Electrodes For Energy Storage Applications Research Articles

Fe-Cu Alloy-Based Flexible Electrodes from Ethaline Ionic Liquid

The effective implementation of energy storage systems within flexible structures has recently become of particular interest. Here, the fabrication of inexpensive flexible electrodes via a number of straightforward methods formed the motivation for this research. Thin film-based Fe-Cu alloys were cathodically electrodeposited on a graphite substrate. As ionic liquids consist purely of ions (not solvent), they have recently been used in some electrochemical applications. In this study, therefore, Fe-Cu alloy coatings were prepared from an ethaline ionic liquid containing iron and copper salts. The electrochemical behaviour of Fe-Cu alloy films was determined by scanning between − 1.0 V and − 0.3 V in 1 M KOH at various scan rates ranging from 5 mV s−1 to 200 mV s−1. These films were characterised in terms of their structural and morphological properties by means of Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and x-ray diffraction (XRD). Formation of iron and copper alloy was differentiated depending on applied potential. The supercapacitive ability of Fe-Cu-coated film observed in 1 M KOH electrolyte demonstrated a specific capacitance of 304 F g−1 at a scan rate of 5 mV s-1. The reaction between the alloy and the electrolyte was mainly controlled by a surface-controlled reaction. An asymmetric supercapacitor was constructed with an Fe-Cu-coated graphite negative electrode and a non-woven graphite positive electrode. Four asymmetric supercapacitors were connected in series and used to light up a blue light-emitting diode. This study shows that ethaline ionic liquid is a promising medium for the preparation of alloy-based electrodes in energy storage applications.

Lignin-based electrodes for energy storage application

As the second most abundant organic polymers in nature, lignin demonstrates advantages of low cost, high carbon content, plentiful functional groups. In recent years, lignin and its derivatives, as well as lignin-derived porous carbon have emerged as promising electrode materials for energy storage application. In this review, recent progress on the design and fabrication of lignin-based electrode materials for energy storage application is summarized. We begin with a brief summary of the separation process and basic chemistry of lignin. Then, the latest development on the fabrication of lignin-based electrodes for supercapacitors and batteries is elaborated separately. Finally, we propose the current challenges and future prospects of the lignin-based electrodes for advanced energy storage devices.

Optimising the fabrication of 3D binder-free graphene electrode for electrochemical energy storage application

Herein, a one-step fabrication of three-dimensional (3D) binder-free graphene-nickel foam (G-Ni) electrode via atmospheric pressure chemical vapour deposition (APCVD) is reported. Graphene thin films were deposited on nickel foam under isobaric conditions in an inert environment. The process parameters such as temperature, time, and the gas flow rate were statistically optimised using design of experiment (DOE) to maximise the yield of graphene. The structural and morphological properties of the fabricated graphene electrode were investigated through X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), and energy dispersive X-ray spectroscopy (EDS). The electrochemical investigations were conducted through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. The results confirmed few-layered graphene with good surface morphology, high purity, and crystallinity of a binder-free electrode. The statistical analysis revealed that the optimal graphene electrode fabrication conditions were 900 °C, 10 min, and 100 sccm, respectively. Moreover, the regressed model and experimental results for the graphene growth were determined to be 3.93 mg/cm2, and 4.01 mg/cm2, respectively. Electrochemically, a specific capacitance value of 62.07 F/g was recorded at a scan rate of 3 mV/s showing an excellent performance of the fabricated 3D graphene electrode for energy storage applications.

Electrochemical Characterization of Single Layer Graphene/Electrolyte Interface: Effect of Solvent on the Interfacial Capacitance

AbstractThe development of the basic understanding of the charge storage mechanisms in electrodes for energy storage applications needs deep characterization of the electrode/electrolyte interface. In this work, we studied the charge of the double layer capacitance at single layer graphene (SLG) electrode used as a model material, in neat (EMIm‐TFSI) and solvated (with acetonitrile) ionic liquid electrodes. The combination of electrochemical impedance spectroscopy and gravimetric electrochemical quartz crystal microbalance (EQCM) measurements evidence that the presence of solvent drastically increases the charge carrier density at the SLG/ionic liquid interface. The capacitance is thus governed not only by the electronic properties of the graphene, but also by the specific organization of the electrolyte side at the SLG surface originating from the strong interactions existing between the EMIm+ cations and SLG surface. EQCM measurements also show that the carbon structure, with the presence of sp2 carbons, affects the charge storage mechanism by favoring counter‐ion adsorption on SLG electrode versus ion exchange mechanism in amorphous porous carbons.

Electrochemical Characterization of Single Layer Graphene/Electrolyte Interface: Effect of Solvent on the Interfacial Capacitance.

The development of the basic understanding of the charge storage mechanisms in electrodes for energy storage applications needs deep characterization of the electrode/electrolyte interface. In this work, we studied the charge of the double layer capacitance at single layer graphene (SLG) electrode used as a model material, in neat (EMIm‐TFSI) and solvated (with acetonitrile) ionic liquid electrodes. The combination of electrochemical impedance spectroscopy and gravimetric electrochemical quartz crystal microbalance (EQCM) measurements evidence that the presence of solvent drastically increases the charge carrier density at the SLG/ionic liquid interface. The capacitance is thus governed not only by the electronic properties of the graphene, but also by the specific organization of the electrolyte side at the SLG surface originating from the strong interactions existing between the EMIm+ cations and SLG surface. EQCM measurements also show that the carbon structure, with the presence of sp2 carbons, affects the charge storage mechanism by favoring counter‐ion adsorption on SLG electrode versus ion exchange mechanism in amorphous porous carbons.

An efficient strategy for transferring carbon nanowalls film to flexible substrate for supercapacitor application

The success to transfer graphene films and its engineering architecture, such as carbon nanowalls (CNWs), from the growth substrate to target substrate with large surface area and minimum structural damage is crucial for the future of graphene-based devices. Herein, we purpose a facile and an efficient strategy for transferring CNWs film grown on SiO2/Si substrate to flexible Indium Tin Oxide-Polyethylene Naphthalate (ITO-PEN) substrate. The feasibility of the proposed transfer method is demonstrated by studying the morpho-structural features of the transferred carbon nanowalls (TCNWs) vs the as-grown CNWs using FE-SEM, TEM, EDX, and Raman spectroscopy characterisation techniques. The transfer method successfully provides non-wrinkle and crack-free TCNWs film that preserve mostly the features of as grown CNWs. The TCNWs films with and without anodically deposited Manganese Oxide (MnO2) nanoparticles are explored as possible electrodes for energy storage applications. The MnO2/TCNWs hybrid film ensures a high areal capacitance of 40.3 mFcm−2 and preserves 75% of its initial capacitance as the charging current density increased from 1.0 to 6.0 mA cm−2 and capacitance retention of 99.5% after 2000 cycles at 1.0 mA cm−2. The contribution of this paper resides in paving the way for creating new opportunities for flexible energy storage devices.

High performance solid state symmetric supercapacitor based on reindeer moss-like structured Al(OH)3/MnO2/FeOOH composite electrode for energy storage applications

Developing an efficient, clean, sustainable, and reliable energy storage system is still a key challenge to resolve the growing demands of energy consumption. In this regard, supercapacitor becomes one of the foremost promising and emerging types of energy storage systems comprising properties of traditional batteries and conventional capacitors. Herein, a binder-free composite electrode of Al(OH)3/MnO2/FeOOH (AMFO) has been synthesized on stainless steel substrate via a facile, eco-friendly, and cost-effective Layer by Layer method at room temperature. The high resolution scaning electron microscopy reveals the mesoporous reindeer moss-like morphology of the synthesized electrode. The supercapacitive behaviour of the synthesized electrode has been explored in 1 M Na2SO4 electrolyte solution by using electrochemical measurement. The highest specific capacity of 2557 C g−1 has been obtained at a scan rate of 5 mV s−1 having wide potential range (−1.10 to 1.05 V). Further, a symmetric prototype supercapacitive device has been fabricated by coupling the AMFO electrodes. The high specific capacitance of 511 F g−1 has been obtained with ultra-high energy and power densities of ∼443 Wh kg−1 and ∼13 kW kg−1, respectively. These results indicate that this electrode has potential practical applications as a power backup, portable electronic device, and energy storage system.

Cellulose Nanofiber Composite with Bimetallic Zeolite Imidazole Framework for Electrochemical Supercapacitors.

Cellulose nanofiber (CNF) and hybrid zeolite imidazole framework (HZ) are an emerging biomaterial and a porous carbonous material, respectively. The composite of these two materials could have versatile physiochemical characteristics. A cellulose nanofiber and cobalt-containing zeolite framework-based composite was prepared using an in-situ and eco-friendly chemical method followed by pyrolysis. The composite was comprised of cobalt nanoparticles decorated on highly graphitized N-doped nanoporous carbons (NPC) wrapped with carbon nanotubes (CNTs) produced from the direct carbonization of HZ. By varying the ratio of CNF in the composite, we determined the optimal concentration and characterized the derived samples using sophisticated techniques. Scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), and X-ray photoelectron spectroscopy (XPS) confirmed the functionalization of CNF in the metallic cobalt-covered N-doped NPC wrapped with CNTs. The CNF–HZNPC composite electrodes show superior electrochemical performance, which is suitable for supercapacitor applications; its specific capacitance is 146 F/g at 1 A/g. Furthermore, the composite electrodes retain a cycling stability of about 90% over 2000 charge–discharge cycles at 10 A/g. The superior electrochemical properties of the cellulose make it a promising candidate for developing electrodes for energy storage applications.

Systematically increased surface area of amorphous sulfurized cobalt-based alloy as a substrate-free electrode for energy application

Having high energy density, high electrical conductivity and at the same time inexpensive and abundance material are key parameters to build an electrode for energy storage applications. Here, we construct sulfurized amorphous cobalt-based alloy with facile and a low-priced method. Samples were etched in H2SO4 with different molarities. Then, it was sulfurized using chemical vapor deposition technique. Existence of sulfur and its combination with Co was confirmed by Raman spectroscopy and X-ray PhotoelectronSpectroscopy. Electrochemical properties were investigated by cyclic voltammetry (CV) and galvanostatic charge-discharge methods. The sample etched in an 8 M H2SO4 had specific capacity of 135 C/g measured at scan rate of 5 mV/s in 1 M KOH. Our results suggest promising application of surface treated amorphous alloy for substrate-free electrodes.

Synergistic effects of Fe and Mn dual-doping in Co3S4 ultrathin nanosheets for high-performance hybrid supercapacitors

Dopant engineering in nanostructured materials is an effective strategy to enhance electrochemical performances via regulating the electronic structures and achieving more active sites. In this work, a robust electrode based on Fe and Mn co-doped Co3S4 (FM-Co3S4) ultrathin nanosheet arrays (NSAs) on the Ni foam substrate is prepared through a facile hydrothermal method followed by a subsequent sulfurization reaction. It has been found that the incorporation of Fe ions is beneficial to higher specific capacity of the final electrode and Mn ions contribute to the excellent rate capability in the reversible redox processes. Density functional theory (DFT) calculations further verify that the Mn doping in the Co3S4 obviously shorten the energy gap of Co3S4, which favors the electrochemical performances. Due to the synergetic effects of different transition metal ions, the as-prepared FM-Co3S4 ultrathin NSAs exhibit a high specific capacity of 390 mAh g−1 at 5 A g−1, as well as superior rate capability and excellent cycling stability. Moreover, the corresponding quasi-solid-state hybrid supercapacitors constructed with the FM-Co3S4 ultrathin NSAs and active carbon exhibit a high energy density of 55 Wh kg−1 at the power density of 752 W kg−1. These findings demonstrate a new platform for developing high-performance electrodes for energy storage applications.

Structural design of pyrene-functionalized TEMPO-containing polymers for enhanced electrochemical storage performance

We demonstrate the importance of rational structural design of pyrene-functionalized radical (i.e. 2,2,6,6-tetramethyl-1-piperidinyloxy, TEMPO) copolymers for enhanced electrochemical performance by providing insightful guidance for designing high-performance polymer-based electrodes for energy storage applications.

Self-supporting carbon-rich SiOC ceramic electrodes for lithium-ion batteries and aqueous supercapacitors.

Fabrication of precursor-derived ceramic fibers as electrodes for energy storage applications remains largely unexplored. Within this work, three little known polymer-derived ceramic (PDC)-based fibers are being studied systemically as potential high-capacity electrode materials for electrochemical energy devices. We report fabrication of precursor-derived SiOC fibermats via one-step spinning from various compositions of siloxane oligomers followed by stabilization and pyrolysis at 800 °C. Electron microscopy, Raman, FTIR, XPS, and NMR spectroscopies reveal transformation from polymer to ceramic stages of the various SiOC ceramic fibers. The ceramic samples are a few microns in diameter with a free carbon phase embedded in the amorphous Si–O–C structure. The free carbon phase improves the electronic conductivity and provides major sites for ion storage, whereas the Si–O–C structure contributes to high efficiency. The self-standing electrodes in lithium-ion battery half-cells deliver a charge capacity of 866 mA h gelectrode−1 with a high initial coulombic efficiency of 72%. As supercapacitor electrode, SiOC fibers maintain 100% capacitance over 5000 cycles at a current density of 3 A g−1.

Direct fabrication of phosphorus-doped nickel sulfide and eco-friendly biomass-derived humic acid as efficient electrodes for energy storage applications

High-performance asymmetric energy storage systems, benefit from both high energy and power densities, as well as long-term stability, have been developed using P-doped NiS–NF and carbonized humic acid as positive and negative electrodes, respectively.

Microwave Assisted Synthesis of MoS2/PANI/ZnO Nanocomposites as a Working Electrode for Energy Storage Applications

Transition metal dichalcogenide and polyaniline doped zinc oxide nanocomposites influence the transition probabilities and electronic structure. In present study, the various concentrations of MoS2/PANI/ZnO nanocomposites are synthesized by microwave assisted method. These nanocomposites are characterized by using XRD, FESEM, HRTEM and FT-IR. The XRD results revealed an average crystallite size of synthesized nanocomposites, which was found to be 19-24 nm. The electrochemical properties of the nanocomposites are studied through the CV, EIS and GCD for the application of supercapacitor as an active electrode material. The MoS2/PANI/ZnO nanocomposites exhibited a specific capacitance of 577 F g-1 and also retained 90% of its initial specific capacitance even after 5000 cycles. Hence MoS2/PANI/ZnO nanocomposites have potential application for energy storage applications.

Modified sol-gel synthesis of Co3O4 nanoparticles using organic template for electrochemical energy storage

The demand for economic and efficient electrode for energy storage devices has been increased with the rapid advancements in the sustainable synthesis of active material. Herein, bioactive compounds as fuel for the synthesis of electrode material (Co3O4 NPs), were investigated. Functionalization of Co3O4 NPs via organic extract of Euphorbia cognata Boiss have not only revealed the rapid and efficient growth of active materials but also ensured an effective interaction between the fabricated electrode and electrolyte solution for charge storage reactions. The synthesized Co3O4 NPs were scrutinized for its optical, structural, compositional and chemical properties and then investigated by galvanostatic charge discharge, cyclicvoltammetry for determination of its energy storage potential. The fabricated electrode was tested at range of scan rates and current densities to evaluate its charge storage potential at different scan rates and current densities. The phytofunctionalized Co3O4 NPs offered a large accessible active sites for charge storage with capacitance of 103 Fg-1, a maximum energy density of 1.9 Whkg−1, and higher power density of 4.7 KWkg−1. Thus, we have demonstrated the sustainable fabrication of electrode for energy storage applications.

Highly Energetic and Stable Gadolinium/Bismuth Molybdate with a Fast Reactive Species, Redox Mechanism of Aqueous Electrolyte

The electronic properties and stability of gadolinium-doped bismuth molybdate composites are critical characteristics that determine the efficiency of storing energy reversibly as a propitious electrode for energy storage applications. Gd-doped Bi2MoO6 is presented, which is based on the orthorhombic phase host Bi2MoO6 lattice, where variable amounts of Gd dopant are substituted in the Bi site, resulting in significantly improved energy storage performance. The doping effects with the aim of better understanding the electronic structure of Gd-doped Bi2MoO6 and fine-tuning the properties of energetically favorable material that possesses the most stable crystal structure are reported. The measured X-ray photoelectron spectra of Gd (4d) confirm the presence of the Gd(III) state. The enhanced stability of Gd0.05Bi1.95MoO6 has been attributed to the ability to distribute electron density evenly. In a three-electrode configuration, using aqueous NaOH electrolyte, the Gd0.05Bi1.95MoO6 electrode demonstrated a high specific areal capacitance of 2.15 F cm–2 (the equivalent of 191.5 mAh g–1). The results reported herein are important as they provide an insight into the factors influencing highly energetic and fast reactive species in the Gd(III) composites, which could be a potential anode material for energy storage applications. The optimized anode material is coupled with Ni–Co–Cu ternary oxide cathode and evaluated as a device. The asymmetric supercapattery showed 153 mAh g–1 at a current density of 4 mA cm–2 with an excellent retention of 89% after 1000 long cycles.

(Invited) Theoretical Study on the Energy Storage Mechanism of Transition-Metal-Carbide MXene By Quantum-Classical Hybrid Simulation

Two-dimensional transition-metal carbide MXenes has been known as a promising material of high-performance electrode for energy storage applications with both non-aqueous and aqueous electrolytes because it has electronic conductivity, ion capability in interlayer nanospace, and the redox activity of Ti. Especially, as an electrode of electrochemical capacitors, MXenes have a unique dependence of capacitance on intercalated cation species and a distinctive behavior that is both capacitive and pseudocapacitive depending on the electrolyte. To better understand electrochemical mechanism of these behaviors, we performed a microscopic theoretical analysis of the electric-double layer (EDL) in the interlayer nanospace of the MXene electrode by combining first-principles calculations based on density functional theory (DFT) and classical implicit solvation theory named three dimensional reference-site interaction model (3D-RISM) method [1]. By using the quantum-classical hybrid simulation, solvation effect at the interlayer nanospace of MXene electrode was taken into consideration appropriately with low computational cost comparable with conventional DFT simulation.For the unique dependence of capacitance on intercalated cation species, our simulation results showed that the capacitance of EDL capacitors can be enhanced by a factor of 1.8, when the water molecules are strongly confined into the two-dimensional nanoslits of titanium carbide MXene electrode. This is because that dipolar polarization of strongly confined water overscreens an external electric field applied on the EDL and enhances capacitance with a characteristically negative dielectric constant of a water molecule [2, 3]. Another investigated feature is the distinctive behavior that is both capacitive and pseudocapacitive depending on the electrolyte. As a result of their electronic states simulated via the quantum-classical hybrid simulation, it was found that the hydration shell of intercalated ions prevents orbital coupling between MXene and the intercalated ions, which leads to the formation of an EDL and capacitive behavior. However, once the cations are partially dehydrated and adsorbed onto the MXene surface directly, because of orbital coupling of the cation states with the MXene states, particularly for surface-termination groups, charge transfer occurs and results in a pseudocapacitive behavior [4].

High mass loading NiCo2O4 with shell-nanosheet/core-nanocage hierarchical structure for high-rate solid-state hybrid supercapacitors

Rational design of advanced structure for transition metal oxides (TMOs) is attractive for achieving high-performance supercapacitors. However, it is hampered by sluggish reaction kinetics, low mass loading, and volume change upon cycling. Herein, hierarchical NiCo2O4 architectures with 2D-nanosheets-shell and 3D-nanocages-core (2D/3D h-NCO) are directly assembled on nickel foam via a facile one-step way. The 2D nanosheets are in-situ generated from the self-evolution of initial NCO nanospheres. This 2D/3D hierarchical structures ensure fast ion/electron transport and maintain the structural integrity to buffer the volume expansion. The 2D/3D h-NCO electrode with an ultrahigh mass loading (30 mg cm−2) achieves a high areal capacity of 4.65 C cm−2 (equivalent to 1.29 mAh cm−2) at a current density of 4 mA cm−2, and retains 3.7 C cm−2 even at 50 mA cm−2. Furthermore, the assembled solid-state hybrid supercapacitor yields a high volumetric energy density of 4.25 mWh cm−3 at a power density of 39.3 mW cm−3, with a high capacity retention of 92.4% after 5000 cycles. Therefore, this work provides a new insight to constuct hierarchical electrodes for energy storage application.

Promising Rice-Husk-Derived Carbon/Ni(OH)2 Composite Materials as a High-Performing Supercapacitor Electrode.

Improving the electrochemical performance of biomass-derived carbon electrode-active materials for supercapacitor applications has recently attracted considerable attention. Herein, we develop hybrid electrode materials from rice-husk-derived porous carbon (RH-C) materials and β-Ni(OH)2 via a facile solid-state reaction strategy comprising two steps. The prepared RH-C/Ni(OH)2 (C–Ni) was investigated using scanning electron microscopy (SEM) (energy-dispersive X-ray spectrometer (EDS)), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) to acquire the physical and chemical information, which was used to demonstrate the successful fabrication of C–Ni. Thermogravimetric analysis (TGA) measurement results confirmed that the thermal stability of C–Ni changed due to the presence of Ni(OH)2. As expected, C–Ni possesses a high capacitance of ∼952 F/g at a current density of 1.0 A/g. This result is higher than that of pure biomass-based carbon materials under the three-electrode system. This facile preparation method, which was used to synthesize the electrode-active materials, can extend to the value-added utility of other waste biomass materials as high-performing supercapacitor electrodes for energy storage applications.

A novel ternary composite aerogel for high-performance supercapacitor

Despite the attractive features of existing supercapacitors (SCs), SC devices still exhibit low mass loading, limited working voltage, low specific capacitance, short cycle life, and unsatisfactory energy density. In this study, we introduced novel self-suspended polyaniline (S-PANI) into a combination of manganese dioxide (MnO2) and reduced graphene oxide (RGO) to propose an efficient SC electrode for energy storage applications. The unique addition of lightweight, highly conductive, exceptionally water-soluble, and unique fibrillar structure S-PANI increased the conductivity of composite aerogels and reduced the ionic diffusion resistance of electrode materials. The introduction of S-PANI significantly improved the dispersion of MnO2 particles and enabled MnO2 to give full play to its pseudopotentiability. The MnO2/S-PANI/P-RGO ternary composite aerogel was prepared by the self-assembly hydrothermal technique where different mass ratios of MnO2, S-PANI, and RGO were used and analyzed. Physical analyses showed that MnO2/S-PANI/P-RGO composite aerogels had a 3D porous network structure and MnO2 nanospheres are evenly disseminated on the surface of RGO nanosheets. The flowable S-PANI reduced the solid-solid contact resistance in the electrode. The developed 3D MnO2/S-PANI/P-RGO composite aerogel electrode displayed a specific capacitance of 571 F g−1 at the current density of 1 A g−1 along with the specific capacitance of 413 F g−1 with an increased current density of 40 A g−1 and the capacity retention rate of 72.6 %. Also, the initial capacitance retention of 96.7 % was attained after 10,000 cycles at a current density of 20 A g−1 is attained, displaying significant and long-term stability of the composite aerogel electrode. In summary, MnO2/S-PANI/P-RGO composite aerogels reported in this study are promising in energy storage applications demanding high specific capacitance and cycle life.