CO2 Solubility Research Articles

Chemical strategies for enhancing CO2-Hydrocarbon miscibility

Carbon dioxide (CO2) flooding holds immense potential for enhancing hydrocarbon recovery and facilitating geological carbon storage. Among CO2 flooding methods, miscible flooding demonstrates significantly higher production compared to immiscible flooding. However, in certain reservoirs, the high miscibility pressure presents a challenge for achieving miscibility under reservoir pressure conditions. Nonionic surfactants offer a solution by reducing the miscibility pressure in hydrocarbon-CO2 systems. In this study, eight nonionic surfactants were assessed, and two of the most effective surfactants were selected. These surfactants were combined to create a novel nonionic surfactant system aimed at lowering the miscibility pressure. The minimum miscibility pressure (MMP) of the hydrocarbon-CO2 system was measured using a slim-tube experiment, and a comparative analysis was conducted between the vanishing interfacial tension method (VIT) and the slim-tube method. Furthermore, the microscopic mechanism by which surfactants reduce the miscibility pressure was studied and analyzed. The findings indicate that the compound nonionic surfactant SF, with a total concentration of 1.0 wt% and a SMF to Span20 ratio of 1:1, reduces the miscibility pressure by 18.30%. The slim-tube data were processed to obtain a narrower range for MMP using criteria such as the crude oil recovery factor (ORF) and the break-over pressure (BOP). The maximum error between MMP measured by the VIT method and the slim-tube experiment is 5.86%, demonstrating the high accuracy of the VIT method in this study. The surfactant effectively reduces the miscibility pressure by decreasing the interfacial tension (IFT) between oil and gas, enhancing the CO2 extraction efficiency on intermediate hydrocarbons within the crude oil, and improving the solubility of CO2 in the crude oil. The findings of this study hold significant guidance for future investigations on the miscibility in the processes of geological CO2 utilization and storage.

Femtoliter oil droplets act as CO2 micropumps for uninterrupted electrochemiluminescence at the water|oil interface

Interfacial effects are well-known to significantly alter chemical reactivity, especially in confined environments, where the surface to volume ratio increases. Here, we observed an inhomogeneity in the electrogenerated chemiluminescence (ECL) intensity decrease over time in a multiphasic system composed of femtoliter water droplets entrapping femtoliter volumes of the 1,2-dichloroethane (DCE) continuous phase. In usual electrochemiluminescence (ECL) reactions involving an ECL chromophore and oxalate ([C2O4]2−), the build-up of CO2 diminishes the ECL signal with time because of bubble formation. We hypothesised that relative solubilities of chemical species in these environments play a dramatic role in interfacial reactivity. Water droplets, loaded with the ECL luminophore [Ru(bpy)3]2+ and the coreactant [C2O4]2− were allowed to stochastically collide and adsorb at the surface of a glassy carbon macroelectrode. When water droplets coalesce on the surface, they leave behind femtoliter droplets of the DCE phase (inclusions). We report the surprising finding that the addition of multiple interfaces, due to the presence of continuous phase’s femtoliter inclusions, allows sustained ECL over time after successive potential applications at the triple-phase boundary between water droplet|electrode|DCE inclusion. When femtoliter droplets of DCE form on the electrode surface, bright rings of ECL are observed during the simultaneous oxidation of [Ru(bpy)3]2+ and [C2O4]2−. Control experiments and finite element modelling allowed us to propose that these rings arise because CO2 that is generated near the 1,2-dichloroethane droplet partitions in due to relative solubility of CO2 in 1,2-dichloroethane and builds up and/or is expelled at the top of the droplet. The small droplets of the DCE phase act as micropumps, pumping away carbon dioxide from the interface. These results highlight the unexpected point that confined microenvironments and their geometry can tune chemical reactions of industrial importance and fundamental interest.

Effect of Tributyl Citrate as a Cosolvent on the Phase Behavior of Crude Oil during CO2 Injection Process

The current research on CO2 cosolvent primarily focuses on reducing the minimum miscibility pressure and improving oil recovery. However, investigations into the impact of additive agents on the phase behavior of crude oil during the CO2 injection process are relatively limited. In this study, we introduced tributyl citrate as a cosolvent to the CO2 injection process. By comparing the phase parameters of crude oil and changes in component composition in the residual oil before and after the addition of tributyl citrate, we explored the influence patterns of this cosolvent during CO2 injection. The experiments show that the optimum concentration of tributyl citrate is 0.3%. After the addition of tributyl citrate, the bubble point pressure of crude oil is reduced from 14.28 MPa to 13.36 MPa, and the density is decreased from 1.00 g/cm3 to 0.95 g/cm3. These alterations of bubble point pressure and density indicate an enhanced solubility of CO2 and improved miscibility with the oil, coinciding with an increased volume expansion coefficient rising from 1.12 to 1.18 under 20 MPa and a decrease in viscosity from 0.73 mPa·s to 0.64 mPa·s. Tributyl citrate primarily affects the properties of crude oil by reducing interfacial tension and the content of heavy components in the dissolution system. The addition of tributyl citrate stabilizes the deposition trend of heavy components in crude oil and promotes the transformation of heavy components into light components, thereby enhancing the efficiency of CO2 extraction. This study provides valuable insights into a novel and simple method to further increase oil recovery in the CO2 injection process.

Tunable gas selectivity of cellulose nanocrystals – Polyethylene glycol composite membranes

The kinetics of the CO2, D2 and CH4 transport through self-supporting cellulose nanocrystals (CNCs) films containing low-molecular weight poly(ethylene glycol) (PEG) additive as plasticizer agent was studied in single gas condition at 293 K and sub-atmospheric feed pressure. Neat CNC and PEG-CNC with 7 wt % PEG films act as impermeable barrier for CO2 and CH4 and exhibit D2 permeability values not larger than 0.05 barrer with penetrant diffusivity in the 10−10 cm2/s range. PEG addition at larger contents improves the permeability and diffusivity of all penetrant gases and gives to the PEG-CNC membrane a CO2 selective character. The CO2 permeability and ideal CO2/D2 selectivity of the PEG-CNC films are 0.42 ± 0.04 barrer and ∼3, respectively, at 14 wt % PEG content, 2.5 ± 0.2 barrer and ∼5 at 21 wt % PEG. The preferred CO2 transport exhibits a solution-selective character being the D2 diffusivity a factor ∼10 larger than the CO2 diffusivity. PEG addition, on the contrary, does not change the D2 selective character for the D2/CH4 gas couple. PEG well mixed with the gas-impermeable CNCs increases the PEG-CNC free volume and preferentially improves the CO2 solubility given the specific interactions between the quadrupolar CO2 penetrant and the dipolar ether groups of the PEG additive.

Review of electrocatalytic reduction of CO2 on carbon supported films

Carbon capture and conversion are becoming increasingly important as atmospheric CO2 concentrations rise and their adverse effects become increasingly evident. CO2 conversion/utilization-related research has gained renewed interest on a variety of platforms, including thermal, solar, biological, photochemical, and electrochemical conversions. Electrochemical routes, using suitable catalysts, are potentially suitable for commercial purposes owing to ease of integration with solvent-based carbon capture processes. This paper summarizes and evaluates the studies conducted within the past decade regarding the feasibility of carbon-based supports utilized in electrocatalytic carbon dioxide reduction. CO2 conversion has been reviewed in a number of reports, focusing on specific sections, such as metallic/bimetallic catalysts, CO2 solubility, and the fabrication of electrodes and electrochemical cells. The number of publications addressing various carbon-based electrocatalysts is increasing, but these materials have not yet been reviewed. Herein, we are focused on three types of electrocatalyst materials: metals, metal-oxides, non-oxides, and combinations thereof with carbon. The scope of this study includes the following: i) carbon-based materials and how they are characterized by distinctive properties, ii) electrocatalytic CO2 conversion techniques, and iii) research cases for carbon allotrope-supported composites used in CO2 reduction. The advancement in analytical tools that provide insight into liquid-phase reactions will benefit the development of catalysts and electrodes that will be effective in converting CO2 into the desired products. Such developments will also be applicable to other systems involving liquid electrolytes or solvents for performing reactions on catalyst surfaces.

Preparation of amino-functionalized polyethylene-silica composite membrane and FDH immobilization

Enzymatic CO2 conversion represents a highly efficient, energy-conserving, and environmentally sustainable approach to mitigating the increasing pressure caused by huge carbon emissions and generating valuable products. However, several challenges associate with the process including the instability and recovery difficulty of free enzyme, as well as low solubility of CO2 in mild conditions. Immobilizing enzyme on the amino-functionalized supports presents a viable solution to these issues. Considering the wide application of polymer hollow fiber membranes in the field of CO2 gas–liquid membrane contactor and the characteristics of hydrophilic, biocompatible, and high specific surface area of silica nanoparticles, the amino-functionalized polyethylene (PE)-silica (APS) composite membranes were fabricated via different routes. The morphologies, the loading rates of modified SiO2 and reusability of APS membranes were characterized for a crude screening. Following that, seven kinds of APS membranes were used as the carriers of formate dehydrogenase (FDH) that could catalyze the reduction of CO2 to formate, and their immobilization efficiency and catalytic performance were compared. The results show that 1# and 2# membranes based on carboxyl-modified PE with a loading rate of 5.5 %∼5.6 % and the reusability of above 99 % were more ideal carriers than others. The enzyme activity recovery rate of APS-immobilized FDH (FDH-APS) was separately 367 % and 256 %, proving the intensification action of carriers on the enzymatic reaction. After 10 cycles of use, the relative activity of two kinds of FDH-APS was around 70 % and 78 %, much higher than corresponding particles or membrane attached FDH (25.3 % and 20.4 %). After storage at 4 °C for 20 days, the relative activity of FDH-APS was 82.7 % and 81.0 %, while it was only 61.4 % for free enzyme.

Experimental and thermodynamic investigation of gemifloxacin solubility in supercritical CO2 for the production of nanoparticles

The effective use of the supercritical technology in the production of new pharmaceutical formulations with greater bioavailability requires the determination of the solubility of pharmaceutical substances in supercritical CO2 (scCO2) at different conditions. In the current work, the solubility of an antibacterial compound, Gemifloxacin, was measured at various temperatures (308 to 338 K), and pressures (120 to 300 bar). This compound has a poor solubility in scCO2 (0.02 × 10−4 to 0.67 × 10−4 mole fraction or 0.0156 to 0.5891 g.kg−1). Furthermore, some popular empirical models and three thermodynamic approaches (SRK and PR equations of state, and the regular solution model) were applied to correlate and predict the solubility of Gemifloxacin in scCO2. The regular solution model with temperature-dependent solubility parameter (mean AARD% = 2.32–4.34) and the SRK-based model (mean AARD% = 7.47), exhibited the highest accuracy in fitting the experimental data.

Density, viscosity, and CO2 solubility in ether-functionalized phosphonium-based bis(trifluoromethanesulfonyl)amide ionic liquids

We measured the densities and viscosities of two ionic liquids, triethyl(methoxymethyl)phosphonium bis(trifluoromethanesulfonyl)amide ([P222(1O1)][TFSA]) and triethyl(2-methoxyethyl)phosphonium bis(trifluoromethanesulfonyl)amide ([P222(2O1)][TFSA]), at atmospheric pressure and 273.15–363.15 K. The high-pressure density at the pressures up to 50 MPa was also measured at 298.15–353.15 K. Meanwhile, CO2 solubility in these phosphonium-based ionic liquids was determined using a magnetic suspension balance at 303.15–333.15 K and pressures up to 6 MPa. The experimental density and viscosity at atmospheric pressure were fitted using quadratic and Vogel-Fulcher-Tammann equations, respectively. The high-pressure density was fitted using the Tait equation and Sanchez-Lacombe equation of state. The properties of the two ether-functionalized ionic liquids were compared to those of triethylpentylphosphonium bis(trifluoromethanesulfonyl)amide [P2225][TFSA]. The density at atmospheric pressure increased in the order [P2225][TFSA] < [P222(2O1)][TFSA] < [P222(1O1)][TFSA]. The introduction of the ether group effectively reduced viscosity in the following order: [P222(1O1)][TFSA] < [P222(2O1)][TFSA] < [P2225][TFSA]. The CO2 solubilities in [P222(1O1)][TFSA] and [P222(2O1)][TFSA] were slightly lower than those in [P2225][TFSA]. In contrast, the molality of CO2 (m1) increased in the order [P2225][TFSA] < [P222(2O1)][TFSA] < [P222(1O1)][TFSA]. Ether functionalized phosphonium-based cations are effective in enhancing the physical absorption of CO2, particularly the molality of CO2.

Experimental and modeling study of CO2 solubility in formation brines at in-situ conditions

The dissolution of CO2 into formation brine, one of the dominant trapping mechanisms for geological carbon storage (GCS) in deep saline aquifers, has been widely investigated. Most experimental and modeling studies focused on the CO2 solubility in synthetic brines. However, rare studies have been performed to investigate CO2 solubility in real formation brines, especially when ion-ion interactions were considered. In this work, the CO2 solubility of seventy formation brines from major basins in China including the Junggar basin, Ordos basin, and North and South Songliao basin was measured at in-situ pressure and temperature conditions. Experimental results show that CO2 solubility has a strong relationship with pressure and total dissolved solids (TDS), while the relationship between solubility and temperature is weak. Three solubility regions were classified in terms of depth. In Regions I and III, CO2 solubility increases with depth and is independent with depth in Region II. However, the effect of salinity on CO2 solubility was observed in all regions. Additionally, a modified Duan's model used for a mixed-salt system was proposed using dataset from this study and literature. Comparisons with Duan's model for CO2 solubility in mixed-salt systems show the average absolute relative deviation equals 5.14%, which reveals a clear improvement in the modified model. In addition, the validation of the model was performed, and results show that the average absolute relative deviation before and after improvement are 12.10% and 5.11%, respectively, indicating the high accuracy of the improved model. Overall, this research improves the understanding of CO2 solubility in real formation brines and illustrates the efficiency and accuracy of the modified model, which is crucial for the evaluation of the CO2 storage capacity, fate of CO2 over storage site life for commercial GCS projects.

Alkylimidazolium-based ionic liquids with tailored anions and cations for CO2 capture.

A systematic investigation was conducted in the present study to determine how various cations and anions affected the solubility of CO2. To investigate the influence of different cations and anions on the solubility of CO2, twelve ILs were synthesized, characterized, and utilized. These ILs comprised five distinct anions (dioctylsulfosuccinate [DOSS], triflouromethanesulfonate [TFMS], dodecylsulfate [DDS], 3-sulfobezoate [SBA], and benzene sulfonate [BS]), and four distinct cations (1-butyl-3-propanenitrile imidazolium [C2CN Bim], 1-hexyl-3-propanenitrile imidazolium [C2CN Him], 1-octyl-3-propanenitrile imidazolium [C2CN Oim], and 1-decyl-3-propanenitrile imidazolium [C2CN Dim]). The synthesized ILs were characterized using NMR and elemental analysis. Their moisture and halide contents were determined. The gravimetric method (MSB) was employed to determine the solubility of CO2 at various pressures (20, 15, 10, 5, and 1 bar). In addition, the effects of temperature on the solubility of CO2 were investigated. The constant of Henry's law (kH) was also calculated, along with thermodynamic properties including standard enthalpy (H0), entropy (S0), and Gibbs free energy (G0).

Impact of water content on minimum miscibility pressure during CO2 flooding in high water-cut reservoirs

This study focused on the X block stratum oil, specifically addressing the application of CO2 displacement technology in enhancing oil recovery under high water content conditions. It systematically investigates the variation of the minimum miscibility pressure (MMP) between CO2 and formation oil at water contents of 0%, 60%, 70%, 80%, and 90%. The research employed slim-tube model simulation experiments and theoretical analysis to explore the impact of different water contents on the physical properties of formation oil and the changes in the interaction mechanism between CO2 and crude oil. The results indicate that the MMP of CO2 flooding is the lowest at 31.11 MPa in the absence of water, reaching the highest value of 37.94 MPa at 90% water content. The MMP of the CO2-formation oil system shows a significant upward trend with increasing water content in the formation, which is related to the stability of the water film, the solubility of CO2, and the interfacial tension between oil and water. Meanwhile, high water content leads to the expansion of formation oil volume, increased viscosity, and compositional changes, collectively influencing the results. This study provides theoretical support for the field application of CO2 flooding and offers critical references for optimizing the oil displacement process.

Reactive capture and electrochemical conversion of CO2 with ionic liquids and deep eutectic solvents.

Ionic liquids (ILs) and deep eutectic solvents (DESs) have tremendous potential for reactive capture and conversion (RCC) of CO2 due to their wide electrochemical stability window, low volatility, and high CO2 solubility. There is environmental and economic interest in the direct utilization of the captured CO2 using electrified and modular processes that forgo the thermal- or pressure-swing regeneration steps to concentrate CO2, eliminating the need to compress, transport, or store the gas. The conventional electrochemical conversion of CO2 with aqueous electrolytes presents limited CO2 solubility and high energy requirement to achieve industrially relevant products. Additionally, aqueous systems have competitive hydrogen evolution. In the past decade, there has been significant progress toward the design of ILs and DESs, and their composites to separate CO2 from dilute streams. In parallel, but not necessarily in synergy, there have been studies focused on a few select ILs and DESs for electrochemical reduction of CO2, often diluting them with aqueous or non-aqueous solvents. The resulting electrode-electrolyte interfaces present a complex speciation for RCC. In this review, we describe how the ILs and DESs are tuned for RCC and specifically address the CO2 chemisorption and electroreduction mechanisms. Critical bulk and interfacial properties of ILs and DESs are discussed in the context of RCC, and the potential of these electrolytes are presented through a techno-economic evaluation.

Amplified Production and Export of Dissolved Inorganic Carbon During Hot and Wet Subtropical Monsoon

AbstractUnderstanding the origins and processes of riverine dissolved inorganic carbon (DIC) is crucial for predicting the global carbon cycle with projected, more frequent climate extremes yet our knowledge has remained fragmented. Here we ask: How and how much do DIC production and export vary across space (shallow vs. deep, uphill vs. depression) and time (daily, seasonal, and annual)? How do the relative contributions of biogenic (soil respiration) and geogenic (carbonate weathering) sources differ under different temperature and hydrological conditions? We answer these questions using a catchment‐scale reactive transport model constrained by stream flow, stable water isotopes, stream DIC, and carbon isotope data from a headwater karstic catchment in southwest China in a subtropical monsoon climate. Results show climate seasonality regulates the timing of DIC production and export. In hot‐wet seasons, high temperature accelerates soil respiration and carbonate weathering (up to a factor of three) via elevating soil CO2 and carbonate solubility, whereas high discharge enhances export by two orders of magnitude compared to cold‐dry seasons. Carbonate weathering is driven more by soil CO2 than water flow. At the annual scale, 92.9% and 7.1% of DIC was produced in shallow and deep zone, respectively, whereas 64.5% and 35.5% of DIC was exported from shallow and deep zone, respectively. These results highlight the uniqueness of subtropical karst areas as synchronous reactors and transporters of DIC during the hot‐wet monsoon, contrasting the asynchronous production and export in other climate regions. A future hotter and wetter climate with more intensive storms in the region may further intensify DIC production and export, accentuating the potential of subtropical karst regions as global hot spots for carbon cycling.

Practical potential of suspension electrodes for enhanced limiting currents in electrochemical CO2 reduction.

CO2 conversion is an important part of the transition towards clean fuels and chemicals. However, low solubility of CO2 in water and its slow diffusion cause mass transfer limitations in aqueous electrochemical CO2 reduction. This significantly limits the partial current densities towards any desired CO2-reduction product. We propose using flowable suspension electrodes to spread the current over a larger volume and alleviate mass transfer limitations, which could allow high partial current densities for CO2 conversion even in aqueous environments. To identify the requirements for a well-performing suspension electrode, we use a transmission line model to simulate the local electric and ionic current distributions throughout a channel and show that the electrocatalysis is best distributed over the catholyte volume when the electric, ionic and charge transfer resistances are balanced. In addition, we used electrochemical impedance spectroscopy to measure the different resistance contributions and correlated the results with rheology measurements to show that particle size and shape impact the ever-present trade-off between conductivity and flowability. We combine the modelling and experimental results to evaluate which carbon type is most suitable for use in a suspension electrode for CO2 reduction, and predict a good reaction distribution throughout activated carbon and carbon black suspensions. Finally, we tested several suspension electrodes in a CO2 electrolyzer. Even though mass transport limitations should be reduced, the CO partial current densities are capped at 2.8 mA cm-2, which may be due to engineering limitations. We conclude that using suspension electrodes is challenging for sensitive reactions like CO2 reduction, and may be more suitable for use in other electrochemical conversion reactions suffering from mass transfer limitations that are less affected by competing reactions and contaminations.

A review on recent advances of cellulose acetate membranes for gas separation.

This review thoroughly investigates the wide-ranging applications of cellulose-based materials, with a particular focus on their utility in gas separation processes. By focusing on cellulose acetate (CA), the review underscores its cost-effectiveness, robust mechanical attributes, and noteworthy CO2 solubility, positioning it as a frontrunner among polymeric gas separation membranes. The synthesis techniques for CA membranes are meticulously examined, and the discourse extends to polymeric blend membranes, underscoring their distinct advantages in gas separation applications. The exploration of advancements in CA-based mixed matrix membranes, particularly the incorporation of nanomaterials, sheds light on the significant versatility and potential improvements offered by composite materials. Fabrication techniques demonstrate exceptional gas separation performance, with selectivity values reaching up to 70.9 for CO2/CH4 and 84.1 for CO2/N2. CA/PEG (polyethylene glycol) and CA/MOF (metal-organic frameworks) demonstrated exceptional selectivity in composite membranes with favorable permeability, surpassing other composite CA membranes. Their selectivity with good permeability lies well above all the synthesised cellulose. As challenges in experimental scale separation emerge, the review seamlessly transitions to molecular simulations, emphasizing their crucial role in understanding molecular interactions and overcoming scalability issues. The significance of the review lies in addressing environmental concerns, optimizing membrane compositions, understanding molecular interactions, and bridging knowledge gaps, offering guidance for the sustainable evolution of CA-based materials in gas separation technologies.

Highly selective capture of sulfur dioxide by low viscosity 1,2,4-triazole + [Emim]Cl deep eutectic solvents

Sulfur dioxide (SO2) is a toxic gas emitted from industrial waste gases, and its removal is crucial to improve the quality of the atmosphere and reduce the harm to human health. In this work, we investigated the absorption of SO2 by deep eutectic solvents (DESs) with low viscosity 1,2,4-triazole (Trtz) and 1-ethyl-3-methylimidazole chloride ([Emim]Cl) under different conditions. We briefly investigated the mechanism of sulfur dioxide absorption by DESs and measured the absorption performance of Trtz + [Emim]Cl DESs for SO2 at different molar ratios. The experimental results show that all Trtz + [Emim]Cl DESs have good capture performance for SO2, among which 298.2 K Trtz + [Emim]Cl (1:3) DES has an absorption capacity of 18.15 mol/kg (102.2 kPa) for SO2, surpassing most previously reported deep eutectic solvents. We found that the solubility of CO2 and N2 is much lower than that of SO2. The absorption capacity of DESs for SO2 is about 452 times that of CO2 and 1530 times that of N2.Therefore, this absorbent has extensive application prospects in the field of SO2 gas capture.

Low molecular weight carbohydrate patterns of mangrove macroalgae from different climatic niches under ocean acidification, warming and salinity variation

Ocean acidification has increased due to the enhanced solubility of CO2 in seawater. Mangrove macroalgae in tropical and subtropical coastal regions can benefit from the higher availability of CO2 for photosynthesis and primary production. However, they can be negatively affected by the simultaneously occurring warming and increased salinity in estuaries. Thus, we analyzed the isolated effects of ocean acidification and the interactive effects of increased temperature and salinity on the low molecular weight carbohydrate (LMWC) contents of the mangrove red macroalgae Bostrychia montagnei and Bostrychia calliptera from Brazilian tropical and subtropical populations. Specimens from both climatic niches were tolerant to pH decreased by CO2 enrichment and enhanced their LMWC contents under increased availability of CO2. Specimens from both climatic niches also accumulated their dulcitol and sorbitol contents to cope with warming and salt stress. Nevertheless, temperature of 34 °C was lethal for tropical macroalgae, while 29 °C and 31 °C were lethal for subtropical B. calliptera under salinity of 35. Tropical and subtropical B. montagnei synthesized dulcitol (5–110 mmol kg−1 dry weight) and sorbitol (5–100 mmol kg−1 dry weight) as osmoregulatory, energy and thermal protection compounds, whereas tropical and subtropical B. calliptera synthesized mainly dulcitol (10–210 mmol kg−1 dry weight). Although digeneaside has an energy function in Bostrychia spp., it is not an osmolyte or thermal protection compound. Our data demonstrated that both tropical and subtropical Bostrychia spp. benefit from ocean acidification by CO2 enrichment, increasing their LMWC contents. However, warming and increased salinity in estuaries will be detrimental to them, even they producing protective metabolites. Multifactorial approaches are recommended to investigate whether negative effects of increased temperature and salinity nullify positive effects of ocean acidification on these Bostrychia species/populations.

(Invited) High-Rate CO2 Reduction Reactions: From Electrocatalysts to Gas-Diffusion Electrodes

Excessive emissions of carbon dioxide (CO2) from the use of fossil fuels are becoming a serious obstacle to the sustainable development of society. Electrochemical CO2 reduction (CO2RR) into value-added products using solar electricity is a promising technology to close the carbon cycle and sequester anthropogenic CO2 into chemical feedstocks.[1] The practical implementation of CO2RR requires a high current density, as the current density for CO2RR is directly correlated to the capital cost of the electrodes and electrochemical cells. The use of gas diffusion electrodes (GDEs) effectively accelerates CO2RR by overcoming the mass transport limitation due to the inherently low diffusion and solubility of CO2 in water. This presentation summarises our recent studies on high-rate CO2RR from the point of view of both novel electrocatalyst designs and appropriate electrode assembly. Single-atom electrocatalysts (SAECs), consisting of single isolated metal sites dispersed on heterogeneous supports, are one of the promising electrocatalysts for high-rate gaseous CO2RR. We have employed various single metal-doped covalent triazine frameworks (M-CTFs) as a platform for CO2RR electrocatalysts on GDEs and systematically investigated them to derive sophisticated design principles using a combined computational and experimental approach.[2-4] The Ni-CTF exhibited both high selectivity and high reaction rate for CO production. In contrast, the Sn-CTF exhibited selective formic acid production, and the faradaic efficiencies (FEs) and partial current density reached 85% and 150 mA/cm2, respectively.[2] These results were in close agreement with the intermediate CO2RR adsorption strength obtained by DFT calculations. In addition to the synthesis of efficient electrocatalysts, the triple phase boundary (TPB) at the GDE, where the catalyst material, electrolyte, and gas pores intersect, needs to be enlarged for high-rate gaseous CO2RR.[5,6] We successfully increased the partial current density for multicarbon products (C2+) over cupric oxide (CuO) nanoparticles on gas diffusion electrodes in neutral electrolytes to a record value of 1.7 A/cm2 by maximizing the area of the CO2RR active interface.[5] In particular, we demonstrated that the thickness of catalyst layers was one highly sensitive factor in determining the maximum current density for C2+. Although the GDE and electrocatalyst used in this case are not unique, the optimized assembly elicits their undermined potential.[1] K. Kamiya, Nakanishi* et al. Chem. Lett. 2021, 50, 166-179. [2] S. Kato, K. Kamiya* et al. Chem. Sci., 2023, 14, 613–620. [3] P. Su, K. Kamiya*et al. , Chem. Sci., 2018, 9, 3941-3947. [4] K. Kamiya* Chem. Sci. 2020, 11, 8339–8349. [5] A. Inoue, K. Kamiya* et al. EES Catal. 2023, 1, 9-16. [6] T. Liu*, K. Kamiya* et al. Small 2022, 18, 2205323.

Quantitative Analysis of CO2 Evolution in an Alkaline Electrolyte Solution By Differential Electrochemical Mass Spectroscopy

CO2 is involved in various main and side reactions of electrochemical energy devices, such as carbon corrosion reactions and alcohol oxidation reactions. Differential electrochemical mass spectroscopy (DEMS) has been intensively applied in acidic electrolyte solutions to analyze these reactions. DEMS is the in-situ electrochemical measurement technique to analyze volatile species with the mass spectrometer (MS). However, the applications of DEMS to alkaline electrolyte solutions have been limited due to the high solubility of CO2 in alkaline solutions. While "conventional DEMS cells," where porous thin-film working electrodes are formed onto polytetrafluoroethylene (PTFE) membrane interface, can quantitatively analyze CO2 that has not dissolved into the electrolyte yet [1], the working electrode materials are limited to those that can be deposited on porous PTFE membrane as porous thin-films. Recently, Möller et al. have developed the DEMS system, which can detect CO2 from general planer electrodes coated by catalyst powders by combining a neutralizer and "dual thin-layer flow cell" [2]. However, due to the relatively low detection limit, quantitative analysis of evolved CO2 has not been accomplished. In this study, we attempt to use high surface area electrodes to enhance the MS signal of CO2 to enable quantitative analysis of evolved CO2. To suppress the in-plane reaction distribution in the flow cell, we integrated an anion exchange membrane into the cell and arranged the counter electrode opposing the working electrode [3] (Fig. 1 (a)).CO-stripping voltammetry was performed to evaluate the CO2 detectability of the constructed DEMS system. The DEMS cell was composed of a commercial Pt/C electrode as the working electrode, a commercial Hg/HgO electrode as the reference electrode, a Pt mesh as the reference electrode, 1 mol dm–3 KOH aq as the electrolyte solution, and 1 mol dm–3 H2SO4 aq as the neutralizer. Figure 1 (b) shows the CO-stripping voltammogram and corresponding MS signal of CO2 (m/z = 44). MS signal of CO2 accompanied by the anodic CO oxidation current is clearly observed from 0.6 to 1.2 V vs. RHE. The calibration constant, which correlates the MS signal of CO2 to partial current for CO2 evolution reaction, is successfully obtained as 2.2 × 10–10, which shows that the DEMS system established in this study can quantitatively analyze CO2. Applications to the carbon corrosion reactions are also presented at the site.

(Invited)The Role of the Catalyst Microenvironment in the Electrochemical Reduction of Carbon Monoxide

Carbon monoxide is already an important raw material for the synthesis of different bulk chemicals (e.g., phosgene and different products thereof). Considering that it can be a building block for the synthesis of virtually any organic compound, carbon monoxide might play an important role in the production of synthetic fuels and other typical petrochemical products. This can be performed under high temperature and pressure conditions in the Fischer-Tropsch process, but electrochemical methods also offer a possible way of forming different chemicals from carbon monoxide.Because of the low solubility of carbon monoxide in water, instead of the routinely used H-cells, its reduction must be performed in gas-fed electrolyzer cells, ensuring a short diffusion length for the reactant. However, even in such devices the surface of the catalyst (nano)particles is typically surrounded by a thin water shell under operating conditions, caused by various effects such as electrowetting, or wetting by the formed products. The practical insolubility of carbon monoxide (that is ca. 30 times lower compared to the solubility of CO2) makes it vital to ensure that the thickness of this hydration layer is minimized, hence the reactant can reach the catalysts' surface in gas phase, meanwhile just enough amount of a proton source – water – is in the immediate vicinity.The phase boundary between the catalyst particles, the liquid phase and the gas reactant can be engineered by using functional catalyst layer additives. Here we will demonstrate a commercial pore sealer for this purpose, ensuring the formation of C2+ products in CORR with high selectivity and rate.1 As no specific interaction between the polymer and the CO reactant was found, we assumed that the most important role of this polymer is to increase the hydrophobicity of the catalyst layer. To challenge this theory, various, systematically chosen polymeric materials were tested as catalyst binders to reveal any possible further contribution of certain motifs (e.g., functional groups, fluorinated backbone etc.), present in these polymers. The electrochemical results are contrasted with the detailed characterization of the structure, wetting and gas adsorption properties of the catalyst layer. Reference Kormányos, B. Endrődi, Z. Zhang, A. Samu, L. Mérai, G. F. Samu, L. Janovák, & C. Janáky (2023). EES Catalysis. https://doi.org/10.1039/D3EY00006K