Electrochemical Potential Window Research Articles

Electrochemical biosensors based on divinyl sulfone conjugation of DNA to graphene oxide electrodes

We immobilized unmodified, single-stranded (ss) DNA oligonucleotides on graphene oxide (GO) using divinyl sulfone (DVS). This is a new and useful method for generating DNA biosensors that avoids the need for modified oligonucleotides with synthetic attachment chemistry. This technique yields time and cost savings. The synthesis of unmodified oligonucleotides is simpler, quicker, and less expensive than modified DNA. DVS has two reactive vinyl groups that can link labile functional groups on the GO surface to the DNA. We show that the DNA nucleobase is covalently bonded to DVS. This opens the use of ubiquitous glassy carbon electrodes (GCE) for fabricating DNA biosensors by drop-casting GO. Reverse-complimentary DNA was detected using multiple electrochemical methods. The results show that DNA can be successfully conjugated to conductive carbon for electrochemical sensors. This is simpler than other methods for functionalizing carbon electrodes. This has clear advantages over gold electrodes in terms of its electrochemical potential window.

An inclusive thermophysical and rheology portrayal of deep eutectic solvents (DES) for metal oxides dissolution enhancement

Eutectic mixtures, in particular, the deep eutectic solvents (DESs) are gaining an overwhelmingly research interest as green solvents and is emerging as an attractive replacement to ionic liquids (ILs) for a variety of industrial applications. In this milieu, we have prepared green DESs by combining choline chloride (ChCl) as hydrogen bond acceptor (HBA) with malonic acid (MA) and ethylene glycol (EG) as hydrogen bond donors (HBDs) at capricious molar ratios. The influence of HBD (their nature and molar ratio) on the prepared DES structure along with the thermophysical properties viz., decomposition temperature, density, speed of sound, electrical conductivity, viscosity, rheology, refractive index, and electrochemical potential window (EPWs) have been experimentally witnessed as a function of temperature. The amendment in the hydrogen bonding networks with the successive addition of HBDs in different molar ratios was evidently inferred using Fourier transform-infrared (FT-IR) spectroscopy. Different thermodynamic models were employed to describe and correlate the obtained results from the measured thermophysical properties. Additionally, the thermal expansion coefficient (αP), free length (Lf), molar entropy (So), isentropic compressibility (κs), molar polarizability (Rm), and free volume (fm) have been calculated based on the experimentally determinedρ, u, and nDrespectively. The cyclic voltammetry (CV) outcomes were rationalized which provided a broad range of Electrochemical potential windows (EPWs) due to the delocalization of charged moieties. In addition, the viscoelastic and rheological measurements exhibited a Newtonian-like behavior. The impact of the varying molar ratio of HBD in the prepared DESs were also perceived for the enhancement of the selected poorly-water soluble metal oxides dissolution with a purpose of making these prepared DESs more promising green solvent for various electro-deposition possesses.

Beyond hierarchical mixed nickel-cobalt hydroxide and ferric oxide formation onto the green carbons for energy storage applications

To attain superior energy density concurrently with high power density, high-performance supercapacitors have been developed. Herein an innovative strategy has been adopted to fabricate unique binder-free electrodes composed of a unique porous structure of binary metal carbonate hydroxide nanomace-decorated hydrothermal porous carbon spheres (PCSs). Hierarchical nickel-cobalt carbonate hydroxide (NiCOCH) nanomaces, directly grown on PCSs, are used as positive electrodes for supercapacitors fabrication. Furthermore, Fe2O3@PCS composites, having benefits of highly reversible redox reaction in the negative potential window and highly porous structure, are employed as the negative electrode in the fabrication of the asymmetric supercapacitors (ASCs). The assembled NiCoCH@PCS// Fe2O3@PCS asymmetric devices with a wide electrochemical potential window not only have the merit of high energy and power densities but also receive benefits from remarkable cycle stability. These encouraging outcomes that are mutually beneficial, make these fabricated ASCs significantly ideal for high-performance electronics.

Electropolishing of Tin in an Amide-Type Ionic Liquid

Anodic dissolution and electropolishing of Sn were investigated in an amide-type ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide. The rate of anodic dissolution was considered to be determined by the diffusion of anodically dissolved Sn(II) species. A large increase in the local viscosity during dissolution was observed in-situ by the impedance-type electrochemical quartz crystal microbalance, reflecting an increase in the local concentration of Sn(II) near the electrode. A shiny and smooth surface was obtained after anodic dissolution at 0.1 V vs Ag∣Ag(I) with agitation. A decrease in the surface roughness estimated by confocal laser scanning microscopy suggested electropolishing of Sn was possible in the ionic liquid within the electrochemical potential window probably due to the formation of the viscous layer near the electrode.

Luminescent MoS2 Quantum Dots with Tunable Operating Potential for Energy-Enhanced Aqueous Supercapacitors.

Wide band gap luminescent MoS2 quantum dots (QDs) and MoS2 nanocrystals (NCs) have been synthesized by using laser-assisted chemical vapour deposition and used as an electrode material in supercapacitors. Size-dependent properties of the MoS2 QDs and NCs were examined by UV–vis absorption, photoluminescence, and Raman spectroscopy. The morphological evolution of the NCs and QDs were characterized by using field emission scanning electron microscopy, high-resolution transmission electron microscopy, and atomic force microscopy. The as-synthesized uniform QDs with a size of ∼2 nm exhibited an extended electrochemical potential window of 0.9 V with a specific capacitance value of 255 F/g, while the NCs values were 205 F/g and 0.8 V and the pristine MoS2 with values of 105 F/g and 0.6 V at a scan rate of 1 mV s–1. A shorter conductive pathway and 3D quantum confinement of MoS2 QDs that exhibited a higher number of active sites ensure that the efficient charge storage kinetics along with the intercalation processes at the available edge sites enable significant widening of operating potential window and enhance the capacitance. The symmetric device constructed with the QDs showed a remarkable device capacitance of 50 F/g at a scan rate of 1 mV s–1 with an energy density of ∼5.7 W h kg–1 and achieved an excellent cycle stability of 10,000 consecutive cycles with ∼95% capacitance retention.

Asymmetric micro-supercapacitors based on electrodeposited Ruo2 and sputtered VN films

Research on micro-supercapacitors remains one of the most important activities in the area of electrochemical energy storage for powering smart and miniaturized electronic devices. Here we design an asymmetric micro-supercapacitor (A-MSC) combining sputtered vanadium nitride film (VN) and electrodeposited hydrous ruthenium oxide (hRuO2) film. Taking advantage of their complementary electrochemical potential windows in 1 M KOH electrolyte, the A-MSC achieves a cell voltage up to 1.15 V, associated to high specific capacitance values for the device (≈ 100 mF cm−2). The energy density of this asymmetric VN / hRuO2 micro-supercapacitor reaches 20 µWh cm−2 at a power density of 3 mW cm−2. Taking benefit from the asymmetric configuration, a 5-fold enhancement factor in energy density is demonstrated for the VN / hRuO2 asymmetric micro-supercapacitor as compared to symmetric VN / VN and hRuO2 / hRuO2 microdevices.

Nanocomposite polymer gel with dispersed alumina as an efficient electrolyte for application in supercapacitors

A nanocomposite polymer gel electrolyte (NCPGE) has been synthesized from polyvinylidene fluoride co-hexafluoropropylene (PVDF-HFP) as the host polymer, ethylene carbonate (EC)/propylene carbonate (PC) as plasticizers, and tetraethylammonium tetrafluoroborate (TEABF4) as an ionic salt by a solution-casting technique, followed by the addition of Al2O3 nanoparticles. The optimal loading of Al2O3 giving the highest ionic conductivity of 6.0 × 10−3 S cm−1 was found to be 18 wt%. An activation energy of 0.107 eV has been calculated from a temperature-dependent conductivity plot, which shows Arrhenius behavior. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared (FTIR) characterizations have been applied to investigate the morphology and structure. The semi-crystalline and porous nature of the NCPGE has been confirmed by SEM and XRD analyses. The ionic transference number was calculated as 0.98 by the DC polarization technique, confirming the dominant ionic nature of the prepared electrolyte. The electrochemical potential window of the NCPGE of about 3.4 V, as estimated by linear sweep voltammetry, makes it suitable for supercapacitor applications.

Self-diffusion in garnet-type Li7La3Zr2O12 solid electrolytes

Tetragonal garnet-type Li7La3Zr2O12 is an important candidate solid electrolyte for all-solid-state lithium ion batteries because of its high ionic conductivity and large electrochemical potential window. Here we employ atomistic simulation methods to show that the most favourable disorder process in Li7La3Zr2O12 involves loss of Li2O resulting in lithium and oxygen vacancies, which promote vacancy mediated self-diffusion. The activation energy for lithium migration (0.45 eV) is much lower than that for oxygen (1.65 eV). Furthermore, the oxygen migration activation energy reveals that the oxygen diffusion in this material can be facilitated at higher temperatures once oxygen vacancies form.

Pyridine-Grafted Nitrogen-Doped Carbon Nanotubes Efficiently Electrochemical Reduce C <sub>2</sub> to CO <sub>2</sub> at High Current Densities Over a Wide Electrochemical Window

Nitrogen-doped carbon nanomaterials for electrochemical reduction of CO2 (CO2 ER) to CO have been extensively investigated, evaluated, and applied recently. Nevertheless, their weak adsorption capacity for CO2usually results in a rapidly decayed CO faradaic efficiencies (FECO) in the course of pursuing a commercial CO current density (j CO ) by increasing the overpotential. Herein, we axially graft pyridine molecules on nitrogen-doped carbon nanotubes to construct a metal-free composite electrocatalyst (Py-N 4 CNT-800) with enhanced CO2 affinity for CO2 ER to efficiently generate CO. Py-N4CNT-800 exhibits a prominent FECO of 96% at -0.99 V (vs. RHE) with a desirable jCO of 18.4 mA cm-2, and FECO can even be maintained above 90% in a wide electrochemical potential window (-0.79 to -1.19 V). In-situ infrared spectra unambiguously indicate that grafted axial pyridine molecules can facilitate the CO2 adsorption and suppress the occurrence of competitive hydrogen evolution reaction (HER). Notably, Py-N4CNT-800 delivers a promising jCO of 217 mA cm-2 at -0.9 V in flow cell, showing a bright prospect of functionstrengthened carbon nanomaterial for industrial applications.

Use of electrical field-flow fractionation for gold nanoparticles after improving separation efficiency by carrier liquid optimization

Electrical field-flow fractionation (ElFFF) is a useful separation technique for nanoparticles, however, it has been limited by polarization/electrical double layer formation which reduces an effective field for separation. With an appropriate direct current (DC) applied voltage, sodium carbonate, FL-70, Triton X-100 and acetonitrile were explored as additive substances for preparation of carrier liquid used in normal ElFFF to enhance an amplitude of effective field by their ionic redox-active species, ionic and nonionic surfactant and wide electrochemical potential window nonionic organic solvent properties, respectively. Effective field was indirectly measured in each carrier liquid by investigating retention behavior of polystyrene latex nanoparticles and gold nanoparticles. Effective field improvement was observed in all carrier liquid types (except FL-70) by which the highest effective field existed in 16 μM sodium carbonate at 1.70 V and 0.01% (V/V) Triton X-100 and 50% (V/V) acetonitrile at 1.90 V as compared to deionized water at 1.90 V. In addition, those carrier liquids were applied for separation of 5 nm and 15 nm gold nanoparticles mixture by which Triton X-100 exhibited the best separation resolution (Rs = 1.11).

Solid-state electrolytes: Advances and perspectives

All-solid-state Li batteries (ASSLiBs) that use solid-state electrolytes (SSEs) to replace liquid organic electrolytes are considered as promising next-generation energy storage devices because of their wide electrochemical potential windows, high safety, and high energy density. Therefore, ASSLiBs have attracted a lot of attention in recent years. In this review, we focus on the main challenges on the synthesis and the electrochemical properties of the SSEs including (i) crystal structures and modification of kinetics of Li-ion migration through doping technology, (ii) synthesis technologies and its effect on the electrochemical performances of the SSEs, and (iii) ambient condition stability and degration of SSEs. Finally, perspectives of future researches on the SSEs are presented.

Salt-solvent mixtures (SSMs): Investigation of physiochemical, thermodynamic and electrochemical properties of multifunctional imidazolium ionic liquids with DMSO

Research on Ionic Liquids (ILs) recently focuses on investigating the properties of ILs salt-solvent mixtures (SSMs). The SSMs gained an unprecedented popularity because it offers wide range of properties necessary for the desired applications. In this work, imidazolium ILs containing nitrile and varying number of ether group coupled with bis(trifluoromethanesulfonyl)imide anion were synthesized. These ILs were mixed with dimethylsulfoxide (DMSO) in various mole ratio to form a salt-solvent mixtures. Density, dynamic viscosity and electrical properties of pure ILs and its mixtures were investigated over a wide temperature range. Thermodynamic properties such as thermal coefficient of expansion, standard entropy and lattice energy of pure ILs increased when the number of ether group on the cation side chain increased. Dynamic viscosities and electrical conductivity of the SSMs were investigated over a wide temperature range and different mole ratio, described by Vogel–Fulcher–Tamman (VFT) equation and Arrhenius equation. The relationship between dynamic viscosity and electrical conductivity was illustrated by Walden's Rule and it revealed that the SSM's have high conductivities at low fluidity, which can be categorized as ‘super ionic liquids’. Electrochemical potential window (EPW) and conductivity results for the SSMs revealed their (Mole ratio ILs =0.8) excellent potential in electrochemical applications.

Towards Active and Stable Bifunctional NiCo2O4 Catalysts for O2 Evolution and Reduction in Alkaline Media

It is particularly challenging to find a bifunctional catalyst capable of accelerating both the O2 evolution reaction (OER) and O2 reduction reaction (ORR) in aqueous solutions. The discovery of such a material would bring reversible fuel cells and metal air batteries much closer to technological fruition. However, in a real device, such a catalyst will need to retain its activity across an enormous potential window of at least 1 V over several years. To the best of our knowledge, little is known about the factors controlling the stability of bifunctional catalysts.In this contribution, we investigate the electrochemical activity and stability of a NiCo2O4 catalyst, synthesized at Johnson Matthey as part of EU funded project FLOWCAMP. Using post-mortem techniques, such as inductively coupled plasma mass spectrometry (ICP-MS), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), we provide experimental evidence about catalyst deactivation mechanisms. Results will also include a spectroelectrochemical in-situ UV-Vis study, that provides insights to the reaction mechanism for the OER. Lastly, the activity and stability of NiCo2O4 catalysts is also evaluated in oxygen-electrode prototypes and characterized in a half-cell configuration.In figure 1 is shown the ORR and OER activity of NiCo2O4 before and after accelerated degradation tests (ADT), in rotating disk electrode (RDE) configuration, employing three different electrochemical potential windows: i) 0.6 VRHE - 1 VRHE; ii) 0.6 VRHE - 1.7 VRHE; and iii) VRHE - 1.7 VRHE. As seen by the blue lines, significant ORR deactivation is observed after cycling across both ORR and OER potentials, whereas a 6% decrease in ORR current at 0.7 VRHE is observed after cycling for 1 hour within the ORR potential window. At the same time, degradation is accompanied by significant redox peak changes, as observed in the inset of Figure 1, which could indicate structural changes occurring during the OER. Post-mortem ICP-MS results indicate that catalyst dissolution accompanies this transformation during the OER. Alongside, in-situ UV-vis experiments identified changes in redox species as a function of applied potential, which are further correlated with the electrochemical current to determine the reaction order with respect to the amount of surface oxidized states.In this presentation, I will clarify the factors that control the activity and stability of NiCo2O4 catalysts, by coupling electrochemical measurements with in-situ UV-vis, and post mortem characterization techniques. In my talk, I will focus on understanding the causes for deactivation of the ORR current, which will aid further design of stable ORR and OER catalysts in alkaline media. A cknowledgements: This work is supported by the project ’’FLOWCAMP’’ (www.flowcamp-project.eu) under the European union’s innovation training network (grant agreement 765289).[1] L. Francàs, S. Corby, S. Selim, L. Dongho, C. A. Mesa, R. Godin, E. Pastor, I. E. L. Stephens, K. Choi, J. R. Durrant “Spectroelectrochemical study of water oxidation on nickel and iron oxyhydroxide electrocatalysts,” Nat. Commun., vol. 10, no. 5208, 2019. Figure 1

Fluoride-Ion Conductivity of La-Sr-F-S Multiple-Anion Compounds

Fluoride-ion batteries using solid-state electrolytes exhibit the high theoretical energy density and one of the candidates for next-generation rechargeable batteries [1]. For fluoride-ion batteries, the ion carrier is monovalent fluoride ion, which can realize the multi-electron reactions of counter cations in active materials of fluoride compounds. However, it is far from practical use because there is no solid electrolyte which has high ionic conductivity and a wide electrochemical potential window like lithium-ion conductors. The previously reported fluoride-ion conductors such as PbSnF4 [2] and La0.9Ba0.1F2.9 [3] contain single carrier ion, fluoride ions. To our best knowledge, there is few report on the solid electrolyte materials containing multiple-anion compounds [4].In the field of material sciences, mixed-anion compounds have recently attracted attention, and unique structures with multiple anions have been reported [5]. Compared with existing materials such as oxides and fluorides, mixed-anion compounds have the possibilities to exhibit innovative functions due to their specific crystal and coordination structure. Therefore, using multiple-anion compounds could realize much higher physical properties than ever before.In this study, we synthesized La-Sr-F-S compounds containing fluoride and sulfides ions as anions by solid-state reaction under vacuum. The crystal structure of the synthesized compound was characterized by X-ray diffraction. In order to measure the conductivity and the fluoride-ion transport number of the synthesized compounds, electrochemical impedance spectroscopy and the DC conductivity measurement were performed, respectively. Moreover, cyclic voltammetry was performed to evaluate electrochemical potential window. In the synthesis, F－- deficient and F－-excess type of La-Sr-F-S compounds were successfully synthesized by controlling the weight ratio of starting materials. We discuss the mechanism to realize fast fluoride ion conduction comparing them.Reference:[1] M.A. Reddy and M. Fichitner, J. Mater. Chem, 21, 17059–17062 (2011).[2] N. I. Sorokin, P. P. Fedorov, O. K. Nikol’skaya, O. A. Nikeeva, E. G. Rakov, and E. I. Ardashinikova, Inorg. Chem., 37, 1178-1182 (2017)[3] C. Rongeat, M. A. Reddy, R. Witter, and M. Fichtner, ACS Appl. Mater. Interfaces, 6(3), 2103-2110 (2014).[4] S. Mater, J. Reau, L. Rabardel, G. Demazeau, and P. Hagenmuller, Solid State Ionics, 11, 77-81(1983).[5] H. Kageyama, K. Hayashi, K. Maeda, J.P. Attfield, Z. Hiroi, J.M. Rondinelli, and K.R. Poeppelmeier, Nature Comm., 9 772(2018)

Effect of Ta-Doping on LLZO Garnet Solid Electrolytes for Solid State Batteries Applications

Compared with conventional lithium-ion batteries, all-solid-state lithium batteries based on inorganic solid electrolytes have shown advantages over conventional lithium-ion batteries, such as explosion resulted from flammable liquid electrolyte, low energy density. Therefore, solid state batteries are considered a promising candidate with better safety features. Among oxide electrolytes, garnet-type LLZO electrolyte exhibits high ionic conductivity and electrochemical potential window. However, it is reported that there are difficulties to prepare Li7La3Zr2O12(LLZO) pellets with high relative density. In this study, LLZO containing Ta ion as a dopant is expected to show more Li vacant sites to enhance its conductivity and density. The LLZO powder calcined at 1200 °C with a cubic phase was confirmed by X-ray diffraction (XRD). The sintered Ta-LLZO pellets exhibit relative density of 88.45% and ionic conductivity of 1.04*10-4 S/cm at room temperature and good electrochemical stability with Li metal. After assembling LiCoO2/Ta-LLZO/Li battery, the discharge capacity reached 105.2 mAh/g for the first cycle.

1-Butyl-3-Methylimidazolium Tetrafluoroborate Ionic Liquid As an Electrolyte for Electrochemical Reduction of Nitrous Oxide.

Nitrous oxide (N2O), of which global warming potential is 310 times of CO2, is a powerful greenhouse gas [1]. The concentration of N2O has increased steadily from various agricultural and industrial activities such as cultivating crops in low-pH soil and manufacturing semiconductor devices [2,3]. Therefore, the importance of studying N2O reduction is emphasized. Thermal decomposition methods focusing on thermal catalyst have been reported, but there are limits such as process temperature and low efficiency [4,5]. Electrochemical reduction of N2O can be an attractive method since it is conducted at low temperatures and has low energy consumption. However, in aqueous solutions, the electrochemical reduction of N2O inevitably accompanies hydrogen evolution reaction (HER), which is the main side reaction. There were many trials to reduce HER through metal and metal oxide catalysts, but they also had limits in terms of efficiency and high cost of noble metal materials [6-9]. Ionic liquids are promising electrolytes in gas reduction field replacing water because they can avoid hydrogen evolution and enhance the solubility of gaseous reactants. Some imidazolium-based ionic liquids were adopted to electrochemical reduction of CO2 because of their favorable properties such as wide electrochemical potential window and high CO2 dissolution capacity [10,11]. Cations of ionic liquids are known to accept oxygen from CO2, and then return to initial state at counter electrode emitting oxygen [12]. According to the same principle, ionic liquids may also be suitable for the electrochemical reduction of N2O.In this study, an ionic liquid/organic solvent mixture was adopted as an electrolyte for the electrochemical reduction of N2O. The ionic liquid and organic solvent used for electrolyte were 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) and propylene carbonate (PC), respectively. The use of [BMIM][BF4] in place of aqueous solutions could improve the solubility of N2O and also avoid the hydrogen evolution reaction, which is the main side reaction in an aqueous solution.Herein we observed the difference of LSV curves in aqueous solution and [BMIM][BF4]. Hydrogen evolution reaction was excluded, but the low current density was obtained in [BMIM][BF4]. The low electrical conductivity and high viscosity of [BMIM][BF4], the main disadvantages in the context of electrochemical reactions, were compensated on introducing PC. We measured the viscosity and electrical conductivity in various [BMIM][BF4]/PC composition, and the composition of the [BMIM][BF4]/PC was optimized considering both the electrical conductivity and N2O stability in the solution. The current and faradaic efficiency could be evaluated during chronoamperometry in aqueous solution and [BMIM][BF4]/PC. For the optimized [BMIM][BF4]/PC, high current efficiency and faradaic efficiency (>90%) were achieved for N2O reduction to N2.Figure captionsFigure 1. LSV curves for Cu electrode in (a) 0.3 M K2SO4 aqueous solution and (b) [BMIM][BF4]. The scan rate was 50 mV s-1.Figure 2. (a) Viscosity (black line) and conductivity (blue line) changes for [BMIM][BF4]/PC according to [BMIM][BF4] content (b) Current efficiency–time curves recorded at –1.3 V vs. SCE in 0.3 M K2SO4 aqueous solution (blue line) and at –2.27 V vs. Fc/Fc+ in 75 vol% [BMIM][BF4] (red line).

Identification of the Active Chemical Species in the Sulfone Based Electrolyte for Rechargeable Aluminum Batteries

Introduction The Li-ion battery is the most dominant as practical rechargeable batteries because of its high energy density, high power density, and high cyclability. However, the energy density of the Li-ion battery is not sufficient for the electric vehicle (EV), which can realize the practical driving range as long as classical gasoline and the internal combustion engine system. Multivalent cation batteries are considered as one of the most promising next-generation power sources for mobile electric devices and EVs. The Al electrode has the highest volumetric energy density (8042 mAh cm-3), which is 4-fold higher than the Li metal electrode (2060 mAh cm-3). Therefore, the rechargeable Al battery has the possibility for the high energy density power sources for EVs. Moreover, Al metal is safer than Li metal because of its high melting point and has higher reserves on the earth than Li. Even though there are several advantages of the rechargeable Al battery, such as high energy density, high safety, and low cost, however, it is difficult to realize rechargeable Al battery because of two factors. The first one is the positive electrode material that can store the Al trivalent cation which strongly adsorb to the positive electrode materials reducing the cyclability of the battery. The second one is the electrolyte solution, which can reversibly deposit/strip Al metal. There are several amounts of researches about rechargeable Al battery, however, almost all of those researches used the solution of AlCl3 in the ionic liquid, 1-ethyl-3-methylimidazolium chloride, as an electrolyte solution. The ionic liquid show excellent reversibility for the Al metal deposit/strip reaction and the active species in the electrolyte solution was already identified as Al2Cl7. We have used the solution of AlCl3 in dipropylsulfone (DPSO2) as the electrolyte solution of the rechargeable Al battery. Here, we tried to identify the active chemical species of the solution of AlCl3 in DPSO2 to understand the difference between our electrolyte solution for rechargeable Al battery and conventional ionic liquid-based electrolyte.Experimental All electrochemical experiments were measured with a glass cell. Mo plates (1.3 × 1.3 cm2) were used as working electrode and current collector. An Al plate (10 mm in diameter) and wire were used as the counter and reference electrodes for three-electrode configuration. A glass fiber filter was used as separator.Results & discussion Figure 1(a) shows the 27Al NMR results of the electrolyte containing different ratios of AlCl3 and DPSO2. Four different Al chemical species (AlCl4 -, Al2Cl7 -, AlCl3-DPSO2, and Al(DPSO2)3) were detected, and we analyzed the ratio of each chemical species in the electrolyte containing different ratios of AlCl3 and DPSO2 (Fig. 1b). AlCl4 - is known as inactive for the electrochemical reaction; therefore, we investigated the remaining three species. Figure 1c shows the CV results of each electrolyte solution. We analyzed the CV result from three different points of view; over voltage for Al deposition, over voltage for Al stripping, and the electrochemical window. The electrolyte with the ratio of AlCl3: DPSO2: toluene = 1: 10 (2): 5, which was mainly consisted of Al(DPSO2)3, show small over voltage for deposition/stripping of Al and wide electrochemical window. The electrolyte with the ratio of AlCl3: DPSO2: toluene = 1: 1.1 (1): 5, which mainly consisted of AlCl3-DPSO2, show large over voltage for deposition/stripping of Al and narrow electrochemical window. The electrolyte with the ratio of AlCl3: DPSO2: toluene = 1: 0.9: 5, which mainly consisted of Al2Cl7 -, which is the same as the ionic liquid-based electrolyte solution, show small over-voltage for deposition of Al, large over voltage for the Al stripping, and narrow electrochemical potential window. These results suggested the superiority of the chemical species of Al(DPSO2)3 and our electrolyte solution of AlCl3: DPSO2: toluene = 1: 10: 5, compared with the ionic liquid-based electrolyte solution, which containing Al2Cl7 - as active species. Figure 1

Electrodeposition of Palladium Nanoparticles on Carbon Nanotubes Dispersed in an Ionic Liquid

Electrodeposition of palladium nanoparticles (PdNPs) was investigated on single walled carbon nanotubes (SWCNTs) or few walled carbon nanotubes (FWCNTs) dispersed in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) containing [PdBr4]2 -. Ionic liquids have been expected to be alternative electrolytes for electrodeposition of various metals and alloys because of such unique characteristics as wider electrochemical potential window, negligible vapor pressure, less flammability, and wider usable temperature range, compared with conventional organic electrolytes. In addition, the ionic liquids have been known to have ability to disperse nanoparticles without any additives[1]. Although several studies have reported the preparation of metal nanoparticles by electrochemical cathodic reduction in ionic liquids, there are some problems in the utilization of the nanoparticles dispersed in ionic liquids. Platinum nanoparticles (PtNPs) prepared in ionic liquids have been reported to be collected on such carbon materials as carbon nanotubes (CNTs) and carbon black with elevating temperature[2,3]. It has been reported that CNTs are dispersed in ionic liquids and act as an electrode[4]. We have already reported the electrodeposition of PtNPs is possible on CNTs dispersed in BMPTFSA containing [PtBr4]2–[5]. The average particle size of the PtNPs was 1.7 nm, which was independent on the concentration of [PtBr4]2– and the kind of CNTs. In the present study, the electrodeposition of PdNPs was investigated on SWCNTs and FWCNTs dispersed in BMPTFSA containing [PdBr4]2– in order to examine the effect of the deposition potential on the average particle size of PdNPs because the deposition potential of Pd is more positive than that of Pt[3,6]. In addition, the effect of the catalyst remaining in CNTs on electrodeposition of PdNPs was examined using high purity (> 99.6% purity) FWCNT synthesized by the fluidized bed method[7].Galvanostatic cathodic reduction was conducted in BMPTFSA containing CNTs and [PdBr4]2– at room temperature, resulted in deposition of NPs, which were identified as metallic Pd by energy dispersive X-ray analysis (EDX) and transmission electron mocroscopy (TEM). The average potential of [PdBr4]2– during the galvanostatic cathodic reduction was –1.2 V, which was close to that reported on a planar glassy carbon electrode[6]. Potentiostatic cathodic reduction at different potentials indicated that the average particle size of PdNPs decreased with lowering the potential. Pd nuclei are considered to occur and grow on the CNTs dispersed in the ionic liquid. As the potential becomes more negative, the cations of the ionic liquid are expected to be accumulated on the surface of the nuclei and CNTs in order to compensate the excess negative charge. The cations strongly attracted on the surface are considered to inhibit the growth of the PdNPs and affect their average particle size. On the other hand, the remaining catalyst in the CNTs was found to have little effect on the average particle size of PdNPs.

Suppressive Effect of Fe Cations on Oxidative Electrolyte Decomposition for Magnesium Rechargeable Batteries

Magnesium rechargeable batteries (MRBs) have attracted considerable attention since Aurbach et al. first proposed the prototype.1 Magnesium (Mg) can be used as the active material in the negative electrode, and has a high theoretical capacity (2205 mAh g-1) and volumetric capacity (3833 mAh cm- 3), the lowest standard electrode potential (−2.36 V vs. standard hydrogen electrode) among metals useable in air, and a relatively low tendency to form dendrites.2,3 Recently, several kinds of active materials that can be used as positive electrodes have been proposed to enhance the energy density of MRBs. As described in a previous report, we have demonstrated that the Mg spinel oxide, MgCo2O4, undergoes an Mg2+ ion insertion/extraction at a relatively high potential (~2.9 V vs. Mg/Mg2+).4 In addition, spinel oxides such as MgMn2O4, MgFe2O4, MgCr2O4, and Co3O4 have also been investigated, with promising results.Although the stability of the electrolytes has been considerably improved,5 the present electrolytes are more or less anodically decomposed on the surface of the positive electrode above ~3 V vs. Mg/Mg2+. This is insufficient for the charge (oxidation) of the positive electrode active materials with redox potentials higher than ~2.5 V vs. Mg/Mg2+. Previous studies concerning electrolytes and positive electrode active materials indicate that the variation in the active material type changes the anodic current associated with the oxidative electrolyte decomposition. Therefore, in the present study, we investigate the catalytic activity of the transition metal ions in the Mg spinel oxides for anodic electrolyte decomposition, specifically by replacing the Mn ions in MgMn2O4 and Co ions in MgCo2O4 with Fe.6 Cyclic voltammograms for Mg(Mn1 - xFex)2O4 were measured using a three-electrode cell at a scan rate of 25 μV s- 1 in the potential range of 1.0–3.2 V vs. Mg/Mg2+, as shown in Fig. 1. In all cyclic voltammograms, the anodic current due to the oxidative decomposition of the electrolyte was observed at potentials more positive than 2.9 V vs. Mg/Mg2+. The current decreases with increasing Fe content in Mg(Mn1 - xFex)2O4. Thus, Fe cations are catalytically less active than Mn in the oxidative decomposition of the electrolyte. Using the low catalytic activity of the Fe ions for the oxidative electrolyte decomposition, we demonstrated that the cyclability of MRBs could be significantly improved by suppressing the anodic electrolyte decomposition. In the presentation, we will demonstrate that Fe in Mg(Co1 - xFex)2O4exhibits a similar effect on the suppression of the oxidative electrolyte decomposition.In conclusion, although suitable electrolytes for MRBs with a sufficiently wide electrochemical potential window remain unavailable, we expect our results to constitute a new approach to improve battery performance independent of electrolyte stability.References Aurbach, Z. Lu, A. Schechter, Y. Gofer, H. Gizbar, R. Turgeman, Y. Cohen, M. Moshkovich, and E. Levi, Nature, 407 724–727 (2000).Matsui, Study on electrochemically deposited Mg metal, J. Power Sources, 196, 7048–7055 (2011).Yagi, A. Tanaka, T. Ichitsubo, and E. Matsubara, ECS Electrochem. Lett., 1(2), D11–D14 (2012).Okamoto, T. Ichitsubo, T. Kawaguchi, Y. Kumagai, F. Oba, S. Yagi, K. Shimokawa, N. Goto, T. Doi, and E. Matsubara, Adv. Sci., 1500072 (2015).Mandai, K. Tatesaka, K. Soh, H. Masu, A. Choudhary, Y. Tateyama, R. Ise, H. Imai, T. Takeguchi, K. Kanamura, Phys. Chem. Chem. Phys., 21, 12100–12111 (2019).Han, S. Yagi, and T. Ichitsubo, J. Power Sources, 435, 226822 (2019). Figure 1

Silicon Nanoparticles in Li-Ion Batteries: Understanding the Role or Particle Size, Surface Oxidation, and Processing Conditions on Composite Electrode Longevity

The high theoretical gravimetric charge density (4200 mAhr g-1), low lithium storage voltage (0 – 0.4 V vs Li metal), elemental abundance, and existing expertise in manufacturing make silicon a promising candidate as an anode material for next generation lithium ion battery (LIB) technology. However, broad adoption of silicon is limited by the rapid electrode failure associated with irreversible process related to repeated charge and discharging. Because of the extreme volume changes of the silicon active material with lithium alloying (~300% at Li3.75Si) the electrode experiences large mechanical stressors. In addition, the highly reducing environment upon lithium silicide formation forces chemical reactions between the active material and electrolyte and other electrode components which result in a heterogeneous interfacial layer called the silicon-electrolyte-interphase (SEI). The role and composition of the SEI is complex, however, the SEI is hypothesized to passivate the Si surface against additional parasitic reactions but is also prone to mechanical degradation from repeated cycling. These aspects of lithium storage in silicon slow the on-ramp of silicon in LIB anodes.To begin to alleviate these irreversible processes in silicon-based electrodes we study the effect of silicon particle size, processing conditions, and electrolyte formulation on the electrode’s cycle stability, rate capability, and calendar life. We find that upon exposure to water, all silicon in our single-nanometer scale particles are oxidized to SiO2, which, we show, has no reversible lithiation capacity in the electrochemical potential window of normal silicon lithiation. We find a very strong relationship between the silicon particle size and the cycle stability, where, smaller silicon particles show a profound improvement on the capacity retention, but, due to the high surface area-to-volume ratio, also have an increased rate of reaction with the electrolyte. These results help to build a more comprehensive understanding on the role the electrode processing conditions and silicon particle size, and provide a foundation for additional work to improve the longevity of silicon in lithium ion battery devices.