Alkali Metal Hydroxide Solutions Research Articles

Synthesis and performance of binder-free porous carbon electrodes in electrochemical capacitors.

Porous binder-free carbon electrodes were obtained by impregnating cellulose filter papers with phenolic resin through soft-salt template synthesis and thermal pyrolysis. These self-standing electrodes were used directly in a supercapacitor device. To understand the impacts of filter paper (FP) thickness on carbon filter paper (CFP) morphology, porosity, and surface functionalities, five different materials were examined. The CFP electrode thickness was adjusted linearly with the FP thickness to produce electrodes ranging from 100 to ∼800 μm. As the thickness of the CFP increased, there was an increase in the specific surface area and oxygen-based functionalities. Electrochemical testing in a 1 M KOH aqueous electrolyte demonstrated that electrode thickness played a key role in electrochemical capacitor (EC) performance, i.e., capacitance enhances linearly when the electrode becomes thinner. For low thicknesses (<280 μm), the capacitance and rate capability decreased slightly with increasing thickness; for high thicknesses, the performance drastically degraded despite the high specific surface area and oxygen surface functionalities. This effect was amplified at high regimes, indicating that high electrode thicknesses and fiber diameters limited electrolyte diffusion in the applied synthesis conditions. Thus, the high material porosity was inaccessible to ion adsorption. Consequently, thinner electrodes showed the highest capacitance (197 F g-1 at 0.1 A g-1) and rate capability (81%) values, exceeding those of their traditional binder-electrode counterparts prepared under similar conditions. Finally, for alkali metal hydroxide solutions, 1 M KOH exhibited a cation match with the salt template (KCl), while CsOH achieved additional capacitance retention (88% at 10 A g-1). Complex ion adsorption mechanisms were observed through a quartz crystal microbalance.

Highly Utilized Active Sites on Pt@Cu/C for Ethanol Electrocatalytic Oxidation in Alkali Metal Hydroxide Solutions

AbstractUsing ethanol electrocatalytic oxidation reaction (EOR) with a lower reaction potential to replace oxygen evolution reaction (OER) and integrating hydrogen evolution reaction (HER) have a promising development prospect for more energy‐saving electrolytic hydrogen production. However, the main challenges of EOR are insufficient catalytic activity, high overpotential, and slow kinetics. Active sites on the electrocatalysts surface are occupied by alkali metal ion hydrate clusters by noncovalent interactions, which is considered to be one of the major causes of these challenges. To reduce the effect of the noncovalent interactions on the catalytic activity of the electrocatalyst, copper is chosen and doped in the form of a single atom in the electrocatalyst (Pt@Cu/C) to increase the electrocatalyst conductivity and make the anode contain more positive charge in this study. Then, alkali metal ion hydrate clusters are difficult to adsorb at the active site of Pt@Cu/C. The EOR electrocatalytic activity of Pt@Cu/C is up to 8184 mA mgPt−1, which is ≈4.8 times as high as that of Pt/C. The two‐electrode hydrogen production device using Pt@Cu/C as anode for coupled EOR&amp;HER requires a smaller voltage of 0.60 V to reach 10 mA cm−2compared with that of Pt/C (0.76 V).

Hydrogen production in a combined electrochemical system: Cathode process

Today, hydrogen is recognized as a promising fuel, which is characterized by high heat generation and combustion temperature. It is also characterized by environmental safety due to the fact that no greenhouse gases are formed during the combustion of hydrogen. There are various methods of hydrogen production: traditional methods, which include electrolysis of water and conversion of hydrocarbons, and thermochemical ones. A cheap method of hydrogen obtaining from natural gas and coke is accompanied by the carbon oxides formationю Thermochemical methods are require high temperatures (up to 1000°C). The method for hydrogen production by electrolysis of aqueous solutions of alkali metal hydroxides is the most energy-intensive. However, it is considered one of the most promising in the European Union. To reduce energy consumption for hydrogen production, the authors suggest replacingthe positive electrode, which normally produces oxygen, with a dissolving anode with an equilibrium potential lower than that of oxygen, such as an iron electrode. In this case, with such a combined electrochemical method, the decomposition voltage in the system will be 0.44 V against 1.23 V with traditional water electrolysis. The overvoltage of iron dissolution in a chloride medium is several tens of millivolts. However, the potential difference between the anode and cathode ΔU becomes smaller than the equilibrium potential difference ΔE0 = 0.44 V. This research aims to substantiate the choice of the composition and concentration of electrolytes: catholyte –to ensure conditions for reducing energy consumption for hydrogen release; anolyte – to prevent passivation of the iron anode, which can lead to the oxygen release. This work results in research of the cathodic process of hydrogen release in the following solutions: 1 M (= mol/L) NaCl with the addition of 1 M hydrochloric acid in the amount of 5, 10, 15, 20 mL. Platinum is used as a cathode for the electrolysis process. The anode material is an iron, St3 grade. It has been found that in the range of changes in the composition of the electrolyte from neutral (1 M NaCl) to acidic (1 M HCl), a change in the mechanism of water discharge is observed. In a neutral medium, the discharging occurs according to the Heyrovsky mechanism, and in an acidic medium - according to the Volmer mechanism. The choice of the anolyte composition and concentration is complicated by the need to provide an acidic medium containing chlorine ions to prevent passivation of the anode. The acidity of the solution must be at least 3 for the successful extraction of dissolution products of the iron anode.

Carbon dioxide capture by the green aqueous sodium hydroxide-glycerol solution in a gas-liquid microchannel contactor

Although organic solutions of alkali metal hydroxides have been considered a well-established technology for CO2 capture, they impose energy loss and a high corrosion rate due to the lack of suitable inhibitors. In this context, glycerol, as an abundant waste by-product of the biodiesel industry, was proposed to explore the CO2 absorption potential in the aqueous solution of sodium hydroxide-glycerol in a T-shaped microchannel contactor with an internal diameter of (ID=800 µm). Applying Response Surface Methodology (RSM), the CO2 absorption experiments were performed under temperatures of 25–45℃, with NaOH+Gly concentrations ranging from (0.2–0.8 M)+ (4–12 wt%), and the inlet gas flow rate of 100–300 ml/min. NaOH concentration was identified as a significant decisive variable on the CO2 absorption efficiency (η) and the overall gas-phase mass transfer coefficient (KGaV). The CO2 absorption efficiency of the developed hybrid solution was reported in the range of 29.28–98.40%. Besides, at concentrated alkali solution, adding glycerol from 4 to 12 wt% will raise the value of KGaV by more than 5.2 folds. This implies that the presence of glycerol in the aqueous NaOH solution not only intensifies the mass transfer performance but also declines the prevailing pollution and hazard wastes.

Radio Brightness Contrasts of Aqueous Solutions of Alkali Metal Hydroxides in the Millimeter Spectral Range

Radio Brightness Contrasts of Aqueous Solutions of Alkali Metal Hydroxides in the Millimeter Spectral Range

Role of Noncovalent Interactions on the Electrocatalytic Oxidation of Ethanol in Alkali Metal Hydroxide Solutions

Ethanol is considered to be one of the most promising fuels for fuel cells. However, ethanol fuel cells have a sluggish Faraday efficiency due to complex interactions between the electrolyte, electrode, and ethanol. Recent studies have further suggested that noncovalent interactions originated from the hydrated alkali metal cations and the adsorbed OHad at the Pt electrode surface also played an important role in the electron transfer. In this regard, the noncovalent interactions in different alkali metal hydroxide (AMH) solutions have been systematically investigated in this study, and it was observed that the noncovalent interactions could result in the occupation of the Pt electrode surface active sites and sluggish migration of ethanol molecules in the electrical double layer, significantly affecting the electro-oxidation efficiency. Further, it was concluded that the electro-oxidation efficiency in different AMH solutions followed the order of K+ > Na+ > Rb+ > Cs+ > Li+ due to the noncovalent interactions.

Tailoring the hydrophilic and hydrophobic reaction fields of the electrode interface on single crystal Pt electrodes for hydrogen evolution/oxidation reactions

Interfacial hydrophobic/hydrophilic reaction fields significantly affect various reactions at the electrode surface. The hydrogen evolution reaction (HER) and the hydrogen oxidation reaction (HOR) have been investigated on single crystal Pt electrodes modified with hydrophobic/hydrophilic cations and anion-exchange copolymers in alkaline solutions. In alkali metal hydroxide solutions, Pt (110) exhibits the highest HER/HOR activity in the low-index planes of Pt. On the low-index planes of Pt, the hydrophilicity of the alkali metal cation in the supporting electrolyte activates the HER/HOR depending on its hydration energy. Hydrophilic cations at the interface facilitate the extraction of hydrogen from the hydrated water. The modification of anion-exchange copolymers with a hydrophobic skeleton on Pt (110) further enhanced the HER/HOR activity. The hydrogen bonding network formed around the hydrophobic species facilitated the mobility of water molecules and the OH− as the reactant/product of the HER/HOR. Appropriately forming hydrophilic and hydrophobic reaction fields at the interface improved the HER/HOR activity.

Tailoring the electrode surface structure by cathodic corrosion in alkali metal hydroxide solution: Nanostructuring and faceting of Au

Nanostructured metals are vital materials in several (electro)chemical applications. Despite the substantial progress in this field, still many limitations are associated with traditional synthetic procedures, including the availability of stable nanoparticles on appropriate supports by avoiding migration and aggregation. On that front, cathodic corrosion has emerged as a powerful technique to tailor the surface structure of metal surfaces on the nanoscale. Cathodic corrosion crucially depends on the electrode potential, the nature and the concentration of cations, as well as the electrode material. Controlling these parameters is essential for applying cathodic corrosion in materials design. In this short review, we discuss the most critical parameters controlling cathodic corrosion and highlight the importance of the nature and the concentration of alkali metal hydroxides in aqueous solution.

Alkali-metal-ions promoted Zr-Al-Beta zeolite with high selectivity and resistance to coking in the conversion of furfural toward furfural alcohol

Zirconium-substituted zeolites prepared by post-synthetic procedure have demonstrated excellent performance in the upgrading process of biomass platform compounds owing to the unique Lewis acid character. However, many pressing questions still surround these materials, especially relating to specific conversion, catalyst stability and substrate scalability. In the present study, a simple alkaline treatment to the Zr-Al-Beta zeolite in alcoholic solution of alkali metal hydroxide was conducted. The modification of alkali-metal ions on both Lewis acid sites and Brønsted acid sites in Zr-Al-Beta was evidenced by XPS and FT-IR spectroscopy (CO and pyridine). The untreated materials displayed poor product selectivity and high coke deposit in the Meerwein-Ponndorf-Verley reduction of furfural and isopropanol; however, the treatment of alkali-metal ions promoted their catalytic performance with improved recalcitrance to deactivation and coking significantly. Both the type of alkali-metal ions and the concentration of alkaline solution influenced the catalytic performance, which were found to correlate to the acidity and textual properties. The optimum reaction result (97.3% yield of furfuryl alcohol at 99.6% conversion of furfural) can be obtained on 0.025 M-Na+-Zr-Al-Beta with high tolerance to the furfural concentration.

Low Temperature Characteristics of Hydrogen Storage Alloy LaMm-Ni4.1Al0.3Mn0.4Co0.45 for Ni-MH Batteries

Nickel hydride batteries (Ni-MH) are known of their good performance and high reliability at temperatures below 0 °C, which is significantly dependent on electrolyte composition. Here we present the low temperature characteristics of pristine AB5-type alloy, LaMm-Ni4.1Al0.3Mn0.4Co0.45, determined in various alkali metal hydroxide solutions. We found that the combination of KOH with NaOH showed a significant effect of enhancement of low temperature performance of the electrode material and diffusion of hydrogen in the alloy. This 6M binary mixed NaOH/KOH electrolyte, comprising 4M KOH component and 2M NaOH component, made it possible to maintain 81.7% and 61.0% of maximum capacity at −20 °C and −30 °C, respectively, enhancing the hydrogen storage properties of the alloy after reheating to room temperature.

Development of the ReaxFF Methodology for Electrolyte-Water Systems.

A new ReaxFF reactive force field has been developed for water-electrolyte systems including cations Li+, Na+, K+, and Cs+ and anions F-, Cl-, and I-. The reactive force field parameters have been trained against quantum mechanical (QM) calculations related to water binding energies, hydration energies and energies of proton transfer. The new force field has been validated by applying it to molecular dynamics (MD) simulations of the ionization of different electrolytes in water and comparison of the results with experimental observations and thermodynamics. Radial distribution functions (RDF) determined for most of the atom pairs (cation or anion with oxygen and hydrogen of water) show a good agreement with the RDF values obtained from DFT calculations. On the basis of the applied force field, the ReaxFF simulations have described the diffusion constants for water and electrolyte ions in alkali metal hydroxide and chloride salt solutions as a function of composition and electrolyte concentration. The obtained results open opportunities to advance ReaxFF methodology to a wide range of applications involving electrolyte ions and solutions.

Corrosion of Hydrogen Storage Metal Alloy LaMm-Ni4.1Al0.3Mn0.4Co0.45 in the Aqueous Solutions of Alkali Metal Hydroxides

Corrosion of pristine AB5-type metal alloy LaMm-Ni4.1Al0.3Mn0.4Co0.45 in the aqueous solutions of alkali metal hydroxides of diverse composition and concentration was tested. Correlation was observed between the alloy corrosion intensity in various hydroxide solutions, and its electrochemical capacity in these electrolytes. Mm(OH)3, CoO(OH), and nickel metal aggregates were detected among the products of selective oxidation of the alloy. High intensity corrosion of the alloy was observed in RbOH and CsOH solutions leading to formation of ternary oxides at the surface of the alloy. Presence of rubidium and cesium ions in the electrolyte were found to create an additional driving force for lanthanides (La and Ce) to leave the lattice of the alloy, thus, enhancing its corrosion. Corrosion, together with mechanical degradation, were found to be the main reasons of deactivation of LaMm-Ni4.1Al0.3Mn0.4Co0.45 alloy upon elongated electrochemical treatment.

Oxygen Electroreduction at High-Index Pt Electrodes in Alkaline Electrolytes: A Decisive Role of the Alkali Metal Cations.

Currently, platinum group metals play a central role in the electrocatalysis of the oxygen reduction reaction (ORR). Successful design and synthesis of new highly active materials for this process mainly rely on understanding of the so-called electrified electrode/electrolyte interface. It is widely accepted that the catalytic properties of this interface are only dependent on the electrode surface composition and structure. Therefore, there are limited studies about the effects of the electrolyte components on electrocatalytic activity. By now, however, several key points related to the electrolyte composition have become important for many electrocatalytic reactions, including the ORR. It is essential to understand how certain “spectator ions” (e.g., alkali metal cations) influence the electrocatalytic activity and what is the contribution of the electrode surface structure when, for instance, changing the pH of the electrolyte. In this work, the ORR activity of model stepped Pt [n(111) × (111)] surfaces (where n is equal to either 3 or 4 and denotes the atomic width of the (111) terraces of the Pt electrodes) was explored in various alkali metal (Li+, Na+, K+, Rb+, and Cs+) hydroxide solutions. The activity of these electrodes was unexpectedly strongly dependent not only on the surface structure but also on the type of the alkali metal cation in the solutions with the same pH, being the highest in potassium hydroxide solutions (i.e., K+ ≫ Na+ > Cs+ > Rb+ ≈ Li+). A possible reason for the observed ORR activity of Pt [n(111) × (111)] electrodes is discussed as an interplay between structural effects and noncovalent interactions between alkali metal cations and reaction intermediates adsorbed at active catalytic sites.

Electro-chemo-mechanical effects of lithium incorporation in zirconium oxide

Understanding the response of functional oxides to extrinsic ion insertion is important for technological applications including electrochemical energy storage and conversion, corrosion, and electronic materials in neuromorphic computing devices. Decoupling the complicated chemical and mechanical effects of ion insertion is difficult experimentally. In this work, we assessed the effect of lithium incorporation in zirconium oxide as a model system, by performing first-principles based calculations. The chemical effect of lithium is to change the equilibria of charged defects. Lithium exists in $\mathrm{Zr}{\mathrm{O}}_{2}$ as a positively charged interstitial defect, and raises the concentration of free electrons, negatively charged oxygen interstitials, and zirconium vacancies. As a result, oxygen diffusion becomes faster by five orders of magnitude, and the total electronic conduction increases by up to five orders of magnitude in the low oxygen partial pressure regime. In the context of Zr metal oxidation, this effect accelerates oxide growth kinetics. In the context of electronic materials, it has implications for resistance modulations via ion incorporation. The mechanical effect of lithium is in changing the volume and equilibrium phase of the oxide. Lithium interstitials together with zirconium vacancies shrink the volume of the oxide matrix, release the compressive stress that is needed for stabilizing the tetragonal phase $\mathrm{Zr}{\mathrm{O}}_{2}$ at low temperature, and promote tetragonal-to-monoclinic phase transformation. By identifying these factors, we are able to mechanistically interpret experimental results in the literature for zirconium alloy corrosion in different alkali-metal hydroxide solutions. These results provide a mechanistic and quantitative understanding of lithium-accelerated corrosion of zirconium alloy, as well as, and more broadly, show the importance of considering coupled electro-chemo-mechanical effects of cation insertion in functional oxides.

Вилучення іонів міді лігніфікованою багасою із водних витяжок грунтів

Analysis of soil contamination with heavy metals has been carried out, which leads to a reduction, and in some cases, to loss of species composition of plants. It is determined that about 20% of the territory of Ukraine is contaminated with heavy metals. The widespread use of copper and its compounds in industry inevitably leads to the entry of Cu (II) into the water and soil environment. The maximum permissible concentration of copper ions in soils is 100 mg / kg (total content) and 3 mg / kg (content of moving forms). Therefore, today, the removal of copper (II), which belongs to heavy metals of the first class of danger, is an important scientific, technical and environmental task. The expediency of increasing the requirements to the quality of soils is substantiated, it makes it necessary to search for new, environmentally friendly and economically viable ways of extracting heavy metal ions, in particular copper (II) from them. This is possible, when using sorbents in soil purification, from plant wastes, chemically or biologically modified. One of the most promising waste for the production of sorbents is the bulk of sugar sorghum (the weight of technical stems of sugar sorghum, which is obtained by mechanical pressing, is discarded). Native (untreated) sorghum waste, as a rule, has low sorption-kinetic characteristics and sorption capacity. Therefore, an urgent problem is the search for methods of treatment of plant polymers in order to reduce the duration of the sorption process and increase their sorption capacity. The purpose of the study is to develop a method for obtaining a sorbent by chemical modification of lignocellulose waste from sugar sorghum and identifying possible directions for its further practical use in agroecology. A method for lignifying the bagasse from sorghum sugar for soil purification is proposed hydrolysis of the crushed plant material with an aqueous solution of mineral (organic) acid, washing with water, activating lignin with an aqueous solution of alkali metal hydroxide, filtering, washing with water, neutralizing the residual alkalinity of the resulting material with an aqueous solution of acid, dehydration (pressing) and drying. The luggage proposed by us can destroy the esters, the free saturated and unsaturated organic acids, the various macromolecular alcohols and some part of the carbohydrates (hemicellulose and pectin), improve the sorption and porous structure by loosening the plant fibers and increase the number of available functional groups capable of joining reactions, complex formation and ion exchange with heavy metal ions. The growth of the sorption capacity of the lignified bagasse is due to an increase in the number of sorption-active centers on which the sorption of heavy metal ions (in particular, copper) may occur due to the formation of cationic and neutral solvate complexes. The sorption properties of untreated and lignified cadavers with respect to copper (II) ions have been studied. It has been established that lignified bagasse can be used in agrotechnologies as a sorbent for soil purification from contamination by copper ions.

Comparative study of hydrogen electrosorption from alkali metals electrolytes and hydrogen sorption from gas phase in AB5 alloy

AB5-type metal alloy (LaMm–Ni4.1Al0.3Mn0.4Co0.45) was investigated in alkali metal hydroxide electrolytes (LiOH, NaOH, KOH, RbOH, CsOH) at various temperatures (0–30°C) with no binding materials used. Limited volume electrode approach (LVE) was used in all electrochemical measurements. PCT Sievert’s method was used to determine maximum hydrogen capacity of the alloy to be 4.7at.H/f.u. (289mAh/g). The highest electrochemical hydrogen capacity, nearly reaching the maximum value, was obtained in 6M KOH solution at 30°C (275.1mAh/g) and in mixed 6M LiOH/KOH solution at 30°C (276.1mAh/g). Temperature influence on electrochemical capacity of the alloy was investigated. In the temperature range of 0–30°C the capacity is high and stable in 6M KOH solution and mixed 6M LiOH/KOH and 6M NaOH/KOH solutions. It is possible to improve the capacity of the alloy by designign mixed alkali metal hydroxide solutions.

Molar Volumes and Heat Capacities of Aqueous Solutions of Potassium Hydroxide and for Water Ionization up to 573 K at 10 MPa

Densities (ρ) and isobaric volumetric heat capacities (σp) of carefully purified aqueous solutions of potassium hydroxide have been measured at concentrations up to 6 mol·kg–1 at a pressure of 10 MPa over the temperature range 323 ≤ T/K ≤ 573 using a vibrating-tube densimeter and a Tian–Calvet differential calorimeter, respectively. Apparent molar volumes (Vϕ) and isobaric heat capacities (Cpϕ) calculated from these data were fitted with modified Redlich–Meyer type equations to derive the corresponding standard molar volumes and heat capacities at infinite dilution. Exact comparisons with literature data were not possible because of pressure differences but the present values, which greatly extend the database for KOH(aq) in terms of precision, temperature and concentration, are broadly compatible with most of the earlier results. Comparison of the present values of Vϕ and Cpϕ for KOH(aq) with corresponding data for solutions of the other alkali metal hydroxides indicated that all of these systems show si...

Phenomenological study of viscosity and density of alkali metal hydroxide solutions

Alkaline solutions are widely used in many industries. For dilute solutions, physicochemical properties, such as solubility of gases, hydration numbers and mobility of ions are well known. A relatively new trend is using concentrated alkaline solutions to obtain ferrates. In these processes, the solution concentration of more than 8 M is used. Studying the processes of transport of matter and charge in concentrated alkaline solutions requires updating the data on the hydration numbers and radii of ions, the effect of concentration, viscosity and nature of electrolytes on them. A method for determining the hydration numbers of alkali metal cations in hydroxide solutions, based on calculating the number of water moles per mole of cations at concentrations close to the limit was proposed. In addition, the influence of ions, strengthening and breaking the solution structure on the density and viscosity of alkali metal solutions was examined. It was shown that primary hydration of ions has the predominant impact on the solution viscosity in dilute solutions, and secondary - in concentrated. It was found that a sharp increase in the solution viscosity with increasing concentration occurs with decreasing distance between ions up to 3,7×10 -7 m. At high concentrations, the solution density is higher in hydrated cations with smaller dimensions. High density of lithium hydroxide solutions in concentrations of from 2 to 4 M can be explained by the fact that the positively hydrated cation is embedded in the structure of water without a significant increase in its volume.

Thermodynamic properties of molybdate ion: reaction cycles and experiments

Abstract Standard molar quantities of molybdate ion entropy, S m 0 , $S_{\rm{m}}^0,$ enthalpy of formation, Δ f H m o , ${\Delta _{\rm{f}}}H_m^{\rm{o}},$ and Gibbs energy of formation, Δ f G m o , ${\Delta _{\rm{f}}}G_{\rm{m}}^{\rm{o}},$ are key data for the thermodynamic properties of molybdenum compounds and complexes, which are at present investigated by an OECD NEA review project. The most reliable method to determine Δ f H m o ${\Delta _{\rm{f}}}H_{\rm{m}}^{\rm{o}}$ of molybdate ion and alkali molybdates directly consists in measuring calorimetrically the enthalpy of dissolution of crystallized molybdenum trioxide and anhydrous alkali molybdates in corresponding aqueous alkali metal hydroxide solutions. Solubility equilibria of sparingly soluble alkaline earth molybdates and silver molybdate lead to trustworthy data for Δ f G m o ${\Delta _{\rm{f}}}G_{\rm{m}}^{\rm{o}}$ of molybdate ion. Thereby the Gibbs energies of the metal molybdates and the corresponding metal ions are combined with the Gibbs energies of dissolution. As reliable values are available for Δ f G m o ${\Delta _{\rm{f}}}G_{\rm{m}}^{\rm{o}}$ of the relevant metal ions the problem reduces to select the best values of solubility constants and Δ f G m o ${\Delta _{\rm{f}}}G_{\rm{m}}^{\rm{o}}$ of alkaline earth molybdates and silver molybdate. There are two independent possibilities to achieve the latter task. (1) Δ f H m o ${\Delta _{\rm{f}}}H_{\rm{m}}^{\rm{o}}$ for alkaline earth molybdates and silver molybdate have been determined by solution calorimetry. Entropy data of molybdenum have been compiled and evaluated recently. CODATA key values are available for S m o $S_{\rm{m}}^{\rm{o}}$ of the other elements involved. Whereas S m o ( CaMoO 4 , cr ) $S_{\rm{m}}^{\rm{o}}({\rm{CaMo}}{{\rm{O}}_4},{\rm{ cr}})$ is well known since decades, low-temperature heat capacity measurements had to be performed recently, but now reliable values for S m o $S_{\rm{m}}^{\rm{o}}$ of Ag2MoO4(cr), BaMoO4(cr) and SrMoO4(cr) are available. (2) Δ f H m o ( BaMoO 4 , cr ) , ${\Delta _{\rm{f}}}H_{\rm{m}}^{\rm{o}}({\rm{BaMo}}{{\rm{O}}_4},{\rm{ cr}}),$ for example, can be obtained from high temperature equilibria also, but the result is less accurate than that of the first method. Once Gibbs energy of formation, Δ f G m o , ${\Delta _{\rm{f}}}G_{\rm{m}}^{\rm{o}},$ and enthalpy of formation, Δ f H m o , ${\Delta _{\rm{f}}}H_{\rm{m}}^{\rm{o}},$ of molybdate ion are known its standard entropy, S m o , $S_{\rm{m}}^{\rm{o}},$ can be calculated.

Structure and Diffusivity of Oxygen in Concentrated Alkali-Metal Hydroxide Solutions: A Molecular Dynamics Simulation Study

Molecular dynamics simulations of oxygen molecules in NaOH and KOH solutions at different temperatures (25-120 degrees C) and concentrations (1:100-1:5, molar ratios) were performed in this study. The interactions of oxygen molecules with the surrounding solvent and solute were clarified by considering the solvent-solvent, oxygen-solvent, and oxygen-solute radial distribution functions. The self-diffusion coefficients of the oxygen molecules and the solute were both determined by analyzing the mean-squared displacement (MSD) curves, using Einstein's relationship. It was concluded that at all concentrations, the diffusion coefficient of oxygen in NaOH solution is smaller than that in the corresponding KOH solution. The diffusion coefficients for hydroxide, Na+, and K+ decrease with increasing solute concentration, following similar trends to those of oxygen. The oxygen diffusion coefficient obtained in this study is in good agreement with the reported experimental value, suggesting that MSD is an attractive approach to study the oxygen diffusion behavior in strong alkaline solutions at elevated temperatures, which are experimentally extremely challenging.