Selective electroreduction of carbon dioxide to formic acid on electrodeposited SnO2@N-doped porous carbon catalysts

Enhancing the Lewis acidity of single atom Tb via introduction of boron to achieve efficient photothermal synergistic CO2 cycloaddition

Nowadays, it is becoming increasingly urgent to lower the escalating carbon dioxide (CO2) to reduce greenhouse effect. Fortunately, it is an ideal strategy by using the inexhaustible solar energy as the driving force to manipulate the cycloaddition reaction, the atomic efficiency of which is 100 %. This work represents the first attempt on utilization of rare-earth metal Tb with atomic dispersion, and the structure of Tb coordinated with 4 N-atoms and 2B-atoms was constructed on interconnected carbon hollow spheres. The introduction of electron-deficient B reduces the electron density of Tb, thereby boosting Lewis acidity and promoting the occurrence of ring-opening reaction. The mechanism exploration enunciates that TbN4B2/C is a photothermal synergistic catalyst, the combined action of photogenerated electrons and strong Lewis acidic site of Tb reduces the free energy of the rate-determining step, and then improving the yield of cyclic carbonate up to 739 mmol g-1h-1.

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.

Energy Applications of Ionic Liquids: Recent Developments and Future Prospects

Ionic liquids (ILs) consisting entirely of ions exhibit many fascinating and tunable properties, making them promising functional materials for a large number of energy-related applications. For example, ILs have been employed as electrolytes for electrochemical energy storage and conversion, as heat transfer fluids and phase-change materials for thermal energy transfer and storage, as solvents and/or catalysts for CO2 capture, CO2 conversion, biomass treatment and biofuel extraction, and as high-energy propellants for aerospace applications. This paper provides an extensive overview on the various energy applications of ILs and offers some thinking and viewpoints on the current challenges and emerging opportunities in each area. The basic fundamentals (structures and properties) of ILs are first introduced. Then, motivations and successful applications of ILs in the energy field are concisely outlined. Later, a detailed review of recent representative works in each area is provided. For each application, the role of ILs and their associated benefits are elaborated. Research trends and insights into the selection of ILs to achieve improved performance are analyzed as well. Challenges and future opportunities are pointed out before the paper is concluded.

Engineering Bismuth-Tin Interface in Bimetallic Aerogel with a 3D Porous Structure for Highly Selective Electrocatalytic CO2 Reduction to HCOOH

Electrochemical reduction of CO₂ (CO₂ RR) into valuable hydrocarbons is appealing in alleviating the excessive CO₂ level. We present the very first utilization of metallic bismuth-tin (Bi-Sn) aerogel for CO₂ RR with selective HCOOH production. A non-precious bimetallic aerogel of Bi-Sn is readily prepared at ambient temperature, which exhibits 3D morphology with interconnected channels, abundant interfaces and a hydrophilic surface. Superior to Bi and Sn, the Bi-Sn aerogel exposes more active sites and it has favorable mass transfer properties, which endow it with a high FE_HCOOH of 93.9 %. Moreover, the Bi-Sn aerogel achieves a FE_HCOOH of ca. 90 % that was maintained for 10 h in a flow battery. In situ ATR-FTIR measurements confirmed that the formation of *HCOO is the rate-determining step toward formic acid generation. DFT demonstrated the coexistence of Bi and Sn optimized the energy barrier for the production of HCOOH, thereby improving the catalytic activity.

Electrochemical Production of Formic Acid from CO2 with Cetyltrimethylammonium Bromide-Assisted Copper-Based Catalysts

The electrochemical reduction of CO₂ (ERC) to valuable chemicals has attracted extensive attention. However, the relatively low selectivity and efficiency of the reaction remain challenges. In this study, Cu electrodes derived from Cu₂ O with predominant (111) facets are synthesized by cetyltrimethylammonium bromide-assisted preparation. The optimized electrode shows a high faradaic efficiency of 90 % for HCOOH obtained by ERC at -2.0 V (vs.SCE), which surpasses most reported Cu electrodes. Based on a comprehensive analysis of the relationship between the catalytic activity and the thickness of the Cu₂ O layer, the catalytic activity of the unit active site on the Cu₂ O-derived Cu electrodes is found to be higher than that on the blank Cu electrode. DFT calculations indicate that OCHO* would be produced preferentially over *COOH in the presence of cetyltrimethylammonium bromide (CTAB). This deduction is verified by testing of the effects of CTAB and KBr addition on HCOO^- selectivity.

Electro-reduction of carbon dioxide at low over-potential at a metal-organic framework decorated cathode

Electrochemical reduction of carbon dioxide is a clean and highly attractive strategy for the production of organic products. However, this is hindered severely by the high negative potential required to activate carbon dioxide. Here, we report the preparation of a copper-electrode onto which the porous metal–organic framework [Cu₂(L)] [H₄L = 4,4′,4″,4′′′-(1,4-phenylenebis(pyridine-4,2,6-triyl))tetrabenzoic acid] can be deposited by electro-synthesis templated by an ionic liquid. This decorated electrode shows a remarkable onset potential for reduction of carbon dioxide to formic acid at −1.45 V vs. Ag/Ag⁺, representing a low value for electro-reduction of carbon dioxide in an organic electrolyte. A current density of 65.8 mA·cm⁻² at −1.8 V vs. Ag/Ag⁺ is observed with a Faradaic efficiency to formic acid of 90.5%. Electron paramagnetic resonance spectroscopy confirms that the templated electro-synthesis affords structural defects in the metal–organic framework film comprising uncoupled Cu(II) centres homogenously distributed throughout. These active sites promote catalytic performance as confirmed by computational modelling.

Electrochemical reduction of carbon dioxide is a highly attractive strategy for the production of organic products of economic value. Here, the authors report the electrochemical reduction of carbon dioxide to formic acid over a copper-based metal–organic framework decorated electrode at low over-potential.

Quantitative Electro-Reduction of CO2 to Liquid Fuel over Electro-Synthesized Metal-Organic Frameworks

Efficient electro-reduction of CO₂ over metal-organic framework (MOF) materials is hindered by the poor contact between thermally synthesized MOF particles and the electrode surface, which leads to low Faradaic efficiency for a given product and poor electrochemical stability of the catalyst. We report a MOF-based electrode prepared via electro-synthesis of MFM-300(In) on an indium foil, and its activity for the electrochemical reduction of CO₂ is assessed. The resultant MFM-300(In)-e/In electrode shows a 1 order of magnitude improvement in conductivity compared with that for MFM-300(In)/carbon-paper electrodes. MFM-300(In)-e/In exhibits a current density of 46.1 mA cm^-2 at an applied potential of -2.15 V vs Ag/Ag⁺ for the electro-reduction of CO₂ in organic electrolyte, achieving an exceptional Faradaic efficiency of 99.1% for the formation of formic acid. The facile preparation of the MFM-300(In)-e/In electrode, coupled with its excellent electrochemical stability, provides a new pathway to develop efficient electro-catalysts for CO₂ reduction.

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.

Cost-effective synthesis of three-dimensional nitrogen-doped nanostructured carbons with hierarchical architectures from the biomass of sea-tangle for the amperometric determination of ascorbic acid

In this work, the three-dimensional nitrogen-doped nanostructured carbons with hierarchical architectures (3D-NNCsHAs) with high density of defective sites, high surface area and pluralities of pore size distributions was prepared through the pyrolysis of sea-tangle (Laminaria japonica), an inexpensive, eco-friendly and abundant precursor. Benefitting from their structural uniqueness, a selective and sensitive ascorbic acid (AA) sensor based on 3D-NNCsHAs was developed. Compared to the glassy carbon electrode (GCE) and the carbon nanotubes modified GCE (CNTs/GCE), the 3D-NNCsHAs modified GCE (3D-NNCsHAs/GCE) presents higher performance towards the electrocatalysis and detection of AA, such as lower detection limit (1 μM), wider linear range (10-4410 μM) and lower electrooxidation peak potential (-0.02 V vs. Ag/AgCl). In addition, 3D-NNCsHAs/GCE also exhibits high anti-interference and anti-fouling abilities for AA detection. Particularly, the fabricated 3D-NNCsHAs/GCE is able to determine AA in real samples and the results acquired are satisfactory. Therefore, the 3D-NNCsHAs can be considered as a kind of novel electrode nanomaterial for the fabrication of selective and sensitive AA sensor for the extensive practical applications ranging from food analysis, to pharmaceutical industry and clinical test.

Low-cost and environment-friendly synthesis of carbon nanorods assembled hierarchical meso-macroporous carbons networks aerogels from natural apples for the electrochemical determination of ascorbic acid and hydrogen peroxide

In this work, the low-cost carbon nanorods assembled hierarchical meso-macroporous carbons networks aerogels (CNs-HMCNAs) was environment-friendly synthesized from a cheap and abundant biomass of apples (Malus pumila Mill) for the first time. The biomass of apples derived CNs-HMCNAs exhibited the unique hierarchical meso-macroporous structure with large specific surface area and high density of edge defective sites. At the CNs-HMCNAs modified GCE (CNs-HMCNAs/GCE), the electron transfer between the glassy carbon electrode (GCE) and the ascorbic acid (AA) (or hydrogen peroxide (H₂O₂)) was effectively enhanced, and thus induced a low overvoltage for AA electrooxidation (or H₂O₂ electroreduction). As an electrochemical AA (or H₂O₂) sensor, the CNs-HMCNAs/GCE exhibited wider linear range, lower detection limit, higher sensitivity and stability than GCE and the carbon nanotubes modified GCE (CNTs/GCE). In particular, the CNs-HMCNAs/GCE showed great potential feasibility in the practical determination of AA (in AA injection, Vitamin C tablet and kiwi juice) or H₂O₂ (in human urine, milk and beer).