CO2 Stream Research Articles

Valorization of waste eggshell for CO2 sorbents production by sol-gel citric acid treatment in a fixed-bed reactor

This study assesses the potential of the eggshells as a promising and alternative CO2 adsorbent. With the aim of enhancing the CO2 capture performance of raw eggshell, it was modified by sol-gel citric acid treatment. Both adsorbents were characterized by N2 adsorption-desorption, XRF, XRD and SEM techniques. Preliminary adsorption tests in TGA revealed that the acid-modified eggshell achieved significantly higher carbonation conversion than the raw eggshell adsorbent in the 650–750 ºC adsorption temperature range, reaching a carbonation conversion of 69% at 700 ºC. The cyclic performance of the modified eggshell, tested in TGA at 700 ºC under 15 vol% CO2, confirmed that sol-gel acid treatment led to a very stable adsorbent, with a slight improvement in CO2 adsorption capacity during the first four cycles (from 0.54 to 0.58 gCO2 gads−1), followed by stable performance due to self-reactivation phenomena. Moreover, additional experiments were carried out in a fixed bed reactor under more realistic conditions to study the influence of temperature (600–750 ºC) and CO2 flow rate (50–125 mL min−1) using the modified eggshell. An increase in temperature under 15 vol% CO2 stream led to a decrease in the carbonation conversion of the adsorbent, with the maximum CO2 uptake at 600 ºC (0.64 gCO2 gads−1). Regarding the role of the CO2 flow rate at 700 ºC, increasing from 75 to 125 mL min−1 CO2 had minimal effect, maintaining a capture amount of approximately 0.49 gCO2 gads−1. These results confirmed the potential of the acid-modified eggshell as a low-cost and environmental friendly adsorbent for CO2 capture, which indeed may significantly improve the economic feasibility of the CCUS processes.

Integrated gasification carbon capture plant using molten carbonate fuel cell: An application to a cement industry

This study presents a novel integrated gasification carbon capture plant (IGCCP) as a post-combustion capture for a cement plant with a capacity of 4200 t clinker per day. The IGCCP includes externally reforming molten carbonate fuel cells (MCFC) fueled with syngas generated from the gasification of plastic wastes and produces low-carbon electricity and a CO2 stream for sequestration. The new thermodynamic model of MCFC developed here assesses the impact of syngas composition and cell temperature on the performances of the IGCCP system. An increase in the equivalence ratio (ER) from 0.20 to 1.00 of the gasification process increases the Nernst voltage loss factor from 86 to 132 mV thereby lowering voltage efficiency, but decreases the fuel demand to the IGCCP from 3462 to 2579 GJ/h. The maximum net generation efficiency is estimated to be 31.1% at ER = 0.33. Raising the cell temperature from 600 °C to 700 °C results in a decrease in ohmic voltage loss thereby increasing both voltage and MCFC efficiencies. Since the power generation increases at a higher cell temperature, the net power generation efficiency also increases but the CO2 capture efficiency remains constant (∼93%). The estimated specific primary energy consumption for CO2 avoided and captured are in the range of (−4.5) – (20.9) GJ/tCO2 and (−5.3) – (6.6) GJ/tCO2, respectively. The IGCCP system fueled by plastic wastes could decarbonize the cement plant completely while producing low-carbon electricity with an emission intensity of 87 kgCO2/MWh.

Evaluating solid sorbents for CO2 capture: linking material properties and process efficiency via adsorption performance

Expanding populations and growing economies result in higher energy needs. Meeting this increasing demand, while lowering carbon emissions, calls for a broad energy mix and commercial deployment of solutions like carbon capture and carbon removal technologies. The scale-up of these solutions is partially hindered by the lack of materials-related information, particularly in the case of solid adsorption-based carbon capture technologies. Furthermore, experimental measurement parameters used and how data is presented lack uniformity, which makes material comparisons extremely difficult. This review examines the current state of solid sorbent characterization for carbon capture, exploring physical and chemical properties, performance parameters, and process indicators. Adsorbent performance parameters demonstrate to be the crucial link between intrinsic material properties and the overall adsorption process effectiveness and therefore are the focus of this work. This paper outlines the relevant techniques used to measure Key Performance Indicators (KPIs) related to adsorption performance such as CO2 adsorption capacity, selectivity, kinetics, ease of regeneration, stability, adsorbent cost, and environmental impact. Additionally, this study highlights the relevant experimental conditions for diluted versus concentrated CO2 streams. Lastly, efforts in harmonizing experimental data sets are considered, and an outlook on solid sorbent characterization for carbon capture processes is presented. Overall, the aim of this work is to provide the reader a critical understanding of KPIs from atomic to process scale, highlighting the importance of experimental data throughout.

Conceptual assessment of sustainable methane production from oxycombustion CO2 capture in waste-to-energy power plants

The worldwide deployment of renewable energy is growing exponentially. However, its intermittency limits its impact on the yearly energy contribution to the grid. Thus, coal remains the largest source of electricity generation in the world. Developing negative emissions technologies, such as Bioenergy with Carbon Capture and Utilization (BECCU), is a promising pathway. This study focuses on integrating waste biomass oxycombustion and a power-to-methane system. A proton exchange membrane electrolysis driven by photovoltaic solar energy is considered to produce hydrogen and oxygen, which is used for oxy-waste combustion in a sub-critical steam power cycle. Depending on the operation strategy, a certain amount of additional O2 would be required, produced by a cryogenic distillation air separation process. At the exit of the boiler, the almost pure CO2 stream is further purified, compressed, and sent to the methanation reactor. A quasi-stationary model of the entire plant is developed to simulate different operation conditions and assess the integration efficiency. The results show an excellent integration of the whole plant, with a yearly average efficiency penalty associated with the CO2 avoided of 6 % points. Since waste biomass is used as fuel, the system provides −610 kg CO2/MWh emissions compared to biomass plants without CO2 capture. Results from a yearly detailed techno-economic analysis show an average levelized cost of electricity of 199.56 €/MWh and an average green methane production cost of around 110.12 €/MWh. These yearly results involve a CO2 capture cost of about 65.66 €/ton CO2, which justify the potential interest in the proposed system for new and retrofitted biomass power plants.

Rh promoted Ni over yttria–zirconia supported catalyst for hydrogen‐rich syngas production through dry reforming of methane

AbstractRh‐promoted YZr‐supported Ni catalyst (5Ni/YZr) is investigated for DRM and characterized with X‐ray diffraction, Raman, infrared spectroscopy, cyclic reduction–oxidation–reduction temperature programmed experiment, thermogravimetry, and transmission electron microscope. Over 5Ni/YZr, some active sites become inactive under the CO2 stream and limit H2 yield to ∼71%. Upon 4 wt% Rh addition over 5Ni/YZr; more than one type of stable active sites (Rh and Ni) generates, moderate basic sites are enhanced, wide ranges of CO2‐interacted surface species (especially bidentate CO2‐adsorbed species) are grown and graphitic carbon proportion over spent catalyst declines. This resulted in 87.35% H2 yield and 86.73% CO yield up to 420 min. 5Ni4Rh/YZr catalyst maintains ∼80% H2 yield at the end of 27 h of DRM reaction.

Reduced Order Machine Learning Models for Accurate Prediction of CO2 Capture in Physical Solvents.

CO2 sorption in physical solvents is one of the promising approaches for carbon capture from highly concentrated CO2 streams at high pressures. Identifying an efficient solvent and evaluating its solubility data at different operating conditions are highly essential for effective capture, which generally involves expensive and time-consuming experimental procedures. This work presents a machine learning based ultrafast alternative for accurate prediction of CO2 solubility in physical solvents using their physical, thermodynamic, and structural properties data. First, a database is established with which several linear, nonlinear, and ensemble models were trained through a systematic cross-validation and grid search method and found that kernel ridge regression (KRR) is the optimum model. Second, the descriptors are ranked based on their complete decomposition contributions derived using principal component analysis. Further, optimum key descriptors (KDs) are evaluated through an iterative sequential addition method with the objective of maximizing the prediction accuracy of the reduced order KRR (r-KRR) model. Finally, the study resulted in the r-KRR model with nine KDs exhibiting the highest prediction accuracy with a minimum root-mean-square error (0.0023), mean absolute error (0.0016), and maximum R2 (0.999). Also, the validity of the database created and ML models developed is ensured through detailed statistical analysis.

Integrated capture and solar-driven utilization of CO2 from flue gas and air

Integrated capture and solar-driven utilization of CO2 from flue gas and air

Continuous carbon capture in an electrochemical solid-electrolyte reactor.

Electrochemical carbon-capture technologies, with renewable electricity as the energy input, are promising for carbon management but still suffer from low capture rates, oxygen sensitivity or system complexity1-6. Here we demonstrate a continuous electrochemical carbon-capture design by coupling oxygen/water (O2/H2O) redox couple with a modular solid-electrolyte reactor7. By performing oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) redox electrolysis, our device can efficiently absorb dilute carbon dioxide (CO2) molecules at the high-alkaline cathode-membrane interface to form carbonate ions, followed by a neutralization process through the proton flux from the anode to continuously output a high-purity (>99%) CO2 stream from the middle solid-electrolyte layer. No chemical inputs were needed nor side products generated during the whole carbon absorption/release process. High carbon-capture rates (440 mA cm-2, 0.137 mmolCO2 min-1 cm-2 or 86.7 kgCO2 day-1 m-2), high Faradaic efficiencies (>90% based on carbonate), high carbon-removal efficiency (>98%) in simulated flue gas and low energy consumption (starting from about 150 kJ per molCO2) were demonstrated in our carbon-capture solid-electrolyte reactor, suggesting promising practical applications.

Thermodynamic screening of candidate ceria and perovskite systems as potential oxygen carrier materials for chemical looping water gas shift

Methane reforming and gasification processes are valuable pathways toward hydrogen production, and currently they represent nearly 79% of the worldwide hydrogen production market share. Chemical looping-water gas shift (CL-WGS) is a promising downstream process that can be integrated with reforming and gasification reactors and utilizes redox active metal oxides as oxygen exchange materials to produce separate streams of H2 and CO2. Thus, this technology can enable the production of high-purity hydrogen coupled with carbon capture without the need for an additional CO2 separation system.Although a number of redox-active metal oxides have been proposed in the literature as viable candidates for CL-WGS, the majority are based on stoichiometric metal oxides. However, non-stoichiometric oxides, which have the benefit of stability, rapid kinetics, and thermodynamic tunability, have only been proposed a handful of times. And of the prior proposed non-stoichiometric materials, none of the so called “water splitting” redox materials of the solar thermochemical H2O splitting (STCH) fields have been discussed for CL-WGS applications, despite their potentially favorable thermodynamic properties. In this research, we have identified 13 potential oxygen carrier materials and screened these for CL-WGS viability based on a simplified closed-system thermodynamic analysis. Ceria (CeO2-δ), CZO20 (Ce0.8Zr0.2O2-δ), and LSMA4060 (La0.6Sr0.4Mn0.4Al0.6O3-δ) are identified to have the most suitable properties in terms of operating temperatures, specific H2 yields, and conversions of syngas, during reduction, and steam, during oxidation. Results show that CZO20 and LSMA4060 have especially excellent reduction and oxidation extents at relatively low operating temperatures. For example, CZO20 and LSMA4060 have 85% syngas and steam conversions when cycled between 485-912 and 100–635 °C, respectively. Results show that only CZO20 is viable for isothermal operation, but higher temperatures are required; at 1023 °C, syngas and steam conversions are 80 and 12%.

Barriers and opportunities for the deployment of CO2 electrolysis in net-zero emissions energy systems

As energy systems across the globe transition toward net-zero emissions, the decarbonization of hard-to-decarbonize sectors, e.g., industry and transportation, is becoming more crucial. Renewable power-driven carbon dioxide (CO2) electrolysis has the potential to facilitate this transition by (1) substituting carbon-intensive petrochemical and fuel production and (2) using CO2 otherwise emitted from industrial processes or CO2 from the atmosphere; however, because of existing technical and economic challenges, the industrial deployment of this technology is not yet imminent. Here, we present an overview of CO2 electrolysis technologies to identify key hurdles in view of the industrial deployment of this technology in net-zero emissions energy systems. From the technology standpoint, catalysts should be developed with enhanced activity, selectivity, and stability/durability as well as membranes and reactors that prevent carbonate formation or crossover, achieve higher reaction rates, e.g., >1 A/cm2, and demonstrate long-term stability, e.g., >5 years. Conversely, from the system integration standpoint, impurity-tolerant CO2 electrolysis systems need to be developed and tested under relevant conditions, e.g., CO2 streams with traces of impurities (NOx, SOx, O2, N2, H2S, etc.). Additionally, the quantification of pros and cons of different integration pathways for CO2 capture and CO2 electrolysis requires further research. Moreover, the integration with variable renewable power sources—e.g., wind and solar photovoltaic power—and electricity markets requires a better understanding. For instance, the value of CO2 electrolysis flexibility in view of variable renewable power supply or dynamic electricity prices is not well understood. As energy systems across the globe transition toward net-zero emissions, the decarbonization of hard-to-decarbonize sectors, e.g., industry and transportation, is becoming more crucial. Renewable power-driven carbon dioxide (CO2) electrolysis has the potential to facilitate this transition by (1) substituting carbon-intensive petrochemical and fuel production and (2) using CO2 otherwise emitted from industrial processes or CO2 from the atmosphere; however, because of existing technical and economic challenges, the industrial deployment of this technology is not yet imminent. Here, we present an overview of CO2 electrolysis technologies to identify key hurdles in view of the industrial deployment of this technology in net-zero emissions energy systems. From the technology standpoint, catalysts should be developed with enhanced activity, selectivity, and stability/durability as well as membranes and reactors that prevent carbonate formation or crossover, achieve higher reaction rates, e.g., >1 A/cm2, and demonstrate long-term stability, e.g., >5 years. Conversely, from the system integration standpoint, impurity-tolerant CO2 electrolysis systems need to be developed and tested under relevant conditions, e.g., CO2 streams with traces of impurities (NOx, SOx, O2, N2, H2S, etc.). Additionally, the quantification of pros and cons of different integration pathways for CO2 capture and CO2 electrolysis requires further research. Moreover, the integration with variable renewable power sources—e.g., wind and solar photovoltaic power—and electricity markets requires a better understanding. For instance, the value of CO2 electrolysis flexibility in view of variable renewable power supply or dynamic electricity prices is not well understood.

CO2 electroreduction to multicarbon products from carbonate capture liquid

CO2 electroreduction to multicarbon products from carbonate capture liquid

Desorption performance of commercial zeolites for temperature-swing CO2 capture

CO2 capture is an inevitable option for carbon reduction, and adsorption-based CO2 capture technology offers a promising way to lowering the energy cost of the most mature amine-scrubbing method. Most of the recent studies focused on pursuing materials with high adsorption capacities, but desorption performance as well as recovery of high purity CO2 are long been overlooked. In this study, four commercial zeolites were screened for CO2 capture from simulated flue gas, among which, 5 A zeolite was selected to systematically investigate the desorption behavior. A more practically available temperature-swing procedure was proposed for desorption and regeneration of the material, and a CO2 stream of over 70% purity with 90% recovery can be achieved by only one-stage adsorption.

Evaluation of CO2 sources for Power-to-Liquid plants producing Fischer-Tropsch products

In addition to the climate crisis’s looming dangers, Europe was recently affected by profoundly volatile energy markets, entailing soaring inflation and political uncertainty. Power-to-Liquid processes have the potential to curb global warming by valorizing CO2 to produce synthetic fuels and platform chemicals while simultaneously substituting fossil energy imports. The impact of the CO2 source, i.e., cement production, biogas upgrading and solid biomass combustion, on Power-to-Liquid plants was evaluated by implementing the designed configuration, including CO2 capture, solid-oxide electrolyzer, Fischer-Tropsch synthesis and steam reforming, in IPSEpro, a stationary equation-based process simulation tool. Maximum Power-to-Liquid efficiency of 63.8% and maximum carbon efficiency of 88.6% were obtained by exploiting CO2 emitted by a biogas upgrading unit. Solid-oxide electrolyzers ranging from 23 MWel. (biogas) to 504 MWel. (cement) are required to process CO2 streams from 4.5 to 100 t/h. In addition, the mass and energy balances of the three considered configurations were determined and embedded in a process flow diagram. The presented study aims to facilitate future decisions concerning carbon capture and utilization policy by assessing the CO2 source’s influence on Power-to-Liquid plants’ key performance indicators. Furthermore, the underlying work supports a sustainable realization of Power-to-Liquid plants by offering a framework for exploiting CO2 sources.

Impact of O2 Content on the Corrosion Behavior of X65 Mild Steel in the Gaseous, Liquid, and Supercritical CO2 Streams

The CO2 stream in a carbon capture utilization and storage application generally includes impurities that could cause internal corrosion of CO2 pipelines. The general and localized corrosion behavior with a variety of O2 concentrations for X65 mild steel both in water-saturated CO2 and CO2-saturated water environments was evaluated using an autoclave. Corrosion tests were performed at 8 MPa and 25°C, 8 MPa and 35°C, and 4 MPa and 35°C to simulate the liquid, supercritical, and gaseous CO2 transportation. Results indicate that notably higher general corrosion rates were recorded at each O2 concentration in the CO2-saturated water phase than those in the water-saturated CO2 environment. The general corrosion rates did not show gradual rise at 0 ppm to 2,000 ppm of O2; instead, a maximum was measured at 1,000 ppm of O2 at 8 MPa and 25°C, and 50 ppm O2 at 8 MPa and 35°C in the water-saturated CO2 environment and 50 ppm at 8 MPa and 25°C, and 100 ppm at 8 MPa and 35°C in the CO2-saturated water environment. The general corrosion rate at 4 MPa and 35°C followed a different changing trend with O2 content from that in 8 MPa, and 25°C and 35°C both in the water-saturated CO2 and the CO2-saturated water environments. Localized corrosion or an average corrosion rate of beyond 0.1 mm/y was identified in each test in the CO2-saturated water environment. When O2 was introduced, a more porous corrosion product scale was detected on the coupon surfaces. A final series of corrosion tests with 100 ppm and 2,000 ppm O2 and 60% and 80% relative humidity in a CO2 environment did not show any sign of localized corrosion attack, and the average corrosion rates were below 0.1 mm/y at 8 MPa, 25°C and 35°C, and 4 MPa and 35°C.

Monitoring the dynamics of acid mine drainage affected stream surface water hydrochemistry at Jaintia Hills, Meghalaya, India.

Streams are pristine natural life-thriving water sources for people living in the mountainous proximity of NE India, where water scarcity is a common occurrence in most villages and towns. In the last few decades, factors like coal mining had drastically reduced the usability of stream water in the region; as such, an attempt has been made to assess the spatiotemporal variation of stream water chemistry affected by acid mine drainage (AMD) at Jaintia Hills, Meghalaya. The water variables were subjected to a multivariate statistical technique of principal component analysis (PCA) to understand their condition at each sampling point while comprehensive pollution index (CPI) and water quality index (WQI) was incorporated to assess the quality status. Maximum WQI was recorded in S4 (541.14) during summer, while minimum value was estimated in winter at S1 (14.65). Throughout the seasons, the WQI revealed "Good" quality in S1 (unimpacted stream), while the impacted streams (S2, S3, and S4) exhibited a "Very poor" to "Water unsuitable for drinking" status. Similarly, in S1, the CPI showed a ranged value of 0.20 to 0.37, presenting a water quality status of "Clean to Sub-Clean," whereas, CPI of the impacted streams indicated "Severely polluted" status. In addition, PCA bi-plot presented higher affinity of free CO2, Pb, SO42-, EC, Fe, and Zn in AMD-impacted streams than in unimpacted streams. The result demonstrates the environmental issues induced by coal mine waste and in particular, stream water being severely affected by AMD in mining areas of Jaintia Hills. Thus, measures to stabilized the mine repercussions and cumulative effects on the water bodies need to be formulated by the government, as stream water will remain the primary water source for the tribal communities in this region.

Flux and stable isotope fractionation of CO2 in a mesic prairie headwater stream

Abstract The carbon dioxide (CO2) fluxes from headwater streams are not well quantified and could be a source of significant carbon, particularly in systems underlain by carbonate lithology. Also, the sensitivity of carbonate systems to changes in temperature will make these fluxes even more significant as climate changes. This study quantifies small-scale CO2 efflux and estimates annual CO2 emission from a headwater stream at the Konza Prairie Long-Term Ecological Research Site and Biological Station (Konza), in a complex terrain of horizontal, alternating limestones and shales with small-scale karst features. CO2 effluxes ranged from 2.2 to 214 g CO2 m−2 day−1 (mean: 20.9 CO2 m−2 day−1). Downstream of point groundwater discharge sources, CO2 efflux decreased, over 2 m, to 3–40% of the point-source flux, while δ13C-CO2 increased, ranging from −9.8 ‰ to −23.2 ‰ V-PDB. The δ13C-CO2 increase was not strictly proportional to the CO2 flux but related to the origin of vadose zone CO2. The high spatial and temporal variability of CO2 efflux from this headwater stream informs those doing similar measurements and those working on upscaling stream data, that local variability should be assessed to estimate the impact of headwater stream CO2 efflux on the global carbon cycle.

Carboxysome‐Inspired Electrocatalysis using Enzymes for the Reduction of CO2 at Low Concentrations**

AbstractThe electrolysis of dilute CO2 streams suffers from low concentrations of dissolved substrate and its rapid depletion at the electrolyte‐electrocatalyst interface. These limitations require first energy‐intensive CO2 capture and concentration, before electrolyzers can achieve acceptable performances. For direct electrocatalytic CO2 reduction from low‐concentration sources, we introduce a strategy that mimics the carboxysome in cyanobacteria by utilizing microcompartments with nanoconfined enzymes in a porous electrode. A carbonic anhydrase accelerates CO2 hydration kinetics and minimizes substrate depletion by making all dissolved carbon available for utilization, while a highly efficient formate dehydrogenase reduces CO2 cleanly to formate; down to even atmospheric concentrations of CO2. This bio‐inspired concept demonstrates that the carboxysome provides a viable blueprint for the reduction of low‐concentration CO2 streams to chemicals by using all forms of dissolved carbon.

Carboxysome-Inspired Electrocatalysis using Enzymes for the Reduction of CO2 at Low Concentrations.

The electrolysis of dilute CO2 streams suffers from low concentrations of dissolved substrate and its rapid depletion at the electrolyte-electrocatalyst interface. These limitations require first energy-intensive CO2 capture and concentration, before electrolyzers can achieve acceptable performances. For direct electrocatalytic CO2 reduction from low-concentration sources, we introduce a strategy that mimics the carboxysome in cyanobacteria by utilizing microcompartments with nanoconfined enzymes in a porous electrode. A carbonic anhydrase accelerates CO2 hydration kinetics and minimizes substrate depletion by making all dissolved carbon available for utilization, while a highly efficient formate dehydrogenase reduces CO2 cleanly to formate; down to even atmospheric concentrations of CO2 . This bio-inspired concept demonstrates that the carboxysome provides a viable blueprint for the reduction of low-concentration CO2 streams to chemicals by using all forms of dissolved carbon.

Synergistic Chemical Looping Process Coupling Natural Gas Conversion and NOx Purification

We present a novel low-temperature chemical looping combustion scheme for simultaneous natural gas conversion into a sequestration-ready CO2 stream and NOx purification. The scheme employs nickel oxide (NiO) supported on ZrO2 as the oxygen carrier. In the process, CH4 reduces the oxidized carrier to Ni/ZrO2 in a co-current moving bed reactor, which is then oxidized back to NiO/ZrO2 by the NOx-laden flue gas in a fluidized bed reactor, completing the oxygen carrier loop. Thermodynamic studies demonstrate that the presence of CO2 does not significantly affect NOx purification performance at different flue gas flow rates. The operating temperatures of the reactors are selected based on NOx-temperature programmed oxidation (TPO) and CH4-temperature programmed reduction (TPR) experiments. Results show that the process can optimally operate at temperatures close to the combustion plants’ flue gas temperature of 400–500 °C, reducing the need for hot utilities. The study conducts comprehensive isothermal and autothermal analyses of the process to evaluate the effects of temperature and carrier flow rate on CH4 conversion, CO2 selectivity, carbon deposition, and NOx conversion. For the autothermal analysis, the CH4 reactor operates adiabatically, while the NOx reactor operates isothermally. Comparative studies with the conventional NOx selective catalytic reduction (SCR) process indicate an exergy efficiency and effective thermal efficiency (ETE) improvement of 9 and 18 percentage points, respectively. The findings suggest that this low-temperature chemical looping process is a promising solution for flue gas NOx treatment, utilizing cheaper natural gas as the reductant and eliminating environmental concerns, such as ammonia or urea slippage. Overall, this study contributes to the development of more efficient and sustainable methods for reducing NOx emissions.

Bifunctional Gas Diffusion Electrode Enables In-situ Separation and Conversion of CO2 to Ethylene from Dilute Stream.

The requirement of concentrated CO2 feedstock significantly limits the economic feasibility of electrochemical CO2 reduction (eCO2 R) as it often involves multiple intermediate processes, including CO2 capture, energy intensive regeneration, compression, and transportation steps. Herein, we report on a bifunctional gas diffusion electrode (BGDE) for separation and electrolysis of CO2 from a low concentration CO2 stream (∼10 vol%). We demonstrate a BGDE for selective production of ethylene (C2 H4 ) by combining high density polyethylene-derived porous carbon (HPC) as a physisorbent with polycrystalline copper as conversion catalyst. Our BGDE shows substantial tolerance to 10 vol% CO2 exhibiting a Faradaic efficiency of ∼45% towards C2 H4 at a current density of 80mA/cm2 over 11hrs, outperforming previous reports that utilised such partial pressure (PCO2 = 0.1 atm and above) at ambient conditions and unaltered polycrystalline copper as catalyst. Molecular dynamics simulation and mixed gas permeability assessment reveal that such selective performance is ensured by high CO2 uptake of microporous HPC as well as continuous desorption owing to molecular diffusion and concentration gradient created by binary flow (CO2 |N2 ) within sorbent boundary. We conclude based on detailed technoeconomic analysis that our in-situ process has the potential to be economically compelling by precluding the C2 H4 production cost associated with the energy intensive intermediate steps of conventional decoupled process. This article is protected by copyright. All rights reserved.