Charge Transfer Resistance Of Electrode Research Articles

Polyaniline/Small‐Sized MXene/Carbon Cloth Electrodes with 3D Hierarchical Porous Structure for All‐Solid‐State Flexible Supercapacitors

The porous structure of electrodes can exert a significant impact on electrochemical performances of supercapacitors. Herein, the polyaniline/small‐sized MXene/carbon cloth (PANI/S‐MXene/CC) electrodes with 3D hierarchical porous structure are fabricated by a facile single‐step pulsed electrodeposition. First, the PANI/S‐MXene nanowires closely overlap each other and form a nanosized pore structure, which provides large specific surface area and abundant ion diffusion channels. Second, the CC with a large pore structure can facilitate permeation of gel electrolyte. S‐MXene with small lateral size not only decreases charge transfer resistance of electrodes, but also ensures an interconnected porous framework. Consequently, the assembled all‐solid‐state flexible device delivers a high areal capacitance (478.4 mF cm−2 at 0.5 mA cm−2), a superior rate capability (307.5 mF cm−2 at 10 mA cm−2), a remarkable energy density (42.5 μWh cm−2), favorable cycle stability (75.4% capacitance retention after 4000 cycles), as well as 93.2% capacitance retention after 180° mechanical bending with 1000 cycles. Herein, it is revealed that size selection of nanomaterials is a priority when the porous structure is designed.

Impact of Graphite Materials on the Lifetime of NMC811/Graphite Pouch Cells: Part II. Long-Term Cycling, Stack Pressure Growth, Isothermal Microcalorimetry, and Lifetime Projection

Part II of this 2-part series examines the impact of competitive graphite materials on NMC811 pouch cell performance using Ultra-High Precision Coulometry (UHPC), isothermal microcalorimetry, and in-situ stack growth. A simple lifetime projection of the best NMC811/graphite cells as a function of operating temperature is made. We show that graphite choice greatly impacts fractional fade, while fractional charge endpoint capacity slippage was largely unchanged due to identical cathodes. We show that an increase in graphite 1st cycle efficiency due to limited redox-active sites—favourable for minimizing Li inventory loss—is concomitant with an increase in negative electrode charge transfer resistance. Further, we demonstrate that cells with competitive artificial graphites (AG) have a lower parasitic heat flow (∼0.060 mW A−1 h−1 at 40 oC) compared to cells with natural graphites (NG), and that the cells with the AGs had minimal stack thickness change with cycling. Finally, we model SEI growth for NMC811 cells limited to 4.06 V with the square-root time model, and project that the best NMC811/graphite cells here can have decades-long lifetimes at 20 –30 °C when Li plating is avoided. Such cells are excellent candidates for grid storage applications where energy density is less important compared to long lifetime.

Boron doped diamond thin films for the electrochemical detection of SARS-CoV-2 S1 protein

Amidst a global pandemic, a precise and widely accessible rapid detection method is needed for accurate diagnosis and contact tracing. The lack of this technology was exposed through the outbreak of SARS-CoV-2 beginning in 2019. This study sets the foundation for the development of a boron doped diamond (BDD)-based impedimetric sensor. While specifically developed for use in the detection of SARS-CoV-2, this technology uses principles that could be adapted to detect other viruses in the future. Boron doped polycrystalline diamond electrodes were functionalized with a biotin-streptavidin linker complex and biotinylated anti-SARS-CoV-2 S1 antibodies. Electrodes were then incubated with the S1 subunit of the SARS-CoV-2 spike surface protein, and an electrical response was recorded using the changes to the electrode's charge transfer resistance (Rct), measured through electrochemical impedance spectroscopy (EIS). Detectable changes in the Rct were observed after 5-min incubation periods with S1 subunit concentrations as low as 1 fg/mL. Incubation with Influenza-B Hemagglutinin protein resulted in minimal change to the Rct, indicating specificity of the BDD electrode for the S1 subunit of SARS-CoV-2. Detection of the S1 subunit in a complex (cell culture) medium was also demonstrated by modifying the EIS protocol to minimize the effects of sample matrix binding. BDD films of varying surface morphologies were investigated, and material characterization was used to give insight into the microstructure-performance relationship of the BDD sensing surface.

Interpretation and Modelling of the Electrochemical Impedance of LiFePO4/Li4Ti5O12 Batteries

Significant effort has been devoted to the research and development of safe lithium ion batteries in the last three decades. The commercial 26650 LiFePO4/Li4Ti5O12 (LFP/LTO) battery has been specifically found in many applications in which safety and cycle-life are of prime importance. The cell consists of olivine LiFePO4 as cathode, which is one of the most thermally stable, non-toxic, and long-cycle-life cathode materials, and spinel Li4Ti5O12 as anode, which features zero-strain Li intercalation, flat and relatively high operating voltage, and high thermal stability. In order to assess and improve the power capability and stability of these safe and long-life batteries, it is important to investigate and understand performance characteristics of individual cell components and interfaces, in order to elucidate the rate determining processes at each electrode. In this work, electrochemical impedance spectroscopy (EIS) analysis facilitated by distribution of relaxation times (DRT) is used to study the LFP/LTO cell at different states of charge (SOC) and SOC history, and an equivalent circuit model (ECM) is proposed in order to better understand the main processes at the anode and cathode and quantify their contribution to the full cell impedance. The modeling and interpretation of the full cell EIS is complicated because the LFP and LTO responses appear over similar frequency ranges. In order to unambiguously separate the anode and cathode contributions, EIS spectra from LTO/Li and LFP/Li half cells were also measured at different SOC and SOC history and the fit results were used to develop the full-cell ECM. The LFP/LTO cell impedance changes slightly only at low SOCs during charge, whereas it changes significantly during discharge. This SOC history dependence, i.e., the EIS response of a particular SOC depending on the previous SOC (Figure 1a), was mainly attributed to the change in the LFP electrode charge transfer process frequency and resistance (Figure 1b). This variation was found to be minimized at high SOCs and maximized at low SOCs (Figure 1), e.g., the LFP electrode charge transfer resistance in the full cell at 90% SOC was 11.3 Ωcm2 in charge vs 11.4 Ωcm2 in discharge (~1% difference) and at 10% SOC was 9.7 Ωcm2 in charge vs 13.3 Ωcm2 in discharge (~37% difference). As seen in the DRT results (Figure 1b), the frequency of the charge transfer process at the LFP electrode showed the same variation, i.e., it happens at 2.15 Hz at 90% SOC in charge vs 1.73 Hz in discharge (~20% difference) and at 1.31 Hz at 10% SOC in charge vs 0.55 Hz in discharge (~42% difference). The LTO electrode showed relatively little change in the charge transfer resistance and frequency with SOC and SOC history (Figure 1b).Figure 1. EIS response from the full 26650 cell at different SOC during charge (red lines) and discharge (back lines): a) shows the Nyquist plots and b) shows the DRT results. The spectra are shown after the truncation of the negative values of -Zimag and are normalized to the surface area of the electrodes. Figure 1

Electrochemical and Microstructural Investigation of in-situ Grown CNTs Network on Carbon Paper as Electrocatalytic Electrode for Fuel Cells

In this study, carbon nanotubes (CNTs) were deposited directly on impregnated Fe/carbon paper (CP) substrate (CNT/CP) utilizing chemical vapor deposition (CVD) process with the aim of using them as electrocatalytic electrode. The influence of wet impregnation conditions and CVD growth parameters on the characteristics of CNTs was investigated. Field emission scanning electron microscopy (FESEM), Energy dispersive spectroscopy (EDS), Transmission electron microscopy (TEM) and Raman spectroscopy were applied to characterize nucleation, growth and morphology of CNTs on CP. Measurement of Contact angle (CA) determined 125.9 and 145.0 ⁰C for CP and CNT/CP that displayed an increase in water repellence and degree hydrophobicity of CNT/CP to 15% than CP. Electrochemical impedance spectroscopy (EIS) analysis indicated the reduction of electrode charge transfer resistance from 5000 ohm value from CNT/CP to ohm value for CP that shows the increment in electrical conductivity of CNTCP. Half-cell test analysis represented that the improvement of performance and the increase of power density to ⁓8 % for Pt/CNT/CP compared to commercial catalyst Pt/C/CP (20 wt%) even with about 42% less Pt loading, can be attributed to strong adhesion of in-situ CNTs to the CP and lower agglomeration of CNTs along with outstanding electrical and thermal conductivity of CNTs. The obtained results indicated that the proposed nanostructure serves as a promising candidate for many technological applications specially carbon nanotube-supported catalyst.

The Effect of Hematite on the Corrosion Behavior of Copper in Saturated Red Soil Solutions

The effect of α-Fe2O3 as a substitute for hematite on the corrosion behavior of copper in saturated red soil solutions was investigated by electrochemical methods and surface analysis. It was observed from experimental results that α-Fe2O3 was stably dispersed in the weakly acidic saturated red soil solutions without an electrochemical reaction with the immersed bare copper. The electrochemical results showed that the charge transfer resistance of each electrode increased first and then decreased as a whole in the same saturated red soil solution while the charge transfer resistance of copper electrodes increased with the addition of α-Fe2O3 from 10 to 50 g/kg. The addition of α-Fe2O3 mainly inhibited the cathodic corrosion behavior of copper. The characterization using SEM–EDS and XRD verified that the main component of the corrosion products was Cu2O on the copper surface in the saturated red soil solutions, with additional α-Fe2O3. α-Fe2O3 acted as a physical barrier to copper corrosion and prevented more dissolved oxygen from reaching the copper surface in the saturated red soil solutions. Therefore, a uniform and compact Cu2O film formed on the copper surface which protected the inner copper substrate from further corrosion. A copper corrosion mechanism was proposed for the saturated red soil solutions, with and without α-Fe2O3.

Communication—Characteristic Charge Transfer Resistance of Electrodes on Lead-Acid Batteries

Lead-acid batteries are widely used as backup in power systems. Recently, charge-transfer resistances on electrode-electrolyte interface have been studied to estimate state of health (SOH) in backup batteries, and some conclusions have been obtained. Charge-transfer resistances do nonlinearly characterize full-scale SOH in specific degradation experiment on 10 Ah batteries. This paper proposes characteristic charge-transfer resistances, combining with charge-transfer resistances to linearly characterize multi-scale SOH on four 500 Ah batteries in parallel experiments. The results provide viable solution for linear estimation of targeting-scale SOH (500 Ah∼250 Ah) on lead-acid batteries.

Controllable atomic-ratio of CVD-grown MoS2-MoO2 hybrid catalyst by soft annealing for enhancing hydrogen evolution reaction

MoS2 has been widely researched as a good catalyst for the hydrogen production, however, the electrochemical applications of MoS2 are still limited because of its low electrical conductivity and electrochemically inert basal plane. In this study, hybrids of MoS2 and MoO2 were used to decrease charge transfer resistance of electrodes. The proportions of MoS2 and MoO2 were controlled by soft annealing without a structural change. The coexistence of MoS2−MoO2 was confirmed by Raman and X-ray diffraction analysis, and the change of chemical compositions (MoS2 to MoO2 ratio) were demonstrated by X-ray photoelectron spectroscopy. By controlling the chemical compositions of MoS2 and MoO2, the optimal ratio of MoS2 and MoO2 (3: 1) showed the highly electrocatalytic activity (η10: 198 mV, Tafel: 66.8 mV dec−1) and outstanding long-term stability compared to other ratios of MoS2 and MoO2.

Electrochemical Properties of Composite Electrodes Containing Lithium-Ion Conducting Solid Particles and Liquid Electrolytes in Lithium-Ion Batteries

Lithium-ion batteries for automotive applications have required to enhance power density, low-temperature performance, life, energy density, and safety. All-solid-state batteries using lithium-ion conducting solid electrolytes have been much interest as candidates to respond to these demands. However, for practical applications, all-solid-state batteries have some problems to solve low charge-discharge performance under high rate and low temperature operations because of low ionic conductivities and large resistances of interface between the solid electrolyte and the active electrode material. We have focused on hybrid electrolytes consisting of lithium-ion conducting solid particles (LCSP) and a gel polymer electrolyte leading to a decrease of cell resistance, especially at low temperatures for LTO cells [1,2]. In this study, we have investigated effects of LCSP with liquid electrolytes in composite electrodes on electrochemical properties and electrode performance in order to develop high-power lithium-ion batteries using the solid electrolytes. NASICON-type Li-Al-Ti-P-O (LATP) particles with a particle size of submicron were used as LCSP. The composite electrodes consisted of LiNi0.5Co0.2Mn0.3O2 (NCM523) as cathode active material, carbon filler, polyvinylidene difluoride binder, and LATP particles, which were coated on aluminum foil as current corrector. Electrochemical measurements of the composite electrodes containing LCSP were performed using a three-electrode glass cell with a lithium metal foil counter electrode, a lithium metal chip reference electrode, a glass filter separator, and LiPF6-based liquid electrolytes. Figure 1 shows typical AC-impedance spectra of the composite electrodes with and without LATP particles at -20°C. The impedance spectra of both electrodes exhibited two depressed semicircles in the high- and low-frequency range, which can be interpreted as resulting from the passivating film formed on the NCM523 active material and the charge transfer process of lithium insertion, respectively. The ohmic resistances at 100 kHz such as the ionic resistance of electrolyte and the resistance of passivating film in the spectra showed no difference between the electrodes with and without LATP. On the other hand, it was noted that the charge transfer resistance of electrode with LATP was significantly smaller than that of electrode without one. Furthermore, the activation energy for the charge transfer of the electrodes with LATP is estimated into 55.7 kJ/mol, which is smaller than that of the electrode without LCSP as shown in Fig. 2. These results indicate that LCSP and liquid electrolytes in the electrodes plays an important role of reducing the charge transfer resistance rather than enhancing the lithium ion conductivity in the electrolytes. Therefore, we consider that LCSP in the electrode enhances to provide lithium ions in the liquid electrolyte to the surface of the active materials, leading to maintain high concentration of lithium ions at the surface of active material. The detail of the mechanism for reducing the charge transfer resistance by containing LCSP to the electrode will be discussed in this presentation. [1] K. Yoshima, Y. Harada and N. Takami, J. Power Sources, 302,283-290(2016). [2] N. Takami, K. Yoshima and Y. Harada, J. Electrochem. Soc., 164,A6254(2017). Figure 1

Resistance Growth in Lithium-Ion Pouch Cells with LiNi0.80Co0.15Al0.05O2 Positive Electrodes and Proposed Mechanism for Voltage Dependent Charge-Transfer Resistance

High nickel content positive electrode materials, like LiNi0.80Co0.15Al0.05O2 (NCA), have been observed to lose capacity due to impedance growth when cycled above 4.1 V vs. Li/Li+. In this paper, we tested pouch cells with NCA positive electrodes and graphite, graphite-SiO, or graphite-SiC negative electrodes. In each case the pouch cells show high resistance at high voltage for every cycle, and resistance growth during cycling that is in part responsible for capacity loss. Symmetric cell experiments were used to show that the high resistance does, in fact, come from the positive electrode charge transfer resistance which is attributed to a thickening rock salt layer on the positive electrode (seen by other researchers). We propose a mechanism to explain why the charge transfer resistance depends on voltage for the positive electrode.

LiFePO4/C cathode material prepared with sphere mesoporous-FePO4 as precursors for lithium-ion batteries

The spherical mesoporous iron phosphate (P-FP) were prepared by liquid phase crystallization method, and then Carbon-coated lithium iron phosphate was synthesized by high temperature solid phase method using the spherical mesoporous iron phosphate as precursors (P-LFP/C) or using the non-mesoporous iron phosphate as precursors (LFP/C). The P-LFP/C were characterized by X-Ray-Diffraction, Scanning-Electron-Microscope, Fourier-Transform Infrared Spectrometer and electrochemical tests. The results show that the initial discharge capacity of the P-LFP/C at 0.1 C increase by 27.10%, reaching 159.29 mAh g−1, and the electrode charge transfer resistance reduce by 88.16%, just 48.32 Ω. compare with the LFP/C. And the P-LFP/C exhibited better discharge capacity at initial 151.78 and 112.11 mAh g−1 at 0.2 C and 5 C rate, respectively. It is beneficial to the lithium ion escaped and embed in the process of charging and discharging and enhanced the electronic conductivity and rate performance of the cathode materials.

Impact of Electrolyte Additive Content on the Lifetime of LiNi0.5Mn0.3Co0.2O2/Artificial and Natural Graphite Cells

The electrolyte comprised of 2 wt% prop-1-ene-1,3 sultone (PES) + 1 wt% tris (trimethylsilyl) phosphite (TTSPi) + 1 wt % ethylene sulfate (DTD) in 1 M LiPF6 in ethylene carbonate: ethyl methyl carbonate (3:7 by weight), called PES211 here, has been reported to function well in Li(NixMnyCoz)O2/graphite cells operated up to 4.4 V. However, the use of PES211 electrolyte usually leads to unwanted lithium plating at room temperature during high rate charging as a result of large negative electrode charge transfer resistance. This problem can be mitigated by decreasing the fraction, x (0 < x < 1), of the additives used in PES211 (xPES211) in the electrolyte. This work studied the impacts on the cell lifetime when x in xPES211 is decreased in NMC532/artificial graphite (AG) and NMC532/natural graphite (NG) pouch cells. Ultra-high precision coulometry measurements and isothermal microcalorimetry tests were used to make comparative studies. All the diagnostic measurements suggested that cells with lower fractions of x in xPES211 would have a shorter lifetime. Long term cycling tests confirmed that the capacity retention decreased with a decreasing fraction of xPES211 in both NMC532/AG and NMC532/NG cells. Differences between artificial and natural graphite negative electrode materials are also discussed.

Graphene Polyaniline/Polyoxometalate Hybrid As Cathode for Lithium Ion Batteries with Improved Lithium Storage Capacity

: polyaniline/polyoxometalate nanospheres hybrid were synthesized via a facile interfacial polymerization method, and evaluated as a cathode material for lithium ion batteries. However, both polyoxometalate and polyaniline/polyoxometalate can be easily dissolved in LiPF6 eletroyte. In order to solve this problem，polyaniline/polyoxometalate nanospheres were first embedded into the interspaces of grapheme, leading to the formation 3D free-standing rGO@PANI/POM hybrid. The molecular cluster battery in which the RGO@PANI/PW12O34 hybrid was adopted as a cathode active material exhibited a higher battery capacity and stability than the PANI/ PW12O34 and the microcrystal polyoxometalate. The phosphotungstic acid polyanions not only exhibit a large theoretical capacity of about 260 mAh g−1, but also reduce the charge transfer resistance of electrode leading to the enhanced reversible capacity and rate capability. Reference [1] Liu, K.; Zheng, J. M.; Zhong, G. M.; Yang, Y. Poly(2,5-dihydroxy1,4-benzoquinonyl sulfide) (PDBS) as a Cathode Material for Lithium Ion Batteries. J. Mater. Chem. 2011, 5, 4125. [2] Shao, L.; Jeon, J. W.; Lutkenhaus, J. L. Polyaniline/Vanadium Pentoxide Layer-by-Layer Electrodes for Energy Storage. Chem. Mater. 2012,24, 181. [3] Zhang, L., Wu, H. B., & Lou, X. W. D. Iron-oxide-based advanced anode materials for lithium-ion Batteries . Advanced Energy Materials, 2014, 4, 1032. ACKNOWLEDGEMENTS This work was financially supported by the National Natural Science Foundation of China (Grant No. 21273195), a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions, and the Natural Science Foundation of Education Committee of Jiangsu Province (12KJB150023).

Key Parameters for the Design of Composites Electrodes for Water Splitting in Alkaline Medium

A study on the hydrogen evolution performances in alkaline medium (KOH 6M) of nickel-based composite electrodes has been carried out. Surface tension characteristics have been tuned by using various polymer binders of different hydrophobic/hydrophilic balances: polyvinyl alcohol (PVOH), polybenzimidazole (PBI), polyethylene oxide (PBI), polyvinidylene fluoride (PVDF), and Polytetrafluoroethylene (PTFE). The composite electrodes fabricated by drop-casting exhibit various contact angles in an extended range from 43° to 115°. They were evaluated by steady-state polarization and electrochemical impedance spectroscopy (EIS) measurements. Electrochemical behavior and mechanism were discussed towards the electrode wettability through the evaluation of electrochemical parameters including the overpotential at 100 mA/cm², kinetic parameter b (mV/dec) and charge transfer resistance (Rct). The bubble coverage, diameter before departure (lift off from the electrode surface) and residence time at the surface are greatly affected by the surface tension of the various electrodes. The comparison of the electrochemical performances revealed the importance of this characteristic for the design of an efficient hydrogen evolution electrode fabricated by a catalyst-binder approach. From Ni-PVOH to Ni-PTFE electrodes with the same catalyst loading, the overpotential at 100 mA/cm² was improved by 150 mV. The kinetic tafel slope was kept close to 116 mV/dec (Volmer-Heyvroski step) for electrodes with a contact angle between 43° to 90 °, increased for contact angles above 90° to reach up to 178 mV/dec for PTFE-based electrode showing the greater contact angle in the series at 115°. Electrochemical impedance spectroscopy (EIS) measurements at various overpotentials show that the bubbles retained at the surface increase the electrode charge transfer resistance. This behavior is assigned to the hidden active sites and justifies the observed decrease in performances of hydrophobic electrodes. This comprehensive study leads to a precise description of the interfacial phenomena at the microscopic scale during gas production by electrolysis and the evaluation of key parameters for the formulation of advanced electrodes.

Electrochemical characterization of poly(fuchsine acid) modified glassy carbon electrode and its application for simultaneous determination of ascorbic acid, epinephrine and uric acid

Electropolymerization of fuchsine acid (FA) was studied by cyclic voltammetry on the surface of a glassy carbon (GC) electrode in different electrolyte media. Then, a novel Au-nanoparticle poly-fuchsine acid film modified glassy carbon electrode (poly(FA)/AuNP/GCE) was constructed for the simultaneous determination of ascorbic acid (AA), epinephrine (EP) and uric acid (UA). The resulting poly(FA)/AuNP modified glassy carbon electrode was characterized by scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and reflectance Fourier transform infrared spectroscopy (ATR-FTIR). The poly(FA) film had an efficient electrocatalytic activity for the oxidation of AA, UA and EP, and decreased the charge transfer resistance of electrode. In addition, the poly(FA)/AuNP/GCE separate oxidation peak potential of AA–EP by 150mV and EP–UA by 180mV, while bare GCE fails to resolve them. Differential pulse voltammetry results exhibited linear dynamic range of 5.0–1120.0μmolL−1 for AA, 0.5–792.7μmolL−1 for EP and 2.85–650.2μmolL−1 for UA with detection limits (S/N=3) of 0.009μmolL−1, 0.01μmolL−1, and 0.03μmolL−1 for AA, EP, and UA, respectively. The diffusion coefficient for the oxidation reaction of EP on AuNP/poly(FA) film coated GC electrode was calculated as 2.6(±0.10)×10−5cm2s−1. The present method was applied to the determination of EP in pharmaceutical samples, AA in commercially available vitamin C tablet, and UA in urine samples.

Effects of Carbon Structure and Mixing Sequence in an Expander on the Capacity of Negative Electrodes in a Traction Battery

Expanders were prepared by mixing barium sulfate, sodium lignosulfonate, and carbon materials by a high speed mixer. Effects of type of carbon materials and mixing sequence on electrochemical property of electrode were studied. Three different carbon materials: medium structure carbon black, high structure carbon black, and multi-wall carbon nanotube, were employed. The amount of charge and charge transfer resistance of electrode using different expanders were investigated by cyclic voltammetry and electrochemical impedance spectroscopy, respectively. Prepared expanders were characterized by a transmission electron microscope and a field emission scanning electron microscope. The capacity of the battery was tested by the high discharge rate test. Negative active materials were characterized by a field emission scanning electron microscope. The results showed that the type of carbon material and mixing sequence influenced the structure of carbon network in an expander and resulted in the change of the amount of charge and charge transfer resistance. All prepared expanders exhibited higher amount of charge and lower charge transfer resistance than those of a commercial expander. The highest amount of charge was obtained when the expander was prepared by mixing medium structure carbon black for 90 s before adding high structure carbon black. The high discharge test shows that the capacity of a battery using NAM prepared by this expander is approximately 10% higher than that using a commercial expander. The higher capacity is due to an increase of the surface area of NAM.

Self-assembly of a thin highly reduced graphene oxide film and its high electrocatalytic activity

A thin highly reduced graphene oxide (rGO) film was self-assembled at the dimethyl formamide (DMF)–air interface through evaporation-induced water-assisted thin film formation at the pentane–DMF interface, followed by complete evaporation of pentane. The thin film was transferred onto various solid substrates for film characterization and electrochemical sensing. UV-visible spectrometry, scanning electron microscopy (SEM), atomic force microscopy (AFM) and electrochemistry techniques were used to characterize the film. An rGO film showing 82.8% of the transmittance at 550 nm corresponds to a few layers of rGO nanosheets. The rGO nanosheets cross-stack with each other, lying approximately in the plane of the film. An rGO film collected on a glassy carbon (GC) electrode exhibited improved electrical conductivity compared to GC, with the electrode charge-transfer resistance (Rct) reduced from 31 Ω to 22 Ω. The as-formed rGO/GC electrode was mechanically very stable, exhibiting significantly enhanced electrocatalytic activity to H2O2 and dopamine. Multiple layers of the rGO films on the GC electrode showed even stronger electrocatalytic activity to dopamine than that of the single rGO film layer. The controllable formation of a stable rGO film on various solid substrates has potential applications for nanoelectronics and sensors/biosensors.

Tin–indium/graphene with enhanced initial coulombic efficiency and rate performance for lithium ion batteries

Abstract Tin is an attractive anode material replacing the current commercial graphite for the next generation lithium ion batteries because of its high theoretical storage capacity and energy density. However, poor capacity retention caused by large volume changes during cycling, and low rate capability frustrate its practical application. In this study, a new ternary composite based on tin–indium alloy (Sn–In) and graphene nanosheet (GNS) was prepared via a facile solvothermal synthesis followed by thermal treatment in hydrogen and argon at 550 °C. Characterizations show that the tin–indium nanoparticles with about 100 nm in size were wrapped between the graphene nanosheets. As an anode for lithium ion batteries, the Sn–In/GNS composite exhibits a remarkably improved electrochemical performance in terms of lithium storage capacity (865.6 mAh g−1 at 100 mA g−1 rate), initial coulombic efficiency (78.6%), cycling stability (83.9% capacity retention after 50 cycles), and rate capability (493.2 mAh g−1 at 600 mA g−1 rate after 25 cycles) compared to Sn/GNS and Sn–In electrode. This improvement is attributed to the introduction of lithium activity metal, indium, which reduces the charge transfer resistance of electrode, and the graphene nanosheet which accommodates the volume change of tin–indium nanoparticles during cycling and improves electrical conductivity of material.

Polyaniline/Polyoxometalate Hybrid Nanofibers as Cathode for Lithium Ion Batteries with Improved Lithium Storage Capacity

Hybrid nanofibers of polyaniline/polyoxometalate are synthesized via a facile interfacial polymerization method for the first time, and evaluated as a cathode material for lithium ion batteries. The hybrid nanofibers with 100 nm diameter consisted of phosphomolybdic acid polyanion, [PMo12O40]3–, and polyaniline matrix. Their 1D geometry improves the utilization of electrode materials and accommodates the volume change during cycling, which enables the significant improvement in lithium storage capacity and capacity retentions. The phosphomolybdic acid polyanions not only exhibit a large theoretical capacity of about 270 mAh g–1, but also reduce the charge transfer resistance of electrode leading to the enhanced reversible capacity and rate capability. The polyaniline/polyoxometalate nanofibers delivered a remarkably improved electrochemical performance in terms of lithium storage capacity (183.4 mAh g–1 at 0.1C rate), cycling stability (80.7% capacity retention after 50 cycles), and rate capability (94.2 ...

Tin indium oxide/graphene nanosheet nanocomposite as an anode material for lithium ion batteries with enhanced lithium storage capacity and rate capability

Tin oxide (SnO2) is a promising candidate as an anode for lithium ion batteries because of its high theoretical capacity. However, poor capacity retention caused by large volume changes during cycling, large initial irreversible capacity, and low rate capability frustrate its practical application. We have developed a ternary nanocomposite based on tin indium oxide (SnO2–In2O3) and graphene nanosheet (GNS) synthesized via a facile solvothermal method. The incorporation of In2O3 into SnO2 can improve the electrochemical property of SnO2 and reduce the charge transfer resistance of electrode leading to the enhanced reversible capacity and rate capability. The graphene nanosheet in the composite electrode can accommodate high volume expansion/contraction during cycling resulting in excellent capacity retention. As an anode for lithium ion batteries, the SnO2–In2O3/GNS nanocomposite exhibits a remarkably improved electrochemical performance in terms of lithium storage capacity (962mAhg−1 at 60mAg−1 rate), initial coulombic efficiency (57.2%), cycling stability (60.8% capacity retention after 50 cycles), and rate capability (393.25mAhg−1 at 600mAg−1 rate after 25 cycles) compared to SnO2/GNS and pure SnO2–In2O3 electrode.