Neutral Aqueous Electrolyte Research Articles

Highly Efficient Electroconversion of CO2 into CH4 by a Metal–Organic Framework with Trigonal Pyramidal Cu(I)N3 Active Sites

High-efficiency electrocatalysts for CO2 reduction reaction are extremely desirable to produce valuable hydrocarbon productions, as well as addressing the current environmental challenges. In this work, we introduce a Cu-based metal–organic framework as a catalyst for the efficient and selective reduction of CO2 to CH4 in neutral aqueous electrolytes. Detailed examination of [Cu4ZnCl4(btdd)3] (Cu4-MFU-4l, H2btdd = bis(1H-1,2,3-triazolo-[4,5-b],[4′,5′-i])dibenzo-[1,4]-dioxin) revealed the highest activity for yielding methane with a Faradaic efficiency of 92%/88% and a partial current density of 9.8/18.3 mA cm–2 at a potential of −1.2/–1.3 V (vs RHE). In situ X-ray absorption and infrared spectroscopy spectra, as well as density functional theory calculations, revealed that the in situ generated trigonal pyramidal Cu(I)N3 acts as the electrochemical active site and that the strong coordination ability of the Cu(I)N3 site and the synergistic effect of adjacent aromatic hydrogen atoms, via hydrogen-bonding interactions, play an important role in stabilizing the key intermediates of carbon dioxide reduction and inhibiting the hydrogen evolution reaction, thus showing a high performance of electroreduction of CO2 to CH4.

Tailoring defective vanadium pentoxide/reduced graphene oxide electrodes for all-vanadium-oxide asymmetric supercapacitors

Vanadium pentoxide is a highly promising cathode material for supercapacitors with neutral aqueous electrolytes. However, the insufficient understanding of energy storage mechanisms involved in the cathode material and the lack of suitable anode materials impede the development of the neutral aqueous-based supercapacitor. Herein, we report a strategy based on defect chemistry to tailor V2O5/reduced graphene oxide hybrid electrodes for assembling all-vanadium-oxide asymmetric supercapacitors. The V2O5 component in the hybrid consists of oxygen-deficient bilayer V2O5 nanobelts obtained by controlled hydrothermal synthesis, which can be mixed with a graphene oxide dispersion and assembled into V2O5/reduced graphene oxide through vacuum filtration followed by annealing. The V2O5/reduced graphene oxide electrodes are easily converted into suitable positive and negative electrodes through electrochemical formation, and along with conventional cation intercalation/deintercalation reactions, a series of oxygen-vacancy-involving reactions render the electrodes typical pseudocapacitive behavior. The formed positive and negative electrodes exhibit excellent performance with specific capacitances of 468.5F g−1 and 406.8F g−1 at 1 A g−1, respectively. The all-vanadium-oxide asymmetric supercapacitor assembled with the formed positive and negative electrodes displays a high energy density and good cycling stability over the potential window of 0–1.7 V, demonstrating its great potential for low-cost, large-scale, and safety-sensitive applications.

Effect of Supporting Background Electrolytes on the Nanostructure Morphologies and Electrochemical Behaviors of Electrodeposited Gold Nanoparticles on Glassy Carbon Electrode Surfaces.

Electrodeposition is an electrochemical method employed to deposit stable and robust gold nanoparticles (AuNPs) on electrode surfaces for creating chemically modified electrodes (CMEs). The use of several electrodeposition techniques with different experimental parameters allow in obtaining various surface morphologies of AuNPs deposited on the electrode surface. By considering the electrodeposition of AuNPs in various background electrolytes could play an important strategy in finding the most suitable formation of the electrodeposited AuNP films on the electrode surface. This is because different electrode roughnesses can have different effects on the electrochemical activities of the modified electrodes. Thus, in this study, the electrodeposition of AuNPs onto the glassy carbon (GC) electrode surfaces in various aqueous neutral and acidic electrolytes was achieved by using the cyclic voltammetry (CV) technique with no adjustable CV parameters. Then, surface morphologies and electrochemical activities of the electrodeposited AuNPs were investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), CV, and electrochemical impedance spectroscopy (EIS). The obtained SEM and 3D-AFM images show that AuNPs deposited at the GC electrode prepared in NaNO3 solution form a significantly better, uniform, and homogeneous electrodeposited AuNP film on the GC electrode surface with nanoparticle sizes ranging from ∼36 to 60 nm. Meanwhile, from the electrochemical performances of the AuNP-modified GC electrodes, characterized by using a mixture of ferricyanide and ferrocyanide ions [Fe(CN6)3–/4–], there is no significant difference observed in the case of charge-transfer resistances (Rct) and heterogeneous electron-transfer rate constants (ko), although there are differences in the surface morphologies of the electrodeposited AuNP films. Remarkably, the Rct values of the AuNP-modified GC electrodes are lower than those of the bare GC electrode by 18-fold, as the Rct values were found to be ∼6 Ω (p < 0.001, n = 3). This has resulted in obtaining ko values of AuNP-modified GC electrodes between the magnitude of 10–2 and 10–3 cm s–1, giving a faster electron-transfer rate than that of the bare GC electrode (10–4 cm s–1). This study confirms that using an appropriate supporting background electrolyte plays a critical role in preparing electrodeposited AuNP films. This approach could lead to nanostructures with a more densely, uniformly, and homogeneously electrodeposited AuNP film on the electrode surfaces, albeit utilizing an easy and simple preparation method.

Oxygen‐Rich Porous Activated Carbon from Eucalyptus Wood as an Efficient Supercapacitor Electrode

Herein, lignin‐rich KOH‐activated porous carbon from eucalyptus wood (named as PACE) is presented as an efficient electrode for supercapacitors (SCs). Compared with the most commonly used higher activation temperature, i.e., 800 °C with KOH (PACE‐800), a more efficient SC is developed by activating carbon with KOH at lesser temperature, i.e., 600 °C (PACE‐600). The high specific capacitance (i.e., 230 F g−1 at 1 A g−1 measured in a 2 m NaCl electrolyte) measured by galvanostatic charge–discharge (GCD) studies is not primarily due to larger surface area, but due to the inherent electron‐rich oxygen‐based functionalities that persist at the lower activation temperature, contributing to the hydrophilic nature to PACE‐600. The mechanism of the capacitive charge storage is deduced from electrochemical impedance spectroscopy (EIS). The application of PACE‐600 as a SC electrode is confirmed from insignificant loss in the specific capacitance after 10 000 charging–discharging cycles, recorded at 10 A g−1. Further, fabrication of higher‐voltage (1.6 V) symmetric SC PACE‐600//PACE‐600 in aqueous neutral electrolyte (2 m NaCl) is presented, which illuminates a red LED (1.8 V) for 1 min after charging for 5 s. The corresponding energy density is calculated to be 41 W h kg−1, and at a power density of 2396 W kg−1.

Novel Aqueous Zinc–Halogenate Flow Batteries as an Offspring of Zinc–Air Fuel Cells for Use in Oxygen‐Deficient Environment

Autonomous and portable electronic devices require cheap energy storage units of ever‐increasing power and energy densities. Zinc/halogenate flow battery is proposed as a new type of reserve or emergency power supply unit. The battery uses a mechanically rechargeable zinc anode in contact with neutral aqueous salt electrolyte, cation‐exchange membrane, and a carbonaceous flow through cathode, at which aqueous acidified halogenate is reduced to halide in a six‐electron process. A new multielectron oxidizer, aqueous iodate, that can be used in other electrochemical power sources, is introduced. It is shown that iodate can be readily reduced in acidic media at cheap carbonaceous electrodes. Electrochemical experiments with stationary and rotating disk glassy carbon electrodes reveal that in acidic aqueous electrolytes reduction of iodate can be as fast as earlier studied reduction of bromate. Theoretical energy densities per reactants of Zn/bromate and Zn/iodate batteries are 1.2 and 1.45 kWh L−1, respectively. Area‐specific power of the single cells of these batteries reaches 0.57 W cm−2 at 50 °C.

Thermodynamic and kinetic examination of the glassy carbon electrode in neutral aqueous electrolytes

Herein we report on the charge storage behaviour of a non-porous planar glassy carbon electrode (GCE) in an aqueous electrolyte of 0.5 M Na2SO4 at temperatures in the range 25 °C to 50 °C. Preliminary cyclic voltammetry (CV) data indicate a decrease in electrode performance at increasing temperatures, and this was supported by detailed analysis of step potential electrochemical spectroscopy (SPECS) data. Kinetic analysis of the deconvoluted SPECS data using the Arrhenius equation has indicated that diffusional charge storage is not thermally activated, instead being possibly influenced by thermal scattering of electrolyte ions. Entropimetric analysis of the SPECS data has generated entropy and enthalpy data for charge storage in this system. These results are discussed in terms of charge storage at this interface. • Entropy and enthalpy of double layer formation has been examined. • The electrified interface extends a significant distance into the electrolyte. • The implications on double layer formation have been discussed.

Amine-Assisted Delaminated 2D Ti3C2Tx MXenes for High Specific Capacitance in Neutral Aqueous Electrolytes.

Electrochemical capacitors using neutral aqueous electrolytes are safer and cheaper and allow diverse current collectors compared with the counterparts using organic or acidic/alkaline electrolytes. Two-dimensional (2D) MXenes have been demonstrated as the high-capacitive materials with high rate performance. However, MXene electrodes often exhibit a limited capacitance in neutral electrolytes, where the reversible electrochemical reactions rely greatly on the structural and surface properties of MXenes depending on their synthesis methods. Herein, a simple and highly efficient strategy, which combines HF etching of Ti3AlC2 powder and subsequent amine-assisted delamination at a low temperature, is developed to synthesize 2D Ti3C2Tx MXenes. The comprehensive results demonstrate that the enlarged interlayer spacing and the presence of more -O-containing functional groups synergistically contribute to the improvement of capacitive performance in neutral electrolytes. The 2D Ti3C2Tx MXenes show excellent electrochemical performance in various neutral electrolytes, and a high specific gravimetric capacitance of 149.8 F/g is achieved in 1.0 M Li2SO4. Furthermore, the flexible solid-state supercapacitors (SCs) with a neutral PVA/LiCl gel electrolyte possess a superior areal capacitance (163.1 mF/cm2) and high energy density (17.6 μWh/cm2 at 0.07 mW/cm2), together with high user safety. This work provides a promising guideline of synthesis strategy for high-capacitive MXenes used in neutral electrolytes, which may promote the development of safe and flexible power sources with a high energy density.

Anti-oxidized electrostatic self-assembly of 3D high-density Polyimide@MXene composite for superior aqueous Mg2+ storage

As a conjugated carbonyl polymer, polyimide (PI) with redox-active sites has attracted increasing research attention owing to its efficient multivalent-ion storage behaviors in low-cost and risk-free neutral aqueous electrolytes. However, the practical applications of PI remain restricted because of its low tapped density, sluggish electron transfer and structural instability. Herein, we developed a novel three-dimensional (3D) high-density PI@MXene composite through efficient electrostatic self-assembly, wherein MXene oxidation could be prevented during composite preparation. Synergistically coupling the conductive layered MXene with electro-active PI provides a 3D architecture with high tapped density (~1.12 g cm−3), enhanced electrochemical kinetics and rapid redox reaction in MgCl2 neutral aqueous electrolytes. These features can be further confirmed via Fourier transform infrared spectroscopy upon charging/discharging and density functional theory (DFT) calculations along with the highest occupied molecular orbital-lowest unoccupied molecular orbital energy gap. As an electrode, the 3D high-density PI@MXene composite exhibits remarkable aqueous Mg2+ storage (~502.2 F g−1) and superior rate and cycling performances than those of most reported polymer-based electrodes in aqueous electrolytes. As proof of concept, we fabricated a flexible Mg-ion storage device with reliable electrochemical performance and ultra-long cycling life over 20 000 cycles, stimulating its application in high-safety portable/wearable electronics.

Pt-Catalyzed D-Glucose Oxidation Reactions for Glucose Fuel Cells

The Pt-catalyzed D-glucose oxidation reaction in neutral electrolytes was investigated for implantable power applications. A reaction mechanism involving two possible oxidation pathways, namely direct and OHads-mediated oxidation, was proposed based on the mass change during electrochemical measurement. PtPd and Pt2Pd were synthesized as anodic catalysts by a solvothermal method, and single-chamber glucose-air fuel cells using a neutral aqueous electrolyte were prototyped successfully. Higher fuel cell performance was achieved with the PtPd catalyst, with a maximum power density of 27.6 μW cm−2 and open-circuit voltage of 0.616 V. Collectively, the present study contributes to maximize the performance of glucose fuel cells.

Hybrid energy storage using nitrogen-doped graphene and layered-MXene (Ti3C2) for stable high-rate supercapacitors

Easy disposal of supercapacitors at their end-of-life is a rarely discussed aspect in research literature. Due to thez demand for stable high-powered devices with significant specific energy, a cost effective and sustainable approach using 2D materials is presented in this work. N-doped graphene synthesized from a cheap and facile exfoliation of graphite in an aqueous salt electrolyte is combined with layered MXene nanostructures in an asymmetric hybrid design to exploit the merits of these electrode materials. The device was tested in a non-corrosive neutral KNO3 aqueous electrolyte and exhibited noteworthy performance. The hybrid device could operate at 1.6 V with a remarkable stability demonstrated by floating tests performed for >3 days and cycling for 25,000 cycles. A 90.4% capacitance retention with only a 0.5% loss in Coulombic efficiency was observed confirming the outstanding stability of these materials in a neutral aqueous electrolyte. The device is able to deliver an average specific energy of 28 Wh kg−1 and a maximum power of 16 Kw kg−1. The device performance is linked to the dopants in the exfoliated graphene sheets and abundant reactive sites in the layered MXene nanostructure which gives rise to rapid ion transport dynamics and efficient charge storage. The findings of this work will pave new routes in achieving safe and reliable supercapacitors using non-corrosive and eco-friendly materials with comparable electrochemical performance to conventional devices.

The Performance of Fibrous CDC Electrodes in Aqueous and Non-Aqueous Electrolytes

The aim of this study was to investigate the electrochemical behaviour of aqueous electrolytes on thin-layer (20 µm) nanoporous carbide-derived carbon (CDC) composite fibrous directly electrospun electrodes without further carbonisation. There have been previously investigated fibrous electrodes, which are produced by applying different post-treatment processes, however this makes the production of fibrous electrodes more expensive, complex and time consuming. Furthermore, in the present study high specific capacitance was achieved with directly electrospun nanoporous CDC-based fibrous electrodes in different neutral aqueous electrolytes. The benefit of fibrous electrodes is the advanced mechanical properties compared to the existing commercial electrode technologies based on pressure-rolled or slurry-cast powder mix electrodes. Such improved mechanical properties are preferred in more demanding applications, such as in the space industry. Electrospinning technology also allows for larger electrode production capacities without increased production costs. In addition to the influence of aqueous electrolyte chemical composition, the salt concentration effects and cycle stability with respect to organic electrolytes are investigated. Cyclic voltammetry (CV) measurements on electrospun electrodes showed the highest capacitance for asymmetrical cells with an aqueous 1 M NaNO3-H2O electrolyte. High CV capacitance was correlated with constant current charge–discharge (CC) data, for which a specific capacitance of 191 F g−1 for the positively charged electrode and 311 F g−1 for the negatively charged electrode was achieved. The investigation of electrolyte salt concentration on fibrous electrodes revealed the typical capacitance dependence on ionic conductivity with a peak capacitance at medium concentration levels. The cycle-life measurements of selected two-electrode test cells with aqueous and non-aqueous electrolytes revealed good stability of the electrospun electrodes.

Electrochemical Behavior of Vanadium Carbide in Neutral Aqueous ElectrolytesSupported by the Science & Technology Department of Jilin Province (Grant Nos. 20180101199JC and 20180101204JC), and Jilin Province/Jilin University Co-construction Project-Funds for New Materials (SXGJSF2017-3).

The V2C compound, belonging to the group of two-dimensional transition metal carbonitrides, or MXenes, has demonstrated a promising electrochemical performance in capacitor applications in acidic electrolytes; however, there is evidence to suggest that V2C is unstable in an acidic environment. On the other hand, the performance of V2C in neutral aqueous electrolytes is still moderate, and has not yet been systematically studied. The charge storage mechanism in a V2C electrode, employed in neutral aqueous electrolytes, is investigated via cyclic voltammetry testing and in situ x-ray diffraction (XRD). Good specific capacitances are achieved, specifically 208 F/g in 0.5 M Li2SO4, 225 F/g in 1 M MgSO4, 120 F/g in 1M Na2SO4, and 104 F/g in 0.5 M K2SO4. Using in situ XRD, we observe that, during the charge and discharge process, the c-lattice parameter shrinks or expands by up to 0.25 Å in MgSO4, and 0.29 Å in Li2SO4 which demonstrates the intercalation/de-intercalation of cations into the d-V2C layer.

Performance of asymmetric supercapacitor fabricated with perovskite‐type Sr 2+ ‐incorporated LaMnO 3 (La 0. 7 Sr 0 . 3 MnO 3 ) nanostructures in neutral 1M Na 2 SO 4 aqueous electrolyte

Strontium (Sr) incorporated LaMnO3 (La0.7Sr0.3MnO3) nanoparticles have been synthesized by ball-milling-assisted solid-state reaction to study their performance as electrode material for energy storage applications. The La0.7Sr0.3MnO3 nanoparticles exhibit superior electrochemical performance in neutral aqueous electrolyte (1 M Na2SO4) in comparison to LaMnO3 and SrMnO3 nanoparticles. This neutral electrolyte provides relatively higher ionic conductivity and viscosity compared to the ionic liquids and a wider potential window compared to the alkaline electrolytes. Electrochemical study of the electrodes prepared using La0.7Sr0.3MnO3 nanoparticles reveals pseudocapacitive behaviors with fast reversible Faradaic charge storage, which plays a key role in charge storage. The composite materials exhibit highest specific capacitance of 393.5 F g−1 at a scan rate of 2 mV s−1. Asymmetric supercapacitors fabricated using La0.7Sr0.3MnO3 nanoparticle and activated carbon operates over a wide potential window of 1.8 V, and it reveals high specific capacitance (197 F g−1) as well as high capacitive retention (87%) even after 4000 charge–discharge cycles.

From onion skin waste to multi-heteroatom self-doped highly wrinkled porous carbon nanosheets for high-performance supercapacitor device

Herein, we report the synthesis of N, S, P-self-doped porous and wrinkled graphene-like carbon nanosheets derived from the abundant waste onion skin via carbonization and activation strategy. The optimized onion skin derived carbon (OnC-900) exhibits highly wrinkled graphene-like morphology and multi-heteroatom doping without any external dopants is confirmed via field emission scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. The OnC-900, acting as a supercapacitor electrode, exhibits excellent specific capacitance of 478 F g−1 at a current density of 1 A g−1 and maintains 241.7 F g−1 even at 6.7 A g−1 in the three-electrode cell indicating its excellent rate capability. The assembled symmetric supercapacitor device using aqueous neutral electrolyte (1 M Na2SO4) delivers outstanding specific energy of 17 Wh kg−1 with a wide potential window up to 1.4 V. The device also exhibits excellent cyclic stability by retaining 93% of initial capacitance over 10,000 cycles at a current density of 3 A g−1. This enhanced performance of the electrode is mainly due to the high specific surface area and the heteroatom co-doping that provides improved surface wettability by polarized surface, induced pseudocapacitance effect, and improved electronic conductivity. These results demonstrate that onion waste derived multi-heteroatom co-doped graphene-like carbon nanosheets have great potential for renewable and sustainable energy storage devices.

Stable α-MoO3 Electrode with a Widened Electrochemical Potential Window for Aqueous Electrochemical Capacitors

α-MoO3 is a promising electrode material for electrocapacitive energy storage. However, it has poor stability in aqueous electrolytes due to dissolution in water. Here, we demonstrate that an α-MoO3 electrode prepared using the electrochemical deposition method is stable over a wide potential window of 2.2 V in a neutral aqueous electrolyte. The improved stability of the α-MoO3 electrode in water is attributable to enhanced electron conductivity, which minimizes the polarization-induced structural collapse, and the dense microstructure of the α-MoO3 film electrode. The widened potential window is related to the electrocatalytic inactivity of the α-MoO3 toward water electrolysis and the high overpotentials of the neutral electrolyte toward H2 and O2 evolution reactions. A symmetric supercapacitor cell fabricated with the electrochemically deposited α-MoO3 electrode delivers a specific energy as high as ∼22 Wh/kg at a specific power of ∼301 W/kg. This work demonstrates that the electrochemical deposition method is a viable approach to fabricating α-MoO3 electrodes for aqueous electrochemical energy storage.

Anti-corrosive Hybrid Electrolytes for Rechargeable Aqueous Zinc Batteries

Aqueous zinc(Zn)-metal cells with cost-effective components and high safety have long been a promising large-scale energy storage system, but Zn anodes are intrinsically unstable with common aqueous electrolytes, causing substantial underutilization of the theoretical capacity. In this work, we report a strictly neutral aqueous Zn electrolyte at a low cost by leveraging the dynamic hydrolysis equilibrium of a dual-salt Zn(Ac)2/NaAc(Ac: CH3COO−) formulation. With the pH regulation, the corrosion and hydrogen evolution encountered in Zn anodes can be suppressed significantly. This hybrid aqueous electrolyte not only enables dendrite-free Zn plating/stripping at a nearly 95% Coulombic efficiency[an increase of 24% compared to that of the single-salt 1 mol/L Zn(Ac)2 electrolyte], but also supports the reversible operation of Zn cells paired with either Na3V2(PO4)3 or iodine cathodes—the former delivers a high output voltage of 1.55 V with an energy level of 99.5 W·h/kg(based on the mass of the cathode), and the latter possesses a high specific capacity of 110.9 mA·h/g while yielding long-term cyclability(thousands of cycles). These findings open up a new avenue of modifying practical electrolytes having targeted properties to stabilize multivalent metal anodes.

Energy storage performance of binder-free ruthenium-oxide nano-needles based free-standing electrode in neutral pH electrolytes

Improving the energy density of symmetric flexible supercapacitors (FSSCs), while maintaining a high-power density under an environmentally safe system, is still a crucial challenge for researchers. The improvement can essentially be grasped by enlarging the voltage window through rational designing/selection of the electrode materials as well as utilizing such electrolytes that have extended stability range and non-corrosive/environmental properties. In this context, an articulate strategy is established, in the first step, fabricating the self-standing porous carbonaceous substrate (carbon nanotubes anchored at carbon fabric, denoted as CNTs-CF), in the second step, metal-oxide nano-needles (RuO2-NNs) decorated architecture was designed on the CNTs-CF substrate which served as a binder-free self-standing electrode (RuO2-NNs@CNTs-CF). The second strategy of regulating the harmless/non-toxic neutral aqueous electrolytes (NaCl, KCl & LiCl) is employed. The optimized performance of RuO2-NNs@CNTs-CF nanostructure holds a higher specific capacitance of 102.75 F g−1 in LiCl electrolyte and able to work at large voltage of 2.0 V, at the same time the retention capability of 98.6 % is achieved over 5000 cycles. Such an extended potential window is approximately twice higher as compared to the previously reported carbonaceous/metal-based supercapacitors using conventional electrolytes (acid/base in the aqueous state). In this regard, the physicochemical characteristics including mobility/diffusion and solvation of the ions are critically considered to find out their effect on the SSCs performance. Moreover, the FSSC device is also assembled using PVA/LiCl gel electrolyte; an excellent energy density of 62.94 W h kg−1 at 596.35 W kg−1 power density, is recorded with an extended voltage window of 2.35 V. The fabrication of RuO2-NNs@CNTs-CF FSSC with most safe and environmentally friendly components would unwrap new opportunities for the development of high-performance safe energy storage devices.

Effect of growth-time on electrochemical performance of birnessite manganese oxide (δ-MnO2) as electrodes for supercapacitors: An insight into neutral aqueous electrolytes

This study demonstrates successful synthesis of nanoflower-like birnessite δ-MnO2 materials through a simple and effective hydrothermal technique. Characterization of the flower-like materials grown at various dwell times were carried out by employing scanning electron microscopy (SEM), X-ray diffractometry (XRD), Brunauer-Emmett-Teller (BET) and Barrett–Joyner–Halenda (BJH) models, and electrochemical analysis to understand the effect of different growth time on their morphological, structural, surface area along with pore size distribution and electrochemical characteristics as electrodes for electrochemical capacitors. Attention is mainly based on electrochemical assessment of the as-synthesized materials with an insight into some neutral aqueous electrolytes, mainly lithium sulphate (1 M Li2SO4) and sodium sulphate (1 M Na2SO4) solutions as potential medium owing to their non-corrosive nature, cost-effectiveness, electrochemical stability and environmentally friendliness. Significant charge propagation, with a high specific capacitance of 387.1 F g-1 was achieved for the half-cell electrode in 1 M Li2SO4 alongside excellent cycling stability for up to 5 000 cycles performed at 3 A g-1 specific current. A comprehensive electrochemical assessment is performed to understanding the relationship between solvated and diffused ions of the neutral electrolytes that could result in fast charge storage kinetics as well as high specific capacitance.

Fabrication of an Organic Redox Capacitor with a Neutral Aqueous Electrolyte Solution

Fabrication of an Organic Redox Capacitor with a Neutral Aqueous Electrolyte Solution

Electrochemical performance of spherical LiCoO2 with high stability in neutral aqueous electrolyte

Layer-structured lithium cobalt oxide (LCO) is one of promising electrode materials for secondary aqueous lithium-ion batteries, yet the effect of structural proton insertion in LCO in neutral aqueous electrolytes cannot be ignored. Present study investigates the electrochemical performance of polycrystalline spherical LCO in neutral aqueous saturated Li2SO4 solution. Herein, we for the first time demonstrate the dependence of LCO stability on the discharge cutoff potential. The applied LCO electrodes show good cycling stability within the potential window of 0.65–1.1 V vs. SCE, while electrochemical impedance spectrum (EIS) analysis detects no sign of proton intercalation. Moreover, the spherical LCO free from the proton intercalation exhibits a superior rate capability with 78% discharge capacity retention at 80 C. The lithium-ion chemical diffusion coefficient being seven times than that of irregular shaped LCO sample can be responsible for such significant rate capability. The cyclability testing depicts the better performance of spherical LCO in comparison with the counterpart, especially in terms of electrode activation time. Post cycling electrode characterization displays that the discharge capacity fading of LCO mainly results from the crystal grain deformation due to high potential cycling and can be alleviated by reducing the depth of charge.