Proton exchange membrane fuel cells (PEMFCs) have emerged as a key research area due to their ability to convert various gaseous energy sources (such as hydrogen and methanol) into electrical energy with high efficiency and zero pollution. The design of the proton exchange membrane (PEM), which is the site for proton transfer, is critical. To explore the influence of characteristic functional groups on proton transfer mechanism in biomimetic proton exchange membranes, the crown ether structure was introduced into polymer backbone chains to mimic biological ion channels. The motion behaviors of proton were qualitatively characterized through molecular dynamics simulation. It was found that protons are strongest complexed in the best matching 18CO6-PEM case based on the analysis of RDF, residence time, interaction energy, and number of hydrogen bonds. The characteristic groups of biological proton channels with smaller or larger pores can help protons detach from the complexation under the action of an electric field. The proton transfer in crown-ether biomimetic proton exchange membranes is not just a single mechanism, but a compromise between two mechanisms in parallel. This work provides a new perspective on designing proton conduction membranes by embedding large ring motifs with intrinsic cavities and the key parameters required for establishing the proton transfer model.

Deep eutectic solvents (DESs) have garnered attention in Li-ion battery (LIB) recycling due to their declared eco-friendly attributes and adjustable metal dissolution selectivity, offering a promising avenue for recycling processes. However, DESs currently lack competitiveness compared to mineral acids, commonly used in industrial-scale LIB recycling. Current research primarily focuses on optimizing DES formulation and experimental conditions to maximize metal dissolution yields in standalone leaching experiments. While achieving yields comparable to traditional leaching systems is important, extensive DES reuse is vital for overall recycling feasibility. To achieve this, evaluating the metal dissolution mechanism can assist in estimating DES consumption rates and assessing process makeup stream costs. The selection of appropriate metal recovery and DES regeneration strategies is essential to enable subsequent reuse over multiple cycles. Finally, decomposition of DES components should be avoided throughout the designed recycling process, as by-products can impact leaching efficiency and compromise the safety and environmental friendliness of DES. In this review, these aspects are emphasized with the aim of directing research efforts away from simply pursuing the maximization of metal dissolution efficiency, towards a broader view focusing on the application of DES beyond the laboratory scale.

In this study L-(+)-tartaric acid was used to extract metals from either pure cathode material (NMC111) or black mass from spent lithium-ion batteries. The leaching efficiencies of Li, Co, Ni, and Mn from NMC111 are > 87% at 70 °C, with an initial solid to liquid ratio of 17, and > 72.4±1.0% from black mass under corresponding conditions. The metals tend to form mixed phases in antisolvent crystallization and seeding has a minimal effect on the final solid composition. Impurities influence both crystal nucleation and growth. By controlling the antisolvent addition rate crystal growth can be promoted. The theoretical dielectric constant of the solution is shown to correlate excellently to the recovery efficiency across different antisolvents, where a value <52 results in over 95% total transition metal recovery efficiency. The correlation can be a powerful tool for quantitative prediction of optimal solvent composition for effective antisolvent crystallization.

Carbon capture technology is a prospective strategy to address the increasing concentration of CO2 in the atmosphere, with the core challenge of developing new cost-effective processes. In this work, the energy analysis and economic evaluation were conducted based on rigorous thermodynamic models and the process simulation results of a novel chemical absorption-dominated hybrid solvent which consists of functional ionic liquid of choline triazole ([Cho][Triz]) and sulfolane (TMS) to separate CO2 from shale gas. The solubility of CO2 and CH4 in different solvents were calculated using phase equilibrium model including the NRTL activity coefficient equation, the RK equation of state, chemical reaction equilibrium equations, and the mass balance equation. The physical properties of the ionic liquid-based solvent systems were calculated with empirical equations which was corrected using experimental data. The results obtained from the thermodynamic models exhibited good agreement with experimental data. Subsequently, the established models and the parameters obtained were embedded into Aspen Plus for further analysis. The total CO2 capture energy consumption of 1.65 GJ·t−1 CO2 and the cost of 48.07 $·t−1 CO2 were achieved using the new solvent when the mass fraction of IL was 60 wt%. Compared with the commercial 30 wt% MDEA carbon capture process, it reduced the energy consumption and economic cost of 64.16 % and 45.59 %, respectively.

With the increasing demand for rechargeable lithium-ion batteries, arises an interest in the recycling processes for such devices. Possible methods include a range of processing conditions yielding different precursors which need to be integrated into upstream production. Here, we demonstrate a synthesis method that is compatible with the organic precursor obtained from citric acid-based leaching of lithium cobalt oxide (LCO) followed by acetone antisolvent crystallization. A lithium cobalt citrate (LCC) precipitate is retrieved and used directly as a precursor to synthesize LiNi1/3Mn1/3Co1/3O2 (NMC111) via a sol-gel method. The organic precursor is the only source of Co and provides a portion of the Li, while complementary metal salts supply the remaining metals in stoichiometric amounts. The role of metal salts (either acetates or sulfates of Ni, Mn and Li) on the quality and performance of the cathode materials is evaluated based on chemical composition and material purity. Electrochemical evaluation of the material produced from metal acetates showed comparable performance to that of a control material. The work connects previously studied methods of downstream leaching and antisolvent extraction with the upstream production of a desired cathode material through sol-gel synthesis. It is shown that our concept provides a path for avoiding primary and hazardous extraction of cobalt as the usage of the obtained citrate from acetone antisolvent crystallization of LCO can be applied as a precursor for NMC111 synthesis, with few steps and applying only non-toxic solvents.

Deep eutectic solvents (DES) are a new class of environmentally friendly, safe, and inexpensive solvents with a remarkable ability to dissolve metal oxides, proposed as green alternatives to traditional acid leaching in the recycling of lithium-ion battery (LIB) cathode materials. In this work, a closed-loop process is targeted, where LiNi_1/3Mn_1/3Co_1/3O₂ (NMC) is leached by a DES (choline chloride and L-(+)-tartaric acid), and the metals are recovered by antisolvent crystallization. Five organic antisolvents have been evaluated, amongst which ethanol provides the highest metal recovery efficiency. The suitability of the solid precipitates as precursors for the sol-gel synthesis of new NMC, and the resulting cycling performance as battery cathodes, have been tested. The effect on the process of impurities Al and Cu from current collectors has been investigated. The impurities partially precipitate with the targeted metals, but the product impurity content can be significantly reduced through the selection of antisolvent, antisolvent-to-leachate ratio, crystallization residence time, and the rate of supersaturation generation in semi-batch mode. The resulting solids can be suitable for direct cathode resynthesis without the addition of a chelating agent, but impurities from current collectors decrease cycling performance. The results highlight the potential of combining DES leaching and antisolvent crystallization as a sustainable and efficient LIB cathode recycling method.

In this work, the excess Gibbs free energy models, i.e., non-random two-liquid (NRTL) model and electrolyte NRTL model, including the original one and those with new strategies (association or hydration), were used to describe the macroscopic properties and interpret the microstructure of ionic liquid (IL) - H2O binary systems, clarifying the role of IL association and ion hydration in model development. To provide systematic data for model development, the enthalpy of mixing of three imidazolium-based IL-H2O systems containing the same cation but different sizes of anions, i.e., Cl-, Br- , and I-, were measured. The models were developed and evaluated based on the newly measured data and the osmotic coefficient from the literature. The results reveal that the model reflecting the intrinsic mechanism of dissociation and hydration gives the best modeling results; and the ionic strength and the degree of IL dissociation as a function of water content can be predicted using the newly established model. The study clarifies the significance of IL association and anion hydration in model development and quantitatively demonstrates how water content influences the microstructure and real species in IL-H2O systems.

In this work, ionic liquids (ILs)-based hybrid solvents, consisting of 1-butyl-3-methylimidazolium acetate (BMAC)-propylene carbonate (PC), were developed for CO2 separation from biogas. The impacts of IL mass fraction and temperature on the absorption capacity, viscosity, and density were studied. Feed gases, including pure CO2, pure CH4, and synthetic biogas, were tested, and the results were evaluated and compared. Thermodynamic modeling was used to represent the newly measured results together with literature data, and a systematic process simulation and evaluation were conducted. The measurements show an enhanced CO2 solubility with an increased BMAC mass fraction and decreased temperature. An increased viscosity was observed with increasing BMAC mass fraction and decreasing temperature. In addition, the type of feed gas holds a neglectable effect on CO2 and CH4 absorption capacities. To find an optimal mass fraction of BMAC-PC and quantify the performance, in the process simulation and evaluation, two types of regeneration blocks, i.e., air-blow regeneration and thermal regeneration, were involved. It shows that the process with thermal regeneration block requires less energy and lower capture cost than the process with the air-blow regeneration, which indicates a superior affinity to thermal regeneration when BMAC is presented in the solvent system. Also, the decrease in PC content firstly decreases and then increases the energy demand, and the minimum energy demand of 23.4 kW can be found with w(IL) = 0.3, which reduces by 33.5% compared to pure PC. Similarly, the minimum capture cost of 68 $/ton-CO2 can be found with w(IL) = 0.3, representing a 21% reduction from the case with pure PC. The further analysis concludes a major reduction in the utility cost by 48%.

Deep eutectic solvents (DESs) have been proposed as green alternatives for recycling lithium-ion battery (LIB) cathode materials. In the present work, a sustainable DES based on choline chloride and L-(+)-tartaric acid has been systematically investigated for leaching of a LIB cathode material (LiCo1/3Ni1/3Mn1/3O2) for the first time. Moreover, in a novel approach, antisolvent crystallization has been applied to recover metals from the DES leachate. The L-(+)-tartaric acid-based DES shows a good leaching capacity and a high leaching rate at 70 °C. Furthermore, antisolvent crystallization is shown to enable a high metal recovery efficiency of cobalt, nickel and manganese (>98.5%). The precipitate from antisolvent crystallization can be used as a precursor for the synthesis of new cathode material, while the remaining DES and antisolvent can be recovered for reuse in the process. This work presents a green, effective and closed-loop metal recovery strategy for recycling LIB cathode materials using a sustainable DES.