity, good chemical resistance, very good optical properties and etc. Very first time, in this study, the GQD is used as a molecular catalyst; here the given volume of GQD around 300 μl is dispersed in as prepared vanadium based electrolyte. It is observed that the CV curve of the GQD incorporated electrolyte showed significant variation in the electrochemical activity of VO2 +/VO2+ redox reaction. The resistive behavior obtained from the EIS analysis of GQD showed highly enhanced values when compared with the bare electrolyte. The addition of GQD in the active electrolyte showed great improvement in the VO2 + to VO2+ redox reaction kinetics which is evidenced from the obtained kinetics parameters such as exchange current density, rate constant and etc. The GQD added electrolyte showed excellent improvisation in the exchange current density value of i 0 = 6.175 × 10−4 A cm−2 which is two-fold higher than the bare electrolyte (i 0 = 2.365 × 10−4 A cm−2). Thus, the idea of using GQD will play potential effect in various electrochemical applications.

A new class of redox flow batteries involving Fe3+/Fe2+ and Mn3+/Mn2+ redox couples in the anolyte and catholyte, respectively being investigated. The proposed novel design of Fe–Mn redox flow battery exhibits significant Coulombic efficiency of around 96%, at a current density of 7 mA cm−2. The Fe–Mn cell shows good capacity retention even after 100 cycles with the coulombic efficiency retaining at ∼95%. Further, high concentration anolyte and catholyte was used which helps to improve the practical energy density of the system (>40 Wh L−1). The overall cost of the system is expected to be significantly lower than the existing redox flow battery systems. Thus, the low-cost and eco-friendly nature of these active species make this flow battery to be a potential candidate for large scale electricity storage applications which further facilitates the full utilisation of the intermittent renewable energy resources.

Few-layered Ni(OH)2 nanosheets (4–5 nm in thickness) are synthesized towards high-performance supercapacitors. The ultrathin Ni(OH)2 nanosheets show high specific capacitance and good rate capability in both three-electrode and asymmetric devices. In the three-electrode device, the Ni(OH)2 nanosheets deliver a high capacitance of 2064 F g−1 at 2 A g−1, and the capacitance still has a retention of 1837 F g−1 at a high current density of 20 A g−1. Such excellent performance is by far one of the best for Ni(OH)2 electrodes. In the two-electrode asymmetric device, the specific capacitance is 248 F g−1 at 1 A g−1, and reaches 113 F g−1 at 20 A g−1. The capacitance of the asymmetric device maintains to be 166 F g−1 during the 4000th cycle at 2 A g−1, suggesting good cycling stability of the device. Besides, the asymmetric device exhibits gravimetric energy density of 22 Wh kg−1 at a power density of 0.8 kW kg−1. The present results demonstrate that the ultrathin Ni(OH)2 nanosheets are highly attractive electrode materials for achieving fast charging/discharging and high-capacity supercapacitors.