Low Electrolyte Concentrations Research Articles

Measurement of the double-layer capacitance of Pt(111) in acidic conditions near the potential of zero charge

Quantifying the charge density stored at the Pt(111)/aqueous interface using the double-layer capacitance close to the potential of zero charge (Cdl,PZC) at 0.30 VNHE is of critical importance to elucidating the structure of the electrical double layer (EDL) in the absence of any competing adsorption processes. Marked discrepancies in the values of Cdl for this interface exist in the literature, which we show are likely attributable to the measurement technique used. To directly observe the predicted Gouy-Chapman capacitance minimum at the PZC in the double-layer window between 0.40-0.55 VRHE, anomalously low electrolyte concentrations (0.1 mM HClO4) are needed. The measurement of accurate values of Cdl,PZC is made highly non-trivial by the extremely large solution resistances (∼80-100 kΩ) measured in this required dilute electrolyte as well as the non-negligible deviations from ideal capacitive behaviour (i.e., constant phase element behaviour) displayed even by this well-ordered model electrochemical system. We provide here a comparison between using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and alternating current-cyclic voltammetry (AC-CV) in determining Cdl,PZC for the Pt(111)/HClO4 interface, for different concentrations of the electrolyte. In particular, even when using optimized experimental parameters, we show that the estimated values of Cdl,PZC at 0.1 mM HClO4 still display a marked discrepancy depending on the technique used, ranging from 27-41 μF cm−2. At higher HClO4 concentrations, the discrepancies are much less pronounced. Importantly, however, the measured deviation from Gouy-Chapman theory, as quantified by the Parsons-Zobel plot slope, remains consistent across these techniques, implying that the EDL structure of the Pt(111)/aqueous interface continues to prove anomalous and enigmatic.

Salt gradient enhanced sensitivity in nanopores for intracellular calcium ion detection

Intracellular calcium ion detection is of great significance for understanding the cell metabolism and signaling pathways. Most of the current ionic sensors either face the size issue or sensitivity limit for the intracellular solution with high background ion concentrations. In this paper, we proposed a calmodulin (CaM) functionalized nanopore for sensitive and selective Ca2+ detection inside living cells. A salt gradient was created when the nanopore sensor filled with a low concentration electrolyte was in contact with a high background concentration solution, which enhanced the surface charge-based detection sensitivity. The nanopore sensor showed a 10 × sensitivity enhancement by application of a 100-fold salt gradient, and a detection limit of sub nM. The sensor had a wide detection range from 1 nM to 1 mM, and allowed for quick calcium ion quantification in a few seconds. The sensor was demonstrated for intracellular Ca2+ detection in A549 cells in response to ionomycin.

Nitrous acid electroreduction on macroporous silver foam

In this paper, silver 3D foams have been synthesized using dynamic hydrogen bubble template and thiocyanate-based deposition bath. The material was used as electrocatalyst for nitrous acid (HNO2) reduction. On this material, we found that overpotential of nitrous acid reduction is decreased by at least 300 mV and the in situ formed nitric oxide (NO) reduction becomes the predominant step when the potential is decreased even further, comparing to flat silver polycrystalline electrode. Another difference between this material and the silver polycrystalline electrode concerns the influence of the nature of supporting electrolyte on the preferred reaction. Precisely, while Ag polycrystalline is preferentially reducing HNO2 into NO in low concentration of perchlorate electrolyte, Ag foam preferentially reduces the in situ formed NO into N2O, in all tested electrolytes, if the same potential range is considered. The initial reduction of HNO2 into NO is better evidenced after the partial removal of thiocyanate species. Finally, the use of isotope 15N in the nitrite salt and of a flow thin layer cell enabled the detection of nitrogen among other gaseous products for both silver foam and flat silver electrode.

Influence of alternating electric field on electrorheological effect of aqueous dispersions of stevensite

Upon deionization of the aqueous dispersion of stevensite, a type of smectite clay minerals, a low-viscosity colorless transparent dispersion is obtained. The phenomenon known as the electrorheological (ER) effect has been previously reported when a weak electric field of several V/mm is applied to the stevensite aqueous dispersion. In this study, the influence of the waveform and frequency of the electric field was investigated while keeping the electric field intensity constant. It was observed that as the acceleration of the applied electric field intensity increased, the stress response to the electric field improved. Increasing the frequency of the electric field led to a reduction in the induced stress; however, it improved the response rate of stress. It has been indicated that even at higher electric field frequencies, the potential for observing the ER effect exists with higher electric field intensities. Maintaining a low electrolyte concentration may facilitate the development of novel ER fluids capable of instantaneously responding to the application or removal of electric fields.

Monolithic Interphase Enables Fast Kinetics for High-Performance Sodium-Ion Batteries at Subzero Temperature.

In spite of the competitive performance at room temperature, the development of sodium-ion batteries (SIBs) is still hindered by sluggish electrochemical reaction kinetics and unstable electrode/electrolyte interphase under subzero environments. Herein, a low-concentration electrolyte, consisting of 0.5M NaPF6 dissolving in diethylene glycol dimethyl ether solvent, is proposed for SIBs working at low temperature. Such an electrolyte generates a thin, amorphous, and homogeneous cathode/electrolyte interphase at low temperature. The interphase is monolithic and rich in organic components, reducing the limitation of Na+ migration through inorganic crystals, thereby facilitating the interfacial Na+ dynamics at low temperature. Furthermore, it effectively blocks the unfavorable side reactions between active materials and electrolytes, improving the structural stability. Consequently, Na0.7Li0.03Mg0.03Ni0.27Mn0.6Ti0.07O2//Na and hard carbon//Na cells deliver a high capacity retention of 90.8 % after 900 cycles at 1C, a capacity over 310 mAh g-1 under -30 °C, respectively, showing long-term cycling stability and great rate capability at low temperature.

Slow sustained releasing LiNO3 from graphite electrode reservoir to regulate solvation structure and stabilize interface

The high de-solvation energy derived from the solvent-rich Li+ solvation sheath and the resultant porous organic-rich electrode/electrolyte interface has hindered the commercialization of low-concentration electrolytes (LCEs). Here, unlike the common method so far reported, we invent an approach of sustained releasing LiNO3 from the graphite (Gr) anode reservoir to optimize the solvation structure and form a stable interface in LCEs. The solubility limit can be overcome by introducing LiNO3 directly in the Gr slurry. Moreover, the stronger binding energy between NO3– and Li+ drives NO3– enter the Li+ solvation sheath, weakening the shielding effect of solvent on Li+, and surprisingly increasing the coordination of PF6- to Li+. Thermodynamically, the corresponding lowest unoccupied molecular orbital energy levels of anions decrease, reducing the de-solvation energy of Li+ and forming a Li3N&LiF-rich solid electrolyte interface (SEI). This inorganic-rich SEI demonstrates advantages of inhibiting the decomposition of solvent and facilitating the transmission of Li+. As a result, the cell with Gr anode containing 1 wt% LiNO3 exhibits superior cycle performance in LCE, almost no degradation within 200 cycles, even higher than that in conventional concentration electrolyte. More importantly, the continuous consumption of NO3– in turn promotes its sustained redissolution from the anode, constituting a virtuous circle of regulating solvation structure, stabilizing interface and improving battery performance. This work blazes a new trail to revive lithium salt additives with low solubility, and expands the design strategy and application prospect of LCEs by building the bridges between regulating the solvation structure and constructing favorable electrode/electrolyte interface.

To achieve fast ion transport of engineered electrolyte and ultra-high rate of defected Nb16W5O55-based anode

The maximum output power and minimum charge time of a lithium-ion battery depend on ion transport and electron transport. The electron conduction/ion diffusion within the electrochemically active materials and the ion mobility of the electrolyte usually represent the fundamental limits of the battery charge and discharge rates. Nb16W5O55 is notable for its exceptional lithium-ion mobility and high electronic conductivity, making it a popular choice for fast-charging anode materials. However, the lithium-ion diffusion capability of the electrolyte is also crucial in determining the overall fast-charging performance of the battery. This can be a limiting factor for Nb16W5O55-based batteries. This work delves into the impact of electrolyte composition on fast-charging performance by examining the electrochemical properties of electrolytes with varying concentrations, in conjunction with molecular dynamics simulation. Specifically, increasing the concentration of LiTFSI salt alters the solvation structure of lithium ions due to the increasing coordination numbers of TFSI− and Li+, which hampers lithium-ion diffusion. Additionally, low-concentration electrolytes struggle with rapid mass transfer due to fewer lithium-ion carriers, limiting ultra-high-rate performance. To address these challenges, the solvation structure of the electrolyte was optimized, leading to enhanced fast-charging and discharging performance.

Sensitive determination of iodide at graphitic carbon nitride-chitosan composite modified screen-printed electrode in urine and salt using cathodic stripping voltammetry

Iodide is an important constituent in various biological processes; hence its determination is important. A simple voltammetric method has been investigated for iodide determination using disposable screen-printed electrode modified with graphitic carbon nitride-chitosan composite (gCN-Chit/SPE). The sensor presented excellent electrocatalytic response towards iodide sensing. The SEM analysis of the modified electrode showed a rough and sheet like morphology. The EDX analysis showed the high content of nitrogen elements in the composite layer of the modified electrode which is crucial for iodide ion sensing. Various parameters such as electrolyte concentration, deposition potential, deposition time etc. were optimized for iodide sensing. The use of low concentration of electrolyte favored the electro-oxidation of iodide. Under the suitable experimental conditions, the gCN-Chit/SPE exhibited good linear performance for iodide in the concentration range from 0.075 to 200 µM with a regression coefficient (R2) of 0.9946 and the limit of detection (LOD) of 0.01 µM. The electrode presented interference free effect for iodide in the presence of relatively high concentration of other substances. The sensor was applied to determine iodide in real samples such as urine, tap water and table salt. In real sample analysis good recoveries in percent was achieved using the developed electrode. Further, the composite layer at the electrode surface provided good mechanical stability and thus could be reused for several determinations. The results confirmed that the design electrochemical sensor could be successfully employed for real sample applications with highly sensitive iodide determination.

Fluorinated solvent molecule tuning to improve electrochemical performances of low-concentration electrolyte

The development of low-concentration electrolyte has a favorable application prospect due to its advantages of saving lithium resources. However, the large-scale application is limited by the formation of high-impedance organic electrode/electrolyte interphase (EEI) and the higher desolvation energy of Li+. Herein, a mixed flurorinated solvents of ethyl difluoroacetate (2F) / ethyl trifluoroacetate (3F) (3:7, in volume ratio) is designed to adjust the interaction between Li+ and the solvents, so as to achieve performance improvements of the low-concentration electrolyte system containing 0.5 M LiPF6. Results shows that 2F solvent greatly weakens the interaction between Li+ and the solvents, and 3F solvent further promotes anions to enter the solvation sheath to form Li(2F)3.0(PF6−)2.3(3F)0.5 structure. It promotes the Li+ desolvation, and brings about the formation of a LiF-rich cathode-electrolyte interface film on the surface of LiFePO4 (LFP) cathode due to the HOMO of the 2F solvent in the solvation sheath of Li+ will be increase as the involvement of PF6− in the solvation sheath of Li+. As a result, the cycling stability and rate performance (130 mAh g−1 at 4 C) of the LFP/Li half-cell are significantly improved. This work provides a new strategy to improve the electrochemical performances of low-concentration electrolytes by fluorinated solvent molecule tuning.

The Effect of Lysozyme on the Aggregation and Charging of Oxidized Carbon Nanohorn (CNHox) in Aqueous Solution

To clarify the effect of proteins on the charging and aggregation–dispersion characteristics of oxidized carbon nanohorn (CNHox), we measured the electrophoretic mobility and stability ratios as a function of concentrations of a model protein, lysozyme (LSZ), and KCl. The zeta potential from the electrophoretic mobility of CNHox was neutralized and reversed by the addition of oppositely charged LSZ. Electrical and hydrophobic interactions between CNHox and LSZ can be attributed to the adsorption and charge reversal of CNHox. The stability ratio of CNHox in the presence or absence of LSZ showed Derjaguin–Landau and Verwey–Overbeek (DLVO) theory-like behavior. That is, the slow aggregation regime, fast aggregation regime, and critical coagulation concentration (CCC) were identified. At the isoelectric point, only the fast aggregation regime was shown. The existence of patch-charge attraction due to the charge heterogeneity on the surface was inferred to have happened due to the enhanced aggregation of CNHox at high LSZ dosage and low electrolyte concentration. The relationship between critical coagulation ionic strength and surface charge density at low LSZ dosage showed that the aggregation of CNHox is in line with the DLVO theory. An obvious decrement in the Hamaker constant at high LSZ dosage can probably be found due to an increased interaction of LSZ-covered parts.

The Construction of Anion-Induced Solvation Structures in Low-concentration Electrolyte for Stable Zinc Anodes.

Aqueous zinc-ion batteries (ZIBs) are promising large-scale energy storage devices because of their low cost and high safety. However, owing to the high activity of H2O molecules in electrolytes, hydrogen evolution reaction and side reactions usually take place on Zn anodes. Herein, additive-free PCA-Zn electrolyte with capacity of suppressing the activity of free and solvated H2O molecules was designed by selecting the cationophilic and solventophilic anions. In such electrolyte, contact ion-pairs and solvent-shared ion-pairs were achieved even at low concentration, where PCA- anions coordinate with Zn2+ and bond with solvated H2O molecules. Simultaneously, PCA- anions also induce the construction of H-bonds between free H2O molecules and them. Therefore, the activity of free and solvated H2O molecules is effectively restrained. Furthermore, since PCA- anions possess a strong affinity with metal Zn, they can also adsorb on Zn anode surface to protect Zn anode from the direct contact of H2O molecules, inhibiting the occurrence of water-triggered side reactions. As a result, plating/stripping behavior of Zn anodes is highly reversible and the coulombic efficiency can reach to 99.43 % in PCA-Zn electrolyte. To illustrate the feasibility of PCA-Zn electrolyte, the Zn||PANI full batteries were assembled based on PCA-Zn electrolyte and exhibited enhanced cycling performance.

Metal‐free two‐dimensional phosphorene‐based electrocatalyst with covalent P–N heterointerfacial reconstruction for electrolyte‐lean lithium–sulfur batteries

AbstractThe use of lithium–sulfur batteries under high sulfur loading and low electrolyte concentrations is severely restricted by the detrimental shuttling behavior of polysulfides and the sluggish kinetics in redox processes. Two‐dimensional (2D) few layered black phosphorus with fully exposed atoms and high sulfur affinity can be potential lithium–sulfur battery electrocatalysts, which, however, have limitations of restricted catalytic activity and poor electrochemical/chemical stability. To resolve these issues, we developed a multifunctional metal‐free catalyst by covalently bonding few layered black phosphorus nanosheets with nitrogen‐doped carbon‐coated multiwalled carbon nanotubes (denoted c‐FBP‐NC). The experimental characterizations and theoretical calculations show that the formed polarized P–N covalent bonds in c‐FBP‐NC can efficiently regulate electron transfer from NC to FBP and significantly promote the capture and catalysis of lithium polysulfides, thus alleviating the shuttle effect. Meanwhile, the robust 1D‐2D interwoven structure with large surface area and high porosity allows strong physical confinement and fast mass transfer. Impressively, with c‐FBP‐NC as the sulfur host, the battery shows a high areal capacity of 7.69 mAh cm−2 under high sulfur loading of 8.74 mg cm−2 and a low electrolyte/sulfur ratio of 5.7 μL mg−1. Moreover, the assembled pouch cell with sulfur loading of 4 mg cm−2 and an electrolyte/sulfur ratio of 3.5 μL mg−1 shows good rate capability and outstanding cyclability. This work proposes an interfacial and electronic structure engineering strategy for fast and durable sulfur electrochemistry, demonstrating great potential in lithium–sulfur batteries.

A Carbonyl and Azo-Based Polymer Cathode for Low-Temperature Na-Ion Batteries.

Due to flexible structure tunability and abundant structure diversity, redox-active polymers are promising cathode materials for developing affordable and sustainable Na-ion batteries (NIBs). However, polymer cathodes still suffer from low capacity, poor cycle life, and sluggish reaction kinetics. Herein, we designed and synthesized a polymer cathode material bearing carbonyl and azo groups as well as extended conjugation structures in the repeating units. The polymer cathode exhibited exceptional electrochemical performance in NIBs in terms of high capacity, long lifetime, and fast kinetics. When coupled with a low-concentration electrolyte, it shows superior performance at low temperatures down to -50 °C, demonstrating great promise for low-temperature battery applications. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) were employed to study the reaction mechanism, interphase structure, and morphological evolution, confirming reversible redox reactions between azo/carbonyl groups in the polymer and Na+/electrons, a NaF-rich interphase, and high structure stability upon cycling. This work provides an effective approach to developing high-performance polymer cathodes for affordable, sustainable, and low-temperature NIBs.

Transformations in crystals of DNA-functionalized nanoparticles by electrolytes.

Colloidal crystals have applications in water treatments, including water purification and desalination technologies. It is, therefore, important to understand the interactions between colloids as a function of electrolyte concentration. We study the assembly of DNA-grafted gold nanoparticles immersed in concentrated electrolyte solutions. Increasing the concentration of divalent Ca2+ ions leads to the condensation of nanoparticles into face-centered-cubic (FCC) crystals at low electrolyte concentrations. As the electrolyte concentration increases, the system undergoes a phase change to body-centered-cubic (BCC) crystals. This phase change occurs as the interparticle distance decreases. Molecular dynamics analysis suggests that the interparticle interactions change from strongly repulsive to short-range attractive as the divalent-electrolyte concentration increases. A thermodynamic analysis suggests that increasing the salt concentration leads to significant dehydration of the nanoparticle environment. We conjecture that the intercolloid attractive interactions and dehydrated states favour the BCC structure. Our results gain insight into salting out of colloids such as proteins as the concentration of salt increases in the solution.

Interface regulation of the Zn anode by using a low concentration electrolyte additive for aqueous Zn batteries.

The Zn metal anode in aqueous Zn batteries faces a number of challenges including instable deposition and corrosion issues. Here, we present an interface environment regulation for a Zn electrode with a low concentration electrolyte additive of 0.1 m 3-aminobenzenesulfonic acid (ASA). ASA prefers to adsorb on the Zn surface over water and creates an ASA-rich interface. It further enters the Zn2+ solvation sheath locally, which shifts the lowest unoccupied molecular orbital from solvated water to ASA. The hydrogen evolution reaction from solvated water reduction is inhibited, and the reduction of solvated ASA generates a stable solid-electrolyte interphase composed of the ion conductor ZnS covered by organic-inorganic mixed components. With the resulting homogenized Zn deposition, continuous Zn stripping in symmetric cells reaches 99.7% depth of discharge (DOD) at a current density of 2 mA cm-2, whereas cell short-circuit takes place at 11.4% DOD in the ASA free ZnSO4 electrolyte. The repeated stripping/plating also realizes 1100 h cycle life at 2 mA cm-2, and a 99.54% stabilized coulombic efficiency is obtained for 500 cycles at 10 mA cm-2.

Effect of low concentration electrolytes on the formation and corrosion resistance of PEO coatings on AM50 magnesium alloy

In this paper, the formation process, morphology, and electrochemical performance of PEO coatings on AM50 magnesium alloy prepared in low concentration phosphate, aluminate, and phosphate-aluminate electrolytes were systematically studied. The results show that the coatings prepared from the phosphate electrolytes have a higher thickness and better corrosion resistance properties compared to the other electrolytes. The coatings prepared from low concentration phosphate-aluminate mixed electrolytes have slightly thinner thickness, a similar coating structure and an order of magnitude lower value of electrochemical impedance compared with phosphate electrolyte coatings. The Coatings prepared from low concentration aluminate electrolytes have the lowest thickness and the worst corrosion resistance properties which gets close to corrosion behavior of the bare AM50 under the same test conditions. Considering application, coatings prepared from single low concentration phosphate electrolytes and low concentration phosphate-aluminate electrolytes have greater potential than single low concentration aluminate coatings. However, reducing the electrolyte concentrations of coating forming ions too much has negative influence on the coating growth rate.

A low concentration electrolyte additive for constructing solid-electrolyte interphase on a Zn metal anode for aqueous batteries.

Zn metal anodes in aqueous batteries experience inhomogeneous deposition and corrosion issues. Herein, we introduced, at a low concentration, dioxane (DX) as an electrolyte additive to stabilize a Zn anode. The oxygen sites of DX endowed it with a strong affinity for Zn and Zn2+, resulting in its adsorption onto the Zn electrode surface and its coordination with Zn2+ locally. The Zn2+-DX species exhibited a decreased lowest unoccupied molecular orbital energy level relative to those of water-involved components. The DX additive not only inhibited side reactions but also generated a stable solid-electrolyte interphase on the Zn electrode, ensuring a uniform Zn deposition. As a result of including the additive, the cycle life of the Zn symmetric cell was extended from 99 h to 2100 h, and the coulombic efficiency in Zn//Cu cell reached 99.5%.

Developing diluted low-concentration electrolyte with a high anion-to-solvent ratio for high-voltage lithium metal batteries

The most positive surface potential (ESPmax) of a diluent can be taken as a descriptor for its anti-solvating power, which guides the rational design of diluted low-concentration electrolyte (DLCE) with a high anion-to-solvent ratio.

Nanoarchitectonics for a long-life and robust Na-ion battery at low temperature with Prussian blue cathode and low-concentration electrolyte

Na-ion batteries are considered as promising battery systems for large-scale energy storage. Although Na-ion batteries exhibit enhanced low-temperature cycling performance compared with lithium-ion batteries, there is still a great challenge to overcome for practical low-temperature applications. In this work, we propose a low-performance Na-ion battery composed of FeNi co-doped Mn-based Prussian cathode (FeNi-MnHCF) and a low-concentration electrolyte (0.5 mol L−1) containing a small amount of 2,2,2-trifluoroethyl acetate (ETFA, 1 wt%). The introduction of ETFA could decrease the viscosity, increase ionic conductivity and change the solvation structure of the electrolyte at low temperature. ETFA could also participate in constructing a uniform, stable, and Na-ion conductive CEI layer, enabling rapid Na-ion transport and effective protection of FeNi-MnHCF. The cells with the ETFA-contained electrolyte and FeNi-MnHCF cathode exhibit excellent rate capability and long cycle life at low temperature. When being cycled at −20 °C, the cell with ETFA could retain 92.1 % of the capacity after 1120 cycles at 1 C. The cell could also show stable cycling after overcharge to 4.8 V or overdischarge to 1.2 V at −20 °C. This work sheds light on the design of long-life and robust Na-ion batteries for sustainable energy storage at low temperature.

Effects of electrolyte type and concentration on the anodic oxidation of 4H-SiC (0001) in slurryless electrochemical mechanical polishing

Slurryless electrochemical mechanical polishing (ECMP) is a promising polishing method for SiC wafers. To achieve a high polishing efficiency, low surface roughness, low cost, and low environmental load, the effects of the electrolyte type and concentration on the anodic oxidation and ECMP of the 4H-SiC (0001) surface were investigated. It is confirmed that the anodic oxidation rate is mainly affected by the conductivity but not the type of electrolyte, and the electric conductivity affects the oxidation current that determines the anodic oxidation rate and performance. The anodic oxidation rate of the SiC surface was restricted by the conductivity at low electrolyte concentrations, and the anodic oxidation rate increased with increasing electrolyte concentration in this stage. The anodic oxidation rate decreased with increasing electrolyte concentration after the conductivity exceeded ∼0.1 S/m, owing to the increasing resistance of the generated oxide layer. Overall, the anodic oxidation uniformity of the SiC surface increased with increasing electrolyte concentration owing to the increasing anodic oxidation current density. The changes in material removal rate of ECMP with increasing electrolyte concentration were consistent with those of the anodic oxidation rate, while the surface roughness obtained by ECMP always decreased with increasing electrolyte concentration. This study provides a new way to improve the performance of slurryless ECMP.