Electrochemical conversion of carbon dioxide to methane in aqueous NaHCO3 solution at less than 273 K

The electrochemical reduction of CO₂ on a Cu electrode was investigated in aqueous NaHCO₃ solution, at low temperature. A divided H-type cell was employed, the catholyte was 0.65 mol dm⁻³ NaHCO₃ aqueous solution and the anolyte was 1.1 mol dm⁻³ KHCO₃ aqueous solution. The temperature during the electrolysis of CO₂ was decreased stepwise to 271 K. Methane and formic acid were obtained as the main products. The maximum Faradaic efficiency of methane was 46% at −2.0 V and 271 K. The efficiency of hydrogen formation, a competing reaction of CO₂ reduction, was significantly depressed with decreasing temperature. Based on the results of this work, the proposed electrochemical method appears to be a viable means for removing CO₂ from the atmosphere and converting it into more valuable chemicals. The synthesis of methane by the electrochemical method might be of practical interest for fuel production and the storage of solar energy.     

Pulse-mode electrochemical reduction of carbon dioxide using copper and copper oxide electrodes for selective ethylene formation

Although the electrochemical reduction of CO₂ at a copper electrode produces hydrocarbons, the activity for the conversion of CO₂ is significantly reduced after several tens of minutes by the deposition of poisoning species on the electrode. In order to solve the poisoning species problem, the electrochemical reduction of CO₂ was carried out using a copper electrode in the pulse electrolysis mode by anodic as well as cathodic polarization. The anodic polarization intervals suppressed the deposition of the poisoning species on the electrode, and the amount of two hydrocarbons produced, CH₄ and C₂H₆, decreased only slightly even after one hour. By choosing the appropriate anodic potential and time duration the selectivity for C₂H₆ formation was significantly enhanced. The enhancement was found to be due to the copper oxide formed on the copper electrode. The selectivity was further improved when the electrochemical reduction was carried out using a copper oxide electrode. The highest efficiency of about 28% was obtained at −3.15 V.     

Calculation for the cathode surface concentrations in the electrochemical reduction of CO2 in KHCO3 solutions

This article presents a mathematical model that predicts the chemical conditions at the electrode surface during the electrochemical reduction of CO₂. Such electrochemical reduction of CO₂ to valuable products is an area of interest for the purpose of reducing green house gas emissions. In the reactions involved, CO₂ acts as both a reactant and a buffer, consequently the estimation of local concentrations at the electrode surface is not trivial and a numerical approach is required. The necessary partial differential equations (PDEs) have been set-up and solved using MATLAB. The results show the local concentrations at the electrode surface to be significantly different from the bulk concentrations under typical reported experimental conditions. The importance of buffer strength and a careful quantification of the degree of mixing produced in the experimental apparatus is demonstrated. The model has also been used to re-examine previously published data, showing that the Tafel slopes in CO₂ reduction are consistent with those reported for the simpler CO reduction system. Further, the effect of pulsed electroreduction was also modeled, showing that pulsing causes corresponding swings in local pH and CO₂ concentrations.     

An ecologically effective water treatment technique using electrochemically generated hydroxyl radicals for in situ destruction of organic pollutants: Application to herbicide 2,4-D

The electrochemical production of Fenton's reagent by simultaneous reduction of dioxygen and ferric ions on a carbon felt electrode, permits a controlled, in situ generation of hydroxyl (OH^·) radicals. The possibility of using electrochemically produced OH radicals for solving environmental problems is investigated. Continuous and controlled production of hydroxyl radicals was achieved by electrochemical reduction of O₂ in the presence of a catalytic amount of ferric or ferrous ion. These radicals are used for remediation of water containing toxic-persistent-bioaccumulative organic pollutants through their transformation into biodegradable compounds or through their mineralization into H₂O and CO₂. A widely used herbicide, 2,4-dichlorophenoxyacetic acid (2,4-D), was selected as a model for a toxic organic pollutant. High pressure liquid chromatography (HPLC) was used to quantify the distribution of the hydroxylated products obtained. Rate constants for the hydroxylation reactions of 2,4-D, 2,4-dichlorophenol (2,4-DCP), 2,4-dichlororesorcinol (2,4-DCR) and 4,6-dichlororesorcinol (4,6-DCR) were determined. The mineralization of 2,4-D and its derivatives was followed by total organic carbon (TOC) measurements. More than 95% of 2,4-D and the intermediates generated during the electrolysis can be mineralized.     

Electrochemical reduction of high pressure CO2 at a Cu electrode in cold methanol

The electrochemical reduction of high pressure CO₂ with a Cu electrode in cold methanol was investigated. A high pressure stainless steel vessel, with a divided H-type glass cell, was employed. The main products from CO₂ by the electrochemical reduction were methane, ethylene, carbon monoxide and formic acid. In the electrolysis of high pressure CO₂ at low temperature, the reduction products were formed in the order of carbon monoxide, methane, formic acid and ethylene. The best current efficiency of methane was of 20% at −3.0 V. The maximum partial current density for CO₂ reduction was approximately 15 mA cm⁻². The partial current density ratio of CO₂ reduction and hydrogen evolution, i(CO₂)/i(H₂), was more than 2.6 at potentials more positive than −3.0 V. This work can contribute to the large-scale manufacturing of fuel gases from readily available and inexpensive raw materials, CO₂-saturated methanol from industrial absorbers (the Rectisol process).     

Development of a continuous reactor for the electro-reduction of carbon dioxide to formate – Part 1: Process variables

This paper reports an experimental investigation into the effects of five process variables on the performance of a bench-scale continuous electrochemical reactor used in the reduction of CO₂ to potassium formate, and interprets the data in terms of reactor engineering for a (speculative) industrial process for electro-reduction of CO₂. The process variables: temperature, catholyte species, catholyte conductivity, cathode specific surface area and cathode thickness were studied, along with CO₂ pressure and current density, in a set of factorial and parametric experiments aimed to unravel their main effects and interactions. These variables showed complex interdependent effects on the reactor performance, as measured by the current efficiency and specific energy for generation of formate (HCO₂⁻). The “best” result has a formate current efficiency of 86% at a superficial current density of 1.3 kA m⁻², with a product solution of 0.08 m KHCO₂ and specific electrochemical energy of 260 kWh per kmole formate. The combined results indicate good prospects for process optimization that could lead to development of an industrial scale reactor.     

Electrochemical reduction of carbon dioxide at ruthenium dioxide deposited on boron-doped diamond

Study of carbon dioxide reduction at RuO₂-coated diamond electrodes showed that conductive metallic oxides are promising electrocatalysts for this process and allow higher reduction products to be obtained. The main reduction products obtained in acidic and neutral media were formic acid and methanol, with product efficiencies as high as 40 and 7.7%, respectively. It was observed that conductive diamond is a very well suited material for studying the electrocatalytic properties of conductive metallic oxides, because its use resulted in a negligible substrate effect. This feature will greatly enhance the ability to understand the relationships between the intrinsic electrochemical behavior and the electrocatalytic behavior, in view of developing new effective electrocatalysts. The use of conductive diamond could also allow better utilization of the electrocatalyst by avoiding the need for thick films.     

Enhanced Bio-Electrochemical Reduction of Carbon Dioxide by Using Neutral Red as a Redox Mediator

Microbial electrosynthetic cells containing Methylobacterium extorquens were studied for the reduction of CO₂ to formate by direct electron injection and redox mediator-assisted approaches, with CO₂ as the sole carbon source. The formation of a biofilm on a carbon felt (CF) electrode was achieved while applying a constant potential of −0.75 V versus Ag/AgCl under CO₂-saturated conditions. During the biofilm growth period, continuous H₂ evolution was observed. The long-term performance for CO₂ reduction of the biofilm with and without neutral red as a redox mediator was studied by an applied potential of −0.75 V versus Ag/AgCl. The neutral red was introduced into the systems in two different ways: homogeneous (dissolved in solution) and heterogeneous (electropolymerized onto the working electrode). The heterogeneous approach was investigated in the microbial system, for the first time, where the CF working electrode was coated with poly(neutral red) by the oxidative electropolymerization thereof. The formation of poly(neutral red) was characterized by spectroscopic techniques. During long-term electrolysis up to 17 weeks, the formation of formate was observed continuously with an average Faradaic efficiency of 4 %. With the contribution of neutral red, higher formate accumulation was observed. Moreover, the microbial electrosynthetic cell was characterized by means of electrochemical impedance spectroscopy to obtain more information on the CO₂ reduction mechanism.     

Electrochemical synthesis of dimethyl carbonate from methanol,CO2 and propylene oxide in an ionic liquid

BACKGROUND: Dimethyl carbonate (DMC) can be used effectively as an environmentally benign substitute for highly toxic phosgene and dimethyl sulfate in carbonylation and methylation, as well as a promising octane booster owing to its high oxygen content. Two‐step transesterification from epoxide, methanol, and CO₂ is widely used in the bulk production of DMC. However, major disadvantages of this process are high energy consumption, and high investment and production costs. A one pot synthesis of DMC from carbon dioxide, methanol, and epoxide was, therefore, developed. But the yields of DMC are below 70% due to the thermodynamic limitation. RESULTS: Electrochemical synthesis of DMC was conducted with platinum electrodes from methanol, CO₂ and propylene oxide in an ionic liquid was conducted. The bmimBr (1‐butyl‐3‐methylimidazolium bromide)‐methanol‐propylene oxide system with CO₂ bubbling allows DMC to be effectively synthesized and a high yield (75.5%) was achieved. CONCLUSION: In this electrolysis, redox reactions of substrates, CO₂, methanol, and propylene oxide, on Pt electrodes were carried out, producing the activated particles, CH₃O^?, CH₃OH⁺, CO₂^? and PO^?, resulting in the effective synthesis of DMC with a 75.5% yield in an ionic liquid (bmimBr). Finally, a mechanism for this synthesis reaction was proposed, which is very different from those reported in the literature. Copyright © 2011 Society of Chemical Industry     

Rapid Carbonation for Calcite from a Solid-Liquid-Gas System with an Imidazolium-Based Ionic Liquid

Aqueous carbonation of Ca(OH)₂ is a complex process that produces calcite with scalenohedral calcite phases and characterized by inadequate carbonate species for effective carbonation due to the poor dissolution of CO₂ in water. Consequently, we report a solid-liquid-gas carbonation system with an ionic liquid (IL), 1-butyl-3-methylimidazolium bromide, in view of enhancing the reaction of CO₂ with Ca(OH)₂. The use of the IL increased the solubility of CO₂ in the aqueous environment and enhanced the transport of the reactive species (Ca²⁺ and CO₃²⁻) and products. The presence of the IL also avoided the formation of the CaCO₃ protective and passivation layer and ensured high carbonation yields, as well as the production of stoichiometric rhombohedral calcite phases in a short time.     

Halide perovskite photocatalysis: progress and perspectives

Organic–inorganic metal halide perovskites (HPs) have emerged as new frontier materials for optoelectronic and energy applications. In addition to various well-known applications, such as solar cells, light-emitting diodes, photodetectors, and resistive switching memories, HPs can be utilized as efficient photocatalysts for numerous electrochemical reactions, including carbon dioxide (CO₂) reduction reactions, hydrogen evolution reaction, photosynthesis, and wastewater treatment. However, the use of HPs toward photo-driven catalysis remains a tremendous challenge owing to their poor stability in polar solvents. Nevertheless, huge progress has been made to counter this critical issue for improving the performance of HPs as efficient photocatalysts in a wide range of applications. In this review, we first introduce the structures and properties of HPs. Next, we highlight the recent approaches on the fabrication of HPs, including thin films and nanostructures. Strategies for implementing HPs in catalysis systems and their working mechanisms are thoroughly summarized and discussed. Lastly, the current challenges and prospects of the application of HPs toward photocatalytic reactions are fully addressed. © 2020 Society of Chemical Industry     

Direct conversion of CO2 with diols,aminoalcohols and diamines to cyclic carbonates,cyclic carbamates and cyclic ureas using heterogeneous catalysts

CO₂ has a large effect on global warming by greenhouse gases, and development of an effective technique for the reduction of CO₂ is a crucial and urgent issue. From the chemical viewpoint, CO₂ is regarded as a stable, safe and abundant C1 resource, and the transformation of CO₂ to valuable chemicals is promising not only for reduction of CO₂ but also for production of useful chemicals. This mini‐review focuses on the direct conversion of CO₂ with diols, aminoalcohols and diamines to cyclic compounds such as cyclic carbonates, cyclic carbamates and cyclic ureas, and in particular discusses the mechanisms for these reactions over heterogeneous catalysts. © 2013 Society of Chemical Industry     

The electrochemical reduction of CO2 to CH4 and C2H4 at Cu/Nafion electrodes (solid polymer electrolyte structures)

The construction of copper/Nafion electrodes (solid polymer electrolyte structures) by an electroless plating method is described. These electrodes were used for the gas phase electrochemical reduction of CO₂ to hydrocarbon products, including CH₄ and C₂H₄. The faradaic efficiencies of the electrodes under ambient conditions with a counter solution of 1 mM H₂SO₄ at a potential of –2.00 V vs. SCE reached a steady-state value of about 20% after 30 min of electrolysis. This corresponded to a rate of total hydrocarbon production of approximately 9.8×10^–7 mole h^–1 cm^–2. Increasing the potential of the electrode to more negative potentials, or increasing the proton concentration of the counter solution, caused a decrease in the faradaic efficiencies due to a relative increase in the rate of proton reduction vs. that of CO₂ reduction. If the proton concentration of the counter solution was decreased to an alkaline pH, hydrocarbon production quickly ceased because of proton starvation.     

The Electro-Reduction of Carbon Dioxide in a Continuous Reactor

This paper reports an investigation into the electro-reduction of CO₂ in a laboratory bench-scale continuous reactor with co-current flow of reactant gas and catholyte liquid through a flow-by 3D cathode of 30^# mesh tinned-copper. Factorial and parametric experiments were carried out in this apparatus with the variables: current (1–8 A), gas phase CO₂ concentration (16–100 vol%) and operating time (10–180 min), using a cathode feed of [CO₂ + N₂] gas and 0.45 m KHCO₃(aq) with an anolyte feed of 1 m KOH(aq), in operation near ambient conditions (ca. 115 kPa(abs), 300 K). The primary and secondary reactions here were respectively the reduction of CO₂ to formate (HCOO⁻) and of water to hydrogen, while up to ca. 5% of the current went to production of CO, CH₄ and C₂H₄. The current efficiency for formate depended on the current density and CO₂ pressure, coupled with the hydrogen over-potential plus mass transfer capacity of the cathode, and decreased with operating time, as tin was lost from the cathode surface. For superficial current densities ranging from 0.22 to 1.78 kA m⁻², the measured values of the performance indicators are: current efficiency for HCOO⁻ = 86–13%, reactor voltage = 3–6 Volt, specific energy for HCOO⁻ = 300–1300 kWh kmol⁻¹, space-time yield of HCOO⁻ = 2 × 10⁻⁴–6 × 10⁻⁴ kmol m⁻³ s⁻¹, conversion of CO₂ = 20–80% and yield of organic products from CO₂ = 6–17%.     

Energy efficiency analysis of CO2 mineral sequestration in magnesium silicate rock using electrochemical steps

A thermodynamic efficiency analysis using the exergy concept is used to assess CO₂ mineral sequestration process routes where electrochemical steps (electrolysis and fuel cells) are used to produce aqueous hydrochloric acid and sodium hydroxide reactant solutions. Results from three recent publications on the subject that come to different conclusions are used for this case study. It is shown that including electrolysis as one of the steps of a magnesium silicate mineral carbonation process route results in input energy requirements that will exceed the output of a fossil fuel-fired power plant that produces the CO₂ that is bound to (hydro-) carbonates. At the same time, fuel cells are not efficient enough to change this.     

Use of carbon dioxide as feedstock for chemicals and fuels: homogeneous and heterogeneous catalysis

CO₂ is considered to play a key role in an eventual climate change, due to its accumulation in the atmosphere. The control of its emission represents a challenging task that requires new ideas and new technologies. The use of perennial energy sources and renewable fuels instead of fossil fuels and the conversion of CO₂ into useful products are receiving increased attention. The utilization of CO₂ as a raw material for the synthesis of chemicals and fuels is an area in which scientists and industrialists are much involved: the implementation of such technology on a large scale would allow a change from a linear use of fossil carbon to its cyclic use, mimicking Nature. In this paper the use of CO₂ as building block is discussed. CO₂ can replace toxic species such as phosgene in low energy processes, or can be used as source of carbon for the synthesis of energy products. The reactions with dihydrogen, alcohols, epoxides, amines, olefins, dienes, and other unsaturated hydrocarbons are discussed, under various reaction conditions, using metal systems or enzymes as catalysts. The formation of products such as formic acid and its esters, formamides, methanol, dimethyl carbonate, alkylene carbonates, carbamic acid esters, lactones, carboxylic acids, and polycarbonates, is described . The factors that have limited so far the conversion of large volumes of CO₂ are analyzed and options for large‐scale CO₂ catalytic conversion into chemicals and fuels are discussed. Both homogeneous and heterogeneous catalysts are considered and the pros and cons of their use highlighted. © 2013 Society of Chemical Industry     

tBu3P/ZnR2 (R=Et,I) Frustrated Lewis Pair Catalysts for Functionalization and Reduction of CO2

The functionalization and reduction of CO₂ are important targets not only because of concerns about its accumulation or the impact of this greenhouse gas on Earth’s climate, but also because of its potential as a C-1 feedstock. In this work, both functionalization and reduction of CO₂ were performed using tBu₃P/ZnR₂ (R=Et, I) “frustrated Lewis pairs” (FLPs). Phosphine-catalyzed carboxylation of alkyl-Zn bonds and catalytic reduction of CO₂ using silanes as hydride sources and tBu₃P/ ZnR₂ (R=Et, I) FLPs as catalysts are reported. This is also the first time Zn-based FLP chemistry in functionalization of CO₂ is reported.     

One‐dimensional productivity assessment for on‐field methane hydrate production using CO2/N2 mixture gas

The direct recovery of methane from gas hydrate‐bearing sediments is demonstrated, where a gaseous mixture of CO₂ + N₂ is used to trigger a replacement reaction in complex phase surroundings. A one‐dimensional high‐pressure reactor (8 m) was designed to test the actual aspects of the replacement reaction occurring in natural gas hydrate (NGH) reservoir conditions. NGH can be converted into CO₂ hydrate by a “replacement mechanism,” which serves double duty as a means of both sustainable energy source extraction and greenhouse gas sequestration. The replacement efficiency controlling totally recovered CH₄ amount is inversely proportional to CO₂ + N₂ injection rate which directly affecting solid ‐ gas contact time. Qualitative/quantitative analysis on compositional profiles at each port reveals that the length more than 5.6 m is required to show noticeable recovery rate for NGH production. These outcomes are expected to establish the optimized key process variables for near future field production tests. © 2014 American Institute of Chemical Engineers AIChE J, 61: 1004–1014, 2015     

925银电极上同步电化学还原NO2-与CO2合成尿素

引言煤炭、石油等化石燃料燃烧的同时会产生大量氮氧化物(NOx)和二氧化碳(CO2),导致地球的生态系统遭受严重破坏[1]。NOx是导致酸雨、光化学烟雾的主要污染物,而CO2是主要的温室气体。目前国内外使用比较广泛的NOx废气处理方法可分为干法和湿法两大类,其中干法可以分为选择性催     

Highly CO2RR activity and electrochemical performance of A-site deficient symmetrical electrode materials (La0.6Sr0.4)1−xFe0.8Ni0.2O3-δ for CO2 electrolysis

A-site deficient (La_0.6Sr_0.4)_1−xFe_0.8Ni_0.2O_3-δ (x = 0, 0.05, 0.1) perovskite oxide materials (LSFN100, LSFN95, and LSFN90) are evaluated as symmetrical electrode materials for CO₂ electrolysis. All three perovskite oxides display pure cubic perovskite structure. The introduction of A-site deficiency results in greater tendency of in-situ exsolution and stronger CO₂ adsorption capacity, which are verified by temperature-programmed reduction of H₂ and temperature-programmed desorption of CO₂. Furthermore, the current densities with LSNF90 symmetrical cell are 1.72, 1.18 and 0.72 A·cm⁻² under the applied voltage of 1.8 V at 850, 800 and 750 °C to electrolysis CO₂, respectively. Low polarization resistance of 0.186, 0.267 and 0.454 Ω·cm² is also observed under open circuit conditions at 850, 800 and 750 °C, respectively. A-site deficiency of perovskite materials reduces the activation energy of oxygen evolution reaction (OER) and carbon dioxide reduction reaction (CO₂RR). Symmetrical cell with LSFN90 electrode shows good electrochemical performance and long-term stability for CO₂ electrolysis.