Single Electrolyte Systems Research Articles

Characterization of the aluminium-air battery utilizing a polypropylene separator with corrosion inhibition ability

Battery energy storage systems are widely used in modern electronic devices and electric vehicles. Metal-air batteries are among the electrochemical energy storage systems that provide high energy density and eco-friendly solutions. Aluminium-air batteries hold a significant advantage with their high theoretical specific energy and have the potential to replace lithium-ion batteries in the future. In this study, the electrical performance and corrosion inhibition characteristics of a polypropylene-based single and dual electrolyte system for aluminium-air batteries were investigated experimentally. The study revealed that a polypropylene separator can reduce the corrosion of the aqueous aluminium-air battery system by up to 40 %, improving the anodic utilization efficiency to 93 %. Electrochemical impedance spectroscopy analysis was used to characterize the single and dual electrolyte aluminium-air battery and propose equivalent circuit models. Compared to 1 M KOH electrolyte in a single electrolyte system, the solution resistance of a dual electrolyte aluminium-air battery was reduced by about 40 % using a combination of 1 M of KOH electrolyte and 1 M of H2SO4. This reduction is attributed to the enhancement of the oxygen reduction reaction at the air cathode. A high KOH electrolyte concentration will increase the corrosion of the aluminium anode but can improve the battery’s voltage. At 3 M KOH electrolyte, the plateau voltage is recorded at about 0.6 V while the discharge time reached 44 min when using aluminium alloy 6061 as the anode. The battery model developed in this work provides a fundamental basis for predicting the performance of aluminium-air battery packs.

Study on the negative effects of low sodium hexametaphosphate concentration on MAO coating

In order to investigate the effect of electrolyte concentration on the wear resistance and corrosion resistance of the microarc oxidized ceramic coatings in a mixed electrolyte system, this study set up a silicate only electrolyte as the control group, and additionally set up a concentration gradient with the concentration of (NaPO3)6 as the variable, and prepared oxidized ceramic coatings on 1060 aluminum alloy. The surface morphology and microstructure of the coatings were observed by scanning electron microscopy, and the phase composition changes in the single electrolyte system and in the mixture were compared by X-ray diffraction mapping. The elemental composition and distribution of the prepared coatings under the mixture were also characterized by energy dispersive spectroscopy. Finally, the wear and corrosion resistance of the coatings were analyzed and studied by friction experiments and electrochemical results and the mechanism of the effect of the continuous addition of (NaPO3)6 on the coating properties was explained. The results show that the coating prepared at low concentration of (NaPO3)6 has poor tribological and corrosion resistance, even worse than the control group. In view of this phenomenon, the research is carried out and the corresponding explanation is made.

High performance aluminum-air battery for sustainable power generation

Metal-air battery is receiving vast attention due to its promising capabilities as an energy storage system for the post lithium-ion era. The electricity is generated through oxidation and reduction reaction within the anode and cathode. Among various types of metal-air battery, aluminum-air battery is the most attractive candidate due to its high energy density and environmentally friendly. In this study, a novel polypropylene-based dual electrolyte aluminum-air battery is developed. Polypropylene pads are used as a medium to absorb the electrolyte, isolate the anode and cathode, control the hydrogen generation in the parasitic reaction. Potassium hydroxide is used as anolyte and sulfuric acid is used as catholyte. Parametric study is conducted to investigate the effect of electrolyte concentration and polypropylene separator thickness on the performance of the battery. The results show that the dual-electrolyte system can boost the open circuit voltage to 2.2 V as compared to the single electrolyte system for 5 M of anolyte while maintaining specific discharge capacity of about 1390.92 mAh.g−1. The maximum peak power density has improved dramatically from 100 mW.cm−2 to 350 mW cm−2 for the dual electrolyte system.

Boron nanosheets induced microstructure and charge transfer tailoring in carbon nanofibrous mats towards highly efficient water splitting

Development of metal-free carbon-based electrocatalysts with high-efficiency and excellent durability towards both oxygen and hydrogen evolution reactions (OER and HER) in a single electrolyte system is crucial yet challenging for sustainable energy generation. In this work, we report a facile and scalable strategy for fabricating self-supporting boron carbon oxynitride nanofibrous (BCNONF) mats with controllable boron contents via electrospinning and subsequent thermal treatment. Notably, the optimal BCNONF mat affords outstanding OER performance in alkaline electrolyte with low overpotential of 403 mV at 10 mA·cm−2, small Tafel slop of 72.9 mV·dec−1, and high stability (88.1% current density retention after 10 h), outperforming the commercial Ir/C benchmark. Moreover, it can serve as a remarkable HER catalyst with better stability than that of the commercial Pt/C counterpart in the same electrolyte, indicating its bifunctional characteristics. When employed as both anode and cathode of an electrolyzer, the self-supporting BCNONF mats exhibit superior activities with a potential of only 1.79 V at 10 mA·cm−2 and high long-term durability (90.6% current density retention after 50 h) for overall water splitting. Furthermore, density functional theory (DFT) calculations reveal that the remarkable OER and HER bifunctional performance of the BCNONF catalyst are originated from the reduced adsorption strength of O atom and the stronger H* adsorption on the BCNO surface as compared to those on CNO surface, which in turn facilitate efficient interfacial charge transfer between the electrocatalytic intermediates and the BCNONF catalyst.

Efficient Bipolar Membrane Water Electrolysis Enabled By Dual-Phase CoP-CoTe2 Nanowires As Bifunctional Electrocatalyst

Water splitting offers an environmentally friendly way for H2 production, especially if the electricity comes from renewable sources such as solar and wind. Significant effort has recently been made to developing cheap and efficient earth-abundant electrocatalysts to make electrolyzed hydrogen economically competitive. Although the substantial progress, the operational voltage of water splitting in a single electrolyte system is still high. Given that the hydrogen evolution reaction (HER) is kinetically favorable in acidic conditions and the oxygen evolution reaction (OER) in alkaline conditions, it would be preferable to realize these half reactions simultaneously in different electrolytes in a single electrolyzer. Moreover, such cell design allows the using of low-cost and earth-abundant catalysts for both HER and OER.In this work we demonstrate the development of a dual-phase cobalt phosphide-cobalt ditelluride (CoP-CoTe2) nanowires, which can be used as efficient bifunctional electrocatalysts for both HER and OER using acid-alkaline dual electrolytes in a two-compartment cell separated by a bipolar membrane (BPM). Using the BPM under "reverse bias" configuration, the bipolar membrane overall water splitting can be accomplished with an onset voltage as low as 1.13 V and a voltage of 1.72 V is needed to deliver 10 mA cm-2. However, water electrolysis can be accomplished at significantly lower external biases, e.g. 1.01 V at 10 mA cm-2, when a "forward bias" conditions was used due to the assistance of electrochemical neutralization. Moreover, this electrolyzer can sustain water splitting for at least 100 h. The bipolar membrane water electrolysis, particularly with the "forward bias" configuration, shows great promise as an alternative to the current technologies.

Dual-phase CoP−CoTe2 nanowires as an efficient bifunctional electrocatalyst for bipolar membrane-assisted acid-alkaline water splitting

Electrochemical water splitting powered by renewable energy (e.g. solar, wind) has been recognized as a sustainable and environmentally-friendly way to produce “green” hydrogen. Significant efforts were dedicated recently to developing cheap and efficient earth-abundant electrocatalysts to make electrolyzed hydrogen economically competitive. Notwithstanding substantial progress, the operational voltage of water splitting in a single electrolyte system is still high, even highly efficient electrocatalysts are used to catalyze the hydrogen evolution (HER) and oxygen evolution reactions (OER). Taking into account that the HER and the OER are kinetically favorable in electrolytes with different pH values, in this work we demonstrate that overall water splitting can be accomplished in acid-alkaline dual electrolytes with an onset voltage as low as 1.13 V, enabled by a bipolar membrane (BPM) under the “reverse bias” condition with the novel dual-phase cobalt phosphide-cobalt ditelluride (CoP-CoTe2) nanowires being used as efficient and durable bifunctional catalysts. Furthermore, we show that using a BPM under the “forward bias” the voltages needed to reach 10 and 100 mA cm−2 can be reduced to 1.01 and 1.37 V, respectively, due to the assistance of electrochemical neutralization resulting from the crossover of electrolytes. The bipolar membrane water electrolysis (BPMWE) can be sustained for at least 100 h without notable degradation.

A Two-Parameter Theoretical Model for Predicting the Activity and Osmotic Coefficients of Aqueous Electrolyte Solutions

A thermodynamic model of electrolyte solutions is proposed. The model consists of a long-range term expressed by the Pitzer–Debye–Huckel equation (PDH) and a short-range term expressed by the molecular interaction volume model (MIVM). The new model was fitted with 39 different types of single electrolyte systems and was compared with the Pitzer equation, and the mean standard deviation (SD) and the mean average relative deviation (ARD%) are 0.0264, 0.0040 and 2.09%, 0.40%, respectively. Meanwhile, the physical meaning of the two electrolyte-specific interaction parameters ( $$B_{ca,s}$$ and $$B_{s,ca}$$ ) of the new model is also discussed. By further comparison with the Pitzer equation and a state-of-the-art model, eUNIQUAC-NRF, the new model exhibits relatively robust extrapolation capability, and also shows the potential ability to predict the activity coefficients of individual ions. In addition, only using binary parameters to predict 29 different types of ternary systems, the overall prediction results of the new model are slightly better than those of the Pitzer equation, and the mean SD and ARD% are 0.0288, 0.0396 and 2.88%, 3.81%, respectively. For some cases involving Rb and Cs, the Pitzer equation needs two ternary adjustable parameters ( $$\theta$$ and $$\psi$$ ) to achieve the prediction accuracy of the new model. Furthermore, we also compared the predictions of the new model with the eUNIQUAC-NRF model for several ternary systems; the new model also shows better performance, and its overall prediction accuracy was about twice that of the eUNIQUAC-NRF model, with the average SD and ARD% values being 0.0261, 0.0546 and 2.63%, 5.80%, respectively.

A Hybrid Electrolytes Design for Capacity‐Equivalent Dual‐Graphite Battery with Superior Long‐Term Cycle Life

AbstractBased on cation/anion graphite intercalation chemistry (GIC) processes, dual‐graphite batteries promise to be an energy storage device of high safety and low cost. However, few single electrolyte systems can simultaneously meet the requirements of both high oxidative stability during high voltage anion‐GIC on cathode and high reversibility upon cation‐GIC on anode. Thus, in order to rigidly remedy the irreversible capacity loss, excessive electrode materials need to be fabricated within full cell, resulting in an imbalance toward capacity‐dependent mass loading proportion between both electrodes. This work introduces a hybrid (dual‐organic) electrolytes design strategy into this promising technology. Segregated by a Nafion‐based separator, an ionic liquid electrolyte within the cathodic side can endure high operation potentials, while high Li‐GIC reversibility can be achieved in a superconcentrated ether‐based electrolyte on the anode side. On a mechanistic level, various cation‐GIC processes conducted in different electrolyte systems are clearly revealed and are summarized based on systematical characterizations. More importantly, after synergistically tuning the advantage and drawback of each electrolyte in this hybrid system, the dual‐graphite full cell assembled with capacity‐equivalent graphite‐based electrodes (1:1 mass loading) demonstrates superior long‐term cycling stability with ultrahigh capacity retention for over 3000 cycles.

Temperature dependence of interaction parameters in electrolyte NRTL model

The electrolyte NRTL model captures the electrolyte solution nonideality over the entire concentration range with two binary interaction parameters. Here, the temperature dependence of the binary parameters is formulated with a Gibbs‐Helmholtz expression containing three temperature coefficients associated with Gibbs energy, enthalpy, and heat capacity contributions. We show the Gibbs energy term is correlated to the excess Gibbs energy of aqueous single electrolyte systems at 298.15 K. With the Gibbs energy term identified, the enthalpy term is correlated to the excess enthalpy at 298.15 K. With the Gibbs energy term and the enthalpy term identified, the heat capacity term is correlated to the excess heat capacity at 298.15 K. Once the temperature coefficients are properly quantified by regressing data of mean ionic activity coefficient, excess enthalpy, and heat capacity at 298.15 K or the equivalents, the model provides a comprehensive thermodynamic framework to represent all thermodynamic properties of electrolyte solutions. © 2015 American Institute of Chemical Engineers AIChE J, 62: 1244–1253, 2016

A quantification of diffusion dialysis process: Single electrolyte system (hydrochloric acid solution)

This study dealt with diffusion dialysis process of single HCl solution as feed. Water osmosis phenomenon was investigated in detail and modified mass transfer equation with the chemical potential difference as driving force was deduced. It mainly included three parts. Firstly, time dependence of diffusate volume was investigated quantitatively, and when the curves were divided into two parts and two different quadratic polynomials were used to fit them, results showed that the fitting accuracy was satisfactory. Secondly, to calculate the solution chemical potential more easily, average mean activity coefficient and average osmotic coefficient were used. Results showed that with the increase in feed concentration, the coefficients increase accordingly. Thirdly, permeability coefficients were investigated to quantify the diffusion dialysis, results illustrated that when λ=5 and θ=0.5, P′HCl and P′H2O were acceptable coefficients to characterize the process. This study can allow a selection of optimum parameters for diffusion dialysis process.

Experimental study and modeling of the influence of mixed electrolytes on adsorption of macromolecules on a hydrophobic resin

The influence of mixed electrolytes on the adsorption of macromolecules on a hydrophobic resin is explored. The macromolecules are native lysozyme, di-PEG-lysozyme-5kDa and pure PEG-6kDa, the adsorbent is Toyopearl PPG-600M, a mildly hydrophobic resin. The solvent is a 25mM aqueous sodium phosphate buffer at pH 7.0 containing additional salts with an overall ionic strength of 3000mM. The studied salts are sodium chloride, ammonium sulfate, sodium sulfate and ammonium chloride. Both pure salts as well as binary and ternary mixtures of these salts with varying ratios of the amounts of the salts are studied. For all solvents adsorption equilibrium isotherms are measured at 25°C. Mixing electrolytes can lead to synergetic effects, i.e. the adsorption in the mixed electrolyte system is sometimes distinctly larger than expected from the results of the single electrolyte systems. The single ions, not the salts, drive the adsorption. A mathematical model is developed, which describes the influence of the different ions and their cross-interactions on the studied adsorption process.

A quantification of diffusion dialysis process: Single electrolyte system (sodium chloride solution)

A quantification of diffusion dialysis process in a single electrolyte system has been investigated in this study. Firstly, the volume of water which permeates from water side to feed side was to be quantified detailedly, and results showed that diffusate solution volume changes over time according with the characteristics of quadratic polynomial (y=a0τ2+b0τ+c0). Secondly, Permeability coefficients of membrane to H2O (PH2O, PH2O′) and NaCl (PNaCl, PNaCl′) were used to quantify diffusion dialysis process. Results showed that with the increase of feed concentration, PNaCl′ and PNaCl decrease, while PH2O′ and PH2O increase. Furthermore, when modifying factor λ=3.30 and ϑ=2.37, comparisons of theoretical and experimental concentrations of NaCl in diffusate solution illustrated that both PH2O′ and PNaCl′ are satisfactory coefficients for characterizing the diffusion dialysis process. In addition, the mathematical model discussed in this study can provide an effective method to deal with the mass transfer process of diffusion dialysis easily and conveniently, especially, is helpful to select an optimum ion exchange membrane to operate diffusion dialysis.

Through-mask anodization of titania dot- and pillar-like nanostructures on bulk Tisubstrates using a nanoporous anodic alumina mask

Nanosized surface topography on an implant material has the capability of stimulating theacceptance of the material in its host surrounding. Fine-tuning of nanotopographyfeature size has been shown to trigger differentiation of mesenchymal stem cellsinto bone cells in vitro. For this purpose we have created well defined nanosizedtitania dot- and pillar-like structures on mechanically polished Ti substrates using athrough-mask anodization technique with an anodic porous alumina template. Theanodization technique allowed the titania structure dimensions to be precisely tunedin the range 15–140 nm in a single electrolyte system. The fabricated surfacesserve as good model surfaces for precise studies of in vitro cell behaviour. Thethrough-mask anodization technique was used directly on bulk Ti surfaces, thusdemonstrating a potential application for patterning of actual Ti implant surfaces.

Electrochemical Formation Process of Si Macropore and Metal Filling for High Aspect Ratio Metal Microstructure Using Single Electrolyte System

Electrochemical Formation Process of Si Macropore and Metal Filling for High Aspect Ratio Metal Microstructure Using Single Electrolyte System

Chemical speciation of organic matter in natural waters. Interaction of nucleotide 5’ mono-, di- and triphosphates with major components of seawater

The interactions of nucleotide 5’ mono-, di- and triphosphates in a multicomponent ionic medium simulating the macro-composition of seawater (Na+, K+, Ca2+, Mg2+, Cl-, SO42-, Synthetic Sea Water, SSW) have been investigated at different ionic strengths and at T= 25°C. A chemical speciation model, according to which all the internal interactions between the components of the ionic medium are taken into account, was applied to determine the effective formation constants of species in the nucleotide-seawater system. The results were compared to protonation parameters calculated from single electrolyte systems. A simpler model (SSW considered as a single salt BA, with Bz+ and Az-), representative of the cation (Na+, K+, Ca2+, Mg2+) and anion (Cl-, SO42-) macro-components of seawater respectively, was also used to calculate the overall complexing ability of the seawater salt towards all the systems here investigated.

Extension of the Wilson model to electrolyte solutions

The Wilson model for non-electrolytes has been extended to model the activity coefficients of electrolytes in aqueous solutions. The excess Gibbs energy of an aqueous electrolyte solution is expressed as a sum of contributions of a long-range and a short-range excess Gibbs energy term. The contribution of the long-range excess Gibbs energy is represented by the Pitzer–Debye–Hückel model. A new expression based on the local composition concept has been developed to account for the contribution of the short-range excess Gibbs energy. The existence of three types of local cells with a central cation, anion or solvent molecule is assumed. Due to the strong like-ion repulsion it is assumed that only counterions can be found in the immediate neighborhood of a central ion. The main difference between this model and the extensions of the NRTL model to electrolytes available in the literature is the assumption that the short-range energy parameter between species in a local cell has an enthalpic rather than Gibbs energy nature. For systems containing only molecular components the new model simplifies to the three-parameter version of the Wilson model. The model has been applied to several single electrolyte systems and it has been shown that it can represent the mean ionic activity coefficients with good accuracy.

Vapour–liquid equilibrium data analysis for mixed solvent–electrolyte systems using neural network models

Two-perceptron artificial neural network correlations were proposed for the prediction of vapor–liquid equilibrium for mixed dual-solvents single electrolyte systems, and validated over an extensive VLE database (2,900 data, 16 binary solvents, 24 salts, 11 cations, 6 anions). Performances of these correlations to predict vapor-phase mole fraction, equilibrium temperature and total pressure, were discussed via comparisons with the experimental data, and the UNIFAC electrolyte model (Kikic, Fermeglia & Rasmussen, 1991). Chemical Engineering Science, 46, 2775–2780.) and the Extended UNIQUAC model (Iliuta, Thomsen & Rasmussen, 2000). Chemical Engineering Science, submitted for publication.). The mean absolute deviations in predicted vapor-phase mole fraction, temperature and pressure for the entire database were 0.025, 1.46 K and 1.68 kPa, respectively.

New local composition model for electrolyte solutions: single solvent, single electrolyte systems

A new model for representation of the excess Gibbs energy of electrolyte solutions is proposed. The model is based on the Electrolyte nrtl model according to Chen. However, considerable modifications have been introduced. The new model contains four adjustable parameters per binary electrolyte–solvent system. A new local composition expression is used, in which an energy correction term has been introduced empirically, based on calculation results from statistical thermodynamics. The paper gives computed values of the new model parameters for 163 aqueous electrolyte systems at 298.15 K. The parameters were obtained by correlating data on molal mean ionic activity coefficients and osmotic coefficients from the open literature. A comparison of the performance of the model is made with the Chen model, and shows that the new model may be used to very high concentrations with very good accuracy. An investigation of the temperature dependence of the model parameters has been made for some electrolyte systems over a wide range of temperatures and concentrations. The results show a slight temperature dependence of two of the parameters, while the two other parameters may be assumed independent of the temperature.

A modified self-consistent local composition model for the thermodynamic properties of single and mixed electrolytes

In the recently developed self-consistent-local composition (SCLC) theory (Ananth and Ramachandran, 1990) the osmotic and activity coefficients in single electrolyte solutions are expressed as sums of several independent contributions. In the present work, the approximate proportionality between certain pairs of these contributions is identified and the model is reformulated with fewer and more orthoganal parameters. The numerical difficulties experienced with the original model in the evaluation of parameters and in the extension of the calculations to mixed electrolyte systems are thus eliminated. The simplified model is shown to correlate the activity and osmotic coefficient data of large number of single and those of mixed electrolyte systems with good accuracy. The osmotic and activity coefficient of single electrolyte solutions are expressed in terms of two binary adjustable parameters and mixed electrolyte systems containing two salts and one solvent are expressed in terms of only one adjustable parameter in addition to the binary parameters determined from the component single electrolyte systems. The theory contains no additional adjustable parameters in the case of multielectrolyte (more than two salts) systems. The model is found to represent satisfactorily the behavior of electrolyte solutions at different temperatures with a single set of temperature-independent parameters.

Dependence of retention of ionic solutes on the composition of the mobile phase electrolytes in partition chromatography

On the basis of the model for partition chromatography of ionic solutes in the presence of background electrolytes, theoretical equations are developed to describe the retention dependence of ionic solutes on the composition of electrolytes in the mobile phase. The theoretical equations were tested by calculating the expected capacity factors of various inorganic ions in the presence of two or three background electrolytes using experimental values obtained in a single electrolyte system. The predictions from the equations agreed well with experimental retention data on hydrophilic polymer packings for both binary (acetone-water) and single solvent (water) systems.