Galvanostatic Charge-discharge Curves Research Articles

Spherical LiMn0.7Fe0.3PO4/C Cathode Materials for Lithium-Ion Batteries

Lithium manganese iron phosphates (LiMnxFe1-xPO4) [1] are attractive as next-generation cathode materials for lithium-ion batteries because they are safer than conventional lithium transition metal oxides (e.g. LiCoO2) [2] and are Co- and Ni-free. However, due to their low electronic conductivity [3], they can deliver much lower electrochemical properties than theoretically expected one. Therefore, many researchers have focused on chemical composition, reducing primary particle size, and carbon coating. On the other hand, granulation of LiMnxFe1-xPO4 primary nanoparticles is effective in improving poor handling of LiMnxFe1-xPO4 primary nanoparticles during cathode slurry preparation. However, electrochemical properties of granulated LiMnxFe1-xPO4 have not been well studied in previous reports. In this study, the electrochemical properties of the spherical LiMn0.7Fe0.3PO4/C composed of primary nanoparticles are reported. Spherical LiMn0.7Fe0.3PO4/C was synthesized by hydrothermal method followed by granulation and carbon coating. The synthesized spherical LiMn0.7Fe0.3PO4/C was characterized using X-ray diffraction (XRD) and scanning electron microscope (SEM). Electrochemical properties of spherical LiMn0.7Fe0.3PO4/C were examined using CR2032 coin-type cells. Fig. 1 (a) shows the SEM images of spherical LiMn0.7Fe0.3PO4/C. As shown in Fig. 1 (a), spherical particle 10 μm in diameter composed of homogeneously sized primary nanoparticles were observed. Fig. 1 (b) shows the galvanostatic charge-discharge curves for spherical LiMn0.7Fe0.3PO4/C at discharge current rates of 0.2, 1, 5, and 10 C in a voltage range of 1.5–4.5 V at 30 °C. Spherical LiMn0.7Fe0.3PO4/C delivered a 0.2 C discharge capacity of 153 mAh g−1. At the 10C rate, spherical LiMn0.7Fe0.3PO4/C also delivered a high discharge capacity of 137 mAh g−1, which was 89 % of the 0.2C discharge capacity. Detailed data of our study including blended cathode of LiNiaMnbCocO2 and spherical LiMn0.7Fe0.3PO4/C will be presented in the meeting.

Unveiling the potential of P3 phase in enhancing the electrochemical performance of a layered oxide cathode

Controlling the phase structure of layered oxide cathodes is considered an effective strategy to realize high-performance Na-ion batteries. Herein, we unveil the synthesis and electrochemical behavior of a hitherto unreported monophasic P3 structure in Na0.75Mn0.75Ni0.25O2 (NNM) calcined at 750 °C. The conversion of P3 to a P2-type single phase (at 850 °C) upon increasing the calcination temperature, with P2/P3 biphasic structures at intermediate temperatures, was confirmed by the Rietveld refinement of the x-ray diffraction (XRD) data. The monophasic P3 cathode showed a specific capacity of 190 mAh/g at 0.1 C and retained 90% of its initial capacity after 200 cycles at 1 C in the 1.5–4.2 V range. The galvanostatic charge-discharge (GCD) curves also showed a decrease in specific capacity with an increase in the P2 phase. The P3-dominant biphasic cathodes displayed superior rate performance, exhibiting capacities up to 97 mAh/g at 6 C, attributed to their smaller particle size and optimal P2/P3 phase fraction. Operando Synchrotron XRD data confirmed the suppression of P3→O′3 + O3 transformation in the biphasic cathode that was present in the monophasic P3 structure during charge-discharge cycling. The superior electrochemical performance and excellent structural stability of biphasic cathodes make them ideal for stationary and mobile storage applications.

Synergistic Effect of Nickel and Cobalt in Nanowire Array for High Energy Storage with Rapid Charge Transfer in Asymmetric Supercapacitor

AbstractWe introduce a unique asymmetric supercapacitor design that combines a vertically aligned Ni−Co alloy‐type nanowire (NiCoNW) array electrode with a graphene flakes (GFs) electrode. The sandwiching of these two electrodes enables the device to operate at a high working potential window of 2.0 V. The improved response of the device is attributed to the asymmetric design and a high charge transfer in the NiCoNWs compared with pure metals. The optimized presence of Co in the alloy increases the rate of hydroxide formation in an alkaline solution during the gas evolution reaction. The use of GFs to modify the graphite electrode (GFs@Graphite) provided a more stable response at high current densities. We obtain extremely stable cyclic voltammetry (CV) plots even at very high scan rates (500 V/s) and galvanostatic charge–discharge curves with longer charge–discharge times. The highest capacitance achieved for the assembled device (Asy‐NiCoNWs/GFs@Graphite) is 339 F/cm3 (volumetric) at a current density of 5.0 A/cm3. In addition, a remarkable cycling retention of ∼100 % is observed after 10000 continuous potential cycles.

Quasi 2D Ruddlesden–Popper perovskite thin film electrode for supercapacitor application: Role of diffusion and capacitive process in charge storage mechanism

Hybrid halide perovskites are the most widely explored materials in the photovoltaic field. Recently they have been investigated for energy storage applications owing to their unique conductivity. Most reports on supercapacitor applications of halide perovskites are based on Methyl ammonium lead iodide (MAPbI3) and Methyl ammonium lead bromide (MAPbBr3) compounds. These halides are prone to degradation owing to external environmental parameters. Hence, one must look for other stable alternative halides. In this scenario, materials that can yield significant results with better stability are Quasi 2D perovskites, which combine the properties of both 3D and 2D perovskites. We successfully synthesized and characterized 4-Fluorobenzylammine hydroiodide spacer cation-based quasi 2D perovskite in this study. A detailed study was carried out on the effect of the precursor concentration and annealing temperature on the morphology and vertical growth of quasi-2D perovskite. An in-depth analysis of these perovskites' graded, phase-segregated growth was performed. Furthermore, we prepared a composite electrode from a mixture of quasi-2D perovskite with acetylene carbon black to obtain better performance. Our results show a maximum specific capacitance of 8.67 F g−1 from Cyclic Voltammetry curves. Further from the Galvanostatic Charge Discharge (GCD) curves, we obtained a capacitance of 3.39 F g−1. It is the highest value obtained for perovskite thin-film based supercapacitor electrode. The material displayed a low charge transfer resistance indicating a better conducting property, and displayed energy and power density of 170 mWh kg−1 and 109 W kg−1, respectively. Further, the contribution of capacitance and diffusion limited process in the charge storage mechanism of these electrodes were quantified. The electrodes could retain 91% capacitance after working for 1000 cycles, emerging as potential energy storage material for the future.

The features of the solvothermal synthesis of SnSe nanosheets and nanoflowers for supercapacitor applications

In this article, orthorhombic SnSe nanoparticles (NPs) are prepared through hydrothermal method by using Olyelamine and Ethylene glycol solvent named as AN-(OA) and AN-(EG). The SEM and TEM images of the AN-(OA) and AN-(EG) NPs show sheet and flower-like shapes, respectively. The cyclic voltammograms (CV) and Galvanostatic charge/discharge (GCD) studies of AN-(OA) and AN-(EG) electrodes are investigated in 0.5 M of KOH electrolyte. The specific capacitance values calculated through CV curves are 443, 240, 172, 138, 118, 130 and 50 (F/g) of AN-(EG) electrode and 224, 116, 80, 62, 52, 31 and 20 (F/g) of AN-(OA) electrode at the scan rate of 10, 20, 30, 40, 50, 60 and 70 (mV/s), respectively. Further, the specific capacitance values calculated through GCD curves are 83, 66, 58 and 55 (F/g) of AN-(EG) electrode and 52, 33, 29 and 27 (F/g) of AN-(OA) electrode at the current density of 1, 2, 3 and 5 (A/g), respectively. The morphology plays a critical role in capacitive performance of NPs.

Copolymer versus bilayer composite: Electrochemical, electrochromic and capacitive properties of benzotriazole and edot containing conjugated polymers

In this study, benzotriazole-based homopolymer (P-TBtz), copolymer (C-TBtzEdot), and bilayer composites (B-TBtzEdot and B-EdotTBtz) were prepared by electrochemical polymerization. B-TBtzEdot and B-EdotTBtz differ only in the sequential deposition orders onto the ITO electrode. Wise selected materials successfully performed their jobs: TBtz introduced a multichromic property to polymer films and Edot improved the charge storage capacity. Electrochemical characterizations of resulting conjugated polymer films were performed by cyclic voltammetry (CV), chronopotentiometry, chronoamperometry, and electrochemical impedance spectroscopy (EIS). For optical and morphological characterization, UV–vis spectroscopy and scanning electron microscopy (SEM) were used, respectively. According to SEM images, all films have different morphologies. Moreover, upon applied potential, change in the absorption spectra and color change was monitored. Besides, the capacitance value of the polymer films was calculated from cyclic voltammogram and galvanostatic charge-discharge curves. C-TBtzEdot had the highest capacitance value as 97.5 F/g at 2 mV/s and 92 F/g at 0.5 A/g.

Phosphorus/Sulfur-Enriched Reduced Graphene Oxide Papers Obtained from Recycled Graphite: Solid-State NMR Characterization and Electrochemical Performance for Energy Storage

The reduction of graphene oxide (GO) by means of thermal and/or chemical treatments leads to the production of reduced graphene oxide (rGO)—a material with improved electrical conductivity and considered a viable and low-cost alternative to pure graphene in several applications, including the production of supercapacitor electrodes. In the present work, GO was prepared by the oxidation of graphite recycled from spent Li-ion batteries using mixtures of sulfuric and phosphoric acids (with different H2SO4/H3PO4 ratios), leading to the production of materials with significant S and P contents. These materials were then thermally reduced, resulting in rGO papers that were investigated by solid-state 13C and 31P nuclear magnetic resonance, along with other methods. The electrochemical properties of the produced rGO papers were evaluated, including the recording of cyclic voltammetry and galvanostatic charge–discharge curves, besides electrochemical impedance spectroscopy analyses. The samples obtained by thermal reduction at 150 °C exhibited good rate capability at high current density and high capacitance retention after a large number of charge–discharge cycles. The results evidenced a strong relationship between the electrochemical properties of the produced materials and their chemical and structural features, especially for the samples containing both S and P elements. The methods described in this work represent, then, a facile and low-cost alternative for the production of rGO papers using graphite recycled from spent batteries, with promising applications as supercapacitor electrodes.

Investigation of Dunaliella salina microalgae as an effective dual-function material for hydrogen production and supercapacitor applications

Today, population growth, industrialization and economic growth increase the consumption of fossil fuels to meet the energy demand. The scarcity of fossil fuels and the harmful gases they generate increase the interest in renewable energy sources. One of these sources is hydrogen energy, which is plentiful in nature and has no negative environmental effects. Sodium borohydride (NaBH4) is a good source of hydrogen, but a catalyst must used for methanolysis. Besides producing energy, it is also important to store it. Supercapacitors are a good alternative to energy storage elements due to their outstanding advantages. In this work, Dunaliella salina (DS) microalgae were used as substrate to synthesize activated carbon for the first time to develop materials that can operate both as a catalyst and an electrode material for supercapacitors. The activated carbon was obtained by carbonization and activation and the taguchi experimental approach was used to minimize the number of experiments. The best hydrogen production rate (HPR) result for DS-9 catalyst with 0.10 g catalyst and 0.25 g NaBH4 at ambient temperature of 60 °C was determined to be 13,085 mL min−1gcat−1. The material with the best HPR value was then used as the electrode material for supercapacitor design. The specific capacitance value for 1 A/g was determined using galvanostatic charge-discharge (GCD) curves to be 216 F/g. In addition, the produced supercapacitor has an energy density of 13.80 W h/kg at a power density of 480 W/kg. The results indicate that the ecologically friendly and cost effective bifunctional materials produced can be used both in reuse of organic wastes and in catalyst and supercapacitor applications.

Effects of plasma on electrochemical performance of carbon cloth-based supercapacitor

In this work, the surface of carbon cloth is treated by plasma jet to improve its hydrophilicity. The symmetrical carbon cloth-based supercapacitor is assembled with the carbon cloth treated by plasma as the active electrodes and sodium chloride solution as the electrolyte. With the discharge time (1 min, 2 min, 3 min) and working gas types (argon, air, helium) of plasma as variables, the effects of different plasma on the hydrophilicity of carbon cloth are observed, and the changes of the electrochemical properties of the supercapacitors with single or double carbon cloth electrodes treated by different plasma are studied. The contact angle test results show that the plasma of different working gases can weaken the hydrophobicity of carbon cloth, and the helium plasma can make the carbon cloth change from hydrophobicity to hydrophilicity. The electric capacity calculated by cyclic voltammetry shows that plasma can increase the electric capacity of carbon cloth-based supercapacitors. The electric capacity of carbon cloth-based supercapacitors with two carbon cloth electrodes treated by plasma is larger than that of single carbon cloth electrode treated by plasma. The argon and helium plasma with longer discharge time can significantly improve the electric capacity of carbon cloth-based supercapacitors. The galvanostatic charge-discharge curve shows that different working gases of plasma can make carbon cloth-based supercapacitors obtain pseudocapacitance, increase the charge-discharge time and electric capacity. From the AC impedance spectrum, it can be concluded that the plasma of any kind of working gas can reduce the impedance and charge transfer resistance of the carbon cloth-based supercapacitor. The longer plasma discharge time lead to the smaller impedance, and the impedance of the supercapacitor with both carbon cloth electrodes treated by plasma is smaller.

Revealing Silicon’s Delithiation Behaviour through Empirical Analysis of Galvanostatic Charge–Discharge Curves

The galvanostatic charge–discharge (GCD) behaviour of silicon (Si) is known to depend strongly on morphology, cycling conditions and electrochemical environment. One common method for analysing GCD curves is through differential capacity, but the data processing required necessarily degrades the results. Here we present a method of extracting empirical information from the delithiation step in GCD data for Si at C-rates above equilibrium conditions. We find that the function is able to quickly and accurately determine the best fit to historical half-cell data on amorphous Si nanowires and thin films, and analysis of the results reveals that the function is capable of distinguishing the capacity contributions from the Li3.5Si and Li2Si phases to the total capacity. The method can also pick up small differences in the phase behaviour of the different samples, making it a powerful technique for further analysis of Si data from the literature. The method was also used for predicting the size of the reservoir effect (the apparent amount of Li remaining in the electrode), making it a useful technique for quickly determining voltage slippage and related phenomena. This work is presented as a starting point for more in-depth empirical analysis of Si GCD data.

The Effect of Copper Sulfide Stoichiometric Coefficient and Morphology on Electrochemical Performance

In this work, CuS, Cu7S4, Cu9S5, Cu7.2S4, and Cu2S with the same morphology were successfully synthesized by the hydrothermal method. According to the calculation, their galvanostatic charge-discharge (GCD) curves were 43.29 (CuS), 86.3 (Cu7S4), 154 (Cu9S5), 185.4 (Cu7.2S4), and 206.9 F/g (Cu2S) at the current density of 1 A/g. The results showed that the energy storage capacity of copper sulfide with the same morphology increased with the increase of the copper sulfide stoichiometric coefficient. At the second part of this work, the agglomerated cuprous sulfide and the microporous cuprous sulfide were successfully prepared, respectively. In addition, the porous spherical cuprous sulfide was annealed to get nano cuprous sulfide. It is found that the specific capacity of the agglomerated structure is the highest, which had reached 206.9 F/g at the current density of 1 A/g, and 547.9 F/g at the current density of 10 A/g after activation.

Methods—Ampero-Coulometry: A New Technique for Understanding Lithium-Sulfur Electrochemistry

Despite limited commercial success, lithium sulfur technology (LST) is still far from competing existing Li-ion technology. One of the main reasons hindering the success of LST is the complexity of lithium-sulfur chemistry during electrochemical charging and discharging. Dissolution of sulfur species in the electrolyte solution exacerbates the difficulties of this system. Therefore, a comprehensive understanding of sulfur species and their kinetics during charge/discharge process is paramount for a high-performance lithium-sulfur battery. We present a new technique we refer to as Ampero-Coulometry, which takes the chronoamperometric (galvanostatic) charge-discharge curves and mathematically transforms them to a series of curves that reveal the cation diffusional rate inside carbon-sulfur porous electrodes at different states of charge/capacity. This technique allowed us to track the overall Li+ ion diffusional rate inside a Li-S cell over a complete state of discharge. As dissolution of sulfur species and their interplay inside a porous sulfur electrode has a significant role in limiting Li-S battery capacity, and method allows correlation between the known mechanism of polysulfide dissolution, the kinetics of a sulfur electrode, and its response.

Nanoparticulate films of WO3 and MoO3 composites for enhancing UV light electrochromic transmittance variation and energy storage applications

Green technologies for the manufacture of optical shutters retain a sustainable development. In this work, the electro-exploding wires and spray coating technologies are employed to deposit nanoparticulate (WO3)1-x(MoO3)x composite films. MoO3 NPs are introduced to enhance electrochromic (EC) transmittance variation of violet and UV light with wavelengths ranging from 330 to 450 nm. Measurements of EC performances of (WO3)1-x(MoO3)x composite films in a potentiostat are carried out to discern beneficial from MoO3 addition. It is observed that the diffusion coefficient and the charge density increase with an increment of MoO3 concentration. The coloration efficiency at 430 nm raises apparently whereas that at 633 nm does not show a significant variation with increasing MoO3 concentrations. In addition, the EC device with ∼12.5% of MoO3 introduced reveals a much higher optical modulation at 430 nm. From the measurements of galvanostatic charge-discharge curves of EC films in the potentiostat, the areal capacitances of 12.9 and 14.0 mF/cm2 are estimated for pure and ∼12.5% MoO3 introduced WO3 EC films. The EC batteries are demonstrated and the enlarged energy storage capability with an addition of MoO3 is observed. The simple introduction of MoO3 into WO3 nanoparticulate films compensates drawbacks of WO3 films and enhances EC performances and energy storage capabilities.

Comparative Study of PEDOT- and PEDOT:PSS Modified δ-MnO2 Cathodes for Aqueous Zinc Batteries with Enhanced Properties

Chemically synthesized layered manganese dioxide (δ-MnO2) modified by poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) dispersion were used as cathode materials for aqueous Zn-ion batteries (AZIBs). A comparative study of electrochemical properties of cathodes with pristine MnO2 and materials chemically modified by conducting polymers in different forms was performed with cycling voltammetry and galvanostatic charge-discharge curves in Zn2+-containing electrolyte solutions. The results of electrochemical tests indicate the significant improvement in specific capacity of electrodes in the sequence MnO2, MnO2/PEDOT and MnO2/PEDOT:PSS composites. The MnO2/PEDOT:PSS electrode delivered a specific discharge capacity of 278 mAh·g−1 at a current density 0.3 A·g−1 after 100 cycles, whereas for MnO2/PEDOT and MnO2 electrodes the values were 238 and 121 mAh·g−1 (capacity retention is 99%, 99.5% and 89%, respectively). These specific capacity values obtained for manganese dioxide-based cathodes are demonstrating the positive role of intrinsically conducting polymer, especially in case of surface modification of electroactive particles by PEDOT:PSS dispersion.

Microwave synthesis of antimony oxide graphene nanoparticles - a new electrode material for supercapacitors.

For the first time, antimony oxide nanoparticles were produced using a microwave technique and evaluated as a supercapacitor electrode. The specific capacitance derived from the material's galvanostatic charge-discharge curve was 98 F g-1 in 1 M Li2SO4 electrolyte at 0.1 A g-1 current density. The charge storage mechanism visible in the CV curve is nearly rectangular and identical to the EDLC charge storage mechanism. Additionally, antimony species were chemically attached to graphene oxide using an antimony(iii) chloride precursor and subsequently microwave aided procedures were used to convert the antimony species to SbO-G nanocomposites. The results of energy-dispersive X-ray spectroscopy demonstrated the pure character of the produced material. In a three-electrode cell arrangement, the resulting composite was electrochemically characterized. The cyclic voltammogram results showed that among the pristine SbO, graphene, and SbO-G materials, SbO-G had a higher specific capacitance value of 37.58 F g-1, at a scan rate of 10 mV s-1. The material has also demonstrated good conductivity characteristics based on electrochemical impedance spectroscopy research. After 3500 galvanostatic charge-discharge cycles, the material had excellent cycling stability of ∼100%. All the remarkable capacitive properties demonstrated by this material indicate that it can be a viable choice in the field of energy storage devices.

What about electrochemical behaviors for aurivillius-phase bismuth tungstate? Capacitive or pseudocapacitive.

Researchers mainly explore the mechanism of pseudocapacitance through studying electrode materials with Faraday pseudocapacitive behavior. Here, we found that Bi2WO6, a typical Aurivillius phase material with pseudo-perovskite structure, showed nearly ideal pseudocapacitive behavior. The cyclic voltammetry curve is approximately rectangular in shape, with no redox peaks, which is similar to that of carbon materials. And the shape of the galvanostatic charge-discharge curve is close to an isosceles triangle. In addition, the kinetic analysis demonstrated that the electrochemical process of the A-Bi2WO6 electrode is dominated by surface processes, not diffusion. The A-Bi2WO6 electrode material presents a great volumetric specific capacitance of 466.5 F cm-3 at 0.5 A g-1. These electrochemical properties confirm that the Bi2WO6 material can serve as an ideal support material to explore pseudocapacitive energy storage. This work also provides guidance for the development of new pseudocapacitive materials.

Chemically synthesized rGO/SiC nanocomposites and their electrochemical performance for supercapacitor electrode

Reduced graphene oxide/silicon carbide (rGO/SiC) nanocomposites (NCs) were synthesized using a simple chemical method varying the contents of SiC from 1 to 9 wt%. in rGO/SiC NCs. The presence of rGO and SiC planes at 24° and 34.2°, 43.3°, and 71.8 respectively in the XRD spectra indicates the successful formation of rGO/SiC NCs. The vibrational bonding related to Si–C and Si–O–Si at 883 and 1051 cm−1 respectively were present in the FTIR spectra of all the NCs supporting the XRD results. The optical band gap varied from 1.53 to 2.11 eV and the formation of rGO and SiC bonding were confirmed from the XPS analysis. The non-linear electrical behavior enhances the mobility and provides a specific capacitance of 442.3–527.3 F/g at a 5 mV/s scan rate and 280.8–997.5 F/g at 2 A/g from cyclic voltammetry (CV) and Galvanostatic Charge-Discharge curves (GCD) respectively with increasing SiC from 1 to 9 wt%. The kinetics of current-generating mechanisms from capacitive effects and diffusive behavior were also quantified suggesting the hybrid nature of the rGO/SiC electrode material. Thus, rGO/SiC NCs are promising electrode materials for next-generation supercapacitor devices for addressing energy challenges.

Pyrolysis of waste plastics-derived carbon nanomaterials on nickel foam for utilization as an efficient binder-free electrode: Effect of catalyst loading on capacitive performance

The pyrolytic liquid and gas products are extensively analyzed for practical applications, but, few applications exist for solid product from waste plastics pyrolysis. This study investigates energy storage potential of waste plastics-derived carbon nano-materials (CNMs), pyrolyzed directly on nickel foam (NF) coated with nickel alumina catalyst, in a two-stage fixed bed reactor. Effect of increasing nickel to aluminum molar ratio (0.05, 0.1, 0.2) in energy storage capacity is studied. Galvanostatic charge-discharge curves, at 0.125 A g−1, show highest specific capacitance of 153.75 F g−1 for 0.1 molar ratio. The reason for such high performance is mainly because of a) greater metal-support interaction by using NF substrate, b) formation of CNMs according to base-growth mechanism, providing metal free surface at the top, and c) the presence of equal amounts of disordered and ordered carbons, resulting in meso- and micro-porous structures, providing high electrolyte availability at the electrode surface. The retained rectangle shape of cyclic voltammetry (CV) curve after 5000 cycles, with 98.5 % capacitance retention, also exhibits stability and durability of produced electrode. Though the fabricated electrode involved no post-treatment, yet, it showed higher performance than commercial CNMs. Therefore, this study open new ways to fabricate environment friendly and economically effective supercapacitors.

High-Surface-Area Graphene Oxide for Next-Generation Energy Storage Applications

Synthesis of high-surface-area graphene oxide for application in next-generation devices is still challenging. In this study, we present a simple and green-chemistry procedure for the synthesis of oxygen-enriched graphene materials, having very large surface areas compared with those reported for powdered graphene-related solids. Using the hydrothermal treatment of carbon nanohorns by a green-chemistry H2O2 oxidant under elevated pressure, the progressive creation of a stable carbon nanomaterial, denoted as open-sensu-shaped graphene oxide (OSSGO) by us, is observed. This oxygen-enriched nanographene contains π–π stacked few-layered graphene ribbons curved at the termini derived from the original cone tip. OSSGO is intensively analyzed and cross-characterized by spectroscopy, diffraction, adsorption, and elemental analysis methods. Based on the obtained results, we propose a mechanism of transformation from horns to a structure with several layers of sensu-form stacked graphene oxide. As this transformation process proceeds gradually, one can obtain numerous transition nanoarchitectures of tunable morphology and surface physicochemistry, including materials with an extremely high surface area. As OSSGO bears a fraction of the electron-withdrawing and O–H acidic functionalities, electrochemical studies, especially galvanostatic charge–discharge curves and specific capacitance values (significantly higher than those for other carbon-based materials), show potential applications in next-generation supercapacitors. As a result of the large surface areas, we also predict future applications in programmable adsorbents and catalysts with broad-range activity, while the list of applications is incomplete.

A systematic approach for selecting suitable morphologies for supercapacitor applications through morphological stability map – A case of Ni-MOF

Nickel metal organic frameworks (Ni MOFs) were synthesized employing microwave technique for supercapacitor applications using Ni(NO3)2·6H2O (=M) and p-benzenedicarboxylic acid (=L) in M:L ratios of 1:1–4:1, 150–200 °C. Flakes, plates, nanoflowers, and globules are obtained and arranged in M:L-Temperature space to yield morphological stability map. Flakes appear at all M:L, 150 °C; plates form at M:L = 1:1, ≥ 165 °C; nanoflowers are seen at M:L ≥ 2:1, 165 °C; globules form at M:L ≥ 2:1, ≥ 180 °C. Cyclic voltammograms from these morphologies within 0 and + 0.6 V vs SCE at 10–100 mV s−1 show redox peaks corresponding to partial diffusion control, substantiated by galvanostatic charge-discharge (GCD) curves. From GCD, globules at M:L = 3:1 exhibit the highest specific capacitance (Csp) of 1361–600 F g−1 at 0.5–5.0 A g−1. This is attributed to their smallest size, presence of monoclinic and γ-NiOOH phases. Further, globules exhibit the lowest charge transfer resistance as estimated from the Nyquist plots showing two incomplete depressed semicircles. This work presents a systematic approach to select suitable Ni MOF morphologies for supercapacitor applications using morphological stability map. Also, it answers the question: “why does a particular morphology exhibit superior charge storage performance?”