Self-standing Electrode Research Articles

Intercalation pseudocapacitance in flexible and self-standing V2O3 porous nanofibers for high-rate and ultra-stable K ion storage

Transition metal oxides possess eminently high capacity based on the conversion reaction by delivering multiple electrons. However, they usually demonstrate limited cycle life and inferior rate capability due to the pulverization and aggregation of active materials. V2O3 is considered to be an attractive electrode material due to its intrinsic tunnel structure provided by 3D V-V framework. Herein, a flexible and self-standing electrode of V2O3 nanoparticles embedded in porous N-doped carbon nanofibers (V2O3@PNCNFs) has been fabricated through a facile electrospinning method and subsequent thermal treatment. Electrochemical kinetic analysis, in situ XRD, ab initio molecular dynamics (AIMD) and density functional theory (DFT) calculation suggest that the potassium storage of V2O3 is dominated by intercalation pseudocapacitance and only up to 1 mol K+ can insert into V2O3 crystal. Different from the conversion reaction in conventional transition metal oxides, in the mechanism of intercalation pseudocapacitance, K+ intercalate into the tunnels of V2O3 accompanied by a faradaic charge-transfer with no crystallographic phase change. This mechanism combines short charging/discharging times with long cycle life, which is reported in PIBs for the first time. This work may open up a new avenue for further development of pseudocapacitive nanomaterials for high-rate and ultra-stable energy storage.

In situ coating nickel organic complexes on free-standing nickel wire films for volumetric-energy-dense supercapacitors

A self-free-standing core-sheath structured hybrid membrane electrodes based on nickel and nickel based metal-organic complexes (Ni@Ni-OC) was designed and constructed for high volumetric supercapacitors. The self-standing Ni@Ni-OC film electrode had a high volumetric specific capacity of 1225.5 C cm−3 at 0.3 A cm−3 and an excellent rate capability. Moreover, when countered with graphene-carbon nanotube (G-CNT) film electrode, the as-assembled Ni@Ni-OC//G-CNT hybrid supercapacitor device delivered an extraordinary volumetric capacitance of 85 F cm−3 at 0.5 A cm−3 and an outstanding energy density of 33.8 at 483 mW cm−3. Furthermore, the hybrid supercapacitor showed no capacitance loss after 10 000 cycles at 2 A cm−3, indicating its excellent cycle stability. These fascinating performances can be ascribed to its unique core-sheath structure that high capacity nano-porous nickel based metal-organic complexes (Ni-OC) in situ coated on highly conductive Ni wires. The impressive results presented here may pave the way to construct s self-standing membrane electrode for applications in high volumetric-performance energy storage.

Enhancement of the performance in Li-O2 cells of a NiCo2O4 based porous positive electrode by Cr(III) doping

Here we discuss the incorporation of Cr(III) as dopant in the spinel lattice of the NiCo2O4 cubic phase and its beneficial effect on the electro-catalytic activity of this material in aprotic Li-O2 cells. To this aim, we synthesized highly porous carbon-free self-standing electrodes constituted by nanostructured undoped and Cr-doped NiCo2O4 grown on open nickel mesh. These materials were characterized by X-ray diffraction, field emission scanning electron microscopy coupled with energy dispersive spectroscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The performance in aprotic Li-O2 cells of the undoped and Cr-doped NiCo2O4 electrodes were tested in galvanostatic cycling using a LiTFSI 1 m in tetraethylene glycol dimethyl ether electrolyte without the incorporation of any carbon conductive agent. Cr(III) doping discloses a remarkable enhancement of more than 300% of the discharge capacity at J = 0.1 mA cm−2. Moreover, the Cr-doped NiCo2O4 material is capable to give reversible limited capacity ORR/OER for 52 and 45 cycles at 0.2 mA cm−2/0.1 mAh cm−2 and 0.1 mA cm−2/0.2 mAh cm−2, respectively, without oxygen flow in static Ar/O2 overpressures (pO2 = 1bar). Pseudo-Tafel data derived by galvanostatic titrations highlight the beneficial effect of Cr(III) doping on the electrode kinetics both for ORR and OER.

Trace Level Co–N Doped Graphite Foams as High-Performance Self-Standing Electrocatalytic Electrodes for Hydrogen and Oxygen Evolution

The development of eco-friendly electrocatalysts with high performance and low cost for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is significant for renewable energy storage. Here, trace level (0.11–0.18 wt %) Co–N doped graphite foam (Co–N/GF) was reported to work as a bifunctional high-performance and self-standing electrode for both HER and OER in alkaline electrolyte. The catalytic activities of Co–N/GFs with different annealing temperatures (600, 700, 800, 900, and 1000 °C) were carefully studied. Among them, Co–N/GF-900 exhibited the best HER activity and Co–N/GF-700 showed the best OER activity, achieving the current density of 10 mA cm–2 at low overpotentials of 165 and 313 mV, respectively. In addition, both of these electrodes exhibited long-term durability. Co–N/GF electrodes were further constructed as a catalytic cathode and anode couple (Co–N/GF-900∥Co–N/GF-700) for overall water splitting, exhibiting a low cell voltage of 1.68 V and good long-term stability. Our ...

Development of 3D interconnected carbon materials derived from Zn-MOF-74@carbon nanofiber web as an efficient metal-free electrocatalyst for oxygen reduction

A novel 3D interconnected web-like carbon material with high electrocatalytic activities toward oxygen reduction reaction (ORR) has been developed for the first time via direct carbonization of a composite (Zn-MOF-74@CNFs) comprising Zn-MOF-74s grown on carbon nanofibers (CNFs) web. The hexagonal pillar shaped Zn-MOF-74s with a diameter which ranges from 300 to 600 nm grow along the CNFs web by solvothermal method. After carbonization of Zn-MOF-74@CNFs, effective interconnections promoting electron transfer are successfully formed between carbonized Zn-MOF-74 (C-Zn-MOF-74) and on CNFs as well as C-Zn-MOF-74 themselves. The extraordinary 3D structure thus fabricated significantly improves the electrocatalytic activity toward ORR. The calculated electron transfers number (n) values for carbonized Zn-MOF-74@CNFs (C-Zn-MOF-74@CNFs) are nearly 4 at potentials ranging from 0.4 to 0.6 V (vs. reversible hydrogen electrode), demonstrating that the ORR process occurs dominantly through a direct four-electron pathway. Tafel slope of C-Zn-MOF-74@CNFs at low over-potential are lower than those from C-Zn-MOF-74 and even commercial Pt/C. Durability is also found to exceed that of commercial Pt/C. This study provides a novel 3D interconnected carbon material as a non-metal ORR electrocatalyst and design strategy for a large-area, self-standing and binder-free carbon-based electrochemical electrode.

Enhanced performance of solid-state Li–O2 battery using a novel integrated architecture of gel polymer electrolyte and nanoarray cathode

The present work proposes a novel strategy to fabricate an integrated architecture of gel polymer electrolyte (GPE)–nanoarray cathode for lithium–O2 batteries (LOBs). As a proof-of-concept experiment, the photo-initiated in situ polymerization of GPE was carried out via incorporating the precursor solution in advance into a self-standing binder-free oxygen electrode of Co3O4 nanosheets array grown on carbon cloth (Co3O4@CC), forming an integrated GPE–Co3O4@CC architecture. The performance of the solid-state LOBs using the GPE–Co3O4@CC assembly is greatly enhanced compared to the counterparts with a traditional cell structure, in which GPE was sandwiched by a lithium metal and a cathode. The enhanced performance is ascribed to the combination of the in situ polymerization of GPE and the versatile structure of nanoarray electrode, which results in abundant interfacial contacts between GPE and electrode. This work presents an alternative way to develop high-performance solid-state LOBs by combining the advantages of both gel polymer electrolytes and nanoarray electrodes.

Heteromorphic NiCo2S4/Ni3S2/Ni Foam as a Self-Standing Electrode for Hydrogen Evolution Reaction in Alkaline Solution.

Considerable works have been devoted on developing high-efficiency nonplatinum electrocatalysts for hydrogen evolution reaction (HER). Herein, 3D heteromorphic NiCo2S4/Ni3S2 nanosheets network has been constructed on Ni foam (denoted as NiCo2S4/Ni3S2/NF) serving as a self-standing electrocatalyst through directly thermal sulfurization of a single-source NiCo-layered double hydroxide precursor. The resultant NiCo2S4/Ni3S2/NF electrode exhibits outstanding electrocatalytic HER performance with an extremely low onset overpotential of 15 mV and long-term durability in alkaline solution. Such enhanced HER performance can be credited to (1) the massive exposed active sites provided by mixed transition metal chalcogenides (NiCo2S4 and Ni3S2), (2) the strong interfacial interaction at NiCo2S4/Ni3S2 heterojunction interfaces with the strengthened H binding, and (3) the porous highly conductive Ni foam substrate with accelerated electron transfer. This work opens up a new direction to fabricate effective and non-noble-metal electrodes for water splitting and hydrogen generation.

Graphene assisted template based LiMn2O4flexible cathode electrodes

In this paper, a systematic method has been developed to produce highly flexible and robust graphene/LiMn2O4 (G/LMO) and graphene/LiCr0.05Mn1.95O4 (G/LCMO) free-standing composite cathode electrodes with increased specific capacity and improved electrochemical capability. Spinel LMO nanorods are synthesized by calcination method followed by a hydrothermal reaction technique. As-synthesized nanorods were then embedded in a graphene layer which will in turn serve as a self-standing binder-free cathode electrode. Spinel LMO and LCMO nanorods with a length of 600 nm and width of 50 nm were then homogenously entrapped and distributed within the layers of conductive graphene structure. This hybrid structure will help to eliminate the use of heavy metal current collectors and electrically resistant binders or even conductive additives. A discharge capacity of 114.5 mAh g−1 is obtained after first cycle and %72 capacity retention is obtained after 250 cycles from G/LCMO freestanding samples. The enhancement in the electrochemical properties is due to the unique freestanding structure of the cathode electrodes.

Self-Template Synthesis of Co-Se-S-O Hierarchical Nanotubes as Efficient Electrocatalysts for Oxygen Evolution under Alkaline and Neutral Conditions.

We develop a facile self-template synthetic method to construct hierarchical Co-Se-S-O (CoSe xS2- x@Co(OH)2) nanotubes on a carbon cloth as a self-standing electrode for electrocatalytic oxygen evolution reaction (OER). In the synthetic process, separate selenization and sulfurization on the Co(OH)F precursor in different solvents have played an important role in constructing CoSe xS2- x (Co-Se-S) hierarchical nanotubes, which was further transformed into the nanotube-like Co-Se-S-O via an in situ electrochemical oxidation process. The Co-Se-S-O obtained by the Kirkendall effect through two stepwise anion-exchange reactions represents the first quaternary Co-Se-S-O nanotube array, which dramatically enhances its surface area and conductivity. Further, it only requires low overpotentials of 230 and 480 mV to achieve a 10 mA cm-2 current density. The OER performance of Co-Se-S-O is much more efficient than that of its monochalcogenide counterparts, as well as the commercial benchmark catalyst IrO2.

3D Foam-Like Composites of Mo2C Nanorods Coated by N-Doped Carbon: A Novel Self-Standing and Binder-Free O2 Electrode for Li-O2 Batteries.

The development of self-standing and binder-free O2 electrodes is significant for enhancing the total specific energy density and suppressing parasitic reactions for Li-O2 batteries, which is still a formidable challenge thus far. Here, a three-dimensional foam-like composite composed of Mo2C nanorods decorated by different amounts of N-doped carbon (Mo2C-NR@xNC (x = 5, 11, and 16 wt %)) was directly employed as the O2 electrode without applications of any binders and current collectors. Mo2C-NR@xNC presents a network microstructure with interconnected macropore and mesoporous channels, which is beneficial to achieving fast Li+ migration and O2 diffusion, facilitating the electrolyte impregnation, and providing enough space for Li2O2 storage. Additionally, the coated N-doped carbon layer can largely improve the electrochemical stability and conductivity of Mo2C. The cell with Mo2C-NR@11NC shows a considerable cyclability of 200 cycles with an overpotential of 0.28 V in the first cycle at a constant current density of 100 mA g-1, a superior reversibility associated with the formation and decomposition of Li2O2 as desired, and a high electrochemical stability. On the basis of the experimental results, the electrochemical mechanism for the cell using Mo2C-NR@11NC is proposed. These results represent a promising process in the development of a self-standing and binder-free foam-based electrode for Li-O2 batteries.

Interface Engineering of Anchored Ultrathin TiO2/MoS2 Heterolayers for Highly-Efficient Electrochemical Hydrogen Production.

An efficient self-standing hydrogen evolution electrode was prepared by in situ growth of stacked ultrathin TiO2/MoS2 heterolayers on carbon paper (CP@TiO2@MoS2). Owing to the high overall conductivity, large electrochemical surface area and abundant active sites, this novel electrode exhibits an excellent performance for hydrogen evolution reaction (HER). Remarkably, the composite electrode shows a low Tafel slope of 41.7 mV/dec, and an ultrahigh cathodic current density of 550 mA/cm2 at a very low overpotential of 0.25 V. This work presents a new universal strategy for the construction of effective, durable, scalable, and inexpensive electrodes that can be extended to other electrocatalytic systems.

New Electrode and Electrolyte Configurations for Lithium-Oxygen Battery.

Cathode configurations reported herein are alternative to the most diffused ones for application in lithium-oxygen batteries, using an ionic liquid-based electrolyte. The electrodes employ high surface area conductive carbon as the reaction host, and polytetrafluoroethylene as the binding agent to enhance the oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) reversibility. Roll-pressed, self-standing electrodes (SSEs) and thinner, spray deposited electrodes (SDEs) are characterized in lithium-oxygen cells using an ionic liquid (IL) based electrolyte formed by mixing lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt and N,N-diethyl-N-(2-methoxyethyl)-N-methylammonium bis(trifluoromethanesulfonyl)imide (DEMETFSI). The electrochemical results reveal reversible reactions for both electrode configurations, but improved electrochemical performance for the self-standing electrodes in lithium-oxygen cells. These electrodes show charge/discharge polarizations at 60 °C limited to 0.4 V, with capacity up to 1 mAh cm-2 and energy efficiency of about 88 %, while the spray deposited electrodes reveal, under the same conditions, a polarization of 0.6 V and energy efficiency of 80 %. The roll pressed electrode combined with the DEMETFSI-LiTFSI electrolyte and a composite Lix Sn-C alloy anode forms a full Li-ion oxygen cell showing extremely limited polarization, and remarkable energy efficiency.

Facile synthesis of a high electrical and ion conductivity junction-less 3D carbon sponge electrode for self-standing lithium ion battery anode.

Lithium ion batteries (LIB) are the most extensively researched and developed batteries. Currently, LIBs are used in various applications such as electric vehicles (EV), hybrid EVs (HEV), plug-in HEVs, and energy storage systems. However, their energy density is insufficient and further improvement is required. In this study, we propose the facile synthesis of a self-standing, junction-less 3D carbon sponge electrode (3DCS) for improving the energy density. A self-standing structure can improve the energy density by reducing non-active materials such as binders and current collectors, in electrodes. We use a kitchenware melamine sponge as the carbon precursor. The utilization of materials mass-produced by existing facilities is crucial for ensuring availability and low costs. Such characteristics are imperative for industrialization. These self-standing 3DCS electrodes, fabricated using available low-cost melamine sponges, demonstrate high charge-rate characteristics with a capacity retention of 81.8% at 4000 mA g−1 and cycle durability with 95.4% capacity retention after 500 cycles, without current collector, binder, and conductive additives. This high availability, low-cost material with excellent characteristics is beneficial for research institutions and companies that do not have facilities.

Vapour induced phase inversion: preparing high performance self-standing sponge-like electrodes with a sulfur loading of over 10 mg cm−2

The vapour induced phase inversion (VIPI) process is used to prepare sponge-like porous electrodes for high performance Li–S batteries.

A rationally designed self-standing V2O5 electrode for high voltage non-aqueous all-solid-state symmetric (2.0 V) and asymmetric (2.8 V) supercapacitors.

The maximum capacitive potential window of certain pseudocapacitive materials cannot be accessed in aqueous electrolytes owing to the low dissociation potential of 1.2 V possessed by water molecules. However, the inferior pseudocapacitance exhibited by the commonly used electrode materials when integrated with non-aqueous electrolytes still remains a challenge in the development of supercapacitors (SC). Proper selection of materials for the electrode and a rational design process are indeed important to overcome these practical intricacies so that such systems can perform well with non-aqueous electrolytes. We address this challenge by fabricating a prototype all-solid-state device designed with high-capacitive V2O5 as the electrode material along with a Li-ion conducting organic electrolyte. V2O5 is synthesized on a pre-treated carbon-fibre paper by adopting an electrochemical deposition technique that effects an improved contact resistance. A judicious electrode preparation strategy makes it possible to overcome the constraints of the low ionic and electrical conductivities imposed by the electrolyte and electrode material, respectively. The device, assembled in a symmetrical fashion, achieves a high specific capacitance of 406 F g-1 (at 1 A g-1). The profitable aspect of using an organic electrolyte is also demonstrated with an asymmetric configuration by using activated carbon as the positive and V2O5 as the negative electrode materials, respectively. The asymmetric device displays a wide working-voltage window of 2.8 V and delivers a high energy density of 102.68 W h kg-1 at a power density of 1.49 kW kg-1. Moreover, the low equivalent series resistance of 9.9 Ω and negligible charge transfer resistance are observed in the impedance spectra, which is a key factor that accounts for such an exemplary performance.

Self-standing NASICON-type electrodes with high mass loading for fast-cycling all-phosphate sodium-ion batteries

A Na-ion battery with high rate capability and long cycling life consists of high mass loading self-standing NaTi2(PO4)3 anode and Na3V2(PO4)3 cathode.

Hierarchical 1D nanofiber-2D nanosheet-shaped self-standing membranes for high-performance supercapacitors

A self-standing 1D double capillary carbon nanofiber-2D NiCo2S4 nanosheet-shaped hierarchical electrode (NiCo2S4@DCCNF) is fabricated for high-performance flexible all-solid-state supercapacitors.

Synergistic Electro-Catalysis of Pd/PdO Nanoparticles and Cr(III)-Doped NiCo2O4 Nanofibers in Aprotic Li-O2 Batteries

In this work we discuss the co-catalysis in aprotic Li-O2 batteries of C-free nanostructured mixed oxide electrodes decorated by Pd/PdO core/shell nanoparticles. A Cr(III) doped NiCo2O4 material has been grown hydrothermally on an open Ni-mesh. Palladium nanoparticles have been synthesized by pulsed lased ablation in liquid acetone in the fs regime and deposited by drop casting onto the surface of the nanostructured mixed oxide electrodes. The resulting electrodes have been calcined at 300°C. The use of laser techniques to produce nanoparticles for aLOBs is here proposed for the first time in the literature, as well as the peculiar combination of Pd/PdO nanoparticles deposited onto C-free Cr(III) doped NiCo2O4 self-standing electrodes. Performance in aprotic Li-O2 batteries have been recorded in galvanostatic conditions and post mortem analysis of the electrode surfaces have been carried out by X-ray photoemission spectroscopy. The use of Pd/PdO nanoparticles as co-catalysts enhances the reversibility of the electrochemical oxygen reduction/evolution reactions. This beneficial effect originates by the decrease of the mean overvoltages compared to the bare Cr(III) doped NiCo2O4 electrodes, and extends the cell calendar life from 16 to 41 fully reversible galvanostatic cycles at J = 0.2 mAcm−2 with capacity limitation of 0.2 mAhcm−2.

On the interaction of carbon electrodes and non conventional electrolytes in high-voltage electrochemical capacitors

This study is essentially based on innovative electrolytes such as the organic salt N-methyl-N-butylpyrrolidinium tetrafluoroborate (Pyr14BF4) dissolved in propylene carbonate (PC) and the pure ionic liquid (N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr14TFSI) and its solution in PC. Activated carbon cloths were used as self-standing binder-free electrodes. It is found that the presence of impurities in carbon electrodes may lead to electrolyte decomposition and electrode degradation which notably affect the electrochemical double-layer capacitor (EDLC) performance. Such processes greatly depend on the composition of both the electrode and the electrolyte, being much less significant with solvent-containing electrolytes. By raising the operation temperature to 60 °C, the EDLC performance in the ionic liquid Pyr14TFSI is notably improved due to a relevant decrease in the viscosity and increase in ionic conductivity. By contrast, the presence of impurities, e.g., Zn and Al, in the electrodes remarkably reduces the electrolyte stability and a thick layer of decomposition products completely covers the carbon fibers after cycling at high temperature. The ionic liquid in solution maintains the high maximum operative voltage of the net ionic liquid whereas its viscosity and ionic conductivity are close to those of the conventional Et4NBF4/PC. Furthermore, the presence of propylene carbonate as solvent prevents to some extent the ionic liquid degradation.

Multimaterial 3D Printing of Graphene-Based Electrodes for Electrochemical Energy Storage Using Thermoresponsive Inks.

The current lifestyles, increasing population, and limited resources result in energy research being at the forefront of worldwide grand challenges, increasing the demand for sustainable and more efficient energy devices. In this context, additive manufacturing brings the possibility of making electrodes and electrical energy storage devices in any desired three-dimensional (3D) shape and dimensions, while preserving the multifunctional properties of the active materials in terms of surface area and conductivity. This paves the way to optimized and more efficient designs for energy devices. Here, we describe how three-dimensional (3D) printing will allow the fabrication of bespoke devices, with complex geometries, tailored to fit specific requirements and applications, by designing water-based thermoresponsive inks to 3D-print different materials in one step, for example, printing the active material precursor (reduced chemically modified graphene (rCMG)) and the current collector (copper) for supercapacitors or anodes for lithium-ion batteries. The formulation of thermoresponsive inks using Pluronic F127 provides an aqueous-based, robust, flexible, and easily upscalable approach. The devices are designed to provide low resistance interface, enhanced electrical properties, mechanical performance, packing of rCMG, and low active material density while facilitating the postprocessing of the multicomponent 3D-printed structures. The electrode materials are selected to match postprocessing conditions. The reduction of the active material (rCMG) and sintering of the current collector (Cu) take place simultaneously. The electrochemical performance of the rCMG-based self-standing binder-free electrode and the two materials coupled rCMG/Cu printed electrode prove the potential of multimaterial printing in energy applications.