Charge Discharge Kinetics Research Articles

Attaining promising efficiency through a Quasi-Solid-State symmetrical supercapacitor and Dye-Sensitized solar cell counter electrode utilizing bifunctional Nitrogen-Doped microporous activated carbon

This study addresses the imperative need for high-performance and sustainable energy storage and conversion technologies by leveraging the unique properties of nitrogen-doped porous carbon (N@WnAC) derived from the waste walnut shells (WnS). In the realm of supercapacitors, the N@WnAC demonstrates remarkable performance in a three-electrode system, showcasing a high specific capacitance value of 276.7 Fg−1 at 1 Ag−1, outstanding stability (96.6 %, 5000 charge–discharge cycles) and favourable rate capability (68.8 % at 10 Ag−1). Moreover, a quasi-solid-state symmetrical supercapacitor (N@WnAC//N@WnAC) is fabricated with PVA/H2SO4 gel electrolyte, underscores outstanding performance by delivering high capacitance (126.2 Fg−1 at 0.5 Ag−1), promising rate capability (71.8 % at 5 Ag−1), favourable long-term stability (93.3 %, 5000 charge–discharge cycles), and faster charge–discharge kinetics compared to conventional counterparts. At the same time, N@WnAC//N@WnAC delivers a high energy density (42.27 Whkg−1 at 0.5 Ag−1) that was retained up to 23.96 Whkg−1 even at 5 Ag−1. Simultaneously, the study explores the potential of N@WnAC as a counter-electrode (CE) in dye-sensitized solar cells (DSSC). The obtained results underscore that unique nitrogen doping enhances the electrocatalytic activity, leading to improved electron transfer kinetics and overall cell performance. Moreover, the N@WnAC CE-based DSSC delivers a promising overall solar-to-electrical conversion efficiency of 5.84 %.

Influence of Ni-doping on CuCo2O4 electrode for enhanced supercapacitor performance and sustainable energy storage

This work provides a revolutionary strategy for creating high-performance supercapacitors by designing and fabricating a unique nanostructured bimetallic oxide electrode. The proposed electrode leveraged the synergistic effects of metal oxides to enhance both energy density and charge-discharge kinetics. Ni-doped CuCo2O4 nanostructures (Cu1-xNixCo2O4) were synthesized in incremental order (x = 0.0, 0.05, 0.10, and 0.15) by facile sol-gel auto-combustion route. The nanostructures analyzed through x-ray diffraction, FTIR spectroscopy, Micro-Raman spectroscopy, x-ray photoelectron spectroscopy (XPS) and Scanning electron microscopy revealed the single phase and polycrystalline nature of CuCo2O4, with some impurity phases of CuO. The surface morphology studies showed numerous pores among the grains of Cu1-xNixCo2O4. Cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical performance of synthesized Cu1-xNixCo2O4 samples. In a 3 M KOH electrolyte solution, the Cu1-xNixCo2O4 electrodes with x = 0.05 exhibited 2340 Fg−1 specific capacitance at 5 mVs−1, demonstrating superior electrochemical performance with excellent rate capability. Furthermore, it exhibited 35.88 Whkg−1 energy density, an exceptional 2484.74 Wkg−1 power density, and retained 99.9 % capacitance after 5000 cycles, demonstrating good stability. The results suggest that porous bimetallic oxide nanostructures can be promising candidates for the development of high-performance, environmentally friendly supercapacitors.

High Capacity and Fast Kinetics Enabled by Metal-Doping in Prussian Blue Analogue Cathodes for Sodium-Ion Batteries.

Prussian blue analogues (PBAs) have gained tremendous attention as promising low-cost electrochemically-tunable electrode materials, which can accommodate large Na+ ions with attractive specific capacity and charge-discharge kinetics. However, poor cycling stability caused by lattice strain and volume change remains to be improved. Herein, metal-doping strategy has been demonstrated in FeNiHCF, Na1.40Fe0.90Ni0.10[Fe(CN)6]0.85 ⋅ 1.3H2O, delivering a capacity as high as 148 mAh g-1 at 10 mA g-1. At an exceptionally high rate of 25.6 A g-1, a reversible capacity of ~55 mAh g-1 still can be obtained with a very small capacity decay rate of 0.02 % per cycle for 1000 cycles, considered one of the best among all metal-doped PBAs. This exhibits the stabilizing effect of Ni doping which enhances structural stability and long-term cyclability. In situ synchrotron X-ray diffraction reveals an extremely small (~1 %) change in unit cell parameters. The Ni substitution is found to increase the electronic conductivity and redox activity, especially at the low-spin (LS) Fe center due to inductive effect. This larger capacity contribution from LS Fe2+C6/Fe3+C6 redox couple is responsible for stable high-rate capability of FeNiHCF. The insight gained in this work may pave the way for the design of other high-performance electrode materials for sustainable sodium-ion batteries.

Fe(III) dihydroxybenzoquinone-based metal organic framework for sodium battery cathodes: Properties, charge-discharge kinetics and redox reaction mechanisms

Sodium batteries are promising energy storage devices that could promote the transition to clean energy. For this purpose, it is desirable to develop safe cathode materials that can be easily produced from cheap and abundant elements. One of the attractive options is Fe2(dhbq)3, a metal-organic framework (MOF) that is synthesized from 2,5-dihydroxybenzoquinone (H2dhbq) and Fe(III) salts. This work provides a comprehensive analysis of Fe2(dhbq)3, including its structure, properties, charge-discharge kinetics, and redox reaction mechanism in sodium batteries. Using a set of experimental and theoretical methods, we show that sodiation of Fe2(dhbq)3 in the potential range of 1.1–3.8 V vs. Na+/Na is accompanied by a reversible two-electron reduction of dhbq ligands, while iron is only marginally involved and formally remains in +3 state. The material delivers a high specific capacity of up to ∼180 mAh g−1. Diffusion of Na+ ions in NaxFe2(dhbq)3 at low-to-moderate sodiation degrees (≥2.2 V vs. Na+/Na) is so fast that it is kinetically indistinguishable from supercapacitance. Additionally, we show that Fe2(dhbq)3 can be synthesized by simply mixing solutions of H2dhbq and salts of Fe(III) at room temperature, which makes its production especially simple and scalable.

Investigation of electrochemical and photoluminescence properties of Dy[formula omitted] doped SrO/BaO/Al2O3 nanocomposite for supercapacitor and display applications

The current study investigates the synthesis and characterization of dysprosium-doped strontium barium aluminum nanocomposites (SBAD NCs), aiming to enhance their suitability for display and supercapacitor applications. SBAD NCs are synthesized by Solution combustion synthesis using aloevera extract as a reducing agent. Multi-phase formation of NCs due to SrO, BaO, and γ-Al2O3 phases was confirmed by PXRD analysis, and crystallite size is found to be in the range of 26 nm to 36 nm. SEM analysis confirmed the surface morphology and the elemental composition was affirmed by the EDAX spectrum which confirmed the purity of the synthesis. The blue shift in the UV–visible absorption peak with increasing dopant concentration suggests a rise in the direct energy band gap from 4.07 eV to 4.11 eV. FTIR analysis confirmed functional groups and fingerprint region affirmed the presence of SrO, BaO, and AlO bonds. Photoluminescence analysis performed under excitation wavelength 276 nm revealed a prominent emission peak at 565 nm, and the CIE values fall in the yellow-green region of visible spectra. The CCT value was found to be 4490 K–4542 K which might find an application as a nanophosphor in cool light-emitting diodes. The tailored nanocomposites exhibit exceptional electrochemical performance characterized by superior specific capacitance, and improved charge–discharge kinetics, as evaluated through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The specific capacitance is found to be in the range of 103.26 F/g to 173.24 F/g at a scan rate of 10 mV/s with increasing Dy3+ dopant concentration from 1 mol% to 9 mol% respectively. The dysprosium-doped SBAD NCs emerge as promising candidates for high-performance energy storage systems and vibrant display technologies, offering a synergistic integration of efficient energy storage and vivid display functionalities.

Atomistic Origins of Asymmetric Charge–Discharge Kinetics in Off-Stoichiometric LiNiO2

Atomistic Origins of Asymmetric Charge–Discharge Kinetics in Off-Stoichiometric LiNiO₂

Optimization of the Porous Structure of Carbon Electrodes for Hybrid Supercapacitors with a Redox Electrolyte Based on Potassium Bromide

This work investigates the electrochemical behavior of hybrid supercapacitors with carbon-based electrodes of different porosity using 5M NaNO3 + 0.5M KBr electrolyte to optimize energy storage processes. Three types of carbon materials were synthesized: activated carbon from rice husk (RH) with a specific surface area of ~2300 m2/g and pore size < 1 nm, and templated carbons from magnesium citrate (MP-8) and glucose with SiO2 as a template (G7), having surface areas of 1976 and 1320 m2/g and pore sizes of 3.4 and 7 nm, respectively. The microporous structure of activated carbon (AC) obtained from RH shows limitations in the diffusion of electrolyte ions, which affects the charge-discharge kinetics. In contrast, the larger mesoporous structures of templated carbons promoted better adsorption and ion transport, significantly affecting the dynamics of redox reactions. The RH/MP-8 hybrid capacitor, combining high surface area and large pore size, demonstrated a 54% increase in specific capacitance, 128% increase in specific energy and 51% increase in energy efficiency at high current densities of 5 A/g, comparing to the symmetric RH/RH hybrid capacitor. This study highlights the critical importance of the relationship between electrode pore structure and electrolyte composition for optimizing supercapacitor performance, which provides valuable information for the development of efficient energy storage technologies.

Exploration of PVP-Combustion Synthesis and Electrochemical Performance of O3-type NaxNi0.33Fe0.33Mn0.33O2 Layered Material for Sodium-Ion Batteries

The performance of sodium-ion batteries critically depends on the cathode materials used, making it essential to explore and optimize suitable candidates. Among them, O3-structured NaNi0.33Fe0.33Mn0.33O2 has emerged as one of the most promising cathode materials due to its outstanding electrochemical properties. However, there still exists a knowledge gap regarding the detailed synthesis conditions and the comprehensive performance of the full cell using this material. In this study, we investigated the influence of synthesis temperature, time, and sodium content on the electrochemical performance and charge-discharge kinetics of O3-structured NaNi0.33Fe0.33Mn0.33O2, prepared via the PVP-gel combustion method. Through systematic analysis, we elucidated the impact of these synthesis parameters on the material’s properties and battery performance. The results revealed that the optimized conditions led to a cathode material with superior electrochemical performance, exhibiting enhanced capacity with 139 mAh g−1 at 0.1 C and 96 mAh g−1 at 10 C. Additionally, a full cell using the optimized cathode material was studied, showing promising performance. This research sheds light on the significance of synthesis parameters in tailoring the electrochemical properties of O3-structured NaNi0.33Fe0.33Mn0.33O2 for sodium-ion batteries. The insights gained from this study hold valuable implications for the further development of practical sodium-ion battery cathode materials.

Ferromagnetic single atom doped boron phosphide monolayers as effective electrocatalysts for Lithium-Sulfur batteries

Ferromagnetic single atom doped BP monolayers are proposed as electrocatalysts for lithium-sulfur batteries. Based on first-principles calculations, it is found that Fe-BP and Ni-BP monolayers exhibit higher electronic conductivity, and their adsorption ability for lithium polysulfides are significantly enhanced compared to the bare BP monolayer, which could effectively suppress the shuttling effect. Besides, the Fe-BP monolayer shows the lowest energy barrier for both sulfur reduction reaction and Li2S decomposition, with a low Li+ diffusion energy barrier of 0.25 eV. Based on these results, Fe-BP monolayer is suggested as a promising single-atom electrocatalyst for sulfur redox reactions which will show fast charge–discharge kinetics and long cycle life in lithium-sulfur batteries.

Anomalous Increase in Double Layer Capacitance in Ionic Liquid-Metal Salt Blends

Supercapacitors provide exiting opportunities for the future of energy storage due to a combination of fast charge-discharge kinetics, high safety, and long device lifetimes. Yet, current supercapacitors have energy densities that are orders of magnitude lower than those of lithium-ion batteries, relegating them to niche uses such as regenerative braking systems. While ionic liquids have shown promise as next generation electrolytes in supercapacitors due to their nonflammable nature, large electrochemical stability window, and predicted large capacitances, neat ionic liquids have capacitances ranging from 5 to 20 µFcm-2 which does not compete with current supercapacitors made with cheaper electrolytes. In this talk, I will discuss how we have substantially increased the capacitance of ionic liquid-electrode interfaces though the addition of metal salt additives containing Li, Na, K, and Mg ions. We maintain the large voltage window while increasing the capacitance to up to 80 µFcm-2 at both positive and negative polarizations of gold electrodes. By conducting complementary surface structuring studies, we elucidate molecular assembly at charged surfaces to understand ion behavior when only surrounded by other ions in solution. We hypothesize that the introduction of metal salts interrupts ion aggregates that exist in concentrated electrolytes, reducing the screening lengths in ionic liquids and thus increasing capacitance. Overall, our study demonstrates that ionic liquids may have transformative promise for next-generation supercapacitors, and highlights new paradigms for tuning interfacial properties via modulation of ion coordination in concentrated electrolytes.

Atomic Layer Deposition of Alumina-Coated Thin-Film Cathodes for Lithium Microbatteries.

This work shows the electrochemical performance of sputter-deposited, binder-free lithium cobalt oxide thin films with an alumina coating deposited via atomic layer deposition for use in lithium-metal-based microbatteries. The Al2O3 coating can improve the charge-discharge kinetics and suppress the phase transition that occurs at higher potential limits where the crystalline structure of the lithium cobalt oxide is damaged due to the formation of Co4+, causing irreversible capacity loss. The electrochemical performance of the thin film is analysed by imposing 4.2, 4.4 and 4.5 V upper potential limits, which deliver improved performances for 3 nm of Al2O3, while also highlighting evidence of Al doping. Al2O3-coated lithium cobalt oxide of 3 nm is cycled at 147 µA cm-2 (~2.7 C) to an upper potential limit of 4.4 V with an initial capacity of 132 mAh g-1 (65.7 µAh cm-2 µm-1) and a capacity retention of 87% and 70% at cycle 100 and 400, respectively. This shows the high-rate capability and cycling benefits of a 3 nm Al2O3 coating.

(Digital Presentation) Electrode and Electrolyte Materials for Thin Film Microbatteries

Electrode and Electrolyte Materials for Thin Film Microbatteries, Aaron O’Donoghue, Louise McGrath, Ian Povey and James Rohan In this work we assess the electrochemical performance of electrodeposited, binder-free V2O5 thin films with Li metal anodes in liquid and polymer gel electrolytes based on a pyrrolidinium based ionic liquid (C4mpyrTFSI). Coulombic efficiencies >99%, with electrode capacities >120 mAh g-1 are obtained in cyclic voltammetry analysis of crystalline V2O5 with C4mpyr-based Ionic liquid (IL) electrolytes. A polymer gel electrolyte suited to layer by layer microbattery fabrication was synthesised and tested with the crystalline V2O5 and gave large electrode capacities at a relatively high rate (110 mAh g-1 at 2 C) similar to those obtained in liquid electrolytes. Stable long-term cycling (up to 400 cycles) is obtained with Li metal anodes without capacity fade or short circuits developing in either the VC containing IL or the polymer gel analogue. In addition, no V2O5 deterioration is observed with the polymer gel electrolyte as the capacity recovered to ~125 mAh g-1 after cycling at 5 C.Furthermore, we assess surface modification of V2O5 by depositing 3nm Al2O3 via ALD which has been shown to improve the charge-discharge kinetics of oxide electrode materials. Coulombic efficiencies >99%, with peak electrode capacities >120 mAh g-1 are obtained and long-term cycling stabilities up to 625 cycles.1) L. M. McGrath and J. F. Rohan, Batteries & Supercaps, 4 (2021) 485 – 492, High rate lithium ion cycling in electrodeposited binder-free thin film vanadium oxide cathodes with lithium metal anodes in ionic liquid and polymer gel analogue electrolytes.2) L. M. McGrath and J. F. Rohan, Molecules, (2020), 25. 6002, Pyrrolidinium containing ionic liquid electrolytes for Li-based batteries.3) T. Teranishi, Y. Yoshikawa, M. Yoneda, A. Kishimoto, J. Halpin, S. O’Brien, M. Modreanu and I. M. Povey, (2018), ACS Applied Energy Materials, 1(7), pp. 3277-3282, Aluminum Interdiffusion into LiCoO2 Using Atomic Layer Deposition for High Rate Lithium Ion Batteries. Figure 1: Charge/Discharge capacity of 3nm Al2O3 coated V2O5 vs Li foil in 1M LiPF6 in EC:DEC (1:1) Figure 1

Glyme solvated Na and Li-ion capacitors based on co-intercalation process using pencil graphite as battery type electrode

Co-intercalation, intercalation of solvated ions received significant research interest in the last decade mainly due to faster charge-discharge kinetics with enhanced diffusion and more excellent stability. Moreover, for the assembly of alkali metal-ion hybrid supercapacitors, with battery type anode and capacitive cathode, a co-intercalation-based anode is a suitable option to avoid the kinetic mismatch between the two electrodes and hence can guarantee better performance. In the present work, we considered pencil graphite (PG B), a cheap and readily available graphite silica composite, as a battery-type anode and commercial activated carbon (AC) as cathode for the assembly of glyme solvated Na and Li-ion capacitors ((PG B/1 M NaCF3SO3 in diglyme/AC) gs−NIC & ((PG B/1 M LiPF6 in tetraglyme/AC) gs−LIC). Such device prototypes could exhibit maximum energy-power storage capability of 78.7 Wh kg−1 and 3.73 kW kg−1 for gs−NIC and 47 Wh kg−1 and 3.13 kW kg−1 for gs−LIC. Besides, the gs−NIC system with the minimum capacity and kinetic imbalance between the two electrodes displayed brilliant cyclic stability of >97% capacity retention after 6000 charge-discharge cycles at a current density of 1 A g−1. However, the co-intercalation electrolyte system (salt and solvent) plays a vital role in the device's overall performance.

Battery-like supercapacitive behavior of urchin-shaped NiCo2O4 and comparison with NiCo2X4 (X = S, Se, Te)

Bimetallic chalcogenides are promising as potential electrode materials for supercapacitors on account of their multiple oxidation states and better electroactivity. Anion effect on the electrochemical performance of urchin-shaped NiCo2X4, (X = O, S, Se, Te) is reported here. These materials crystallize in spinel cubic and monoclinic phases. Electron micrographs show that the materials possess a nanorod-like morphology that protrude from surfaces of microspheres. This gives it urchin-like appearance. Their structure enables ion permeability allowing for improved charge-discharge kinetics. The specific capacities obtained from 3-electrode electrochemical cell measurements are 137 mAh g−1 (492 C g−1), 108 mAh g−1 (390 C g−1), 76 mAh g−1 (272 C g−1) and 72 mAh g−1 (258 C g−1), respectively, for NiCo2O4, NiCo2S4, NiCo2Se4, and NiCo2Te4 at 2 A g−1. An asymmetric Swagelok device is fabricated for each chalcogenide material. Due to well-defined morphology and sufficient specific surface area, NiCo2O4 proved to be the best material delivering a maximum energy density of 34 Wh kg−1 and power density of 6 kW kg−1 followed by NiCo2Te4 delivering 22 Wh kg−1 and 11.25 kW kg−1. Higher electrical conductivity of the telluride-based materials makes them efficient supercapacitor electrodes. Selenium-based materials display better cyclic stability owing to the monoclinic phase.

Role of Oxygen Vacancy Ordering and Channel Formation in Tuning Intercalation Pseudocapacitance in Mo Single-Ion-Implanted CeO2-x Nanoflakes.

Metal oxide pseudocapacitors are limited by low electrical and ionic conductivities. The present work integrates defect engineering and architectural design to exhibit, for the first time, intercalation pseudocapacitance in CeO2-x. An engineered chronoamperometric electrochemical deposition is used to synthesize 2D CeO2-x nanoflakes as thin as ∼12 nm. Through simultaneous regulation of intrinsic and extrinsic defect concentrations, charge transfer and charge-discharge kinetics with redox and intercalation capacitances together are optimized, where reduction increases the gravimetric capacitance by 77% to 583 F g-1, exceeding the theoretical capacitance (562 F g-1). Mo ion implantation and reduction processes increase the specific capacitance by 133%, while the capacitance retention increases from 89 to 95%. The role of ion-implanted Mo6+ is critical through its interstitial solid solubility, which is not to alter the energy band diagram but to facilitate the generation of electrons and to establish the midgap states for color centers, which facilitate electron transfer across the band gap, thus enhancing n-type semiconductivity. Critically, density functional theory simulations reveal, for the first time, that the reduction causes the formation of ordered oxygen vacancies that provide an atomic channel for ion intercalation. These channels enable intercalation pseudocapacitance but also increase electrical and ionic conductivities. In addition, the associated increased active site density enhances the redox such that the 10% of the Ce3+ available for redox (surface only) increases to 35% by oxygen vacancy channels. These findings are critical for any oxide system used for energy storage systems, as they offer both architectural design and structural engineering of materials to maximize the capacitance performance by achieving accumulative surface redox and intercalation-based redox reactions during the charge/discharge process.

Cobalt-Based Double Catalytic Sites on Mesoporous Carbon as Reversible Polysulfide Catalysts for Fast-Kinetic Li-S Batteries.

Li-S batteries are considered to be the most promising next-generation advanced energy-storage systems. However, the sluggish reaction kinetics and the "shuttle effect" of lithium polysulfides (LiPSs) severely limit their battery performances. To overcome the complex and multiphase sulfur redox chemistry of LiPSs, in this study, we propose a new type of cobalt-based double catalytic sites (DCSs) codoped mesoporous carbon to immobilize and reversibly catalyze the LiPS intermediates in the cycling process, thus eliminating the shuttle effect and improving the charge-discharge kinetics. The theoretical calculation shows that the well-designed DCS configuration endows LiPSs with both strong and weak binding capabilities, which will facilitate the synergistic and reversible catalytic conversion. Furthermore, the experimental results also confirm that the DCS structure shows significantly enhanced catalytic kinetics than the single catalytic sites. The Li-S battery equipped with the DCS structure displays an extremely high discharge capacity of 918 mA h g-1 at a current density of 0.2 C and can reach a capacity of 867 mA h g-1 after 200 cycles with an ultralow capacity attenuation rate of 0.028% for each cycle. This study opens new avenues to address the catalytic requirements both in discharging and charging processes.

Ni-Co sulfide hollow nanoboxes with enhanced lattice interfaces for high performance hybrid supercapacitors

Bimetallic sulfides have been suggested as a novel class of electrode materials for supercapacitors (SCs) due to their high conductivity, rich redox active sites and wide operating potential window. To improve the property, tremendous efforts have been devoted to controlling the morphology, structure and size of bimetallic sulfides. We report here a strategy to achieve Ni-Co sulfide hollow nanoboxes with rich lattice interfaces and widespread mesopores via ion-exchange process. The lattice interfaces in the nanoboxes play a key role in improving the performance by developing more active sites. The thin nano-shell with porous structure makes it highly permeable for efficient ion diffusion, yet shortens the electron transport pathway. Such synergistic effects endow the Ni-Co sulfide hollow nanoboxes with high specific capacity of 789.0 C g−1 at 1 A g−1 and excellent rate capability of 82.1% capacity retention at 20 A g−1. Quantitative analysis of capacitive contribution sheds light on the rapid charge-discharge kinetics. Additionally, the as-fabricated hybrid SC, using optimized Ni-Co sulfide (Ni/Co molar ratio: 1/1) as anode and active rice husk carbon as cathode, exhibits a high energy density of 46.7 Wh kg−1 at power density of 400 W kg−1 and remarkable cycling stability of 82.7% at 5 A g−1 after 10,000 cycles, demonstrative of potential application for high-performance SCs.

Metal ion-induced capacitance modulation in near-isostructural complexes-derived electrochromic coordination polymers

Coordination polymers and metal–organic frameworks have attracted immense attention across different fields of science as materials with numerous functional applications. Herein, we report the use of coordination polymers obtained from near-isostructural metal (Mn2+, Fe2+, and Co2+) bipyridine complexes as electrode materials in a symmetric supercapacitor test cell. The variation in the central metal ion (Mn2+ vs. Fe2+ vs. Co2+) in these nearly identical coordination complexes was found to dictate the capacitive performance of the coordination polymers obtained via Pd(II) cross-linking. The central metal ion not only influences the porosity, Brunauer–Emmett–Teller (BET) surface area (6.5 (Mn), 10.4 (Fe), and 29.7 (Co) m2/g), and the areal capacitance, but also the performance parameters such as the cycling stability and charge–discharge kinetics as well as the charge transfer mechanism. A 3:4:5 ratio for the areal capacitance values (9.1 (Mn), 12.2 (Fe), and 15.4 (Co) mF cm−2 at a scan rate of 5 mV/s) corroborates the modulative effect of the metal center. The cycling stabilities of these coordination polymers also followed the same order. At higher current densities (>0.50 mA cm−2), the supercapacitors fabricated from the Mn-coordination polymer were found to charge and discharge at faster rates, whereas those fabricated from Fe- or Co-coordination polymers continued to discharge at similar rates, indicating similar pore volumes for the latter as confirmed by BET surface area measurements. Although the materials used in this study resulted in modest capacitive performance, the possibilities to enhance their surface area and crystallinity is envisaged to result in the development of new, multifunctional non-carbon electrode materials with efficient electrochemical storage characteristics and tunable electro-optical properties.

Side-View Operando Optical Microscopy Analysis of a Graphite Anode to Study Its Kinetic Hysteresis.

Operando analyses have provided several breakthroughs in the construction of high-performance materials and devices, including energy storage systems. However, despite the advances in electrode engineering, the formidable issues of lithium intercalation and deintercalation kinetics cannot be investigated by using planar observations. This study concerns side-view operando observation by optical microscopy of a graphite anode based on its color changes during electrochemical lithiation. Since the graphite color varies according to the optical energy gap during lithiation and delithiation, this technique can be used to study the corresponding charge-discharge kinetics. In addition, the cell configuration uses liquid electrolytes similar to commercial cells, allowing practical application. Furthermore, this side-view observation has shown that microscale spatial variations in rate and composition control the insertion and deinsertion, revealing the kinetics throughout the whole electrode. The results of this study could enhance the fundamental understanding of the kinetics of battery materials.

Controllable synthesis of gossamer-like Nb2O5-RGO nanocomposite and its application to supercapacitor

The gossamer-like Nb2O5-RGO nanocomposite was synthesized through a solvothermal treatment, and the Nb2O5 nanoparticles were uniformly coated on the RGO sheets. The size of the Nb2O5 nanoparticles is about 200–700 nm. The applications of Nb2O5-RGO as supercapacitor were then explored systematically. The morphology, textural structure, and physicochemical property of Nb2O5-RGO were investigated by using SEM, TEM, XRD, FT-IR, TG, and Raman. The electrochemical performance of RGO, Nb2O5, and Nb2O5-RGO was assessed through CV and galvanostatic charge-discharge test. The experimental results show that gossamer-like Nb2O5-RGO exhibits partial faradic pseudocapacitance and good electrical double layer capacitance property. The specific capacitance value 299.23 Fg−1 of Nb2O5-RGO nanocomposite is about 2.7 and 1.7 times higher than that of Nb2O5 and RGO, retaining 87.72% of its initial capacitance after 2000 cycles under the optimized conditions, which demonstrate that more ordered binary architecture Nb2O5-RGO nanocomposite along with easy synthesis possesses faster charge-discharge kinetics and excellent supercapacitive performance.