Revealing the role and working mechanism of confined ionic liquids in solid polymer composite electrolytes

The confined ionic liquid(IL) in solid polymer composite electrolytes(SCPEs) can improve the performance of lithium metal batteries. However, the impact/role and working mechanism of confined IL in SCPEs remain ambiguous. Herein, IL was immobilized on SiO_(2)(SiO_(2)@IL-C) and then used to prepare the confined SCPEs together with LiTFSI and PEO to study the impacts of confined-IL on the properties and performance of electrolytes and reveal the Li+transport mechanism. The results show that, compared to the IL-unconfined SCPE, the IL-confined ones exhibit better performance of electrolytes and cells, such as higher ionic conductivity, higher t+Li, and wider electrochemical windows, as well as more stable cycle performance, due to the increased dissociation degree of lithium salt and enlarged polymer amorphousness. The finite-element/molecular-dynamics simulations suggest that the IL confined on the SiO_(2) provided an additional Li+transport pathway(Li+→ SiO_(2)@IL-C) that can accelerate ion transfer and alleviate lithium dendrites, leading to ultrastable stripping/plating cycling over 1900 h for the Li/SCPEs/Li symmetric cells. This study demonstrates that IL-confinement is an effective strategy for the intelligent approach of high-performance lithium metal batteries.

Hybrid data-driven and physics-based modeling for viscosity prediction of ionic liquids

Viscosity is one of the most important fundamental properties of fluids.However,accurate acquisition of viscosity for ionic liquids(ILs)remains a critical challenge.In this study,an approach integrating prior physical knowledge into the machine learning(ML)model was proposed to predict the viscosity reliably.The method was based on 16 quantum chemical descriptors determined from the first principles calculations and used as the input of the ML models to represent the size,structure,and interactions of the ILs.Three strategies based on the residuals of the COSMO-RS model were created as the output of ML,where the strategy directly using experimental data was also studied for comparison.The performance of six ML algorithms was compared in all strategies,and the CatBoost model was identified as the optimal one.The strategies employing the relative deviations were superior to that using the absolute deviation,and the relative ratio revealed the systematic prediction error of the COSMO-RS model.The CatBoost model based on the relative ratio achieved the highest prediction accuracy on the test set(R^(2)=0.9999,MAE=0.0325),reducing the average absolute relative deviation(AARD)in modeling from 52.45% to 1.54%.Features importance analysis indicated the average energy correction,solvation-free energy,and polarity moment were the key influencing the systematic deviation.

Melting points of ionic liquids:Review and evaluation

The melting points of ionic liquids(ILs)reported since 2020 were surveyed,collected,and reviewed,which were further combined with the previous data to provide a database with 3129 ILs ranging from 177.15 to 645.9 K in melting points.In addition,the factors that affect the melting point of ILs from macro,micro,and thermodynamic perspectives were summarized and analyzed.Then the development of the quantitative structure-property relationship(QSPR),group contribution method(GCM),and conductor-like screening model for realistic solvents(COSMO-RS)for predicting the melting points of ILs were reviewed and further analyzed.Combined with the evaluation together with the preliminary study conducted in this work,it shows that COSMO-RS is more promising and possible to further improve its performance,and a framework was thus proposed.

CO_2/N_2 separation using supported ionic liquid membranes with green and cost-effective [Choline][Pro]/PEG200 mixtures

The high price and toxicity of ionic liquids(ILs) have limited the design and application of supported ionic liquid membranes(SILMs) for CO_2 separation in both academic and industrial fields. In this work, [Choline][Pro]/polyethylene glycol 200(PEG200) mixtures were selected to prepare novel SILMs because of their green and costeffective characterization, and the CO_2/N_2 separation with the prepared SILMs was investigated experimentally at temperatures from 308.15 to 343.15 K. The temperature effect on the permeability, solubility and diffusivity of CO_2 was modeled with the Arrhenius equation. A competitive performance of the prepared SILMs was observed with high CO_2 permeability ranged in 343.3–1798.6 barrer and high CO_2/N_2 selectivity from 7.9 to 34.8.It was also found that the CO_2 permeability increased 3 times by decreasing the viscosity of liquids from 370 to38 m Pa·s. In addition, the inherent mechanism behind the significant permeability enhancement was revealed based on the diffusion-reaction theory, i.e. with the addition of PEG200, the overall resistance was substantially decreased and the SILMs process was switched from diffusion-control to reaction-control.

Ionic liquids/deep eutectic solvents for CO_(2) capture:Reviewing and evaluating

The CO_(2)solubilities(including CO_(2)Henry’s constant)in physical-and chemical-based ILs/DESs and the COSMO-RS models describing these properties were comprehensively collected and summarized.The summarized results indicate that chemical-based ILs/DESs are superior to physical-based ILs/DESs for CO_(2)capture,especially those ILs have functionalized cation and anion,and superbase DESs;some of the superbase DESs have higher CO_(2)solubilities than those of ILs;the best physical-and chemical-based ILs,as well as physical-and chemicalbased DESs are[BMIM][BF4](4.20 mol kg^(-1)),[DETAH][Im](11.91 mol kg^(-1)),[L-Arg]-Gly 1:6(4.92 mol kg^(-1))and TBD-EG 1:4(12.90 mol kg^(-1)),respectively.Besides the original COSMO-RS mainly providing qualitative predictions,six corrected COSMO-RS models have been proposed to improve the prediction performance based on the experimental data,but only one model is with universal parameters.The newly determined experimental results were further used to verify the perditions of original and corrected COSMO-RS models.The comparison indicates that the original COSMO-RS qualitatively predicts CO_(2)solubility for some but not all ILs/DESs,while the quantitative prediction is incapable at all.The original COSMO-RS is capable to predict CO_(2)Henry’s constant qualitatively for both physical-based ILs and DESs,and quantitative prediction is only available for DESs.For the corrected COSMO-RS models,only the model with universal parameters provides quantitative predictions for CO_(2)solubility in physical-based DESs,while other corrected models always show large deviations(>83%)compared with the experimental CO_(2)Henry’s constants.

Ionic liquids for CO_(2) electrochemical reduction

Electrochemical reduction of CO_(2) is a novel research field towards a CO_(2)-neutral global economy and combating fast accelerating and disastrous climate changes while finding new solutions to store renewable energy in value-added chemicals and fuels.Ionic liquids(ILs),as medium and catalysts(or supporting part of catalysts)have been given wide attention in the electrochemical CO_(2) reduction reaction(CO_(2) RR)due to their unique advantages in lowering overpotential and improving the product selectivity,as well as their designable and tunable properties.In this review,we have summarized the recent progress of CO_(2) electro-reduction in IL-based electrolytes to produce higher-value chemicals.We then have highlighted the unique enhancing effect of ILs on CO_(2) RR as templates,precursors,and surface functional moieties of electrocatalytic materials.Finally,computational chemistry tools utilized to understand how the ILs facilitate the CO_(2) RR or to propose the reaction mechanisms,generated intermediates and products have been discussed.

Prediction and verification of heat capacities for pure ionic liquids

The heat capacity of ionic liquids is an important physical property,and experimental measuring is usually used as a common method to obtain them.Owing to the huge number of ionic liquids that can be potentially synthesized,it is desirable to acquire theoretical predictions.In this work,the Conductor-like Screening Model for Real Solvents(COSMO-RS)was used to predict the heat capacity of pure ionic liquids,and an intensive literature survey was conducted for providing a database to verify the prediction of COSMO-RS.The survey shows that the heat capacity is available for 117 ionic liquids at temperatures ranging 77.66-520 K since 2004,and the 4025 data points in total with the values from 76.37 to 1484 J·mol^(-1)·K^(-1) have been reported.The prediction of heat capacity with COSMO-RS can only be conducted at two temperatures(298 and 323 K).The comparison with the experimental data proves the prediction reliability of COSMO-RS,and the average relative deviation(ARD)is 8.54%.Based on the predictions at two temperatures,a linear equation was obtained for each ionic liquid,and the heat capacities at other temperatures were then estimated via interpolation and extrapolation.The acquired heat capacities at other temperatures were then compared with the experimental data,and the ARD is only 9.50%.This evidences that the heat capacity of a pure ionic liquid follows a linear equation within the temperature range of study,and COSMO-RS can be used to predict the heat capacity of ionic liquids reliably.

Solubilities of CO_2, CH_4,H_2,CO and N_2 in choline chloride/urea

Solubilities of CO_2, CH_4, H_2, CO and N_2 in choline chloride/urea(ChCl/Urea) were investigated at temperatures ranging from 308.2 to328.2 K and pressures ranging from 0.6 to 4.6 MPa. The results show that the solubilities of gases increase with increasing pressure and decreasing temperature. The solubility of CO_2 is higher than that of CH_4, H_2, CO and N_2, which indicates that ChCl/Urea may be used as a potential solvent for CO_2 capture from the gas mixture. Solubility of CO_2 in ChCl/Urea was fitted by Non-Random Two-Liquid and Redlich-Kwong(NRTL-RK) model, and solubility of CH_4, H_2, CO or N_2 in ChCl/Urea was fitted by Henry's Law. The standard enthalpy, standard Gibbs energy and standard entropy of gases were calculated. Additionally, the CO_2/CH_4 selectivities in water, dry ChCl/Urea and aqueous ChCl/Urea were further discussed.

Physicochemical properties and structure of fluid at nano-/micro-interface:Progress in simulation and experimental study

In modern chemical engineering processes, the involvement of solid/fluid interface is the most important component of process intensification techniques, such as confined membrane separation and catalysis. In the review, we summarized the research progress of the latest theoretical and experimental works to elucidate the contribution of interface to the fluid properties and structures at nano-and micro-scale. We mainly focused on water, alcohol aqueous solution, and ionic liquids, because they are classical systems in interfacial science and/or widely involved in the industrialization process. Surface-induced fluids were observed in all reviewed systems and played a critical role in physicochemical properties and structures of outside fluid. It can even be regarded as a new interface, when the adsorption layer has a strong interaction with the solid surface. Finally, we proposed a perspective on scientific challenges in the modern chemical engineering processes and outlined future prospects.

Advances and challenges of electrolyzers for large-scale CO_(2) electroreduction

CO_(2) electroreduction(CO_(2) ER)to high value-added chemicals is considered as a promising technology to achieve sustainable carbon neutralization.By virtue of the progressive research in recent years aiming at design and understanding of catalytic materials and electrolyte systems,the CO_(2) ER performance(such as current density,selectivity,stability,CO_(2) conversion,etc.)has been continually increased.Unfortunately,there has been relatively little attention paid to the large-scale CO 2 electrolyzers,which stand just as one obstacle,alongside series-parallel integration,challenging the practical application of this infant technology.In this review,the latest progress on the structures of low-temperature CO_(2) electrolyzers and scale-up studies was systematically overviewed.The influence of the CO_(2) electrolyzer configurations,such as the flow channel design,gas diffusion electrode(GDE)and ion exchange membrane(IEM),on the CO_(2) ER performance was further discussed.The review could provide inspiration for the design of large-scale CO_(2) electrolyzers so as to accelerate the industrial application of CO_(2) ER technology.

Experimental studies of air-blast atomization on the CO_(2)capture with aqueous alkali solutions

In this work,an air-blast atomizing column was used to study the CO2 capture performance with aqueous MEA(mono-ethanol-amine)and Na OH solutions.The effects of gas flow rate,the liquid to gas ratio(L/G),the CO2 concentration on the CO2 removal efficiency(η)and the volumetric overall mass transfer coefficient(KGav)were investigated.The air-blast atomizing column was also compared with the pressure spray tower on the studies of the CO2 capture performance.For the aqueous MEA and Na OH solutions,the experimental results show that theηdecreases with increasing gas flow rate and CO2 concentration while it increases with increasing L/G.The effects on KGavare more complicated than those forη.When the CO2 concentration is low(3 vol%),KGavincreases with increasing gas flow rate while decreases with increasing L/G.However,when the CO2 concentration is high(9.5 vol%),as the gas flow rate and L/G increases,KGavincreases first and then decreases.The aqueous MEA solution achieves higherηand KGavthan the aqueous Na OH solution.The air-blast atomizing column shows a good performance on CO2 capture.

The biomethane producing potential in China： A theoretical and practical estimation

Biomethane has been developed rapidly in many countries as a renewable energy which upgraded from biogas. China also began to pay attention to it even though we still at a initial stage, primarily, understanding the hiomethane potential and development prospect, choosing appropriate biomass as the biomethane source is very important. In this work, the theoretical and practical biomethane producing potential from five main bio- mass resources in China were estimated with appropriate methods based on the data collected, and during cal- culation, two appropriate energy crops were assumed to be planted on marginal lands for biomethane production. Our estimation showed that the theoretical and practical biomethane potentials in China can reach to 888.78 and 316.30 billion m3 per year, agricultural waste should be the preferential development biomass, and planting energy crops on marginal lands is the most promising way to enhance biomethane production in China. Finally, biomethane is compared with natural gas, and the result showed that 48.15% of the practical biomethane potential can meet the total Chinese natural gas consumption in 2013.

Viscous behavior of 1-hexyl-methylimidazolium bis(trifluoromethylsulfonyl)imide/titanium dioxide/polyethylene glycol

Viscous behavior is important for the process design, especially for the non-Newtonian fluid. In this study, the viscous behaviors of slurry, i.e., 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)im ide([Hmim][NTf_(2)])/titanium dioxide(TiO_(2))-polyethylene glycol(PEG200), were determined experimentally and systematically. The pressure drop was estimated when [Hmim][NTf_(2)]/TiO_(2)-PEG200 was used as the solvent in the absorption/desorption towers. The results show that the slurry belongs to the non-Newtonian fluid with shear-thinning behavior. High temperature and low solid content are beneficial to reduce the viscosity of [Hmim][NTf_(2)]/TiO_(2)-PEG200, and the presence of [Hmim][NTf_(2)] can effectively reduce the viscosity of the slurry. In addition, high temperature is preferable for reducing the pressure drop, and the pressure drop of slurry with the solid content value of 8.0%(mass) can reduce by 28.0%when the temperature increases from 313 to 333 K.

Effect of dimethyl carbonate on the behavior of water confined in carbon nanotube

The dehydration of water by dimethyl carbonate(DMC)is of great significance for its application in electrochemistry and oil industry.With the rapid development of nanomaterial,one-dimensional(e.g.carbon nanotube(CNT))and two-dimensional(e.g.lamellar graphene)materials have been widely used for molecular sieving.In this work,the molecular behavior of dimethyl carbonate/water mixture confined in CNT with varying diameters was studied based on molecular dynamics simulation.Due to different van der Waals interactions for the components in the mixtures with the solid surface,DMC molecules are preferentially adsorbed on the inner surface of the pore wall and formed an adsorption layer.Comparing with the pure water molecules confined in CNT,the adsorption DMC layer shows notable effect on the local compositions and microstructures of water molecules under nanoconfinement,which may result in different water mobility.Our analysis shows that the surface-induced DMC molecules can destroy the hydrogen bonding network of water molecules and result in an uniform and dispersed distribution of water molecules in the tube.These clear molecular understandings can be useful in material design for membrane separation.

Thermodynamic analysis and modification of Gibbs–Thomson equation for melting point depression of metal nanoparticles

Abnormal melting point depression of metal nanoparticles often occurs in heterogeneous catalytic reactions,which leads to a reduction in the stability of reactive nanoclusters.To study this abnormal phenomenon,the original and surface-energy modified Gibbs-Thomson equations were analyzed in this work and further modified by considering the effect of the substrate.The results revealed that the original Gibbs-Thomson equation was not suitable for the particles with radii smaller than 10 nm.Moreover,the performance of the surface-energy modified Gibbs-Thomson equation was improved,and the deviation was reduced to(-350-100)K,although further modification of the equation by considering the interfacial effect was necessary for the small particles(r<5 nm).The new model with the interfacial effect improved the model performance with a deviation of approximately-50 to 20 K,where the interfacial effect can be predicted quantitatively from the thermodynamic properties of the metal and substrate.Additionally,the micro-wetting parameterα_W can be used to qualitatively study the overall impact of the substrate on the melting point depression.

Efficient SO_(2)removal using aqueous ionic liquid at low partial pressure

The development of novel absorbents is essential for SO_(2)removal.In this study,a novel ionic liquid(IL,[BHEP][HSO_(4)])was prepared,and water was selected as the co-solvent.The density and viscosity of aqueous[BHEP][HSO_(4)]were measured and the SO_(2)absorption performance was systematically investigated.Furthermore,the thermodynamic properties of SO_(2)in aqueous[BHEP][HSO_(4)]were calculated.Additionally,the mechanism of SO_(2)absorption in aqueous[BHEP][HSO_(4)]was confirmed using Fouriertransform infrared and nuclear magnetic resonance spectroscopy.It showed that[BHEP][HSO_(4)]absorbed0.302 g·g^(-1)(g SO_(2)/g IL)at an SO_(2)partial pressure of 2000μl·L^(-1)at 303.2 K,and the SO_(2)desorption enthalpy was-39.63 k J·mol^(-1).The mechanistic study confirmed the chemical absorption of SO_(2)in aqueous[BHEP][HSO_(4)].

Preface to special issue on frontiers of chemical engineering thermodynamics

“Thermodynamics is the only physical theory of universal content concerning which I am convinced that,within the framework of the applicability of its basic concepts,it will never be overthrown.”—Albert Einstein Chemical Engineering plays an essential role in modern society.It has been used to produce a wide variety of important materials,for example,the plastic drinking-water bottles,the jet fuels for transoceanic flights,and raw materials for assembling CPUs.Chemical Engineering is also on the frontline to manufacture massive masks,gloves,testing kits,and vaccines to fight against COVID-19 globally.

Emerging strategies and developments in oxygen reduction reaction using high-performance platinum-based electrocatalysts

The global practical implementation of proton exchange membrane fuel cells(PEMFCs)heavily relies on the advancement of highly effective platinum(Pt)-based electrocatalysts for the oxygen reduction reaction(ORR).To achieve high ORR performance,electrocatalysts with highly accessible reactive surfaces are needed to promote the uncovering of active positions for easy mass transportation.In this critical review,we introduce different approaches for the emerging development of effective ORR electrocatalysts,which offer high activity and durability.The strategies,including morphological engineering,geometric configuration modification via supporting materials,alloys regulation,core-shell,and confinement engineering of single atom electrocatalysts(SAEs),are discussed in line with the goals and requirements of ORR performance enhancement.We review the ongoing development of Pt electrocatalysts based on the syntheses,nanoarchitecture,electrochemical performances,and stability.We eventually explore the obstacles and research directions on further developing more effective electrocatalysts.

Recent applications of ionic liquids in quasi-solid-state lithium metal batteries

Quasi-solid-state lithium metal batteries are considered as one of the most promising energy storage devices,and the application of ionic liquids(ILs)as a new generation of functionalized electrolyte components in lithium metal batteries has become one of the research focuses.In this review,the very recent research work related to using ILs to develop quasi-solid-state electrolytes and their influences on the performances of quasi-solid-state lithium metal batteries were surveyed and summarized,suggesting that the introduction of ILs can improve the ionic conductivity,broaden the electrochemical stability window,and enhance the electrochemical stability of the selected electrolytes.Moreover,using ILs to prepare high-performance electrodes with unique microstructures and uniform distribution of fillers were also introduced.The composite quasi-solid-state electrolytes were suggested as the mainstream of electrolytes in the future due to the combination of the advantages of inorganic and polymer quasi-solid-state electrolytes,and their development challenges in high energy and high safety quasisolid-state lithium metal batteries were also discussed.

Electrochemical CO_(2) reduction with ionic liquids: review and evaluation

The increasing CO_(2) emission,as the chief culprit causing numerous environmental problems,could be addressed by the electrochemical CO_(2) reduction(CO_(2)R)to the added-value carbon-based chemicals.Ionic liquids(ILs)as electrolytes and co-catalysts have been widely studied to promote CO_(2)R owing to their unique advantages.Among the potential products of CO_(2)R,those only containing one carbon atom,named C1 products,including CO,CH_(3)OH,CH_(4),and syngas,are easier to achieve than others.In this study,we first summarized the research status on CO_(2)R to these C1 products,and then,the state-of-theart experimental results were used to evaluate the economic potential and environmental impact.Considering the rapid development in CO_(2)R,future scenarios with better CO_(2)R performances were reasonably assumed to predict the future business for each product.Among the studied C1 products,the research focuses on CO,where satisfactory results have been achieved.The evaluation shows that producing CO via CO_(2)R is the only profitable route at present.CH3OH and syngas of H2/CO(1:1)as the targeted products can become profitable in the foreseen future.In addition,the life cycle assessment(LCA)was used to evaluate the environmental impact,showing that CO_(2)R to CH4 is the most environmentally friendly pathway,followed by the syngas of H_(2)/CO(2:1)and CO,and the further improvement of the CO_(2)R performance can make all the studied C1 products more environmentally friendly.Overall,CO is the most promising product from both economic and environmental impact aspects.