Nernst-Einstein Equation Research Articles

Hydration and Diffusion of H+, Li+, Na+, Cs+ Ions in Cation-Exchange Membranes Based on Polyethylene- and Sulfonated-Grafted Polystyrene Studied by NMR Technique and Ionic Conductivity Measurements.

The main particularities of sulfonate groups hydration, water molecule and alkaline metal cation translation mobility as well as ionic conductivity were revealed by NMR and impedance spectroscopy techniques. Cation-exchange membranes MSC based on cross-linked sulfonated polystyrene (PS) grafted on polyethylene with ion-exchange capacity of 2.5 mg-eq/g were investigated. Alkaline metal cation hydration numbers (h) calculated from temperature dependences of 1H chemical shift of water molecule for membranes equilibrated with water vapor at RH = 95% are 5, 6, and 4 for Li+, Na+, and Cs+ ions, respectively. These values are close to h for equimolar aqueous salt solutions. Water molecules and counter ions Li+, Na+, and Cs+ diffusion coefficients were measured by pulsed field gradient NMR on the 1H, 7Li, 23Na, and 133Cs nuclei. For membranes as well as for aqueous chloride solutions, cation diffusion coefficients increased in the following sequence: Li+ < Na+ < Cs+. Cation and water molecule diffusion activation energies in temperature range from 20 °C to 80 °C were close to each other (about 20 kJ/mol). The cation conductivity of MSC membranes is in the same sequence, Li+ < Na+ < Cs+ << H+. The conductivity values calculated from the NMR diffusion coefficients with the use of the Nernst–Einstein equation are essentially higher than experimentally determined coefficients. The reason for this discrepancy is the heterogeneity of membrane pore and channel system. Ionic conductivity is limited by cation transfer in narrow channels, whereas the diffusion coefficient characterizes ion mobility in wide pores first of all.

Mobility-viscosity decoupling and cation transport in water-in-salt lithium electrolytes

Two super-concentrated aqueous electrolyes, or water-in-salt electrolytes, comprising the lithium trifluoromethanesulfonate (LiTf-H2O) binary system, and the ternary system with bis(trifluoromethanesulfonyl)-imide (LiTFSI-LiTf-H2O), were analyzed in relation to their conductivity, viscosity, diffusion of all the species and cationic transport number. The conductivity–viscosity and the ionic diffusion-viscosity decoupling were analyzed by means of the Walden law and the Stokes–Einstein relationship, respectively. The results, including those already reported for LiTFSI-H2O, reveal the existence of a significant decoupling of the Li+ mobility from the solution viscosity, while the corresponding anions follow the classical hydrodynamic behavior. The Li+ apparent transport number, derived from the self-diffusion coefficients measured by NMR, increases with concentration, due to the decoupling. These facts strongly support the formation of two types of nano-domains in the superconcentrated salt solutions with different mobility characteristics: a region formed by a net of anions with restricted mobility, percolated by clusters of reduced local viscosity that boost the mobility of Li+ ions. Finally, the difference between the experimental conductivity and that calculated using the Nernst–Einstein equation was rationalized in terms of the velocity correlation and resistance coefficients calculated using the measured transport coefficients.

Effect of PAMAM Dendrimers on Interactions and Transport of LiTFSI and NaTFSI in Propylene Carbonate-Based Electrolytes.

Poly(amidoamine) (PAMAM)-based electrolytes are prepared by dissolving the PAMAM half-generations G1.5 or G2.5 in propylene carbonate (PC), either with lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) or sodium bis(trifluoromethylsulfonyl)imide (NaTFSI) salts. The solutions, designed for ion battery applications, are studied in terms of ions transport properties. Raman Spectroscopy reveals information about the interactions between cations and PAMAM dendrimers as well as full dissociation of the salts in all solutions. Pulsed-field gradient Nuclear Magnetic Resonance (PFG NMR), measured as a function of both temperature and PAMAM concentration, are obtained for the cation, anion, solvent, and dendrimer molecules using lithium (7Li), sodium (23Na), fluorine (19F), and hydrogen (1H) NMR, respectively. It was found that lithium diffusion is slow compared to the larger TFSI anion and decreases with PAMAM concentration due to interactions between cation and dendrimer. Comparison of conductivities calculated from diffusion coefficients using the Nernst–Einstein equation, with conductivity measurements obtained from Impedance Spectroscopy (IS), shows slightly higher IS conductivities, caused among others by PAMAM conductivity.

Electrical resistivity model for quantifying concrete chloride diffusion coefficient

The effects of chloride salts on concrete durability have been financially and logistically overwhelming. Current test methods for quantifying diffusivity of chlorides in concrete are time consuming and demanding. A comprehensive electrical resistivity model has been developed to quantify the chloride diffusion coefficient of concrete. The model employs the modified Nernst-Einstein equation along with an ionic concentration sub-model, a pore solution conductivity sub-model, and a binder hydration sub-model. The sub-models, which account for the concentrations of Na+, K+, Ca2+, and OH− ions in the pore solution derived from the binder degree of hydration, binder chemical composition, and alkalis binding to the cement hydration products, are included to accurately quantify the conductivity of the pore solution. Moreover, an experimental program was developed to verify and validate the accuracy and completeness of the electrical resistivity model. The experimental variables are volume fraction of coarse aggregate, water to binder ratio, total binder content, and silica fume (SF) and ground granulated blast furnace slag (GGBFS) as supplementary cementing materials (SCMs). The model results are found statistically equal to experimentally quantified chloride diffusion coefficient values and possess high accuracy and precision for a wide range of concrete mixture, binder composition and age.

(Invited) Strain Effects on Li Ion Conductivity – Migration, Defect Correlations, and Structural Changes

Elastic or plastic strain at cathode/electrolyte interfaces can affect the charge transfer kinetics in all-solid-state Li-ion batteries. Quantifying this effect both for Li ion conduction within the solid electrolyte material and for the Li transfer ability at the interface is important for understanding the kinetics of solid state batteries. Depending on the strain tensor, the impact could be beneficial or, alternatively, detrimental. While it is generally known that isotropic tensile strain increases the ionic conductivity and compressive strain decreases it [1], how different strain fields act upon Li ion conduction is not yet assessed. Existing studies show a non-trivial decrease/increase of Li-ion migration energies depending on relative alignment of migration direction and strain field [2], making quantitative estimates of conductivity changes difficult to predict. Here, we study the effect of strain on Li ion conductivity of β-Li3PS4 by means of Ab Initio Molecular Dynamics (AIMD) simulations. Ionic conductivity is directly calculated from AIMD trajectories using Nernst–Einstein equation, as it is linearly proportional to the diffusivity of the center-of-mass of all Li-ions [3]. Our calculations indicate that biaxial strain could substantially promote correlated motions of Li-ions, which in turn could increase ionic conductivity of β-Li3PS4. The effect depends on direction of applied strain, and the underlying structural changes increasing ionic conductivity are discussed.[1] Y. Wang, W.D. Richards, S.P. Ong, L.J. Miara, J.C. Kim, Y. Mo and G. Ceder, Design principles for solid-state lithium superionic conductors, Nat. Mater. 14 , 1026–1031 (2015)[2] C. O’Rourke and B. Morgan, Interfacial strain effects on lithium diffusion pathways in the spinel solid electrolyte Li-doped MgAl2O4, Phys. Rev. M 2, 045403 (2018)[3] A. Marcolongo and N. Marzari, Ionic correlations and failure of Nernst-Einstein relation in solid-state electrolytes, Phys. Rev. M 1, 025402 (2017)

The Slice-Resistivity method to measure the chloride ion diffusion coefficient of cementitious materials

Most of the existing experimental and research methods for the diffusion of chloride ions in cement-based materials use an applied electric field test method with electrodes, which are unable to eliminate the effect of polarization. In this study, the relationship between resistivity and chloride ion diffusion coefficient (CIDC) is established by the Nernst-Einstein equation. Based on the non-contract electrical resistivity measurement technique, the resistivity of cement-based material is measured by the Slice-Resistivity method, in which the chloride ion diffusion coefficient can be obtained with no polarization effect. In the experiments undertaken, the chloride ion diffusion coefficients of samples with 0.3, 0.4, 0.5 water-cement ratios and aggregate volume fractions of 12%, 22% were calculated at 3, 7, 14 and 28 days ages. It was found that the size of the slices has no influence on the results; however a decrease of the water-cement ratio as well as an increase of aggregate volume would lower the chloride ion diffusion coefficient. According to the experimental results and the Bruggeman model, a new general equation describing the relationship between w/c, curing time, aggregate volume and the chloride ion diffusion coefficient is proposed. In addition, simulation based on the homogenization method is applied to predict the equivalent chloride ion diffusion coefficient of the samples added aggregate. The results show that the simulation results are consistent with the experimental results, especially for 14 and 28 days.

Impact of Frictional Interactions on Conductivity, Diffusion, and Transference Number in Ether- and Perfluoroether-Based Electrolytes

There is growing interest in fluorinated electrolytes due to their high-voltage stability. We use full electrochemical characterization based on concentrated solution theory to investigate the underpinnings of conductivity and transference number in tetraglyme/LiTFSI mixtures (H4) and a fluorinated analog, C8-DMC, mixed with LiFSI (F4). Conductivity is significantly lower in F4 than in H4, and F4 exhibits negative cation transference numbers, while that of H4 is positive at most salt concentrations. By relating Stefan-Maxwell diffusion coefficients, which quantify ion-solvent and cation-anion frictional interactions, to conductivity and transference number, we determine that at high salt concentrations, the origin of differences in transference number is differences in anion-solvent interactions. We also define new Nernst-Einstein-like equations relating conductivity to Stefan-Maxwell diffusion coefficients. In H4 at moderate to high salt concentrations, we find that all molecular interactions must be included. However, we demonstrate another regime, in which conductivity is controlled by cation-anion interactions. The applicability of this assumption is quantified by a pre-factor, which is similar to the “ionicity” pre-factor that is often included in the Nernst-Einstein equation. In F4, is unity at all salt concentrations, indicating that ionic conductivity is entirely controlled by the Stefan-Maxwell diffusion coefficient quantifying cation-anion frictional interactions.

A Predictive Thermodynamic-Based Model for Proton Conductivity of Proton Exchange Membranes Based on Poly(Benzimidazole)/Poly(Acrylic Acid) Blend

To predict the novel poly(benzimidazole):poly(acrylic acid) (PBI:PAA) blend membranes proton conductivity, an ionic conductivity equation combined with thermodynamic model is proposed where different proton transport mechanisms including Grotthuss, vehicle and surface hopping mechanisms are considered in calculations. Based on the PAA titration behavior, by increasing the number-average molecular weight (), apparent acidity of PAA decreases. Hence, to calculate the concentration of protons involved in different mechanisms, a new modification in the predictive model is suggested by considering acidity and its relation with Effect of temperature, PAA molar ratio and on the membranes proton conductivity is investigated theoretically and compared with experimental data. The conductivity of membranes is increased by increasing the and molar ratio of PAA where the highest proton conductivity is attributed to the membrane with PAA of = 105 g · mol−1 and molar ratio of PBI:PAA = 1:4. The experimental proton conductivity and predicted results show a good agreement in comparison to the previous models based on Nernst–Einstein equation, indicating that acidic behavior, which is usually omitted in theoretical models, has an important effect on the total proton conductivity of PBI:Polyacid membranes, especially at higher temperatures.

Mobility of Cations and Water Molecules in Sulfocation-Exchange Membranes Based on Polyethylene and Sulfonated Grafted Polystyrene

The main patterns of the hydration of sulfo groups, the translational mobility of water molecules, alkali metal cations, and ionic conductivity in sulfocation-exchange membranes (MSC) based on polyethylene and sulfonated grafted polystyrene have been investigated using NMR and impedance spectroscopy techniques. It has been shown that at moisture contents λ < 4 (λ is the number of water molecules per sulfo group) the H+ counterions in the membranes form diaquahydrogen ions $${{{\text{H}}}_{{\text{5}}}}{\text{O}}_{{\text{2}}}^{ + }{\text{.}}$$ In the temperature range below 0°C at λ < 12, water molecules retain high mobility and do not form the ice phase. Water molecules diffusion coefficients (for the H+ form, the average diffusion coefficient of water molecules and acidic protons) and first for ion-exchange systems, and the diffusion coefficients of counterions Li+, Na+, and Cs+ have been measured by pulsed field gradient 1H, 7Li, 23Na, and 133Cs NMR spectroscopy. In MSC membranes in contact with water, the self-diffusion coefficients of cations increase in the Li+ < Na+ < Cs+ series. The cation conductivity values are in the same Li+ < Na+ < Cs+$$ \ll $$ H+ sequence. The cation conductivity values calculated from the self-diffusion coefficients based on the Nernst–Einstein equation are essentially higher than the experimental values.

Sensor-based time-dependent formation factor in prediction of chloride ingress in mortar

Characterisation of chloride ingress rate is crucial for service life predictions in reinforced concrete. In this study, the time-dependent chloride diffusion coefficient (DCl(t)) was determined using real-time non-destructive embedded sensors. First, the time-dependent formation factor was established based on continuous electrical conductivity data from the sensors, which provided DCl(t) by the Nernst–Einstein equation. Twelve mortar mixtures were included that varied in water/cementitious materials ratio (w/c) and supplementary cementitious material (SCM) content. A numerical model of chloride diffusion using the established DCl(t) was developed by solving Fick's second law of diffusion using the finite-difference method. The model's predictions agreed well with experimental chloride profiles available in the literature. The results of chloride ingress simulation for all tested mixtures clearly showed the effect of reducing the w/c and using more SCM on slowing the rate of chloride ingress. Furthermore, the developed DCl(t) relations were used to establish a diffusion decay coefficient (mdiff) for all tested mixtures, leading to the development of empirical formulations for DCl(t) and mdiff as a function of w/c and SCM content. The results of this study demonstrate the potential of the implemented non-destructive technique in efficient assessment of transport properties of mortar related to chloride ingress.

Ion Pairing Controls Physical Properties of Ionic Liquid-Solvent Mixtures.

The dissolution of room temperature ionic liquids (RTILs) in organic solvents has been shown to enhance ion dynamics. We previously used molecular dynamics (MD) simulations to study the ionic liquid ([BMIM+][Tf2N-]) in 22 unique solvents over a wide range of concentrations. By screening over a large parameter space, we reached several conclusions: (1) ion diffusivity increases monotonically as a function of increasing ionic liquid composition, (2) pure solvent diffusivity strongly correlates with ion diffusivity, and (3) conductivity predicted by the Nernst-Einstein (NE) equation has a maximum at intermediate compositions of ionic liquid. Building off this work, we now utilize the same parameter space to study the structure of ([BMIM+][Tf2N-]) solvated in organic solvents. We explore ion correlations through a number of structural and thermodynamic properties, including liquid densities, pair correlation functions, ion pairing and ion caging lifetimes, and free energy calculations. Through these analyses, we find that some solvents are much more effective at screening ion-ion interactions than others and that these differences impact the ion dynamics in these mixtures. In general, the strong pairing of ionic liquids negatively impacts transport properties, but some solvents can robustly screen these interactions, resulting in greatly enhanced ion dynamics. These results uncover trends connecting ionic liquid structure to transport, which can help in the design of new electrolytes for energy storage devices, such as electrical double layer capacitors and batteries.

Oxygen isotope exchange in proton-conducting oxides based on lanthanum scandates

A method of the oxygen isotope exchange with equilibration of the gas phase was used in order to obtain the temperature dependences of the oxygen surface exchange and diffusion coefficients of the proton-conducting oxides La1–xSrxScO3–δ (x = 0; 0.04; 0.09) in the temperature range of 600–900 °C and oxygen pressure of 1.01 kPa. The diffusion and oxygen surface exchange coefficients increase with the strontium content in oxides. The rates of the individual stages of the oxygen exchange process on the surface of the oxides were determined. The oxygen incorporation was revealed to be rate-determining for the undoped LaScO3 oxide. However, for the strontium-doped oxides La1–xSrxScO3–δ (x = 0.04; 0.09), the difference between the rates of oxygen dissociative adsorption and oxygen incorporation decreases with increasing the strontium concentration, in a way that for the La0.91Sr0.09ScO3−δ oxide these stages become competing. The possible reasons for these differences in oxygen surface exchange kinetics were analyzed in this paper. Using the obtained oxygen diffusion coefficients, the oxygen-ionic conductivities in accordance with the Nernst-Einstein equation, and the contributions of the oxygen-ion and proton components of the total conductivity of the La1–xSrxScO3–δ (x = 0.04; 0.09) oxides in the wet reducing atmosphere (pH2O = 2.35 kPa, pO2 = 10−15 Pa) were calculated. The proton transference numbers were found to be close to unit at the wet reducing atmospheres in the temperature range of 500–600°С.

Effect of Temperature and Water Content on the Properties of Solid Protic Electrolyte of Tetra Calixarene Sulfonic Acid: NMR Study

The methods of 1H NMR and pulsed field gradient NMR are used to study the protic solid electrolyte of calix[4]arene-para-sulfonic acid in the temperature range of –15 to 24°C and water content λ of 1.6 to 5.7 H2O molecules per SO3H. Analysis of the 1H signal intensity in NMR spectra showed that no ice phase is formed in the whole studied temperature and water content range. The hydration numbers of H+(H2O)h complexes are calculated on the basis of the temperature dependences of chemical shift values. The pulsed field gradient NMR technique is used to determine self-diffusion coefficients. Activation energies Eact are calculated on the basis of the temperature dependences of self-diffusion coefficients. Good agreement of the data on diffusion Eact and protic conductivity are shown. A corollary of the Nernst–Einstein equation is used to calculate the values of protic conductivity on the basis of self-diffusion data. The calculated values of protic conductivity in the water content λ range of 1.6 to 5.7 agree with the data obtained experimentally.

Transport anomalies emerging from strong correlation in ionic liquid electrolytes

Strong ionic interactions in concentrated ionic liquids is shown to result in significant correlations and deviations from ideal solution behavior. We use rigorous concentrated solution theory coupled with molecular dynamics simulations to compute and explain the unusual dependence of transport properties on cation concentration in the Na+-Pyr13+-FSI− ionic liquid electrolyte. When accounting for intra- and inter-species correlation, beyond the commonly used uncorrelated Nernst-Einstein equation, an anomalously low and even negative transference number emerges for xNaFSI lower than 0.2. With increasing concentration the transference number monotonically increases, approaching unity, while the total conductivity decreases as the system transitions to a state resembling a single-ion solid-state electrolyte. The degree of spatial ionic association is explored further by employing unsupervised single-linkage clustering algorithm. We emphasize that strong ion-ion coupling in the electrolyte significantly impacts the trade-off between key electrolyte transport properties, and consequently governs the power density of the battery.

Correlations from Ion Pairing and the Nernst-Einstein Equation.

We present a new approximation to ionic conductivity well suited to dynamical atomic-scale simulations, based on the Nernst-Einstein equation. In our approximation, ionic aggregates constitute the elementary charge carriers, and are considered as noninteracting species. This approach conveniently captures the dominant effect of ion-ion correlations on conductivity, short range interactions in the form of clustering. In addition to providing better estimates to the conductivity at a lower computational cost than exact approaches, this new method allows us to understand the physical mechanisms driving ion conduction in concentrated electrolytes. As an example, we consider Li^{+} conduction in poly(ethylene oxide), a standard solid-state polymer electrolyte. Using our newly developed approach, we are able to reproduce recent experimental results reporting negative cation transference numbers at high salt concentrations, and to confirm that this effect can be caused by a large population of negatively charged clusters involving cations.

Ion transport and association study of glyme-based electrolytes with lithium and sodium salts

Glyme solvents are a promising avenue of research in novel electrolytes, due to their thermal and chemical stability, large electrochemical window, and tunable properties. This work investigates the transport properties of LiPF6 and NaPF6 salts in Monoglyme (G1), Diglyme (G2), and Tetraglyme (G4). Self-Diffusion coefficients, and degrees of ion association were found through spectroscopic techniques. Raman and Fourier-Transform Infrared (FTIR) spectroscopy exhibited an absorbance peak at 740 cm−1, corresponding to the a1g mode; known to signify the presence of solvent-separated and contact ion pairs. The increased intensity of this peak for G1 compared to G4 suggests that the electrolyte exhibits stronger association with decreasing solvent size. Nuclear Magnetic Resonance Diffusometry measurements yield self-diffusion coefficients for 7Li, 23Na, and 19F across all samples to be on the order of 10−9 m2s−1 in G1, to 10−11 m2s−1 in G4. Comparison of conductivities calculated from the measured diffusivities and the Nernst-Einstein equation with conductivity measurements deduced from Electrochemical Impedance Spectroscopy (EIS) determined the ion association degree; the electrolytes were shown to exhibit stronger ion pairing with increased temperature which is attributed to a decrease in the dielectric constant of the solvents with increasing temperature. Additionally, the ion association was shown to decrease with increasing solvent molecular size, consistent with FTIR findings.

A sandwich-structured double-battery device for direct evaluation of lithium diffusion coefficients and phase transition in electrodes of lithium ion batteries

Li diffusion efficiency reflects the kinetics of Li intercalation/de-intercalation in solid electrode materials and determines the rate performances of Li ion batteries. Traditional techniques including the electrochemical impedance spectroscopy, potential intermittent titration technique, potential relaxation technique, galvanostatic intermittent titration technique, and cyclic voltammetry, could lead to significant disagreement on Li chemical diffusion coefficients due to the limited reliability of the parameters required for calculating Li diffusion coefficients. Based on the Nernst-Einstein equation, a double-battery system is proposed for the direct measurement of chemical diffusion coefficients of Li in solid electrodes. With the double-battery system, Li diffusion coefficients in the intercalation/de-intercalation of graphite electrodes featured with phase-transition and double-phase regions, are measured efficiently, with consistent values in the range of 10−10–10−9 cm2/s. The direct measurement then allows for the evaluation of the diffusion barrier associated with Li intercalation/de-intercalation in the electrodes.

Comparative Study of Alkali-Cation-Based (Li+ , Na+ , K+ ) Electrolytes in Acetonitrile and Alkylcarbonates.

The development of a suitable functional electrolyte is urgently required for fast-charging and high-voltage alkali-ion (Li, Na, K) batteries as well as next-generation hybrids supercapacitors. Many recent works focused on an optimal selection of electrolytes for alkali-ion based systems and their electrochemical performance but the understanding of the fundamental aspect that explains their different behaviour is rare. Herein, we report a comparative study of transport properties for LiPF6 , NaPF6 , KPF6 in acetonitrile (AN) and a binary mixture of ethylene carbonate (EC), dimethyl carbonate (DMC): (EC/DMC : 1/1, weigh) through conductivities, densities and viscosities measurements in wide temperature domain. By application of the Stokes-Einstein, Nernst-Einstein, and Jones Dole equations, the effective ionic solvated radius of cation (reff ), the ionic dissociation coefficient (αD ) and structuring Jones Dole's parameters (A, B) for salt are calculated and discussed according to solvent or cation nature as a function of temperature. From the results, we demonstrate that better mobility of potassium can be explained by the nature of the ion-ion and ion-solvent interactions due to its polarizability. In the same time, the predominance of triple ions in the case of K+ , is a disadvantage at high concentration.

Characterization of Aqueous 1-Ethyl-3-Methylimidazolium Ionic Liquids for Calculation of Ion Dissociation.

We employ precise measuring techniques to determine the densities, viscosities, and ionic conductivities of three aqueous 1-ethyl-3-methylimidazolium [emim]+ ionic liquid (IL) systems with minimal experimental uncertainty. We simultaneously present a novel method for estimating ion dissociation relying only on these three measurements and the estimated Stokes radii of the ions based on the Stokes-Einstein and Nernst-Einstein equations. Ion dissociation values are estimated across a range of IL concentrations, emphasizing dilute IL regions, using ionic radii calculated from widely used UNIQUAC and UNIFAC values. With these approximations and assuming the presence of only ion pairs, the ion dissociation of all three ILs reaches a minimum value at a water mole fraction of about 0.98. Upon further dilution with water, the ion dissociation increases as the system approaches infinite dilution of the IL. We postulate that the apparent minimum in the ion dissociation is caused by the Stokes radii of the cation and anion increasing as the concentration becomes more dilute, due to the formation of ion triplets.

Understanding the behavior of mixtures of protic-aprotic and protic-protic ionic liquids: Conductivity, viscosity, diffusion coefficient and ionicity

We have investigated the physicochemical properties such as electrical conductivity, viscosity and diffusion coefficient for the binary mixtures of protic ionic liquids with aprotic ionic liquids and of protic with protic ionic liquids at 298.15 K. A significant enhancement in the electrical conductivity is observed for the binary mixtures of ionic liquids, as compared to those of the constituent pure ionic liquids and varied with the composition of the mixtures. The viscosity of binary mixtures of protic with aprotic ionic liquids, 1‑butyl‑3‑methylimidazoliumbis(trifluoromethylsulfonyl)imide [bmIm][NTf2], 1‑butyl‑1‑methylpyrrolidiumbis(trifluoromethylsulfonyl)imide [bmPyrr][NTf2] and 1,3-dimethylimidazolium methyl sulfate, [mmIm][CH3SO4] decreases with an increase in the composition of the [HmIm][CH3COO]. On the contrary, the viscosity for binary mixtures of protic with protic ionic liquid, 1‑methylpyrrolidium acetate [HmPyrr][CH3COO] and 4‑methylmorpholine acetate [HmMorph][CH3COO] increases upon the addition of 1‑methylimidazolium acetate [HmIm][CH3COO]. The self diffusion coefficients were determined for all the binary mixtures of ionic liquids by using Pulsed Gradient Spin Echo (PGSE) NMR method. Self diffusion coefficients of [bmIm][NTf2]-[HmIm][CH3COO], [bmPyrr][NTf2]-[HmIm][CH3COO], [mmIm][CH3SO4]-[HmIm][CH3COO] are enhanced, while those of [HmPyrr][CH3COO]-[HmIm][CH3COO] and [HmMorph][CH3COO]-[HmIm][CH3COO] decreases on addition of [HmIm][CH3COO]. This is converse in the case of viscosity. Furthermore, the above correlations were interpreted with the help of NMR spectroscopy on the basis of interactions of ions in the binary mixtures of ionic liquids. Finally, we have quantified the ionicity through the Nernst–Einstein equation and have confirmed the validity of the Walden rule for the binary mixture of ionic liquids.