Ionic liquids (ILs) and deep eutectic solvents (DESs) have been suggested as eco-friendly alternatives to organic solvents. A trace amount of water is often unavoidable as impurity, and water is also added on purpose to reduce their problematically high viscosity and lower their high price. Understanding the distinct effects of water on the properties of ILs/DESs is highly important. In this review, we collect published experimental and theoretical results for IL/DES–H₂O systems at varied water concentrations and analyze them. Results from mechanistic studies, thermodynamic modelling and advanced experiments are collected and critically discussed. Six commonly studied IL/DES–H₂O systems were selected to map experimental observations onto microscopic results obtained in mechanistic studies. A great variety of distinct contours of the excess properties can be observed over the entire compositional range, indicating that the properties of IL/DES–H₂O systems are highly unpredictable. Mechanistic studies clearly demonstrate that the added H₂O rapidly changes the heterogeneous 3D structures of pure ILs/DESs, leading to very different properties and behaviour. There are similarities between aqueous electrolytes and IL/DES solutions but the bulky and asymmetric organic cations in ILs/DESs do not conform to the standard salt dissolution and hydration concepts. Thermodynamic modelling previously assumes ILs/DESs to be either a neutral ion-pair or completely dissociated ions, neglecting specific ion hydration effects. A new conceptual framework is suggested for thermodynamic modelling of IL/DES–H₂O binary systems to enable new technologies for their practical applications.

Sustainable and effective methods for biomass pretreatment and biomass cascade utilization are reviewed in this work.

Coal gasification is recognized as the core technology of clean coal utilization that exhibits significant advantages in hydrogen-rich syngas production and CO₂ emission reduction. This review briefly discusses the recent research progress on various coal gasification techniques, including conventional coal gasification (fixed bed, fluidized bed, and entrained bed gasification) and relatively new coal gasification (supercritical water gasification, plasma gasification, chemical-looping gasification, and decoupling gasification) in terms of their gasifiers, process parameters (such as coal type, temperature, pressure, gasification agents, catalysts, etc.), advantages, and challenges. The capacity and potential of hydrogen production through different coal gasification technologies are also systematically analyzed. In this regard, the decoupling gasification technology based on pyrolysis, coal char–CO₂ gasification, and CO shift reaction shows remarkable features in improving comprehensive utilization of coal, low-energy capture and conversion of CO₂, as well as efficient hydrogen production. As the key unit of decoupling gasification, this work also reviews recent research advances (2019–2023) in coal char–CO₂ gasification, the influence of different factors such as coal type, gasification agent composition, temperature, pressure, particle size, and catalyst on the char–CO₂ gasification performance are studied, and its reaction kinetics are also outlined. This review serves as guidance for further excavating the potential of gasification technology in promoting clean fuel production and mitigating greenhouse gas emissions.

LiF‐rich solid‐electrolyte‐interphase (SEI) can suppress the formation of lithium dendrites and promote the reversible operation of lithium metal batteries. Regulating the composition of naturally formed SEI is an effective strategy, while understanding the impact and role of fluorine (F)‐based Li‐salts on the SEI characteristics is unavailable. Herein, LiFSI, LiTFSI, and LiPFSI are selected to prepare solid polymer electrolytes (SPEs) with poly(ethylene oxide) and polyimide, investigating the effects of molecular size, F contents and chemical structures (F‐connecting bonds) of Li‐salts and revealing the formation of LiF in the SEI. It is shown that the F‐connecting bond is more significant than the molecular size and F element contents, and thus the performances of cells using LiPFSI are slightly better than LiTFSI and much better than LiFSI. The SPE containing LiPFSI can generate a high amount of LiF, and SPEs containing LiPFSI and LiTFSI can generate Li₃N, while there is no Li₃N production in the SEI for the SPE containing LiFSI. The preferential breakage bonds in LiPFSI are related to its position to Li anode, where Li‐metal as the anode is important in forming LiF, and consequently the LiPFSI reduction mechanism is proposed. This study will boost other energy storage systems beyond Li‐ion chemistries.