Fixation of CO2 by electrocatalytic reduction and electropolymerization in ionic liquid-H2O solution

Ionic Liquids in Metal, Photo-, Electro-, and (Bio) Catalysis

Ionic liquids (ILs) have unique physicochemical properties that make them advantageous for catalysis, such as low vapor pressure, non-flammability, high thermal and chemical stabilities, and the ability to enhance the activity and stability of (bio)catalysts. ILs can improve the efficiency, selectivity, and sustainability of bio(transformations) by acting as activators of enzymes, selectively dissolving substrates and products, and reducing toxicity. They can also be recycled and reused multiple times without losing their effectiveness. ILs based on imidazolium cation are preferred for structural organization aspects, with a semiorganized layer surrounding the catalyst. ILs act as a container, providing a confined space that allows modulation of electronic and geometric effects, miscibility of reactants and products, and residence time of species. ILs can stabilize ionic and radical species and control the catalytic activity of dynamic processes. Supported IL phase (SILP) derivatives and polymeric ILs (PILs) are good options for molecular engineering of greener catalytic processes. The major factors governing metal, photo-, electro-, and biocatalysts in ILs are discussed in detail based on the vast literature available over the past two and a half decades. Catalytic reactions, ranging from hydrogenation and cross-coupling to oxidations, promoted by homogeneous and heterogeneous catalysts in both single and multiphase conditions, are extensively reviewed and discussed considering the knowledge accumulated until now.

Electrochemical Synthesis of Unique Nanomaterials in Ionic Liquids

The review considers the features of the processes of the electrochemical synthesis of nanostructures in ionic liquids (ILs), including the production of carbon nanomaterials, silicon and germanium nanoparticles, metallic nanoparticles, nanomaterials and surface nanostructures based on oxides. In addition, the analysis of works on the synthesis of nanoscale polymer films of conductive polymers prepared using ionic liquids by electrochemical methods is given. The purpose of the review is to dwell upon an aspect of the applicability of ILs that is usually not fully reflected in modern literature, the synthesis of nanostructures (including unique ones that cannot be obtained in other electrolytes). The current underestimation of ILs as an electrochemical medium for the synthesis of nanomaterials may limit our understanding and the scope of their potential application. Another purpose of our review is to expand their possible application and to show the relative simplicity of the experimental part of the work.

Ionic Liquids and Deep Eutectic Solvents for CO2 Conversion Technologies-A Review

Ionic liquids (ILs) have a wide range of potential uses in renewable energy, including CO2 capture and electrochemical conversion. With the goal of providing a critical overview of the progression, new challenges, and prospects of ILs for evolving green renewable energy processes, this review emphasizes the significance of ILs as electrolytes and reaction media in two primary areas of interest: CO2 electroreduction and organic molecule electrosynthesis via CO2 transformation. Herein, we briefly summarize the most recent advances in the field, as well as approaches based on the electrochemical conversion of CO2 to industrially important compounds employing ILs as an electrolyte and/or reaction media. In addition, the review also discusses the advances made possible by deep eutectic solvents (DESs) in CO2 electroreduction to CO. Finally, the critical techno-commercial issues connected with employing ILs and DESs as an electrolyte or ILs as reaction media are reviewed, along with a future perspective on the path to rapid industrialization.

Highly efficient Co centers functionalized by nitrogen-doped carbon for the chemical fixation of CO2

CO₂, the main greenhouse gas, has received considerable attention due to environmental issues. From a scientific perspective, CO₂ as a cheap and abundant carbon source, could be applied in synthesizing more valuable chemicals such as urea, formic acid, and cyclic carbonates. However, the high bond energy of C[double bond, length as m-dash]O (750 kJ mol^-1) and the non-polarity property make CO₂ molecules difficult to activate. In this paper, we have carefully designed a low-cost, stable and, most importantly, highly efficient Co-based heterocatalyst Co@N _x C functionalized by nitrogen-doped carbon to activate CO₂ molecules and convert it into cyclic carbonates. The CO₂ conversion process could be triggered at very mild conditions (60 °C and 1 bar CO₂). We carefully adjusted the nitrogen content in the carbon support to enhance the catalytic performance of Co centers via the interface effect. Consequently, the optimal catalyst displayed extraordinary activity toward the cycloaddition of CO₂ with styrene oxide as high conversion (92%) and selectivity (>99%) were achieved in 4 h without byproducts.

Electroreduction of CO2 in Ionic Liquid-Based Electrolytes

Electroreduction of carbon dioxide (CO₂) to value-added chemicals and fuels is a promising approach for sustainable energy conversion and storage. Many electrocatalysts have been designed for this purpose and studied extensively. The role of the electrolyte is particularly interesting and is pivotal for designing electrochemical devices by taking advantage of the synergy between electrolyte and catalyst. Recently, ionic liquids as electrolytes have received much attention due to their high CO₂ adsorption capacity, high selectivity, and low energy consumption. In this review, we present a comprehensive overview of the recent progress in CO₂ electroreduction in ionic liquid-based electrolytes, especially in the performance of different catalysts, the electrolyte effect, as well as mechanism studies to understand the reaction pathway. Perspectives on this interesting area are also discussed for the construction of novel electrochemical systems.

Heterogeneous electrochemical CO2 reduction using nonmetallic carbon-based catalysts: current status and future challenges

Electrochemical CO₂ reduction (ECR) offers an important pathway for renewable energy storage and fuels production. It still remains a challenge in designing highly selective, energy-efficient, robust, and cost-effective electrocatalysts to facilitate this kinetically slow process. Metal-free carbon-based materials have features of low cost, good electrical conductivity, renewability, diverse structure, and tunability in surface chemistry. In particular, surface functionalization of carbon materials, for example by doping with heteroatoms, enables access to unique active site architectures for CO₂ adsorption and activation, leading to interesting catalytic performances in ECR. We aim to provide a comprehensive review of this category of metal-free catalysts for ECR, providing discussions and/or comparisons among different nonmetallic catalysts, and also possible origin of catalytic activity. Fundamentals and some future challenges are also described.

Revealing the Origin of Activity in Nitrogen-Doped Nanocarbons towards Electrocatalytic Reduction of Carbon Dioxide

Carbon nanotubes (CNTs) are functionalized with nitrogen atoms for reduction of carbon dioxide (CO2 ). The investigation explores the origin of the catalyst's activity and the role of nitrogen chemical states therein. The catalysts show excellent performances, with about 90 % current efficiency for CO formation and stability over 60 hours. The Tafel analyses and density functional theory calculations suggest that the reduction of CO2 proceeds through an initial rate-determining transfer of one electron to CO2 , which leads to the formation of carbon dioxide radical anion (CO2 (.-) ). The initial reduction barrier is too high on pristine CNTs, resulting in a very high overpotentials at which the hydrogen evolution reaction dominates over CO2 reduction. The doped nitrogen atoms stabilize the radical anion, thereby lowering the initial reduction barrier and improving the intrinsic activity. The most efficient nitrogen chemical state for this reaction is quaternary nitrogen, followed by pyridinic and pyrrolic nitrogen.

Recent Advances in Inorganic Heterogeneous Electrocatalysts for Reduction of Carbon Dioxide

In view of the climate changes caused by the continuously rising levels of atmospheric CO2 , advanced technologies associated with CO2 conversion are highly desirable. In recent decades, electrochemical reduction of CO2 has been extensively studied since it can reduce CO2 to value-added chemicals and fuels. Considering the sluggish reaction kinetics of the CO2 molecule, efficient and robust electrocatalysts are required to promote this conversion reaction. Here, recent progress and opportunities in inorganic heterogeneous electrocatalysts for CO2 reduction are discussed, from the viewpoint of both experimental and computational aspects. Based on elemental composition, the inorganic catalysts presented here are classified into four groups: metals, transition-metal oxides, transition-metal chalcogenides, and carbon-based materials. However, despite encouraging accomplishments made in this area, substantial advances in CO2 electrolysis are still needed to meet the criteria for practical applications. Therefore, in the last part, several promising strategies, including surface engineering, chemical modification, nanostructured catalysts, and composite materials, are proposed to facilitate the future development of CO2 electroreduction.

A review of catalysts for the electroreduction of carbon dioxide to produce low-carbon fuels

This paper reviews recent progress made in identifying electrocatalysts for carbon dioxide (CO2) reduction to produce low-carbon fuels, including CO, HCOOH/HCOO(-), CH2O, CH4, H2C2O4/HC2O4(-), C2H4, CH3OH, CH3CH2OH and others. The electrocatalysts are classified into several categories, including metals, metal alloys, metal oxides, metal complexes, polymers/clusters, enzymes and organic molecules. The catalyts' activity, product selectivity, Faradaic efficiency, catalytic stability and reduction mechanisms during CO2 electroreduction have received detailed treatment. In particular, we review the effects of electrode potential, solution-electrolyte type and composition, temperature, pressure, and other conditions on these catalyst properties. The challenges in achieving highly active and stable CO2 reduction electrocatalysts are analyzed, and several research directions for practical applications are proposed, with the aim of mitigating performance degradation, overcoming additional challenges, and facilitating research and development in this area.

Switching the reaction course of electrochemical CO₂ reduction with ionic liquids

The ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim][Tf2N]) offers new ways to modulate the electrochemical reduction of carbon dioxide. [emim][Tf2N], when present as the supporting electrolyte in acetonitrile, decreases the reduction overpotential at a Pb electrode by 0.18 V as compared to tetraethylammonium perchlorate as the supporting electrolyte. More interestingly, the ionic liquid shifts the reaction course during the electrochemical reduction of carbon dioxide by promoting the formation of carbon monoxide instead of oxalate anion. With increasing concentration of [emim][Tf2N], a carboxylate species with reduced CO2 covalently bonded to the imidazolium ring is formed along with carbon monoxide. The results highlight the catalytic effects of the medium in modulating the CO2 reduction products.

Silver supported on titania as an active catalyst for electrochemical carbon dioxide reduction

Although significant research efforts have focused on the exploration of catalysts for the electrochemical reduction of CO2 , considerably fewer reports have described how support materials for these catalysts affect their performance, which includes their ability to reduce the overpotential, and/or to increase the catalyst utilization and selectivity. Here Ag nanoparticles supported on carbon black (Ag/C) and on titanium dioxide (Ag/TiO2 ) were synthesized. In a flow reactor, 40 wt % Ag/TiO2 exhibited a twofold higher current density for CO production than 40 wt % Ag/C. Faradaic efficiencies of the 40 wt % Ag/TiO2 catalyst exceeded 90 % with a partial current density for CO of 101 mA cm(-2) ; similar to the performance of unsupported Ag nanoparticle catalysts (AgNP) but at a 2.5 times lower Ag loading. A mass activity as high as 2700 mA mgAg (-1)  cm(-2) was achieved. In cyclic voltammetry tests in a three-electrode cell, Ag/TiO2 exhibited a lower overpotential for CO2 reduction than AgNP, which, together with other data, suggests that TiO2 stabilizes the intermediate and serves as redox electron carrier to assist CO2 reduction while Ag assists in the formation of the final product, CO.

Efficient solar-driven synthesis, carbon capture, and desalinization, STEP: solar thermal electrochemical production of fuels, metals, bleach

STEP (solar thermal electrochemical production) theory is derived and experimentally verified for the electrosynthesis of energetic molecules at solar energy efficiency greater than any photovoltaic conversion efficiency. In STEP the efficient formation of metals, fuels, chlorine, and carbon capture is driven by solar thermal heated endothermic electrolyses of concentrated reactants occuring at a voltage below that of the room temperature energy stored in the products. One example is CO(2) , which is reduced to either fuels or storable carbon at a solar efficiency of over 50% due to a synergy of efficient solar thermal absorption and electrochemical conversion at high temperature and reactant concentration. CO(2) -free production of iron by STEP, from iron ore, occurs via Fe(III) in molten carbonate. Water is efficiently split to hydrogen by molten hydroxide electrolysis, and chlorine, sodium, and magnesium from molten chlorides. A pathway is provided for the STEP decrease of atmospheric carbon dioxide levels to pre-industial age levels in 10 years.

Efficient acid-base bifunctional catalysts for the fixation of CO(2) with epoxides under metal- and solvent-free conditions

A series of acid-base bifunctional catalysts (ABBCs) that contain one or two Brønsted acidic sites in the cationic part and a Lewis-basic site in the anionic part are used as efficient catalysts for the synthesis of cyclic carbonates by cycloaddition of CO(2) to epoxides, without the use of additional co-catalyst or co-solvent. The effects of the catalyst structures and various reaction parameters on the catalytic performance are investigated in detail. Almost complete conversion can be achieved in 1 h for propylene oxide using [{(CH(2))(3)COOH}(2) im]Br under mild reaction conditions (398 K and 2 MPa). Furthermore, the catalyst can be recycled over five times without substantial loss of catalytic activity. This protocol is found to be applicable to a variety of terminal epoxides, producing the corresponding cyclic carbonates in good yields and high selectivities. A synergistic effect of the acidic and the basic sites as well as suitable hydrogen-bonding strength of ABBCs are considered crucial for the reaction to proceed smoothly. The activities of the ABBCs increase remarkably with increasing carboxylic-acid chain length of the cation. This metal- and solvent-free process thus represents an environmentally friendly process for BTC-catalyzed conversion of CO(2) into value-added chemicals.

Anode catalysts for direct ethanol fuel cells utilizing directly solar light illumination

Shine a light: A PtNiRu/TiO(2) anode catalyst for direct ethanol fuel cells shows photocatalytic activity. The peak current density for ethanol oxidation under solar light illumination is 2-3 times greater than that in the absence of solar light. Ethanol is oxidized by light-generated holes, and the electrons are collected by the TiO(2) support to generate the oxidation current.Novel PtNiRu/TiO(2) anode catalysts for direct ethanol fuel cells (DEFCs) were prepared from PtNiRu nanoparticles (1:1:1 atomic ratios) and a nanoporous TiO(2) film by a sol-gel and electrodeposition method. The performances of the catalysts for ethanol oxidation were investigated by cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. The results indicate a remarkable enhancement of activity for ethanol oxidation under solar light illumination. Under solar light illumination, the generated oxidation peak current density is 24.6 mA cm(-2), which is about 2.5 times higher than that observed without solar light (9.9 mA cm(-2)). The high catalytic activity of the PtNiRu/TiO(2) complex catalyst for the electrooxidation of ethanol may be attributed to the modified metal/nanoporous TiO(2) film, and the enhanced electrooxidation of ethanol under solar light may be due to the photogeneration of holes in the modified nanoporous TiO(2) film.