Carbon nanotubes (CNTs) are materials with exceptional electrical, thermal, mechanical, and optical properties. Ever since it was demonstrated that they also possess interesting thermoelectric ...properties, they have been considered a promising solution for thermal energy harvesting. In this study, we present a simple method to enhance their performance. For this purpose, thin films obtained from high-quality single-walled CNTs (SWCNTs) were doped with a spectrum of inorganic and organic halide compounds. We studied how incorporating various halide species affects the electrical conductivity, the Seebeck coefficient, and the Power Factor. Since thermoelectric devices operate under non-ambient conditions, we also evaluated these materials' performance at elevated temperatures. Our research shows that appropriate dopant selection can result in almost fivefold improvement to the Power Factor compared to the pristine material. We also demonstrate that the chemical potential of the starting CNT network determines its properties, which is important for deciphering the true impact of chemical and physical functionalization of such ensembles.
Shuttling protons in ammonia synthesis
An electrochemical route to ammonia could substantially lower the greenhouse gas emissions associated with the current thermal Haber-Bosch process. One ...relatively promising option under study involves reductive formation of lithium nitride, which can be protonated to ammonia. However, the ethanol used to date as a local proton source in these studies may degrade under the reaction conditions. Suryanto
et al.
report the use of a tetraalkyl phosphonium salt in place of ethanol (see the Perspective by Westhead
et al.
). This cation can stably undergo deprotonation–reprotonation cycles and, as an added benefit, it enhances the ionic conductivity of the medium.
Science
, abg2371, this issue p.
1187
; see also abi8329, p.
1149
A phosphonium cation acts as a stable proton shuttle during electrochemical ammonia synthesis.
Ammonia (NH
3
) is a globally important commodity for fertilizer production, but its synthesis by the Haber-Bosch process causes substantial emissions of carbon dioxide. Alternative, zero-carbon emission NH
3
synthesis methods being explored include the promising electrochemical lithium-mediated nitrogen reduction reaction, which has nonetheless required sacrificial sources of protons. In this study, a phosphonium salt is introduced as a proton shuttle to help resolve this limitation. The salt also provides additional ionic conductivity, enabling high NH
3
production rates of 53 ± 1 nanomoles per second per square centimeter at 69 ± 1% faradaic efficiency in 20-hour experiments under 0.5-bar hydrogen and 19.5-bar nitrogen. Continuous operation for more than 3 days is demonstrated.
Low solubility of terephthalic acid in common solvents makes its industrial production very difficult and not environmentally benign. Ionic liquids are known for their extraordinary solvent ...properties, with capability to dissolve a wide variety of materials, from common solvents to cellulose, opening new possibilities to find more suitable solvents for terephthalic acid. This work presents studies on the solubility of terephthalic acid in ionic liquids, and demonstrates that terephthalic acid is soluble in ionic liquids, such as 1-ethyl-3-methylimidazolium diethylphosphate, 1-butyl-3-methylimidazolium acetate, and dialkylimidazolium chlorides up to four times higher than in DMSO. Additionally, the temperature effect and correlation of ionic liquid structure with solubility efficiency are discussed.
Carbohydrate moieties were combined with various cross-linkable anions (thiocyanate SCN, tetracyanoborate TCB, tricyanomethanide TCM, and dicyanamide DCA) and investigated as precursors for the ...synthesis of nitrogen-doped and nitrogen-/sulfur-co-doped carbons. The influence of the molecular structures of the precursors on their thermophysical properties and the properties of the derived carbon materials was elucidated and compared to petroleum-derived analogs. A carbohydrate-based ionic liquid featuring an SCN anion yielded more carbon residues upon carbonization than its 1-ethyl-3-methylimidazolium analog, and the resulting dual-doping of the derived carbon material translated to enhanced catalytic activity in the oxygen reduction reaction.
As a result of strict regulations of phthalate plasticizers, alternative non-phthalate forms are desired and increasingly used. This work presents a synthetic method for alternative plasticizers ...(dialkyl succinates and adipates) via esterification of succinic and adipic acid with alcohols: butan-1-ol and 2-ethylhexan-1-ol. Ionic liquids were synthesized by the reaction of triethylamine with over-equimolar (1:2.7) amounts of sulfuric(VI) acid, which were used as an acidic catalyst and solvent. The two-phase liquid–liquid system was formed during the reaction due to immiscibility of the esters with the ionic liquid. This phenomenon is a driving force of this process, shifting the equilibrium toward the product formation. As a result, dialkyl succinates and adipates were obtained in high yields (99%) and selectivities (>99%), under mild reaction conditions at 70–80 °C and using a 4:1 molar ratio of alcohol to acid and 15 mol% of catalyst. The catalyst was recycled 10 times without any loss of activity. This alternative method is highly competitive: it involves a simple procedure for product isolation as well as a high yield and purity of the resulting esters. These advantages make this method sustainable and promising for industrial applications.
Phase change materials (PCMs) that store and release thermal energy via a reversible phase transition in the intermediate temperature range are a promising solution for renewable energy storage as ...they can be durable and inexpensive. Towards the development and understanding of new intermediate PCMs, this work describes a family of pyridinium ionic liquids and their thermophysical properties that show the potential of protic ionic liquids in the PCM field. Various pyridine structural isomers were used to explore the molecular patterns that affect the enthalpy of fusion and melting. The results show that small structural variations in the cation can change the thermophysical properties drastically; for example, melting temperatures varied between 357 ± 1 K and 499 ± 1 K, and enthalpies of fusion covered a wide spectrum from 38 to 190 J g−1 ± 5%. The most promising results in terms of PCM application, and one of the best among all protic ionic liquids reported thus far, were obtained for 2-hydroxypyridinium methanesulfonate 2-OHpyHCH3SO3 (Tm = 433 K and ΔHf = 190 J g−1).
•Thermophysical properties of pyridinium ionic liquids have been described.•Pyridinium ionic liquids were investigated as promising phase change materials.•One of the most promising materials is 2-hydroxypyridinium methanesulfonate which exhibits Tm = 433 K and enthalpy of fusion ΔHf = 190 J g−1.
Inexpensive Brønsted acidic ionic liquids based on trimethylamine and sulfuric acid are proposed as both solvents and catalysts in the synthesis of alternative plasticizer bis(2-ethylhexyl) ...terephthalate, which has a broad spectrum of applications in plasticization processes. The utilization of 50 mol % of Brønsted ionic liquid led to the full conversion of terephthalic acid after 8 h of reaction at 120 °C. Additionally, a 100% selectivity of bis(2-ethylhexyl) terephthalate was obtained. The advantage of the presented reaction system is based on the formation of a biphasic system during the reaction. The bottom phase consists of an ionic liquid and water, and the upper phase is created by the ester and unreacted alcohol. This phenomenon helps overcome the equilibrium of the reaction and drives it towards a high yield of product. The presented new approach is proposed as a safe, cost-effective, and alternative method to conventional processes with organometallic compounds that, in turn, leads to greener and a more economically viable technology.
Crystallization of alloys from a molten state is a fundamental process underpinning metallurgy. Here the direct imaging of an intermetallic precipitation reaction at equilibrium in a liquid‐metal ...environment is demonstrated. It is shown that the outer layers of a solidified intermetallic are surprisingly unstable to the depths of several nanometers, fluctuating between a crystalline and a liquid state. This effect, referred to herein as crystal interface liquefaction, is observed at remarkably low temperatures and results in highly unstable crystal interfaces at temperatures exceeding 200 K below the bulk melting point of the solid. In general, any liquefaction process would occur at or close to the formal melting point of a solid, thus differentiating the observed liquefaction phenomenon from other processes such as surface pre‐melting or conventional bulk melting. Crystal interface liquefaction is observed in a variety of binary alloy systems and as such, the findings may impact the understanding of crystallization and solidification processes in metallic systems and alloys more generally.
The phenomenon of solid metal surface liquefaction within liquid metal environments, represents an intriguing equilibrium state, defying common expectations by oscillating between a solid and liquid phase at temperatures significantly below the intermetallic compounds' conventional melting point. This discovery promises to advance the understanding of fundamental chemistry in metallic systems, offering insights into their behavior and potential applications.
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