Electrochemical Charge Storage Research Articles

Influence of Surface Groups on Electrochemical Properties of Molten Salt Synthesized Ti3C2Tx in Mild Aqueous Electrolytes

MXene, notable for its excellent electrical conductivity and tunable surface groups, has garnered widespread attention in the field of electrochemical energy storage. Here, Ti3C2Tx MXene was synthesized by a Lewis acid molten salt‐shielded synthesis (MS3). The surface groups (‐Cl, ‐O) were modified by washing Ti3C2Tx samples with various solutions (deionized water, 0.5 M hydrochloric acid (HCl), 0.5 M ammonium persulfate solution (APS)) and/or thermal treatments under an argon atmosphere at 300 °C, 500 °C, and 700 °C. It is shown that deionized water and HCl solution washing have minimal impact on the surface groups, while APS washing can increase the content of ‐O surface group. Conversely, thermal treatment may remove the ‐O. Electrochemical charge storage behavior of these Ti3C2Tx variants were further investigated in a 1 M acetate electrolyte buffered at pH=5.0. It is indicated that the ‐Cl surface group is electrochemically inert, whereas the ‐O may significantly improve the charge storage performance. Ti3C2Tx with high ‐O content delivered an impressive maximum capacity of 155 C g‐1. This research underscores the crucial role of surface groups on the electrochemical performance of Ti3C2Tx in mild aqueous electrolytes, offering valuable insights for future modifications and applications of Ti3C2Tx in energy storage technologies.

Electrochemical charge storage performance of (Mn, Ni, Mo, Co, Fe)3O4 high entropy oxide nanoparticles produced via thermal plasma route

Highly complex high entropy metal oxides (HEOs) have several unique characteristics, such as more active sites and material stability that improve the electrochemical charge storage capacity. In this study, HEOs (Mn, Ni, Mo, Co, Fe)3O4 nanoparticles were synthesized using a thermal plasma route and its electrochemical energy storage performance was studied with two distinct electrolytes such as 1 M KOH and NaOH. The X-ray diffraction analysis revealed the phase pure spinel structured HEOs with crystalline size ranging from 13 to 29 nm. Scanning electron microscopy and electron dispersive X-ray spectroscopy results revealed the quasi-spherical morphology and uniform distribution of constitutional cations in the as-synthesized HEOs. The X-ray photoelectron spectroscopy results identified the oxidation states of cations in spinel HEOs. The charge/discharge studies of as-synthesized HEOs showed a specific capacitance of 215 F g-1 /26.9 mAh g-1 at a current density of 2 A g-1 in 1 M KOH electrolyte which is 156 % greater than 1 M NaOH electrolyte. Furthermore, a high capacitance retention of 91 % was achieved after completing 3000 cycles at 10 A g-1 current density which indicates that the HEOs have excellent charge/discharge reversibility. Electrochemical impedance spectroscopy revealed that the solution and charge transfer resistances of HEOs electrodes were 1.04 and 3.2 Ω, respectively. This novel synthesis strategy attempts to overcome the difficulties experienced by established methods for bulk manufacture of phase pure HEOs since thermal plasma method is a rapid and a single-step approach for the bulk production of nanomaterial.

Lithium storage behaviour of AgNbO3 perovskite: Understanding electrochemical activation and charge storage mechanisms

In this study, a model AgNbO3 perovskite is prepared via polyacrylamide synthesis technique, and the underlying unique Li+storage mechanism is studied. This structure is projected to provide low Li+ storage capacity due to all occupied crystallographic sites. It delivered a specific capacity of 17 mAh.g−1 at 0.1A.g−1 within the potential range of 1.2–3.0 V vs. Li+/Li. However, at lower potentials, the material undergoes activation for Li+ storage by a multistep structural transition that included in-situ Ag-exsolution from the A-site of the lattice and an electrochemically induced crystalline-to-amorphous transition. At low potential the materials delivers high specific capacity (226 mAh.g−1 at 0.1 A.g−1 in 0.01–3 V vs. Li+/Li potential range) due to the contribution of improved Nb-redox activity and nanoscale Ag-Li (de)alloying mechanisms that were comprehensively examined utilizing advanced characterization tools. In addition, good capacity retention of 72 mAh.g−1 at high current density of 2A.g−1 and an excellent cyclic stability with coulombic efficiencies above 99.9 % are obtained for 2500 cycles at 1 A.g−1 underlining the performance and the stability of AgNbO3. This study introduces an alternative approach for tailoring electrode material using an electrochemically driven in-situ activation process. It also serves as a paradigm for the use of exsolved materials as negative electrodes in fast-charging batteries, paving the way for a better understanding of charge storage mechanisms in perovskites.

Enhancement in supercapacitive performance of calcium phosphate nanoneedles through Ni-ion incorporation: Insights into atomic and electronic structures

Phosphates have emerged as promising materials for electrochemical charge storage applications. However, a comprehensive understanding of their storage mechanism remains elusive. The present work reports the impact of nickel ion doping on hydroxyapatite (PH) prepared by a wet-chemical route. X-ray diffraction (XRD) reveals the formation of NiO and Raman and Fourier-transform infrared (FTIR) analyses demonstrate the suppression of phosphate modes on doping. The incorporation of Ni ions induces nanoneedles morphology, effectively engineering the surface area and volume of the material. Notably, specific capacitance significantly improves to 415.35 Fg-1 at 10 mAg−1 for Ni-incorporated PH (0.1 M of Ni) (0.1NH), a remarkable enhancement compared to 166.77 Fg-1 at 10 mAg−1 for pristine (PH). X-ray photoelectron spectroscopy (XPS) confirms the mixed valence state of Ni2+/3+ and the presence of Ni–O bonding on Ni incorporation. Moreover, X-ray absorption spectroscopy (XAS) reveals the formation of Ni–O–Ni clusters, enhanced charge transfer by Ni ions, and optimized coordination of Ni–O bonds. The comprehensive correlation established between the phase, morphology, and electronic and local atomic structures elucidates the excellent electrochemical charge storage performance. This investigation sheds light on the potential of Ni-doped hydroxyapatite as a promising material for electrochemical applications, contributing valuable insights for the design and optimization of advanced energy storage systems.

Screen-printed electrodes based on hybrids of poly(ortho-ethoxyaniline) and reduced graphene oxide

Screen-printed electrodes (SPEs) based on hybrids of the conducting polymer poly(ortho-ethoxyaniline) (POEA), graphene oxide (GO) and reduced graphene oxide (rGO) were produced and characterized. The SPEs were produced from conductive inks based on graphite and alkyd resin and were modified with hybrids of POEA with GO, and rGO. The hybrids POEA-GO and POEA-rGO were produced by chemical polymerization of o-ethoxyaniline (orthophenitidine) in 1.0 mol L−1 with GO or rGO dispersed into the monomer solution. The SPEs were modified by the replacement of 5 % in mass of graphite by 5 % in mass of POEA-GO or POEA-rGO hybrids. The hybrids were characterized by Raman and FT-IR spectroscopies and XRD analyses. The modified SPEs, SPE/POEA, SPE/POEA-GO, and SPE/POEA-rGO were characterized by scanning electron microscopy, and by cyclic voltammetry, and electrochemical impedance spectroscopy (EIS). The electrodes based on the rGO hybrid, SPE/POEA-rGO, showed a significant reduction of the charge transfer resistance obtained by EIS by a factor of 3 compared with SPE/POEA, from 4.62 kΩ to 1.48 kΩ, without changing the redox behaviour of POEA. The methodology used to produce SPE/POEA-rGO is a simple, effective, scalable, and low-cost alternative to produce POEA-based electrodes for applications such as in electrochemical sensors and charge storage devices.

Fabrication and Investigation of a MoS2/Fe3O4/PANI Composite for Supercapacitor Applications

AbstractThis study investigates a successful fabrication of MoS2/Fe3O4/PANI composite by chemical co‐precipitation method. The facile hydrothermal approach was employed to synthesize a MoS2/Fe3O4 composite, followed by the utilization of a conventional chemical oxidation strategy to produce a PANI coating on the composite, thereby generating an active material for electrochemical reactions and a structure facilitating the transportation of ions via multiple pathways. The fabricated MoS2/Fe3O4/PANI composite was characterized by SEM, ICP, XRD, FT‐IR, and so on. In this study, we delved into the electrochemical charge storage feature of MoS2/Fe3O4/PANI. The electrochemical characteristics of the nanocomposite were assessed through the implementation of cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronopotentiometry techniques in a 3 M KOH electrolytic solution, utilizing nickel foam as both a material support and current collector for two electrode configurations. The findings indicate that MoS2, as the support matrix, possesses notable attributes such as a substantial surface area, elevated electrical conductivity, and varied oxidation states. As a result, the electrical conductivity performance of the MoS2/Fe3O4/PANI composite, which includes well‐dispersed Fe3O4 nano‐cubes on the surfaces of MoS2, is significantly enhanced. In comparison to pure Fe3O4, the resultant composite revealed improved specific capacitances of 401 F/g at 1.25 A g−1, along with outstanding cyclic stability of 89.3 even after undergoing 5000 cycles. The superior electrochemical properties observed may be ascribed to both the proficient electrical conductivity of MoS2 and the incorporation of Fe3O4 particles, which are anchored onto the MoS2. The results prove that MoS2/Fe3O4/PANI hybrid composite holds as highly efficient electrode material for supercapacitor.

Enhancing the Electrical and Photoelectrical Efficacy with the Synergistic SrO–ZnO Nano‐Heterosystem

Development of the sustainable materials for consolidation of the energy sustainability needs special emphasis in the current era of the increasing energy demand. In compliance with this, present investigation reports first investigation on the amended sustainable production conjugated with the microwave process of the strontium oxide (SrO) and zinc oxid (ZnO) forming SrO–ZnO nanoscale heterostructure. The band gap of the prepared green nanomaterial was tuned reducing it from 5.8 to 3.6 eV upon the formation of the nanocomposite. With the mixed cubic and hexagonal phase, these particles have average crystallite size of 66.4 nm and irregular shape. The electro‐catalytic assays have expressed the bifunctional role of the SrO–ZnO towards generation of the oxygen and hydrogen. However, it has an excellent hydrogen production capacity with the lower overpotential of 126 mV and Tafel slopes 123.6 mV dec−1. In addition, this nanomaterial has also exhibited superior electrochemical charge storage for batter applications with the unit capacity of 541.7 mAH g−1 and Rs = 0.4 Ω, reflecting facilitated diffusion at the interface. In terms of photovoltaic applications, SrO–ZnO nanocomposite has effectively passivated the perovskite solar cells by improving efficiency from 7.2% to 15.1%. Such an improved performance is associated with the chemical synergism.

Peptide‐Based Assemblies for Supercapacitor Applications

The increased focus on green energy storage devices and the related rapid advancement in biomedical technologies makes the investigation of biocompatible integrated systems with medical relevance increasingly important. Peptides and their assembled morphologies with their innate biocompatibility and biodegradability are emerging as promising candidates in this respect due to their structural attributes which can be easily tuned to form supramolecular 3D architectures with extended pathways for ionic mobility. However, to comprehend their applicability in energy storage devices, it is crucial to explore their self‐assembling characteristics, charge‐storage mechanisms, and coating efficacies. Herein, all these aspects are compiled with specific emphasis on peptide‐based systems for supercapacitor applications. The electrochemical charge storage mechanisms that are used for categorizing conventional supercapacitors with the theories and mechanisms outlining biological electron transfer, such as tunneling, hopping, superexchange, and flickering resonance, are collated. Furthermore, the characterization techniques solely pertaining to the study of such systems and their role in predicting the morphology of self‐assembly patterns which could directly impact the overall electrochemical properties are also addressed. Finally, some of the critical challenges associated with these systems while realizing their future potential in the field of sustainable energy storage devices are highlighted.

A high-performance asymmetric supercapacitor based on morphologically tuned CoB anode and heterostructured graphitic carbon nitride/MoSe2 cathode

Transition metal borides (TMBs) are among the fascinating electrode materials for supercapacitors. TMBs have high theoretical capacity, however the narrow potential window, structural deterioration during redox cycling, and fairly small surface area remains a major limitation. To resolve these, we synthesize cobalt boride (CoB) in different morphologies by initiating the reaction with different precursors namely, zeolitic imidazolic framework-67 (ZIF-67), Co layered hydroxide (SLH), and CoCl2. CoB synthesis from ZIF-67, SLH, and CoCl2 results in nanoflower, nanoplate, and nanowire morphology. CoB in nanowire morphology, shows highest charge storage of 273 F g−1 at 1 A g−1 due to 1D structure that endow plentiful surface area, high conductivity, ample electroactive sites and structural stability. We also engineer layer structure of molybdenum selenide (MoSe2) to favorably expand interlayer distance to enhance atomic surface exposure by successfully inserting graphitic carbon nitride (gCN) nanosheets into adjacent MoSe2 layers. Herein, asymmetric supercapacitor, CoB||gCN/MoSe2 displays a wide potential window of 1.5 V, remarkable energy density of 97.44 Wh kg−1 at 621.3 W kg−1 along with 93 % capacitance retention after 10 k GCD cycles. The research reported here demonstrates the great application potential for the asymmetric devices based on CoB||gCN/MoSe2 for the future of electrochemical charge storage devices.

Multi‐scale structure engineering of covalent organic framework for electrochemical charge storage

AbstractCovalent organic frameworks (COFs), which are constructed by linking organic building blocks via dynamic covalent bonds, are newly emerged and burgeoning crystalline porous copolymers with features including programmable topological architecture, pre‐designable periodic skeleton, well‐defined micro‐/meso‐pore, large specific surface area, and customizable electroactive functionality. Those benefits make COFs as promising candidates for advanced electrochemical energy storage. Especially, for now, structure engineering of COFs from multi‐scale aspects has been conducted to enable optimal overall electrochemical performance in terms of structure durability, electrical conductivity, redox activity, and charge storage. In this review, we give a fundamental and insightful study on the correlations between multi‐scale structure engineering and eventual electrochemical properties of COFs, started with introducing their basic chemistries and charge storage principles. The careful discussion on the significant achievements in structure engineering of COFs from linkages, redox sites, polygon skeleton, crystal nanostructures, and composite microstructures, and further their effects on the electrochemical behavior of COFs are presented. Finally, the timely cutting‐edge perspectives and in‐depth insights into COF‐based electrode materials to rationally screen their electrochemical behaviors for addressing future challenges and implementing electrochemical energy storage applications are proposed.

Cyclic Voltammetry to Study Dynamics of Ion Insertion in Porous Materials

Electrochemical charge storage in porous materials is associated with ion adsorption at the meso/nanopores surface (physical insertion) and/or insertion in the bulk material (chemical insertion). The first process is capacitive whereas the second is Faradaic. A model is brought about for describing the cyclic voltammetry responses of these systems and their dependence upon the various intrinsic and operational governing parameters. These responses may be considered as illustrating the behaviors expected in working conditions in terms of diagnosis of the main phenomena at work and of their mutual interactions, namely, dynamics of double‐layer charging, transport in solution, transport in the pores, interfacial transfer kinetics, and transport in the material bulk. Several limiting cases are examined in details and discussed, focusing on the effect of scan rate as a widely used diagnostic tool.

Pseudocapacitive properties of polypyrrole – ferrimagnetic CoFe2O4 composites

This investigation is motivated by increasing interest in materials combining advanced electrochemical charge storage properties and spontaneous magnetization. Pseudocapacitive properties of ferrimagnetic CoFe2O4 (CFO) are observed in a potential window of -0.6 -+0.2 V in Na2SO4 electrolyte. This finding opens an avenue for the fabrication of advanced composites containing conducting polypyrrole (PPy) polymer and CFO. Composite materials show outstanding capacitive properties, which are achieved at a low resistance for electrodes with high active mass. Electrochemical studies reveal synergistic contribution of CFO and PPy. At low charging/discharging rates the composite materials exhibit higher capacitance, compared to the total contribution of individual components. At high charging/discharging rates, the capacitance of composites is significantly higher than the capacitances of PPy or CFO. The composite materials show lower resistance, than resistances of the individual components. The addition of PPy to CFO results in reduced charge transfer resistance and enables better utilization of pseudocapacitive properties of CFO. The relaxation frequency and capacitance retention decreased with increasing PPy content. The investigation of capacitive properties of the composites provides evidence of beneficial magnetohydrodynamic effect of ferrimagnetic CFO particles. The ability to enhance capacitance at high charging rates opens an avenue for the development of high power pseudocapacitors.

Optimum iron-pyrophosphate electronic coupling to improve electrochemical water splitting and charge storage

Tuning the electronic properties of transition metals using pyrophosphate (P2O7) ligand moieties can be a promising approach to improving the electrochemical performance of water electrolyzers and supercapacitors, although such a material’s configuration is rarely exposed. Herein, we grow NiP2O7, CoP2O7, and FeP2O7 nanoparticles on conductive Ni-foam using a hydrothermal procedure. The results indicated that, among all the prepared samples, FeP2O7 exhibited outstanding oxygen evolution reaction and hydrogen evolution reaction with the least overpotential of 220 and 241 mV to draw a current density of 10 mA/cm2. Theoretical studies indicate that the optimal electronic coupling of the Fe site with pyrophosphate enhances the overall electronic properties of FeP2O7, thereby enhancing its electrochemical performance in water splitting. Further investigation of these materials found that NiP2O7 had the highest specific capacitance and remarkable cycle stability due to its high crystallinity as compared to FeP2O7, having a higher percentage composition of Ni on the Ni-foam, which allows more Ni to convert into its oxidation states and come back to its original oxidation state during supercapacitor testing. This work shows how to use pyrophosphate moieties to fabricate non-noble metal-based electrode materials to achieve good performance in electrocatalytic splitting water and supercapacitors.

Ni‐Co‐based bimetal organic framework as superior electrode material for hydrogen evolution reaction and supercapacitors

AbstractMetal‐organic frameworks (MOFs) possess several desirable properties, including a homogeneous crystal structure, variable porosity, high surface area, and a notable adsorption affinity, making them highly promising contenders for deployment as electrode materials in supercapacitors (SCs) and water electrolyzers, which are acknowledged for the ever‐increasing demand for instantaneous energy. Herein, we report the rationally assembled Ni‐Co‐based bimetallic MOF compounds using a glutaric acid as an organic ligand and low‐temperature hydrothermal treatment that surmounts the electrocatalytic and electrochemical charge storage activity in an alkaline medium. The NiCo‐MOF surpassed the hydrogen evolution reaction (HER) among other as‐synthesized materials, exhibiting the least overpotential of 182 mV at 10 mA/cm2 of current density, showed splendid kinetics with a turnover frequency of 2.86 s−1, and higher stability after 1000 HER cycles in 1 M KOH. Furthermore, NiCo‐MOF impetuses were employed for SC application and displayed the highest specific capacitance of 978 F/g than Ni‐MOF (706 F/g) and Co‐MOF (91 F/g) at 1 A/g of current density. Theoretical studies exhibited that the optimal electronic coupling and synergistic effect due to Ni‐Co sites enhances the overall electronic properties of NiCo‐MOF. Therefore, enhancing its electrochemical performance concerning water‐splitting and charge storage. This study showcases a novel approach for producing ultrathin and flexible bimetallic MOF‐based electrode material to enrich the performance in electrocatalytic HER and SCs.

Effect of synthesis routes on electrochemical properties as supercapacitor electrode for novel spinel (CuNiFeMnCo)3O4 high entropy oxide

AbstractThe aim of the present study is to investigate the effect of synthesis routes on phase evolution, microstructure, change in ionic state and their co‐relation with electrochemical charge storage, and magnetic properties of novel (CuNiFeMnCo)3O4 high entropy spinel oxide (HESO). We successfully synthesized novel (CuNiFeMnCo)3O4 HESO through two different synthesis methods, that is, sol‐gel and reverse coprecipitation methods abbreviated as SA‐1 and SA‐2, respectively. The XRD analysis for both samples reveals the formation of inverse spinel phase (space group Fd‐3m) with the lattice constant of 8.3602 and 8.2502 Å for SA‐1 and SA‐2, respectively. The sample synthesized through the sol‐gel method possessed porous morphology, whereas the sample synthesized through the reverse coprecipitation method had spherical particles. The x‐ray photoelectron spectroscopy confirmed the presence of +2 and +3 ionic states for Fe, Ni, and Co, while Cu has a + 2 state and Mn exist in +3 and +4 states for both the synthesized samples. The ionic states of all cations remain invariant irrespective of the synthesis methods. However, the concentration of oxygen vacancy is significantly different for samples synthesized through different routes. Both the HESO electrodes show the electrochemical double‐layer capacitive type behavior in 2 M KOH electrolytic solution. The value of maximum specific capacitance is 38.46 and 34.24 F/g at a scan rate of 5 mV/s for SA‐1 and SA‐2, respectively. Moreover, the electrodes have capacity retention of 90 and 99% for 1000 cycles at a scan rate of 50 mV/s for SA‐1 and SA‐2, respectively. The magnetic property of the synthesized HESO samples was also investigated, and the found values of magnetization and coercivity are 1.79 emu/g and 54.9 Oe and 8.5 emu/g and 67.69 Oe for SA‐1 and SA‐2, respectively.

Unraveling the electrochemical charge storage dynamics of defective Oxides-Based cathodes toward High-Performance aqueous Zinc-Ion batteries

Aqueous Zinc ion batteries (AZIBs) show tremendous potential for large-scale energy storage infrastructure owing to high affordability and high safety but are plagued by the undesired rate capability and inevitable capacity deterioration of the used cathodes. Defect engineering has been recognized as one of the most effective strategies for the electrochemical performance enhancement of cathodes. However, its underlying electrochemical kinetics and performance-enhancing mechanism are still immature. Herein, we performed comprehensive studies on the charge storage dynamics with the prototypical of defective manganese oxides (d-ZMO) by combining the three-dimensional (3D) Bode map and theoretical calculations. Bode analysis reveals that the d-ZMO exhibits the most significant values of real capacitance and the largest phase angle compared to that of the pristine MnO2 (MO) electrode, demonstrating the validity of defects on the electrochemical kinetic enhancement. Further theoretical results indicate the lowest zinc ions diffusion energy barrier (0.52 eV) of d-ZMO (1.23 eV of MO) with significantly enhanced ion kinetics, corroborating well with the Bode analysis. As expected, the configured AZIBs with d-ZMO cathode deliver an appreciable specific capacity of 419.7 mAh·g−1 (at 0.1 A·g−1) and exceptional cycle stability with capacity retention of 81.76 % (at 3 A·g−1) after 1000 cycles.

CoOx @NiMoN/Ti3 C2 Tx Interface for Stable High-Performance Electrochemical Energy Storage Devices.

Transition metal nitrides (TMNs) are promising electrode materials for use in high-performance electrochemical energy storage devices due to their unique properties, which include a high conductivity, pseudocapacitance, and energy density. However, structural instability during electrochemical reactions has limited their practical deployment for energy storage devices. In this context, the present study fabricated a CoOx @NiMoN/Ti3 C2 Tx electrode via in situ growth on Ni foam using hydrothermal treatment with post-nitrogenization. The effect of atomic layer deposition (ALD) of CoOx on the TMN/Ti3 C2 Tx interface and the consequent electrochemical charge storage mechanisms areinvestigated in detail. The proposed CoOx @NiMoN/Ti3 C2 Tx electrode delivers an impressive specific capacity in a 2m potassium hydroxide (KOH) electrolyte and isthen employed in both a hybrid solid-state supercapacitor (HSSC) with reduced graphene oxide and a symmetric SC in a 2m KOH + polyvinyl alcohol (PVA) gel electrolyte. Outstanding charge storage and high capacity retention during cyclic testing areobserved for both energy storage devices. The exceptional electrochemical performance of the fabricated electrode isa result of its high conductivity and high number of active sites. Here a feasible new strategy is demonstrated for the fabrication of stable energy storage devices with a high energy density using TMNs and MXenes.

Polycrystalline phases grown in-situ engendering unique mechanism of charge storage in polyaniline-graphite composite

We report on a simple surfactant/template free chemical route for the synthesis of semi-polycrystalline polyaniline-graphite (SPani-graphite) composite and its application as an electroactive material in electrochemical charge storage. The synthesized material exhibits well-defined poly-crystallographic lattices in high resolution transmission electron micrographs and sharp peaks in x-ray diffraction spectra suggesting crystalline nature of the material. The specific capacitance computed from the galvanostatic charge-discharge (GCD) data obtained from 3-electrode cell configuration using 1 M aq. Na2SO4 as an electrolyte was 111.4 F g−1 at a current density of 0.1 A g−1 which rises to 269 F g−1 at an elevated current density of 1.0 A g−1. A similar pattern of increase in the specific capacitance values with an increase in the current density was observed in the results obtained from 2-electrode symmetric device configuration using polymer gel electrolyte (xanthan gum in 1 M aq. Na2SO4). The specific capacitance computed from the GCD data obtained from the device configuration was 20 F g−1 at the current density of 1.0 A g−1. The device delivers an energy density of 1.7 Wh kg−1 and a power density of 2.48 kWh kg−1 at an applied current density of 0.5 A g−1 suggesting an excellent rate capability and power management. In addition, the device exhibits ⁓92 % specific capacitance retention up to 8000 continuous GCD cycles and ⁓80 % coulombic efficiency up to 10,000 continuous GCD cycles indicating excellent cycling stability. The unique feature of increasing specific capacitance with respect to applied current density is attributed to the presence of semi-polycrystalline phases in the SPani-graphite matrix. The material behaves as a surface redox supercapacitor and its unique mechanism of charge storage is discussed in detail in the article.

Enhancing Charge Storage of Mo2Ti2C3 MXene by Partial Oxidation

AbstractDriving the pseudocapacitive redox intercalation in 2DMXenes with neutral electrolytes is important for safer, more sustainable, and improved electrochemical charge storage. Single transition metal MXenes, such as Ti3C2, have shown great promise for energy storage, owing to their high conductivity and redox activity. Mixed metallic MXenes, such as out‐of‐plane ordered Mo2Ti2C3, have remained underexplored in energy storage because of the absence of redox activity in most of the electrolytes. Simultaneous structural modifications and instigating intercalation pseudocapacitance in neutral electrolytes could be a viable strategy for enhancing their electrochemical properties. Herein, a facile synthesis of partially oxidized Mo2Ti2C3 MXene (PO‐Mo2Ti2C3) exhibiting improved charge storage capability is demonstrated. Optical, structural, and spectroscopic analyses indicate the formation of oxide nanostructures upon thermal oxidation of Mo2Ti2C3 . This leads to an enhanced energy storage capability with remarkably improved cyclability as well as a high Coulombic efficiency in a neutral LiCl electrolyte. This work highlights the importance of structural modifications of MXenes to enhance their charge storage and shows the promise of less explored double transition metal MXenes in energy storage.

Scalable synthesis of binder-free hierarchical MnCo2O4 nanospikes/Ni(OH)2 nanosheets composite electrodes for high-capacity supercapatteries

Supercapatteries have received great attention in recent years due to its excellent charging storage capabilities. The effective electrochemically active surface area of the electrode is crucial in obtaining high capacity in supercapatteries. Herein, we present a scalable synthesis of binder-free hierarchical MnCo2O4 (MCO) nanospikes/Ni(OH)2 (NiOH) nanosheets (MCO/NiOH) nanocomposites for supercapattery electrode application. The MCO/NiOH nanocomposites are synthesized by the two-step hydrothermal method at low-cost without affecting nanostructures and further used as electrodes in fabricating a supercapattery. The synergistic effect of the NiOH nanosheets and MCO nanospikes helps to enhance the electrochemical charge storage performance when compared to their counterparts. The growth of NiOH nanosheets over the MCO nanospikes helps to suppress the self-discharge nature of MCO nanospikes otherwise. The MCO/NiOH//activated carbon supercapattery fabricated in the asymmetric configuration delivers a maximum specific capacity of 890C/g with a high energy density of 75.2 Wh/kg. The MCO/NiOH//activated carbon supercapattery exhibits a capacity retention of 86 % after completing 5000 charge/discharge cycles. Therefore, MCO/NiOH nanocomposite electrodes are capable candidates for the next-generation electrochemical energy storage systems.