CO2 Conversion Processes Research Articles

(Invited) Hybrid and Functionalized Heterocatalysts for Photoelectrochemical Water Splitting and Electrochemical Carbon Dioxide Reduction

The reduction of carbon dioxide is a very inert process that requires breaking the double C=O bond in the stable CO2 molecule. There is a need for conversion of carbon dioxide, a potent greenhouse gas and a contributor to the global climate change, to useful carbon-based fuels or useful chemicals. Our contribution addresses the low-temperature CO2-conversion processes based on electrocatalytic and photoelectrochemical approaches. In the realistic electrolysis cells, the reduction of CO2 (at cathode or photocathode) would have to be accompanied by water oxidation (at anode or photoanode).Our interest is in the PEM electrolyzers utilizing the proton exchange polymer electrolyte membranes (as separators between anode and cathode compartments) allowing electrolysis at low pH’s and, in principle, capable of yielding higher current densities than alkaline electrolyzers. Nevertheless, under such conditions, the parasitic hydrogen evolution reaction is likely to become predominant and complicate formation of any CO2-reduction products. Our preliminary results with the copper or ruthenium containing tungsten oxide nanorods as catalytic materials are promising with respect to the investigations in acid media.Recent advances (including our studies) in photoelectrochemical water splitting are based on semiconducting photoanodes (typically n-type semiconducting metal oxides) combined either with a metallic cathode (e.g. Pt) or with a p-type semiconductor as a photocathode should be mentioned here in a context of the development of the CO2-electrolyzers exploring photoelectrocatalytic properties and operating under illumination. Among representative examples of metal oxides with n-type semiconducting and promising photoelectrocatalytic properties, tungsten oxide (WO3) should be mentioned. The WO3-based semiconductors are highly stable in acid media, and they are characterized by an energy band gap of 2.5-2.7 eV thus allowing absorption of a reasonable fraction of the solar spectrum up to ca. 500 nm. It comes from our research that, upon illumination, the onset potential for photooxidation of water (in acid medium) is as low as 0.45 V (vs. RHE) what is of practical importance to the energy efficient photoelectrolysis. Further improvement of performance of photoactive metal oxides, e.g. through doping with certain anions or oxo-species will be discussed. Utilization of such systems in the CO2-electrolyzers would require, however, development of practical cathodes (CO2-reduction) operating in acid media that will be addressed during presentation. In our work, the solar energy will be absorbed by a suitable semiconductor to drive water oxidation to oxygen and protons, whereas the reduction of CO2 will be achieved electrochemically with use of a proper (selective) catalyst. By utilizing the aqueous acidic medium, no external hydrogen is required for the CO2-reduction process because the H+ ions not only exist at sufficiently large population but they are generated in situ during the anodic reaction. Coupling of the two processes in a single unit leading to one-step photoelectrochemical/electrocatalytic approach should be possible (e.g. with use of a tandem cell) but, in practice, physical separation of the two reactions in photoanodic (photoelectrochemical water oxidation) and cathodic (carbon dioxide electroreduction) compartments is necessary to increase efficiency and to limit charge recombination. Conversion of CO2 to CO (accompanied by H2-evolution) is an attractive target because syngas (CO + H2) can be utilized for manufacturing of many useful chemicals including synthetic fuels via the Fischer-Tropsch type process.

Bicarbonate or Carbonate Processes for Coupling Carbon Dioxide Capture and Electrochemical Conversion

Designing a scalable system to capture CO₂ from the air and convert it into valuable chemicals, fuels, and materials could be transformational for mitigating climate change. Climate models predict that negative greenhouse gas emissions will be required by the year 2050 in order to stay below a 2 °C change in global temperature. The processes of CO₂ capture, CO₂ conversion, and finally product separation all require significant energy inputs; devising a system that simultaneously minimizes the energy required for all steps is an important challenge. To date, a variety of prototype or pilot-level CO₂ capture and/or conversion systems have been designed and built targeting the individual objectives of either capture or conversion. One approach has focused on CO₂ removal from the atmosphere and storage of pure pressurized CO₂. Other efforts have concentrated on CO₂ conversion processes, such as electrochemical reduction or fermentation. Only a few concepts or analyses have been developed for complete end-to-end processes that perform both CO₂ capture and transformation.

Stabilized and Immobilized Carbonic Anhydrase on Electrospun Nanofibers for Enzymatic CO2 Conversion and Utilization in Expedited Microalgal Growth.

Carbonic anhydrases convert CO2 to bicarbonate at a high turnover rate up to 106 s-1, but their actual applications in CO2 conversion processes are hampered by their poor stability. This study reports highly loaded and stabilized bovine carbonic anhydrase (bCA) upon being immobilized onto electrospun polymer nanofibers in the form of enzyme precipitate coating (EPC). The EPC protocol, consisting of enzyme covalent attachment, precipitation, and cross-linking, maintained 65.3% of initial activity even after being incubated in aqueous solution at room temperature under shaking at 200 rpm for 868 days. EPC also showed strong resistance to the treatment of the metal chelation agent, ethylenediaminetetraacetic acid, and molecular dynamic simulation was carried out to elucidate the prevention of metal leaching from the active site of bCA upon being cross-linked in the form of EPC. Highly stable EPC with high bCA loading was employed for the conversion of bubbling CO2 to bicarbonate, and the bicarbonate solution was utilized as a carbon source for expedited microalgae growth in a separate bioreactor. The addition of EPC in the bubbling CO2 reactor resulted in 134 and 231% accelerated microalgae growths compared to the controls with and without 25 mM sodium bicarbonate, respectively. EPC with high enzyme loading and unprecedentedly successful stabilization of enzyme stability has a great potential to be used for the development of various enzyme-mediated CO2 conversion and utilization technologies.

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 Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> 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@NxC 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.

Catalysts for hydrogenation of CO2 into components of motor fuels

CO2 is a harmful greenhouse gas, a product of chemical emissions, the combustion of fossil fuels and car exhausts, and it is a widely available source of carbon. The review considers various ways of hydrogenation of carbon dioxide into components of motor fuels - methanol, dimethyl ether, ethanol, hydrocarbons - in the presence of heterogeneous catalysts. At each route of conversion of CO2 (into oxygenates or hydrocarbons) the first stage is the formation of CO by the reverse water gas shift (rWGS) reaction, which must be taken into account when catalysts of process are choosing. The influence of chemical nature, specific surface area, particle size and interaction between catalyst components, as well as the method of its production on the CO2 conversion processes is analyzed. It is noted that the main active components of CO2 conversion into methanol are copper atoms and ions which interact with the oxide components of the catalyst. There is a positive effect of other metals oxides additives with strong basic centers on the surface on the activity of the traditional copper-zinc-aluminum oxide catalyst for the synthesis of methanol from the synthesis gas. The most active catalysts for the synthesis of DME from CO2 and H2 are bifunctional. These catalysts contain both a methanol synthesis catalyst and a dehydrating component, such as mesoporous zeolites with acid centers of weak and medium strength, evenly distributed on the surface. The synthesis of gasoline hydrocarbons (≥ C5) is carried out through the formation of CO or CH3OH and DME as intermediates on multifunctional catalysts, which also contain zeolites. Hydrogenation of CO2 into ethanol can be considered as an alternative to the synthesis of ethanol through the hydration of ethylene. High activation energy of carbon dioxide, harsh synthesis conditions as well as high selectivity for hydrocarbons, in particular methane remains the main problems. Further increase of selectivity and efficiency of carbon dioxide hydrogenation processes involves the use of nanocatalysts taking into account the mechanism of CO2 conversion reactions, development of methods for removing excess water as a by-product from the reaction zone and increasing catalyst stability over time.

Scaling up syngas production with controllable H2/CO ratio in a highly efficient, compact, and durable solid oxide coelectrolysis cell unit-bundle

High-temperature coelectrolysis of H2O and CO2 by using solid oxide coelectrolysis cells (SOC) is considered to be among the most efficient processes for CO2 conversion as these SOCs can efficiently utilize both heat and renewable electrical energy. One of the key components is the development of highly efficient, modular SOC cells and stacks to further scale up the CO2 conversion process towards industrial applications. In this study, we developed highly efficient and durable flat-tubular solid oxide coelectrolysis cells (FT-SOCs) and investigated the electrochemical performance (I-V, EIS, long-term galvanostatic test) of single cells and a 6-cell bundle for CO2-H2O coelectrolysis to produce syngas with controllable H2/CO ratios. The FT-SOC with an active area of 40 cm2 reached a maximum current density of −3.2A/cm2 at 1.6 V at 800 °C and an H2O/CO2 ratio of 2. In the 6-cell FT-SOC bundle, 90% CO2 conversion was achieved by producing high-quality syngas with flexible H2/CO ratios and stable long-term operation for continuous 500 h. The results of this study show that by using an FT-SOC bundle, scalable and controllable syngas quality could be produced and integrated with the multitude of downstream processes.

Engineering of Ruthenium-Iron Oxide Colloidal Heterostructures: Improved Yields in CO2 Hydrogenation to Hydrocarbons.

Catalytic CO2 reduction to fuels and chemicals is a major pursuit in reducing greenhouse gas emissions. One approach utilizes the reverse water-gas shift reaction, followed by Fischer-Tropsch synthesis, and iron is a well-known candidate for this process. Some attempts have been made to modify and improve its reactivity, but resulted in limited success. Now, using ruthenium-iron oxide colloidal heterodimers, close contact between the two phases promotes the reduction of iron oxide via a proximal hydrogen spillover effect, leading to the formation of ruthenium-iron core-shell structures active for the reaction at significantly lower temperatures than in bare iron catalysts. Furthermore, by engineering the iron oxide shell thickness, a fourfold increase in hydrocarbon yield is achieved compared to the heterodimers. This work shows how rational design of colloidal heterostructures can result in materials with significantly improved catalytic performance in CO2 conversion processes.

Engineering of Ruthenium–Iron Oxide Colloidal Heterostructures: Improved Yields in CO2 Hydrogenation to Hydrocarbons

AbstractCatalytic CO2 reduction to fuels and chemicals is a major pursuit in reducing greenhouse gas emissions. One approach utilizes the reverse water‐gas shift reaction, followed by Fischer–Tropsch synthesis, and iron is a well‐known candidate for this process. Some attempts have been made to modify and improve its reactivity, but resulted in limited success. Now, using ruthenium–iron oxide colloidal heterodimers, close contact between the two phases promotes the reduction of iron oxide via a proximal hydrogen spillover effect, leading to the formation of ruthenium–iron core–shell structures active for the reaction at significantly lower temperatures than in bare iron catalysts. Furthermore, by engineering the iron oxide shell thickness, a fourfold increase in hydrocarbon yield is achieved compared to the heterodimers. This work shows how rational design of colloidal heterostructures can result in materials with significantly improved catalytic performance in CO2 conversion processes.

Critical operating conditions for enhanced energy-efficient molten salt CO2 capture and electrolytic utilization as durable looping applications

CO2 electro-splitting is a promising approach for energy storage and conversion. In this paper, captured CO2 (in the form of carbonate ions) can be electrochemically converted into hollow carbon spheres and ultrathin carbon sheets via an energy-efficient molten salt electrolysis process in CaO-containing molten LiCl–KCl. During electrolysis, oxygen anions (O2−) acting as a CO2 absorbent are concurrently generated on the cathode to reproduce CO32− by carbonation with CO2, setting up a closed loop between sequential CO2 absorption and electrochemical conversion. The dissociated O2− in the melt exhibits more than 80% carbonation efficiency. However, CaO are easily solidified on the cathode when O2− is over-saturated in the melt. More importantly, the solidified CaO poorly reacts with CO2, leading to a cathodic deactivation effect and higher energy consumption for CO2 electro-splitting. To enhance the kinetics of CO2 conversion, it was found that applying forced convection by bubbling CO2 near the cathode, operating under lower current density, and higher temperature can effectively inhibit the cathodic deactivation effect, leading to a durable and more energy-efficient CO2 conversion process. The energy consumption for producing 1 kg of carbon from CO2 is much lower at higher operating temperature, i.e. 16.3 kW h/kg at 650 °C and 31.4 kW h/kg at 450 °C. The critical operating conditions for durable looping are calculated by finely coupling current density with O2− dissociation kinetics. The coupled current densities are 4.41, 9.60, and 27.3 mA/cm2 at 450, 550, and 650 °C, respectively.

US REG sells life sciences assets

It has been appraised that the world energy spending will more than double by 2050. The global energy depends mostly on fossil fuels at present, while the estimated amount of fossil-fuel deposits goes on decreasing. The greater part of fossil fuels may be exhausted within next hundred years. In view of this situation, the electrochemical and selective conversion process of CO2 to ethylene that can be driven by the electricity derived from renewable energy is attractive, since CO2 can be utilized as an energy carrier regardless of fossil fuel. The developed CO2 conversion process takes place under rather specific conditions involving three-phase (gas/solution/solid) interface, concentrated solution of potassium halide, low pH, and copper or Cu(I) halide-confined metal electrode. Herein, the bases for leading to the augmentation of the efficiency and selectivity in the electrochemical reduction of CO2 to ethylene are discussed in association with the reduction pathway.

Hybrid and Functionalized Interfaces for Photoelectrochemical Water Splitting and Electrocatalytic Carbon Dioxide Reduction

The reduction of carbon dioxide is a very inert process that requires breaking the double C=O bond in the stable CO2 molecule. There is a need for conversion of carbon dioxide, a potent greenhouse gas and a contributor to the global climate change, to useful carbon-based fuels or useful chemicals. Our contribution addresses the low-temperature CO2-conversion processes based on electrocatalytic and photoelectrochemical approaches. In the realistic electrolysis cells, the reduction of CO2 (at cathode or photocathode) would have to be accompanied by water oxidation (at anode or photoanode). Our interest is in the PEM electrolyzers utilizing the proton exchange polymer electrolyte membranes (as separators between anode and cathode compartments) allowing electrolysis at low pH’s and, in principle, capable of yielding higher current densities than alkaline electrolyzers. Nevertheless, under such conditions, the parasitic hydrogen evolution reaction is likely to become predominant and complicate formation of any CO2-reduction products. Our preliminary results with the copper or ruthenium containing tungsten oxide nanorods as catalytic materials are promising with respect to the investigations in acid media. Recent advances (including our studies) in photoelectrochemical water splitting are based on semiconducting photoanodes (typically n-type semiconducting metal oxides) combined either with a metallic cathode (e.g. Pt) or with a p-type semiconductor as a photocathode should be mentioned here in a context of the development of the CO2-electrolyzers exploring photoelectrocatalytic properties and operating under illumination. Among representative examples of metal oxides with n-type semiconducting and promising photoelectrocatalytic properties, tungsten oxide (WO3) should be mentioned. The WO3-based semiconductors are highly stable in acid media, and they are characterized by an energy band gap of 2.5-2.7 eV thus allowing absorption of a reasonable fraction of the solar spectrum up to ca. 500 nm. It comes from our research that, upon illumination, the onset potential for photooxidation of water (in acid medium) is as low as 0.45 V (vs. RHE) what is of practical importance to the energy efficient photoelectrolysis. Further improvement of performance of photoactive metal oxides, e.g. through doping with certain anions or oxo-species will be discussed. Utilization of such systems in the CO2-electrolyzers would require, however, development of practical cathodes (CO2-reduction) operating in acid media that will be addressed during presentation. In our work, the solar energy will be absorbed by a suitable semiconductor to drive water oxidation to oxygen and protons, whereas the reduction of CO2 will be achieved electrochemically with use of a proper (selective) catalyst. By utilizing the aqueous acidic medium, no external hydrogen is required for the CO2-reduction process because the H+ ions not only exist at sufficiently large population but they are generated in situ during the anodic reaction. Coupling of the two processes in a single unit leading to one-step photoelectrochemical/electrocatalytic approach should be possible (e.g. with use of a tandem cell) but, in practice, physical separation of the two reactions in photoanodic (photoelectrochemical water oxidation) and cathodic (carbon dioxide electroreduction) compartments is necessary to increase efficiency and to limit charge recombination. Conversion of CO2 to CO (accompanied by H2-evolution) is an attractive target because syngas (CO + H2) can be utilized for manufacturing of many useful chemicals including synthetic fuels via the Fischer-Tropsch type process.

Mechanistic Insights into Selective CO2 Conversion via RWGS on Transition Metal Phosphides: A DFT Study

Selective conversion of CO2 to CO via the reverse water gas shift (RWGS) reaction is an attractive CO2 conversion process, which may be integrated with many industrial catalytic processes such as Fischer−Tropsch synthesis to generate added value products. The development of active and cost friendly catalysts is of paramount importance. Among the available catalyst materials, transition metal phosphides (TMPs) such as MoP and Ni2P have remained unexplored in the context of the RWGS reaction. In the present work, we have employed density functional theory (DFT) to first investigate the stability and geometries of selected RWGS intermediates on the MoP (0001) surface, in comparison to the Ni2P (0001) surface. Higher adsorption energies and Bader charges are observed on MoP (0001), indicating better stability of intermediates on the MoP (0001) surface. Furthermore, mechanistic investigation using potential energy surface (PES) profiles showcased that both MoP and Ni2P were active toward RWGS reaction with the direct path (CO2* → CO* + O*) favorable on MoP (0001), whereas the COOH-mediated path (CO2* + H* → COOH*) favors Ni2P (0001) for product (CO and H2O) gas generation. Additionally, PES profiles of initial steps to CO activation revealed that direct CO decomposition to C* and O* is favored only on MoP (0001), while H-assisted CO activation is more favorable on Ni2P (0001) but could also occur on MoP (0001). Furthermore, our DFT calculations also ascertained the possibility of methane formation on Ni2P (0001) during the RWGS process, while MoP (0001) remained more selective toward CO generation.

A novel concept of bicarbonate-carbon utilization via an absorption-microalgae hybrid process assisted with nutrient recycling from soybean wastewater

Abstract A novel ammonia absorption-microalgae hybrid CO2 capture and conversion process was investigated in this study. Using rich ammonia solution (ammonium bicarbonate) as a nutrient source for microalgae cultivation, the challenge of energy-intensive regeneration may potentially be overcome. To provide other nutrients for microalgae apart from ammonium bicarbonate, soybean wastewater was used to replace BG-11 medium for resource recycling and could adjust the pH of cultivation solution to reduce the threat of NH3 escape and inhibition. Chlorella sp. L166 and L38 were cultivated in ammonium bicarbonate solution using 5-times and 10-times diluted soybean wastewater under two culture modes (direct and batch feeding). The experimental results indicated that microalgae growth could be promoted by using 5-times diluted soybean wastewater as a cultivation medium with a removal rate of 50–65% COD, 70–80% NH3-N and 95–100% TP from a wastewater purification perspective. In the hybrid system, the NH3 escape ratio decreased to 15.8% with a carbon conversion efficiency of over 60%, and effectively achieved carbon and nitrogen utilization with 78.8 mg/L/d of microalgae biomass.

Direct Conversion of CO2 to Multi-Layer Graphene using Cu-Pd Alloys.

A straightforward one‐step process was developed, in which CO2 gas is directly converted into multi‐layer graphene via atmospheric pressure chemical vapor deposition (APCVD). A bimetallic alloy film based on Cu and Pd was employed as the catalyst and substrate. In this study, we found that the quantity of Cu required for the CO2 conversion process is high (>82 at %). The findings gained in this study serve as a foundation for further studies of metallic alloys for the thermo‐reduction of CO2 to graphene under CVD conditions.

Combining CO2 conversion and N2 fixation in a gliding arc plasmatron

Industry needs a flexible and efficient technology to convert CO2 into useful products, which fits in the Carbon Capture and Utilization (CCU) philosophy. Plasma technology is intensively being investigated for this purpose. A promising candidate is the gliding arc plasmatron (GAP). Waste streams of CO2 are often not pure and contain N2 as important impurity. Therefore, in this paper we provide a detailed experimental and computational study of the combined CO2 and N2 conversion in a GAP. Is it possible to take advantage of the presence of N2 in the mixture and to combine CO2 conversion with N2 fixation? Our experiments and simulations reveal that N2 actively contributes to the process of CO2 conversion, through its vibrational levels. In addition, NO and NO2 are formed, with concentrations around 7000 ppm, which is slightly too low for valorization, but by improving the reactor design it must be possible to further increase their concentrations. Other NO-based molecules, in particular the strong greenhouse gas N2O, are not formed in the GAP, which is an important result. We also compare our results with those obtained in other plasma reactors to clarify the differences in underlying plasma processes, and to demonstrate the superiority of the GAP.

Hierarchical and ultrathin copper nanosheets synthesized via galvanic replacement for selective electrocatalytic carbon dioxide conversion to carbon monoxide

Electrochemical conversion of carbon dioxide (CO2) to desirable products with high selectivity and efficiency remains critical challenges in balancing carbon cycle for sustainable society. Herein, we demonstrate the hierarchical porous architectures assembled by ultrathin copper (Cu) nanosheets (NS) via a simple galvanic replacement method for the improved selectivity of CO2 conversion with a large current density. Specifically, the optimized hierarchical Cu electrodes achieve high selectivity and activity to convert CO2 into CO, showing a Faradaic efficiency (FE) of 74.1%, record-high partial current density of 23.0 mA cm−2, and turnover frequency of 0.092 s-1 for CO product as well as FE of 24.8% for H2 at potential of -1.0 V vs RHE. The onset potential for the CO2 conversion is -0.29 V vs RHE. Theoretical calculations indicate that the abundant vacancy defects exposed on ultrathin Cu nanosheets can accelerate the initial kinetics of CO formation during the CO2 conversion process. As demonstrated by experimental and computational analyses, the unique hierarchical architecture of integrated Cu electrode contributes the outstanding electrocatalytic performance due to the rapid mass and electrons transport as well as the abundant active sites and associated intrinsic activity.

Surface-Halogenation-Induced Atomic-Site Activation and Local Charge Separation for Superb CO2 Photoreduction.

Solar-energy-driven CO2 conversion into value-added chemical fuels holds great potential in renewable energy generation. However, the rapid recombination of charge carriers and deficient reactive sites, as two major obstacles, severely hampers the photocatalytic CO2 reduction activity. Herein, a desirable surface halogenation strategy to address the aforementioned concerns over a Sillén-related layer-structured photocatalyst Bi2 O2 (OH)(NO3 ) (BON) is demonstrated. The surface halogen ions that are anchored on the Bi atoms by replacing surface hydroxyls on the one hand facilitate the local charge separation, and, on the other hand, activate the hydroxyls that profoundly boost the adsorption of CO2 molecules and protons and facilitate the CO2 conversion process, as evidenced by experimental and theoretical results collectively. Among the three series of BON-X (X = Cl, Br, and I) catalysts, BON-Br shows the most substantially enhanced CO production rate (8.12 µmol g-1 h-1 ) without any sacrificial agents or cocatalysts, ≈73 times higher than that of pristine Bi2 O2 (OH)(NO3 ), also exceeding that of the state-of-the-art photocatalysts reported to date. This work presents a surface polarization protocol for engineering charge behavior and reactive sites to promote photocatalysis, which shows great promise to the future design of high-performance materials for clean energy production.

Investigation of CO2 Splitting Process Under Atmospheric Pressure Using Multi-electrode Cylindrical DBD Plasma Reactor

In this paper, the CO2 splitting process was performed under atmospheric pressure in a multi-electrode cylindrical dielectric barrier discharge (DBD) plasma reactor. The influence of the plasma processing parameters including discharge voltage, discharge length and gas flow rate was investigated. Besides, the effect of the similar specific energy input (SEI) values obtained using different plasma powers and gas flow rates was studied. The experimental results indicated that the CO2 conversion and energy efficiency increased along with the increased discharge length due to the increased residence time and the enhanced electric field. The increase of the applied voltage and hence the plasma power or the decrease of the gas flow rate generated enhanced effect on CO2 conversion while negative influence on energy efficiency. In addition, by comparing the energy efficiency at similar SEI values obtained with different discharge powers and gas flow rates, it was found that the gas flow rate played a more important role in CO2 conversion. The proposed multi-electrode plasma reactor led to the highest CO2 conversion of 18.50% and maximum energy efficiency of 12.83%. Compared with other types of cylindrical DBD plasma reactors, the multi-electrode design proposed in this work can give a similar CO2 conversion and higher energy efficiency. The multi-electrode design can enhance the local electric field at the electrode edges, leading to the enhanced corona discharge and the generation of more micro-discharges, which is considered to be responsible for enhanced CO2 conversion process.

Highly Efficient Solar‐Driven Carbon Dioxide Reduction on Molybdenum Disulfide Catalyst Using Choline Chloride‐Based Electrolyte

AbstractConversion of CO2 to energy‐rich chemicals using renewable energy is of much interest to close the anthropogenic carbon cycle. However, the current photoelectrochemical systems are still far from being practically feasible. Here the successful demonstration of a continuous, energy efficient, and scalable solar‐driven CO2 reduction process based on earth‐abundant molybdenum disulfide (MoS2) catalyst, which works in synergy with an inexpensive hybrid electrolyte of choline chloride (a common food additive for livestock) and potassium hydroxide (KOH) is reported. The CO2 saturated hybrid electrolyte utilized in this study also acts as a buffer solution (pH ≈ 7.6) to adjust pH during the reactions. This study reveals that this system can efficiently convert CO2 to CO with solar‐to‐fuel and catalytic conversion efficiencies of 23% and 83%, respectively. Using density functional theory calculations, a new reaction mechanism in which the water molecules near the MoS2 cathode act as proton donors to facilitate the CO2 reduction process by MoS2 catalyst is proposed. This demonstration of a continuous, cost‐effective, and energy efficient solar driven CO2 conversion process is a key step toward the industrialization of this technology.

Reversible Solid Oxide Cell (ReSOC) as flexible polygeneration plant integrated with CO2 capture and reuse

This work presents the concept of a Reversible Solid Oxide Cell (ReSOC) system localized in an urban residential district. The system is operated as a polygeneration plant that acts as interface between the electricity grid and the local micro-grid of the district. The ReSOC plant produces hydrogen via electrolysis during periods of low electricity demand (i.e., low-priced electricity). Hydrogen is used for multiple city needs: public mobility (H2 bus fleet), electricity production delivered to the micro-grid during peak-demand hours, and heat (accumulated in a storage) provided to the local district heating (DH) network. An additional option analyzed is the use of part of the H2 to produce DME using CO2 captured from biogas obtained from municipal solid wastes. The DME is used for fueling a fleet of trucks for the garbage collection in the residential district. A traditional CO2 removal process based on liquid MEA thermally integrated with the ReSOC system is studied. A time-resolved model interfaces the steady-state operating points with the thermal storage and the loads (electrical, H2 buses, DME trucks, heat), implementing constraints of thermal and H2 self-sufficiency on the system. Neglecting the DME option, the average daily roundtrip electric efficiency is about 38%, while the annual efficiency, which includes H2 mobility and thermal energy to DH, reaches 68%. When the DME option is considered, the thermal demand for CO2 removal and conversion process reduces the heat availability for DH, while the need for additional H2 for DME synthesis increases the electricity consumption for water electrolysis: both these phenomena imply a reduction of system efficiency (-9%) proportional to DME demand.